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Riaud M, Maxwell J, Soria-Bretones I, Dankner M, Li M, Rose AAN. The role of CRAF in cancer progression: from molecular mechanisms to precision therapies. Nat Rev Cancer 2024; 24:105-122. [PMID: 38195917 DOI: 10.1038/s41568-023-00650-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 11/27/2023] [Indexed: 01/11/2024]
Abstract
The RAF family of kinases includes key activators of the pro-tumourigenic mitogen-activated protein kinase pathway. Hyperactivation of RAF proteins, particularly BRAF and CRAF, drives tumour progression and drug resistance in many types of cancer. Although BRAF is the most studied RAF protein, partially owing to its high mutation incidence in melanoma, the role of CRAF in tumourigenesis and drug resistance is becoming increasingly clinically relevant. Here, we summarize the main known regulatory mechanisms and gene alterations that contribute to CRAF activity, highlighting the different oncogenic roles of CRAF, and categorize RAF1 (CRAF) mutations according to the effect on kinase activity. Additionally, we emphasize the effect that CRAF alterations may have on drug resistance and how precision therapies could effectively target CRAF-dependent tumours. Here, we discuss preclinical and clinical findings that may lead to improved treatments for all types of oncogenic RAF1 alterations in cancer.
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Affiliation(s)
- Melody Riaud
- Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada
- Lady Davis Institute, Jewish General Hospital, Montreal, Quebec, Canada
| | - Jennifer Maxwell
- Lady Davis Institute, Jewish General Hospital, Montreal, Quebec, Canada
- Division of Experimental Medicine, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
| | - Isabel Soria-Bretones
- Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada
- Lady Davis Institute, Jewish General Hospital, Montreal, Quebec, Canada
- Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada
| | - Matthew Dankner
- Lady Davis Institute, Jewish General Hospital, Montreal, Quebec, Canada
- Faculty of Medicine, McGill University, Montreal, Quebec, Canada
- Rosalind & Morris Goodman Cancer Institute, McGill University, Montreal, Quebec, Canada
| | - Meredith Li
- Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada
| | - April A N Rose
- Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada.
- Lady Davis Institute, Jewish General Hospital, Montreal, Quebec, Canada.
- Division of Experimental Medicine, Faculty of Medicine, McGill University, Montreal, Quebec, Canada.
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2
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The 14-3-3 Proteins as Important Allosteric Regulators of Protein Kinases. Int J Mol Sci 2020; 21:ijms21228824. [PMID: 33233473 PMCID: PMC7700312 DOI: 10.3390/ijms21228824] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 11/20/2020] [Accepted: 11/20/2020] [Indexed: 12/14/2022] Open
Abstract
Phosphorylation by kinases governs many key cellular and extracellular processes, such as transcription, cell cycle progression, differentiation, secretion and apoptosis. Unsurprisingly, tight and precise kinase regulation is a prerequisite for normal cell functioning, whereas kinase dysregulation often leads to disease. Moreover, the functions of many kinases are regulated through protein–protein interactions, which in turn are mediated by phosphorylated motifs and often involve associations with the scaffolding and chaperon protein 14-3-3. Therefore, the aim of this review article is to provide an overview of the state of the art on 14-3-3-mediated kinase regulation, focusing on the most recent mechanistic insights into these important protein–protein interactions and discussing in detail both their structural aspects and functional consequences.
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3
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Liau NPD, Venkatanarayan A, Quinn JG, Phung W, Malek S, Hymowitz SG, Sudhamsu J. Dimerization Induced by C-Terminal 14-3-3 Binding Is Sufficient for BRAF Kinase Activation. Biochemistry 2020; 59:3982-3992. [PMID: 32970425 DOI: 10.1021/acs.biochem.0c00517] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The Ras-RAF-MEK-ERK signaling axis, commonly mutated in human cancers, is highly regulated to prevent aberrant signaling in healthy cells. One of the pathway modulators, 14-3-3, a constitutive dimer, induces RAF dimerization and activation by binding to a phosphorylated motif C-terminal to the RAF kinase domain. Recent work has suggested that a C-terminal "DTS" region in BRAF is necessary for this 14-3-3-mediated activation. We show that the catalytic activity and ATP binding affinity of the BRAF:14-3-3 complex is insensitive to the presence or absence of the DTS, while the ATP sites of both BRAF molecules are identical and available for binding. We also present a crystal structure of the apo BRAF:14-3-3 complex showing that the DTS is not required to attain the catalytically active conformation of BRAF. Rather, BRAF dimerization induced by 14-3-3 is the key step in activation, allowing the active BRAF:14-3-3 tetramer to achieve catalytic activity comparable to the constitutively active oncogenic BRAF V600E mutant.
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4
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Nussinov R, Tsai CJ, Jang H. Does Ras Activate Raf and PI3K Allosterically? Front Oncol 2019; 9:1231. [PMID: 31799192 PMCID: PMC6874141 DOI: 10.3389/fonc.2019.01231] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Accepted: 10/28/2019] [Indexed: 12/11/2022] Open
Abstract
The mechanism through which oncogenic Ras activates its effectors is vastly important to resolve. If allostery is at play, then targeting allosteric pathways could help in quelling activation of MAPK (Raf/MEK/ERK) and PI3K (PI3K/Akt/mTOR) cell proliferation pathways. On the face of it, allosteric activation is reasonable: Ras binding perturbs the conformational ensembles of its effectors. Here, however, we suggest that at least for Raf, PI3K, and NORE1A (RASSF5), that is unlikely. Raf's long disordered linker dampens effective allosteric activation. Instead, we suggest that the high-affinity Ras–Raf binding relieves Raf's autoinhibition, shifting Raf's ensemble from the inactive to the nanocluster-mediated dimerized active state, as Ras also does for NORE1A. PI3K is recruited and allosterically activated by RTK (e.g., EGFR) at the membrane. Ras restrains PI3K's distribution and active site orientation. It stabilizes and facilitates PIP2 binding at the active site and increases the PI3K residence time at the membrane. Thus, RTKs allosterically activate PI3Kα; however, merging their action with Ras accomplishes full activation. Here we review their activation mechanisms in this light and draw attention to implications for their pharmacology.
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Affiliation(s)
- Ruth Nussinov
- Cancer and Inflammation Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, National Cancer Institute at Frederick, Frederick, MD, United States.,Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Chung-Jung Tsai
- Cancer and Inflammation Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, National Cancer Institute at Frederick, Frederick, MD, United States
| | - Hyunbum Jang
- Cancer and Inflammation Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, National Cancer Institute at Frederick, Frederick, MD, United States
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5
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Dynamic Protein Allosteric Regulation and Disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1163:25-43. [DOI: 10.1007/978-981-13-8719-7_2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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6
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Kondo Y, Ognjenović J, Banerjee S, Karandur D, Merk A, Kulhanek K, Wong K, Roose JP, Subramaniam S, Kuriyan J. Cryo-EM structure of a dimeric B-Raf:14-3-3 complex reveals asymmetry in the active sites of B-Raf kinases. Science 2019; 366:109-115. [PMID: 31604311 DOI: 10.1126/science.aay0543] [Citation(s) in RCA: 114] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 09/11/2019] [Indexed: 12/17/2022]
Abstract
Raf kinases are important cancer drug targets. Paradoxically, many B-Raf inhibitors induce the activation of Raf kinases. Cryo-electron microscopy structural analysis of a phosphorylated B-Raf kinase domain dimer in complex with dimeric 14-3-3, at a resolution of ~3.9 angstroms, shows an asymmetric arrangement in which one kinase is in a canonical "active" conformation. The distal segment of the C-terminal tail of this kinase interacts with, and blocks, the active site of the cognate kinase in this asymmetric arrangement. Deletion of the C-terminal segment reduces Raf activity. The unexpected asymmetric quaternary architecture illustrates how the paradoxical activation of Raf by kinase inhibitors reflects an innate mechanism, with 14-3-3 facilitating inhibition of one kinase while maintaining activity of the other. Conformational modulation of these contacts may provide new opportunities for Raf inhibitor development.
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Affiliation(s)
- Yasushi Kondo
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Jana Ognjenović
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20814, USA
| | - Saikat Banerjee
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Deepti Karandur
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Alan Merk
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20814, USA
| | - Kayla Kulhanek
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Kathryn Wong
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Jeroen P Roose
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Sriram Subramaniam
- University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
| | - John Kuriyan
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA. .,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA.,Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.,Divisions of Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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7
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Terrell EM, Morrison DK. Ras-Mediated Activation of the Raf Family Kinases. Cold Spring Harb Perspect Med 2019; 9:cshperspect.a033746. [PMID: 29358316 DOI: 10.1101/cshperspect.a033746] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The extracellular signal-regulated kinase (ERK) cascade comprised of the Raf, MEK, and ERK protein kinases constitutes a key effector cascade used by the Ras GTPases to relay signals regulating cell growth, survival, proliferation, and differentiation. Of the ERK cascade components, the regulation of the Raf kinases is by far the most complex, involving changes in subcellular localization, protein and lipid interactions, as well as alterations in the Raf phosphorylation state. The Raf kinases interact directly with active, membrane-localized Ras, and this interaction is often the first step in the Raf activation process, which ultimately results in ERK activation and the downstream phosphorylation of cellular targets that will specify a particular biological response. Here, we will examine our current understanding of how Ras promotes Raf activation, focusing on the molecular mechanisms that contribute to the Raf activation/inactivation cycle.
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Affiliation(s)
- Elizabeth M Terrell
- Laboratory of Cell and Developmental Signaling, NCI-Frederick, Frederick, Maryland 21702
| | - Deborah K Morrison
- Laboratory of Cell and Developmental Signaling, NCI-Frederick, Frederick, Maryland 21702
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8
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Autoinhibition in Ras effectors Raf, PI3Kα, and RASSF5: a comprehensive review underscoring the challenges in pharmacological intervention. Biophys Rev 2018; 10:1263-1282. [PMID: 30269291 PMCID: PMC6233353 DOI: 10.1007/s12551-018-0461-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Accepted: 09/17/2018] [Indexed: 02/06/2023] Open
Abstract
Autoinhibition is an effective mechanism that guards proteins against spurious activation. Despite its ubiquity, the distinct organizations of the autoinhibited states and their release mechanisms differ. Signaling is most responsive to the cell environment only if a small shift in the equilibrium is required to switch the system from an inactive (occluded) to an active (exposed) state. Ras signaling follows this paradigm. This underscores the challenge in pharmacological intervention to exploit and enhance autoinhibited states. Here, we review autoinhibition and release mechanisms at the membrane focusing on three representative Ras effectors, Raf protein kinase, PI3Kα lipid kinase, and NORE1A (RASSF5) tumor suppressor, and point to the ramifications to drug discovery. We further touch on Ras upstream and downstream signaling, Ras activation, and the Ras superfamily in this light, altogether providing a broad outlook of the principles and complexities of autoinhibition.
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9
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Winters JL, Davila JI, McDonald AM, Nair AA, Fadra N, Wehrs RN, Thomas BC, Balcom JR, Jin L, Wu X, Voss JS, Klee EW, Oliver GR, Graham RP, Neff JL, Rumilla KM, Aypar U, Kipp BR, Jenkins RB, Jen J, Halling KC. Development and Verification of an RNA Sequencing (RNA-Seq) Assay for the Detection of Gene Fusions in Tumors. J Mol Diagn 2018; 20:495-511. [DOI: 10.1016/j.jmoldx.2018.03.007] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 02/15/2018] [Accepted: 03/19/2018] [Indexed: 02/07/2023] Open
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10
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RAF inhibitors promote RAS-RAF interaction by allosterically disrupting RAF autoinhibition. Nat Commun 2017; 8:1211. [PMID: 29084939 PMCID: PMC5662619 DOI: 10.1038/s41467-017-01274-0] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Accepted: 09/01/2017] [Indexed: 12/19/2022] Open
Abstract
First-generation RAF inhibitors paradoxically induce ERK signaling in normal and tumor cells exhibiting RAS activity. Compound-induced RAF dimerization through stabilization of the RAF ON/active state by inhibitors has emerged as a critical contributing factor. RAF inhibitors also enhance RAS−RAF association. Although this event is thought to play a key role in priming RAF activation, the underlying mechanism is not known. Here we report that RAF inhibitors induce the disruption of intramolecular interactions between the kinase domain and its N-terminal regulatory region independently of RAS activity. This provides a molecular basis to explain the induction of RAS−RAF association by RAF inhibitors, as well as the co-operativity observed between RAS activity and RAF kinase inhibitors in driving RAF activation. Profiling of second-generation RAF inhibitors confirmed their improved mode of action, but also revealed liabilities that allowed us to discern two properties of an ideal RAF inhibitor: high-binding affinity to all RAF paralogs and maintenance of the OFF/autoinhibited state of the enzyme. RAF family kinases transmit signals from activated RAS at the plasma membrane to downstream kinases to control cell proliferation, differentiation and survival. Here the authors shed light on the molecular mechanisms whereby small molecule RAF inhibitors induce RAS-RAF association and paradoxical RAF activation.
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11
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Jain P, Fierst TM, Han HJ, Smith TE, Vakil A, Storm PB, Resnick AC, Waanders AJ. CRAF gene fusions in pediatric low-grade gliomas define a distinct drug response based on dimerization profiles. Oncogene 2017; 36:6348-6358. [PMID: 28806393 PMCID: PMC5680138 DOI: 10.1038/onc.2017.276] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 06/26/2017] [Accepted: 07/05/2017] [Indexed: 01/07/2023]
Abstract
Pediatric low-grade gliomas (PLGGs) are commonly associated with BRAF gene fusions that aberrantly activate the mitogen-activated protein kinase (MAPK) signaling pathway. This has led to PLGG clinical trials utilizing RAF- and MAPK pathway-targeted therapeutics. Whole-genome profiling of PLGGs has also identified rare gene fusions involving another RAF isoform, CRAF/RAF1, in PLGGs and cancers occuring in adults. Whereas BRAF fusions primarily dysregulate MAPK signaling, the CRAF fusions QKI-RAF1 and SRGAP3-RAF1 aberrantly activate both the MAPK and phosphoinositide-3 kinase/mammalian target of rapamycin (PI3K/mTOR) signaling pathways. Although ATP-competitive, first-generation RAF inhibitors (vemurafenib/PLX4720, RAFi) cause paradoxical activation of the MAPK pathway in BRAF-fusion tumors, inhibition can be achieved with ‘paradox breaker’ RAFi, such as PLX8394. Here we report that, unlike BRAF fusions, CRAF fusions are unresponsive to both generations of RAFi, vemurafenib and PLX8394, highlighting a distinct responsiveness of CRAF fusions to clinically relevant RAFi. Whereas PLX8394 decreased BRAF-fusion dimerization, CRAF-fusion dimerization is unaffected primarily because of robust protein–protein interactions mediated by the N-terminal non-kinase fusion partner, such as QKI. The pan-RAF dimer inhibitor, LY3009120, could suppress CRAF-fusion oncogenicity by inhibiting dimer-mediated signaling. In addition, as CRAF fusions activate both the MAPK and PI3K/mTOR signaling pathways, we identify combinatorial inhibition of the MAPK/mTOR pathway as a potential therapeutic strategy for CRAF-fusion-driven tumors. Overall, we define a mechanistic distinction between PLGG-associated BRAF- and CRAF/RAF1 fusions in response to RAFi, highlighting the importance of molecularly classifying PLGG patients for targeted therapy. Furthermore, our study uncovers an important contribution of the non-kinase fusion partner to oncogenesis and potential therapeutic strategies against PLGG-associated CRAF fusions and possibly pan-cancer CRAF fusions.
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Affiliation(s)
- P Jain
- Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USA.,Cell and Molecular Graduate Group, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.,Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - T M Fierst
- Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Department of Neurosurgery, Temple University School of Medicine, Philadelphia, PA, USA
| | - H J Han
- Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USA.,Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - T E Smith
- Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - A Vakil
- Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - P B Storm
- Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USA.,Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Center of Childhood Cancer Research, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Center for Data Driven Discovery in Biomedicine (D3b), The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - A C Resnick
- Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USA.,Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Center of Childhood Cancer Research, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Center for Data Driven Discovery in Biomedicine (D3b), The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Department of Biomedical and Health Informatics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - A J Waanders
- Center of Childhood Cancer Research, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Center for Data Driven Discovery in Biomedicine (D3b), The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Division of Oncology, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.,Department of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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12
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Abstract
RAF family kinases were among the first oncoproteins to be described more than 30 years ago. They primarily act as signalling relays downstream of RAS, and their close ties to cancer have fuelled a large number of studies. However, we still lack a systems-level understanding of their regulation and mode of action. The recent discovery that the catalytic activity of RAF depends on an allosteric mechanism driven by kinase domain dimerization is providing a vital new piece of information towards a comprehensive model of RAF function. The fact that current RAF inhibitors unexpectedly induce ERK signalling by stimulating RAF dimerization also calls for a deeper structural characterization of this family of kinases.
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13
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Preclinical Murine Models for Lung Cancer: Clinical Trial Applications. BIOMED RESEARCH INTERNATIONAL 2015; 2015:621324. [PMID: 26064932 PMCID: PMC4433653 DOI: 10.1155/2015/621324] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Accepted: 11/24/2014] [Indexed: 12/18/2022]
Abstract
Murine models for the study of lung cancer have historically been the backbone of preliminary preclinical data to support early human clinical trials. However, the availability of multiple experimental systems leads to debate concerning which model, if any, is best suited for a particular therapeutic strategy. It is imperative that these models accurately predict clinical benefit of therapy. This review provides an overview of the current murine models used to study lung cancer and the advantages and limitations of each model, as well as a retrospective evaluation of the uses of each model with respect to accuracy in predicting clinical benefit of therapy. A better understanding of murine models and their uses, as well as their limitations may aid future research concerning the development and implementation of new targeted therapies and chemotherapeutic agents for lung cancer.
