The Experts below are selected from a list of 73806 Experts worldwide ranked by ideXlab platform
Ethan Dmitrovsky - One of the best experts on this subject based on the ideXlab platform.
-
Cyclin D1 as a Target for Cancer Chemoprevention
Clinical Cancer Research, 2007Co-Authors: Ethan Dmitrovsky, Qing Feng, David Sekula, Konstantin H. Dragnev, Xi Liu, Fabrizio Galimberti, Steven R. Blumen, Candice C. Black, Vincent A. Memoli, David W. JohnstoneAbstract:AACR Centennial Conference: Translational Cancer Medicine-- Nov 4-8, 2007; Singapore CN04-03 Tobacco carcinogen-treatment of immortalized human bronchial epithelial (HBE) cells uncovered novel cancer chemoprevention targets. Treatment of these cells with classical and non-classical retinoid receptor agonists highlighted induced Cyclin D1 proteasomal degradation as a molecular pharmacologic target for cancer chemoprevention. We previously reported Cyclin D1 was often aberrantly expressed in human pre-malignant and malignant lung tissues. This helped provide a rationale to target Cyclin D1 in clinical trials. To understand engaged mechanisms, the role of Cyclin D1 in chemoprevention was studied in relevant pre-clinical models. Chemoprevention of tobacco-carcinogen exposed HBE cells by retinoic acid receptor (RAR) and retinoid X receptor (RXR) agonists, among other agents, was linked to Cyclin D1 proteasomal degradation. This was proposed as a chemopreventive mechanism since induced Cyclin D1 proteolysis conferred cell cycle arrest at G1 and in turn permitted repair of genomic DNA damage by carcinogens. Threonine 286 mutation stabilized Cyclin D1 protein, implicating a phosphorylation event in this regulation. A phospho-specific anti-Cyclin D1 antibody that can recognize phosphorylation changes at threonine 286 was used to confirm in immunoblot analysis that phosphorylation occurred. Glycogen synthase kinase (GSK) inhibitors revealed this kinase regulated post-translational regulation of Cyclin D1, but not other D-type Cyclins. To elucidate which of the 18 lysines present in Cyclin D1 mediated ubiquitin-dependent degradation, these residues were engineered with individual or multiple mutations. Domains responsible for triggering Cyclin D1 degradation were identified and these results will be presented. These stabilizing mutations shared an ability to preferentially localize Cyclin D1 to the nucleus likely sequestering this protein from cytosolic degradation enzymes. An important role for Cyclin D1 in chemoprevention was independently shown using small interfering RNAs (siRNAs) that targeted this species for repression. To uncover other involved degradation programs, gene profiling experiments were performed using carcinogen-transformed and chemoprevented HBE cells. Those studies independently identified the E1-like ubiquitin-activating enzyme (UBE1L) and its physical partner, ISG15, as engaged in regulating Cyclin D1 stability. Since treatment with epidermal growth factor (EGF) augmented HBE cell growth and Cyclin D1 expression, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) was used to block these effects. Together, these in vitro experiments provided a strong rationale to conduct proof of principle trials using agents that targeted Cyclin D1. Proof of principle trials monitor changes in pharmacodynamic targets in pre-treatment versus post-treatment tumor biopsies. Changes are then related to pharmacokinetic measurements of a drug in plasma and tumor. Results of proof of principle trials will be presented that use a rexinoid (bexarotene), an EGFR-TKI (erlotinib), or a bexarotene and erlotinib combination regimen to target effectively Cyclin D1 expression in lung cancer cases. A phase I clinical trial using bexarotene and erlotinib to target lung and aerodigestive tract cancers showed encouraging anti-tumor activity against lung cancer. This set the stage for an ongoing phase II combination therapy trial with bexarotene and erlotinib for relapsed lung cancer, as will be discussed. This led to translating this work back to the laboratory using useful animal models for lung cancer chemoprevention studies. One that will be presented is a human surfactant C promoter-driven Cyclin E mouse transgenic model that targets expression to the lung and spontaneously activated Cyclin D1 expression. Notably, these mice develop pre-malignant and malignant (adenocarcinoma) lung lesions with features highly reminiscent of those found in clinical lung carcinogenesis. Stable cell lines have been derived from these murine lung cancers. This makes possible the study of anti-neoplastic effects of chemopreventive agents ex vivo . These cells are able to form lung tumors following tail vein injections into syngeneic mice. This opens up the prospect for rapid assessment of chemopreventive agent effects in vivo . Taken together, these and other findings that will be presented strongly implicate Cyclin D1 as a novel molecular pharmacological target for cancer chemoprevention.
-
Uncovering residues that regulate Cyclin D1 proteasomal degradation
Oncogene, 2007Co-Authors: Qing Feng, David Sekula, Rolf Müller, Sarah J. Freemantle, Ethan DmitrovskyAbstract:Cyclin D1 regulates G1 cell-cycle progression and is aberrantly expressed in carcinogenesis. Proteasomal degradation of Cyclin D1 was highlighted as a cancer chemopreventive mechanism. To understand this mechanism better, residues responsible for degradation and ubiquitination of Cyclin D1 were investigated. Eighteen lysines in Cyclin D1 had single, double or multiple mutations engineered before transfection into BEAS-2B human bronchial epithelial (HBE) cells to evaluate stabilities after all-trans-retinoic acid (RA) or cycloheximide treatments. Specific mutations stabilized Cyclin D1, including substitutions of lysines surrounding the Cyclin box domain that inhibited RA-mediated degradation and extended the Cyclin D1 half-life. Mutation of all Cyclin D1 lysines blocked polyubiquitination. N-terminus (but not C-terminus) modification stabilized Cyclin D1. Ubiquitination-resistant mutants preferentially localized Cyclin D1 to the nucleus, directly implicating subcellular localization in regulating Cyclin D1 degradation. Taken together, these findings uncover specific residues conferring ubiquitination of Cyclin D1. These provide a mechanistic basis for proteasomal degradation of Cyclin D1.
-
Cyclin D1 as a target for chemoprevention.
