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Rakesh Kumar - One of the best experts on this subject based on the ideXlab platform.
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molecular pathways targeting P21 Activated Kinase 1 signaling in cancer opportunities challenges and limitations
Clinical Cancer Research, 2012Co-Authors: Jeyanthy Eswaran, Anil A Shah, Rakesh KumarAbstract:The evolution of cancer cells involves deregulation of highly regulated fundamental pathways that are central to normal cellular architecture and functions. The P21-Activated Kinase 1 (PAK1) was initially identified as a downstream effector of the GTPases Rac and Cdc42. Subsequent studies uncovered a plethora of its new functions in growth factor and steroid receptor signaling, cytoskeleton remodeling, cell survival, oncogenic transformation, and gene transcription, largely through systematic discovery of its direct, physiologically relevant substrates. PAK1 is widely up-regulated in several human cancers including hormone-dependent cancer, and is intimately linked to tumor progression and therapeutic resistance. These exciting developments combined with the Kinase-independent role of PAK1-centered phenotypic signaling in cancer cells elevated PAK1 as an attractive drug target. The structural and biochemical studies revealed the precise mechanism of PAK1 activation, offering the possibilities to develop PAK1-targeted cancer therapeutic approaches. In addition, emerging reports suggest the potential of PAK1 and its specific phosphorylated substrates as cancer prognostic markers. Here, we summarize the PAK1 molecular pathways in human cancer and discuss the current status of PAK1 targeted anti-cancer therapies.
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Nuclear P21-Activated Kinase 1 in breast cancer packs off tamoxifen sensitivity.
Cancer research, 2006Co-Authors: Suresh K. Rayala, Poonam R. Molli, Rakesh KumarAbstract:There is significant clinical interest in the factors that influence the development of tamoxifen resistance in estrogen receptor-α (ER-α)–positive breast cancers. Recent studies suggest that in ER-positive breast tumor cells, elevated protein levels, and in particular, nuclear localization of P21-Activated Kinase 1 (PAK1), is associated with the progressive limitation of tamoxifen sensitivity. These phenotypic effects of PAK1 in model systems are mechanistically linked with the ability of PAK1 to phosphorylate ER-α on serine 305 and subsequent secondary activation of serine 118. These findings prompt further investigation of how nuclear signaling by PAK1 may affect estrogen's action and whether tamoxifen resistance might be prevented or reversed by PAK1 inhibition. (Cancer Res 2006; 66(12): 5985-8)
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nuclear localization and chromatin targets of P21 Activated Kinase 1
Journal of Biological Chemistry, 2005Co-Authors: Rajesh R Singh, Zhibo Yang, Chunying Song, Rakesh KumarAbstract:Pak1 (P21-Activated Kinase 1), a conserved, mammalian signaling Kinase, is a downstream effector of small GTPases Rac1 and Cdc42 and of growth factor signaling. Until now, a major focus of study has been on the cytosolic functions of Pak1, where it is an important modulator of cytoskeletal reorganization, consequently playing a major role in cell survival, migration, and invasion. In this report, we demonstrate the nuclear localization of Pak1 upon stimulation by epidermal growth factor. Three nuclear localization signals (NLSs) were identified in the N-terminal domain of Pak1. With mutational analysis, the importance of each NLS was elucidated. Mutation of all three NLSs eliminated the nuclear localization of Pak1. Expression of Pak1 as a fusion protein with Gal4-DNA binding domain and Gal4-luciferase activity showed that Pak1 might increase transcription. To identify the potential targets of nuclear Pak1, we used a Pak1-specific chromatin immunoprecipitation-based screening assay and identified a series of Pak1-interacting target chromatins, including phosphofructoKinase-muscle isoform (PFK-M) and nuclear factor of Activated T-cell (NFAT1) genes. Pak1 associated with the upstream enhancer sequence and promoter of PFK-M and was involved in the stimulation of the PFK-M expression. It also associated with a portion of the NFAT1 gene and its upstream region, leading to the repression of NFAT1 expression. These investigations provide proof-of-principle evidence that Pak1 could influence the expression of its putative chromatin targets in both a positive and a negative manner. Together, for the first time, these findings defined the NLSs of the Pak1, its association with chromatin, and the resulting modulation of transcription, thus opening new avenues to further the search for nuclear Pak1 functions and identify putative Pak1-interacting nuclear proteins.
