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Bahar ME, Kim HJ, Kim DR. Targeting the RAS/RAF/MAPK pathway for cancer therapy: from mechanism to clinical studies. Signal Transduct Target Ther 2023; 8:455. [PMID: 38105263 PMCID: PMC10725898 DOI: 10.1038/s41392-023-01705-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 11/03/2023] [Accepted: 11/12/2023] [Indexed: 12/19/2023] Open
Abstract
Metastatic dissemination of solid tumors, a leading cause of cancer-related mortality, underscores the urgent need for enhanced insights into the molecular and cellular mechanisms underlying metastasis, chemoresistance, and the mechanistic backgrounds of individuals whose cancers are prone to migration. The most prevalent signaling cascade governed by multi-kinase inhibitors is the mitogen-activated protein kinase (MAPK) pathway, encompassing the RAS-RAF-MAPK kinase (MEK)-extracellular signal-related kinase (ERK) pathway. RAF kinase is a primary mediator of the MAPK pathway, responsible for the sequential activation of downstream targets, such as MEK and the transcription factor ERK, which control numerous cellular and physiological processes, including organism development, cell cycle control, cell proliferation and differentiation, cell survival, and death. Defects in this signaling cascade are associated with diseases such as cancer. RAF inhibitors (RAFi) combined with MEK blockers represent an FDA-approved therapeutic strategy for numerous RAF-mutant cancers, including melanoma, non-small cell lung carcinoma, and thyroid cancer. However, the development of therapy resistance by cancer cells remains an important barrier. Autophagy, an intracellular lysosome-dependent catabolic recycling process, plays a critical role in the development of RAFi resistance in cancer. Thus, targeting RAF and autophagy could be novel treatment strategies for RAF-mutant cancers. In this review, we delve deeper into the mechanistic insights surrounding RAF kinase signaling in tumorigenesis and RAFi-resistance. Furthermore, we explore and discuss the ongoing development of next-generation RAF inhibitors with enhanced therapeutic profiles. Additionally, this review sheds light on the functional interplay between RAF-targeted therapies and autophagy in cancer.
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Affiliation(s)
- Md Entaz Bahar
- Department of Biochemistry and Convergence Medical Sciences and Institute of Medical Science, Gyeongsang National University, College of Medicine, Jinju, South Korea
| | - Hyun Joon Kim
- Department of Anatomy and Convergence Medical Sciences and Institute of Medical Science, Gyeongsang National University, College of Medicine, Jinju, South Korea
| | - Deok Ryong Kim
- Department of Biochemistry and Convergence Medical Sciences and Institute of Medical Science, Gyeongsang National University, College of Medicine, Jinju, South Korea.
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Degirmenci U, Wang M, Hu J. Targeting Aberrant RAS/RAF/MEK/ERK Signaling for Cancer Therapy. Cells 2020; 9:E198. [PMID: 31941155 PMCID: PMC7017232 DOI: 10.3390/cells9010198] [Citation(s) in RCA: 308] [Impact Index Per Article: 77.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 12/29/2019] [Accepted: 01/10/2020] [Indexed: 12/13/2022] Open
Abstract
The RAS/RAF/MEK/ERK (MAPK) signaling cascade is essential for cell inter- and intra-cellular communication, which regulates fundamental cell functions such as growth, survival, and differentiation. The MAPK pathway also integrates signals from complex intracellular networks in performing cellular functions. Despite the initial discovery of the core elements of the MAPK pathways nearly four decades ago, additional findings continue to make a thorough understanding of the molecular mechanisms involved in the regulation of this pathway challenging. Considerable effort has been focused on the regulation of RAF, especially after the discovery of drug resistance and paradoxical activation upon inhibitor binding to the kinase. RAF activity is regulated by phosphorylation and conformation-dependent regulation, including auto-inhibition and dimerization. In this review, we summarize the recent major findings in the study of the RAS/RAF/MEK/ERK signaling cascade, particularly with respect to the impact on clinical cancer therapy.
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Affiliation(s)
- Ufuk Degirmenci
- Division of Cellular and Molecular Research, National Cancer Centre Singapore, 11 Hospital Crescent, Singapore 169610, Singapore
| | - Mei Wang
- Cancer and Stem Cell Biology Program, Duke-NUS Medical School, 8 College Road, Singapore 169857, Singapore
| | - Jiancheng Hu
- Division of Cellular and Molecular Research, National Cancer Centre Singapore, 11 Hospital Crescent, Singapore 169610, Singapore
- Cancer and Stem Cell Biology Program, Duke-NUS Medical School, 8 College Road, Singapore 169857, Singapore
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Structural snapshots of RAF kinase interactions. Biochem Soc Trans 2018; 46:1393-1406. [PMID: 30381334 DOI: 10.1042/bst20170528] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Revised: 07/25/2018] [Accepted: 07/30/2018] [Indexed: 02/07/2023]
Abstract
RAF (rapidly accelerated fibrosarcoma) Ser/Thr kinases (ARAF, BRAF, and CRAF) link the RAS (rat sarcoma) protein family with the MAPK (mitogen-activated protein kinase) pathway and control cell growth, differentiation, development, aging, and tumorigenesis. Their activity is specifically modulated by protein-protein interactions, post-translational modifications, and conformational changes in specific spatiotemporal patterns via various upstream regulators, including the kinases, phosphatase, GTPases, and scaffold and modulator proteins. Dephosphorylation of Ser-259 (CRAF numbering) and dissociation of 14-3-3 release the RAF regulatory domains RAS-binding domain and cysteine-rich domain for interaction with RAS-GTP and membrane lipids. This, in turn, results in RAF phosphorylation at Ser-621 and 14-3-3 reassociation, followed by its dimerization and ultimately substrate binding and phosphorylation. This review focuses on structural understanding of how distinct binding partners trigger a cascade of molecular events that induces RAF kinase activation.
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Pfeiffer V, Götz R, Camarero G, Heinsen H, Blum R, Rapp UR. Impaired neuronal maturation of hippocampal neural progenitor cells in mice lacking CRAF. PLoS One 2018; 13:e0192067. [PMID: 29590115 PMCID: PMC5873938 DOI: 10.1371/journal.pone.0192067] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Accepted: 01/16/2018] [Indexed: 11/19/2022] Open
Abstract
RAF kinases are major constituents of the mitogen activated signaling pathway, regulating cell proliferation, differentiation and cell survival of many cell types, including neurons. In mammals, the family of RAF proteins consists of three members, ARAF, BRAF, and CRAF. Ablation of CRAF kinase in inbred mouse strains causes major developmental defects during fetal growth and embryonic or perinatal lethality. Heterozygous germline mutations in CRAF result in Noonan syndrome, which is characterized by neurocognitive impairment that may involve hippocampal physiology. The role of CRAF signaling during hippocampal development and generation of new postnatal hippocampal granule neurons has not been examined and may provide novel insight into the cause of hippocampal dysfunction in Noonan syndrome. In this study, by crossing CRAF-deficiency to CD-1 outbred mice, a CRAF mouse model was established which enabled us to investigate the interplay of neural progenitor proliferation and postmitotic differentiation during adult neurogenesis in the hippocampus. Albeit the general morphology of the hippocampus was unchanged, CRAF-deficient mice displayed smaller granule cell layer (GCL) volume at postnatal day 30 (P30). In CRAF-deficient mice a substantial number of abnormal, chromophilic, fast dividing cells were found in the subgranular zone (SGZ) and hilus of the dentate gyrus (DG), indicating that CRAF signaling contributes to hippocampal neural progenitor proliferation. CRAF-deficient neural progenitor cells showed an increased cell death rate and reduced neuronal maturation. These results indicate that CRAF function affects postmitotic neural cell differentiation and points to a critical role of CRAF-dependent growth factor signaling pathway in the postmitotic development of adult-born neurons.
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Affiliation(s)
- Verena Pfeiffer
- University of Würzburg, Institute of Anatomy and Cell Biology, Koellikerstraße 6, Würzburg, Germany
- University of Würzburg, Institute for Medical Radiation and Cell Research (MSZ), Versbacher Strasse 5, Würzburg, Germany
- * E-mail:
| | - Rudolf Götz
- University of Würzburg, Institute for Medical Radiation and Cell Research (MSZ), Versbacher Strasse 5, Würzburg, Germany
- Institute for Clinical Neurobiology, University Hospital Würzburg, Versbacher Strasse 5, Würzburg, Germany
| | - Guadelupe Camarero
- University of Würzburg, Institute for Medical Radiation and Cell Research (MSZ), Versbacher Strasse 5, Würzburg, Germany
| | - Helmut Heinsen
- University of Würzburg, Department of Psychiatry, Psychosomatics and Psychotherapy, Margarethe-Höppel-Platz 1, Würzburg, Germany
- Universidade de Sao Paulo Faculdade de Medicina, Pathology—LIM 44 Sao Paulo, SP, Brazil
| | - Robert Blum
- Institute for Clinical Neurobiology, University Hospital Würzburg, Versbacher Strasse 5, Würzburg, Germany
| | - Ulf Rüdiger Rapp
- University of Würzburg, Institute for Medical Radiation and Cell Research (MSZ), Versbacher Strasse 5, Würzburg, Germany
- Department of Lung Development and Remodeling, Max Planck Institute for Heart and Lung Research, Parkstr.1, Bad Nauheim, Germany
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Zaballos MA, Santisteban P. Key signaling pathways in thyroid cancer. J Endocrinol 2017; 235:R43-R61. [PMID: 28838947 DOI: 10.1530/joe-17-0266] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Accepted: 08/04/2017] [Indexed: 12/16/2022]
Abstract
Whole genome sequencing approaches have provided unprecedented insights into the genetic lesions responsible for the onset, progression and dedifferentiation of various types of thyroid carcinomas. Through these efforts, the MAPK and PI3K signaling cascades have emerged as the main activation pathways implicated in thyroid tumorigenesis. The nature of these essential pathways is highly complex, with hundreds of components, multiple points of crosstalk, different subcellular localizations and with the ability to potentially regulate many cellular processes. Small-molecule inhibitors targeting key kinases of these pathways hold great promise as novel therapeutics and several have reached clinical trials. However, while some remarkable responses have been reported, the development of resistance remains a matter of concern and limits the benefit for patients. In this review, we discuss the latest findings on the major components of the MAPK and PI3K pathways, including their mechanisms of activation in physiological and pathological contexts, their genetic alterations with respect to the different types of thyroid carcinomas and the more relevant drugs designed to block their activity.