Lung Cancer, 2003Co-Authors: W. Jeffrey Petty, Konstantin H. Dragnev, Ethan DmitrovskyAbstract:Lung cancer is the leading cause of cancer mortality. Chemoprevention is an attractive strategy to combat this major public health problem. Pre-clinical and clinical studies have identified diverse candidate chemopreventive agents that affect cellular proliferation, differentiation, apoptosis and tumor angiogenesis, among other pathways. These pharmacological agents are undergoing testing through use of pre-clinical models and clinical trials. These studies have uncovered Cyclin D1 as a chemoprevention target and a surrogate marker of chemopreventive response in the lung. Chemoprevention of tobacco-carcinogen transformed human bronchial epithelial (HBE) cells appears to be due at least partly to degradation of Cyclin D1. These studies of cultured HBE cells were extended to the in vivo setting by examination of preneoplastic bronchial lesions that established the frequent aberrant expression of Cyclin D1 in lung carcinogenesis. Certain retinoids, natural and synthetic derivatives of vitamin A, repress Cyclin D1, but activation of the epidermal growth factor receptor (EGFR) induces Cyclin D1. Retinoids and specific chemopreventive agents can activate the proteasome-dependent degradation of Cyclin D1 and also repress EGFR expression, thereby reducing Cyclin D1 levels. These actions oppose the mitogenic effects of Cyclin D1. This is hypothesized to trigger G1 arrest and thereby permit repair of carcinogenic damage of genomic DNA. These and other pre-clinical and clinical studies that will be reviewed here indicate that Cyclin D1 and perhaps other Cyclins are attractive pharmacological targets for lung cancer chemoprevention.
Richard G Pestell - One of the best experts on this subject based on the ideXlab platform.
-
Kinase independent oncogenic Cyclin D1.
Aging, 2015Co-Authors: Mathew C. Casimiro, Andrew Arnold, Richard G PestellAbstract:Strong evidence implicates Cyclin D1 overexpression as a driving force in breast cancer and many other types of human tumors. Cyclin D1 overexpression is found in up to 50% of human breast cancers, and the pattern of Cyclin D1 overexpression in tissues along the spectrum from normal epithelium to invasive breast cancer suggests its involvement in the earliest stages of mammary carcinogenesis. The importance of Cyclin D1 as a driver oncogene is reinforced by the frequent clonal selection of Cyclin D1 gene amplification, found in 15-20% of breast cancers, associated with poor prognosis, and by the fact that tissue-specific overexpression of Cyclin D1 in transgenic mice results in mammary hyperplasia and adenocarcinoma [1]. However, the precise mechanisms through which Cyclin D1 overexpression contributes to breast tumorigenesis have been controversial. Specifically, while Cyclin D1's role in the pathogenesis of breast cancer may well involve, at least in part, the well-established binding/activation of its catalytic partner kinases CDK4/6, with subsequent hyperphosphorylation of pRB and G1-S cell cycle transition, several lines of evidence have suggested that Cyclin D1, especially when overexpressed in the setting of cancer, may also act through other, CDK-independent, mechanisms. These alternative mechanisms of Cyclin D1 action carry tremendous potential significance, for example in the rational targeting of new therapeutic agents. Our recent study [2] is perhaps the most direct test of this hypothesis performed in a highly relevant in vivo model system. The induction of chromosomal instability is known to promote genetic rearrangements, tumorigenesis and the molecular genetic chaos associated with poor outcome cancers. The early drivers to chromosomal instability are poorly understood. Our recent studies showed that modest overexpression of Cyclin D1 is sufficient for the induction of chromosomal instability within 3 cell divisions, both in vitro and in vivo. Furthermore we showed the induction of CIN occurred independently of the kinase function. In ChIP-Seq Cyclin D1 associates with genes governing chromosomal instability (CIN) [3]. Using a kinase dead mutant of Cyclin D1 (Cyclin D1KE) we showed Cyclin D1 induced - mitotic spindle architecture changes of chromosomal instability and supernumerary centrosomes aneuploidy and other features of CIN. In cdk4/6−/− 3T3 cells Cyclin D1WT and Cyclin D1KE induced aneuploidy to a similar degree compared to control cells. Cyclin D1KE induced aneuploidy to a similar extent in absence or presence of cdk4/6 agonist. Crucially, sustained transgenic expression of Cyclin D1KE induced mammary adenocarcinoma with similar kinetics to that of a Cyclin D1WT transgene [1]. ChIP-Seq studies demonstrated recruitment in the context of local chromatin of either Cyclin D1KE or Cyclin D1WT to the genes governing CIN. Thus, cdk-activating function of Cyclin D1 was not necessary for the induction of either chromosomal instability or murine mammary tumorigenesis. Understanding the different contexts and causes of Cyclin D1 overexpression in breast cancer may be exceedingly important in considering its tumorigenic mechanisms. In this regard Cyclin D1 knockout mice are resistant to breast cancer, however recent studies have shown that Cyclin D1 genetic deletion abrogates the formation of progenitor cells that in turn give rise to cancer. Cyclin D1−/−KE rescue mice are resistant to ErbB2 mediated tumorigenesis [4]. Elegant studies by Hinds' group identified a progenitor population of cells in mouse mammary gland (parity-identified mammary cells: PI-MEC) that require Cyclin D1 kinase activity for self renewal and differentiation [5]. An analysis on the Cyclin D1−/− KE rescue confirmed that the resistance to ErbB2 driven tumorigenesis is linked to near total absence of the PI-MEC, making those progenitor cells the likely target for ErbB2 induced tumorigenesis. Cyclin D1 kinase activity is therefore required for mammary progenitor cells self-renewal and activity, highlighting this key role for Cyclin D1 during development. In contrast, our recent study of mice bearing the MMTV-Cyclin D1KE transgene addressed whether Cyclin D1 overexpression can directly induce mammary tumorigenesis in a kinase independent manner, with a robust answer of ‘yes’. The MMTV-ErbB2 and MMTV-Cyclin D1 models are distinct. MMTV-ErbB2 induced mouse tumorigenesis represents a good model for human breast cancers with HER2 amplification, and the role of CyclinD1 when expressed secondary/downstream to other events (like ErbB2 amplification) may well be kinase dependent. In contrast, MMTV-Cyclin D1 mice better represent the sizeable group of Cyclin D1-amplified cancers, induced by primary, driver-level overexpression of the Cyclin D1 oncogene. Cyclin D1 oncogene activation is a prevalent molecular driver of human cancer, playing key roles in breast, squamous cell, esophageal carcinoma, mantle cell lymphoma, multiple myeloma, and many other devastating human malignancies. Our novel in vivo evidence shows this mechanism can be kinase-independent, counter to the generally accepted “CDK-centric” paradigm of the tumorigenic activity of Cyclin D1. In the clinical realm, these observations suggest that some therapeutic agents now approved or in development, most notably CDK4/6 inhibitors, will have limited efficacy in Cyclin D1-amplified cancers since they target only the kinase partners of Cyclin D1. Thus, without minimizing the improved progression-free survival associated with pharmacologic CDK4/6 inhibition in ER+ breast cancers, our data suggest that in the subset of tumors with, and potentially addicted to, Cyclin D1 amplification or rearrangement, a more effective path to impactful tumor shrinkage as opposed to slowing of growth will be to develop agents that target Cyclin D1 directly. In summary, while Cyclin D1 kinase activity is important in tumorigenesis, additional distinct kinase-independent mechanisms, including induction of chromosomal instability, are helping drive some tumors and attempts to exploit this finding using precision medicine should be encouraged.