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dynein light chain 1 a P21 Activated Kinase 1 interacting substrate promotes cancerous phenotypes
Cancer Cell, 2004Co-Authors: Ratna K Vadlamudi, Rozita Bagheriyarmand, Zhibo Yang, Seetharaman Balasenthil, Diep Nguyen, Aysegul A Sahin, Petra Den Hollander, Rakesh KumarAbstract:We identified dynein light chain 1 (DLC1) as a physiologic substrate of P21-Activated Kinase 1 (Pak1). Pak1-DLC1 interaction plays an essential role in cell survival, which depends on Pak1's phosphorylation of DLC1 on Ser88. Pak1 associates with the complex of DLC1 and BimL, a proapoptotic BH3-only protein, and phosphorylates both proteins. Phosphorylation of BimL by Pak1 prevents it from interacting with and inactivation of Bcl-2, an antiapoptotic protein. Overexpression of DLC1 but not DLC1-Ser88Ala mutant promotes cancerous properties of breast cancer cells. DLC1 protein level is elevated in more than 90% of human breast tumors. The regulation of cell survival functions by Pak1-DLC1 interaction represents a novel mechanism by which a signaling Kinase might regulate the cancerous phenotypes.
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P21 Activated Kinase 1 phosphorylates and transactivates estrogen receptor α and promotes hyperplasia in mammary epithelium
The EMBO Journal, 2002Co-Authors: Rui An Wang, Ratna K Vadlamudi, Abhijit Mazumdar, Rakesh KumarAbstract:Stimulation of P21-Activated Kinase-1 (Pak1) induces cytoskeleton reorganization and signaling pathways in mammary cancer cells. Here, we show that inhibition of Pak1 Kinase activity by a dominant-negative fragment or by short interference RNA markedly reduced the estrogen receptor-α (ER) transactivation functions. To understand the role of Pak1 in mammary glands, we developed a murine model expressing constitutively active Thr423 glutamic acid Pak1 driven by the β-lactoglobulin promoter. We show that mammary glands from these mice developed widespread hyperplasia associated with apocrine metaplasia and lobuloalveolar hyperdevelopment during lactation. Mammary tissues with active Pak1 also exhibited an increased activation of mitogen-Activated protein Kinase and stimulated transactivation functions of the ER and expression of endogenous ER target genes. Furthermore, Pak1 directly phosphorylated the activation function-2 domain of the ER at the N-terminal residue Ser305, and its mutation to Ala (S305A) abolished the Pak1-mediated phosphorylation and transactivation functions of the ER, while its mutation to glutamic acid (S305E) promoted transactivation activity of ER. These findings reveal a novel role for the Pak1–ER pathway in promoting hyperplasia in mammary epithelium.
Jonathan Chernoff - One of the best experts on this subject based on the ideXlab platform.
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P21-Activated Kinase 2 Regulates Endothelial Development and Function through the Bmk1/Erk5 Pathway.
Molecular and cellular biology, 2015Co-Authors: Maria Radu, Klaus P. Hoeflich, Karen Lyle, Olga Villamar-cruz, Hartmut Koeppen, Jonathan ChernoffAbstract:P21-Activated Kinases (Paks) have been shown to regulate cytoskeleton rearrangements, cell proliferation, attachment, and migration in a variety of cellular contexts, including endothelial cells. However, the role of endothelial Pak in embryo development has not been reported, and currently, there is no consensus on the endothelial function of individual Pak isoforms, in particular P21-Activated Kinase 2 (Pak2), the main Pak isoform expressed in endothelial cells. In this work, we employ genetic and molecular studies that show that Pak2, but not Pak1, is a critical mediator of development and maintenance of endothelial cell function. Endothelial depletion of Pak2 leads to early embryo lethality due to flawed blood vessel formation in the embryo body and yolk sac. In adult endothelial cells, Pak2 depletion leads to severe apoptosis and acute angiogenesis defects, and in adult mice, endothelial Pak2 deletion leads to increased vascular permeability. Furthermore, ubiquitous Pak2 deletion is lethal in adult mice. We show that many of these defects are mediated through a newly unveiled Pak2/Bmk1 pathway. Our results demonstrate that endothelial Pak2 is essential during embryogenesis and also for adult blood vessel maintenance, and they also pinpoint the Bmk1/Erk5 pathway as a critical mediator of endothelial Pak2 signaling.
