STUDIES ON THE EXPRESSION OF THE MOLONEY MURINE SARCOMA VIRUS ONCOGENE, V-MOS

Abstract

MoMSV is a retrovirus that causes sarcomas in vivo and cellular transformation of cells in culture. It derived by recombination between MoMLV and a cellular sequence, c-mos. Although MoMSV has been sequenced little is known about its mechanism of transcription.;Viral specific probes identified two v-mos subgenomic transcripts of 2.2 kDa and 2.1 kDa in size and suggested the following structure for these RNAs: U5+leader-mos-U3+R-polyA. The difference between the 2.2 kDa and 2.1 kDa transcripts map at the 5' end of the v-mos sequence. Experiments to locate the splice junction of these v-mos messages indicated that none of them use the acceptor splicing site of the envelope gene that is 5' to the v-mos sequence. This result explains in part the heterogeneity in size seen in Northern blots. The viral and cellular interactions that render a normal cell into a transformed phenotype by the action of a single gene are unknown. We have developed a cell-virus system where the effects of v-mos expression can be studied.;Infection of rat myoblasts by MoMSV results in cell death after 5 days of exposure to the virus. This effect seems to be mos-specific since other viruses including MoMLV, KiMSV and Musrc (a recombinant virus between MoMLV and the v-src gene from RSV) does not result in cell death. Western blot analysis of acutely MoMSV infected myoblasts using anti-mos sera detects p37mos. In addition, normal cells contain a protein of 55 000 daltons, p55, also detected by this mos-antisera. The cytopathic effect of MoMSV infection can be prevented if the cells are grown at 40(DEGREES)C, the cytocidal effect can be restored if cells are shift to 37(DEGREES)C. RNA and protein analysis of these cells at both temperature shows an inverse correlation between MoMSV transcription and the levels of p55 in acutely MoMSV infected myoblasts. p55 seems to be one of the target of v-mos action. p55 is a cytoplasmic protein. Its role is unknown but it might be involved in the maintenance of the normal phenotype.