-
Cyclin D1 induces chromosomal instability.
Oncotarget, 2012Co-Authors: Mathew C. Casimiro, Richard G PestellAbstract:Cyclin D1 was originally identified as a candidate oncogene activated in a subset of parthyroid tumors through genetic rearrangement [1]. We now understand that Cyclin D1 is a member of a family of Cyclins that regulate progression through the cell cycle in a stepwise fashion from commitment to DNA replication through to cell division and cytokinesis [2]. Cyclin D1 binds the Cyclin dependent kinases cdk4 and 6 to phosphorylate the retinoblastoma protein (RB) and initiate transition from G1 to S-phase. In addition to interacting with its principal substrate, RB, Cyclin D1-Cdk4 acts on other substrates that have well defined roles within, carcinogenesis (Smad3) and mitochondrial function (Nrf1) [3]. There are a number of Cyclin D1 functions that are independent of an associated kinase. Cyclin D1 is a modulator of co-regulators such as BRCA1 and nuclear receptors. Hulit et al was the first to show the abundance of Cyclin D1 determines TF recruitment in the context of local chromatin, and did so in vivo [4]. Fu et al was the first to show Cyclin D1 is recruited in the context of local chromatin, which in turn recruited chromatin modifying proteins (SUV39, HP1α, p300, HDAC 1, and HDAC 3) and altered the acetylation and methylation of chromatin associated histones [5]. Cyclin D1 thus regulates transcription at the chromatin level by interacting with histone deacetylases and various transcription factors to regulate genes that contribute to differentiation and proliferation [4]. Cyclin D1 promoter occupancy assessed by ChIP-ChIP technology mapped Cyclin D1 to approximately 900 genes [6]. We extended these studies to the whole genome to map at high resolution, using ChIP-Seq, the global genomic footprint for Cyclin D1 [7]. We identified 3,222 regions (intervals) associated with Cyclin D1, approximately 70% of these intervals were within 10kb of 2, 840 genes with a high density located within 500bp of the transcriptional start point. We next investigated the transcription factor motifs enriched at the interval region and found the top hits included ERα, Sp1 and Ctcf. Interestingly Ctcf is a zinc finger DNA binding protein that regulates transcription, governs enhancer function and is involved in sister chromatid cohesion. We next interrogated the functional pathways associated with the genes bound by Cyclin D1. One of the most enriched terms was cell division; most of the genes being involved in G2/M phase and cellular mitosis. Increased abundance of Cyclin D1 during G2/M has previously been described [8]. We used ChIP to verify that Cyclin D1 bound the regulatory regions of genes involved in mitosis and QT-PCR to demonstrate that the gene transcripts were induced in Cyclin D1 rescued CcnD1−/− fibroblasts. Misregulation of genes that govern the mitotic phase often lead to chromosomal instability (CIN). Whether a cause or a consequence of tumorigenesis, CIN itself is recognized as promoting transformation, associated with poor prognosis and metastasis. Understanding the transcriptional role of Cyclin D1 in promoting CIN is of considerable clinical importance since it is commonly over expressed in breast, pancreatic, lung cancer and lymphoma. In CcnD1−/− fibroblasts rescued with Cyclin D1, the induction of polyploidy occurred in 3 cell division assessed by FACS analysis. In order to further classify the chromosomal abnormalities we employed spectral karyotyping (SKY), a whole genome painting assay that can recognize complex genomic rearrangements. Cyclin D1 induced aneuploidy in a relatively short amount of time and a large number of translocations, both reciprocal and nonreciprocal. Nonreciprocal translocations can be potently transforming since they can carry oncogenes at the breakpoint. A leading cause of aneuploidy is multipolar spindles caused by abnormal number or structure of centrosomes. In order to investigate the fidelity of the mitotic process we used high-resolution confocal microscopy to observe fibroblasts stained with markers of spindles (α-tubulin) and centrosomes (γ-tubulin). In Cyclin D1 rescued CcnD1−/− fibroblasts over 50% of the cells exhibited multiple centrosomes that give rise to increase multipolar spindles in prometaphase/metaphase. The abnormalities were also evident at the mitotic plate since measurements of the plate width were significantly increased in Cyclin D1 rescued fibroblasts. We developed mouse model systems to investigate the potential for Cyclin D1 to induce CIN in vivo. In a mammary gland specific Tet-inducible model the acute expression profile regulated by Cyclin D1 after 7 days was enriched in genes that rank highly with CIN. We also used a mammary gland targeted model (MMTV) to continuously express Cyclin D1. The mice started to develop mammary gland tumors at 400 days and the tumor-free incidence was 40% in MMTV-Cyclin D1. The gene expression profile of the tumors showed enrichment for the CIN signature. We next compared Cyclin D1 expression and the highest ranking CIN genes to a breast cancer expression database and discovered that expression of genes promoting CIN are highly enriched in luminal subtype and that high Cyclin D1 and CIN expression correlate specifically in the luminal B subtype. There is increasing interest in employing drugs in the clinic that exploit CIN in tumors. The high CIN expression index in luminal B breast cancer provides a basis for using Cdk and CIN inhibitors as a targeted therapeutic approach.