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Abstract A15: Megakaryocyte differentiation is regulated by P21-Activated Kinase 2
RAS Effectors - Basic Biology, 2014Co-Authors: Rachelle Kosoff, Jonathan ChernoffAbstract:Megakaryocytes (MKs) mature and differentiate into multi-nucleated cells in the bone marrow, and migrate from the osteoblastic niche to the vascular niche by means of an SDF-1a gradient, culminating in the release of platelets into circulation. Failure to do so results in myeloproliferative disorders, which can manifest with extremely reduced platelet counts. Regulation of this process is controlled by MAPK signaling, cytoskeletal and microtubule-associated proteins and GTPases. P21-Activated Kinase 2 (Pak2) regulates the cytoskeleton through the MAPK and RhoA signaling pathways, both required for MK differentiation and cytokinesis. In our study, we demonstrate that Pak2 is essential for proper MK differentiation and polyploidization, in vitro and in vivo. Pak2 deletion, upon cre induction specifically in hematopoietic tissues (Mx1-cre), reduces peripheral blood platelet counts (thrombocytopenia) by 50%. Bone marrow histology demonstrates hyperplastic MKs coinciding with reduced platelet counts. Analysis of bone marrow by flow cytometry demonstrates altered MK differentiation, observed by elevated MK stem cell precursors in the bone marrow (CD150+CD41+). Increased stem cell potential of MKs deficient for Pak2 results in increased colony forming units (CFU-Mks). Additionally, Pak2-null MKs have increased levels of polyploidization. Signaling to MLC2 and GEF-H1 are altered in Pak2-deficient MKs, both previously shown to regulate MK differentiation and polyploidization, respectively. In summary, Pak2 is a negative regulator of MK stem cell differentiation as well as polyploidization. Since Pak2 negatively regulates polyploidization, this leads to therapeutic uses for Pak family inhibitors in the treatment for acute megakaryoblastic leukemia, a fatal disorder which presents with an accumulation of immature MKs, due to a failure to differentiate into mature MKs. Citation Format: Rachelle E. Kosoff, Jonathan Chernoff. Megakaryocyte differentiation is regulated by P21-Activated Kinase 2. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A15. doi: 10.1158/1557-3125.RASONC14-A15
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The role of P21-Activated Kinase in the initiation of atherosclerosis
BMC cardiovascular disorders, 2012Co-Authors: Krishna A. Jhaveri, Jonathan Chernoff, John M. Sanders, P Debnath, Martin A. SchwartzAbstract:Background: P21-Activated Kinase (PAK) has been implicated in the inflammatory activation of endothelial cells by disturbed fluid shear stress, which is the initiating stimulus in atherosclerosis. The study addresses whether PAK1 contributes to inflammatory marker expression in endothelial cells at atherosclerosis-susceptible regions of arteries in vivo. Method: Aortas from WT and PAK1 -/- C57BL/6J mice on a normal chow diet were fixed, dissected and processed for immunohistochemistry using a panel of inflammatory markers. We visualized and quantified staining in the endothelium at the greater and lesser curvatures of the arch of aorta, as atherosclerosis-resistant and susceptible regions, respectively. Results: Fibronectin, VCAM-1 and the Activated RelA NF-κB subunit were localized to the lesser curvature and decreased in PAK1-/- mice. The Activated RelB NF-κB subunit was also localized to the lesser curvature but was increased in PAK1-/- mice. Low levels of staining for ICAM-1 and the monocyte/macrophage marker Mac2 indicated that overall inflammation in this tissue was minimal. Conclusion: These data show that PAK1 has a significant pro-inflammatory function at atherosclerosis-prone sites in vivo. These effects are seen in young mice with very low levels of inflammation, suggesting that inflammatory activation of the endothelium is primarily biomechanical. Activation involves NF-κB, expression of leukocyte recruitment receptors and fibronectin deposition. These results support and extend in vitro studies demonstrating that PAK contributes to activation of inflammatory pathways in endothelial cells by fluid shear stress.