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Affiliation(s)
- Miguel A Zaballos
- Instituto de Investigaciones Biomédicas 'Alberto Sols'Consejo Superior de Investigaciones Científicas (CSIC), Universidad Autónoma de Madrid (UAM), Centro de Investigación Biomédica en Red de Cáncer (CIBERONC), Instituto de Salud Carlos III (ISCIII), Madrid, Spain
| | - Pilar Santisteban
- Instituto de Investigaciones Biomédicas 'Alberto Sols'Consejo Superior de Investigaciones Científicas (CSIC), Universidad Autónoma de Madrid (UAM), Centro de Investigación Biomédica en Red de Cáncer (CIBERONC), Instituto de Salud Carlos III (ISCIII), Madrid, Spain
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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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Madureira P, de Mello RA. BRAF and MEK Gene Rearrangements in Melanoma: Implications for Targeted Therapy. Mol Diagn Ther 2014; 18:285-91. [DOI: 10.1007/s40291-013-0081-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
The protein kinase B-Raf is a critical component of the Ras/MAPK signaling pathway. An oncogenic B-Raf mutation that constitutively activates the kinase was identified in z50% of melanoma patients and in other cancers. A structure-guided drug discovery approach enabled the development of Zelboraf, a targeted inhibitor of oncogenic B-Raf. This drug has been used successfully in the clinic to treat metastatic melanoma patients harboring B-Raf mutations.
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Affiliation(s)
- Matthew J Davis
- Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520, USA
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Jeong D, Jeong Y, Lee S, Lee H, Lee W, Kim H, Park D, Park S, Mu W, Cho HD, Oh MH, Lee SS, Yang SH, Kim CJ. Detection of BRAF(V600E) Mutations in Papillary Thyroid Carcinomas by Peptide Nucleic Acid Clamp Real-Time PCR: A Comparison with Direct Sequencing. KOREAN JOURNAL OF PATHOLOGY 2012; 46:61-7. [PMID: 23109980 PMCID: PMC3479705 DOI: 10.4132/koreanjpathol.2012.46.1.61] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 12/29/2011] [Accepted: 01/10/2012] [Indexed: 12/19/2022]
Abstract
BACKGROUND Papillary thyroid carcinoma (PTC) of the thyroid is the most common endocrine malignancy. High prevalence of an activating point mutation of BRAF gene, BRAF(V600E), has been reported in PTC. We assessed the efficiency of peptide nucleic acid clamp real-time polymerase chain reaction (PNAcqPCR) for the detection of BRAF(V600E) mutation in PTC in comparison with direct sequencing (DS). METHODS A total of 265 thyroid lesions including 200 PTCs, 5 follicular carcinomas, 60 benign lesions and 10 normal thyroid tissues were tested for BRAF(V600E) mutation by PNAcqPCR and DS. RESULTS The sensitivity and accuracy of the PNAcqPCR method were both higher than those of DS for the detection of the BRAF(V600E) mutation. In clinical samples, 89% of PTCs harbored the BRAF(V600E) mutation, whereas 5 follicular carcinomas, 50 benign lesions and 10 normal thyroid tissues lacked the mutation. The mutation was associated with aggressive clinical behaviors as extrathyroid invasion (p=0.015), lymph node metastasis (p=0.002) and multiple tumor numbers (p=0.016) with statistical significance. CONCLUSIONS The PNAcqPCR method is efficiently applicable for the detection of the BRAF(V600E) mutation in PTCs in a clinical setting.
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Affiliation(s)
- Dongjun Jeong
- Department of Pathology, Soonchunhyang University College of Medicine, Cheonan, Korea
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Tyr phosphatase-mediated P-ERK inhibition suppresses senescence in EIA + v-raf transformed cells, which, paradoxically, are apoptosis-protected in a MEK-dependent manner. Neoplasia 2011; 13:120-30. [PMID: 21403838 DOI: 10.1593/neo.101152] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Revised: 11/12/2010] [Accepted: 11/18/2010] [Indexed: 01/01/2023] Open
Abstract
Activation of the Ras-Raf-extracellular signal-regulated kinase (ERK) pathway causes not only proliferation and suppression of apoptosis but also the antioncogenic response of senescence. How these contrasting effects are reconciled to achieve cell transformation and cancer formation is poorly understood. In a system of two-step carcinogenesis (dedifferentiated PC EIA, transformed PC EIA-polyoma-middle T [PC EIA + Py] and PC EIA-v-raf [PC EIA + raf] cells], v-raf cooperated with EIA by virtue of a strong prosurvival effect, not elicited by Py-middle T, evident toward serum-deprivation-and H(2)O(2)-induced apoptosis. Apoptosis was detected by DNA fragmentation and annexin V staining. The prosurvival function of v-raf was, in part, mitogen-activated protein kinase/ERK kinase (MEK)-dependent, as shown by pharmacological MEK inhibition. The MEK-dependent antiapoptotic effect of v-raf was exerted despite a lower level of P-ERK1/2 in EIA + raf cells with respect to EIA + Py/EIA cells, which was dependent on a high tyrosine phosphatase activity, as shown by orthovanadate blockade. An ERK1/2 tyrosine phosphatase was likely involved. The high tyrosine phosphatase activity was instrumental to the complete suppression of senescence, detected by β-galactosidase activity, because tyrosine phosphatase blockade induced senescence in EIA + raf but not in EIA + Py cells. High tyrosine phosphatase activity and evasion from senescence were confirmed in an anaplastic thyroid cancer cell line. Therefore, besides EIA, EIA + raf cells suppress senescence through a new mechanism, namely, phosphatase-mediated P-ERK1/2 inhibition, but, paradoxically, retain the oncogenic effects of the Raf-ERK pathway. We propose that the survival effect of Raf is not a function of absolute P-ERK1/2 levels at a given time but is rather dynamically dependent on greater variations after an apoptotic stimulus.
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Soares P, Preto A, Sobrinho-Simões M. BRAF V600E mutation in papillary thyroid carcinoma: a potential target for therapy? Expert Rev Endocrinol Metab 2009; 4:467-480. [PMID: 30736186 DOI: 10.1586/eem.09.29] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This article reviews the therapeutic significance of the close genotype-phenotype association in papillary thyroid carcinoma, namely regarding the association between genetic alterations in RET, BRAF or RAS genes and the histopathological variants of papillary thyroid carcinoma. Based upon the aforementioned review on morphology and molecular pathology, the most recent prognostic and therapeutic data are reviewed and the role of targeted therapies, namely those interfering with BRAF-activated pathways are discussed, which may play a role in the treatment of patients with papillary thyroid carcinoma unresponsive to radioactive iodine.
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Affiliation(s)
- Paula Soares
- a Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP), Rua Dr Roberto Frias, s/n, 4200-4465 Porto, Portugal and Department of Pathology, Medical Faculty of the University of Porto, 4200-465 Porto, Portugal.
| | - Ana Preto
- b Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP), Rua Dr Roberto Frias, s/n, 4200-4465 Porto, Portugal and Molecular and Environmental Biology Centre (CBMA), Department of Biology, University of Minho, Campus de Gualtar, 4710-4057 Braga, Portugal.
| | - Manuel Sobrinho-Simões
- c Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP), Rua Dr Roberto Frias, s/n, 4200-465 Porto, Portugal and Department of Pathology, Medical Faculty of the University of Porto, 4200-465 Porto, Portugal and Department of Pathology, Hospital de S. João, Porto, Portugal.
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Baljuls A, Schmitz W, Mueller T, Zahedi RP, Sickmann A, Hekman M, Rapp UR. Positive regulation of A-RAF by phosphorylation of isoform-specific hinge segment and identification of novel phosphorylation sites. J Biol Chem 2008; 283:27239-54. [PMID: 18662992 DOI: 10.1074/jbc.m801782200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In mammals the RAF family of serine/threonine kinases consists of three members, A-, B-, and C-RAF. Activation of RAF kinases involves a complex series of phosphorylations. Although the most prominent phosphorylation sites of B- and C-RAF are well characterized, little is known about regulatory phosphorylation of A-RAF. Using mass spectrometry, we identified here a number of novel in vivo phosphorylation sites in A-RAF. In particular, we found that Ser-432 participates in MEK binding and is indispensable for A-RAF signaling. On the other hand, phosphorylation within the activation segment does not contribute to epidermal growth factor-mediated activation. Furthermore, we show that the potential 14-3-3 binding domains in A-RAF are phosphorylated independently of its activation status. Of importance, we identified a novel regulatory domain in A-RAF (referred to as IH-segment) positioned between amino acids 248 and 267 that contains seven putative phosphorylation sites. Three of these sites, serines 257, 262, and 264, regulate A-RAF activation in a stimulatory manner. The spatial model of the A-RAF fragment, including residues between Ser-246 and Glu-277, revealed a switch of charge at the molecular surface of the IH-region upon phosphorylation, suggesting a mechanism in which the high accumulation of negative charges may lead to an electrostatic destabilization of protein-membrane interaction resulting in depletion of A-RAF from the plasma membrane. Together, we provide here for the first time a detailed analysis of in vivo A-RAF phosphorylation status and demonstrate that regulation of A-RAF by phosphorylation exhibits unique features compared with B- and C-RAF.
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Affiliation(s)
- Angela Baljuls
- Institute for Medical Radiation and Cell Research, University of Wuerzburg, 97078 Wuerzburg, Germany
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Baljuls A, Mueller T, Drexler HCA, Hekman M, Rapp UR. Unique N-region Determines Low Basal Activity and Limited Inducibility of A-RAF Kinase. J Biol Chem 2007; 282:26575-90. [PMID: 17613527 DOI: 10.1074/jbc.m702429200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In mammals the RAF family of serine/threonine kinases consists of three members, A-, B-, and C-RAF. A prominent feature of RAF isoforms regards differences in basal and inducible kinase activities. To elucidate the nature of these differences, we studied the role of the nonconserved residues within the N-region (Negative-charge regulatory region). The nonconserved amino acids in positions -3 and +1 relative to the highly conserved serine 299 in A-RAF and serine 338 in C-RAF have so far not been considered as regulatory residues. Here we demonstrate the essential role of these residues in the RAF activation process. Substitution of tyrosine 296 in A-RAF to arginine led to a constitutively active kinase. In contrast, substitution of glycine 300 by serine (mimicking B- and C-RAF) acts in an inhibitory manner. Consistent with these data, the introduction of glycine in the analogous position of C-RAF (S339G mutant) led to a constitutively active C-RAF kinase. Based on the three-dimensional structure of the catalytic domain of B-RAF and using the sequences of the N-regions of A- and C-RAF, we searched by molecular modeling for the putative contact points between these two moieties. A tight interaction between the N-region residue serine 339 of C-RAF and arginine 398 of the catalytic domain was identified and proposed to inhibit the kinase activity of RAF proteins, because abrogation of this interaction contributes to RAF activation. Furthermore, tyrosine 296 in A-RAF favors a spatial orientation of the N-region segment, which enables a tighter contact to the catalytic domain, whereas a glutamine residue at this position in C-RAF abrogates this interaction. Considering this observation, we suggest that tyrosine 296, which is unique for A-RAF, is a major determinant of the low activating potency of this RAF isoform.
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Affiliation(s)
- Angela Baljuls
- Institute for Medical Radiation and Cell Research, University of Wuerzburg, 97078 Wuerzburg, Germany
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Yokoyama T, Takano K, Yoshida A, Katada F, Sun P, Takenawa T, Andoh T, Endo T. DA-Raf1, a competent intrinsic dominant-negative antagonist of the Ras-ERK pathway, is required for myogenic differentiation. ACTA ACUST UNITED AC 2007; 177:781-93. [PMID: 17535970 PMCID: PMC2064279 DOI: 10.1083/jcb.200703195] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ras activates Raf, leading to the extracellular-regulated kinase (ERK)–mitogen-activated protein kinase pathway, which is involved in a variety of cellular, physiological, and pathological responses. Thus, regulators of this Ras–Raf interaction play crucial roles in these responses. In this study, we report a novel regulator of the Ras–Raf interaction named DA-Raf1. DA-Raf1 is a splicing isoform of A-Raf with a wider tissue distribution than A-Raf. It contains the Ras-binding domain but lacks the kinase domain, which is responsible for activation of the ERK pathway. As inferred from its structure, DA-Raf1 bound to activated Ras as well as M-Ras and interfered with the ERK pathway. The Ras–ERK pathway is essential for the negative regulation of myogenic differentiation induced by growth factors. DA-Raf1 served as a positive regulator of myogenic differentiation by inducing cell cycle arrest, the expression of myogenin and other muscle-specific proteins, and myotube formation. These results imply that DA-Raf1 is the first identified competent, intrinsic, dominant-negative antagonist of the Ras–ERK pathway.
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Affiliation(s)
- Takashi Yokoyama
- Department of Biology, Graduate School of Science, Chiba University, Chiba 263-8522, Japan
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15
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Willard MD, Willard FS, Li X, Cappell SD, Snider WD, Siderovski DP. Selective role for RGS12 as a Ras/Raf/MEK scaffold in nerve growth factor-mediated differentiation. EMBO J 2007; 26:2029-40. [PMID: 17380122 PMCID: PMC1852785 DOI: 10.1038/sj.emboj.7601659] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2006] [Accepted: 02/27/2007] [Indexed: 12/13/2022] Open
Abstract
Regulator of G-protein signaling (RGS) proteins accelerate GTP hydrolysis by heterotrimeric G-protein alpha subunits and thus inhibit signaling by many G protein-coupled receptors. Several RGS proteins have a multidomain architecture that adds further complexity to their roles in cell signaling in addition to their GTPase-accelerating activity. RGS12 contains a tandem repeat of Ras-binding domains but, to date, the role of this protein in Ras-mediated signal transduction has not been reported. Here, we show that RGS12 associates with the nerve growth factor (NGF) receptor tyrosine kinase TrkA, activated H-Ras, B-Raf, and MEK2 and facilitates their coordinated signaling to prolonged ERK activation. RGS12 is required for NGF-mediated neurite outgrowth of PC12 cells, but not outgrowth stimulated by basic fibroblast growth factor. siRNA-mediated knockdown of RGS12 expression also inhibits NGF-induced axonal growth in dissociated cultures of primary dorsal root ganglia neurons. These data suggest that RGS12 may play a critical, and receptor-selective, role in coordinating Ras-dependent signals that are required for promoting and/or maintaining neuronal differentiation.
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Affiliation(s)
- Melinda D Willard
- Department of Pharmacology, University of North Carolina, Chapel Hill, NC, USA
- UNC Neuroscience Center, University of North Carolina, Chapel Hill, NC, USA
- Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, USA
| | - Francis S Willard
- Department of Pharmacology, University of North Carolina, Chapel Hill, NC, USA
- UNC Neuroscience Center, University of North Carolina, Chapel Hill, NC, USA
- Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, USA
| | - Xiaoyan Li
- UNC Neuroscience Center, University of North Carolina, Chapel Hill, NC, USA
| | - Steven D Cappell
- Department of Pharmacology, University of North Carolina, Chapel Hill, NC, USA
| | - William D Snider
- UNC Neuroscience Center, University of North Carolina, Chapel Hill, NC, USA
| | - David P Siderovski
- Department of Pharmacology, University of North Carolina, Chapel Hill, NC, USA
- UNC Neuroscience Center, University of North Carolina, Chapel Hill, NC, USA
- Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, USA
- Department of Pharmacology, UNC-Chapel Hill School of Medicine, 1106 ME Jones Bldg, CB 7365, Manning Dr Chapel Hill, NC 27599-7365, USA. Tel.: +1 919 843 9363; Fax: +1 919 966 5640; E-mail:
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16
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Kyriakis JM. The integration of signaling by multiprotein complexes containing Raf kinases. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1773:1238-47. [PMID: 17276528 DOI: 10.1016/j.bbamcr.2006.11.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Revised: 10/27/2006] [Accepted: 11/01/2006] [Indexed: 12/18/2022]
Abstract
In vivo, eukaryotic cells are subjected simultaneously to a broad array of signals ranging from mitogens and inflammatory inputs to environmental stresses and developmental cues. The combinatorial nature of cellular signaling necessitates that a cell integrate its signal transduction pathways so as to implement rapidly and efficiently an appropriate suite of responses. Emerging evidence indicates that, over the course of evolution, cells have developed multiprotein signaling complexes, or "signalosomes" that mediate the coordinate regulation of different signaling pathways. Such molecular signal integration contrasts with the classical notion of signaling complexes assembled by scaffold proteins-entities that function to segregate specific pathways from one another. This review will focus on two signal integrating multiprotein complexes that involve Raf family kinases: the MLK3-B-Raf-Raf-1 complex and the Raf-1-Mst-2 complex.
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Affiliation(s)
- John M Kyriakis
- The Molecular Cardiology Research Institute, Tufts-New England Medical Center and the Department of Medicine, Tufts University School of Medicine, 750 Washington Street, Boston, MA 02111, USA.
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Kumagai A, Namba H, Takakura S, Inamasu E, Saenko VA, Ohtsuru A, Yamashita S. No evidence of ARAF, CRAF and MET mutations in BRAFT1799A negative human papillary thyroid carcinoma. Endocr J 2006; 53:615-20. [PMID: 16896265 DOI: 10.1507/endocrj.k06-058] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The MAPK signaling pathway plays a crucial role in tumorgenesis and cell proliferation in human papillary thyroid carcinoma (PTC). Ret/PTC rearrangements, RAS and BRAF mutations, the main non-overlapping genetic alterations all leading to MAPK cascade activation, are cumulatively identified in 60-80% of PTCs. In approximately one-fourth of the cases, oncogenic background potentially contributing to MAPK activation in PTC might be different. We therefore attempted to evaluate the mutational status of genes encoding other members of RAF family known to act upstream of MAPKs, ARAF and CRAF (RAF-1). In addition we also analyzed the MET gene that encodes hepatocyte growth factor/scatter factor receptor overexpressed in most of PTCs and a MAPK cascade contributor. In 129 Japanese patients with PTC, BRAF(T1799A) was detected in 65 cases (50.4%), and the remaining 64 tumor specimens were subjected to mutation analysis of kinase domains of ARAF, CRAF and MET genes, and hotspots of K- and N-RAS genes. No ARAF, CRAF, MET, K- and N-RAS mutations were revealed. Based on these observations, we concluded that despite the fact that ARAF, CRAF and MET are actively expressed, alterations of these genes are rare in PTC and unlikely to play a perceptible role in the molecular pathogenesis of this type of human malignancy.
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Affiliation(s)
- Atsushi Kumagai
- Department of Molecular Medicine, Atomic Bomb Disease Institute, Graduate School of Biomedical Sciences, Nagasaki University, Sakamoto, Nagaski, Japan
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18
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Abstract
Raf kinase signaling has been thoroughly investigated over the last 20 years. A-Raf, B-Raf and C-Raf, the 3 mammalian members of the Raf family, are involved in a variety of cellular processes such as growth, proliferation, survival, differentiation and transformation. The detection of B-RAF mutations in a wide variety of human cancers, the description of wildtype and mutant B-RAF as tumor antigens in melanoma and the promising outcome of clinical trials evaluating the Raf inhibitor Nexavar (Sorafenib, BAY 43-9006) have sparked a broad interest in the scientific community. After a short historical detour and an introduction into Raf kinase signaling, we are going to discuss here recent outcomes of Raf kinase research with respect to tumor formation and give an overview on current efforts to develop anticancer therapies interfering with aberrant Raf kinase signaling.
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Affiliation(s)
- Ralf Schreck
- Institut für Medizinische Strahlenkunde und Zellforschung, MSZ, Universität Würzburg, Würzburg, Germany
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Chen AP, Ohno M, Giese KP, Kühn R, Chen RL, Silva AJ. Forebrain-specific knockout of B-raf kinase leads to deficits in hippocampal long-term potentiation, learning, and memory. J Neurosci Res 2006; 83:28-38. [PMID: 16342120 DOI: 10.1002/jnr.20703] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Raf kinases are downstream effectors of Ras and upstream activators of the MEK-ERK cascade. Ras and MEK-ERK signaling play roles in learning and memory (L&M) and neural plasticity, but the roles of Raf kinases in L&M and plasticity are unclear. Among Raf isoforms, B-raf is preferentially expressed in the brain. To determine whether B-raf has a role in synaptic plasticity and L&M, we used the Cre-LoxP gene targeting system to derive forebrain excitatory neuron B-raf knockout mice. This conditional knockout resulted in deficits in ERK activation and hippocampal long-term potentiation (LTP) and impairments in hippocampus-dependent L&M, including spatial learning and contextual discrimination. Despite the widespread expression of B-raf, this mutation did not disrupt other forms of L&M, such as cued fear conditioning and conditioned taste aversion. Our findings demonstrate that B-raf plays a role in hippocampal ERK activation, synaptic plasticity, and L&M.
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Affiliation(s)
- Adele P Chen
- Department of Neurobiology, Brain Research Institute, University of California, Los Angeles, 90095-1761, USA
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20
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Nakamura N, Carney JA, Jin L, Kajita S, Pallares J, Zhang H, Qian X, Sebo TJ, Erickson LA, Lloyd RV. RASSF1A and NORE1A methylation and BRAFV600E mutations in thyroid tumors. J Transl Med 2005; 85:1065-75. [PMID: 15980887 DOI: 10.1038/labinvest.3700306] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
We analyzed RASSF1A and NORE1A methylation and BRAF mutation in 89 thyroid tumors, 42 non-neoplastic thyroid tissues and three thyroid tumor cell lines using polymerase chain reaction (PCR), methylation-specific PCR, Western blotting and DNA sequencing in order to study thyroid tumor pathogenesis and progression. RASSF1A promoter methylation was present in all three thyroid cell lines and in 27/78 (35%) of benign and malignant thyroid tumors. We showed for the first time that there was generally good agreement between RASSF1A methylation status and RASSF1A protein expression. We also examined for the first time NORE1A promoter region methylation in thyroid cell lines and primary tumors and showed that two of three thyroid cell lines were methylated in the NORE1A promoter region, while all primary thyroid tumors analyzed (n=51) were unmethylated. BRAF mutation was present in 38% of papillary thyroid carcinomas (PTC), including 20% of PTC with a follicular variant pattern and 67% of the tall cell variant of PTC. Hyalinizing trabecular tumors (n=23), which had nuclear features similar to PTC, did not have BRAF mutations, indicating that the presence of BRAF mutations can help to separate these two tumor types. Phospho-MEK expression was increased in the NPA cell line, which had a BRAF mutation, supporting the importance of the BRAF pathway alterations in PTC pathogenesis. These results indicate that RASSF1A epigenetic changes are an early event in thyroid tumor pathogenesis and progression and that NORE1A methylation is uncommon in primary thyroid tumors. BRAF mutation occurs later in thyroid tumor progression and is restricted mainly to PTC and anaplastic thyroid carcinoma.
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Affiliation(s)
- Nobuki Nakamura
- Department of Laboratory Medicine and Pathology, Mayo Clinic Medical College, Rochester, MN 55905, USA
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21
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Lee JW, Soung YH, Kim SY, Park WS, Nam SW, Min WS, Kim SH, Lee JY, Yoo NJ, Lee SH. Mutational analysis of the ARAF gene in human cancers. APMIS 2005; 113:54-7. [PMID: 15676015 DOI: 10.1111/j.1600-0463.2005.apm1130108.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Deregulation of RAS signal transduction has been implicated in the malignant growth of human cancer cells. The BRAF gene, encoding a RAF family member in the downstream pathway of RAS, is somatically mutated in a number of human cancers, raising the possibility that other RAF family members might be mutated in human cancers. In this study we analyzed the genomic DNAs for the detection of somatic mutations of the ARAF gene in 60 human cancer cell lines and 323 primary human cancer tissues, including colorectal carcinomas, gastric carcinomas, ovarian tumors and acute leukemias. The MOLT-4 leukemia cell line was found to harbor an ARAF gene mutation resulting in an amino acid substitution (A451T) at the activation segment in the kinase domain of ARAF. In the cancer tissues we could not detect any ARAF gene mutation. Our data indicate that, in contrast to the BRAF gene, the ARAF gene is rarely mutated in human cancers, and suggest that alterations of the RAS pathway by ARAF gene mutation may not play an important role in the pathogenesis of human cancers.
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Affiliation(s)
- Jong Woo Lee
- Department of Pathology, College of Medicine, The Catholic University of Korea, Seoul, Korea
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22
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Mahon ES, Hawrysh AD, Chagpar RB, Johnson LM, Anderson DH. A-Raf associates with and regulates platelet-derived growth factor receptor signalling. Cell Signal 2004; 17:857-68. [PMID: 15763428 DOI: 10.1016/j.cellsig.2004.11.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2004] [Revised: 11/03/2004] [Accepted: 11/03/2004] [Indexed: 11/25/2022]
Abstract
Raf kinases are important intermediates in epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) mediated activation of the mitogen-activated protein kinase (MAPK) pathway. In this report, we show that the A-Raf kinase is associated with activated EGF receptor complexes and with PDGF receptor (PDGFR) complexes independent of prior PDGF treatment. The ability of A-Raf to associate with receptor tyrosine kinases could provide a Ras-GTP-independent mechanism for the membrane localization of A-Raf. Expression of a partially activated A-Raf mutant resulted in decreased tyrosine phosphorylation of the PDGFR, specifically on Y857 (autophosphorylation site) and Y1021 (phospholipase Cgamma1 (PLCgamma1) binding site), but not the binding sites for other signalling proteins (Nck, phosphatidylinositol 3'-kinase (PI3K), RasGAP, Grb2, SHP). Activated A-Raf expression also altered the activation of PLCgamma1, and p85-associated PI3K. Thus, A-Raf can regulate PLCgamma1 signalling via a PDGFR-dependent mechanism and may also regulate PI3K signalling via a PDGFR-independent mechanism.
