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Distinct requirement for an intact dimer interface in wild-type, V600E and kinase-dead B-Raf signalling. EMBO J 2012; 31:2629-47. [PMID: 22510884 DOI: 10.1038/emboj.2012.100] [Citation(s) in RCA: 102] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Accepted: 03/23/2012] [Indexed: 12/11/2022] Open
Abstract
The dimerisation of Raf kinases involves a central cluster within the kinase domain, the dimer interface (DIF). Yet, the importance of the DIF for the signalling potential of wild-type B-Raf (B-Raf(wt)) and its oncogenic counterparts remains unknown. Here, we show that the DIF plays a pivotal role for the activity of B-Raf(wt) and several of its gain-of-function (g-o-f) mutants. In contrast, the B-Raf(V600E), B-Raf(insT) and B-Raf(G469A) oncoproteins are remarkably resistant to mutations in the DIF. However, compared with B-Raf(wt), B-Raf(V600E) displays extended protomer contacts, increased homodimerisation and incorporation into larger protein complexes. In contrast, B-Raf(wt) and Raf-1(wt) mediated signalling triggered by oncogenic Ras as well as the paradoxical activation of Raf-1 by kinase-inactivated B-Raf require an intact DIF. Surprisingly, the B-Raf DIF is not required for dimerisation between Raf-1 and B-Raf, which was inactivated by the D594A mutation, sorafenib or PLX4720. This suggests that paradoxical MEK/ERK activation represents a two-step mechanism consisting of dimerisation and DIF-dependent transactivation. Our data further implicate the Raf DIF as a potential target against Ras-driven Raf-mediated (paradoxical) ERK activation.
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202
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Differential sensitivity of melanoma cell lines with differing B-Raf mutational status to the new oncogenic B-Raf kinase inhibitor UI-152. Cancer Lett 2012; 320:215-24. [PMID: 22425959 DOI: 10.1016/j.canlet.2012.03.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Revised: 02/27/2012] [Accepted: 03/05/2012] [Indexed: 01/07/2023]
Abstract
Activating mutations in B-Raf kinase are common in malignant melanoma, an aggressive tumor of neuroectodermal origin. In the present study, the antiproliferative effect of the new oncogenic B-Raf targeting drug UI-152 on two types of melanoma cell lines with differing B-Raf mutational status was examined, and the underlying mechanisms were investigated. In cellular assays, UI-152 displayed high selectivity for tumor cells bearing B-Raf(V600E), showing more than 1000-fold higher inhibition of their proliferation than wild-type B-Raf-bearing cells. As expected, UI-152 completely abolished MEK-ERK phosphorylation in A375P cells harboring B-Raf(V600E). In SK-MEL-2 cells expressing B-Raf(WT), UI-152 caused the paradoxical activation of the MAPK pathway but to a much lesser extent than that observed of other oncogenic B-Raf inhibitors. These data suggest that UI-152 may be a more ideal B-Raf inhibitor capable of preserving potency against oncogenic B-Raf while minimizing the paradoxical activation of MAPK signaling. In addition, we showed that UI-152 treatment of A375P cells simultaneously induced cellular autophagy and apoptosis. However, autophagy inhibition with 3-methyladenine and inhibition of apoptosis by overexpression of the X-linked inhibitor of apoptosis failed to rescue melanoma cells from UI-152-induced cell death, implying that apoptosis and autophagy may cooperate in the induction of cell death in UI-152-treated cells. Collectively, our data suggest that UI-152 may be an effective B-Raf inhibitor and a potential therapeutic strategy for B-Raf(WT) and Ras mutant melanoma.
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203
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Reactive oxygen species and epidermal growth factor are antagonistic cues controlling SHP-2 dimerization. Mol Cell Biol 2012; 32:1998-2009. [PMID: 22411627 DOI: 10.1128/mcb.06674-11] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The SHP-2 tyrosine phosphatase plays key regulatory roles in the modulation of the cell response to growth factors and cytokines. Over the past decade, the integration of genetic, biochemical, and structural data has helped in interpreting the pathological consequences of altered SHP-2 function. Using complementary approaches, we provide evidence here that endogenous SHP-2 can dimerize through the formation of disulfide bonds that may also involve the catalytic cysteine. We show that the fraction of dimeric SHP-2 is modulated by growth factor stimulation and by the cell redox state. Comparison of the phosphatase activities of the monomeric self-inhibited and dimeric forms indicated that the latter is 3-fold less active, thus pointing to the dimerization process as an additional mechanism for controlling SHP-2 activity. Remarkably, dimers formed by different SHP-2 mutants displaying diverse biochemical properties were found to respond differently to epidermal growth factor (EGF) stimulation. Although this differential behavior cannot be rationalized mechanistically yet, these findings suggest a possible regulatory role of dimerization in SHP-2 function.
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204
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Abstract
Copper (Cu) is essential for development and proliferation, yet the cellular requirements for Cu in these processes are not well defined. We report that Cu plays an unanticipated role in the mitogen-activated protein (MAP) kinase pathway. Ablation of the Ctr1 high-affinity Cu transporter in flies and mouse cells, mutation of Ctr1, and Cu chelators all reduce the ability of the MAP kinase kinase Mek1 to phosphorylate the MAP kinase Erk. Moreover, mice bearing a cardiac-tissue-specific knockout of Ctr1 are deficient in Erk phosphorylation in cardiac tissue. in vitro investigations reveal that recombinant Mek1 binds two Cu atoms with high affinity and that Cu enhances Mek1 phosphorylation of Erk in a dose-dependent fashion. Coimmunoprecipitation experiments suggest that Cu is important for promoting the Mek1-Erk physical interaction that precedes the phosphorylation of Erk by Mek1. These results demonstrate a role for Ctr1 and Cu in activating a pathway well known to play a key role in normal physiology and in cancer.
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205
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The role of autophagy in cytotoxicity induced by new oncogenic B-Raf inhibitor UI-152 in v-Ha-ras transformed fibroblasts. Biochem Biophys Res Commun 2012; 417:857-63. [DOI: 10.1016/j.bbrc.2011.12.061] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Accepted: 12/14/2011] [Indexed: 12/18/2022]
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206
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Matsuda Y, Fukumoto M. Sorafenib: complexities of Raf-dependent and Raf-independent signaling are now unveiled. Med Mol Morphol 2011; 44:183-9. [PMID: 22179180 DOI: 10.1007/s00795-011-0558-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Accepted: 07/15/2011] [Indexed: 12/13/2022]
Abstract
Hepatocellular carcinoma (HCC) is the most common primary cancer worldwide. The only current drug available for clinical treatment of HCC is sorafenib, which inhibits multiple signaling kinases including Raf family members, platelet-derived growth factor receptor, vascular endothelial growth factor receptors 1 and 2, c-Kit, and Fms-like tyrosine kinase 3. Many studies have revealed that the mechanism underlying the antitumor effect of sorafenib is complex. Because sorafenib inhibits C-Raf more potently than B-Raf, the therapeutic efficacy of sorafenib is strongly influenced by the relative expression and activity of B-Raf and C-Raf and the complex interactions between these factors. Moreover, Rafindependent signaling mechanisms have recently emerged as important pathways of sorafenib-induced cell death. Basic research studies have suggested that using sorafenib as part of a combination therapy may improve its effect, although this has yet to be confirmed by clinical evidence. Further studies of the functional mechanism of sorafenib are required to advance the development of targeted therapy for HCC. To aid future work on sorafenib, we here review the current literature pertaining to sorafenib signaling and its clinical efficacy in both monotherapy and combination therapy.
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Affiliation(s)
- Yasunobu Matsuda
- Department of Medical Technology, Niigata University Graduate School of Health Sciences, Asahimachi-dori, Niigata, Japan.