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regulation of akt pkb activity by P21 Activated Kinase in cardiomyocytes
Journal of Molecular and Cellular Cardiology, 2008Co-Authors: Kai Mao, Satoru Kobayashi, Zahara M. Jaffer, Yuan Huang, Paul A. Volden, Jonathan Chernoff, Qiangrong LiangAbstract:Akt/PKB is a critical regulator of cardiac function and morphology, and its activity is governed by dual phosphorylation at active loop (Thr308) by phosphoinositide-dependent protein Kinase-1 (PDK1) and at carboxyl-terminal hydrophobic motif (Ser473) by a putative PDK2. P21-Activated Kinase-1 (Pak1) is a serine/threonine protein Kinase implicated in the regulation of cardiac hypertrophy and contractility and was shown previously to activate Akt through an undefined mechanism. Here we report Pak1 as a potential PDK2 that is essential for Akt activity in cardiomyocytes. Both Pak1 and Akt can be Activated by multiple hypertrophic stimuli or growth factors in a phosphatidylinositol-3-Kinase (PI3K)-dependent manner. Pak1 overexpression induces Akt phosphorylation at both Ser473 and Thr308 in cardiomyocytes. Conversely, silencing or inactivating Pak1 gene diminishes Akt phosphorylation in vitro and in vivo. Purified Pak1 can directly phosphorylate Akt only at Ser473, suggesting that Pak1 may be a relevant PDK2 responsible for AKT Ser473 phosphorylation in cardiomyocytes. In addition, Pak1 protects cardiomyocytes from cell death, which is blocked by Akt inhibition. Our results connect two important regulators of cellular physiological functions and provide a potential mechanism for Pak1 signaling in cardiomyocytes.
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Regulation of Akt/PKB activity by P21-Activated Kinase in cardiomyocytes.
Journal of molecular and cellular cardiology, 2007Co-Authors: Kai Mao, Satoru Kobayashi, Zahara M. Jaffer, Yuan Huang, Paul A. Volden, Jonathan Chernoff, Qiangrong LiangAbstract:Akt/PKB is a critical regulator of cardiac function and morphology, and its activity is governed by dual phosphorylation at active loop (Thr308) by phosphoinositide-dependent protein Kinase-1 (PDK1) and at carboxyl-terminal hydrophobic motif (Ser473) by a putative PDK2. P21-Activated Kinase-1 (Pak1) is a serine/threonine protein Kinase implicated in the regulation of cardiac hypertrophy and contractility and was shown previously to activate Akt through an undefined mechanism. Here we report Pak1 as a potential PDK2 that is essential for Akt activity in cardiomyocytes. Both Pak1 and Akt can be Activated by multiple hypertrophic stimuli or growth factors in a phosphatidylinositol-3-Kinase (PI3K)-dependent manner. Pak1 overexpression induces Akt phosphorylation at both Ser473 and Thr308 in cardiomyocytes. Conversely, silencing or inactivating Pak1 gene diminishes Akt phosphorylation in vitro and in vivo. Purified Pak1 can directly phosphorylate Akt only at Ser473, suggesting that Pak1 may be a relevant PDK2 responsible for AKT Ser473 phosphorylation in cardiomyocytes. In addition, Pak1 protects cardiomyocytes from cell death, which is blocked by Akt inhibition. Our results connect two important regulators of cellular physiological functions and provide a potential mechanism for Pak1 signaling in cardiomyocytes.
Gary M Bokoch - One of the best experts on this subject based on the ideXlab platform.
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Phosphorylation of RhoGDI by P21-Activated Kinase 1.
Methods in enzymology, 2006Co-Authors: Céline Dermardirossian, Gary M BokochAbstract:Abstract Rho GTPase activation is partially regulated at the level of guanine nucleotide dissociation inhibitors, or GDIs. The binding of Rho GTPases to GDIs has been shown to dramatically reduce the action of guanine nucleotide exchange factors (GEFs) to initiate Rho GTPase activation. The GDI–GTPase complex thus serves as a major point of regulation of Rho GTPase activity and function. It is likely that specific mechanisms exist to dissociate individual members of the Rho GTPase family from cytosolic Rho GDI complexes to facilitate the activation process. Such dissociation would likely be tightly coupled to GEF‐mediated guanine nucleotide exchange and membrane association of the Activated GTPase, resulting in effector binding and functional responses. Accumulating evidence suggests that the phosphorylation of either the Rho GTPases themselves and/or phosphorylation of GDIs might serve as a mechanism for regulating the formation and/or dissociation of Rho GTPase–GDI complexes. Indeed, the selective release of Rac1 from RhoGDI complexes induced by the P21‐Activated Kinase‐regulated phosphorylation of RhoGDI has been reported. We describe here methods for the analysis of RhoGDI phosphorylation and regulation by P21‐Activated Kinase 1 (Pak1).
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mechanism of P21 Activated Kinase 6 mediated inhibition of androgen receptor signaling
Journal of Biological Chemistry, 2004Co-Authors: Nicolas Schrantz, Jean Da Silva Correia, Bruce Fowler, Zijie Sun, Gary M BokochAbstract:PAK6 was first identified as an androgen receptor (AR)-interacting protein able to inhibit AR-mediated transcriptional responses. PAK6 is a serine/threonine Kinase belonging to the P21-Activated Kinase (PAK) family implicated in actin reorganization and cell motility, gene transcription, apoptosis, and cell transformation. We investigated the biochemical basis for inhibition of AR signaling by PAK6. We compared the Kinase activity of PAK6 with two other well characterized members of the PAK family, PAK1 and PAK4. Like PAK4, PAK6 possesses a constitutive basal Kinase activity that, unlike PAK1, is not modulated by the binding of active Rac or Cdc42 GTPases. In order to test the involvement of PAK6 Kinase activity in suppression of AR-mediated transcription, we generated Kinase-dead (K436A) and Kinase-active (S531N) mutants of PAK6. We show that PAK6 Kinase activity is required for effective PAK6-induced repression of AR signaling. Suppression does not depend upon GTPase binding to PAK6 and is not mimicked by the closely related PAK1 and PAK4 isoforms. Kinase-dependent inhibition by PAK6 extended to the enhanced AR-mediated transcription seen in the presence of coactivating molecules and to the action of AR coinhibitors. Active PAK6 inhibited nuclear translocation of the stimulated AR, suggesting a possible mechanism for inhibition of AR responsiveness. Finally, we observe that autophosphorylated, active PAK6 protein is differently expressed among prostate cancer cell lines. Modulation of PAK6 activity may be responsible for regulation of AR signaling in various forms of prostate cancer.
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P21 Activated Kinase pak1 is phosphorylated and Activated by 3 phosphoinositide dependent Kinase 1 pdk1
Journal of Biological Chemistry, 2000Co-Authors: Charles C King, Elisabeth M Gardiner, Frank Zenke, Benjamin P Bohl, Alexandra C Newton, Brian A Hemmings, Gary M BokochAbstract:In this study, we show that phosphorylated 3-phosphoinositide-dependent Kinase 1 (PDK1) phosphorylates P21-Activated Kinase 1 (PAK1) in the presence of sphingosine. We identify threonine 423, a conserved threonine in the activation loop of Kinase subdomain VIII, as the PDK1 phosphorylation site on PAK1. Threonine 423 is a previously identified PAK1 autophosphorylation site that lies within a PAK consensus phosphorylation sequence. After pretreatment with phosphatases, autophosphorylation of PAK1 occurred at all major sites except threonine 423. A phosphothreonine 423-specific antibody detected phosphorylation of recombinant, catalytically inactive PAK1 after incubation with wild-type PAK1, indicating phosphorylation of threonine 423 occurs by an intermolecular mechanism. The biological significance of PDK1 phosphorylation of PAK1 at threonine 423 in vitro is supported by the observation that these two proteins interact in vivo and that PDK1-phosphorylated PAK1 has an increased activity toward substrate. An increase of phosphorylation of catalytically inactive PAK1 was observed in COS-7 cells expressing wild-type, but not catalytically inactive, PDK1 upon elevation of intracellular sphingosine levels. PDK1 phosphorylation of PAK1 was not blocked by pretreatment with wortmannin or when PDK1 was mutated to prevent phosphatidylinositol binding, indicating this process is independent of phosphatidylinositol 3-Kinase activity. The data presented here provide evidence for a novel mechanism for PAK1 regulation and activation.
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P21 Activated Kinase 1 phosphorylates the death agonist bad and protects cells from apoptosis
Molecular and Cellular Biology, 2000Co-Authors: Mary Ann Sells, Annette Schurmann, Andrew Mooney, L C Sanders, Honggang Wang, John C Reed, Gary M BokochAbstract:Bad is a critical regulatory component of the intrinsic cell death machinery that exerts its death-promoting effect upon heterodimerization with the antiapoptotic proteins Bcl-2 and Bcl-xL. Growth factors promote cell survival through phosphorylation of Bad, resulting in its dissociation from Bcl-2 and Bcl-xL and its association with 14-3-3τ. Survival of interleukin 3 (IL-3)-dependent FL5.12 lymphoid progenitor cells is attenuated upon treatment with the Rho GTPase-inactivating toxin B from Clostridium difficile. P21-Activated Kinase 1 (PAK1) is Activated by IL-3 in FL5.12 cells, and this activation is reduced by the phosphatidylinositol 3-Kinase inhibitor LY294002. Overexpression of a constitutively active PAK mutant (PAK1-T423E) promoted cell survival of FL5.12 and NIH 3T3 cells, while overexpression of the autoinhibitory domain of PAK (amino acids 83 to 149) enhanced apoptosis. PAK phosphorylates Bad in vitro and in vivo on Ser112 and Ser136, resulting in a markedly reduced interaction between Bad and Bcl-2 or Bcl-xL and the increased association of Bad with 14-3-3τ. Our findings indicate that PAK inhibits the proapoptotic effects of Bad by direct phosphorylation and that PAK may play an important role in cell survival pathways.
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A role for P21-Activated Kinase in endothelial cell migration.
The Journal of cell biology, 1999Co-Authors: William B. Kiosses, Gary M Bokoch, R. Hugh Daniels, Carol A. Otey, Martin A. SchwartzAbstract:The serine/threonine P21-Activated Kinase (PAK) is an effector for Rac and Cdc42, but its role in regulating cytoskeletal organization has been controversial. To address this issue, we investigated the role of PAK in migration of microvascular endothelial cells. We found that a dominant negative (DN) mutant of PAK significantly inhibited cell migration and in-creased stress fibers and focal adhesions. The DN effect mapped to the most NH2-terminal proline-rich SH3-binding sequence. Observation of a green fluorescent protein-tagged α-actinin construct in living cells revealed that the DN construct had no effect on membrane ruffling, but dramatically inhibited stress fiber and focal contact motility and turnover. Constitutively active PAK inhibited migration equally well and also increased stress fibers and focal adhesions, but had a somewhat weaker effect on their dynamics. In contrast to their similar effects on motility, DN PAK decreased cell contractility, whereas active PAK increased contractility. Active PAK also increased myosin light chain (MLC) phosphorylation, as indicated by staining with an antibody to phosphorylated MLC, whereas DN PAK had little effect, despite the increase in actin stress fibers. These results demonstrate that although PAK is not required for extension of lamellipodia, it has substantial effects on cell adhesion and contraction. These data suggest a model in which PAK plays a role coordinating the formation of new adhesions at the leading edge with contraction and detachment at the trailing edge.
Martin A. Schwartz - One of the best experts on this subject based on the ideXlab platform.