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Affiliation(s)
- Elizabeth S Mahon
- Department of Biochemistry, University of Saskatchewan, 107 Wiggins Ave., Saskatoon, Saskatchewan, Canada S7N 5E5
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23
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Hekman M, Wiese S, Metz R, Albert S, Troppmair J, Nickel J, Sendtner M, Rapp UR. Dynamic changes in C-Raf phosphorylation and 14-3-3 protein binding in response to growth factor stimulation: differential roles of 14-3-3 protein binding sites. J Biol Chem 2003; 279:14074-86. [PMID: 14688280 DOI: 10.1074/jbc.m309620200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Phosphorylation events play a crucial role in Raf activation. Phosphorylation of serines 259 and 621 in C-Raf and serines 364 and 728 in B-Raf has been suggested to be critical for association with 14-3-3 proteins. To study the functional consequences of Raf phosphorylations at these positions, we developed and characterized phosphospecific antibodies directed against 14-3-3 binding epitopes: a monoclonal phosphospecific antibody (6B4) directed against pS621 and a polyclonal antibody specific for B-Raf-pS364 epitope. Although 6B4 detected both C- and B-Raf in Western blots, it specifically recognizes the native form of C-Raf but not B-Raf. Contrary to B-Raf, a kinase-dead mutant of C-Raf was found to be only poorly phosphorylated in the Ser-621 position. Moreover, serine 259 to alanine mutation prevented the Ser-621 phosphorylation suggesting an interdependence between these two 14-3-3 binding domains. Direct C-Raf.14-3-3 binding studies with purified proteins combined with competition assays revealed that the 14-3-3 binding domain surrounding pS621 represents the high affinity binding site, whereas the pS259 epitope mediates lower affinity binding. Raf isozymes differ in their 14-3-3 association rates. The time course of endogenous C-Raf activation in mammalian cells by nerve growth factor (NGF) has been examined using both phosphospecific antibodies directed against 14-3-3 binding sites (6B4 and anti-pS259) as well as phosphospecific antibodies directed against the activation domain (anti-pS338 and anti-pY340/pY341). Time course of Ser-621 phosphorylation, in contrast to Ser-259 phosphorylation, exhibited unexpected pattern reaching maximal phosphorylation within 30 s of NGF stimulation. Phosphorylation of tyrosine 340/341 reached maximal levels subsequent to Ser-621 phosphorylation and was coincident with emergence of kinase activity. Taken together, we found substantial differences between C-Raf.14-3-3 binding epitopes pS259 and pS621 and visualized for the first time the sequence of the essential C-Raf phosphorylation events in mammalian cells in response to growth factor stimulation.
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Affiliation(s)
- Mirko Hekman
- Institute for Medical Radiation and Cell Research, University of Wuerzburg, 97078 Wuerzburg
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24
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Chen DB, Davis JS. Epidermal growth factor induces c-fos and c-jun mRNA via Raf-1/MEK1/ERK-dependent and -independent pathways in bovine luteal cells. Mol Cell Endocrinol 2003; 200:141-54. [PMID: 12644307 DOI: 10.1016/s0303-7207(02)00379-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Epidermal growth factor (EGF) modulates the actions of gonadotropins in the corpus luteum. The membrane-associated EGF receptors undergo rapid tyrosine phosphorylation and internalization upon ligand binding in ovarian cells, including luteal cells. However, little is known about the post-receptor signaling events induced by EGF that lead to the transcriptional regulation of EGF-responsive genes in the ovary. The present study was designed to examine in bovine luteal cells (1) activation of the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) signaling cascade (Raf/MEK/ERK) by EGF; (2) mRNA expression of AP-1 transcription factors, i.e. c-fos and c-jun, in response to EGF; and (3) the role of ERK in EGF-induced expression of c-fos and c-jun mRNA. Raf-1 and B-Raf, but not A-Raf, were activated by EGF (10 ng/ml) and the pharmacological protein kinase C (PKC) activator phorbol myristate acetate (PMA, 20 nM). Activation of Raf resulted in the phosphorylation and activation of MAPK kinase (MEK1) which subsequently activated ERKs. Treatment with EGF-induced the phosphorylation of both ERK2 and ERK1 in a time and concentration dependent manner. Additionally, activated ERK was found in the nucleus of the cells following treatment with EGF (10 ng/ml) and PMA (PMA, 20 nM) for 5 min. Depletion of PKC by chronic PMA treatment (2.5 microM, 24 h) only partially inhibited the stimulatory effects of EGF on Raf-1, ERK2 and ERK1. These data demonstrate that PKC-dependent and independent-mechanisms are involved in EGF activation of the Raf/MEK/ERK signaling cascade in bovine luteal cells. EGF rapidly and transiently stimulated the expression of c-fos and c-jun mRNA in bovine luteal cells. Maximal induction of c-fos and c-jun mRNA by EGF occurred within 30 min of treatment with 10 ng/ml EGF. Treatment with the MEK1 inhibitor PD098059 (50 microM) abolished EGF-induced ERK activation. However, blocking EGF-induced ERK activation by pretreatment with PD098059 only partially attenuated EGF-induced c-fos and c-jun mRNA expression. Thus, additional pathways are implicated in the regulation of c-fos and c-jun mRNA expression by EGF in bovine luteal cells.
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Affiliation(s)
- Dong-bao Chen
- The Women's Research Institute, Department of Obstetrics and Gynecology, University of Kansas School of Medicine-Wichita, 1010 North Kansas, Wichita 67214, USA.
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25
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Le Mellay V, Houben R, Troppmair J, Hagemann C, Mazurek S, Frey U, Beigel J, Weber C, Benz R, Eigenbrodt E, Rapp UR. Regulation of glycolysis by Raf protein serine/threonine kinases. ADVANCES IN ENZYME REGULATION 2002; 42:317-32. [PMID: 12123723 DOI: 10.1016/s0065-2571(01)00036-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Véronique Le Mellay
- Institut für Medizinische, Strahlenkunde und Zellforschung (MSZ), Universität Würzburg, Versbacher Str. 5, Germany
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26
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Mercer K, Chiloeches A, Hüser M, Kiernan M, Marais R, Pritchard C. ERK signalling and oncogene transformation are not impaired in cells lacking A-Raf. Oncogene 2002; 21:347-55. [PMID: 11821947 DOI: 10.1038/sj.onc.1205101] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2001] [Revised: 10/19/2001] [Accepted: 10/27/2001] [Indexed: 11/09/2022]
Abstract
Previous studies have indicated an important role for the Raf family of protein kinases in controlling cellular responses to extracellular stimuli and activated oncogenes, through their ability to activate the MEK/ERKs. To investigate the specific role of A-Raf in this process we generated A-Raf deficient mouse embryonic fibroblasts (MEFs) and embryonic stem (ES) cells by gene targeting and characterized their ability to undergo proliferation, differentiation, apoptosis, ERK activation, and transformation by oncogenic Ras and Src. The A-Raf deficient cells are not disrupted for any of these processes, despite the fact that this protein is normally expressed at high levels in both cell types. This implies either that A-Raf plays no role in MEK/ERK activation, that its function is fully compensated by other Raf proteins or MEK kinases or that its role in MEK/ERK activation is highly tissue-specific. Interestingly, B-Raf and Raf-1 activity towards MEK as measured by the immunoprecipitation kinase cascade assay are both significantly increased in the A-Raf deficient MEFs.
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Affiliation(s)
- Kathryn Mercer
- Department of Biochemistry, University of Leicester, University Road, Leicester LE1 7RH, UK
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27
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Wiese S, Pei G, Karch C, Troppmair J, Holtmann B, Rapp UR, Sendtner M. Specific function of B-Raf in mediating survival of embryonic motoneurons and sensory neurons. Nat Neurosci 2001; 4:137-42. [PMID: 11175873 DOI: 10.1038/83960] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Embryonic sensory and motoneurons depend on neurotrophic factors for survival. Here we show that their survival requires B-Raf, which, in this function, cannot be substituted by C-Raf. Sensory and motoneurons from b-raf-deficient mice do not respond to neurotrophic factors for their survival. However, these primary neurons can be rescued by transfection of a b-raf expression plasmid. In contrast, c-raf-deficient neurons survive in response to neurotrophic factors, similarly to neurons from wild-type mice. This points to an essential and specific function of B-Raf in mediating survival of sensory and motoneurons during development.
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Affiliation(s)
- S Wiese
- Klinische Forschergruppe Neuroregeneration, Department of Neurology, University of Wuerzburg, Josef-Schneider-Str.11, 97080 Wuerzburg, Germany
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28
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Liu D, Yang X, Yang D, Songyang Z. Genetic screens in mammalian cells by enhanced retroviral mutagens. Oncogene 2000; 19:5964-72. [PMID: 11146547 DOI: 10.1038/sj.onc.1203992] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Genetic approaches such as retrovirus-mediated mutagenesis and cDNA expression libraries have contributed greatly to our understanding of signal transduction in mammalian cells. However, previously described methods for retroviral insertional mutagenesis are hindered by low mutagenesis rates and difficulties in cloning mutated genes. cDNA expression library methods are usually cell-type dependent and bias towards abundant and short messages. With the near completion of the genome projects, alternative genetic methods are needed where large numbers of genes can be more easily isolated and biochemically studied. We have developed a novel retrovirus-mediated genetic screening method in cultured cells. To achieve efficient and regulated mutagenesis, we constructed Enhanced Retroviral Mutagen (ERM) vectors that contained several engineered sequences (e.g., an ERM Tag and a splice donor) controlled by a tetracycline-responsive promoter. Endogenous genes can thus be randomly activated and tagged in a conditional system. NIH3T3 cells were used to screen for focus-forming genes using the ERM strategy. We showed that these added sequences increased the screening efficiency by >10-fold, and allowed more direct identification of the genes targeted. Sequence analysis of approximately 10% of the >600 focus clones recovered revealed both known oncogenes and novel factors such as protein kinases and GTP/GDP exchange proteins. The ERM strategy should help to facilitate large-scale gene identification in diverse pathways and integrate both genetic (with the completion of the genome projects) and functional information more readily.