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207
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RAF inhibitor resistance is mediated by dimerization of aberrantly spliced BRAF(V600E). Nature 2011; 480:387-90. [PMID: 22113612 PMCID: PMC3266695 DOI: 10.1038/nature10662] [Citation(s) in RCA: 1115] [Impact Index Per Article: 85.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Accepted: 10/20/2011] [Indexed: 01/07/2023]
Abstract
Activated RAS promotes dimerization of members of the RAF kinase family. ATP-competitive RAF inhibitors activate ERK signalling by transactivating RAF dimers. In melanomas with mutant BRAF(V600E), levels of RAS activation are low and these drugs bind to BRAF(V600E) monomers and inhibit their activity. This tumour-specific inhibition of ERK signalling results in a broad therapeutic index and RAF inhibitors have remarkable clinical activity in patients with melanomas that harbour mutant BRAF(V600E). However, resistance invariably develops. Here, we identify a new resistance mechanism. We find that a subset of cells resistant to vemurafenib (PLX4032, RG7204) express a 61-kDa variant form of BRAF(V600E), p61BRAF(V600E), which lacks exons 4-8, a region that encompasses the RAS-binding domain. p61BRAF(V600E) shows enhanced dimerization in cells with low levels of RAS activation, as compared to full-length BRAF(V600E). In cells in which p61BRAF(V600E) is expressed endogenously or ectopically, ERK signalling is resistant to the RAF inhibitor. Moreover, a mutation that abolishes the dimerization of p61BRAF(V600E) restores its sensitivity to vemurafenib. Finally, we identified BRAF(V600E) splicing variants lacking the RAS-binding domain in the tumours of six of nineteen patients with acquired resistance to vemurafenib. These data support the model that inhibition of ERK signalling by RAF inhibitors is dependent on levels of RAS-GTP too low to support RAF dimerization and identify a novel mechanism of acquired resistance in patients: expression of splicing isoforms of BRAF(V600E) that dimerize in a RAS-independent manner.
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208
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The secret life of kinases: functions beyond catalysis. Cell Commun Signal 2011; 9:23. [PMID: 22035226 PMCID: PMC3215182 DOI: 10.1186/1478-811x-9-23] [Citation(s) in RCA: 133] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Accepted: 10/28/2011] [Indexed: 02/07/2023] Open
Abstract
Protein phosphorylation participates in the regulation of all fundamental biological processes, and protein kinases have been intensively studied. However, while the focus was on catalytic activities, accumulating evidence suggests that non-catalytic properties of protein kinases are essential, and in some cases even sufficient for their functions. These non-catalytic functions include the scaffolding of protein complexes, the competition for protein interactions, allosteric effects on other enzymes, subcellular targeting, and DNA binding. This rich repertoire often is used to coordinate phosphorylation events and enhance the specificity of substrate phosphorylation, but also can adopt functions that do not rely on kinase activity. Here, we discuss such kinase independent functions of protein and lipid kinases focussing on kinases that play a role in the regulation of cell proliferation, differentiation, apoptosis, and motility.
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209
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Opioid Receptor Trafficking and Signaling: What Happens After Opioid Receptor Activation? Cell Mol Neurobiol 2011; 32:167-84. [DOI: 10.1007/s10571-011-9755-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Accepted: 09/04/2011] [Indexed: 01/14/2023]
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210
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Strong negative feedback from Erk to Raf confers robustness to MAPK signalling. Mol Syst Biol 2011; 7:489. [PMID: 21613978 PMCID: PMC3130559 DOI: 10.1038/msb.2011.27] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2010] [Accepted: 04/14/2011] [Indexed: 12/23/2022] Open
Abstract
This study shows that MAPK signalling is robust against protein level changes due to a strong negative feedback from Erk to Raf. Surprisingly, robustness is provided through a fast post-translational mechanism although variation of Erk levels occurs on a timescale of days. MAPK signalling is robust against variation in protein level. Robustness is mediated by a negative feedback to Raf. Loss of negative feedback due to mutation in B-Raf opens the door for targeted intervention.
Protein levels within signal transduction pathways vary strongly from cell to cell. For example, it has been reported that concentrations of the last kinase within the MAPK signalling module, Erk, varies about four-fold between clonal cells under the same conditions. In the present study, we analysed how signalling pathways can still process information quantitatively despite strong heterogeneity in protein levels. Mathematical analysis of isolated phosphorylation–dephosphorylation cycles predicts that phosphorylation of a signalling molecule is proportional to the protein concentration. We systematically perturbed the protein levels of Erk in human cell lines by siRNA. We found that the steady-state phosphorylation of Erk is very robust against perturbations of Erk protein level, suggesting that there are mechanisms that provide robustness to the pathway against protein fluctuations. Using mathematical modelling, we identified three potential mechanisms that may provide robustness against fluctuating protein levels: 1. Kinetic effects (saturation of the activating kinase Mek), 2. Transcriptional negative feedbacks, 3. Negative feedbacks on the post-translational level. By experimental analysis of the systems, which included analysis of Erk phosphorylation under Mek overexpression, measuring transcript levels of negative feedback regulators, and application of generic inhibitors of transcription and translation, we could exclude kinetic effects and transcriptional negative feedback as mechanisms of robustness. By analysing a panel of cell lines, we found that cells are robust as long as the signal passes through Raf-1. In contrast, cells where the pathway is activated by a mutation in B-Raf lose robustness. Detailed molecular analysis of the system shows that a single post-translational feedback to Raf mediates robustness. Thus, robustness is provided through a fast post-translational mechanism although variation of Erk levels occurs on a timescale of days. Protein levels within signal transduction pathways vary strongly from cell to cell. Here, we analysed how signalling pathways can still process information quantitatively despite strong heterogeneity in protein levels. We systematically perturbed the protein levels of Erk, the terminal kinase in the MAPK signalling pathway in a panel of human cell lines. We found that the steady-state phosphorylation of Erk is very robust against perturbations of Erk protein level. Although a multitude of mechanisms exist that may provide robustness against fluctuating protein levels, we found that one single feedback from Erk to Raf-1 accounts for the observed robustness. Surprisingly, robustness is provided through a fast post-translational mechanism although variation of Erk levels occurs on a timescale of days.
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211
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Chung E, Kondo M. Role of Ras/Raf/MEK/ERK signaling in physiological hematopoiesis and leukemia development. Immunol Res 2011; 49:248-68. [PMID: 21170740 DOI: 10.1007/s12026-010-8187-5] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Recent research on hematological malignancies has shown that malignant cells often co-opt physiological pathways to promote their growth and development. Bone marrow homeostasis requires a fine balance between cellular differentiation and self-renewal; cell survival and apoptosis; and cellular proliferation and senescence. The Ras/Raf/MEK/ERK pathway has been shown to be important in regulating these biological functions. Moreover, the Ras/Raf/MEK/ERK pathway has been estimated to be mutated in 30% of all cancers, thus making it the focus of many scientific studies which have lead to a deeper understanding of cancer development and help to elucidate potential weaknesses that can be targeted by pharmacological agents [1]. In this review, we specifically focus on the role of this pathway in physiological hematopoiesis and how augmentation of the pathway may lead to hematopoietic malignancies. We also discuss the challenges and success of targeting this pathway.
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Affiliation(s)
- Eva Chung
- Department of Immunology, Duke University Medical Center, 101 Jones Building, DUMC Box 3010, Research Drive, Durham, NC 27710, USA
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212
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Abstract
BRAF, a cytoplasmic serine-threonine protein kinase, plays a critical role in cell signaling as an activator within the mitogen-activated protein kinase (MAPK) pathway. The most common BRAF mutation is the V600E transversion, which causes constitutive kinase activity. This mutation has been found in a multitude of human cancers, including both papillary thyroid cancer (PTC) and papillary-derived anaplastic thyroid cancer (ATC), in which it initiates follicular cell transformation. With such a high frequency of BRAF mutations in PTC (44%) and PTC-derived ATC (24%), research in BRAF(V600E) detection for diagnostic purposes has shown high sensitivity and specificity for tumor cell presence. BRAF(V600E) in PTC has also provided valuable prognostic information, as its presence has been correlated with more aggressive and iodine-resistant phenotypes. Such findings have initiated research in targeting oncogenic BRAF in cancer therapeutics. Although multiple phase II clinical trials in patients with iodine-refractory metastatic PTC have shown significant efficacy for sorafenib, a first-generation BRAF inhibitor, the mechanism by which it mediates its effect remains unclear because of multiple additional kinase targets of sorafenib. Additionally, preclinical and clinical studies investigating combination therapy with agents such as selective (PLX 4032) and potent (BAY 73-4506 and ARQ 736) small-molecule BRAF inhibitors and MAP/extracellular signal-regulated kinase (ERK) kinase inhibitors (AZD6244) hold great promise in the treatment of BRAF(V600E) cancers and may eventually play a powerful role in changing the clinical course of PTC and ATC.
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Affiliation(s)
- Lisa M Caronia
- Ohio State University College of Medicine, Divisions of Surgical Oncology and Medical Oncology, James Cancer Center & Solove Research Institute, Columbus, OH 43210, USA
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213
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McKay MM, Freeman AK, Morrison DK. Complexity in KSR function revealed by Raf inhibitor and KSR structure studies. Small GTPases 2011; 2:276-281. [PMID: 22292131 DOI: 10.4161/sgtp.2.5.17740] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 08/03/2011] [Accepted: 08/12/2011] [Indexed: 01/07/2023] Open
Abstract
The Ras, Raf, MEK and ERK proteins form an essential signal transduction pathway that is aberrantly activated in many human cancers. Kinase suppressor of Ras (KSR) is a conserved positive modulator of this pathway, and since its discovery, there has been a concerted effort to elucidate KSR function in both normal and aberrant Ras/ERK signaling. The KSR proteins possess a C-terminal region that is closely related to the Raf family kinase domain; however, mammalian KSR proteins lack a key catalytic residue, suggesting a role as a pseudokinase. Like many other pseudokinases, KSR has scaffolding activities and interacts with Raf, MEK and ERK to provide spatio-temporal regulation of ERK activation. Recently, significant advances have been made that further our understanding of how KSR proteins function in normal and oncogenic signaling. The newly solved KSR2/MEK1 structure has revealed important mechanistic details for how KSR regulates MEK activation and has raised questions regarding KSR kinase activity. In addition, KSR expression levels have been found to alter the effects of Raf inhibitors on oncogenic Ras/ERK signaling. Specifically, KSR1 competes with C-Raf for inhibitor-induced binding to B-Raf and in doing so attenuates the paradoxical activating effect of these drugs on ERK signaling.
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Affiliation(s)
- Melissa M McKay
- Laboratory of Cell and Developmental Signaling; Center for Cancer Research; National Cancer Institute-Frederick; Frederick, MD USA
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214
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Freeman AK, Morrison DK. 14-3-3 Proteins: diverse functions in cell proliferation and cancer progression. Semin Cell Dev Biol 2011; 22:681-7. [PMID: 21884813 PMCID: PMC3221730 DOI: 10.1016/j.semcdb.2011.08.009] [Citation(s) in RCA: 190] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Accepted: 08/16/2011] [Indexed: 12/27/2022]
Abstract
The 14-3-3 proteins were the first phosphoserine/phosphothreonine-binding proteins to be discovered, a finding that provided the foundation for their prominent role in cell signaling. 14-3-3 family members interact with a wide spectrum of proteins including transcription factors, biosynthetic enzymes, cytoskeletal proteins, signaling molecules, apoptosis factors, and tumor suppressors. The interaction with 14-3-3 can have a profound effect on a target protein, altering its localization, stability, conformation, phosphorylation state, activity, and/or molecular interactions. Thus, by modulating the function of a diverse array of binding partners, 14-3-3 proteins have become key regulatory components in many vital cellular processes - processes that are crucial for normal growth and development and that often become dysregulated in human cancer. This review will examine the recent advances that further elucidate the role of 14-3-3 proteins in normal growth and cancer signaling with a particular emphasis on the signaling pathways that impact cell proliferation, cell migration, and epithelial-to-mesenchymal transition.
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Affiliation(s)
- Alyson K. Freeman
- Laboratory of Cell and Developmental Signaling, NCI-Frederick, Frederick, MD 21702
| | - Deborah K. Morrison
- Laboratory of Cell and Developmental Signaling, NCI-Frederick, Frederick, MD 21702
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215
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Steelman LS, Chappell WH, Abrams SL, Kempf RC, Long J, Laidler P, Mijatovic S, Maksimovic-Ivanic D, Stivala F, Mazzarino MC, Donia M, Fagone P, Malaponte G, Nicoletti F, Libra M, Milella M, Tafuri A, Bonati A, Bäsecke J, Cocco L, Evangelisti C, Martelli AM, Montalto G, Cervello M, McCubrey JA. Roles of the Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR pathways in controlling growth and sensitivity to therapy-implications for cancer and aging. Aging (Albany NY) 2011; 3:192-222. [PMID: 21422497 PMCID: PMC3091517 DOI: 10.18632/aging.100296] [Citation(s) in RCA: 454] [Impact Index Per Article: 34.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Dysregulated signaling through the Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR pathways is often the result of genetic alterations in critical components in these pathways or upstream activators. Unrestricted cellular proliferation and decreased sensitivity to apoptotic-inducing agents are typically associated with activation of these pro-survival pathways. This review discusses the functions these pathways have in normal and neoplastic tissue growth and how they contribute to resistance to apoptotic stimuli. Crosstalk and commonly identified mutations that occur within these pathways that contribute to abnormal activation and cancer growth will also be addressed. Finally the recently described roles of these pathways in cancer stem cells, cellular senescence and aging will be evaluated. Controlling the expression of these pathways could ameliorate human health.
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Affiliation(s)
- Linda S Steelman
- Department of Microbiology and Immunology, East Carolina University, Greenville, NC 27858, USA
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216
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Abstract
Raf are conserved, ubiquitous serine/protein kinases discovered as the cellular elements hijacked by transforming retroviruses. The three mammalian RAF proteins (A, B and CRAF) can be activated by the human oncogene RAS, downstream from which they exert both kinase-dependent and kinase-independent, tumor-promoting functions. The kinase-dependent functions are mediated chiefly by the MEK/ERK pathway, whose activation is associated with proliferation in a broad range of human tumors. Almost 10 years ago, activating BRAF mutations were discovered in a subset of human tumors, and in the past year treatment with small-molecule RAF inhibitors has yielded unprecedented response rates in melanoma patients. Thus, Raf qualifies as an excellent molecular target for anticancer therapy. This review focuses on the role of BRAF and CRAF in different aspects of carcinogenesis, on the success of molecular therapies targeting Raf and the challenges they present.
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217
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14-3-3 protein beta/alpha as a urinary biomarker for renal cell carcinoma: proteomic analysis of cyst fluid. Anal Bioanal Chem 2011; 401:245-52. [PMID: 21553213 DOI: 10.1007/s00216-011-5057-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2011] [Revised: 04/06/2011] [Accepted: 04/22/2011] [Indexed: 01/22/2023]
Abstract
Although various samples, including tissue, cells, serum, and urine, from patients with renal cell carcinoma (RCC) have been analyzed, biomarkers with diagnostic value have yet to be identified. We used a proteomics approach to analyze cyst fluid in cases of cyst-associated RCC to identify accessible and abundant proteins that are overexpressed and/or secreted by RCC cells. Proteins in the cyst fluid were separated by reverse-phase high-performance liquid chromatography and agarose two-dimensional gel electrophoresis and were identified by tandem mass spectrometry. We conducted a National Center for Biotechnology Information search and a MEDLINE search to predict the function of these identified proteins and to select a tumor-marker candidate protein. Our search resulted in the identification and selection of the differentially regulated protein known as 14-3-3 protein beta/alpha, which was overexpressed in cyst fluid from cyst-associated RCC but has not been previously associated with RCC. We then measured its incidence through Western blotting of various normal and RCC samples (serum, urine, tissue, and cyst fluid). The expression levels of 14-3-3 protein beta/alpha were higher in urine samples from patients with RCC than in samples from healthy volunteers. Receiver operating characteristic (ROC) curve analyses were performed to assess this potential biomarker; these data (area under the ROC curve value was 0.8813) indicate a high degree of accuracy for this screening method. 14-3-3 Protein beta/alpha may be a diagnostically useful biomarker for early diagnosis of RCC.
