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Nakayama I, Hirota T, Shinozaki E. BRAF Mutation in Colorectal Cancers: From Prognostic Marker to Targetable Mutation. Cancers (Basel) 2020; 12:cancers12113236. [PMID: 33152998 PMCID: PMC7694028 DOI: 10.3390/cancers12113236] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Revised: 10/28/2020] [Accepted: 10/29/2020] [Indexed: 12/14/2022] Open
Abstract
Simple Summary Colorectal cancer with a mutation in an oncogene BRAF has paid much attention, as it comprises a population with dismal prognosis since two decades ago. A series of research since then has successfully changed this malignancy to be treatable with specific treatment. Here we thoroughly overviewed the basic, translational and clinical studies on colorectal cancer with BRAF mutation from a physician’s viewpoint. Accumulating lines of evidence suggest that intervention of the trunk cellular growth signal transduction pathway, namely EGFR-RAS-RAF-MEK-ERK pathway, is a clue to controlling this disease. However, it is not so straightforward. Recent studies unveil the diverse and plastic nature of this signal transduction pathway. We will introduce our endeavor to conquer this condition, based on newly arriving datasets, and discuss how we could open the door to future development of CRC treatment. Abstract The Raf murine sarcoma viral oncogene homolog B (BRAF) mutation is detected in 8–12% of metastatic colorectal cancers (mCRCs) and is strongly correlated with poor prognosis. The recent success of the BEACON CRC study and the development of targeted therapy have led to the determination of BRAF-mutated mCRCs as an independent category. For nearly two decades, a growing body of evidence has established the significance of the BRAF mutation in the development of CRC. Herein, we overview both basic and clinical data relevant to BRAF-mutated CRC, mainly focusing on the development of treatment strategies. This review is organized into eight sections, including clinicopathological features, molecular features, prognosis, the predictive value of anti-epidermal growth factor receptor (EGFR) therapy, resistant mechanisms for BRAF-targeting treatment, the heterogeneity of the BRAF mutation, future perspectives, and conclusions. A characterization of the canonical mitogen-activated protein kinase (MAPK) pathway is essential for controlling this malignancy, and the optimal combination of multiple interventions for treatments remains a point of debate.
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Affiliation(s)
- Izuma Nakayama
- Department of Gastroenterological Chemotherapy, Cancer Institute Hospital of the Japanese Foundation for Cancer Research (JFCR), Tokyo 135-8550, Japan
- Correspondence: (I.N.); (E.S.); Tel.: +81-3-3520-0111
| | - Toru Hirota
- Department of Experimental Pathology, Cancer Institute of the Japanese Foundation for Cancer Research (JFCR), Tokyo 135-8550, Japan;
| | - Eiji Shinozaki
- Department of Gastroenterological Chemotherapy, Cancer Institute Hospital of the Japanese Foundation for Cancer Research (JFCR), Tokyo 135-8550, Japan
- Correspondence: (I.N.); (E.S.); Tel.: +81-3-3520-0111
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Yuan J, Dong X, Yap J, Hu J. The MAPK and AMPK signalings: interplay and implication in targeted cancer therapy. J Hematol Oncol 2020; 13:113. [PMID: 32807225 PMCID: PMC7433213 DOI: 10.1186/s13045-020-00949-4] [Citation(s) in RCA: 228] [Impact Index Per Article: 57.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 08/04/2020] [Indexed: 02/06/2023] Open
Abstract
Cancer is characterized as a complex disease caused by coordinated alterations of multiple signaling pathways. The Ras/RAF/MEK/ERK (MAPK) signaling is one of the best-defined pathways in cancer biology, and its hyperactivation is responsible for over 40% human cancer cases. To drive carcinogenesis, this signaling promotes cellular overgrowth by turning on proliferative genes, and simultaneously enables cells to overcome metabolic stress by inhibiting AMPK signaling, a key singular node of cellular metabolism. Recent studies have shown that AMPK signaling can also reversibly regulate hyperactive MAPK signaling in cancer cells by phosphorylating its key components, RAF/KSR family kinases, which affects not only carcinogenesis but also the outcomes of targeted cancer therapies against the MAPK signaling. In this review, we will summarize the current proceedings of how MAPK-AMPK signalings interplay with each other in cancer biology, as well as its implications in clinic cancer treatment with MAPK inhibition and AMPK modulators, and discuss the exploitation of combinatory therapies targeting both MAPK and AMPK as a novel therapeutic intervention.
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Affiliation(s)
- Jimin Yuan
- Department of Urology, Shenzhen People's Hospital (The Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, 518020, Guangdong, China.
- Geriatric Department, Shenzhen People's Hospital (The Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, 518020, Guangdong, China.
| | - Xiaoduo Dong
- Shenzhen People's Hospital, 1017 Dongmen North Road, Shenzhen, 518020, China
| | - Jiajun Yap
- Cancer and Stem Cell Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore
| | - Jiancheng Hu
- Cancer and Stem Cell Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore.
- Division of Cellular and Molecular Research, National Cancer Centre Singapore, 11 Hospital Drive, Singapore, 169610, Singapore.
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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: 281] [Impact Index Per Article: 70.3] [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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4
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Stefan E, Troppmair J, Bister K. Targeting the Architecture of Deregulated Protein Complexes in Cancer. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2017; 111:101-132. [PMID: 29459029 DOI: 10.1016/bs.apcsb.2017.07.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The architectures of central signaling hubs are precisely organized by static and dynamic protein-protein interactions (PPIs). Upon deregulation, these PPI platforms are capable to propagate or initiate pathophysiological signaling events. This causes the acquisition of molecular features contributing to the etiology or progression of many diseases, including cancer, where deregulated molecular interactions of signaling proteins have been best studied. The reasons for PPI-dependent reprogramming of cancer-initiating cells are manifold; in many cases, mutations perturb PPIs, enzyme activities, protein abundance, or protein localization. Consequently, the pharmaceutical targeting of PPIs promises to be of remarkable therapeutic value. For this review we have selected three key players of oncogenic signaling which are differently affected by PPI deregulation: two (the small G proteins of the RAS family and the transcription factor MYC) are considered "undruggable" using classical drug discovery approaches and in the case of the third protein discussed here, PKA, standard kinase inhibitors, may be unsuitable in the clinic. These circumstances require alternative strategies, which may lie in pharmaceutical drug interference of critical PPIs accountable for oncogenic signaling.
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Affiliation(s)
- Eduard Stefan
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria.
