The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Bruno D Fonseca - One of the best experts on this subject based on the ideXlab platform.
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pharmacological and genetic evaluation of proposed roles of mitogen activated protein kinase extraCellular signal regulated kinase kinase mek extraCellular signal regulated kinase erk and p90 rsk in the control of mtorc1 protein signaling by phorbol
Journal of Biological Chemistry, 2011Co-Authors: Bruno D Fonseca, Tommy Alain, Leona K Finestone, Brandon P H Huang, Mark Rolfe, Tian Jiang, Greco Hernandez, Christopher F BennettAbstract:The mammalian target of rapamycin complex 1 (mTORC1) links the control of mRNA translation, Cell growth, and metabolism to diverse stimuli. Inappropriate activation of mTORC1 can lead to cancer. Phorbol esters are naturally occurring products that act as potent tumor promoters. They activate isoforms of protein kinase C (PKCs) and stimulate the oncogenic MEK/ERK signaling cascade. They also activate mTORC1 signaling. Previous work indicated that mTORC1 activation by the phorbol ester PMA (phorbol 12-myristate 13-acetate) depends upon PKCs and may involve MEK. However, the precise mechanism(s) through which they activate mTORC1 remains unclear. Recent studies have implicated both the ERKs and the ERK-activated 90-kDa ribosomal S6 kinases (p90(RSK)) in activating mTORC1 signaling via phosphorylation of TSC2 (a regulator of mTORC1) and/or the mTORC1 component raptor. However, the relative importance of each of these kinases and phosphorylation events for the activation of mTORC1 signaling is unknown. The recent availability of MEK (PD184352) and p90(RSK) (BI-D1870) inhibitors of improved specificity allowed us to address the roles of these protein kinases in controlling mTORC1 in a variety of human and Rodent Cell types. In parallel, we used specific shRNAs against p90(RSK1) and p90(RSK2) to further test their roles in regulating mTORC1 signaling. Our data indicate that p90(RSKs) are dispensable for the activation of mTORC1 signaling by phorbol esters in all Cell types tested. Our data also reveal striking diversity in the requirements for MEK/ERK in the control of mTORC1 between different Cell types, pointing to additional signaling connections between phorbol esters and mTORC1, which do not involve MEK/ERK. This study provides important information for the design of efficient strategies to combat the hyperactivation of mTORC1 signaling by oncogenic pathways.
Wayne D Bowen - One of the best experts on this subject based on the ideXlab platform.
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sigma 1 and sigma 2 receptors are expressed in a wide variety of human and Rodent tumor Cell lines
Cancer Research, 1995Co-Authors: Bertold J Vilner, Christy S John, Wayne D BowenAbstract:Abstract Thirteen tumor-derived Cell lines of human and nonhuman origin and from various tissues were examined for the presence and density of sigma-1 and sigma-2 receptors. Sigma-1 receptors of a crude membrane fraction were labeled using [3H](+)-pentazocine, and sigma-2 receptors were labeled with [3H]1,3-di-o-tolylguanidine ([3H]DTG); in the presence or absence of dextrallorphan. [3H](+)-Pentazocine-binding sites were heterogeneous. In Rodent Cell lines (e.g., C6 glioma, N1E-115 neuroblastoma, and NG108-15 neuroblastoma × glioma hybrid), human T47D breast ductal carcinoma, human NCI-H727 lung carcinoid, and human A375 melanoma, [3H](+)-pentazocine bound to high- and low-affinity sites with Kd1 = 0.67–7.0 nm, Bmax1 = 25.5–108 fmol/mg protein, Kd2 = 127–600 nm, and Bmax2 = 942–5431 fmol/mg protein. However, [3H](+)-pentazocine bound to a single site in other Cell lines. In human U-138MG glioblastoma, SK-N-SH neuroblastoma, and LNCaP.FGC prostate, Kd = 28–61 nm and Bmax = 975–1196 fmol/mg protein, whereas in ThP-1 leukemia Kd = 146 nm and Bmax = 1411 fmol/mg protein. The sigma-1-like nature of [3H](+)-pentazocine-binding sites was confirmed by competition studies which revealed high affinity for haloperidol and enantioselectivity for (+)-pentazocine over (-)-pentazocine. Interestingly, human MCF-7 breast adenocarcinoma showed little or no specific binding of [3H](+)-pentazocine, suggesting the absence of sigma-1 receptors in this Cell line. All Cell lines examined expressed a high density of sigma-2 receptors with Kd values for [3H]DTG ranging from 20 to 101 nm and Bmax values of 491 to 7324 fmol/mg protein. Competition studies indicated possible heterogeneity of sigma-2 receptors. While sites labeled by [3H]DTG in all Cell lines tested exhibited affinity for haloperidol and preference for (-)-pentazocine over the (+)-enantiomer, human Cell lines generally showed 4- to 7-fold lower affinity for haloperidol and approximately 10-fold lower affinity for (-)-pentazocine compared with the Rodent Cell lines. The high density of sigma-1 and sigma 2-binding sites in these Cell lines suggests important Cellular functions in cancer, as well as potential diagnostic utility for tumor-imaging agents which target sigma sites. These Cell lines may be useful as model systems in which to study the functions of sigma sites in normal tissues, as well as their possible role in tumor biology.