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218
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Buchstaller HP, Burgdorf L, Finsinger D, Stieber F, Sirrenberg C, Amendt C, Grell M, Zenke F, Krier M. Design and synthesis of isoquinolines and benzimidazoles as RAF kinase inhibitors. Bioorg Med Chem Lett 2011; 21:2264-9. [DOI: 10.1016/j.bmcl.2011.02.108] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Revised: 02/24/2011] [Accepted: 02/25/2011] [Indexed: 01/07/2023]
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219
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Baljuls A, Mahr R, Schwarzenau I, Müller T, Polzien L, Hekman M, Rapp UR. Single substitution within the RKTR motif impairs kinase activity but promotes dimerization of RAF kinase. J Biol Chem 2011; 286:16491-503. [PMID: 21454547 DOI: 10.1074/jbc.m110.194167] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The serine/threonine kinase RAF is a central component of the MAPK cascade. Regulation of RAF activity is highly complex and involves recruitment to membranes and association with Ras and scaffold proteins as well as multiple phosphorylation and dephosphorylation events. Previously, we identified by molecular modeling an interaction between the N-region and the RKTR motif of the kinase domain in RAF and assigned a new function to this tetrapeptide segment. Here we found that a single substitution of each basic residue within the RKTR motif inhibited catalytic activity of all three RAF isoforms. However, the inhibition and phosphorylation pattern of C-RAF and A-RAF differed from B-RAF. Furthermore, substitution of the first arginine led to hyperphosphorylation and accumulation of A-RAF and C-RAF in plasma membrane fraction, indicating that this residue interferes with the recycling process of A-RAF and C-RAF but not B-RAF. In contrast, all RAF isoforms behave similarly with respect to the RKTR motif-dependent dimerization. The exchange of the second arginine led to exceedingly increased dimerization as long as one of the protomers was not mutated, suggesting that substitution of this residue with alanine may result in similar a structural rearrangement of the RAF kinase domain, as has been found for the C-RAF kinase domain co-crystallized with a dimerization-stabilizing RAF inhibitor. In summary, we provide evidence that each of the basic residues within the RKTR motif is indispensable for correct RAF function.
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Affiliation(s)
- Angela Baljuls
- Theodor-Boveri Institute of Bioscience, Department of Microbiology, University of Wuerzburg, Wuerzburg, Germany.
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220
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Matallanas D, Birtwistle M, Romano D, Zebisch A, Rauch J, von Kriegsheim A, Kolch W. Raf family kinases: old dogs have learned new tricks. Genes Cancer 2011; 2:232-60. [PMID: 21779496 PMCID: PMC3128629 DOI: 10.1177/1947601911407323] [Citation(s) in RCA: 272] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
First identified in the early 1980s as retroviral oncogenes, the Raf proteins have been the objects of intense research. The discoveries 10 years later that the Raf family members (Raf-1, B-Raf, and A-Raf) are bona fide Ras effectors and upstream activators of the ubiquitous ERK pathway increased the interest in these proteins primarily because of the central role that this cascade plays in cancer development. The important role of Raf in cancer was corroborated in 2002 with the discovery of B-Raf genetic mutations in a large number of tumors. This led to intensified drug development efforts to target Raf signaling in cancer. This work yielded not only recent clinical successes but also surprising insights into the regulation of Raf proteins by homodimerization and heterodimerization. Surprising insights also came from the hunt for new Raf targets. Although MEK remains the only widely accepted Raf substrate, new kinase-independent roles for Raf proteins have emerged. These include the regulation of apoptosis by suppressing the activity of the proapoptotic kinases, ASK1 and MST2, and the regulation of cell motility and differentiation by controlling the activity of Rok-α. In this review, we discuss the regulation of Raf proteins and their role in cancer, with special focus on the interacting proteins that modulate Raf signaling. We also describe the new pathways controlled by Raf proteins and summarize the successes and failures in the development of efficient anticancer therapies targeting Raf. Finally, we also argue for the necessity of more systemic approaches to obtain a better understanding of how the Ras-Raf signaling network generates biological specificity.
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Affiliation(s)
- David Matallanas
- Systems Biology Ireland, University College Dublin, Dublin, Ireland
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221
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Moon BS, Kim HY, Kim MY, Yang DH, Lee JM, Cho KW, Jung HS, Choi KY. Sur8/Shoc2 Involves Both Inhibition of Differentiation and Maintenance of Self-Renewal of Neural Progenitor Cells via Modulation of Extracellular Signal-Regulated Kinase Signaling. Stem Cells 2011; 29:320-31. [DOI: 10.1002/stem.586] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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222
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Polzien L, Baljuls A, Albrecht M, Hekman M, Rapp UR. BAD contributes to RAF-mediated proliferation and cooperates with B-RAF-V600E in cancer signaling. J Biol Chem 2011; 286:17934-44. [PMID: 21317286 DOI: 10.1074/jbc.m110.177345] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BAD (Bcl-2 antagonist of cell death) belongs to the proapoptotic BH3-only subfamily of Bcl-2 proteins. Physiological activity of BAD is highly controlled by phosphorylation. To further analyze the regulation of BAD function, we investigated the role of recently identified phosphorylation sites on BAD-mediated apoptosis. We found that in contrast to the N-terminal phosphorylation sites, the serines 124 and 134 act in an antiapoptotic manner because the replacement by alanine led to enhanced cell death. Our results further indicate that RAF kinases represent, besides PAK1, BAD serine 134 phosphorylating kinases. Importantly, in the presence of wild type BAD, co-expression of survival kinases, such as RAF and PAK1, leads to a strongly increased proliferation, whereas substitution of serine 134 by alanine abolishes this process. Furthermore, we identified BAD serine 134 to be strongly involved in survival signaling of B-RAF-V600E-containing tumor cells and found that phosphorylation of BAD at this residue is critical for efficient proliferation in these cells. Collectively, our findings provide new insights into the regulation of BAD function by phosphorylation and its role in cancer signaling.
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Affiliation(s)
- Lisa Polzien
- Department of Microbiology, Biocenter, University of Würzburg, 97074 Würzburg, Germany.
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223
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Udell CM, Rajakulendran T, Sicheri F, Therrien M. Mechanistic principles of RAF kinase signaling. Cell Mol Life Sci 2011; 68:553-65. [PMID: 20820846 PMCID: PMC11114552 DOI: 10.1007/s00018-010-0520-6] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2010] [Revised: 08/24/2010] [Accepted: 08/25/2010] [Indexed: 12/19/2022]
Abstract
The RAF family of kinases are key components acting downstream of receptor tyrosine kinases and cells employ several distinct mechanisms to strictly control their activity. RAF transitions from an inactive state, where the N-terminal regulatory region binds intramolecularly to the C-terminal kinase domain, to an open state capable of executing the phosphoryl transfer reaction. This transition involves changes both within and between the protein domains in RAF. Many different proteins regulate the transition between inactive and active states of RAF, including RAS and KSR, which are arguably the two most prominent regulators of RAF function. Recent developments have added several new twists to our understanding of RAF regulation. Among others, dimerization of the RAF kinase domain is emerging as a crucial step in the RAF activation process. The multitude of regulatory protein-protein interactions involving RAF remains a largely untapped area for therapeutic applications.
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Affiliation(s)
- Christian M. Udell
- Laboratory of Intracellular Signaling, Département de pathologie et de biologie cellulaire, Institute for Research in Immunology and Cancer, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montreal, QC H3C 3J7 Canada
| | - Thanashan Rajakulendran
- Centre for Systems Biology, Samuel Lunenfeld Research Institute, Toronto, ON M5G 1X5 Canada
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8 Canada
| | - Frank Sicheri
- Centre for Systems Biology, Samuel Lunenfeld Research Institute, Toronto, ON M5G 1X5 Canada
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8 Canada
| | - Marc Therrien
- Laboratory of Intracellular Signaling, Département de pathologie et de biologie cellulaire, Institute for Research in Immunology and Cancer, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montreal, QC H3C 3J7 Canada
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224
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Ahnstedt H, Säveland H, Nilsson O, Edvinsson L. Human cerebrovascular contractile receptors are upregulated via a B-Raf/MEK/ERK-sensitive signaling pathway. BMC Neurosci 2011; 12:5. [PMID: 21223556 PMCID: PMC3023719 DOI: 10.1186/1471-2202-12-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2010] [Accepted: 01/11/2011] [Indexed: 11/11/2022] Open
Abstract
Background Cerebral ischemia results in a rapid increase in contractile cerebrovascular receptors, such as the 5-hydroxytryptamine type 1B (5-HT1B), angiotensin II type 1 (AT1), and endothelin type B (ETB) receptors, in the vessel walls within the ischemic region, which further impairs local blood flow and aggravates tissue damage. This receptor upregulation occurs via activation of the mitogen-activated protein kinase pathway. We therefore hypothesized an important role for B-Raf, the first signaling molecule in the pathway. To test our hypothesis, human cerebral arteries were incubated at 37°C for 48 h in the absence or presence of a B-Raf inhibitor: SB-386023 or SB-590885. Contractile properties were evaluated in a myograph and protein expression of the individual receptors and activated phosphorylated B-Raf (p-B-Raf) was evaluated immunohistochemically. Results 5-HT1B, AT1, and ETB receptor-mediated contractions were significantly reduced by application of SB-590885, and to a smaller extent by SB-386023. A marked reduction in AT1 receptor immunoreactivity was observed after treatment with SB-590885. Treatment with SB-590885 and SB-386023 diminished the culture-induced increase of p-B-Raf immunoreactivity. Conclusions B-Raf signaling has a key function in the altered expression of vascular contractile receptors observed after organ culture. Therefore, specific targeting of B-Raf might be a novel approach to reduce tissue damage after cerebral ischemia by preventing the previously observed upregulation of contractile receptors in smooth muscle cells.