| | - Jakob Troppmair
- Daniel Swarovski Research Laboratory, Medical University of Innsbruck, Innsbruck, Austria
| | - Klaus Bister
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria
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Mahapatra DK, Asati V, Bharti SK. MEK inhibitors in oncology: a patent review (2015-Present). Expert Opin Ther Pat 2017; 27:887-906. [DOI: 10.1080/13543776.2017.1339688] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Debarshi Kar Mahapatra
- Dadasaheb Balpande College of Pharmacy, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur, India
| | - Vivek Asati
- Institute of Pharmaceutical Sciences, Guru Ghasidas Vishwavidyalaya (A Central University), Bilaspur, India
| | - Sanjay Kumar Bharti
- Institute of Pharmaceutical Sciences, Guru Ghasidas Vishwavidyalaya (A Central University), Bilaspur, India
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6
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Stefan E, Bister K. MYC and RAF: Key Effectors in Cellular Signaling and Major Drivers in Human Cancer. Curr Top Microbiol Immunol 2017; 407:117-151. [PMID: 28466200 DOI: 10.1007/82_2017_4] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The prototypes of the human MYC and RAF gene families are orthologs of animal proto-oncogenes that were originally identified as transduced alleles in the genomes of highly oncogenic retroviruses. MYC and RAF genes are now established as key regulatory elements in normal cellular physiology, but also as major cancer driver genes. Although the predominantly nuclear MYC proteins and the cytoplasmic RAF proteins have different biochemical functions, they are functionally linked in pivotal signaling cascades and circuits. The MYC protein is a transcription factor and together with its dimerization partner MAX holds a central position in a regulatory network of bHLH-LZ proteins. MYC regulates transcription conducted by all RNA polymerases and controls virtually the entire transcriptome. Fundamental cellular processes including distinct catabolic and anabolic branches of metabolism, cell cycle regulation, cell growth and proliferation, differentiation, stem cell regulation, and apoptosis are under MYC control. Deregulation of MYC expression by rearrangement or amplification of the MYC locus or by defects in kinase-mediated upstream signaling, accompanied by loss of apoptotic checkpoints, leads to tumorigenesis and is a hallmark of most human cancers. The critically controlled serine/threonine RAF kinases are central nodes of the cytoplasmic MAPK signaling cascade transducing converted extracellular signals to the nucleus for reshaping transcription factor controlled gene expression profiles. Specific mutations of RAF kinases, such as the prevalent BRAF(V600E) mutation in melanoma, or defects in upstream signaling or feedback loops cause decoupled kinase activities which lead to tumorigenesis. Different strategies for pharmacological interference with MYC- or RAF-induced tumorigenesis are being developed and several RAF kinase inhibitors are already in clinical use.
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Affiliation(s)
- Eduard Stefan
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innrain 80-82, 6020, Innsbruck, Austria
| | - Klaus Bister
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innrain 80-82, 6020, Innsbruck, Austria.
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7
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Asati V, Mahapatra DK, Bharti SK. PI3K/Akt/mTOR and Ras/Raf/MEK/ERK signaling pathways inhibitors as anticancer agents: Structural and pharmacological perspectives. Eur J Med Chem 2016; 109:314-41. [PMID: 26807863 DOI: 10.1016/j.ejmech.2016.01.012] [Citation(s) in RCA: 375] [Impact Index Per Article: 46.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 01/08/2016] [Accepted: 01/09/2016] [Indexed: 12/17/2022]
Abstract
The protein kinases regulate cellular functions such as transcription, translation, proliferation, growth and survival by the process of phosphorylation. Over activation of signaling pathways play a major role in oncogenesis. The PI3K signaling pathway is dysregulated almost in all cancers due to the amplification, genetic mutation of PI3K gene and the components of the PI3K pathway themselves. Stimulation of the PI3K/Akt/mTOR and Ras/Raf/MEK/ERK pathways enhances growth, survival, and metabolism of cancer cells. Recently, the PI3K/Akt/mTOR and Ras/Raf/MEK/ERK signaling pathways have been identified as promising therapeutic targets for cancer therapy. The kinase inhibitors with enhanced specificity and improved pharmacokinetics have been considered for design and development of anticancer agents. This review focuses primarily on the Ras/Raf/MEK/ERK and PI3K/Akt/mTOR signaling pathways as therapeutic targets of anticancer drugs, their specific and dual inhibitors, structure activity relationships (SARs) and inhibitors under clinical trials.
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Affiliation(s)
- Vivek Asati
- Institute of Pharmaceutical Sciences, Guru Ghasidas Vishwavidyalaya (A Central University), Bilaspur 495009, Chhattisgarh, India
| | - Debarshi Kar Mahapatra
- Institute of Pharmaceutical Sciences, Guru Ghasidas Vishwavidyalaya (A Central University), Bilaspur 495009, Chhattisgarh, India
| | - Sanjay Kumar Bharti
- Institute of Pharmaceutical Sciences, Guru Ghasidas Vishwavidyalaya (A Central University), Bilaspur 495009, Chhattisgarh, India.
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8
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Holderfield M, Deuker MM, McCormick F, McMahon M. Targeting RAF kinases for cancer therapy: BRAF-mutated melanoma and beyond. Nat Rev Cancer 2014; 14:455-67. [PMID: 24957944 PMCID: PMC4250230 DOI: 10.1038/nrc3760] [Citation(s) in RCA: 576] [Impact Index Per Article: 57.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The identification of mutationally activated BRAF in many cancers altered our conception of the part played by the RAF family of protein kinases in oncogenesis. In this Review, we describe the development of BRAF inhibitors and the results that have emerged from their analysis in both the laboratory and the clinic. We discuss the spectrum of RAF mutations in human cancer and the complex interplay between the tissue of origin and the response to RAF inhibition. Finally, we enumerate mechanisms of resistance to BRAF inhibition that have been characterized and postulate how strategies of RAF pathway inhibition may be extended in scope to benefit not only the thousands of patients who are diagnosed annually with BRAF-mutated metastatic melanoma but also the larger patient population with malignancies harbouring mutationally activated RAF genes that are ineffectively treated with the current generation of BRAF kinase inhibitors.
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Affiliation(s)
| | | | - Frank McCormick
- Corresponding Authors: Frank McCormick & Martin McMahon, Diller Family Cancer Research Bldg., 1450 Third Street, University of California, San Francisco, CA 94158, USA, &
| | - Martin McMahon
- Corresponding Authors: Frank McCormick & Martin McMahon, Diller Family Cancer Research Bldg., 1450 Third Street, University of California, San Francisco, CA 94158, USA, &
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9
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Griewank KG, Scolyer RA, Thompson JF, Flaherty KT, Schadendorf D, Murali R. Genetic alterations and personalized medicine in melanoma: progress and future prospects. J Natl Cancer Inst 2014; 106:djt435. [PMID: 24511108 DOI: 10.1093/jnci/djt435] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
High-throughput sequencing technologies are providing new insights into the genetic alterations involved in melanomagenesis. It appears likely that most genetic events important in the pathogenesis of melanoma will be discovered over the next few years. Genetic analysis is also increasingly being used to direct patient care. In parallel with the discovery of new genes and the elucidation of molecular pathways important in the development of melanoma, therapies targeting these pathways are becoming available. In other words, the age of personalized medicine has arrived, characterized by molecular profiling of melanoma to identify the relevant genetic alterations and the abnormal signaling mechanisms involved, followed by selection of optimal, individualized therapies. In this review, we summarize the key genetic alterations in melanoma and the development of targeted agents against melanomas bearing specific mutations. These developments in melanoma serve as a model for the implementation of personalized medicine for patients with all cancers.
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Affiliation(s)
- Klaus G Griewank
- Affiliations of authors: Department of Dermatology, University Hospital, University Duisburg-Essen, Essen, Germany (KGG, DS); Royal Prince Alfred Hospital, Camperdown, NSW, Australia (RAS); University of Sydney, Camperdown, NSW, Australia (RAS, JFT); Melanoma Institute Australia, North Sydney, NSW, Australia (RAS, JFT); Center for Melanoma, Massachusetts General Hospital Cancer Center, Boston, MA (KTF); Department of Pathology, and Center for Molecular Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY (RM)
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10
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Abstract
Retroviruses are the original source of oncogenes. The discovery and characterization of these genes was made possible by the introduction of quantitative cell biological and molecular techniques for the study of tumour viruses. Key features of all retroviral oncogenes were first identified in src, the oncogene of Rous sarcoma virus. These include non-involvement in viral replication, coding for a single protein and cellular origin. The MYC, RAS and ERBB oncogenes quickly followed SRC, and these together with PI3K are now recognized as crucial driving forces in human cancer.
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Affiliation(s)
- Peter K Vogt
- The Scripps Research Institute, La Jolla, California 92037, USA.
