title: Blockade of autocrine stimulation in simian sarcoma virus-transformed cells reverses down-regulation of platelet-derived growth factor receptors.
abstract: The viral (v)-sis oncogene encodes a protein (p28sis) that is structurally homologous to platelet-derived growth factor (PDGF). We have shown that simian sarcoma virus (SSV)-transformed cells containing the v-sis oncogene release a Mr 20,000 substance that is recognized by antisera to synthetic peptide sequences contained in p28sis. Medium conditioned by SSV-transformed cells competes with 125I-labeled PDGF for specific PDGF receptor sites, initiates DNA synthesis, and stimulates tyrosine phosphorylation of the PDGF receptor when added to normal cells. When normal cells are co-cultured with SSV-transformed cells, the PDGF receptors of the normal cells are down-regulated by factors released from the transformed cells. Thus, SSV-transformed cells release material that is functionally similar to PDGF. We have used anti-phosphotyrosine antibodies to purify PDGF receptors and to detect PDGF-stimulated receptors in normal cells. SSV-transformed cells have no PDGF receptors detectable by these antibodies or by 125I-labeled PDGF binding studies. However, when SSV-transformed cells are exposed to suramin, a compound that blocks binding of PDGF to its receptors, the receptors reappear on the cell surface and within 8 hr are present at the same levels as in control cells. These "new" receptor sites can be phosphorylated in response to PDGF. Thus, the absence of PDGF receptors in SSV-transformed cells is due to down-regulation of the receptors by an autocrine mechanism that can be blocked by suramin.
mesh_terms: D000818:Animals; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D005796:Genes; D005814:Genes, Viral; D007668:Kidney; D020575:Oncogene Proteins v-sis; D009857:Oncogenes; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics; D011505:Protein-Tyrosine Kinases; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017479:Receptors, Platelet-Derived Growth Factor; D012190:Retroviridae / Q000235:genetics*; D012842:Sarcoma Virus, Woolly Monkey / Q000235:genetics*; D014764:Viral Proteins / Q000235:genetics*
chemical_list: D020575:Oncogene Proteins v-sis; D010982:Platelet-Derived Growth Factor; D011956:Receptors, Cell Surface; D014764:Viral Proteins; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor