Structure and biological activity of v-raf, a unique oncogene transduced by a retrovirus.

Abstract

We have molecularly cloned a unique acutely transforming replication-defective mouse type C virus (3611-MSV) and characterized its acquired oncogene. The viral genome closely resembles Moloney (M) murine leukemia virus (MuLV), except for a substitution in M-MuLV in the middle of p30 and the middle of the polymerase gene (pol). Heteroduplex analysis revealed that 2.4 kilobases of M-MuLV DNA were replaced by 1.2 kilobases of cellular DNA. The junctions between viral and cellular sequences were determined by DNA sequence analysis to be 517 nucleotides into the p30 sequence and 1,920 nucleotides into the polymerase sequence. Comparison of the transforming gene from 3611-MSV, designated v-raf, with previously isolated retrovirus oncogenes either by direct hybridization or by comparison of restriction fragments of their cellular homologs shows it to be unique. Transfection of NIH 3T3 cells with cloned 3611-MSV proviral DNA leads to highly efficient transformation and the recovered virus elicits tumors in mice typical of the 3611-MSV virus. Transfected NIH 3T3 cells express two 3611-MSV-specific polyproteins (P75 and P90), both of which contain NH2-terminal gag gene-encoded components linked to the acquired sequence (v-raf) translational product. The cellular homolog, c-raf, is present in one or two copies per haploid genome in mouse and human DNA.Retroviruses act as natural vectors for the transduction of at least some cellular genes, designated proto-oncogenes (1, 2), which bring about malignant transformation of infected cells. The cellular origin of a retroviral transforming gene (v-onc) was first demonstrated for v-src, the oncogene of Rous sarcoma virus (3, 4). Since then, 14 additional v-onc genes present in different acutely transforming retroviruses of avian and mammalian origin have been described, each similarly derived from cellular genes (c-onc) (1, 2). At least six of the v-onc genes code for functionally related tyrosine-specific protein kinases (5, 6), several of which appear to have a common evolutionary origin (7-9). Although the v-onc genes that do not encode protein kinase make up an evolutionarily more diverse group, some, such as v-kis and v-has, also appear to be members of gene families (10).The significance for human disease of c-onc genes had been purely hypothetical prior to the recent demonstration by DNA transfection that active forms of such genes may be associated with human cancers (11,12). Furthermore, human c-onc genes are associated with specific translocations characteristic of certain types of human cancer (13)(14)(15). These findings emphasize the potential importance of onc genes for an understanding of human malignancy and point to a need for a more complete accounting of such genes in human DNA.The isolation of retroviral oncogenes has in the past been sporadic and limited mainly to isolations from spontaneous tumors. More recently we have designed experiments to generate acutely transforming retroviruses by growth of IdUrd-induced endogenous type C viruses in chemicall...

Epidermal growth factor (EGF) suppresses staurosporine-induced apoptosis by inducing mcl-1 via the mitogen-activated protein kinase pathway

“…The plasmid which expresses mcl-1 antisense transcript was picked and checked by both restriction enzyme digestions and sequencing. Plasmid 3611-MSV that contains MSV LTR driven v-raf (Rapp et al, 1983) …”

Cooperative cell transformation by Myc/Mil(Raf) involves induction of AP-1 and activation of genes implicated in cell motility and metastasis

“…The v-mil oncogene identified in MH2 (Jansen et al, 1983a, b) is the avian ortholog of the mammalian v-raf oncogene Sutrave et al, 1984) that was independently defined as a single oncogenic determinant in murine retrovirus 3611-MSV (Rapp et al, 1983). The c-mil(raf) proto-oncogene encodes the serine/threonine-specific protein kinase c-Mil(Raf) that is an important part of a conserved signalling pathway transducing signals from the cell surface to the nucleus (Bister and Jansen, 1986;Wellbrock et al, 2004).…”

Differential regulation of Raf isozymes by growth versus differentiation inducing factors in PC12 pheochromocytoma cells

“…Signal transmission involves recruitment of a highly conserved protein kinase cascade consisting of the dual-specificity mitogen-activated protein kinase kinase (MEK) and its substrate, a serine/threonine specific mitogen-activated protein kinase (MAPK). Early work with an oncogenic version of Raf-1 (v-Raf) that was transduced as part of a retrovirus, 3611 MSV [1], demonstrated that constitutive expression of Raf-1 kinase also influenced differentiation processes (reviewed by Rapp et al [2]). Specifically, upon infection of newborn mice an altered fate was observed in erythroid, B/myeloid and epithelial lineages [3] and upon infection of progenitor cells in culture erythroid, adipocyte or neuronal differentiation was induced [4][5][6][7].…”