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11
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Michaloglou C, Vredeveld LCW, Mooi WJ, Peeper DS. BRAF(E600) in benign and malignant human tumours. Oncogene 2007; 27:877-95. [PMID: 17724477 DOI: 10.1038/sj.onc.1210704] [Citation(s) in RCA: 194] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Of the RAF family of protein kinases, BRAF is the only member to be frequently activated by mutation in cancer. A single amino acid substitution (V600E) accounts for the vast majority and results in constitutive activation of BRAF kinase function. Its expression is required to maintain the proliferative and oncogenic characteristics of BRAF(E600)-expressing human tumour cells. Although BRAF(E600) acts as an oncogene in the context of additional genetic lesions, in primary cells it appears to be associated rather with transient stimulation of proliferation. Eventually, BRAF(E600) signalling triggers cell cycle arrest with the hallmarks of cellular senescence, as is illustrated by several recent studies in cultured cells, animal models and benign human lesions. In this review, we will discuss recent advances in our understanding of the role of BRAF(E600) in benign and malignant human tumours and the implications for therapeutic intervention.
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Affiliation(s)
- C Michaloglou
- Division of Molecular Genetics, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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12
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Leicht DT, Balan V, Kaplun A, Singh-Gupta V, Kaplun L, Dobson M, Tzivion G. Raf kinases: function, regulation and role in human cancer. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:1196-212. [PMID: 17555829 PMCID: PMC1986673 DOI: 10.1016/j.bbamcr.2007.05.001] [Citation(s) in RCA: 203] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2006] [Revised: 05/01/2007] [Accepted: 05/02/2007] [Indexed: 12/25/2022]
Abstract
The Ras-Raf-MAPK pathway regulates diverse physiological processes by transmitting signals from membrane based receptors to various nuclear, cytoplasmic and membrane-bound targets, coordinating a large variety of cellular responses. Function of Raf family kinases has been shown to play a role during organism development, cell cycle regulation, cell proliferation and differentiation, cell survival and apoptosis and many other cellular and physiological processes. Aberrations along the Ras-Raf-MAPK pathway play an integral role in various biological processes concerning human health and disease. Overexpression or activation of the pathway components is a common indicator in proliferative diseases such as cancer and contributes to tumor initiation, progression and metastasis. In this review, we focus on the physiological roles of Raf kinases in normal and disease conditions, specifically cancer, and the current thoughts on Raf regulation.
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Affiliation(s)
| | | | | | | | | | | | - Guri Tzivion
- To whom correspondence should be addressed: Karmanos Cancer Institute, Wayne State University, 4100 John R., HWCRC 716, Detroit, MI 48201, Tel: 313-576-8311, Fax: 313-576-8308, E-mail:
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13
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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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14
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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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15
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Hartl M, Karagiannidis AI, Bister K. Cooperative cell transformation by Myc/Mil(Raf) involves induction of AP-1 and activation of genes implicated in cell motility and metastasis. Oncogene 2006; 25:4043-55. [PMID: 16491116 DOI: 10.1038/sj.onc.1209441] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2005] [Revised: 01/11/2006] [Accepted: 01/12/2006] [Indexed: 01/26/2023]
Abstract
Avian fibroblasts transformed simultaneously by the v-myc and v-mil(raf) oncogenes of acute leukemia and carcinoma virus MH2 contain elevated levels of c-Fos and c-Jun, major components of the transcription factor complex AP-1. To define specific transcriptional targets in these cells, subtractive hybridization techniques were employed leading to the identification of strongly upregulated genes including OPN (osteopontin), 126MRP, and rac2. OPN is a cytokine and cell attachment protein which has been implicated in human tumor progression and metastasis, the calcium binding 126MRP protein is related to the human S100 protein family involved in invasive cell growth, and the Rac2 protein belongs to the Rho family of small GTPases regulating actin reorganization and cell migration. Promoter analysis indicated that OPN activation is mediated by a non-consensus AP-1 binding site located close to the transcription start site. Electrophoretic mobility shift assays, chromatin immunoprecipitation and transcriptional reporter gene analyses showed that c-Fos and c-Jun bind specifically to this site and that c-Fos efficiently transactivates the OPN promoter. High-level expression of OPN, 126MRP, or Rac2 proteins from a retroviral vector led to partial cell transformation, documented by morphological changes and anchorage-independent growth. The specific activation in v-myc/v-mil(raf)-transformed cells of target genes with intrinsic oncogenic potential may provide an explanation for the longstanding observation that concomitant expression of these oncogenes leads to strongly enhanced oncogenicity in vivo and in vitro compared to cell transformation by v-myc or v-mil(raf) alone.
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Affiliation(s)
- M Hartl
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria.
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16
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Abstract
More than 20 years ago, Raf was discovered as a cellular oncogene transduced by transforming retroviruses. Since then, the three Raf isoforms have been intensively studied, mainly as the kinases linking Ras to the MEK/ERK signaling module. As this pathway is activated in human cancer, the Raf kinases are considered promising therapeutic targets, and we have learned a lot about their regulation, targets, and functions. Do they still hold surprises? Recent gene targeting studies indicate that they do. This review focuses on the regulation and biology of the best-studied Raf isoform, Raf-1, in the context of its kinase-independent functions.
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Affiliation(s)
- Manuela Baccarini
- Max F. Perutz Laboratories, Department of Microbiology and Immunobiology, The University of Vienna, Vienna Biocenter, Dr. Bohr Gasse 9, 1030 Vienna, Austria.
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17
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Wellbrock C, Karasarides M, Marais R. The RAF proteins take centre stage. Nat Rev Mol Cell Biol 2004; 5:875-85. [PMID: 15520807 DOI: 10.1038/nrm1498] [Citation(s) in RCA: 875] [Impact Index Per Article: 43.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Since their discovery over 20 years ago, the RAF proteins have been intensely studied. For most of that time, the focus of the field has been the C-RAF isoform and its role as an effector of the RAS proteins. However, a report that implicates B-RAF in human cancer has highlighted the importance of all members of this protein kinase family and recent studies have uncovered intriguing new data relating to their complex regulation and biological functions.
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Affiliation(s)
- Claudia Wellbrock
- Signal Transduction Team, Cancer Research UK Centre of Cell and Molecular Biology, The Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK
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18
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Brummer T, Stéhelin D, Misawa Y, Reth M. A revised and complete map of the chicken c-mil/raf-1 locus. Oncogene 2004; 23:3128-31. [PMID: 14968114 DOI: 10.1038/sj.onc.1207434] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The chicken c-mil/raf-1 gene (formerly also known as c-mht) was originally identified in the search for the cellular counterpart to the v-mil oncogene of the Mill Hill 2 retrovirus and was among the first cellular proto-oncogenes discovered. Although the c-mil/raf-1 promotor, as well as the exons transduced into v-mil, were characterized in detail, an entire map of this locus has never been published. Here, we now report the location of five previously unmapped exons. In addition, we have noticed inconsistent numbering of the c-mil/raf-1 exons in the literature and the GenBank database. Thus, we provide here a complete map of the c-mil/raf-1 gene and a revision of the exon numbers. Comparison of the chicken c-mil/raf-1 gene with those of other vertebrates suggests that the numbers and lengths of the translated exons of the raf-1 locus were established early in the vertebrate lineage and have been conserved during the divergent evolution of teleosts and tetrapods.