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Affiliation(s)
- Hilda Ahnstedt
- Department of Clinical Sciences, Lund University, Sweden.
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225
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Sturm OE, Orton R, Grindlay J, Birtwistle M, Vyshemirsky V, Gilbert D, Calder M, Pitt A, Kholodenko B, Kolch W. The mammalian MAPK/ERK pathway exhibits properties of a negative feedback amplifier. Sci Signal 2010; 3:ra90. [PMID: 21177493 DOI: 10.1126/scisignal.2001212] [Citation(s) in RCA: 186] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Three-tiered kinase modules, such as the Raf-MEK (mitogen-activated or extracellular signal-regulated protein kinase kinase)-ERK (extracellular signal-regulated kinase) mitogen-activated protein kinase pathway, are widespread in biology, suggesting that this structure conveys evolutionarily advantageous properties. We show that the three-tiered kinase amplifier module combined with negative feedback recapitulates the design principles of a negative feedback amplifier (NFA), which is used in electronic circuits to confer robustness, output stabilization, and linearization of nonlinear signal amplification. We used mathematical modeling and experimental validation to demonstrate that the ERK pathway has properties of an NFA that (i) converts intrinsic switch-like activation kinetics into graded linear responses, (ii) conveys robustness to changes in rates of reactions within the NFA module, and (iii) stabilizes outputs in response to drug-induced perturbations of the amplifier. These properties determine biological behavior, including activation kinetics and the response to drugs.
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Affiliation(s)
- Oliver E Sturm
- Department of Computing Science, University of Glasgow, Glasgow G12 8QQ, UK.
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226
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Wimmer R, Baccarini M. Partner exchange: protein-protein interactions in the Raf pathway. Trends Biochem Sci 2010; 35:660-8. [PMID: 20621483 DOI: 10.1016/j.tibs.2010.06.001] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Revised: 05/27/2010] [Accepted: 06/07/2010] [Indexed: 01/07/2023]
Abstract
The three-tiered Raf-MEK-ERK kinase module is activated downstream of Ras and has been traditionally linked to cellular proliferation. Mammals have three Raf, two Mek and two Erk genes. Recently, the analysis of protein-protein interactions in the pathway has begun to provide a rationale for the redundancy within each tier. New results show that the MEK-ERK-activating unit consists of Raf hetero- and homodimers; downstream of Raf, MEK1-MEK2 heterodimers and ERK dimers are required for temporal and spatial pathway regulation. Finally, C-Raf mediates pathway crosstalk downstream of Ras by directly binding to and inhibiting kinases engaged in other signaling cascades. Given the roles of these interactions in tumorigenesis, their study will provide new opportunities for molecule-based therapies that target the pathway.
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Affiliation(s)
- Reiner Wimmer
- University of Vienna, Center for Molecular Biology, Max F. Perutz Laboratories, Doktor-Bohr-Gasse 9, A-1030 Vienna, Austria
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227
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Calcineurin increases glucose activation of ERK1/2 by reversing negative feedback. Proc Natl Acad Sci U S A 2010; 107:22314-9. [PMID: 21135229 DOI: 10.1073/pnas.1016630108] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
In pancreatic β cells, ERK1 and ERK2 participate in nutrient sensing, and their activities rise and fall as a function of glucose concentration over the physiologic range. Glucose metabolism triggers calcium influx and release of calcium from intracellular stores to activate ERK1/2. Calcium influx also activates the calcium-dependent phosphatase calcineurin, which is required for maximal ERK1/2 activation by glucose. Calcineurin controls insulin gene expression by ERK1/2-dependent and -independent mechanisms. Here, we show that, in β cells, glucose activates the ERK1/2 cascade primarily through B-Raf. Glucose activation of B-Raf, like that of ERK1/2, is calcineurin-sensitive. Calcineurin binds to B-Raf in both unstimulated and stimulated cells. We show that B-Raf is a calcineurin substrate; among calcineurin target residues on B-Raf is T401, a site of negative feedback phosphorylation by ERK1/2. Blocking calcineurin activity in β cells prevents dephosphorylation of B-Raf T401 and decreases B-Raf and ERK1/2 activities. We conclude that the major calcineurin-dependent event in glucose sensing by ERK1/2 is the activation of B-Raf.
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228
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Wallace DP. Cyclic AMP-mediated cyst expansion. Biochim Biophys Acta Mol Basis Dis 2010; 1812:1291-300. [PMID: 21118718 DOI: 10.1016/j.bbadis.2010.11.005] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2010] [Revised: 11/12/2010] [Accepted: 11/16/2010] [Indexed: 12/29/2022]
Abstract
In polycystic kidney disease (PKD), intracellular cAMP promotes cyst enlargement by stimulating mural epithelial cell proliferation and transepithelial fluid secretion. The proliferative effect of cAMP in PKD is unique in that cAMP is anti-mitogenic in normal renal epithelial cells. This phenotypic difference in the proliferative response to cAMP appears to involve cross-talk between cAMP and Ca(2+) signaling to B-Raf, a kinase upstream of the MEK/ERK pathway. In normal cells, B-Raf is repressed by Akt (protein kinase B), a Ca(2+)-dependent kinase, preventing cAMP activation of ERK and cell proliferation. In PKD cells, disruption of intracellular Ca(2+) homeostasis due to mutations in the PKD genes relieves Akt inhibition of B-Raf, allowing cAMP stimulation of B-Raf, ERK and cell proliferation. Fluid secretion by cystic cells is driven by cAMP-dependent transepithelial Cl(-) secretion involving apical cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channels. This review summarizes the current knowledge of cAMP-dependent cyst expansion, focusing on cell proliferation and Cl(-)-dependent fluid secretion, and discusses potential therapeutic approaches to inhibit renal cAMP production and its downstream effects on cyst enlargement. This article is part of a Special Issue entitled: Polycystic Kidney Disease.
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Affiliation(s)
- Darren P Wallace
- Department of Internal Medicine, University of Kansas Medical Center, Kansas City, KS, USA.
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229
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Cirit M, Wang CC, Haugh JM. Systematic quantification of negative feedback mechanisms in the extracellular signal-regulated kinase (ERK) signaling network. J Biol Chem 2010; 285:36736-44. [PMID: 20847054 PMCID: PMC2978602 DOI: 10.1074/jbc.m110.148759] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2010] [Revised: 08/20/2010] [Indexed: 12/28/2022] Open
Abstract
Cell responses are actuated by tightly controlled signal transduction pathways. Although the concept of an integrated signaling network replete with interpathway cross-talk and feedback regulation is broadly appreciated, kinetic data of the type needed to characterize such interactions in conjunction with mathematical models are lacking. In mammalian cells, the Ras/ERK pathway controls cell proliferation and other responses stimulated by growth factors, and several cross-talk and feedback mechanisms affecting its activation have been identified. In this work, we take a systematic approach to parse the magnitudes of multiple regulatory mechanisms that attenuate ERK activation through canonical (Ras-dependent) and non-canonical (PI3K-dependent) pathways. In addition to regulation of receptor and ligand levels, we consider three layers of ERK-dependent feedback: desensitization of Ras activation, negative regulation of MEK kinase (e.g. Raf) activities, and up-regulation of dual-specificity ERK phosphatases. Our results establish the second of these as the dominant mode of ERK self-regulation in mouse fibroblasts. We further demonstrate that kinetic models of signaling networks, trained on a sufficient diversity of quantitative data, can be reasonably comprehensive, accurate, and predictive in the dynamical sense.
