Cell Surface Retention Sequence Binding Protein-1 Interacts with the v-sis Gene Product and Platelet-derived Growth Factor β-Type Receptor in Simian Sarcoma Virus-transformed Cells

Abstract

The cell surface retention sequence (CRS) binding protein-1 (CRSBP-1) is a newly identified membrane glycoprotein which is hypothesized to be responsible for cell surface retention of the oncogene v-sis and c-sis gene products and other secretory proteins containing CRSs. In simian sarcoma virus-transformed NIH 3T3 cells (SSV-NIH 3T3 cells), a fraction of CRSBP-1 was demonstrated at the cell surface and underwent internalization/recycling as revealed by cell surface 125I labeling and its resistance/sensitivity to trypsin digestion. However, the majority of CRSBP-1 was localized in intracellular compartments as evidenced by the resistance of most of the 35S-metabolically labeled CRSBP-1 to trypsin digestion, and by indirect immunofluorescent staining. CRSBP-1 appeared to form complexes with proteolytically processed forms (generated at and/or after the trans-Golgi network) of the v-sis gene product and with a approximately 140-kDa proteolytically cleaved form of the platelet-derived growth factor (PDGF) beta-type receptor, as demonstrated by metabolic labeling and co-immunoprecipitation. CRSBP-1, like the v-sis gene product and PDGF beta-type receptor, underwent rapid turnover which was blocked in the presence of 100 microM suramin. In normal and other transformed NIH 3T3 cells, CRSBP-1 was relatively stable and did not undergo rapid turnover and internalization/recycling at the cell surface. These results suggest that in SSV-NIH 3T3 cells, CRSBP-1 interacts with and forms ternary and binary complexes with the newly synthesized v-sis gene product and PDGF beta-type receptor at the trans-Golgi network and that the stable binary (CRSBP-1.v-sis gene product) complex is transported to the cell surface where it presents the v-sis gene product to unoccupied PDGF beta-type receptors during internalization/recycling.