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P21 Activated Kinase 4 promotes prostate cancer progression through creb
Oncogene, 2013Co-Authors: Myungjin Park, Eun-young Shin, H S Lee, C S Lee, S T You, D J Kim, B H Park, M J Kang, W D Heo, Martin A. SchwartzAbstract:Prostate cancer is initially androgen-dependent but, over time, usually develops hormone- and chemo-resistance. The present study investigated a role for P21-Activated Kinase 4 (PAK4) in prostate cancer progression. PAK4 activation was markedly inhibited by H89, a specific protein Kinase A (PKA) inhibitor, and PAK4 was Activated by the elevation of cAMP. The catalytic subunit of PKA interacted with the regulatory domain of PAK4, and directly phosphorylated PAK4 at serine 474 (S474). Catalytically active PAK4 enhanced the transcriptional activity of CREB independent of S133 phosphorylation. Stable knockdown of PAK4 in PC-3 and DU145 prostate cancer cells inhibited tumor formation in nude mice. Decreased tumorigenicity correlated with decreased expression of CREB and its targets, including Bcl-2 and cyclin A1. Additionally, in androgen-dependent LNCap-FGC cells, PAK4 regulated cAMP-induced neuroendocrine differentiation, which is known to promote tumor progression. Finally, PAK4 enhanced survival and decreased apoptosis following chemotherapy. These results suggested that PAK4 regulates progression toward hormone- and chemo-resistance in prostate cancer, and this study identified both a novel activation mechanism and potential downstream effector pathways. Therefore, PAK4 may be a promising therapeutic target in prostate cancer.
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The role of P21-Activated Kinase in the initiation of atherosclerosis
BMC cardiovascular disorders, 2012Co-Authors: Krishna A. Jhaveri, Jonathan Chernoff, John M. Sanders, P Debnath, Martin A. SchwartzAbstract:Background: P21-Activated Kinase (PAK) has been implicated in the inflammatory activation of endothelial cells by disturbed fluid shear stress, which is the initiating stimulus in atherosclerosis. The study addresses whether PAK1 contributes to inflammatory marker expression in endothelial cells at atherosclerosis-susceptible regions of arteries in vivo. Method: Aortas from WT and PAK1 -/- C57BL/6J mice on a normal chow diet were fixed, dissected and processed for immunohistochemistry using a panel of inflammatory markers. We visualized and quantified staining in the endothelium at the greater and lesser curvatures of the arch of aorta, as atherosclerosis-resistant and susceptible regions, respectively. Results: Fibronectin, VCAM-1 and the Activated RelA NF-κB subunit were localized to the lesser curvature and decreased in PAK1-/- mice. The Activated RelB NF-κB subunit was also localized to the lesser curvature but was increased in PAK1-/- mice. Low levels of staining for ICAM-1 and the monocyte/macrophage marker Mac2 indicated that overall inflammation in this tissue was minimal. Conclusion: These data show that PAK1 has a significant pro-inflammatory function at atherosclerosis-prone sites in vivo. These effects are seen in young mice with very low levels of inflammation, suggesting that inflammatory activation of the endothelium is primarily biomechanical. Activation involves NF-κB, expression of leukocyte recruitment receptors and fibronectin deposition. These results support and extend in vitro studies demonstrating that PAK contributes to activation of inflammatory pathways in endothelial cells by fluid shear stress.
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P21 Activated Kinase signaling regulates oxidant dependent nf κb activation by flow
Circulation Research, 2008Co-Authors: Wayne A Orr, Brett R. Blackman, Cornelia Hahn, Martin A. SchwartzAbstract:Disturbed blood flow induces inflammatory gene expression in endothelial cells, which promotes atherosclerosis. Flow stimulates the proinflammatory transcription factor nuclear factor (NF)-κB through integrin- and Rac-dependent production of reactive oxygen species (ROS). Previous work demonstrated that NF-κB activation by flow is matrix-specific, occurring in cells on fibronectin but not collagen. Activation of P21-Activated Kinase (PAK) followed the same matrix-dependent pattern. We now show that inhibiting PAK in cells on fibronectin blocked NF-κB activation by both laminar and oscillatory flow in vitro and at sites of disturbed flow in vivo. Constitutively active PAK rescued flow-induced NF-κB activation in cells on collagen. Surprisingly, PAK was not required for flow-induced ROS production. Instead, PAK modulated the ability of ROS to activate the NF-κB pathway. These data demonstrate that PAK controls NF-κB activation by modulating the sensitivity of cells to ROS.