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Affiliation(s)
- Murat Cirit
- From the Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695
| | - Chun-Chao Wang
- From the Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695
| | - Jason M. Haugh
- From the Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695
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230
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Vakiani E, Solit DB. KRAS and BRAF: drug targets and predictive biomarkers. J Pathol 2010; 223:219-29. [PMID: 21125676 DOI: 10.1002/path.2796] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2010] [Revised: 09/22/2010] [Accepted: 09/24/2010] [Indexed: 12/11/2022]
Abstract
Three decades have passed since RAS was first identified as the transformative factor in the Harvey and Kirsten strains of the mouse sarcoma virus. RAS and several of its downstream effectors, including BRAF, have since been shown to be commonly mutated in broad range of human cancers and biological studies have confirmed that RAS pathway activation promotes tumour initiation, progression and metastatic spread in many contexts. With the identification of RAS mutation as a strong predictor of clinical resistance to EGFR-targeted therapies, RAS mutational testing has been incorporated into the routine clinical care of patients with colorectal and lung cancers. This article reviews the current understanding of RAS signalling as it relates to cancer biology, current efforts to develop inhibitors of RAS and its key downstream effectors and the technical challenges of RAS mutational testing in the clinical setting.
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Affiliation(s)
- Efsevia Vakiani
- Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA
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231
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Nek10 mediates G2/M cell cycle arrest and MEK autoactivation in response to UV irradiation. Mol Cell Biol 2010; 31:30-42. [PMID: 20956560 DOI: 10.1128/mcb.00648-10] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Appropriate cell cycle checkpoint control is essential for the maintenance of cell and organismal homeostasis. Members of the Nek (NIMA-related kinase) family of serine/threonine protein kinases have been implicated in the regulation of various aspects of the cell cycle. We explored the cellular functions of Nek10, a novel member of the Nek family, and demonstrate a role for Nek10 in the cellular UV response. Nek10 was required for the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling upon UV irradiation but not in response to mitogens, such as epidermal growth factor stimulation. Nek10 physically associated with Raf-1 and MEK1 in a Raf-1-dependent manner, and the formation of this complex was necessary for Nek10-mediated MEK1 activation. Nek10 did not affect the kinase activity of Raf-1 but instead promoted the autophosphorylation-dependent activation of MEK1. The appropriate maintenance of the G(2)/M checkpoint following UV irradiation required Nek10 expression and ERK1/2 activation. Taken together, our results uncover a role for Nek10 in the cellular response to UV irradiation.
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232
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Kaplan FM, Shao Y, Mayberry MM, Aplin AE. Hyperactivation of MEK-ERK1/2 signaling and resistance to apoptosis induced by the oncogenic B-RAF inhibitor, PLX4720, in mutant N-RAS melanoma cells. Oncogene 2010; 30:366-71. [PMID: 20818433 DOI: 10.1038/onc.2010.408] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Activating mutations in B-RAF and N-RAS occur in ∼60 and ∼15% of melanomas, respectively. The most common mutation in B-RAF is V600E, which activates B-RAF and the downstream MEK-ERK1/2 pathway. Thus, B-RAF(V600E) is a viable therapeutic target. PLX4720 is a selective inhibitor of mutant B-RAF and its analog, PLX4032, is currently undergoing clinical trials in melanoma. However, the effects of PLX4720 across the genotypic spectrum in melanoma remain unclear. Here, we describe that PLX4720 treatment rapidly induces hyperactivation of the MEK-ERK1/2 pathway in mutant N-RAS melanoma cells. Furthermore, we demonstrate that C-RAF is the major RAF isoform involved in this process. Importantly, PLX4720-induced hyperactivation of the MEK-ERK1/2 pathway promotes resistance to apoptosis in both non-invasive and invasive mutant N-RAS melanoma cells but does not enhance cell cycle properties. These findings underscore the need to genotypically stratify melanoma patients before enrollment on a mutant B-RAF inhibitor trial.
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Affiliation(s)
- F M Kaplan
- Department of Cancer Biology and Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA
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233
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Roskoski R. RAF protein-serine/threonine kinases: structure and regulation. Biochem Biophys Res Commun 2010; 399:313-7. [PMID: 20674547 DOI: 10.1016/j.bbrc.2010.07.092] [Citation(s) in RCA: 245] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Accepted: 07/25/2010] [Indexed: 01/02/2023]
Abstract
A-RAF, B-RAF, and C-RAF are a family of three protein-serine/threonine kinases that participate in the RAS-RAF-MEK-ERK signal transduction cascade. This cascade participates in the regulation of a large variety of processes including apoptosis, cell cycle progression, differentiation, proliferation, and transformation to the cancerous state. RAS mutations occur in 15-30% of all human cancers, and B-RAF mutations occur in 30-60% of melanomas, 30-50% of thyroid cancers, and 5-20% of colorectal cancers. Activation of the RAF kinases requires their interaction with RAS-GTP along with dephosphorylation and also phosphorylation by SRC family protein-tyrosine kinases and other protein-serine/threonine kinases. The formation of unique side-to-side RAF dimers is required for full kinase activity. RAF kinase inhibitors are effective in blocking MEK1/2 and ERK1/2 activation in cells containing the oncogenic B-RAF Val600Glu activating mutation. RAF kinase inhibitors lead to the paradoxical increase in RAF kinase activity in cells containing wild-type B-RAF and wild-type or activated mutant RAS. C-RAF plays a key role in this paradoxical increase in downstream MEK-ERK activation.
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Affiliation(s)
- Robert Roskoski
- Blue Ridge Institute for Medical Research, 3754 Brevard Road, Suite 116, Box 19, Horse Shoe, NC 28742, USA.
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234
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235
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Poulikakos PI, Zhang C, Bollag G, Shokat KM, Rosen N. RAF inhibitors transactivate RAF dimers and ERK signalling in cells with wild-type BRAF. Nature 2010; 464:427-30. [PMID: 20179705 PMCID: PMC3178447 DOI: 10.1038/nature08902] [Citation(s) in RCA: 1386] [Impact Index Per Article: 99.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2009] [Accepted: 02/16/2010] [Indexed: 12/25/2022]
Affiliation(s)
- Poulikos I Poulikakos
- Program in Molecular Pharmacology and Chemistry and Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA
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236
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Pathological roles of MAPK signaling pathways in human diseases. Biochim Biophys Acta Mol Basis Dis 2010; 1802:396-405. [DOI: 10.1016/j.bbadis.2009.12.009] [Citation(s) in RCA: 1521] [Impact Index Per Article: 108.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2009] [Revised: 11/26/2009] [Accepted: 12/01/2009] [Indexed: 12/13/2022]
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237
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Xu TR, Vyshemirsky V, Gormand A, von Kriegsheim A, Girolami M, Baillie GS, Ketley D, Dunlop AJ, Milligan G, Houslay MD, Kolch W. Inferring Signaling Pathway Topologies from Multiple Perturbation Measurements of Specific Biochemical Species. Sci Signal 2010; 3:ra20. [DOI: 10.1126/scisignal.2000517] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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238
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Kilili GK, Kyriakis JM. Mammalian Ste20-like kinase (Mst2) indirectly supports Raf-1/ERK pathway activity via maintenance of protein phosphatase-2A catalytic subunit levels and consequent suppression of inhibitory Raf-1 phosphorylation. J Biol Chem 2010; 285:15076-15087. [PMID: 20212043 DOI: 10.1074/jbc.m109.078915] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many tumor suppressor proteins act to blunt the effects of mitogenic signaling pathways. Loss of function mutations in the merlin tumor suppressor underlie neurofibromatosis type 2 (NF2), a familial autosomal dominant cancer syndrome. Studies of Drosophila suggest that Hippo (hpo) is required for inhibition of cell proliferation mediated by dMer, the orthologue of human merlin. Mammalian sterile 20-like kinase-2 (Mst2) is a mammalian Hpo orthologue, and numerous studies implicate Mst2 as a tumor suppressor. Mst2 is negatively regulated by the proto-oncoprotein Raf-1 in a manner independent of the kinase activity of Raf-1. We sought to determine whether, in mammalian cells, merlin could positively regulate Mst2. We also sought to determine whether Mst2, in addition to being negatively regulated by Raf-1, might itself reciprocally regulate Raf-1. In contrast to findings from Drosophila, we find no evidence that mammalian merlin positively regulates mammalian Mst2. Instead, surprisingly, RNA interference silencing of Mst2 leads to elevated inhibitory phosphorylation of Raf-1 at Ser-259 and impaired Raf-1 kinase activity. Consequent to this, ERK pathway activation and cell proliferation are attenuated. Phosphatase-2A (PP2A) dephosphorylates Raf-1 Ser-259 in response to mitogens. Interestingly RNA interference silencing of Mst2 triggers a striking proteasome-dependent decrease in the levels of the catalytic subunit of PP2A (PP2A-C). A similar effect is achieved upon silencing of large tumor suppressor (LATS)-1 and LATS2, direct substrates of Mst2. Our studies reveal a more complex role for Mst2 than previously thought. The Mst2 --> LATS1/2 pathway, by maintaining PP2A-C levels, may, in some situations, positively affect mitogenic signaling.