T. K. Hei - One of the best experts on this subject based on the ideXlab platform.
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Modulating factors in the expression of radiation-induced oncogenic transformation
Environmental Health Perspectives, 1990Co-Authors: E. J. Hall, T. K. HeiAbstract:Many assays for oncogenic transformation have been developed ranging from those in established Rodent Cell lines where morphological alteration is scored, to those in human Cells growing in nude mice where tumor invasiveness is scored. In general, systems that are most quantitative are also the least relevant in terms of human carcinogenesis and human risk estimation. The development of Cell culture systems has made it possible to assess at the Cellular level the oncogenic potential of a variety of chemical, physical and viral agents. Cell culture systems afford the opportunity to identify factors and conditions that may prevent or enhance Cellular transformation by radiation and chemicals. Permissive and protective factors in radiation-induced transformation include thyroid hormone and the tumor promoter TPA that increase the transformation incidence for a given dose of radiation, and retinoids, selenium, vitamin E, and 5-aminobenzamide that inhibit the expression of transformation. Densely ionizing alpha-particles, similar to those emitted by radon daughters, are highly effective in inducing transformations and appear to interact in a supra-additive fashion with asbestos fibers. The activation of a known dominant oncogene has not yet been demonstrated in radiation-induced oncogenic transformation. The most likely mechanism for radiation activation of an oncogene would be via the production of a chromosomal translocation. Radiation also efficiently induces deletions and may thus lead to the loss of a suppressor gene.
Kazushi Inoue - One of the best experts on this subject based on the ideXlab platform.
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ras raf arf signaling critically depends on the dmp1 transcription factor
Molecular and Cellular Biology, 2005Co-Authors: Ramesh Sreeramaneni, Asif Chaudhry, Martin Mcmahon, Charles J Sherr, Kazushi InoueAbstract:The INK4a-ARF locus on human chromosome 9p21 is disrupted in approximately 40% of human cancers (42). This unusual locus encodes two distinct tumor suppressor proteins, p16INK4a and p14ARF (p19Arf in the mouse), encoded in part via alternative reading frames. p16Ink4a binds to cyclin-dependent kinase 4 (Cdk4) to inhibit Rb phosphorylation, whereas p19Arf binds to the p53 negative regulator, Mdm2, thereby stabilizing and activating p53 (26, 47). Arf is induced by potentially harmful growth-promoting signals stemming from overexpression of a variety of oncoproteins, including c-Myc, E2F-1, mutated Ras, v-Abl, and β-catenin (47). This forces incipient cancer Cells to undergo p53-dependent proliferative arrest or apoptosis, providing a powerful mode of tumor suppression. In turn, Arf-null mice are highly prone to spontaneous tumor development and die of various forms of cancer by 15 months of age (21, 22). Recently, the creation of Arf-GFP knock-in mice has provided direct experimental evidence that the Arf promoter monitors latent oncogenic signals in vivo (56). How Arf responds to oncogenic Ras signaling remains unclear. Ras family proteins play crucial roles in the control of Cell growth and differentiation (29). Overexpression of activated Ras initiates DNA synthesis independent of growth factor stimulation. In immortal Rodent Cell lines, transformation by oncogenic Ras involves its ability to bind and activate a series of effector proteins, including Raf-1, phosphoinositide 3-OH kinase [PI(3)K], and Ral-GDS (23). Each of these molecules, in turn, activates distinct downstream targets, thereby producing different aspects of the transformed phenotype. The Ras-Raf interaction initiates the mitogen-activated protein kinase (MAPK) cascade, which involves the sequential activation of a series of protein kinases that transmit mitogenic signals to nuclear transcription factors. These kinases include Raf-1, the MEKs (MEK1 and MEK2), and the ERKs (ERK1 and ERK2). On the other hand, the ability of Ras to activate PI(3)K promotes membrane ruffling (20), and the Ral-GDS proteins act as exchange factors that can activate the Ral family of small GTPases (50). Although each of these effector pathways contributes to the transforming activity of Ras in established Rodent fibroblast Cell lines, activation of the Raf-MEK-ERK pathway is sufficient for transformation (10). Paradoxically, sustained