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14
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Kashatus JA, Nascimento A, Myers LJ, Sher A, Byrne FL, Hoehn KL, Counter CM, Kashatus DF. Erk2 phosphorylation of Drp1 promotes mitochondrial fission and MAPK-driven tumor growth. Mol Cell 2015; 57:537-51. [PMID: 25658205 DOI: 10.1016/j.molcel.2015.01.002] [Citation(s) in RCA: 488] [Impact Index Per Article: 54.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Revised: 11/20/2014] [Accepted: 12/29/2014] [Indexed: 02/08/2023]
Abstract
Ras is mutated in up to 30% of cancers, including 90% of pancreatic ductal adenocarcinomas, causing it to be constitutively GTP-bound, and leading to activation of downstream effectors that promote a tumorigenic phenotype. As targeting Ras directly is difficult, there is a significant effort to understand the downstream biological processes that underlie its protumorigenic activity. Here, we show that expression of oncogenic Ras or direct activation of the MAPK pathway leads to increased mitochondrial fragmentation and that blocking this phenotype, through knockdown of the mitochondrial fission-mediating GTPase Drp1, inhibits tumor growth. This fission is driven by Erk2-mediated phosphorylation of Drp1 on Serine 616, and both this phosphorylation and mitochondrial fragmentation are increased in human pancreatic cancer. Finally, this phosphorylation is required for Ras-associated mitochondrial fission, and its inhibition is sufficient to block xenograft growth. Collectively, these data suggest mitochondrial fission may be a target for treating MAPK-driven malignancies.
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Affiliation(s)
- Jennifer A Kashatus
- Department of Microbiology, Immunology and Cancer Biology, University of Virginia Health System, Charlottesville, VA 22908, USA
| | - Aldo Nascimento
- Department of Microbiology, Immunology and Cancer Biology, University of Virginia Health System, Charlottesville, VA 22908, USA
| | - Lindsey J Myers
- Department of Microbiology, Immunology and Cancer Biology, University of Virginia Health System, Charlottesville, VA 22908, USA
| | - Annie Sher
- Department of Pharmacology and Cancer Biology, Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA
| | - Frances L Byrne
- Department of Pharmacology, University of Virginia Health System, Charlottesville, VA 22908, USA
| | - Kyle L Hoehn
- Department of Pharmacology, University of Virginia Health System, Charlottesville, VA 22908, USA
| | - Christopher M Counter
- Department of Pharmacology and Cancer Biology, Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA
| | - David F Kashatus
- Department of Microbiology, Immunology and Cancer Biology, University of Virginia Health System, Charlottesville, VA 22908, USA.
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15
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Holderfield M, Deuker MM, McCormick F, McMahon M. Targeting RAF kinases for cancer therapy: BRAF-mutated melanoma and beyond. Nat Rev Cancer 2014; 14:455-67. [PMID: 24957944 PMCID: PMC4250230 DOI: 10.1038/nrc3760] [Citation(s) in RCA: 588] [Impact Index Per Article: 58.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The identification of mutationally activated BRAF in many cancers altered our conception of the part played by the RAF family of protein kinases in oncogenesis. In this Review, we describe the development of BRAF inhibitors and the results that have emerged from their analysis in both the laboratory and the clinic. We discuss the spectrum of RAF mutations in human cancer and the complex interplay between the tissue of origin and the response to RAF inhibition. Finally, we enumerate mechanisms of resistance to BRAF inhibition that have been characterized and postulate how strategies of RAF pathway inhibition may be extended in scope to benefit not only the thousands of patients who are diagnosed annually with BRAF-mutated metastatic melanoma but also the larger patient population with malignancies harbouring mutationally activated RAF genes that are ineffectively treated with the current generation of BRAF kinase inhibitors.
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Affiliation(s)
| | | | - Frank McCormick
- Corresponding Authors: Frank McCormick & Martin McMahon, Diller Family Cancer Research Bldg., 1450 Third Street, University of California, San Francisco, CA 94158, USA, &
| | - Martin McMahon
- Corresponding Authors: Frank McCormick & Martin McMahon, Diller Family Cancer Research Bldg., 1450 Third Street, University of California, San Francisco, CA 94158, USA, &
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16
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Okuda K. A new model to evaluate Raf signaling in hematopoietic cells. Int J Oncol 2013; 43:903-10. [PMID: 23820731 DOI: 10.3892/ijo.2013.2002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 05/29/2013] [Indexed: 11/05/2022] Open
Abstract
The Raf/MEK/ERK pathway is thought to be critical in mediating cell survival and proliferation by cytokine receptors. However, the exact contribution of Raf is complex and not well understood. A better understanding of Raf signaling is important because of the recent observation that B-Raf is frequently mutated in various human cancers. We have generated a new model system that activates Raf directly by linking the extracytoplasmic and transmembrane domains of the erythropoietin receptor (EPOR) with the catalytic domain of Raf (CR3). This synthetic oncogene in which dimerization can be controlled by an exogenous ligand, is fixed at the cellular membrane, while the endogenous Raf is normally activated by binding with Ras. The chimeric receptor EPOR/CR3 was stably expressed in Ba/F3 cells which lack EPO receptors. Although the lines remained dependent on IL-3 for proliferation, EPO treatment reduced the rate of cell death in the absence of IL-3. Also, EPO was synergistic with sub-optimal concentrations of IL-3 in inducing long-term cell proliferation, but did not augment proliferation of cells cultured with full concentrations of IL-3. EPO induced a rapid activation of ERK and also phosphorylation of endogenous Raf. It also induced tyrosine phosphorylation of several cellular proteins. The MEK1 inhibitor PD98059 reduced EPO-induced tyrosine phosphorylation, suggesting these substrates are downstream of MEK kinase. Interestingly, PD98059 also reduced the phosphorylation of endogenous Raf, indicating there is a positive feedback mechanism in Raf activation. We conclude that Raf can be activated by a mechanism that induces clustering at the cell membrane, and that this leads directly to activation of MEK and ERK. This EPOR/CR3 system may serve as a useful model to evaluate the unknown Raf kinase pathway and the effects of signal transduction inhibitors for Raf as a target.
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Affiliation(s)
- Keiko Okuda
- Department of Molecular Diagnostics and Therapeutics, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, Japan
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17
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MEK-1 activates C-Raf through a Ras-independent mechanism. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:976-86. [PMID: 23360980 DOI: 10.1016/j.bbamcr.2013.01.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2012] [Revised: 12/29/2012] [Accepted: 01/15/2013] [Indexed: 12/16/2022]
Abstract
C-Raf is a member of the Ras-Raf-MEK-ERK mitogen-activated protein kinase (MAPK) signaling pathway that plays key roles in diverse physiological processes and is upregulated in many human cancers. C-Raf activation involves binding to Ras, increased phosphorylation and interactions with co-factors. Here, we describe a Ras-independent in vivo pathway for C-Raf activation by its downstream target MEK. Using (32)P-metabolic labeling and 2D-phosphopeptide mapping experiments, we show that MEK increases C-Raf phosphorylation by up-to 10-fold. This increase was associated with C-Raf kinase activation, matching the activity seen with growth factor stimulation. Consequently, coexpression of wildtype C-Raf and MEK was sufficient for full and constitutive activation of ERK. Notably, the ability of MEK to activate C-Raf was completely Ras independent, since mutants impaired in Ras binding that are irresponsive to growth factors or Ras were fully activated by MEK. The ability of MEK to activate C-Raf was only partially dependent on MEK kinase activity but required MEK binding to C-Raf, suggesting that the binding results in a conformational change that increases C-Raf susceptibility to phosphorylation and activation or in the stabilization of the phosphorylated-active form. These findings propose a novel Ras-independent mechanism for activating the C-Raf and the MAPK pathway without the need for mutations in the pathway. This mechanism could be of significance in pathological conditions or cancers overexpressing C-Raf and MEK or in conditions where C-Raf-MEK interaction is enhanced due to the down-regulation of RKIP and MST2.
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18
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Degen M, Natarajan E, Barron P, Widlund HR, Rheinwald JG. MAPK/ERK-dependent translation factor hyperactivation and dysregulated laminin γ2 expression in oral dysplasia and squamous cell carcinoma. THE AMERICAN JOURNAL OF PATHOLOGY 2012; 180:2462-78. [PMID: 22546478 DOI: 10.1016/j.ajpath.2012.02.028] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Revised: 02/02/2012] [Accepted: 02/07/2012] [Indexed: 01/13/2023]
Abstract
Lesions displaying a variety of dysplastic changes precede invasive oral and epidermal squamous cell carcinoma (SCC); however, there are no histopathological criteria for either confirming or staging premalignancy. SCCs and dysplasias frequently contain cells that abnormally express the γ2 subunit of laminin-332. We developed cell culture models to investigate γ2 dysregulation. Normal human keratinocytes displayed density-dependent repression of γ2, whereas premalignant keratinocytes and SCC cells overexpressed γ2 and secreted laminin assembly intermediates. Neoplastic cells had hyperactive EGFR/MAPK(ERK) signaling coordinate with overexpressed γ2, and EGFR and MEK inhibitors normalized γ2 expression. Keratinocytes engineered to express HPV16 E6 or activated mutant HRAS, cRAF1, or MEK1 lost density repression of γ2 and shared with neoplastic cells signaling abnormalities downstream of ERK, including increased phosphorylation of S6 and eIF4 translation factors. Notably, qPCR results revealed that γ2 overexpression was not accompanied by increased γ2 mRNA levels, consistent with ERK-dependent, eIF4B-mediated translation initiation of the stem-looped, 5'-untranslated region of γ2 mRNA in neoplastic cells. Inhibitors of MEK, but not of TORC1/2, blocked S6 and eIF4B phosphorylation and γ2 overexpression. Immunostaining of oral dysplasias identified γ2 overexpression occurring within fields of basal cells that had elevated p-S6 levels. These results reveal a causal relationship between ERK-dependent translation factor activation and laminin γ2 dysregulation and identify new markers of preinvasive neoplastic change during progression to SCC.
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Affiliation(s)
- Martin Degen
- Department of Dermatology, Brigham and Women's Hospital and Harvard Skin Disease Research Center, Boston, MA, USA
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19
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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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20
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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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21
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Robinson JP, VanBrocklin MW, Guilbeault AR, Signorelli DL, Brandner S, Holmen SL. Activated BRAF induces gliomas in mice when combined with Ink4a/Arf loss or Akt activation. Oncogene 2009; 29:335-44. [PMID: 19855433 DOI: 10.1038/onc.2009.333] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Mutations in receptor tyrosine kinase (RTK) growth factor receptors (epidermal growth factor receptor, platelet-derived growth factor receptor, MET and ERBB2), which result in downstream activation of the RAS/RAF/MEK/ERK mitogen-activated protein kinase (MAPK) pathway and PI(3)K/Akt pathway, are found in almost all high-grade gliomas and MAPK signaling is necessary for continued glioma maintenance. In addition, BRAF is mutated in the majority of low-grade gliomas and its expression and activity is significantly increased in the majority of high-grade gliomas. Although the importance of RTKs and RAS signaling in glioma development has been shown, the role of BRAF has yet to be characterized. We evaluated the effect of activated BRAF in glioma formation using the retroviral replication-competent avian leukosis virus long terminal repeat, splice acceptor (RCAS)/TVA system to transfer genes encoding activated forms of BRAF, KRas, Akt and Cre to nestin-expressing neural progenitor cells in Ink4a/Arf(lox/lox) mice in vivo. Although expression of activated BRAF alone is not sufficient for tumorigenesis, the combination of activated BRAF and Akt or BRAF with Ink4a/Arf loss is transforming. Interestingly, activated BRAF generates gliomas with characteristics similar to activated KRas in the context of Akt but not Ink4a/Arf loss. Our studies show a role for BRAF activation and signaling in glioma development and as potential target for glioma therapy.
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Affiliation(s)
- J P Robinson
- Drug Development Department, Nevada Cancer Institute, Las Vegas, NV 89135, USA
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22
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Oncogenic RAF1 rearrangement and a novel BRAF mutation as alternatives to KIAA1549:BRAF fusion in activating the MAPK pathway in pilocytic astrocytoma. Oncogene 2009; 28:2119-23. [PMID: 19363522 PMCID: PMC2685777 DOI: 10.1038/onc.2009.73] [Citation(s) in RCA: 239] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Pilocytic astrocytomas (PAs), WHO malignancy grade I, are the most frequently occurring central nervous system tumour in 5- to 19-year-olds. Recent reports have highlighted the importance of MAPK pathway activation in PAs, particularly through a tandem duplication leading to an oncogenic BRAF fusion gene. Here, we report two alternative mechanisms resulting in MAPK activation in PAs. Firstly, in striking similarity to the common BRAF fusion, tandem duplication at 3p25 was observed, which produces an in-frame oncogenic fusion between SRGAP3 and RAF1. This fusion includes the Raf1 kinase domain, and shows elevated kinase activity when compared with wild-type Raf1. Secondly, a novel 3 bp insertion at codon 598 in BRAF mimics the hotspot V600E mutation to produce a transforming, constitutively active BRaf kinase. Although these two alterations are not common, they bring the number of cases with an identified 'hit' on the Ras/Raf-signalling pathway to 36 from our series of 44 (82%), confirming its central importance to the development of pilocytic astrocytomas.
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Montagut C, Sharma SV, Shioda T, McDermott U, Ulman M, Ulkus LE, Dias-Santagata D, Stubbs H, Lee DY, Singh A, Drew L, Haber DA, Settleman J. Elevated CRAF as a potential mechanism of acquired resistance to BRAF inhibition in melanoma. Cancer Res 2008; 68:4853-61. [PMID: 18559533 DOI: 10.1158/0008-5472.can-07-6787] [Citation(s) in RCA: 406] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Activating BRAF kinase mutations arise in approximately 7% of all human tumors, and preclinical studies have validated the RAF-mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase-ERK signaling cascade as a potentially important therapeutic target in this setting. Selective RAF kinase inhibitors are currently undergoing clinical development, and based on the experience with other kinase-targeted therapeutics, it is expected that clinical responses to these agents, if observed, will lead to the eventual emergence of drug resistance in most cases. Thus, it is important to establish molecular mechanisms underlying such resistance to develop effective therapeutic strategies to overcome or prevent drug resistance. To anticipate potential mechanisms of acquired resistance to RAF inhibitors during the course of treatment, we established drug-resistant clones from a human melanoma-derived cell line harboring the recurrent V600E activating BRAF mutation, which exhibits exquisite sensitivity to AZ628, a selective RAF kinase inhibitor. We determined that elevated CRAF protein levels account for the acquisition of resistance to AZ628 in these cells, associated with a switch from BRAF to CRAF dependency in tumor cells. We also found that elevated CRAF protein levels may similarly contribute to primary insensitivity to RAF inhibition in a subset of BRAF mutant tumor cells. Interestingly, AZ628-resistant cells demonstrating either primary drug insensitivity or acquired drug resistance exhibit exquisite sensitivity to the HSP90 inhibitor geldanamycin. Geldanamycin effectively promotes the degradation of CRAF, thereby revealing a potential therapeutic strategy to overcome resistance to RAF inhibition in a subset of BRAF mutant tumors.
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Affiliation(s)
- Clara Montagut
- Center for Molecular Therapeutics, Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, Massachusetts, USA
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24
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Dow LE, Elsum IA, King CL, Kinross KM, Richardson HE, Humbert PO. Loss of human Scribble cooperates with H-Ras to promote cell invasion through deregulation of MAPK signalling. Oncogene 2008; 27:5988-6001. [DOI: 10.1038/onc.2008.219] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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25
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Constitutive activation of Raf-1 induces glioma formation in mice. Neoplasia 2008; 10:501-10. [PMID: 18472967 DOI: 10.1593/neo.08206] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2008] [Revised: 02/14/2008] [Accepted: 02/15/2008] [Indexed: 01/27/2023] Open
Abstract
In human glioblastoma multiforme (GBM), RAS activity is upregulated in the majority of the tumors. Furthermore, the levels of phospho-mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK), a downstream effector of RAS, are also increased. In mice, activated KRas cooperates with the loss of INK4a-ARF locus or with activated Akt to induce gliomas, confirming an important role for this pathway in glioma biology. However, to correctly target therapies against the RAS signaling pathway, it is necessary to identify the effectors that contribute to RAS-mediated gliomagenesis. In this study, we investigated the contribution of RAF signaling in glioma oncogenesis. We find that the levels of RAF-1 and BRAF proteins and RAF kinase activity are increased in human GBM samples. We confirm the importance of this finding by demonstrating a causal role for a constitutively active Raf-1 mutant in glioma formation in mice. Specifically, we find that activated Raf-1 cooperates with Arf loss or Akt activation to generate gliomas similar to activated KRas under the same conditions. Our study suggests that the oncogenic effect of KRas in glioma formation may be transduced at least in part through Raf signaling and that therapeutic targeting of this pathway may be beneficial in glioma treatment.
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26
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Campbell PM, Singh A, Williams FJ, Frantz K, Ulkü AS, Kelley GG, Der CJ. Genetic and pharmacologic dissection of Ras effector utilization in oncogenesis. Methods Enzymol 2008; 407:195-217. [PMID: 16757325 DOI: 10.1016/s0076-6879(05)07017-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Ras proteins function as signaling nodes that are activated by diverse extracellular stimuli. Equally complex for this family of molecular switches is the multitude of downstream effectors and the pathways that they traverse to translate extracellular signals into a spectrum of cellular consequences. To better understand the individual and collective roles of these effector signaling networks, both genetic and pharmacological tools have been developed. By either stimulating or ablating specific components in a cascade downstream of Ras activation, one can gain insight into the specific signaling underlying a particular Ras phenotype, for example, malignant transformation. In this chapter, we describe the use of activating and dominant-negative mutations, both artificial and naturally occurring, of Ras and its effectors, as well as pharmacological inhibitors used to probe the effector pathways (Raf kinase, phosphoinositol 3-kinase, Tiam1, phospholipase C epsilon, and RalGEF) implicated in Ras-mediated oncogenesis.
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Affiliation(s)
- Paul M Campbell
- Department of Pharmacology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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27
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Wang J, Yen A. A MAPK-positive feedback mechanism for BLR1 signaling propels retinoic acid-triggered differentiation and cell cycle arrest. J Biol Chem 2007; 283:4375-86. [PMID: 18006504 DOI: 10.1074/jbc.m708471200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
MAPK signaling is required for retinoic acid (RA)-triggered G(0) cell cycle arrest and cell differentiation, but the mechanism is not well defined. In this study, RA is found to cause MAPK activation with sustained association of RAF to MEK or ERK, leading to a MAPK-dependent accumulation of p21(Waf1/Cip1) and binding to CDK2 blocking G(1)/S transition. BLR1, a chemokine receptor, was found to function as a critical component of RA-triggered MAPK signaling. Unlike wild-type parental cells, RA-treated BLR1 knock-out cells failed to show RAF and consequential MEK and ERK phosphorylation, failed to accumulate CDK inhibitors that control G(1)/S transition, and failed to differentiate and arrest in response to RA, whereas ectopically overexpressing BLR1 enhanced MAPK signaling and caused accelerated RA-induced differentiation and arrest. Ectopic overexpression of RAF enhanced BLR1 expression in response to RA, whereas inhibition of RAF or MEK by inhibitors or knockdown of RAF by short interfering RNA diminished RA-induced BLR1 expression and attenuated differentiation and growth arrest. Ectopic expression of the RAF CR3, the catalytically active domain, in the BLR1 knock-out restored RA-induced MAPK activation and the ability to differentiate and arrest, indicating that RAF effects MAPK signaling by BLR1 to propel differentiation/arrest. Taken together, RA induces cell differentiation and growth arrest through activation of a novel MAPK pathway with BLR1 as a critical component in a positive feedback mechanism that may contribute to the prolonged MAPK signaling propelling RA-induced cell cycle arrest and differentiation.
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Affiliation(s)
- Jianrong Wang
- Department of Biomedical Sciences, Cornell University, Ithaca, New York 14853, USA
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28
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Boehm JS, Zhao JJ, Yao J, Kim SY, Firestein R, Dunn IF, Sjostrom SK, Garraway LA, Weremowicz S, Richardson AL, Greulich H, Stewart CJ, Mulvey LA, Shen RR, Ambrogio L, Hirozane-Kishikawa T, Hill DE, Vidal M, Meyerson M, Grenier JK, Hinkle G, Root DE, Roberts TM, Lander ES, Polyak K, Hahn WC. Integrative genomic approaches identify IKBKE as a breast cancer oncogene. Cell 2007; 129:1065-79. [PMID: 17574021 DOI: 10.1016/j.cell.2007.03.052] [Citation(s) in RCA: 480] [Impact Index Per Article: 28.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2006] [Revised: 01/16/2007] [Accepted: 03/22/2007] [Indexed: 01/12/2023]
Abstract
The karyotypic chaos exhibited by human epithelial cancers complicates efforts to identify mutations critical for malignant transformation. Here we integrate complementary genomic approaches to identify human oncogenes. We show that activation of the ERK and phosphatidylinositol 3-kinase (PI3K) signaling pathways cooperate to transform human cells. Using a library of activated kinases, we identify several kinases that replace PI3K signaling and render cells tumorigenic. Whole genome structural analyses reveal that one of these kinases, IKBKE (IKKepsilon), is amplified and overexpressed in breast cancer cell lines and patient-derived tumors. Suppression of IKKepsilon expression in breast cancer cell lines that harbor IKBKE amplifications induces cell death. IKKepsilon activates the nuclear factor-kappaB (NF-kappaB) pathway in both cell lines and breast cancers. These observations suggest a mechanism for NF-kappaB activation in breast cancer, implicate the NF-kappaB pathway as a downstream mediator of PI3K, and provide a framework for integrated genomic approaches in oncogene discovery.
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Affiliation(s)
- Jesse S Boehm
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA
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29
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Leicht DT, Balan V, Kaplun A, Singh-Gupta V, Kaplun L, Dobson M, Tzivion G. Raf kinases: function, regulation and role in human cancer. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:1196-212. [PMID: 17555829 PMCID: PMC1986673 DOI: 10.1016/j.bbamcr.2007.05.001] [Citation(s) in RCA: 206] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2006] [Revised: 05/01/2007] [Accepted: 05/02/2007] [Indexed: 12/25/2022]
Abstract
The Ras-Raf-MAPK pathway regulates diverse physiological processes by transmitting signals from membrane based receptors to various nuclear, cytoplasmic and membrane-bound targets, coordinating a large variety of cellular responses. Function of Raf family kinases has been shown to play a role during organism development, cell cycle regulation, cell proliferation and differentiation, cell survival and apoptosis and many other cellular and physiological processes. Aberrations along the Ras-Raf-MAPK pathway play an integral role in various biological processes concerning human health and disease. Overexpression or activation of the pathway components is a common indicator in proliferative diseases such as cancer and contributes to tumor initiation, progression and metastasis. In this review, we focus on the physiological roles of Raf kinases in normal and disease conditions, specifically cancer, and the current thoughts on Raf regulation.
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Affiliation(s)
| | | | | | | | | | | | - Guri Tzivion
- To whom correspondence should be addressed: Karmanos Cancer Institute, Wayne State University, 4100 John R., HWCRC 716, Detroit, MI 48201, Tel: 313-576-8311, Fax: 313-576-8308, E-mail:
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O'Hayer KM, Counter CM. A genetically defined normal human somatic cell system to study ras oncogenesis in vivo and in vitro. Methods Enzymol 2006; 407:637-47. [PMID: 16757358 DOI: 10.1016/s0076-6879(05)07050-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Transgenic mice, cultured murine cells, and human cancer cell lines have widely been used to study Ras oncogenesis. Although extremely valuable systems, they could not be used to study Ras function in genetically defined human cells. In this regard, Ras is required for tumor formation in normal human somatic cells expressing SV-40 T/t antigens, which inactivate the tumor suppressors p53 and Rb and activate the oncogene c-Myc, and hTERT, the catalytic subunit of telomerase. Such a system allows not only the general requirements of Ras to be dissected in matched cells from different organisms or tissues but also the individual pathways required for tumor growth to be defined in human cells. This review will detail the methods of creating stable T/t Ag, TERT, Ras-expressing cell lines, as well as commonly used techniques of soft agar and xenograft tumor formation.
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Affiliation(s)
- Kevin M O'Hayer
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina, USA
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31
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Lim KH, Counter CM. Reduction in the requirement of oncogenic Ras signaling to activation of PI3K/AKT pathway during tumor maintenance. Cancer Cell 2005; 8:381-92. [PMID: 16286246 DOI: 10.1016/j.ccr.2005.10.014] [Citation(s) in RCA: 154] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2005] [Revised: 10/13/2005] [Accepted: 10/21/2005] [Indexed: 11/17/2022]
Abstract
While tumors become addicted to oncogenes like Ras, the microenvironment in which tumor cells reside changes during tumorigenesis; the cells are surrounded initially by normal tissue and later by tumor tissue. Hence, we asked if Ras exerts its oncogenic effects through the same set of effectors during different stages of tumorigenesis. We now show in human cells that the Ras effector pathways MAPK, RalGEF, and PI3K are required to initiate tumor growth. Conversely, activation of the PI3K/AKT pathway replaced Ras once tumors formed, although other effectors were still activated independently of Ras, presumably by factors provided upon the establishment of a tumor microenvironment. Thus, as tumorigenesis progresses the addiction of cancers to their initiating oncogene is reduced to, at least in the case of Ras, the PI3K/AKT pathway.
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Affiliation(s)
- Kian-Huat Lim
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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Cornelis S, Bruynooghe Y, Van Loo G, Saelens X, Vandenabeele P, Beyaert R. Apoptosis of hematopoietic cells induced by growth factor withdrawal is associated with caspase-9 mediated cleavage of Raf-1. Oncogene 2005; 24:1552-62. [PMID: 15674327 DOI: 10.1038/sj.onc.1208401] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The Raf-1 serine/threonine kinase is a key protein that is implicated in the transmission of many growth and cell survival signals. In the present study we demonstrate that apoptosis of hematopoietic cells induced by IL-3-deprivation is associated with the cleavage of Raf-1, resulting in the separation of the N-terminal regulatory domain and the C-terminal kinase domain. Raf-1 cleavage specifically occurs upon triggering of the mitochondrial death pathway, and coincides with the activation of specific caspases. Moreover, Bcl-2 overexpression or treatment with the caspase inhibitor z-VAD.fmk completely prevented Raf-1 cleavage, whereas caspase inhibition by treatment of cells with Ac-DEVD.fmk or z-IETD.fmk, or CrmA overexpression had no effect. Furthermore, in vitro cleavage studies indicate that caspase-9, which is the apical protease in the mitochondrial death pathway, is able to cleave Raf-1 at position D279. Cell fractionation studies showed that the Raf-1 C-terminal fragment that is generated upon IL-3 withdrawal is localized predominantly to the mitochondria. In addition, constitutive expression of this C-terminal Raf-1 fragment fused to a mitochondrial targeting sequence in Ba/F3 pre-B cells significantly delays apoptosis induced by IL-3 withdrawal. These results suggest an important role for caspase-9 mediated cleavage of Raf-1 in the negative feedback regulation of hematopoietic cell apoptosis induced by growth factor withdrawal.
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Affiliation(s)
- Sigrid Cornelis
- Unit of Molecular Signal Transduction in Inflammation, Department for Molecular Biomedical Research, VIB-Ghent University, Technologiepark 927, B-9052 Ghent-Zwijnaarde, Belgium
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Dougherty MK, Müller J, Ritt DA, Zhou M, Zhou XZ, Copeland TD, Conrads TP, Veenstra TD, Lu KP, Morrison DK. Regulation of Raf-1 by direct feedback phosphorylation. Mol Cell 2005; 17:215-24. [PMID: 15664191 DOI: 10.1016/j.molcel.2004.11.055] [Citation(s) in RCA: 447] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Revised: 10/22/2004] [Accepted: 11/24/2004] [Indexed: 10/25/2022]
Abstract
The Raf-1 kinase is an important signaling molecule, functioning in the Ras pathway to transmit mitogenic, differentiative, and oncogenic signals to the downstream kinases MEK and ERK. Because of its integral role in cell signaling, Raf-1 activity must be precisely controlled. Previous studies have shown that phosphorylation is required for Raf-1 activation, and here, we identify six phosphorylation sites that contribute to the downregulation of Raf-1 after mitogen stimulation. Five of the identified sites are proline-directed targets of activated ERK, and phosphorylation of all six sites requires MEK signaling, indicating a negative feedback mechanism. Hyperphosphorylation of these six sites inhibits the Ras/Raf-1 interaction and desensitizes Raf-1 to additional stimuli. The hyperphosphorylated/desensitized Raf-1 is subsequently dephosphorylated and returned to a signaling-competent state through interactions with the protein phosphatase PP2A and the prolyl isomerase Pin1. These findings elucidate a critical Raf-1 regulatory mechanism that contributes to the sensitive, temporal modulation of Ras signaling.
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Affiliation(s)
- Michele K Dougherty
- Laboratory of Protein Dynamics and Signaling, National Cancer Institute-Frederick, Frederick, MD 21702, USA
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34
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Rowinsky EK, Patnaik A. The development of protein farnesyltransferase and other ras-directed therapeutics for malignant diseases. ACTA ACUST UNITED AC 2005. [DOI: 10.1517/14728214.5.2.161] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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35
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Zhang J, Lodish HF. Constitutive activation of the MEK/ERK pathway mediates all effects of oncogenic H-ras expression in primary erythroid progenitors. Blood 2004; 104:1679-87. [PMID: 15166036 DOI: 10.1182/blood-2004-04-1362] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Oncogenic mutations in ras genes frequently occur in patients with myeloid disorders, and in these patients erythropoiesis is often affected. Previously, we showed that expression of oncogenic H-ras in purified mouse primary fetal liver erythroid progenitors blocks terminal erythroid differentiation and supports erythropoietin (Epo)-independent proliferation. As a first step in understanding the underlying molecular mechanisms we examined the signaling pathways downstream of Ras in primary erythroid cells. We found that 3 major pathways are abnormally activated by oncogenic H-ras: Raf/ERK (extracellular signal-regulated kinase), phosphatidyl inositol 3 (PI3)-kinase/Akt, and RalGEF/RalA. However, only constitutive activation of the MEK (MAPK [mitogen-activated protein kinase]/ERK kinase)/ERK pathway alone could recapitulate all of the effects of oncogenic H-ras expression in blocking erythroid differentiation and inducing Epo-independent proliferation. Although expression of a constitutively active Akt kinase (ca.Akt) in erythroid progenitors does not significantly affect erythroid differentiation in the presence of Epo, coexpression of ca.Akt together with a constitutively active MEK causes prolonged Epo-independent proliferation of erythroid progenitors in addition to a block in differentiation. Moreover, the effects of oncogenic H-ras expression on primary erythroid cells are blocked by the addition of U0126, a specific inhibitor of MEK1 and MEK2, allowing normal terminal erythroid proliferation and differentiation. Our data suggest that the interruption of constitutive MEK/ERK signaling is a potential therapeutic strategy to correct impaired erythroid differentiation in patients with myeloid disorders.
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Affiliation(s)
- Jing Zhang
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA
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36
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Abstract
Stimulation of the erythropoietin (EPO) receptor triggers a cascade of signaling events. We reported that EPO upregulates c-myc expression through 2 pathways in BaF3-EpoR cells--a phosphatidylinositol 3-kinase (PI3K) pathway operating on transcriptional initiation and a Raf-1-mitogen-activated protein kinase (MAPK) pathway affecting elongation. We now show that EPO induces phosphorylation of Raf-1 at serine 338 and within the carboxy-terminal domain, resulting in an electrophoretic mobility change (hyperphosphorylation). Importantly, MEK 1 inhibitor PD98059 blocked only the hyperphosphorylation of Raf-1 but not the phosphorylation at serine 338. This inhibition of Raf-1 hyperphosphorylation resulted in increased kinase activity of Raf-1 and increased phosphorylation of MEK, suggesting that the hyperphosphorylation of Raf-1 inhibits its MEK kinase activity. Deletion of the first 184 amino acids of Raf-1, which are involved in its interaction with Ras, had no effect on EPO-induced phosphorylation. Introducing the dominant-negative N17Ras or GAP had no effect on EPO-induced kinase activity of Raf-1 and ELK activation. N17Ras failed to inhibit ELK activation in another cell line-Rauscher murine erythroleukemia- which expresses the EPO receptor endogenously and differentiates in response to the hormone. These results indicate the presence of a Ras-independent mechanism for Raf-1 and MEK activation in these cells.
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Affiliation(s)
- Changmin Chen
- Laboratory for Cell and Molecular Biology, Division of Hematology and Oncology, Beth Israel Deaconess Medical Center, and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA
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Harding A, Hsu V, Kornfeld K, Hancock JF. Identification of residues and domains of Raf important for function in vivo and in vitro. J Biol Chem 2003; 278:45519-27. [PMID: 12954633 DOI: 10.1074/jbc.m303106200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Random mutagenesis and genetic screens for impaired Raf function in Caenorhabditis elegans were used to identify six loss-of-function alleles of lin-45 raf that result in a substitution of a single amino acid. The mutations were classified as weak, intermediate, and strong based on phenotypic severity. We engineered these mutations into the homologous residues of vertebrate Raf-1 and analyzed the mutant proteins for their underlying biochemical defects. Surprisingly, phenotype strength did not correlate with the catalytic activity of the mutant proteins. Amino acid substitutions Val-589 and Ser-619 severely compromised Raf kinase activity, yet these mutants displayed weak phenotypes in the genetic screen. Interestingly, this is because these mutant Raf proteins efficiently activate the MAPK (mitogen-activated protein kinase) cascade in living cells, a result that may inform the analysis of knockout mice. Equally intriguing was the observation that mutant proteins with non-functional Ras-binding domains, and thereby deficient in Ras-mediated membrane recruitment, displayed only intermediate strength phenotypes. This confirms that secondary mechanisms exist to couple Ras to Raf in vivo. The strongest phenotype in the genetic screens was displayed by a S508N mutation that again did not correlate with a significant loss of kinase activity or membrane recruitment by oncogenic Ras in biochemical assays. Ser-508 lies within the Raf-1 activation loop, and mutation of this residue in Raf-1 and the equivalent Ser-615 in B-Raf revealed that this residue regulates Raf binding to MEK. Further characterization revealed that in response to activation by epidermal growth factor, the Raf-S508N mutant protein displayed both reduced catalytic activity and aberrant activation kinetics: characteristics that may explain the C. elegans phenotype.
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Affiliation(s)
- Angus Harding
- Institute for Molecular Bioscience and Department of Molecular and Cellular Pathology, University of Queensland, Brisbane 4072, Australia
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38
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Chong H, Guan KL. Regulation of Raf through phosphorylation and N terminus-C terminus interaction. J Biol Chem 2003; 278:36269-76. [PMID: 12865432 DOI: 10.1074/jbc.m212803200] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Raf kinase is a key component in regulating the MAPK pathway. B-Raf has been reported as an oncogene and is mutated in 60% of human melanomas. The main focus of Raf regulation studies has been on phosphorylation, dephosphorylation, and scaffolding proteins; however, Raf also has its own auto-regulatory domain. Removal of the N-terminal regulatory domain, initially discovered in the viral Raf oncogene (v-Raf), results in a kinase domain with high basal activity independent of Ras activation. In this report, we show that activating phosphorylations are still required for activity of the truncated C-terminal kinase domain (called 22W). The interaction between the N-terminal regulatory domain and the C-terminal kinase domain is disrupted by activated Ras. Mutations in the Ras binding domain, cysteine-rich domain, or S259A do not affect the inhibition of 22W by the N-terminal domain. When phosphomimetic residues are substituted at the activating sites (DDED) in 22W, this results in a higher basal activity that is no longer inhibited by expression of the N-terminal domain, although binding to the N-terminal domain still occurs. Although the interaction between 22W/DDED and the N-terminal domain may be in a different conformation, the interaction is still disrupted by activated Ras. These data demonstrate that N-terminal domain binding to the kinase domain inhibits the activity of the kinase domain. However, this inhibition is relieved when the C-terminal kinase domain is activated by phosphorylation.
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Affiliation(s)
- Huira Chong
- Department of Biological Chemistry and the Institute of Gerontology, University of Michigan, Ann Arbor, Michigan 48109, USA
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39
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Akimov SS, Belkin AM. Opposing roles of Ras/Raf oncogenes and the MEK1/ERK signaling module in regulation of expression and adhesive function of surface transglutaminase. J Biol Chem 2003; 278:35609-19. [PMID: 12832399 DOI: 10.1074/jbc.m303488200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Tissue transglutaminase (tTG) serves as a potent and ubiquitous integrin-associated adhesion co-receptor for fibronectin on the cell surface and affects several key integrin functions. Here we report that in fibroblasts, activated H-Ras and Raf-1 oncogenes decrease biosynthesis, association with beta1 integrins, and surface expression of tTG because of down-regulation of tTG mRNA. In turn, the reduction of surface tTG inhibits adhesion of H-Ras- and Raf-1-transformed cells on fibronectin and, in particular, on its tTG-binding fragment I(6)II(1,2)I(7-9), which does not interact directly with integrins. Analysis of Ras/Raf downstream signaling with specific pharmacological inhibitors reveals that the decrease in tTG expression is mediated by the p38 MAPK, c-Jun NH2-terminal kinase, and phosphatidylinositol 3-kinase pathways. In contrast, increased activation of the ERK pathway by constitutively active MEK1 stimulates tTG mRNA expression, biosynthesis, and surface expression of tTG, whereas MEK inhibitors or dominant negative MEK1 exert an opposite effect. This modulation of surface tTG by ERK signaling alters adhesion of cells on fibronectin and its fragment that binds tTG. Furthermore, transient stimulation of ERK signaling in untransformed fibroblasts by adhesion on fibronectin or growth factors elevates tTG biosynthesis, increases complex formation with beta1 integrins, and raises surface expression of tTG. Finally, ERK activation is required for growth factor-induced redistribution of tTG on the surface of adherent fibroblasts and co-clustering of beta1 integrins and tTG at cell-matrix adhesion contacts. Together, our data indicate that down-regulation of surface tTG by Ras and Raf oncogenes contributes to adhesive deficiency of transformed fibroblasts, whereas stimulation of biosynthesis and surface expression of tTG by the MEK1/ERK module promotes and sustains cell-matrix adhesion of untransformed cells. Contrasting effects of Ras/Raf oncogenes and their immediate downstream signaling module, MEK1/ERK, on tTG expression are consistent with adhesive function of surface tTG.
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Affiliation(s)
- Sergey S Akimov
- Department of Biochemistry, The Holland Laboratory, American Red Cross, Rockville, Maryland 20855, USA
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Haughn L, Hawley RG, Morrison DK, von Boehmer H, Hockenbery DM. BCL-2 and BCL-XL restrict lineage choice during hematopoietic differentiation. J Biol Chem 2003; 278:25158-65. [PMID: 12721288 DOI: 10.1074/jbc.m212849200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Differentiation of hematopoietic cells from multipotential progenitors is regulated by multiple growth factors and cytokines. A prominent feature of these soluble factors is promotion of cell survival, in part mediated by expression of either of the anti-apoptotic proteins, BCL-2 and BCL-XL. The complex expression pattern of these frequently redundant survival factors during hematopoiesis may indicate a role in lineage determination. To investigate the latter possibility, we analyzed factor-dependent cell-Patersen (FDCP)-Mix multipotent progenitor cells in which we stably expressed BCL-2 or BCL-XL. Each factor maintained complete survival of interleukin-3 (IL-3)-deprived FDCP-Mix cells but, unexpectedly, directed FDCP-Mix cells along restricted and divergent differentiation pathways. Thus, IL-3-deprived FDCP-Mix BCL-2 cells differentiated exclusively to granulocytes and monocytes/macrophages, whereas FDCP-Mix BCL-XL cells became erythroid. FDCP-Mix BCL-2 cells grown in IL-3 were distinguished from FDCP-Mix and FDCP-Mix BCL-XL cells by a striking reduction in cellular levels of Raf-1 protein. Replacement of the BCL-2 BH4 domain with the related BCL-XL BH4 sequence resulted in a switch of FDCP-Mix BCL-2 cells to erythroid fate accompanied by persistence of Raf-1 protein expression. Moreover, enforced expression of Raf-1 redirected FDCP-Mix BCL-2 cells to an erythroid fate, and prohibited generation of myeloid cells. These results identify novel roles for BCL-2 and BCL-XL in cell fate decisions beyond cell survival. These effects are associated with differential regulation of Raf-1 expression, perhaps involving the previously identified interaction between BCL-2-BH4 and the catalytic domain of Raf-1.
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Affiliation(s)
- Loralee Haughn
- Divisions of Human Biology and Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
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41
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Abstract
Molecules considered as autoantigens in autoimmune sensorineural hearing loss and Meniere's diseases are type II collagens, type IX collagens, 30 kD proteins of inner ear membranes, laminin, 68 kD proteins of inner ear, PO protein, Raf I protein and beta-tubulin are reviewed in relation to molecular mechanisms of autoimmune injury of inner ear resulting in hearing loss.
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Affiliation(s)
- T J Yoo
- Department of Medicine, University of Tennessee Health Science Center, Memphis 38163, USA.
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42
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Huang Y, Li H, Hutchison CE, Laskey J, Kieber JJ. Biochemical and functional analysis of CTR1, a protein kinase that negatively regulates ethylene signaling in Arabidopsis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2003; 33:221-33. [PMID: 12535337 DOI: 10.1046/j.1365-313x.2003.01620.x] [Citation(s) in RCA: 210] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
CTR1 encodes a negative regulator of the ethylene response pathway in Arabidopsis thaliana. The C-terminal domain of CTR1 is similar to the Raf family of protein kinases, but its first two-thirds encodes a novel protein domain. We used a variety of approaches to investigate the function of these two CTR1 domains. Recombinant CTR1 protein was purified from a baculoviral expression system, and shown to possess intrinsic Ser/Thr protein kinase activity with enzymatic properties similar to Raf-1. Deletion of the N-terminal domain did not elevate the kinase activity of CTR1, indicating that, at least in vitro, this domain does not autoinhibit kinase function. Molecular analysis of loss-of-function ctr1 alleles indicated that several mutations disrupt the kinase catalytic domain, and in vitro studies confirmed that at least one of these eliminates kinase activity, which indicates that kinase activity is required for CTR1 function. One missense mutation, ctr1-8, was found to result from an amino acid substitution within a new conserved motif within the N-terminal domain. Ctr1-8 has no detectable effect on the kinase activity of CTR1 in vitro, but rather disrupts the interaction with the ethylene receptor ETR1. This mutation also disrupts the dominant negative effect that results from overexpression of the CTR1 amino-terminal domain in transgenic Arabidopsis. These results suggest that CTR1 interacts with ETR1 in vivo, and that this association is required to turn off the ethylene-signaling pathway.
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Affiliation(s)
- Yafan Huang
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
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43
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Xiang X, Zang M, Waelde CA, Wen R, Luo Z. Phosphorylation of 338SSYY341 Regulates Specific Interaction between Raf-1 and MEK1. J Biol Chem 2002; 277:44996-5003. [PMID: 12244094 DOI: 10.1074/jbc.m203953200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The present study characterizes the interaction between the Raf-1 kinase domain and MEK1 and examines whether the magnitude of their interaction correlates to the ability of Raf to phosphorylate MEK1. Here we show that the minimal domain required for the Raf kinase activity starts from tryptophan 342. Maximal binding of the Raf kinase domain to MEK1 and its kinase activity are achieved upon phosphorylation of the region (338)SSYY(341) in response to 4beta-12-O-tetradecanoylphorbol-13-acetate (TPA), or mutation of Y340Y341 to aspartic acids. Conversely, the TPA-stimulated MEK binding and kinase activity are diminished when this region is deleted or Ser(338) and Ser(339) are mutated to alanines. We also show that the integrity of the Raf ATP-binding site is necessary for the interaction between Raf-1 and MEK1. Furthermore, two MEK-binding sites are identified; the first is localized between amino acids 325 and 349, and the second is within the region between amino acids 350 and 648. Separately, the binding of each site to MEK1 is weak, but in a cis context, they give rise to a much stronger association, which can be further stimulated by TPA. Finally, we find that tryptophan 342, which is conserved among the Raf family and other protein kinases, is essential for the Ser(338) phosphorylation of the full-length Raf and its binding to MEK1. Taken together, our results indicate that the phosphorylation of Ser(338) and Tyr(341) on Raf exerts an important effect on reconfiguring the two MEK-binding sites. As a result, these two sites coordinate to form a high affinity MEK-binding epitope, leading to a marked increase in Raf kinase activity.