-
Examining the role of Cyclin D1 in breast cancer
Future oncology (London England), 2011Co-Authors: Marco A. Velasco-velázquez, Mathew C. Casimiro, Emanuele Loro, Nora Homsi, Richard G PestellAbstract:Cyclin D1 overexpression is found in more than 50% of human breast cancers and causes mammary cancer in transgenic mice. Dysregulation of Cyclin D1 gene expression or function contributes to the loss of normal cell cycle control during tumorigenesis. Recent studies have demonstrated that Cyclin D1 conducts additional specific functions to regulate gene expression in the context of local chromatin, promote cellular migration and inhibit mitochondrial metabolism. It is anticipated that these additional functions contribute to the pathology associated with dysregulated Cyclin D1 abundance. This article discusses evidence that examines the significance of Cyclin D1 in breast cancer with emphasis on its role in breast cancer stem cell expansion.
-
Cyclin D1 regulation of mitochondrial function in breast cancer
Cancer Research, 2007Co-Authors: Chenguang Wang, Toshiyuki Sakamaki, Mathew C. Casimiro, Andrew A. Quong, Lifeng Tian, Richard G PestellAbstract:4472 Cyclin D1 is overexpressed in human breast cancers and is sufficient for the development of murine mammary tumors. The Cyclin D1 gene encodes a regulatory subunit of the holoenzyme that phosphorylates and inactivates the pRb tumor suppressor protein to promote nuclear DNA synthesis. In addition to the ability of Cyclin D1 to form a holoenzyme with cdk4/6, we and others have previously shown that Cyclin D1 regulates distinct cellular functions through physical association with nuclear receptors and transcriptional coregulators. In knockdown experiments using siRNA against Cyclin D1 we observed that both mitochondial size and activity were increased, this observation was validated using Cyclin D1 anti-sense transgenic mice. Mammary epithelial cells obtained from Cyclin D1 anti-sense transgenic mice demonstrated induction of genes governing mitochondrial function and glycolysis. Reciprocal expression of these genes was observed in mammary tumors induced by mammary gland targeted Cyclin D1 overexpression. Global gene expression profiling and functional analysis of mammary epithelial cell-targeted Cyclin D1 anti-sense transgenics demonstrated Cyclin D1 inhibits mitochondrial activity, and aerobic glycolysis in vivo . We further examined the mitochondrial components including mitochondrial transcriptional factor A (mtTFA) and mitochondrial nuclear respiratory factor 1 (NRF-1) that are key regulators of mitochondrial DNA synthesis and function. Cyclin D1 repressed expression of mtTFA and inhibited D-loop transcriptional activity. NRF-1, which induces nuclear-encoded mitochondrial genes, was transcriptionally repressed and its activity was inhibited by Cyclin D1. Cyclin D1 levels and NRF-1 expression were inversely correlated during cell cycle progression. In addition, NRF-1- and Cyclin D1-regulated genes were inversely correlated by microarray expression profiling. Cyclin D1 associated with NRF-1 in vivo by immunoprecipitation and in mammalian two-hybrid assays. Screening for the potential phosphorylation site of NRF-1 demonstrated that Cyclin D1-dependent kinase phosphorylated NRF-1 at Serine 47. In summary, in addition to regulating nuclear DNA synthesis, Cyclin D1 regulates mitochondrial function in vivo , coordinating metabolic substrate utilization within the cell.
-
Cyclin D1 Induction of Cellular Migration Requires p27KIP1
Cancer research, 2006Co-Authors: Xuanmao Jiao, Chenguang Wang, Sanjay Katiyar, Liangping Yuan, Michael P. Lisanti, Richard G PestellAbstract:The Cyclin D1 gene is amplified and overexpressed in human breast cancer, functioning as a collaborative oncogene. As the regulatory subunit of a holoenzyme phosphorylating Rb, Cyclin D1 promotes cell cycle progression and a noncatalytic function has been described to sequester the Cyclin-dependent kinase inhibitor protein p27. Cyclin D1 overexpression correlates with tumor metastasis and Cyclin D1–deficient fibroblasts are defective in migration. The genetic mechanism by which Cyclin D1 promotes migration and movement is poorly understood. Herein, Cyclin D1 promoted cellular migration and cytokinesis of mammary epithelial cells. Cyclin D1 enhanced cellular migratory velocity. The induction of migration by Cyclin D1 was abolished by mutation of K112 or deletion of NH2-terminal residues 46 to 90. These mutations of Cyclin D1 abrogated physical interaction with p27KIP1. Cyclin D1−/− cells were p27KIP1 deficient and the defect in migration was rescued by p27KIP1 reintroduction. Conversely, the Cyclin D1 rescue of Cyclin D1−/− cellular migration was reversed by p27KIP1 small interfering RNA. Cyclin D1 regulated p27KIP1 abundance at the posttranslational level, inhibiting the Skp2 promoter, Skp2 abundance, and induced p27KIP1 phosphorylation at Ser10. Together, these studies show Cyclin D1 promotes mammary epithelial cell migration. p27KIP1 is required for Cyclin D1–mediated cellular migration. (Cancer Res 2006; 66(20): 9986-94)
J. Alan Diehl - One of the best experts on this subject based on the ideXlab platform.
-
to Cyclin D1 Overexpression in Human Cancer
2008Co-Authors: Olena Barbash, Petia Zamfirova, Douglas I. Lin, Xiangmei Chen, Ke Yang, Hiroshi Nakagawa, Anil K. Rustgi, J. Alan DiehlAbstract:SUMMARY SCF Fbx4 was recently identified as the E3 ligase for Cyclin D1. We now describe cell-cycle-dependent phosphorylation and dimerization of Fbx4 that is regulated by GSK3b and is defective in human cancer. We present data demonstrating that a pathway involving Ras-Akt-GSK3b controls the temporal phosphorylation and dimerization of the SCF Fbx4 E3 ligase. Inhibition of Fbx4 activity results in accumulation of nuclear Cyclin D1 and oncogenic transformation. The importance of this regulatory pathway for normal cell growth is emphasized by the prevalence of mutations in Fbx4 in human cancer that impair dimerization. Collectively, these data reveal that inactivation of the Cyclin D1 E3 ligase likely contributes to Cyclin D1 overexpression in a significant fraction of human cancer.