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Affiliation(s)
- Tilman Brummer
- Department of Molecular Immunology, Institute for Biology III, Albert-Ludwigs-University of Freiburg and Max-Planck-Institut for Immunobiology, Freiburg 79108, Germany
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McNagny KM, Graf T. Acute avian leukemia viruses as tools to study hematopoietic cell differentiation. Curr Top Microbiol Immunol 1996; 212:143-62. [PMID: 8934817 DOI: 10.1007/978-3-642-80057-3_13] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- K M McNagny
- Differentiation Programme, European Molecular Biology Laboratory, Heidelberg, Germany
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20
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Aoki M, Hamada F, Sugimoto T, Sumida S, Akiyama T, Toyoshima K. The human cot proto-oncogene encodes two protein serine/threonine kinases with different transforming activities by alternative initiation of translation. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)41587-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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21
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Terry A, Fulton R, Stewart M, Onions DE, Neil JC. Pathogenesis of feline leukemia virus T17: contrasting fates of helper, v-myc, and v-tcr proviruses in secondary tumors. J Virol 1992; 66:3538-49. [PMID: 1316466 PMCID: PMC241135 DOI: 10.1128/jvi.66.6.3538-3549.1992] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
A naturally occurring feline thymic lymphosarcoma (T17) provided the unique observation of a T-cell antigen receptor beta-chain gene (v-tcr) transduced by a retrovirus. The primary tumor contained three classes of feline leukemia virus (FeLV) provirus, which have now been characterized in more detail as (i) v-tcr-containing recombinant proviruses, (ii) v-myc-containing recombinant proviruses, and (iii) apparently full-length helper FeLV proviruses. The two transductions appear to have been independent events, with distinct recombinational junctions and no sequence overlap in the host-derived inserts. The T17 tumor cell line releases large numbers of FeLV particles of low infectivity; all three genomes are encapsidated, but passage of FeLV-T17 on feline fibroblast and lymphoma cells led to selective loss of the recombinant viruses. The oncogenic potential of the T17 virus complex was, therefore, tested by infection of neonatal cats with virus harvested directly from the primary T17 tumor cell line. A single inoculation of FeLV-T17 caused persistent low-grade infection culminating in thymic lymphosarcoma and acute thymic atrophy, which was accelerated by coinfection with the weakly pathogenic FeLV subgroup A (FeLV-A)/Glasgow-1 helper. Molecularly cloned FeLV-tcr virus (T-31) rescued for replication by a weakly pathogenic FeLV-A/Glasgow-1 helper virus was similarly tested in vivo and induced thymic atrophy and thymic lymphosarcomas. Most FeLV-T17-induced tumors manifested either v-myc or an activated c-myc allele and had undergone rearrangement of endogenous T-cell antigen receptor beta-chain genes, supporting the proposition that the oncogenic effects of c-myc linked to the FeLV long terminal repeat are targeted to a specific window in T-cell differentiation. However, neither the FeLV-T17-induced tumors nor the T-31 + FeLV-A-induced tumors contained clonally represented v-tcr sequences. Only one of the FeLV-T17-induced tumors contained detectable v-tcr proviruses, at a low copy number. While v-tcr does not have a readily transmissible oncogenic function, a more restricted role is not excluded, perhaps involving antigenic peptide-major histocompatibility complex recognition by the T-cell receptor complex. Such a function could be obscured by the genetic diversity of the outbred domestic cat host.
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MESH Headings
- Animals
- Atrophy
- Base Sequence
- Cats
- Cells, Cultured
- Gene Rearrangement, beta-Chain T-Cell Antigen Receptor
- Genes, myc
- Helper Viruses
- Leukemia Virus, Feline/genetics
- Leukemia Virus, Feline/pathogenicity
- Lymphoma, Non-Hodgkin/microbiology
- Molecular Sequence Data
- Proviruses/genetics
- Proviruses/pathogenicity
- Receptors, Antigen, T-Cell, alpha-beta/genetics
- Sequence Homology, Nucleic Acid
- Serial Passage
- Thymus Gland/pathology
- Thymus Neoplasms/microbiology
- Transduction, Genetic/genetics
- Tumor Virus Infections/genetics
- Tumor Virus Infections/pathology
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Affiliation(s)
- A Terry
- Beatson Institute for Cancer Research, Cancer Research Campaign Beatson Laboratories, Bearsden, Glasgow
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22
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Lenzi D, Radke K, Wilson M. Clonal cells from embryonic retinal cell lines express qualitative electrophysiological differences. JOURNAL OF NEUROBIOLOGY 1991; 22:823-36. [PMID: 1723422 DOI: 10.1002/neu.480220804] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Cells from the embryonic quail retina were immortalized with the v-mil oncogene and cloned by limiting dilution. Their phenotype was examined using the whole-cell patch clamp method. Three membrane currents, IK(IR), INa and IK, were found at different frequencies within a sample of 170 cells drawn from a large clone. Nearly all combinations of these three markers were found and the frequency of combinations showed that the markers assorted independently. Examination of clones of less than 10 cells showed that heterogeneity originates with a high probability within clones, arguing that chromosomal mutation, for example, is unlikely to account for phenotypic diversity. A possible explanation is that phenotypic differences between cells might reflect the local exchange of instructive signals. If so, then the genes for the three phenotypic markers are controlled independently.
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Affiliation(s)
- D Lenzi
- Department of Zoology, University of California, Davis 95616
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23
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Abstract
One objective of this review is to sort through and collate the recent data that suggest that human cellular oncogenes, which have been implicated as the etiologic agents in both animal and human malignancies, have also the potential to be employed as clinical tools in the struggle against cancer. For nearly 10 years, reports have been suggesting that advantage can be taken of cellular oncogenes as to their use as diagnostic and prognostic indicators of cancer and eventually as therapeutic cancer agents. It is also the purpose of this review to give an objective evaluation of these predictions. Moreover, this review will try to highlight some of the significant advances in this most rapidly evolving field of biology. Although the enormity of what has been learned about cellular oncogenes is nothing less than impressive, it is the view here that the routine implementation of oncogenes into the clinical setting will not become evident as early as the many predictions had purported.
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Affiliation(s)
- S Demczuk
- Karolinska Institute, NOVUM, Huddinge, Sweden
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24
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Korge G, Heide I, Sehnert M, Hofmann A. Promoter is an important determinant of developmentally regulated puffing at the Sgs-4 locus of Drosophila melanogaster. Dev Biol 1990; 138:324-37. [PMID: 2156737 DOI: 10.1016/0012-1606(90)90200-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Sgs-4 is one of the eight known genes coding for larval secretion proteins in Drosophila melanogaster. High-level transcription of the endogenous Sgs genes in salivary glands is accompanied by chromosome puffing at the Sgs gene loci. Naturally occurring mutations of the Sgs-4 promoter region diminish both the level of Sgs-4 expression and the puff size; in null-producers no puff is formed. P element-mediated transformation experiments were performed to clarify this apparent causal relation between transcription and puffing. Sgs-4 upstream sequences, unchanged or recombined with sequences from differently expressed alleles, were fused with Sgs-4 coding and downstream sequences or with the coding sequence of the viral oncogene v-mil. Analyses of the expression of these fragments at the RNA and protein levels and of their capacity for puff formation demonstrate uncoupling of transcription and puffing. That is, high-level transcription is independent of chromosome puffing and does not necessarily induce puffing, and developmentally regulated chromosome puffing is independent of significant transcriptional activity within the puff. Our results show that the strength of the Sgs-4 promoter located within the upstream region from -1 to -840 determines the formation of a puff. No specific effects could be detected on either transcription or puffing by decondensed versus compact chromatin adjoining the transposed DNA at the sites of insertion in transformants. A model in which trans-acting factors binding to the promoter region initiate puffing is proposed.