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Affiliation(s)
- D Liu
- Verna and Marrs Mclean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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29
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MacNicol MC, Muslin AJ, MacNicol AM. Disruption of the 14-3-3 binding site within the B-Raf kinase domain uncouples catalytic activity from PC12 cell differentiation. J Biol Chem 2000; 275:3803-9. [PMID: 10660530 DOI: 10.1074/jbc.275.6.3803] [Citation(s) in RCA: 40] [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
A number of Raf-associated proteins have recently been identified, including members of the 14-3-3 family of phosphoserine-binding proteins. Although both positive and negative regulatory functions have been ascribed for 14-3-3 interactions with Raf-1, the mechanisms by which 14-3-3 binding modulates Raf activity have not been fully established. We report that mutational disruption of 14-3-3 binding to the B-Raf catalytic domain inhibits B-Raf biological activity. Expression of the isolated B-Raf catalytic domain (B-Rafcat) induces PC12 cell differentiation in the absence of nerve growth factor. By contrast, the B-Rafcat 14-3-3 binding mutant, B-Rafcat S728A, was severely compromised for the induction of PC12 cell differentiation. Interestingly, the B-Rafcat 14-3-3 binding mutant retained significant in vitro catalytic activity. In Xenopus oocytes, the analogous full-length B-Raf 14-3-3 binding mutant blocked progesterone-stimulated maturation and the activation of endogenous mitogen-activated protein kinase kinase and mitogen-activated protein kinase. Similarly, the full-length B-Raf 14-3-3 binding mutant inhibited nerve growth factor-stimulated PC12 cell differentiation. We conclude that 14-3-3 interaction with the catalytic domain is not required for kinase activity per se but is essential to couple B-Raf catalytic activity to downstream effector activation.
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Affiliation(s)
- M C MacNicol
- Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA
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30
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Silvy M, Martin PM, Chajry N, Berthois Y. Differential dose-dependent effects of epidermal growth factor on gene expression in A431 cells: evidence for a signal transduction pathway that can bypass Raf-1 activation. Endocrinology 1998; 139:2382-91. [PMID: 9564849 DOI: 10.1210/endo.139.5.5981] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Epidermal growth factor (EGF), which plays an important role in normal and tumoral cell growth regulation, displays an ambivalent dose-dependent effect on the proliferation of epithelial cells overexpressing EGF receptor. However, the underlying molecular mechanisms remain obscure. In this study we have examined the regulation of amphiregulin (AR) gene expression by growth inhibitory (10(-9) M) and stimulatory (10(-12) M) EGF concentrations in A431 cells. The time course of AR messenger RNA (mRNA) accumulation was different with 10(-12) and 10(-9) M EGF; AR induction by 10(-9) M EGF peaked between 1 and 1.5 h, then decreased to the basal level within 2 h. Conversely, the induction by 10(-12) M EGF was slightly delayed, but persisted for 4 h. The involvement of tyrosine phosphorylation in AR induction by EGF was suggested by the ability of the tyrosine phosphatase inhibitor sodium orthovanadate to prolong AR expression induced by 10(-12) or 10(-9) M EGF. In the presence of the protein phosphatase 2A inhibitor, okadaic acid, 10(-9) M EGF induced a persistent accumulation of AR mRNA. On the contrary, okadaic acid abrogated the stimulation of AR mRNA level induced by a low EGF concentration, suggesting that both EGF concentrations activated distinct regulatory mechanisms. The signaling components involved in the differential activities of EGF in A431 cells were then examined. We previously reported a relationship between the ambivalent activity of EGF and the p42-mitogen-activated protein (MAP) kinase activity. Thus, 10(-12) M EGF induced a sustained MAP kinase activation, whereas 10(-9) M EGF led to a sharp, but transitory, activation. The MAP kinases are activated by MAP kinase kinases (MEK1 and MEK2). Whereas no significant effect of 10(-12) M EGF could be detected, 10(-9) M EGF was shown to activate MEK1 and, to a lesser extent, MEK2. Also, both MAP kinase activation and AR induction by 10(-9) M, but not by 10(-12) M, EGF were inhibited by the MEK1 inhibitor PD98059. Moreover, the involvement of c-Raf-1 in the signaling pathway induced by EGF was verified. A concentration of 10(-9) M EGF induced stimulation of c-Raf-1 kinase activity, whereas 10(-12) M EGF not only failed to activate c-Raf-1, but led to a moderate decrease in its kinase activity. These results demonstrate that in EGF receptor-overexpressing cells, EGF may differently affect gene expression and cell proliferation through distinct mechanisms of regulation.
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Affiliation(s)
- M Silvy
- Laboratoire Interactions Cellulaires Intratumorales, CJF INSERM 9311, IFR Jean Roche, Faculté de Médecine Secteur Nord, Marseille, France
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31
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DeAizpurua HJ, Cram DS, Naselli G, Devereux L, Dorow DS. Expression of mixed lineage kinase-1 in pancreatic beta-cell lines at different stages of maturation and during embryonic pancreas development. J Biol Chem 1997; 272:16364-73. [PMID: 9195943 DOI: 10.1074/jbc.272.26.16364] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Events controlling differentiation to insulin-secreting beta-cells in the pancreas are not well understood, although beta-cells are thought to arise from pluripotent ductal precursor cells. To search for signaling proteins that might be involved in beta-cell maturation, we analyzed protein kinase expression in two developmentally and functionally distinct pancreatic beta-cell lines, RIN-5AH and RIN-A12, by reverse transcriptase polymerase chain reaction. A number of tyrosine and serine/threonine kinases were identified in both lines. One protein kinase, mixed lineage kinase-1 (MLK-1), was expressed at both the RNA and protein levels in RIN-5AH cells, which display an immature beta-cell phenotype, but was not detected in the more mature RIN-A12 cells. Furthermore, levels of MLK-1 mRNA and protein were increased after brief stimulation of RIN-5AH cells with either the differentiation inducer, sodium butyrate, or with serum after serum starvation. These increases in expression were independent of phenotypic markers such as insulin secretion or surface expression of major histocompatibility class I- and A2B5-reactive ganglioside. In addition, increases in MLK-1 expression in the stimulated RIN-5AH cells were accompanied by phosphorylation of MLK-1 on serine but not tyrosine. Antisense oligonucleotides to two distinct regions of MLK-1 caused RIN-5AH cells, but not RIN-A12 cells, to adopt a highly undifferentiated morphology, with a reduction in DNA synthesis and MLK-1 protein levels and elevated glucagon mRNA levels, but with no effect on insulin mRNA. In an immunohistochemical survey of embryonic mouse tissues, we found that temporal expression of MLK-1 was regulated in a tissue-specific manner. In the embryonic pancreas, MLK-1 expression was evident in ductal cells from day 13 to 16 but was not detected in late stage gestation or neonatal pancreas. These data suggest that MLK-1 is regulated in immature pancreatic beta-cells and their ductal precursors at the level of functional maturity and may therefore play a role in beta-cell development.
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Affiliation(s)
- H J DeAizpurua
- Burnet Clinical Research Unit, Walter and Eliza Hall Institute of Medical Research, Post Office, Royal Melbourne Hospital, Parkville 3050, Australia.
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32
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Abstract
Karyophilic and acidic clusters were found in most nonmembrane serine/threonine protein kinases whose primary structure was examined. These karyophilic clusters might mediate the anchoring of the kinase molecules to transporter proteins for their regulated nuclear import and might constitute the nuclear localization signals (NLS) of the kinase molecules. In contrast to protein transcription factors that are exclusively nuclear possessing strong karyophilic peptides composed of at least four arginines (R) and lysines (K) within an hexapeptide flanked by proline and glycine helix-breakers, protein kinases often contain one histidine and three K+R residues; this is proposed to specify a weak NLS structure resulting in the nuclear import of a fraction of the total cytoplasmic kinase molecules as well as in their weak retention in the different ionic strength nuclear environment. Putative NLS peptides in protein kinases may also contain hydrophobic or bulky aromatic amino acids proposed to further diminish their capacity to act as strong NLS. Most kinases lacking karyophilic clusters (c-Mos, v-Mos, sea star MAP, and yeast KIN28, SRA1, SRA3, TPK1, TPK2) also lack acidic clusters, which is in contrast to most kinases containing both acidic and karyophilic peptides; this and the presence of R/K clusters in the transporter proteins supports a role of acidic clusters on kinases in nuclear import. Cyclins B lack karyophilic signals and are proposed to be imported into nuclei via their association with Cdc2.
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Affiliation(s)
- T Boulikas
- Institute of Molecular Medical Sciences, Palo Alto, California 94306, USA
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33
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Bogoyevitch MA, Marshall CJ, Sugden PH. Hypertrophic agonists stimulate the activities of the protein kinases c-Raf and A-Raf in cultured ventricular myocytes. J Biol Chem 1995; 270:26303-10. [PMID: 7592840 DOI: 10.1074/jbc.270.44.26303] [Citation(s) in RCA: 131] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We detected expression of two Raf isoforms, c-Raf and A-Raf, in neonatal rat heart. Both isoforms phosphorylated, activated, and formed complexes with mitogen-activated protein kinase kinase 1 in vitro. However, these isoforms were differentially activated by hypertrophic stimuli such as peptide growth factors, endothelin-1 (ET1), or 12-O-tetradecanoylphorbol-13-acetate (TPA) that activate the mitogen-activated protein kinase cascade. Exposure of cultured ventricular myocytes to acidic fibroblast growth factor activated c-Raf but not A-Raf. In contrast, TPA produced a sustained activation of A-Raf and only transiently activated c-Raf. ET1 transiently activated both isoforms. TPA and ET1 were the most potent activators of c-Raf and A-Raf. Both utilized protein kinase C-dependent pathways, but stimulation by ET1 was also partially sensitive to pertussis toxin pretreatment. cRaf was inhibited by activation of cAMP-dependent protein kinase although A-Raf was less affected. Fetal calf serum, phenylephrine, and carbachol were less potent activators of c-Raf and A-Raf. These results demonstrate that A-Raf and c-Raf are differentially regulated and that A-Raf may be an important mediator of mitogen-activated protein kinase cascade activation when cAMP is elevated.