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Affiliation(s)
- Xiaoqin Xiang
- Diabetes and Metabolism Research Unit, Endocrinology Section, Evans Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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44
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Abstract
Advances in our understanding of the molecular pathways and genetic mutations that control tumor cell proliferation and metastasis present an opportunity to develop novel, mechanism-based therapeutic strategies. Ras mutations are the most frequently activated oncogenes in human tumors, with over 30% expressing ras mutations. Molecular dissection of the signaling pathway and the mechanisms of ras anchorage, post-translational modification, and downstream effector signaling of ras now under intensive investigation will help us to design additional methods for ras-directed therapy in an effort to reach an optimal treatment for human tumors that will most likely comprise a combination of modalities targeted at the different underlying genetic defects. The successes and limitations of ras-targeted therapies must be viewed in light of the increasing understanding of the complexity of the ras-signaling pathway. Only now are we beginning to discover the many functions of this integrated pathway, such as the differences between the actions of various ras isoforms that may affect our choice of therapeutic approach. Many of these Ras therapeutic targets have shown success in preclinical studies, and some have shown efficacy in clinical trials with minimal toxicities. Compounds that block ras-transforming activity without affecting normal ras function seem more attractive for the future development of ras-targeted therapy. FTIs may partially fulfill such requirements. Based on their specific, novel, and mechanism-based action; minimal toxicity; and encouraging responses in clinical trials, the development of Ras therapeutic targets as single agents or in combination with conventional chemotherapy and radiotherapy should be pursued.
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Affiliation(s)
- Irene M Ghobrial
- Division of Medical Oncology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
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45
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Fiordalisi JJ, Holly SP, Johnson RL, Parise LV, Cox AD. A distinct class of dominant negative Ras mutants: cytosolic GTP-bound Ras effector domain mutants that inhibit Ras signaling and transformation and enhance cell adhesion. J Biol Chem 2002; 277:10813-23. [PMID: 11799108 DOI: 10.1074/jbc.m107684200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytosolic GTP-bound Ras has been shown to act as a dominant negative (DN) inhibitor of Ras by sequestering Raf in non-productive cytosolic complexes. Nevertheless, this distinct class of DN mutants has been neither well characterized nor extensively used to analyze Ras signaling. In contrast, DN Ras17N, which functions by blocking Ras guanine nucleotide exchange factors, has been well characterized and is widely used. Cytosolic GTP-bound Ras mutants could be used to inhibit particular Ras effectors by introducing additional mutations (T35S, E37G or Y40C) that permit them to associate selectively with and inhibit Raf, RalGDS, or phosphoinositide 3-kinase, respectively. When the wild-type Ras effector binding region is used, cytosolic Ras should associate with all Ras effectors, even those that are not yet identified, making these DN Ras mutants effective inhibitors of multiple Ras functions. We generated cytosolic GTP-bound H-, N-, and K-Ras, and we assessed their ability to inhibit Ras-induced phenotypes. In fibroblasts, cytosolic H-, N-, and K-Ras inhibited Ras-induced Elk-1 activation and focus formation, induced a flattened cell morphology, and increased adhesion to fibronectin through modulation of a beta(1)-subunit-containing integrin, thereby demonstrating that DN activity is not limited to a subset of Ras isoforms. We also generated cytosolic GTP-bound Ras effector domain mutants (EDMs), each of which reduced the ability of cytosolic GTP-bound Ras proteins to inhibit Elk-1 activation and to induce cell flattening, implicating multiple pathways in these phenotypes. In contrast, Ras-induced focus formation, platelet-derived growth factor (PDGF)-, or Ras-induced phospho-Akt levels and cell adhesion to fibronectin were affected by T35S and Y40C EDMs, whereas PDGF- or Ras-induced phospho-Erk levels were affected only by the T35S EDM, implying that a more limited set of Ras-mediated pathways participate in these phenotypes. These data constitute the first extensive characterization of this functionally distinct class of DN Ras inhibitor proteins.
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Affiliation(s)
- James J Fiordalisi
- Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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Hsu V, Zobel CL, Lambie EJ, Schedl T, Kornfeld K. Caenorhabditis elegans lin-45 raf is essential for larval viability, fertility and the induction of vulval cell fates. Genetics 2002; 160:481-92. [PMID: 11861555 PMCID: PMC1461998 DOI: 10.1093/genetics/160.2.481] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The protein kinase Raf is an important signaling protein. Raf activation is initiated by an interaction with GTP-bound Ras, and Raf functions in signal transmission by phosphorylating and activating a mitogen-activated protein (MAP) kinase kinase named MEK. We identified 13 mutations in the Caenorhabditis elegans lin-45 raf gene by screening for hermaphrodites with abnormal vulval formation or germline function. Weak, intermediate, and strong loss-of-function or null mutations were isolated. The phenotype caused by the most severe mutations demonstrates that lin-45 is essential for larval viability, fertility, and the induction of vulval cell fates. The lin-45(null) phenotype is similar to the mek-2(null) and mpk-1(null) phenotypes, indicating that LIN-45, MEK-2, and MPK-1 ERK MAP kinase function in a predominantly linear signaling pathway. The lin-45 alleles include three missense mutations that affect the Ras-binding domain, three missense mutations that affect the protein kinase domain, two missense mutations that affect the C-terminal 14-3-3 binding domain, three nonsense mutations, and one small deletion. The analysis of the missense mutations indicates that Ras binding, 14-3-3-binding, and protein kinase activity are necessary for full Raf function and suggests that a 14-3-3 protein positively regulates Raf-mediated signaling during C. elegans development.
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Affiliation(s)
- Virginia Hsu
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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47
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Zhang L, Bewick M, Lafrenie RM. EGFR and ErbB2 differentially regulate Raf-1 translocation and activation. J Transl Med 2002; 82:71-8. [PMID: 11796827 DOI: 10.1038/labinvest.3780396] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Epidermal growth factor receptor (EGFR) and HER-2/ErbB2 are members of the Erb family of signaling receptors. ErbB2 is overexpressed in many different cancers and has been linked to enhanced malignancy of tumors. We have examined the cellular translocation of Raf-1 during EGF-dependent signal transduction in two breast tumor cell lines, BT20 and SKBR3. Treatment of BT-20 breast cancer cells, which express EGFR, with EGF resulted in rapid (5 minutes) accumulation of EGFR and Raf-1 into plasma membrane-associated endocytotic vesicles. However, at later time points (30 minutes) only EGFR was endocytosed and Raf-1 dissociated from the plasma membrane and was found in the cytosol. In SKBR3 breast cancer cells, which express high levels of EGFR and ErbB2, treatment with EGF also resulted in rapid accumulation of EGFR and Raf-1 into endocytotic vesicles, but EGFR endocytosis was inhibited and Raf-1 remained associated with the plasma membrane for a prolonged period. The role of ErbB2 in the retention of Raf-1 at the plasma membrane was confirmed in BT-20 cells transfected with ErbB2. BT-20 cells expressing ErbB2 and treated with EGF retained Raf-1 at the plasma membrane for prolonged periods, whereas Raf-1 rapidly dissociated from the plasma membrane in EGF-stimulated cells transfected with a control vector. The presence of Raf-1 at the plasma membrane correlated with activation of Raf-1 and MAP kinase. Cells that expressed ErbB2 and treated with EGF showed prolonged activation of Raf-1 and MAP kinase compared with cells that expressed low levels of ErbB2. These results suggest that expression of ErbB2 promoted retention of Raf-1 in the plasma membrane, resulting in prolonged activation of the MAP kinase cascade, which may contribute to enhanced malignancy in ErbB2-expressing cancers.
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Affiliation(s)
- Lianfeng Zhang
- Division of Tumor Biology, Northeastern Ontario Regional Cancer Centre, 41 Ramsey Lake Road, Sudbury, Ontario, Canada P3E 5J1
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Kieber JJ. The ethylene response pathway in Arabidopsis. ANNUAL REVIEW OF PLANT PHYSIOLOGY AND PLANT MOLECULAR BIOLOGY 2001; 48:277-96. [PMID: 11541139 DOI: 10.1146/annurev.arplant.48.1.277] [Citation(s) in RCA: 153] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The simple gas ethylene influences a diverse array of plant growth and developmental processes including germination, senescence, cell elongation, and fruit ripening. This review focuses on recent molecular genetic studies, principally in Arabidopsis, in which components of the ethylene response pathway have been identified. The isolation and characterization of two of these genes has revealed that ethylene sensing involves a protein kinase cascade. One of these genes encodes a protein with similarity to the ubiquitous Raf family of Ser/Thr protein kinases. A second gene shows similarity to the prokaryotic two-component histidine kinases and most likely encodes an ethylene receptor. Additional elements involved in ethylene signaling have only been identified genetically. The characterization of these genes and mutants will be discussed.
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Affiliation(s)
- J J Kieber
- Department of Biological Sciences, University of Illinois at Chicago 60607, USA
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49
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Kerkhoff E, Rapp UR. The Ras-Raf relationship: an unfinished puzzle. ADVANCES IN ENZYME REGULATION 2001; 41:261-7. [PMID: 11384750 DOI: 10.1016/s0065-2571(00)00023-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- E Kerkhoff
- Institut für Medizinische Strahlenkunde und Zellforschung (MSZ), Versbacher Str. 5, 97078, Würzburg, Germany
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50
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McCubrey JA, Steelman LS, Blalock WL, Lee JT, Moye PW, Chang F, Pearce M, Shelton JG, White MK, Franklin RA, Pohnert SC. Synergistic effects of pi3k/akt on abrogation of cytokine-dependency induced by oncogenic raf. ADVANCES IN ENZYME REGULATION 2001; 41:289-323. [PMID: 11384752 DOI: 10.1016/s0065-2571(00)00021-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- J A McCubrey
- Department of Microbiology and Immunology, Brody School of Medicine at East Carolina University, Greenville, NC 27858, USA.
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