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Affiliation(s)
- G Korge
- Institut für Genetik der Freien Universität Berlin, West Germany
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25
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Chen C, Biegalke BJ, Eisenman RN, Linial ML. FH3, a v-myc avian retrovirus with limited transforming ability. J Virol 1989; 63:5092-100. [PMID: 2555545 PMCID: PMC251171 DOI: 10.1128/jvi.63.12.5092-5100.1989] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
We have isolated a new acute avian transforming virus which contains the oncogene myc. This virus, designated FH3, was isolated after injection of a 10-day-old chick embryo with avian leukosis virus. While FH3 shares many properties with other v-myc-containing avian retroviruses, it also has several unique properties. The primary target for transformation in vitro is chicken macrophages; infection of chicken fibroblasts does not lead to complete morphological transformation. FH3 also exhibits a limited host range, in that Japanese quail macrophages and fibroblasts are infected but are not completely transformed. FH3 induces in vivo a limited tumor type if injected into 10-day-old chick embryos; only a cranial myelocytoma, which does not appear to be metastatic, can be detected. The v-myc gene of FH3 is expressed predominantly as a P145 Gag-Myc protein which is encoded by a ca. 8-kilobase genomic RNA. This FH3-encoded polyprotein is localized in the nucleus of all infected cells, whether or not they are transformed.
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Affiliation(s)
- C Chen
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104
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26
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Pirollo KF, Garner R, Yuan SY, Li L, Blattner WA, Chang EH. raf involvement in the simultaneous genetic transfer of the radioresistant and transforming phenotypes. Int J Radiat Biol 1989; 55:783-96. [PMID: 2565939 DOI: 10.1080/09553008914550831] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We examined a human Alu+ mouse tertiary transformant derived from a noncancerous skin fibroblast cell line which exhibits the unique characteristic of being resistant to the killing effects of ionizing radiation. This transformed cell line was found to contain activated human c-raf-1, and demonstrated an increased level of radioresistance indicating the simultaneous transfer of both the transforming and radiation-resistant phenotypes. We have also found a relationship between the presence of activated oncogenes, specifically those with serine/threonine kinase activity and the radioresistant phenotype.
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Affiliation(s)
- K F Pirollo
- Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
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27
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Affiliation(s)
- R W Storms
- Department of Microbiology, University of Texas, Austin 78712-1095
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28
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Abstract
This paper has reviewed, in a broad sense, the potential involvement of the oncogenes and their progenitors, the protooncogenes, in signal transduction pathways. The membrane-associated oncogene products appear to be connected with the generation and/or regulation of secondary messengers, particularly those associated with Ca2+/phospholipid-dependent activation of the serine/threonine kinase protein kinase C. Activation of transmembrane receptors, either through binding their native ligand or through point mutations that lead to constitutive expression, results in the expression of their intrinsic tyrosine-specific protein kinases. In PDGF-stimulated cells, this results in the increased turnover of phosphatidylinositols and the subsequent release of IP3 (Habenicht et al., 1981; Berridge et al., 1984). This coincides with activation of a PI kinase activity (Kaplan et al., 1987). Likewise, the fms product, which is the receptor for CSF-1, induces a guanine nucleotide-dependent activation of phospholipase C (Jackowski et al., 1986). Receptor functions are potentially regulated through differential binding of ligands (as proposed with PDGF), through interactions with other receptors, and through the "feedback" regulation mediated by protein kinase C. PDGF stimulation leads to modulation of the EGF receptor through protein kinase C (Bowen-Pope et al., 1983; Collins et al., 1983; Davis and Czech, 1985). Similarly, the neu product becomes phosphorylated on tyrosine residues following treatment of cells with EGF, although the neu protein does not bind EGF itself (King et al., 1988; Stern and Kamps, 1988). The tyrosine kinases of the src family are not receptors themselves, although they may mediate specific receptor-generated signals. The clck product is physically and functionally associated with the T-cell receptors CD4 and CD8, and becomes active upon specific stimulation of cells expressing those markers (Veillette et al., 1988a,b). The precise physiological role of the src family products has not been established, but their kinase activity is intrinsic to that function. The v- and c-src products are hyperphosphorylated during mitosis (Chackalaparampil and Shalloway, 1988), which correlates with periods of reduced cell-to-cell adhesion and communication (Warren and Nelson, 1987; Azarnia et al., 1988). Furthermore, pp60c-src is associated with a PI kinase activity when complexed with MTAg of polyoma virus, suggesting a function in stimulating increased turnover of the phosphatidylinositols (Heber and Courtneidge, 1987; Kaplan et al., 1987).(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- R W Storms
- Department of Microbiology, University of Texas, Austin 78712
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29
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Palmieri S. Oncogene requirements for tumorigenicity: cooperative effects between retroviral oncogenes. Curr Top Microbiol Immunol 1989; 148:43-91. [PMID: 2684549 DOI: 10.1007/978-3-642-74700-7_2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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30
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Affiliation(s)
- R C Schwartz
- Department of Microbiology and Public Health, Michigan State University, East Lansing 48824-1101
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31
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Béchade C, Dambrine G, David-Pfeuty T, Esnault E, Calothy G. Transformed and tumorigenic phenotypes induced by avian retroviruses containing the v-mil oncogene. J Virol 1988; 62:1211-8. [PMID: 3346945 PMCID: PMC253129 DOI: 10.1128/jvi.62.4.1211-1218.1988] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Avian retrovirus MH2 contains two oncogenes, v-mil and v-myc. We have previously shown that a spontaneous mutant of MH2 (PA200-MH2), expressing only the v-mil oncogene, is able to induce proliferation of quiescent neuroretina cells. In this study, we investigated the transforming and tumorigenic properties of v-mil. PA200 induced fibrosarcomas in about 60% of the injected chickens, whereas inoculation of MH2 resulted mainly in the appearance of kidney carcinomas. Analysis of several parameters of transformation showed that PA200, in contrast to MH2, induced only limited in vitro transformation of fibroblasts and neuroretina cells. These results suggest that v-myc is the major transforming and tumorigenic gene in MH2-infected cells. This low in vitro transforming capacity differentiates v-mil not only from other avian oncogenes, but also from the homologous murine v-raf gene.
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Affiliation(s)
- C Béchade
- Institut Curie-Biologie, Centre Universitaire, Orsay, France
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32
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Biegalke BJ, Heaney ML, Bouton A, Parsons JT, Linial M. MC29 deletion mutants which fail to transform chicken macrophages are competent for transformation of quail macrophages. J Virol 1987; 61:2138-42. [PMID: 3295297 PMCID: PMC254234 DOI: 10.1128/jvi.61.7.2138-2142.1987] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
A number of MC29 mutants with deleted myc genes have been previously characterized. Many of these mutants have been found to be defective for transformation of chicken macrophages in vitro and for tumor induction in chickens. Such mutants are capable of transforming Japanese quail macrophages in vitro and inducing a high incidence of tumors in Japanese quail. Thus, Japanese quail may contain a factor(s) capable of complementing the defective transforming proteins encoded by some deleted v-myc genes.
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33
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Biegalke B, Linial M. Retention or loss of v-mil sequences after propagation of MH2 virus in vivo or in vitro. J Virol 1987; 61:1949-56. [PMID: 3033322 PMCID: PMC254202 DOI: 10.1128/jvi.61.6.1949-1956.1987] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
During propagation of the defective avian retrovirus MH2 in the presence of replication-competent helper virus, deletion of portions of the viral genome occurred frequently. After transformation of quail cells in vitro, v-mil sequences were lost, leading to populations of MH2 viruses which were highly deficient for mil gene expression but which could transform macrophage and fibroblast cells in vitro with high efficiency. In contrast, after induction of tumors in quail with mil-deficient MH2 viral stocks, a majority of the tumor DNAs contained mil+ proviruses, suggesting that there is selection for retention of the v-mil gene in vivo and that the mil protein may play a role in the oncogenicity of MH2 virus. We also isolated MH2-transformed cell lines which contained deleted proviruses arising from packaging and subsequent integration of the subgenomic v-myc-encoding mRNA. Some of these cell lines produced viruses which encoded abnormal v-myc proteins and had altered in vitro transforming properties. These altered phenotypes may be caused by mutations within the v-myc gene.