overexpression of oncogenic Ras and its various effectors in nonimmortalized Cells has the capacity to elicit irreversible Cell cycle arrest by upregulating the levels of p16Ink4a, p19Arf, and p53 in mice and p16INK4a and p53 in humans (29, 33, 44, 48, 57). The ability of oncogenic Ras to induce premature senescence depends on the activity of the Raf-MEK-ERK pathway that mediates proliferation (25) but is nullified in primary mouse embryo fibroblasts (MEFs) lacking either Arf or p53 (21, 33, 48). Among known Arf activators, the Dmp1 transcription factor (cyclin D-interacting Myb-like protein 1) is a bona fide tumor suppressor (18, 19). Dmp1 was originally isolated in a yeast two-hybrid screen of a murine T-lymphocyte library with cyclin D2 as bait (14). The protein binds to nonameric CCCG(G/T)ATG(T/C) DNA consensus sequences, a subset of which is also bound by proteins of the Ets family. Dmp1 can physically interact with any of the three D-type cyclins, each of which can interfere, in a Cdk4-independent manner, with Dmp1's ability to bind to DNA (15). Overexpression of Dmp1 in mouse fibroblasts arrests Cell cycle progression, an effect that can be overridden by coexpression of D-type cyclins (15). Importantly, Dmp1 directly binds to the Arf promoter to activate its expression, thereby inducing p53-dependent Cell cycle arrest (17). Several lines of evidence have implicated Dmp1 in the process by which Ras induces Arf and p53. When primary Dmp1-null MEFs were explanted into culture and continuously passaged, p19Arf and p53 levels remained uncharacteristically low and the Cells exhibited a prolonged proliferative capacity, readily yielding established Cell lines that retained wild-type Arf and p53. Such Cells were susceptible to transformation by oncogenic Ras alone without any requirement for an immortalizing oncogene, such as Myc or adenovirus E1A. Thus, the activity of the Arf-p53 pathway is strikingly impaired in Dmp1-null Cells (18). Dmp1-null mice are prone to spontaneous tumor development in their second year of life, and tumor formation was accelerated when the animals were neonatally treated with ionizing radiation or dimethylbenzanthracene (18, 19), a carcinogen that induces Ras mutations in vivo (37). When crossed onto a Dmp1+/− or Dmp1−/− background, lymphomas induced by an Eμ-Myc transgene were greatly accelerated with no differences between cohorts lacking one or two Dmp1 alleles. The retention and expression of the wild-type Dmp1 allele in tumors arising in heterozygotes indicated that Dmp1 is haplo-insufficient for tumor suppression (19, 38). Interestingly, the combined frequencies of p53 mutation and Arf deletion in the Dmp1−/− and Dmp1+/− lymphomas were significantly lower than those in Dmp1+/+ tumors (∼14% versus ∼50%). Thus, Dmp1 is a physiological regulator of the Arf-p53 pathway in vivo (19). The present studies were undertaken in an attempt to define the mechanism(s) by which Ras induces Arf. Here we show that Dmp1 is a key mediator of this process.
Kathy A Mason - One of the best experts on this subject based on the ideXlab platform.
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radiosensitization of human and Rodent Cell lines by ino 1001 a novel inhibitor of poly adp ribose polymerase
Cancer Letters, 2004Co-Authors: William A Brock, Luka Milas, Sherry Bergh, Ruth Lo, Csaba Szabo, Kathy A MasonAbstract:Abstract Inhibition of poly(ADP-ribose) polymerase (PARP) by a novel, potent inhibitor, INO-1001, was examined in two Rodent and one human fibroblast Cell lines, after single and fractionated radiation treatments. Since PARP plays a role in the early events following DNA damage and influences the effectiveness of DNA repair, its inhibition has been proposed to constitute a drug target for the development of novel radiosensitizers. We found that INO-1001 effectively inhibited PARP activity at non-cytotoxic concentrations. Combination treatment of 10 μM INO-1001 and a single dose of radiation resulted in significant radiosensitization of all three Cells lines (enhancement ratios 1.4–1.6). This radioenhancement was even greater when the drug and radiation were given as fractionated treatments (enhancement ratio 8.0). Apoptosis (as evaluated by TUNEL staining) was not enhanced by the treatments, suggesting that inhibiting PARP enzyme activity by INO-1001 enhanced radiation-induced Cell killing by interfering with DNA repair mechanisms, resulting in necrotic Cell death. INO-1001 therefore, appears to have potential as a potent enhancer of radiation sensitivity, without any intrinsic cytotoxicity from the drug alone.
