Rapid turnover of the platelet-derived growth factor receptor in sis-transformed cells and reversal by suramin. Implications for the mechanism of autocrine transformation.

In cells transformed by either v-sis or c-sis, the majority of the newly synthesized platelet-derived growth factor (PDGF) receptors fail to reach the cell surface and are rapidly degraded. This rapid turnover (t1/2 less than 30 min) appears to result from interaction of the sis gene product with the PDGF receptor in the endoplasmic reticulum and/or Golgi apparatus during their intracellular routing from the endoplasmic reticulum to the plasma membrane or extracellular compartment. Several lines of evidence support this hypothesis. 1) Both the 160-kDa precursor and the intracellular 180-kDa mature form of the PDGF receptor possessed ligand binding activity for PDGF; 2) both the 160-kDa precursor and the 180-kDa mature form of the receptor in sis-transformed cells were found to be activated (phosphorylated); 3) protamine, a competitive inhibitor for PDGF or v-sis gene product binding to the cell-surface receptor, did not affect the rapid turnover of the PDGF receptor in sis-transformed cells; 4) suramin, an inhibitor for PDGF or v-sis gene product binding to the PDGF receptor, not only reversed the rapid turnover of the PDGF receptor in sis-transformed cells, but also increased the secretion of sis gene products; and 5) rapid turnover of the PDGF receptor was only observed in sis-transformed cells but not in cells transformed by other oncogenes. We suggest that the persistence of a mitogenic signal from cellular organelles, arising from the intracellular interaction of sis gene products with newly synthesized PDGF receptors, is the mechanism for autocrine transformation by sis.