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34
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Abstract
An avian retrovirus containing only the v-mil oncogene (PA200-MH2) was analyzed for its ability to induce a transformed phenotype in chicken embryo fibroblasts. Infected cultures exhibited an altered morphology, disarranged actin cable filaments, and a decrease in the amount of cell surface fibronectin. In addition, these cells showed a high level of plasminogen activator protease activity and were also capable of growth in low serum concentrations. In contrast, PA200-MH2 was very inefficient at inducing foci under agar and colonies in semisolid medium relative to the Mill Hill 2 and Rous sarcoma viruses. This inefficiency was further reflected in vivo by the total inability of PA200-MH2 to induce wing tumors in young birds. However, 40% of the birds inoculated in the wing web with PA200-MH2-infected cells did develop slow-growing tumors at the site of injection, with no evidence of hematopoietic involvement. Our results indicate that the v-mil oncogene is transforming both in vitro and in vivo and that each of the oncogenes in the Mill Hill 2 virus, v-mil and v-myc, can independently transform fibroblasts. These data suggest that v-mil is functionally related to its homologous murine counterpart, v-raf, which also transforms fibroblasts.
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35
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Neil JC, Forrest D. Mechanisms of retrovirus-induced leukaemia: selected aspects. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 907:71-91. [PMID: 3032259 DOI: 10.1016/0304-419x(87)90019-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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36
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Fulton R, Forrest D, McFarlane R, Onions D, Neil JC. Retroviral transduction of T-cell antigen receptor beta-chain and myc genes. Nature 1987; 326:190-4. [PMID: 3029597 DOI: 10.1038/326190a0] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Support for multistage models of oncogenesis has been provided by several highly leukaemogenic retrovirus isolates that have transduced more than one host cell gene. Where functional studies have been performed, these retroviral oncogenes show synergy for in vitro transformation and leukaemogenesis. In naturally occurring feline leukaemias associated with feline leukaemia virus (FeLV), retroviral transduction of myc is a frequent oncogenic mechanism. But evidence suggesting that the FeLV v-myc genes might be insufficient for leukaemogenesis was provided by the latency (12 weeks) and clonality of FeLV/v-myc-induced tumours and the absence of demonstrable in vitro transformation by these viruses. In the search for secondary leukaemogenic events in FeLV/v-myc tumours, we have identified a case of FeLV transduction of a T-cell antigen receptor beta-chain gene. The proviruses carrying this gene (which we have named v-tcr) were a separate population from those carrying v-myc. In its normal role, the T-cell receptor beta-chain forms part of a multimeric complex involved in antigen recognition and T-cell activation. We suggest that v-tcr is a novel viral oncogene which assisted v-myc in the genesis of a naturally occurring case of thymic lymphosarcoma.
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37
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Abstract
The effects of oncogenic retroviruses on the expression of differentiation markers were studied in monolayer cultures of chick and quail embryo neuroretinas. Transformation by Rous sarcoma virus (RSV) did not affect the appearance of synapses, and the expression of glutamic acid decarboxylase was stimulated by pp60v-src, the product of the src gene. Quail embryo neuroretina cells transformed by Mill Hill 2 (which contains the two oncogenes v-mil and v-myc) were induced to proliferate into permanent cultures that synthesized crystallins and produced lentoid bodies. In contrast, transformation with a temperature-sensitive mutant of RSV reversibly blocked the production of crystallins and lentoid bodies. These data show that given cellular genes can respond differently to distinct oncogenes.
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38
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Martin P, Henry C, Denhez F, Amouyel P, Bechade C, Calothy G, Debuire B, Stehelin D, Saule S. Characterization of a MH2 mutant lacking the v-myc oncogene. Virology 1986; 153:272-9. [PMID: 3739230 DOI: 10.1016/0042-6822(86)90030-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
We have previously reported that a virus, MH2-PA200, lacking the ability to transform quail embryo cells, could be isolated from wild type (wt) MH2 stocks passaged on chicken neuroretina cells. We report here the molecular cloning and extensive characterization of this MH2-PA200 provirus. Molecularly cloned MH2-PA200 DNA was found to stimulate the growth of neuroretina cells by transfection assays and our results indicate that this recombinant virus was derived from the RAV-1 helper virus, in which v-mil and a small part of v-myc of MH2 were acquired at the expense of helper (delta gag-pol-delta env) sequences. In order to assess the precise boundary between the myc and env genes we determined the nucleotide sequence of the junction fragment and showed that 11 of 13 nucleotides of the env gene were identical to the myc sequence at the recombination point. The nucleotide sequence of the myc-env junction fragment of another similar and independently generated MH2 mutant showed similarly 9 nucleotides of homology between the env and myc sequences at the recombination point that took place at another site, suggesting that a homologous recombination occurred between MH2 and RAV-1 viruses to generate MH2-PA200 and similar mutants.
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39
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Patschinsky T, Jansen HW, Blöcker H, Frank R, Bister K. Structure and transforming function of transduced mutant alleles of the chicken c-myc gene. J Virol 1986; 59:341-53. [PMID: 3016301 PMCID: PMC253083 DOI: 10.1128/jvi.59.2.341-353.1986] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
A small retroviral vector carrying an oncogenic myc allele was isolated as a spontaneous variant (MH2E21) of avian oncovirus MH2. The MH2E21 genome, measuring only 2.3 kilobases, can be replicated like larger retroviral genomes and hence contains all cis-acting sequence elements essential for encapsidation and reverse transcription of retroviral RNA or for integration and transcription of proviral DNA. The MH2E21 genome contains 5' and 3' noncoding retroviral vector elements and a coding region comprising the first six codons of the viral gag gene and 417 v-myc codons. The gag-myc junction corresponds precisely to the presumed splice junction on subgenomic MH2 v-myc mRNA, the possible origin of MH2E21. Among the v-myc codons, the first 5 are derived from the noncoding 5' terminus of the second c-myc exon, and 412 codons correspond to the c-myc coding region. The predicted sequence of the MH2E21 protein product differs from that of the chicken c-myc protein by 11 additional amino-terminal residues and by 25 amino acid substitutions and a deletion of 4 residues within the shared domains. To investigate the functional significance of these structural changes, the MH2E21 genome was modified in vitro. The gag translational initiation codon was inactivated by oligonucleotide-directed mutagenesis. Furthermore, all but two of the missense mutations were reverted, and the deleted sequences were restored by replacing most of the MH2E21 v-myc allele by the corresponding segment of the CMII v-myc allele which is isogenic to c-myc in that region. The remaining two mutations have not been found in the v-myc alleles of avian oncoviruses MC29, CMII, and OK10. Like MH2 and MH2E21, modified MH2E21 (MH2E21m1c1) transforms avian embryo cells. Like c-myc, it encodes a 416-amino-acid protein initiated at the myc translational initiation codon. We conclude that neither major structural changes, such as in-frame fusion with virion genes or internal deletions, nor specific, if any, missense mutations of the c-myc coding region are necessary for activation of the basic oncogenic function of transduced myc alleles.