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Affiliation(s)
- Geoffrey K Kilili
- Molecular Cardiology Research Institute, Tufts Medical Center, and the Department of Biochemistry, Tufts University Sackler School of Graduate Biomedical Sciences, Boston, Massachusetts 02111
| | - John M Kyriakis
- Molecular Cardiology Research Institute, Tufts Medical Center, and the Department of Biochemistry, Tufts University Sackler School of Graduate Biomedical Sciences, Boston, Massachusetts 02111.
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239
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Heidorn SJ, Milagre C, Whittaker S, Nourry A, Niculescu-Duvas I, Dhomen N, Hussain J, Reis-Filho JS, Springer CJ, Pritchard C, Marais R. Kinase-dead BRAF and oncogenic RAS cooperate to drive tumor progression through CRAF. Cell 2010; 140:209-21. [PMID: 20141835 PMCID: PMC2872605 DOI: 10.1016/j.cell.2009.12.040] [Citation(s) in RCA: 1145] [Impact Index Per Article: 81.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2009] [Revised: 11/03/2009] [Accepted: 12/18/2009] [Indexed: 12/18/2022]
Abstract
We describe a mechanism of tumorigenesis mediated by kinase-dead BRAF in the presence of oncogenic RAS. We show that drugs that selectively inhibit BRAF drive RAS-dependent BRAF binding to CRAF, CRAF activation, and MEK-ERK signaling. This does not occur when oncogenic BRAF is inhibited, demonstrating that BRAF inhibition per se does not drive pathway activation; it only occurs when BRAF is inhibited in the presence of oncogenic RAS. Kinase-dead BRAF mimics the effects of the BRAF-selective drugs and kinase-dead Braf and oncogenic Ras cooperate to induce melanoma in mice. Our data reveal another paradigm of BRAF-mediated signaling that promotes tumor progression. They highlight the importance of understanding pathway signaling in clinical practice and of genotyping tumors prior to administering BRAF-selective drugs, to identify patients who are likely to respond and also to identify patients who may experience adverse effects.
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Affiliation(s)
- Sonja J Heidorn
- The Institute of Cancer Research, Signal Transduction Team, Section of Cell and Molecular Biology, 237 Fulham Road, London SW3 6JB, UK
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240
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Disruption of angiogenesis and tumor growth with an orally active drug that stabilizes the inactive state of PDGFRbeta/B-RAF. Proc Natl Acad Sci U S A 2010; 107:4299-304. [PMID: 20154271 DOI: 10.1073/pnas.0909299107] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Kinases are known to regulate fundamental processes in cancer including tumor proliferation, metastasis, neovascularization, and chemoresistance. Accordingly, kinase inhibitors have been a major focus of drug development, and several kinase inhibitors are now approved for various cancer indications. Typically, kinase inhibitors are selected via high-throughput screening using catalytic kinase domains at low ATP concentration, and this process often yields ATP mimetics that lack specificity and/or function poorly in cells where ATP levels are high. Molecules targeting the allosteric site in the inactive kinase conformation (type II inhibitors) provide an alternative for developing selective inhibitors that are physiologically active. By applying a rational design approach using a constrained amino-triazole scaffold predicted to stabilize kinases in the inactive state, we generated a series of selective type II inhibitors of PDGFRbeta and B-RAF, important targets for pericyte recruitment and endothelial cell survival, respectively. These molecules were designed in silico and screened for antivascular activity in both cell-based models and a Tg(fli1-EGFP) zebrafish embryogenesis model. Dual inhibition of PDGFRbeta and B-RAF cellular signaling demonstrated synergistic antiangiogenic activity in both zebrafish and murine models of angiogenesis, and a combination of previously characterized PDGFRbeta and RAF inhibitors validated the synergy. Our lead compound was selected as an orally active molecule with favorable pharmacokinetic properties which demonstrated target inhibition in vivo leading to suppression of murine orthotopic tumors in both the kidney and pancreas.
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Halaban R, Zhang W, Bacchiocchi A, Cheng E, Parisi F, Ariyan S, Krauthammer M, McCusker JP, Kluger Y, Sznol M. PLX4032, a selective BRAF(V600E) kinase inhibitor, activates the ERK pathway and enhances cell migration and proliferation of BRAF melanoma cells. Pigment Cell Melanoma Res 2010; 23:190-200. [PMID: 20149136 PMCID: PMC2848976 DOI: 10.1111/j.1755-148x.2010.00685.x] [Citation(s) in RCA: 267] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BRAFV600E/K is a frequent mutationally active tumor-specific kinase in melanomas that is currently targeted for therapy by the specific inhibitor PLX4032. Our studies with melanoma tumor cells that are BRAFV600E/K and BRAFWT showed that, paradoxically, while PLX4032 inhibited ERK1/2 in the highly sensitive BRAFV600E/K, it activated the pathway in the resistant BRAFWT cells, via RAF1 activation, regardless of the status of mutations in NRAS or PTEN. The persistently active ERK1/2 triggered downstream effectors in BRAFWT melanoma cells and induced changes in the expression of a wide-spectrum of genes associated with cell cycle control. Furthermore, PLX4032 increased the rate of proliferation of growth factor-dependent NRAS Q61L mutant primary melanoma cells, reduced cell adherence and increased mobility of cells from advanced lesions. The results suggest that the drug can confer an advantage to BRAFWT primary and metastatic tumor cells in vivo and provide markers for monitoring clinical responses.
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Affiliation(s)
- Ruth Halaban
- Department of Dermatology, Yale University School of Medicine, New Haven, CT, USA.
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242
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Hatzivassiliou G, Song K, Yen I, Brandhuber BJ, Anderson DJ, Alvarado R, Ludlam MJC, Stokoe D, Gloor SL, Vigers G, Morales T, Aliagas I, Liu B, Sideris S, Hoeflich KP, Jaiswal BS, Seshagiri S, Koeppen H, Belvin M, Friedman LS, Malek S. RAF inhibitors prime wild-type RAF to activate the MAPK pathway and enhance growth. Nature 2010; 464:431-5. [DOI: 10.1038/nature08833] [Citation(s) in RCA: 1256] [Impact Index Per Article: 89.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Accepted: 01/18/2010] [Indexed: 02/07/2023]
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243
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Wei H, Zhou MM. Regulation of Raf activity by dimerization. Pigment Cell Melanoma Res 2010; 23:156-7. [PMID: 20067555 DOI: 10.1111/j.1755-148x.2010.00672.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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244
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Karreth FA, DeNicola GM, Winter SP, Tuveson DA. C-Raf inhibits MAPK activation and transformation by B-Raf(V600E). Mol Cell 2010; 36:477-86. [PMID: 19917255 DOI: 10.1016/j.molcel.2009.10.017] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2009] [Revised: 08/10/2009] [Accepted: 09/17/2009] [Indexed: 10/20/2022]
Abstract
Activating B-Raf mutations that deregulate the MAPK pathway commonly occur in cancer. Whether additional proteins modulate the enzymatic activity of oncogenic B-Raf is unknown. Here we show that the proto-oncogene C-Raf paradoxically inhibits B-Raf(V600E) kinase activity through the formation of B-Raf(V600E)-C-Raf complexes. Although all Raf family members associate with oncogenic B-Raf, this inhibitory effect is specific to C-Raf. Indeed, a B-Raf(V600E) isoform with impaired ability to interact with C-Raf exhibits elevated oncogenic potential. Human melanoma cells expressing B-Raf(V600E) display a reduced C-Raf:B-Raf ratio, and further suppression of C-Raf increases MAPK activation and proliferation. Conversely, ectopic C-Raf expression lowers ERK phosphorylation and proliferation. Moreover, both oncogenic Ras and Sorafenib stabilize B-Raf(V600E)-C-Raf complexes, thereby impairing MAPK activation. This inhibitory function of C-Raf on B-Raf(V600E)-mediated MAPK activation may explain the lack of co-occurrence of B-Raf(V600E) and oncogenic Ras mutations, and influence the successful clinical development of small molecule inhibitors for B-Raf(V600E)-driven cancers.