-
Nuclear accumulation of Cyclin D1 and cancer
Cancer Research, 2005Co-Authors: J. Alan Diehl, Andrew B. Gladden, Rebecca Woolery, Mariusz A. WasikAbstract:Proc Amer Assoc Cancer Res, Volume 46, 2005 SY08-1 Progression through each phase of the cell cycle is driven by complexes composed of a regulatory, Cyclin, and a catalytic, CDK, subunit. G1 phase progression is initiated by mitogenic stimulation, which in turn initiates the expression and assembly of the D-type Cyclins (D1, D2, D3) with their catalytic partner CDK4/6. The D-type Cyclins are unique in that they respond directly to mitogenic signaling pathways rather than to signals intrinsic to cell cycle progression. Cyclin D1 expression requires Ras-dependent activation of the Raf-Mek-Erk kinase module. While the MAPK module signals Cyclin D1 expression, maximal accumulation of Cyclin D1 also depends on PI-3K-dependent inactivation of glycogen synthase kinase 3 beta (GSK-3β). GSK-3β-dependent phosphorylation of Cyclin D1 on threonine 286 (Thr-286) triggers the ubiquitination and proteolysis of Cyclin D1 via the 26S-proteasome during S-phase. Although Cyclin D1 accumulates in the nucleus during the G1 interval, it relocalizes to the cytoplasm during S-phase. It is now clear that phosphorylation of Cyclin D1 at Thr-286 not only promotes Cyclin D1 proteolysis, but also CRM1 binding, and thus, Cyclin D1/CDK4 nuclear export. This temporal regulation of Cyclin D1 wherein it accumulates in the nucleus during G1 and is relocalized to the cytoplasm during S-phase implies that while the essential functions of Cyclin D1 may require its nuclear localization, the redistribution of Cyclin D1/CDK4 complexes to the cytoplasm following G1 implies that regulation of Cyclin D1 nucleo-cytoplasmic distribution is necessary for maintaining cellular homeostasis. Cyclin D1 overexpression has been documented in an increasing number of solid tumors including esophageal, colonic, breast, and head and neck carcinomas. In addition to involvement in solid tumors, Cyclin D1 was identified as the BcL-1 oncogene associated with the chromosomal translocation t(11;14)(q13;q32) in mantle cell lymphoma (MCL). MCL is an aggressive B-cell lymphoma, with a variable initial response to standard chemotherapeutic treatments and high incidence of relapse resulting in the overall poor survival. Cyclin D1 is invariably expressed due to translocation in MCL. Noteworthy, initial attempts to establish Cyclin D1 as a dominant B-cell oncogene via overexpression in transgenic mice in were unsuccessful while attempts to model genetic changes associated with other human B-cell malignancies, such as those associated with Burkitt (c-myc) and follicular lymphoma (BcL-2), have been successful. While overexpression of wild type Cyclin D1 is not itself sufficient for oncogenic transformation even in vitro we have recently found that Cyclin D1 mutants that remain constitutively nuclear due to impaired Thr-286 phosphorylation, can transform cultured murine fibroblasts. These results imply that the inability of overexpressed wild type Cyclin D1 to promote B-cell lymphomas in transgenic mice reflects the capacity of lymphocytes to maintain proper temporal regulation of Cyclin D1 activity through regulated nuclear export. In lieu of the transforming ability of the Cyclin D1-T286A mutant compared with wild type D1, we have investigated the possibility that constitutively nuclear localization of Cyclin D1 is sufficient to drive lymphoid malignancies in mice. We have generated mice expressing Flag-D1-T286A under the control of the immunoglobulin enhancer, Eμ. The product of the D1-T286A transgene binds with CDK4 and p27 but not with CDK6 in lymphocytes. Mice expressing the Eμ D1-T286A transgene have a decreased life span due to the onset of malignant B cell lymphomas with an average latency of 14 months. Tumors are uniformly B-cell lymphomas with some degree of disseminated disease. We have begun to investigate whether known tumor suppressor pathways are targeted through secondary mutations in the observed lymphomas. Thus far, we have observed a subset of tumors wherein the ARF/Mdm2/p53 pathway is disrupted. We have also found that a majority of tumors overexpress either the Bcl-2 or Bcl-xL anti-apoptotic proteins. Our results suggest the ability of Cyclin D1 to promote neoplastic growth is dependent upon its constitutive nuclear localization throughout the cell cycle and collectively suggest that disruption of Cyclin D1 nuclear export will contribute to human malignancy. Indeed, we have identified mutations that specifically disrupt Cyclin D1 nuclear export in human cancer. Our data are consistent with a model wherein deregulation of Cyclin D1 nuclear export contributes to human neoplastic growth.
-
Hsc70 regulates accumulation of Cyclin D1 and Cyclin D1-dependent protein kinase.