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Affiliation(s)
- M A Bogoyevitch
- National Heart and Lung Institute, Imperial College of Science, Technology and Medicine, London, United Kingdom
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34
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Reuter CW, Catling AD, Jelinek T, Weber MJ. Biochemical analysis of MEK activation in NIH3T3 fibroblasts. Identification of B-Raf and other activators. J Biol Chem 1995; 270:7644-55. [PMID: 7706312 DOI: 10.1074/jbc.270.13.7644] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Numerous potential activators of MEK have been identified, including c-Raf-1, B-Raf, c-Mos, and a family of MEK kinases. However, little information gives insight into the activators actually utilized in vivo. To address this, we have used column chromatography and a coupled MEK activation assay to identify in NIH3T3 cells, two major MEK activators, and a third insulin-specific activator. The first MEK activator has an apparent M(r) of 40,000-50,000, was immunologically distinct from A-Raf, B-Raf, c-Raf-1, c-MEKK, c-Mos, MEK1, and MEK2, and was rapidly activated by serum, platelet-derived growth factor (PDGF), insulin, thrombin, and phorbol ester. The second MEK activator was identified as B-Raf. Activation of 93-95 kDa B-Raf was observed in column fractions and B-Raf immunoprecipitates from cytosolic and particulate fractions after stimulation with serum or PDGF, but not insulin. c-Raf-1 from cytosol did not exhibit MEK activator activity; however, c-Raf-1 immunoprecipitates from the particulate fraction revealed MEK activator activity that was enhanced after stimulation with PDGF or phorbol ester, but not serum or insulin. Both c-Mos and c-MEKK were present in NIH3T3 fibroblasts but did not show MEK activator activity. These data provide direct evidence that 93-95-kDa B-Raf isozymes and an unidentified 40-50-kDa MEK activator are major agonist-specific MEK activators in NIH3T3 fibroblasts.
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Affiliation(s)
- C W Reuter
- Department of Microbiology, University of Virginia Health Sciences Center, School of Medicine, Charlottesville 22908, USA
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35
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Affiliation(s)
- L Wiesmüller
- Heinrich-Pette-Institut für exp. Virologie und Immunologie, Universität Hamburg, F.R.G
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36
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Mitogen-activated protein kinase/extracellular signal-regulated protein kinase activation by oncogenes, serum, and 12-O-tetradecanoylphorbol-13-acetate requires Raf and is necessary for transformation. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)37478-1] [Citation(s) in RCA: 173] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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37
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Wood KW, Roberts TM. Oncogenes and protein kinases in neuronal growth-factor action. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1155:133-50. [PMID: 8357824 DOI: 10.1016/0304-419x(93)90002-t] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- K W Wood
- Division of Cellular and Molecular Biology, Dana-Farber Cancer Institute, Boston, MA 02115
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38
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Zhang XF, Settleman J, Kyriakis JM, Takeuchi-Suzuki E, Elledge SJ, Marshall MS, Bruder JT, Rapp UR, Avruch J. Normal and oncogenic p21ras proteins bind to the amino-terminal regulatory domain of c-Raf-1. Nature 1993; 364:308-13. [PMID: 8332187 DOI: 10.1038/364308a0] [Citation(s) in RCA: 682] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In higher eukaryotes, the Ras and Raf-1 proto-oncoproteins transduce growth and differentiation signals initiated by tyrosine kinases. The Ras polypeptide and the amino-terminal regulatory domain of Raf-1 (residues 1-257) are shown to interact, directly in vitro and in a yeast expression system. Raf-1 (1-257) binds GTP-Ras in preference to GDP-Ras, and inhibits Ras-GAP activity. Mutations in and around the Ras effector domain impair Ras binding to Raf-1 (1-257) and Ras transforming activity in parallel.
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Affiliation(s)
- X F Zhang
- Diabetes Unit, Harvard Medical School, Charlestown, Massachusetts
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39
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Abstract
We have identified proteins that interact with H-Ras using a two hybrid system screen of a mouse cDNA library. Approximately 50% of the clones identified encoded portions of the c-Raf and A-Raf serine/threonine kinases. Overlaps among these clones define a conserved 81 residue region of the N-terminus of Raf as the Ras interaction region. We show that Raf interacts with wild-type and activated Ras, but not with an effector domain mutant of Ras or with a dominant-interfering Ras mutant. Using purified bacterially expressed fusion proteins, we show, furthermore, that Ras and the N-terminal region of Raf associate directly in vitro and that this interaction is dependent on GTP bound to Ras.
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Affiliation(s)
- A B Vojtek
- Fred Hutchinson Cancer Research Center, Seattle, Washington 98104
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40
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Winer MA, Wadewitz AG, Wolgemuth DJ. Members of the raf gene family exhibit segment-specific patterns of expression in mouse epididymis. Mol Reprod Dev 1993; 35:16-23. [PMID: 8507475 DOI: 10.1002/mrd.1080350104] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The proto-oncogene c-raf-1 and the related genes A-raf and B-raf encode serine/threonine protein kinases thought to be involved in regulating gene expression by acting as part of second-messenger signaling pathways within the cell. Among the tissues in which A-raf and c-raf-1 have been shown to be expressed was mouse epididymis. The present studies were undertaken to determine if the raf family genes exhibited specificity in their pattern of expression that might be indicative of specific function in the epididymis. Northern and in situ hybridization analyses demonstrated that c-raf-1 mRNA was expressed as a 3.1 kb transcript at uniform levels throughout the length of the epididymis in all types of epididymal epithelial cells. Neither the germ cell-specific testicular transcripts nor the somatic transcripts of B-raf were detected by either Northern or in situ hybridization analysis in any region of the epididymis. A-raf, expressed as two transcripts of 2.6 and 4.3 kb, was the only gene examined which exhibited a segment-specific pattern of expression, being highest in the principal epithelial cells of the proximal caput epididymis and decreasing progressively in more distal regions of the tubule. These studies indicate that each raf gene exhibits a characteristic pattern of expression in the epididymis; A-raf in particular may play a unique regulatory role in the regionalized functions of the epididymis.
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Affiliation(s)
- M A Winer
- Center for Reproductive Sciences, Columbia University College of Physicians and Surgeons, New York, New York 10032
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41
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Abstract
cDNA clones presumably containing a transforming gene were isolated from transformed NIH3T3 cells, which were obtained by the transfection of DNA from peripheral blood lymphocytes of a familial adenomatous polyposis patient. Sequence analysis of the cDNA clones showed that the gene contained an activated B-raf, the 5' half of which was replaced by the human small nuclear ribonucleoprotein E protein gene and an unknown gene. A partial genomic physical map of the transforming gene was made on the basis of the physical map of the cDNA clones, indicating that rearrangements had occurred during the transfection. The human B-raf gene was shown to be located on chromosome 7 by Southern blotting analysis of rodent-human somatic cell hybrid DNA using the B-raf cDNA as a probe.
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Affiliation(s)
- T Kamiyama
- Department of Hygiene and Oncology, Tokyo Medical and Dental University School of Medicine
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42
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Qureshi S, Alexandropoulos K, Rim M, Joseph C, Bruder J, Rapp U, Foster D. Evidence that Ha-Ras mediates two distinguishable intracellular signals activated by v-Src. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)37090-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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43
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Nerve growth factor stimulates the activities of the raf-1 and the mitogen-activated protein kinases via the trk protooncogene. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42084-4] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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44
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Martin W, Lenz E, Grohé B, Willecke K. Suppression of transformed phenotype in hybrids of v-fgr and v-raf transformed rat-1 cells with rat embryonic fibroblasts is due to transcriptional inactivation of viral oncogenes. Exp Cell Res 1992; 200:41-7. [PMID: 1563491 DOI: 10.1016/s0014-4827(05)80069-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Rat-1 cells that had been transformed to tumorigenicity by transfection with the retroviral oncogenes v-raf from 3611-murine sarcoma virus, or v-fgr from Gardner-Rasheed feline sarcoma virus were fused with rat embryonic fibroblasts at an early passage. In both fusion experiments hybrid cells were isolated that exhibited normal morphology, anchorage requirement for proliferation, and either no tumorigenicity (v-fgr) or extended latency periods for tumor growth (v-raf) in nude mice. Transcription of viral oncogenes is drastically reduced in hybrid cells (at least 30-fold compared to their transformed parental cells), while the half-life of the corresponding transcripts is not effected. In the chromatin of hybrid cells the integrated retroviral oncogenes are as sensitive to degradation with pancreatic DNase I as the endogenous actin gene. Thus the observed down regulation of proviral transcript levels does not correlate with changes in chromatin structure. We conclude that in hybrids of (v-fgr)- and (v-raf)-transformed Rat-1 cells with embryonic fibroblasts, transcription of the retroviral oncogenes appears to be repressed by trans-acting factors of the normal parental cell.