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40
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Symonds G, Quintrell N, Stubblefield E, Bishop JM. Dispersed chromosomal localization of the proto-oncogenes transduced into the genome of Mill Hill 2 or E26 leukemia virus. J Virol 1986; 59:172-5. [PMID: 3012116 PMCID: PMC253054 DOI: 10.1128/jvi.59.1.172-175.1986] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Both Mill Hill 2 and E26 retroviruses have transduced two cellular genes--c-myc and c-mil/mht (Mill Hill 2) and c-myb and c-ets (E26). We localized the genes transduced by these viruses to different chromosomes: c-myc and c-myb to relatively large chromosomes and c-mil/mht and c-ets to microchromosomes. Thus, like avian erythroblastosis virus, each of these retroviruses has transduced two cellular genes unlinked in the chicken genome.
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41
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Peters G, Lee AE, Dickson C. Concerted activation of two potential proto-oncogenes in carcinomas induced by mouse mammary tumour virus. Nature 1986; 320:628-31. [PMID: 3010125 DOI: 10.1038/320628a0] [Citation(s) in RCA: 114] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The induction of tumours by retroviruses lacking transduced oncogenes can involve the transcriptional or functional activation of cellular proto-oncogenes by an integrated provirus. Thus, the two cellular genes int-1 and int-2, identified as common targets for activation by mouse mammary tumour virus (MMTV), may constitute previously unrecognized oncogenes. In tumours, proviral insertion at these loci leads to expression of messenger RNAs which are undetectable in normal mammary glands. Here we report that in a survey of the two transcriptional activity and structural integrity of the two int loci in 30 BR6 mouse mammary tumours, around 50% of the tumours expressed both of these genes, in ostensibly monoclonal cell populations. Our data suggest that int-1 and int-2 may act cooperatively in the genesis of mammary carcinomas. However, because three tumours (10%) involved neither gene, and because in five cases activation occurred in the apparent absence of an adjacent provirus, it is clear that other loci and mechanisms contribute to tumorigenesis.
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42
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Abstract
We have used a rabbit antiserum directed against a portion of the MC29 viral myc protein expressed in bacteria to characterize the cellular myc protein from three different avian bursal lymphoma cell lines (1104HI, 1104BI S13, BK25), and from normal chick embryo cells. The phosphorylated myc proteins immunoprecipitated from these cells varied in molecular weight from 58 to 62 kDa and localized to the cell nucleus, as shown by cell fractionation experiments. Pulse-chase experiments established that these proteins had short half-lives ranging from 12 min for the myc proteins from the 1104BI S13 cell line to 25 min for myc proteins from both the 1104HI and the BK25 cell lines. The structural relatedness of the proteins was established by comparing their partial proteolytic digestion products (Cleveland analysis) with the partial proteolytic digestion products of the MH2 viral myc protein. The anti-myc-serum also immunoprecipitated a 48-kDa protein from each of the bursal cell lines. We have identified this protein as a breakdown product of the bursal cell myc proteins. The different size and number of these bursal cell myc proteins may be a direct result of the specific site of integration as well as the orientation of the retrovirus LTR sequence relative to the adjacent cellular myc allele.
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Li Y, Turck CM, Teumer JK, Stavnezer E. Unique sequence, ski, in Sloan-Kettering avian retroviruses with properties of a new cell-derived oncogene. J Virol 1986; 57:1065-72. [PMID: 3754014 PMCID: PMC252840 DOI: 10.1128/jvi.57.3.1065-1072.1986] [Citation(s) in RCA: 149] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The Sloan-Kettering viruses (SKVs) are a group of transforming retroviruses that were isolated from chicken embryo cells which had been infected with the avian leukosis virus transformation-defective Bratislava 77 (tdB77). Each of the SKV isolates was shown to contain multiple genomes of different sizes indicating the presence of several viruses in addition to tdB77. To identify and characterize the putative transforming gene(s) of the SKVs, we used hybridization selection to isolate the fraction of a representative cDNA which was SKV specific. Both solution and blot hybridization studies with viral RNAs showed that the specific probe contained a sequence, ski, that was at least partially held in common by the multiple SKV genomes. This conclusion was confirmed by the observation that a molecularly cloned ski probe also hybridized to each of the multiple SKV genomes. Southern blots of chicken DNA revealed homologs of ski (c-ski) which were not associated with endogenous viral loci. Results showing that c-ski was expressed in polyadenylated cytoplasmic RNA of uninfected chicken cells indicated that it is a functional gene. Other data showed that c-ski was conserved in avian and mammalian evolution, suggesting a functional role for the gene in species other than chickens. Using ski cDNA in solution hybridizations with viral RNAs and in Southern blot hybridization with cloned retroviral oncogenes, we did not detect any relationship between ski and any of 15 previously identified oncogenes.
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Bister K, Jansen HW. Oncogenes in retroviruses and cells: biochemistry and molecular genetics. Adv Cancer Res 1986; 47:99-188. [PMID: 3022566 DOI: 10.1016/s0065-230x(08)60199-2] [Citation(s) in RCA: 74] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Cleveland JL, Jansen HW, Bister K, Fredrickson TN, Morse HC, Ihle JN, Rapp UR. Interaction between Raf and Myc oncogenes in transformation in vivo and in vitro. J Cell Biochem 1986; 30:195-218. [PMID: 3084503 DOI: 10.1002/jcb.240300303] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
3611 MSV, a raf-oncogene-transducing murine retrovirus, induces fibrosarcomas and erythroid hyperplasia in newborn mice after a latency of 4-8 wk. In contrast, new recombinant murine retroviruses carrying the myc oncogene (J-3, J-5 construct viruses) do not induce tumors before greater than 9 wk. A combination of both oncogenes in an infectious murine retrovirus (J-2) induces hematopoietic neoplasms in addition to less prominent fibrosarcomas and pancreatic adenocarcinoma 1-3 wk after inoculation. The hematologic neoplasms consist of immunoblastic lymphomas of T and B cell lineage and erythroblastosis. If animals were inoculated with a variant of the J-3 virus, which induces altered foci in cultures of NIH 3T3 cells, carcinoma developed in the pancreas with a 2-6 mo latency. In parallel to the synergistic action of both oncogenes on hematopoietic cells in vivo, we find that raf-oncogene-induced transformation of bone marrow cells in culture is enhanced by the addition of myc, which by itself does not transform these cells when grown in standard media. We conclude that concomitant expression of raf and myc oncogenes in hematopoietic and epithelial cells alters their respective transforming activities. The contribution of v-myc in this synergism was examined by use of a series of recombinant murine retroviruses capable of expressing the avian v-myc to study the effect of altered myc expression on hematopoietic/lymphoid cells. With either interleukin 3- or interleukin 2-dependent cell lines, introduction of the recombinant viruses abrogated the requirement for IL 3 or IL 2 for growth, and associated with this was the suppression of c-myc expression. The findings suggest that myc is a component in the signal transduction pathway for IL 3 and IL 2 and support an autoregulatory mechanism of c-myc expression. In contrast to v-myc, expression of v-raf in primary lymphoid/hematopoietic cells has an immortalizing function without abrogating the requirement for IL 3 for growth. This suggests that v-raf and v-myc affect different components of growth regulation, as, for example, commitment (v-myc) and cell cycle progression (v-raf).