Molecular and cellular biology, 2003Co-Authors: J. Alan Diehl, Wensheng Yang, Ronald A. Rimerman, Hua Xiao, Andrew EmiliAbstract:The Cyclin D-dependent kinase is a critical mediator of mitogen-dependent G1 phase progression in mammalian cells. Given the high incidence of Cyclin D1 overexpression in human neoplasias, the nature and complexity of Cyclin D complexes in vivo have been subjects of intense interest. Besides its catalytic partner, the nature and complexity of Cyclin D complexes in vivo remain ambiguous. To address this issue, we purified native Cyclin D1 complexes from proliferating mouse fibroblasts by affinity chromatography and began to identify and functionally characterize the associated proteins. In this report, we describe the identification of Hsc70 and its functional importance for Cyclin D1 and Cyclin D1-dependent kinase maturation. We demonstrate that Hsc70 associates with newly synthesized Cyclin D1 and is a component of a mature, catalytically active Cyclin D1/CDK4 holoenzyme complex. Our data suggest that Hsc70 promotes stabilization of newly synthesized Cyclin D1, thereby increasing its availability for assembly with CDK4. In addition, our data demonstrate that Hsc70 remains bound to Cyclin D1 following its assembly with CDK4 and Cip/Kip proteins, where it ensures the formation of a catalytically active complex.
-
Cycling to Cancer with Cyclin D1
Cancer biology & therapy, 2002Co-Authors: J. Alan DiehlAbstract:Genetic aberrations in the regulatory circuits that govern transit through the G(1) phase of the cell cycle occur frequently in human cancer and overexpression of the G(1) phase Cyclin, Cyclin D1, is one of the most commonly observed alterations. Cyclin D1 accumulates and activates its cognate CDK (CDK4/6) in response to mitogenic growth factors in early to mid G(1) phase. The resulting Cyclin D1-dependent kinase initiates the phosphorylation-dependent inactivation of the retinoblastoma tumor suppressor protein. Mitogen-dependent activation of the Cyclin D1 kinase occurs through increased transcription, protein accumulation, Cyclin/CDK assembly, reduced Cyclin proteolysis, and decreased nuclear export. Perturbations at any step, which result in reduced growth factor requirements for Cyclin D1/CDK activation, will provide cells with a distinct growth advantage over their normal counterparts and thus likely represents an early event in neoplasia.
-
Phosphorylation-dependent regulation of Cyclin D1 nuclear export and Cyclin D1–dependent cellular transformation
Genes & development, 2000Co-Authors: Jodi R Alt, John L Cleveland, Mark Hannink, J. Alan DiehlAbstract:GSK-3β-dependent phosphorylation of Cyclin D1 at Thr-286 promotes the nuclear-to-cytoplasmic redistribution of Cyclin D1 during S phase of the cell cycle, but how phosphorylation regulates redistribution has not been resolved. For example, phosphorylation of nuclear Cyclin D1 could increase its rate of nuclear export relative to nuclear import; alternatively, phosphorylation of cytoplasmic Cyclin D1 by GSK-3β could inhibit nuclear import. Here, we report that GSK-3β-dependent phosphorylation promotes Cyclin D1 nuclear export by facilitating the association of Cyclin D1 with the nuclear exportin CRM1. D1-T286A, a Cyclin D1 mutant that cannot be phosphorylated by GSK-3β, remains nuclear throughout the cell cycle, a consequence of its reduced binding to CRM1. Constitutive overexpression of the nuclear Cyclin D1-T286A in murine fibroblasts results in cellular transformation and promotes tumor growth in immune compromised mice. Thus, removal of Cyclin D1 from the nucleus during S phase appears essential for regulated cell division.
Karen E. Knudsen - One of the best experts on this subject based on the ideXlab platform.
-
Cyclin D1 goes metabolic: dual functions of Cyclin D1 in regulating lipogenesis.
Cell Cycle, 2012Co-Authors: Karen E. KnudsenAbstract:Recent findings have revolutionized thinking in terms of how D-type Cyclins control diverse cellular processes including development, cellular proliferation and carcinogenesis. The D-Cyclin consists of three members with overlapping functions, Cyclin D1, Cyclin D2 and Cyclin D3.1 Biochemically, D-type Cyclins function in late G1 phase as catalysts for Cyclin-dependent kinases 4 and/or 6 (CDK4/6). D-type Cyclin production is generally enhanced by mitogenic stimuli, and enrichment of the D-Cyclins initiates the cell cycle engine. Binding of Cyclin D1 to CDK4/6 induces kinase activity and promotes cell cycle progression through phosphorylation of the retinoblastoma tumor suppressor protein, RB, thereby suppressing the ability of RB to attenuate cell cycle advancement. As such, elevated Cyclin D1 expression in model systems drives unchecked cellular proliferation and promoting tumor growth.2 High levels of Cyclin D1 are in fact associated with numerous human malignancies, including both breast cancer and hepatocellular carcinoma. Moreover, a variant of Cyclin D1 that arises from alternative splicing of the CCND1 transcript, gives rise to a highly oncogenic form of the protein (Cyclin D1b), which is associated with aggressive tumor phenotypes.3 Given the importance of D-Cyclins in controlling the phenotypes associated with human cancers, this aspect of Cyclin D function has been widely studied and is well understood. While the pro-proliferative actions of Cyclin D1 are largely mediated by CDKs, it is clear that the D-Cyclins harbor a number of critical, CDK-independent functions. Strikingly, unbiased biochemical analysis revealed that a major fraction of endogenous Cyclin D1 is found in association with transcription factors.4 Subsequent analyses demonstrated that Cyclin D1 is found at promoters and is a key mediator of selected transcription factor functions. The ability of Cyclin D1 to regulate transcription appears to underpin major in vivo activity; exemplifying this, the retinal hypoplastic phenotype of the Cyclin D1-knockout mouse results from loss of Cyclin D1-mediated Notch signaling. The finding that Cyclin D1-controlled transcriptional regulation controls in vivo phenotypes is consistent with a litany of previous studies identifying Cyclin D1 as a regulator of nuclear receptors. Cyclin D1 associates with and modulates function of the androgen receptor (AR),5 estrogen receptor alpha (ER),6 PPAR-gamma,7 thyroid hormone receptor beta (TR-B) and multiple nuclear receptor co-regulators. Morever, Cyclin D1 can regulate androgen and estrogen metabolism in the liver, further implicating the protein as a major effector of hormone action.8 In a new study by Hanse and colleagues,9 