Identification and purification of PDGF/sis-like proteins from nuclei of simian sarcoma virus-transformed fibroblasts

Abstract

The platelet-derived growth factor (PDGF) is a potent mitogen for cells derived from mesenchyme and is highly related to the transforming protein of the simian sarcoma virus (SSV), p28v-sis. Both PDGF and p28v-sis appear to initiate DNA synthesis and cell proliferation through an interaction with PDGF cell surface receptors but the identity of the PDGF induced signals which are recognized within the nucleus is unknown. It has been suggested that PDGF is directly transported to the nucleus although conflicting data have been obtained when nuclear fractions have been analysed for PDGF-like proteins. Specific antisera recognizing PDGF and p28v-sis were used to isolate and partially characterize proteins from nuclei of SSV-transformed NRK fibroblasts. Nuclear proteins of 66, 65, and 44 kD were identified in immunoprecipitates. These proteins were displaced competitively from binding to anti-PDGF antisera by either PDGF or by mitogenically active recombinant v-sis protein homodimers and the proteins were not recognized by non-immune sera. Proteins of 66, 65, and 44 kD also were partially purified from nuclear extracts with anti-PDGF immunoaffinity chromatography and were identified in silver stained PAGE gels. The data establish the presence of proteins antigenically related to PDGF within the nuclei of SSV-transformed cells and suggest possible roles of nuclear proteins related antigenically to PDGF and p28v-sis in cell growth and transformation.