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Affiliation(s)
- Florian A Karreth
- Li Ka Shing Centre, Cambridge Research Institute, Cancer Research UK, Robinson Way, Cambridge CB2 0RE, UK
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245
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Abstract
Some 25 years ago, Raf was discovered as the transforming principle shared by a murine sarcoma and an avian carcinoma virus. Thus, Raf and tumorigenesis have been connected from the very beginning. Ten years later, the work of many groups instated Raf as the link between Ras, the oncogene most frequently mutated in human cancers, and the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK/ERK) module, which with its manifold substrates can contribute to different aspects of carcinogenesis. Finally, the discovery of activating B-Raf mutations in a subset of human cancers, notably melanomas, conclusively established Raf as a major player in tumor development. Recent studies in animal models now show that endogenous C-Raf is essential for the development and maintenance of Ras-induced epidermal tumors. Surprisingly, the role of C-Raf in this case is not that of an mitogen-activated protein kinase activator, but rather that of an endogenous inhibitor of Rho signaling, expanding the range of tumor-related Raf targets. This review focuses on old and new targets of Raf in tumorigenesis.
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Affiliation(s)
- Théodora S Niault
- Center for Molecular Biology, Max F Perutz Laboratories, University of Vienna, Doktor-Bohr-Gasse 9, 1030 Vienna, Austria
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246
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Impact of feedback phosphorylation and Raf heterodimerization on normal and mutant B-Raf signaling. Mol Cell Biol 2009; 30:806-19. [PMID: 19933846 DOI: 10.1128/mcb.00569-09] [Citation(s) in RCA: 175] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The B-Raf kinase is a Ras pathway effector activated by mutation in numerous human cancers and certain developmental disorders. Here we report that normal and oncogenic B-Raf proteins are subject to a regulatory cycle of extracellular signal-regulated kinase (ERK)-dependent feedback phosphorylation, followed by PP2A- and Pin1-dependent dephosphorylation/recycling. We identify four S/TP sites of B-Raf phosphorylated by activated ERK and find that feedback phosphorylation of B-Raf inhibits binding to activated Ras and disrupts heterodimerization with C-Raf, which is dependent on the B-Raf pS729/14-3-3 binding site. Moreover, we find that events influencing Raf heterodimerization can alter the transforming potential of oncogenic B-Raf proteins possessing intermediate or impaired kinase activity but have no significant effect on proteins with high kinase activity, such as V600E B-Raf. Mutation of the feedback sites or overexpression of the Pin1 prolyl-isomerase, which facilitates B-Raf dephosphorylation/recycling, resulted in increased transformation, whereas mutation of the S729/14-3-3 binding site or expression of dominant negative Pin1 reduced transformation. Mutation of each feedback site caused increased transformation and correlated with enhanced heterodimerization and activation of C-Raf. Finally, we find that B-Raf and C-Raf proteins containing mutations identified in certain developmental disorders constitutively heterodimerize and that their signaling activity can also be modulated by feedback phosphorylation.
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247
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Can BAD pores be good? New insights from examining BAD as a target of RAF kinases. ACTA ACUST UNITED AC 2009; 50:147-59. [PMID: 19895838 DOI: 10.1016/j.advenzreg.2009.10.025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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248
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Moretti S, De Falco V, Tamburrino A, Barbi F, Tavano M, Avenia N, Santeusanio F, Santoro M, Macchiarulo A, Puxeddu E. Insights into the molecular function of the inactivating mutations of B-Raf involving the DFG motif. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:1634-45. [PMID: 19735675 DOI: 10.1016/j.bbamcr.2009.09.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2008] [Revised: 08/28/2009] [Accepted: 09/01/2009] [Indexed: 12/19/2022]
Abstract
BRAF gene mutations have been associated with human cancers. Among the naturally occurring mutations, two that involve amino acids of the conserved DFG motif in the activation loop (D594V and G596R), appear to be inactivating. Aim of this study was to analyze the molecular mechanisms involved in the loss of function of B-Raf inactivating mutation G596R. Furthermore, the ability of the B-Raf DFG motif mutants to generate heterodimers with C-Raf and the possible functional consequences of the B-Raf/C-Raf heterodimer formation was examined. Wet molecular experiments in HEK293T cells demonstrate that B-Raf(G596R) is a kinase-impaired mutant. Molecular dynamics simulations show that the loss of function of B-Raf(G596R) depends on a restraining effect of Arg596 on the catalytic residue Asp594, which results in the loss of the appropriate spatial localization and/or conformation of the latter necessary for anchoring ATP to the enzyme. Exploration of B-Raf/C-Raf heterodimer formation indicates the occurrence of functioning heterodimers in the case of all the DFG B-Raf mutants, independently from the expected differences in spatial conformation of the activation loop, although the transforming activity of the mutants appear negligible. In conclusion, this study delivers novel information on the functional properties of the B-Raf DFG motif inactivating mutants and on the mechanisms driving B-Raf/C-Raf heterodimerization and consequent C-Raf transactivation.
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Affiliation(s)
- Sonia Moretti
- Dipartimento di Medicina Interna, Università di Perugia, Perugia, Italy
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249
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Rajakulendran T, Sahmi M, Lefrançois M, Sicheri F, Therrien M. A dimerization-dependent mechanism drives RAF catalytic activation. Nature 2009; 461:542-5. [PMID: 19727074 DOI: 10.1038/nature08314] [Citation(s) in RCA: 360] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2009] [Accepted: 07/24/2009] [Indexed: 11/09/2022]
Abstract
The ERK (extracellular signal-regulated kinase) pathway is an evolutionarily conserved signal transduction module that controls cellular growth, differentiation and survival. Activation of receptor tyrosine kinases (RTKs) by the binding of growth factors initiates GTP loading of RAS, which triggers the initial steps in the activation of the ERK pathway by modulating RAF family kinase function. Once activated, RAF participates in a sequential cascade of phosphorylation events that activate MEK, and in turn ERK. Unbridled signalling through the ERK pathway caused by activating mutations in RTKs, RAS or RAF has been linked to several human cancers. Of note, one member of the RAF family, BRAF, is the most frequently mutated oncogene in the kinase superfamily. Not surprisingly, there has been a colossal effort to understand the underlying regulation of this family of kinases. In particular, the process by which the RAF kinase domain becomes activated towards its substrate MEK remains of topical interest. Here, using Drosophila Schneider S2 cells, we demonstrate that RAF catalytic function is regulated in response to a specific mode of dimerization of its kinase domain, which we term the side-to-side dimer. Moreover, we find that the RAF-related pseudo-kinase KSR (kinase suppressor of Ras) also participates in forming side-to-side heterodimers with RAF and can thereby trigger RAF activation. This mechanism provides an elegant explanation for the longstanding conundrum about RAF catalytic activation, and also provides an explanation for the capacity of KSR, despite lacking catalytic function, to directly mediate RAF activation. We also show that RAF side-to-side dimer formation is essential for aberrant signalling by oncogenic BRAF mutants, and identify an oncogenic mutation that acts specifically by promoting side-to-side dimerization. Together, our data identify the side-to-side dimer interface of RAF as a potential therapeutic target for intervention in BRAF-dependent tumorigenesis.
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Affiliation(s)
- Thanashan Rajakulendran
- Centre for Systems Biology, Samuel Lunenfeld Research Institute, Toronto, Ontario M5G 1X5, Canada
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250
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Abstract
The extracellular signal-regulated kinase cascade is a central signaling pathway that is stimulated by various extracellular stimuli. The signals of these stimuli are then transferred by the cascade's components to a large number of targets at distinct subcellular compartments, which in turn induce and regulate a large number of cellular processes. To achieve these functions, the cascade exhibits versatile and dynamic subcellular distribution that allows proper temporal and spatial modulation of the appropriate processes. In this review, we discuss the intracellular localizations of different components of the ERK cascade, and the impact of these localizations on their activation and specificity.
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Affiliation(s)
- Zhong Yao
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot, Israel
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