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Matrix-specific P21-Activated Kinase activation regulates vascular permeability in atherogenesis
The Journal of cell biology, 2007Co-Authors: A. Wayne Orr, Rebecca A. Stockton, Michael B. Simmers, John M. Sanders, Ian J. Sarembock, Brett R. Blackman, Martin A. SchwartzAbstract:Elevated permeability of the endothelium is thought to be crucial in atherogenesis because it allows circulating lipoproteins to access subendothelial monocytes. Both local hemodynamics and cytokines may govern endothelial permeability in atherosclerotic plaque. We recently found that P21-Activated Kinase (PAK) regulates endothelial permeability. We now report that onset of fluid flow, atherogenic flow profiles, oxidized LDL, and proatherosclerotic cytokines all stimulate PAK phosphorylation and recruitment to cell–cell junctions. Activation of PAK is higher in cells plated on fibronectin (FN) compared to basement membrane proteins in all cases. In vivo, PAK is Activated in atherosclerosis-prone regions of arteries and correlates with FN in the subendothelium. Inhibiting PAK in vivo reduces permeability in atherosclerosis-prone regions. Matrix-specific PAK activation therefore mediates elevated vascular permeability in atherogenesis.
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P21 Activated Kinase regulates endothelial permeability through modulation of contractility
Journal of Biological Chemistry, 2004Co-Authors: Rebecca A. Stockton, Martin A. Schwartz, Erik SchaeferAbstract:Endothelial cells lining the vasculature have close cell-cell associations that maintain separation of the blood fluid compartment from surrounding tissues. Permeability is regulated by a variety of growth factors and cytokines and plays a role in numerous physiological and pathological processes. We examined a potential role for the P21-Activated Kinase (PAK) in the regulation of vascular permeability. In both bovine aortic and human umbilical vein endothelial cells, PAK is phosphorylated on Ser141 during the activation downstream of Rac, and the phosphorylated subfraction translocates to endothelial cell-cell junctions in response to serum, VEGF, bFGF, TNFα, histamine, and thrombin. Blocking PAK activation or translocation prevents the increase in permeability across the cell monolayer in response to these factors. Permeability correlates with myosin phosphorylation, formation of actin stress fibers, and the appearance of paracellular pores. Inhibition of myosin phosphorylation blocks the increase in permeability. These data suggest that PAK is a central regulator of endothelial permeability induced by multiple growth factors and cytokines via an effect on cell contractility. PAK may therefore be a suitable drug target for the treatment of pathological conditions where vascular leak is a contributing factor, such as ischemia and inflammation.
Christopher A Walsh - One of the best experts on this subject based on the ideXlab platform.
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sequence analysis of P21 Activated Kinase 3 pak3 in chronic schizophrenia with cognitive impairment
Schizophrenia Research, 2008Co-Authors: Eric M Morrow, Anna Kane, Donald C Goff, Christopher A WalshAbstract:The P21-Activated Kinase PAK3 is critical for cognitive development and truncating mutations cause non-syndromic mental retardation (MR). Missense mutations are also associated with psychotic disorders, most commonly with schizophrenia involving premorbid MR, namely "pfropfschizophrenie". We set out to measure the frequency of sequence variants in PAK3 in schizophrenia without premorbid MR. We conducted complete gene reseqeuncing of all coding exons and exon-intron boundaries in patients with schizophrenia with cognitive impairment but without premorbid MR. Deleterious variants in schizophrenia alone were rare (<1/159 or 0.6%). Thereby, while PAK3 remains a strong biological candidate in psychosis, evidence from human genetics provides strongest support for a link to pfropfschizophrenie and not to schizophrenia without premorbid intellectual disability.
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Sequence analysis of P21-Activated Kinase 3 (PAK3) in chronic schizophrenia with cognitive impairment.
Schizophrenia research, 2008Co-Authors: Eric M Morrow, Anna Kane, Donald C Goff, Christopher A WalshAbstract:The P21-Activated Kinase PAK3 is critical for cognitive development and truncating mutations cause non-syndromic mental retardation (MR). Missense mutations are also associated with psychotic disorders, most commonly with schizophrenia involving premorbid MR, namely "pfropfschizophrenie". We set out to measure the frequency of sequence variants in PAK3 in schizophrenia without premorbid MR. We conducted complete gene reseqeuncing of all coding exons and exon-intron boundaries in patients with schizophrenia with cognitive impairment but without premorbid MR. Deleterious variants in schizophrenia alone were rare (