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MESH Headings
- Animals
- Animals, Newborn
- Base Sequence
- Cell Division
- Cell Line
- Cell Transformation, Viral
- Cells, Cultured
- DNA, Recombinant/metabolism
- Electrophoresis, Polyacrylamide Gel
- Fibrosarcoma/analysis
- Fibrosarcoma/microbiology
- Gene Expression Regulation
- Interleukin-2/pharmacology
- Interleukin-3
- Lymphokines/pharmacology
- Lymphoma/analysis
- Lymphoma/microbiology
- Mice
- Mice, Inbred Strains
- Neoplasm Proteins/analysis
- Neoplasms, Experimental/pathology
- Neoplasms, Experimental/physiopathology
- Oncogenes
- Proto-Oncogene Proteins/metabolism
- Proto-Oncogene Proteins/pharmacology
- Proto-Oncogene Proteins c-myc
- Retroviridae/metabolism
- Sarcoma, Experimental/analysis
- Sarcoma, Experimental/microbiology
- Time Factors
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Abstract
As many as 40 distinct oncogenes of viral and cellular origin have been identified to date. Many of these genes can be grouped into functional classes on the basis of their effects on cellular phenotype. These groupings suggest a small number of mechanisms of action of the oncogene-encoded proteins. Some data suggest that, in the cytoplasm, these proteins may regulate levels of critical second messenger molecules; in the nucleus, these proteins may modulate the activity of the cell's transcriptional machinery. Many of the gene products can also be related to a signaling pathway that determines the cell's response to growth-stimulating factors. Because some of these genes are expressed in nongrowing, differentiated cells, the encoded proteins may in certain tissues mediate functions that are unrelated to cellular growth control.
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Bechade C, Calothy G, Pessac B, Martin P, Coll J, Denhez F, Saule S, Ghysdael J, Stéhelin D. Induction of proliferation or transformation of neuroretina cells by the mil and myc viral oncogenes. Nature 1985; 316:559-62. [PMID: 2993899 DOI: 10.1038/316559a0] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The genome of the avian retrovirus MH2 contains, in addition to the v-myc oncogene shared with three other avian retroviruses (MC29, CMII and OK-10), a second cell-derived oncogene, v-mil (refs 1-3). Like the three other viruses, which contain only v-myc, MH2 induces mainly liver and kidney carcinomas in fowl and transforms fibroblasts and macrophages in vitro. However, MH2 and MC29 differ in their biological properties when assayed on cultures of chicken embryo neuroretina (NR) cells. Indeed, NR cells, which normally do not multiply in vitro, are induced to proliferate and become transformed upon infection with MH2, whereas infection with MC29 has no apparent effect on these cells. To analyse the functions of the two oncogenes of MH2, we isolated spontaneous and in vitro-constructed mutants of this virus and investigated their effects on NR cell multiplication and transformation. We report here that expression of v-mil is sufficient to induce NR cell proliferation, although it does not result in cell transformation. In addition, viruses expressing only the v-myc oncogene fail to induce any detectable change in NR cells. However, cooperation of the two oncogenes is required to achieve transformation of NR cells by MH2.
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Jansen HW, Bister K. Nucleotide sequence analysis of the chicken gene c-mil, the progenitor of the retroviral oncogene v-mil. Virology 1985; 143:359-67. [PMID: 2998016 DOI: 10.1016/0042-6822(85)90376-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The nucleotide sequence of the chicken gene c-mil was determined within and around all regions homologous to the oncogene v-mil of avian retrovirus MH2. The regions of homology to the previously determined v-mil sequence, ranging in size from 28 to 177 base pairs (bp), are distributed over 14 kilobase pairs (kbp) of the chicken genome and are organized in 11 exons. All exon-intron boundaries of c-mil, except the 5' boundary of exon 1 and the 3' boundary of exon 11, were unambiguously defined by the identification of consensus splice donor and acceptor sites precisely at positions where homology to v-mil ceases or resumes. The homology to v-mil starts within the coding sequence of exon 1 and ends within the 3' untranslated region of exon 11, 12 nucleotides downstream from the nonsense codon terminating the large open reading frame shared between c-mil and v-mil. The c-mil and v-mil sequences differ at only 7 out of 1153 nucleotide positions, and the predicted sequences of v-mil and c-mil proteins differ by one conservative and four nonconservative substitutions among 379 amino acid residues. Hence, the carboxy-terminal domains of the MH2 gag-mil hybrid protein and of the putative c-mil protein are very similar. However, the amino-terminal domain of the cellular protein is possibly encoded by additional 5' c-mil sequences not present in the transduced v-mil oncogene, while that of the MH2 hybrid protein is encoded by viral gag sequences. The sequence analysis also revealed that c-mil and c-myc derived sequences are immediately adjacent on the MH2 genome carrying both the v-mil and the v-myc oncogene. Hence, transduction of c-mil into MH2 involved recombination, at the 3' site, with either the c-myc locus or a previously transduced v-myc gene, and, at the 5' site, with gag sequences of the transducing virus. At both sites, no significant homologies were found between the sequence elements involved in the recombination.
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Crisanti P, Lorinet AM, Calothy G, Pessac B. Glutamic acid decarboxylase activity is stimulated in quail retina neuronal cells transformed by Rous sarcoma virus and is regulated by pp60v-src. EMBO J 1985. [PMID: 2992933 PMCID: PMC554369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Rous sarcoma virus (RSV) stimulates in quail embryo neuro-retina (NR) cultures the specific activity of glutamic acid decarboxylase (GAD), the enzyme responsible for the synthesis of gamma-aminobutyric acid, a major inhibitory neurotransmitter in NR and in central nervous system. In quail embryo NR cultures transformed by ts NY-68, a thermodependent transformation-defective mutant of RSV, stimulation of GAD activity is regulated by pp60v-src, the product of the src gene of RSV. Fibroblasts and myoblasts have a very low GAD activity that is not stimulated after transformation by RSV. Neuronal clones, previously derived from ts NY-68-transformed established NR cell lines, have a high GAD activity which is regulated by pp60v-src, while other clones have a low GAD activity apparently not regulated by pp60v-src. These data indicate that pp60v-src selectively activates the expression of GAD in distinct neuronal cells of quail embryo NR cultures transformed by RSV. GAD activity is also stimulated in NR cells infected with viruses containing v-mil.
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Jansen HW, Patschinsky T, Walther N, Lurz R, Bister K. Molecular and biological properties of MH2D12, a spontaneous mil deletion mutant of avian oncovirus MH2. Virology 1985; 142:248-62. [PMID: 4060574 DOI: 10.1016/0042-6822(85)90333-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Avian oncogenic retrovirus MH2 carries two cell-derived oncogenes, v-mil and v-myc. From an infectious stock of MH2 a spontaneous deletion mutant, MH2D12, that has lost most of the v-mil gene but has retained a complete and functional v-myc gene, has been isolated. Nonproducer quail embryo cells transformed by MH2D12 in the absence of helper virus contain two virus-specific proteins: a gag-related protein of 53,000 Da (p53gag), and a v-myc gene product of 59,000/61,000 Da (p59/61v-myc) indistinguishable from the v-myc protein encoded by MH2. MH2D12 viral RNA contains all T1-oligonucleotides specific for the MH2 v-myc gene but none of those characteristic for the v-mil gene. The genetic structure of molecularly cloned proviral DNA of MH2D12 was revealed by restriction mapping, blot hybridization, heteroduplex analysis, and nucleotide sequencing. The MH2D12 provirus is homologous to the MH2 genome but has suffered a deletion of 1271 nucleotides from the central region encompassing the 3' end of delta gag and all of v-mil except the very 3' 31 nucleotides directly adjacent to the v-myc gene. A nine-nucleotide overlap of homology to gag or mil at the delta gag/delta mil junction suggests that recombination between homologous sequence elements of the delta gag and v-mil domains of MH2 was involved in the genesis of MH2D12. The nucleotide sequence analysis predicts that the carboxyterminal 17 amino acids of p53gag are encoded by the residual v-mil sequences and by intron-derived v-myc sequences. Transformation of quail embryo cells by MH2D12 can be assayed by focus and colony formation of transformed cells. This indicates that the v-mil gene is not essential for these activities. However, size and morphology of foci and colonies, and cellular morphology of cultured MH2D12-transformed cell lines can easily be distinguished from those observed in cell transformation by MH2 and resemble more those seen in cell transformation by viruses containing the myc oncogene only.
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