The \-sis oncogene is the transforming oncogene of the simian sarcoma virus. The oncogenic sequences of the Parodi-Irgens (PI) FSV are homologous with the v-sis sequences of the simian sarcoma virus but very little is known about this feline virus-encoded protein. The -v-sis oncogene product is a protein of 28 kDa, which shares 92% homology with the platelet-derived growth factor (PDGF) B chain. V-sis is presumed to transform cells via autocrine activation of the endogenous PDGF receptor. The location of these autocrine interactions between the v-Sis protein and PDGF receptors remains somewhat controversial; however, it is thought that internal autoactivation of PDGF receptors may be essential for transformation by v-Sis. V-Sis can transform fibroblasts in culture and causes fibrosarcomas in vivo.
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