Cyclin D1 was identified as a critical mediator of de novo hepatic lipogenesis, manifest by both CDK-dependent and CDK-independent mechanisms. Initial studies demonstrated that Cyclin D1 inhibits lipogenesis in primary rat hepatocytes, and was associated with altered lipogenic gene expression programs that are distinct from the role of Cyclin D1 in facilitating injury-induced hepatocyte proliferation. The underlying mechanisms hinge upon two distinct actions of Cyclin D1. First, Cyclin D1 negatively regulates ChREBP (carbohydrates response element-binding protein) expression and activity in a manner dependent on CDK4 function. The ChREBP transcription factor is typically activated by high glucose and promotes expression of genes whose functions are important for mediating hepatic lipogenesis. By contrast, Cyclin D1 binds to and suppress the function of HNF4α (Hepatocyte nuclear factor 4 alpha), a member of the nuclear receptor superfamily that influences liver function. Cyclin D1 suppresses binding of HNF4α to chromatin at regulatory regions of target genes associated with lipogenesis, and the impact of Cyclin D1 was further confirmed by the observation that Cyclin D1 knockdown enhanced both HNF4α activity and lipogenesis. Finally, the relationship between liver regeneration and the lipogenic response was examined with a focus on Cyclin D1 activity; as expected, injury introduced by partial hepatectomy induced Cyclin D1 expression and hepatocyte cell cycle advancement. Notably, injury-induced cellular proliferation was associated with a concomitant suppression of lipogenic gene expression. Combined, these findings suggest that altered metabolic function during liver regeneration may be attributed to more than alteration of hepatic mass, but may be controlled by the induction of Cyclin D1-mediated transcription regulation. As the study establishes a new link between cell cycle regulation and hepatic metabolism, the implications of these Cyclin D1 functions for liver development, homeostasis and cancer should be explored. On balance, these studies provide further impetus for discerning the cellular and biological impact of Cyclin D1-mediated transcriptional regulation.9
-
Cyclin D1 polymorphism aberrant splicing and cancer risk
Oncogene, 2006Co-Authors: Karen E. Knudsen, Alan J Diehl, Christopher A Haiman, Erik S KnudsenAbstract:The Cyclin D1 proto-oncogene exercises powerful control over the mechanisms that regulate the mitotic cell cycle, and excessive Cyclin D1 expression and/or activity is common in human cancers. Although somatic mutations of the Cyclin D1 locus are rarely observed, mounting evidence demonstrates that a specific polymorphism of Cyclin D1 (G/A870) and a protein product of a potentially related alternate splicing event (Cyclin D1b) may influence cancer risk and outcome. Herein, we review the epidemiological and functional literatures that link these alterations of Cyclin D1 to human tumor development and progression.
-
Specificity of Cyclin D1 for androgen receptor regulation.
Cancer research, 2003Co-Authors: Christin E. Petre-draviam, Stephen L. Cook, Craig J. Burd, Thomas W. Marshall, Yelena B. Wetherill, Karen E. KnudsenAbstract:Androgen receptor (AR) activity is required for prostate growth, differentiation, and secretion. Deregulation of AR activity results in inappropriate mitogenic signaling and is thought to contribute both to the initiation and progression of prostate cancers. Cyclin D1 functions as a strong AR corepressor by directly interacting with and inhibiting receptor activity. However, the extent to which Cyclin D1 functions to inhibit AR activity under conditions associated with cancer progression has not been determined. We now demonstrate that Cyclin D1 action is conserved in multiple tumor cell backgrounds, inhibiting AR-dependent gene activation in breast, bladder, and androgen-independent prostatic adenocarcinoma cell lines. In androgen-dependent prostatic adenocarcinomas, Cyclin D1 effectively muted androgen-stimulated target gene expression in a manner analogous to dominant negative ARs. The ability of Cyclin D1 to inhibit AR activity was conserved with regard to target promoter, repressing transactivation from mouse mammary tumor virus, probasin, and prostate-specific antigen promoters. Inappropriate, nonligand AR activation, postulated to act through regulation of receptor phosphorylation, was also sensitive to Cyclin D1 regulation. Moreover, we show that several phosphorylation site mutants of the AR were equally inhibited by Cyclin D1 as compared with the wild-type receptor. Given these data establishing the potency of Cyclin D1-mediated repression, we evaluated the ability of Cyclin D1 to inhibit tumor-derived AR alleles and polymorphisms associated with tumor progression and increased prostate cancer risk. We demonstrate that the AR alleles and polymorphisms tested respond completely to Cyclin D1 corepressor activity. In addition, activation of a common tumor-derived AR allele by 17β-estradiol and progesterone was inhibited through ectopic expression of Cyclin D1. Taken together, these data establish the potency of Cyclin D1 as an AR corepressor and provide support for additional studies examining the efficacy of developing novel prostate cancer therapies for both androgen-dependent and -independent tumors.
Raymond Lai - One of the best experts on this subject based on the ideXlab platform.
-
Cyclin D1 Expression in Dysplastic Nevi
2009Co-Authors: Carol Ewanowich, Russell K. Brynes, L. Jeffrey Medeiros, Althea Mccourty, Raymond LaiAbstract:Abstract Objective.—We previously surveyed Cyclin D1 expression in common acquired nevi, Spitz nevi, and malignant melanomas and reported that benign nevi maintain a zonal pattern of Cyclin D1 expression, in contrast with malignant melanomas. Our aim was to extend those observations by examining Cyclin D1 expression in dysplastic nevi. Methods.—Cyclin D1 overexpression in 23 dysplastic nevi was detected by an immunohistochemical technique. The extent of atypia of the nevi was graded as mild, moderate, or severe, using previously established criteria. Results.—Cyclin D1 overexpression in dysplastic nevi maintained a zonal pattern, similar to Spitz nevi. Cyclin D1 overexpression was greatest in the region of the epidermal-dermal junction and was significantly less prominent in the papillary and reticular dermis, suggesting that Cyclin D1 expression is under cell control and correlates with maturation of nevus cells. Cyclin D1 overexpression also correlated with cytologic atypia, as dysplastic nevi with mode...