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Affiliation(s)
- W Martin
- Institut für Genetik (Abt. Molekulargenetik), Universität Bonn, Federal Republic of Germany
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45
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Derry JM, Barnard PJ. Physical linkage of the A-raf-1, properdin, synapsin I, and TIMP genes on the human and mouse X chromosomes. Genomics 1992; 12:632-8. [PMID: 1572636 DOI: 10.1016/0888-7543(92)90286-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Genes encoding the neuron-specific phosphoprotein synapsin I (SYN1), the glycoprotein tissue inhibitor of metalloproteinases (TIMP), the proto-oncogene A-raf-1 (ARAF1), and properdin (PFC), a positive regulator of the alternative pathway of human complement, lie within a conserved synteny encompassing the proximal short arm of the human X chromosome (Xp21.1-p11) and the centromeric end of the mouse X chromosome (A1-A5). We have used a mouse interspecific cross to demonstrate genetic linkage of Syn-1, Timp, and Araf and also show physical linkage, with Timp lying only 10 kb from Araf, within an intron of the Syn-1 gene. Detailed restriction mapping shows that Timp is transcribed in the same direction as Araf but in the opposite direction to the Syn-1 gene. Analysis of the corresponding region of the human X chromosome indicates a similar arrangement and in addition shows that the properdin gene lies within 5 kb of the 5' end of the synapsin I gene.
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Affiliation(s)
- J M Derry
- MRC Molecular Neurobiology Unit, MRC Centre, Cambridge, United Kingdom
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46
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Whorf RC, Tobet SA. Expression of the Raf-1 protein in rat brain during development and its hormonal regulation in hypothalamus. JOURNAL OF NEUROBIOLOGY 1992; 23:103-19. [PMID: 1527522 DOI: 10.1002/neu.480230202] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
To study mechanisms involved in the sexual differentiation of the rat brain, the expression of the protein product of the proto-oncogene c-raf-1 (Raf-1) was examined. Biochemical and immunocytochemical analyses localized Raf-1 in embryonic rat brain regions and demonstrated hormonally induced changes in Raf-1 expression. For this study an affinity-purified anti-peptide antiserum specific for Raf-1 (NH-44) was used. Western blots revealed an approximately 77 kD polypeptide isolated in the cytosol of developing rat brains. Raf-1 levels were highest in the embryonic (E) day 22 female hypothalamus (HYP), and approximately twofold higher than levels detected in male HYP at E22 as determined by quantitative protein dot blot and semiquantitative Western blot analyses. Raf-1 levels in HYP were greater than those in either brain stem (BS) or cortex. Immunocytochemical analysis revealed high levels of Raf-1 in selective brain regions (e.g., the ventromedial nucleus in the HYP, the mitral cell layers in the main and accessory olfactory bulbs (OB), and the locus coeruleus) at E22 and postnatal (P) day 1. Lower levels of immunoreactivity were observed in many areas of the perinatal neuraxis. To test hormonal regulation of Raf-1, testosterone propionate (TP) was administered to pregnant rats on E17; male and female fetuses were examined on E22. This treatment significantly decreased Raf-1 levels in female HYP, but not in male HYP, as determined by Western blot analysis. No significant sex difference or response to prenatal hormone treatments were observed in either brain stem or cortex. No significant sex difference was noted postnatally, and administration of TP 3 h after birth did not change Raf-1 levels examined 24 h later. In summary, Raf-1 was localized within selective regions of the rat brain, and its expression was altered by exogenous prenatal hormonal stimulation. One role for Raf-1 in signal transduction may be to delimit hormonal critical periods in sexual differentiation of the brain.
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Affiliation(s)
- R C Whorf
- Department of Biochemistry and Molecular Biology, E. K. Shriver Center, Waltham, Massachusetts 02254
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47
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Heidecker G, Kölch W, Morrison DK, Rapp UR. The role of Raf-1 phosphorylation in signal transduction. Adv Cancer Res 1992; 58:53-73. [PMID: 1312290 DOI: 10.1016/s0065-230x(08)60290-0] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- G Heidecker
- Viral Pathology Section, NCI-Frederick Cancer Research and Development Center Frederick, Maryland 21702
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48
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Colotta F, Polentarutti N, Mantovani A. Differential expression of Raf-1 protooncogene in resting and activated human leukocyte populations. Exp Cell Res 1991; 194:284-8. [PMID: 2026180 DOI: 10.1016/0014-4827(91)90366-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In this study we examined by Northern blot analysis the expression of Raf-1 protooncogene in normal human peripheral blood leukocytes. Unlike thymocytes, circulating lymphocytes did not express appreciable levels of Raf-1 mRNA. In contrast, polymorphonuclear cells (PMN) had high levels of Raf-1 transcripts. Also density gradient separated monocytes showed Raf-1 mRNA but at lower levels compared to PMN. Expression of Raf-1 was constitutive inasmuch as it was not induced by the purification procedure. The half-life of Raf-1 mRNA in PMN was greater than 4 h. Functional activation of PMN and monocytes with various stimuli (phorbol esters, tumor necrosis factor, colony stimulating factors, LPS) did not affect Raf-1 expression. By contrast, density gradient purified monocytes allowed to adhere to plastic for 1 h expressed augmented levels of Raf-1. Monocytes cultivated in suspension or allowed to adhere to plastic showed an half-life of Raf-1 transcripts of, respectively, more than 4 h and less than 30 min. Circulating lymphocytes stimulated with mitogens (PHA, conA, anti-CD3 antibodies, and Staphylococcus aureus) also expressed high levels of transcripts of this protooncogene. PHA-induced transcripts in lymphocytes had an half-life greater than 4 h. The pattern of expression of Raf-1 in resting and activated leukocytes suggests that this protooncogene may play a role in expression of differentiated functions and activation of these cells.
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Affiliation(s)
- F Colotta
- Centro Catullo e Daniela Borgomainerio, Istituto di Ricerche Farmacologiche Mario Negri, Milano, Italy
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49
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Oláh Z, Komoly S, Nagashima N, Joó F, Rapp UR, Anderson WB. Cerebral ischemia induces transient intracellular redistribution and intranuclear translocation of the raf proto-oncogene product in hippocampal pyramidal cells. Exp Brain Res 1991; 84:403-10. [PMID: 2065747 DOI: 10.1007/bf00231462] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In this report we describe changes in the intracellular redistribution of raf serine/threonine protein kinase (product of the raf proto-oncogene family) in hippocampal neurons following cerebral ischemia in Mongolian gerbils. For immunohistochemical localization studies polyclonal antisera specific for each of the A, B, and Raf-1 isotypes of raf, as well as a pan-raf antisera, were employed. Of these, only sera recognizing B-raf, as well as the general v-raf (raised against the conserved C-terminal region) were positive, indicating that B-raf is the major isotype in this neuronal region. Three different ischemic models were used (repeated 3 times for two min and single 5 or 15 min occlusions, of the common carotid arteries) to demonstrate that ischemic insult causes redistribution of raf protein kinase into the cell nucleus of hippocampal neurons. Increased amounts of raf protein in the nuclei of pyramidal cells following ischemia was confirmed by Western blot analysis of isolated nuclear fractionations. Moreover, an elevation in the level of nuclear raf protein also was detected in the contralateral (i.e. non-occluded hemisphere) neurons of CA1 and CA3 subfields 4 days after the ischemic insult indicating a possible transsynaptic increase in the amount of raf protein along with redistribution. The intranuclear translocation of the immunoreactive material started from the perinucleolar rim and with time extended throughout the nucleus. Enhanced levels and altered redistribution of the raf polypeptide in the nuclei of pyramidal cells of the CA3 subfield appears to be reversible and returns to the normal level 12 days following the ischemic insult.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- Z Oláh
- Laboratory of Cellular Oncology, National Cancer Institute, Bethesda, MD 20892
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50
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Kolch W, Heidecker G, Lloyd P, Rapp UR. Raf-1 protein kinase is required for growth of induced NIH/3T3 cells. Nature 1991; 349:426-8. [PMID: 1992343 DOI: 10.1038/349426a0] [Citation(s) in RCA: 391] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Many growth factors regulate the cytoplasmic Raf-1 protein kinase, consistent with its having a central role in transduction of growth signals. The kinase is ubiquitously expressed and can promote proliferation, presumably in a manner dependent on growth-factor receptors and membrane-associated oncogenes. We have now examined the dependence of serum- and TPA (12-O-tetradecanoylphorbol-13-acetate)-regulated NIH/3T3 cell growth on RAF-1 kinase to determine whether Raf-1 is essential for receptor signalling. We inhibited Raf-1 function by expressing c-raf-1 antisense RNA or kinase-defective c-raf-1 mutants. Antisense RNA for c-raf-1 interferes with proliferation of normal NIH/3T3 cells and reverts raf-transformed cells. In revertant cells, DNA replication induced by serum or TPA was eliminated or reduced proportionately to the reduction in Raf protein levels. Expression of a kinase-defective Raf-1 mutant (craf301) or a regulatory domain fragment (HCR) inhibited serum-induced NIH/3T3-cell proliferation and raf transformation even more efficiently. Inhibition by antisense RNA or craf301 blocked proliferation and transformation by Ki- and Ha-ras oncogenes. We conclude that raf functions as an essential signal transducer downstream of serum growth factor receptors, protein kinase C and ras.
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Affiliation(s)
- W Kolch
- Laboratory of Viral Carcinogenesis, NIH/NCI, Frederick Cancer Research and Development Center, Maryland 21702-1201
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