-
Cyclin D1 Expression in Dysplastic Nevi
Archives of Pathology & Laboratory Medicine, 2001Co-Authors: Carol Ewanowich, Russell K. Brynes, L. Jeffrey Medeiros, Althea Mccourty, Raymond LaiAbstract:Abstract Objective.—We previously surveyed Cyclin D1 expression in common acquired nevi, Spitz nevi, and malignant melanomas and reported that benign nevi maintain a zonal pattern of Cyclin D1 expression, in contrast with malignant melanomas. Our aim was to extend those observations by examining Cyclin D1 expression in dysplastic nevi. Methods.—Cyclin D1 overexpression in 23 dysplastic nevi was detected by an immunohistochemical technique. The extent of atypia of the nevi was graded as mild, moderate, or severe, using previously established criteria. Results.—Cyclin D1 overexpression in dysplastic nevi maintained a zonal pattern, similar to Spitz nevi. Cyclin D1 overexpression was greatest in the region of the epidermal-dermal junction and was significantly less prominent in the papillary and reticular dermis, suggesting that Cyclin D1 expression is under cell control and correlates with maturation of nevus cells. Cyclin D1 overexpression also correlated with cytologic atypia, as dysplastic nevi with moderate or severe cytologic atypia contained a greater percentage of Cyclin D1–positive cells than did nevi with mild atypia. Six dysplastic nevi with many Cyclin D1–positive cells were assessed by fluorescence in situ hybridization studies using Cyclin D1–specific and chromosome 11 centromeric probes. In all cases, there was no evidence of 11q13 translocation, amplification, or trisomy of chromosome 11. Conclusions.—Cyclin D1 may be involved in the pathogenesis of dysplastic nevi. Cyclin D1 overexpression does not appear to be explained by Cyclin D1 locus amplification or translocation in most cases, and it may be a result of other cell abnormalities that up-regulate the protein level of Cyclin D1.
-
Cyclin D1 expression in dysplastic nevi: an immunohistochemical study.
Archives of pathology & laboratory medicine, 2001Co-Authors: Carol Ewanowich, Russell K. Brynes, L. Jeffrey Medeiros, Althea Mccourty, Raymond LaiAbstract:Objective We previously surveyed Cyclin D1 expression in common acquired nevi, Spitz nevi, and malignant melanomas and reported that benign nevi maintain a zonal pattern of Cyclin D1 expression, in contrast with malignant melanomas. Our aim was to extend those observations by examining Cyclin D1 expression in dysplastic nevi. Methods Cyclin D1 overexpression in 23 dysplastic nevi was detected by an immunohistochemical technique. The extent of atypia of the nevi was graded as mild, moderate, or severe, using previously established criteria. Results Cyclin D1 overexpression in dysplastic nevi maintained a zonal pattern, similar to Spitz nevi. Cyclin D1 overexpression was greatest in the region of the epidermal-dermal junction and was significantly less prominent in the papillary and reticular dermis, suggesting that Cyclin D1 expression is under cell control and correlates with maturation of nevus cells. Cyclin D1 overexpression also correlated with cytologic atypia, as dysplastic nevi with moderate or severe cytologic atypia contained a greater percentage of Cyclin D1-positive cells than did nevi with mild atypia. Six dysplastic nevi with many Cyclin D1--positive cells were assessed by fluorescence in situ hybridization studies using Cyclin D1--specific and chromosome 11 centromeric probes. In all cases, there was no evidence of 11q13 translocation, amplification, or trisomy of chromosome 11. Conclusions Cyclin D1 may be involved in the pathogenesis of dysplastic nevi. Cyclin D1 overexpression does not appear to be explained by Cyclin D1 locus amplification or translocation in most cases, and it may be a result of other cell abnormalities that up-regulate the protein level of Cyclin D1.
-
Cyclin D1 overexpression in Spitz nevi: an immunohistochemical study.
The American Journal of dermatopathology, 1999Co-Authors: Tetsuro Nagasaka, Russell K. Brynes, L. Jeffrey Medeiros, Althea Mccourty, Raymond Lai, Tomoko Harada, Maruf SaddikAbstract:The morphologic distinction between Spitz nevus and malignant melanoma can be difficult. Because Cyclin D1 has been reported to be overexpressed in malignant melanomas, but not in common acquired nevi, we hypothesized that Cyclin D1 might be a useful marker to distinguish Spitz nevi from malignant melanoma. Thus, we assessed for Cyclin D1 expression in 11 Spitz nevi (10 compound and 1 intradermal) and 9 malignant melanomas (4 Clark stages I-III and 5 Clark stages IV-V) using an immunohistochemical method and routinely fixed and processed tissues. The Cyclin D1 results were arbitrarily divided into three groups: 0% to 10%, >10% to 25%, and >25%. We confirmed the observations reported previously by others that Cyclin D1 is expressed in malignant melanomas but not in common acquired nevi. Unexpectedly, a relatively high number of Cyclin D1-positive cells (i.e., >10%) was also found in all cases of Spitz nevus. However, unlike malignant melanoma, the Cyclin D1 positivity in Spitz nevi was present in a zonal pattern. In other words, the number of Cyclin D1-positive cells decreased as the lesion extended more deeply, with the number of positive cells in the reticular dermis being less than that in the papillary dermis. Fluorescence in situ hybridization methods were used to assess amplification of 11q13, the locus harboring the Cyclin D1 gene, in four cases of Spitz nevus; all were disomic. Using the antibody MIB-1, we compared Cyclin D1 expression to the proliferation rate in Spitz nevi. Despite the high Cyclin D1 positivity, all Spitz nevi had a relatively low number of MIB-1-positive cells (mean=3.2%), which was significantly lower than that of malignant melanomas (mean=15.3%) (p < 0.001). Thus, unlike malignant melanoma, there appears to be a dissociation between Cyclin D1 overexpression and cell proliferation in Spitz nevi.
