title: Intracellular turnover, novel secretion, and mitogenically active intracellular forms of v-sis gene product in simian sarcoma virus-transformed cells. Implications for intracellular loop autocrine transformation.
abstract: In simian sarcoma virus (SSV)-transformed cells (SSV-NRK, SSV-NIH 3T3, and SSV-NP1 cells), the v-sis gene product was synthesized as a 36-kDa glycopolypeptide with one endoglycosidase (Endo) H-sensitive oligosaccharide chain and formed a dimer (p72) with a half-time of less than 5 min. p72 was proteolytically processed to generate sequentially p68 and p58 in the endoplasmic reticulum/Golgi complex, p44 in the post-Golgi complex compartments, and p27 in an endosomal/lysosomal compartment. A portion (20-30%) of p72 and p68 later became Endo H-resistant but Endo F-sensitive. During processing, the v-sis gene products exhibited rapid turnover, possibly in the endoplasmic reticulum and/or Golgi complex. The rate of turnover correlated with the tumorigenicity previously reported in these SSV-transformed cells. All three SSV-transformed cells secreted v-sis gene product (p44). p44 was secreted but remained tightly associated with the cell surface. This novel secretion provided an efficient system for the interaction of p44 with the cell surface platelet-derived growth factor receptor which resulted in the intracellular formation of p27. A fraction of secreted p44 was converted extracellularly to a 27-kDa product (extracellular p27) after a longer time in culture. The identical N-terminal amino acid sequence of p44 and extracellular p27 (H2N-SLGSLSVAEPAMIA) indicated a preferential site (Lys110-Arg111) for the proteolytic processing. The intracellular turnover of the v-sis gene product and its correlation with tumorigenicity as well as the demonstration of mitogenically active intracellular forms of v-sis gene product support the hypothesis of intracellular loop autocrine transformation.
authors: Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, Missouri 63104.
authors: V B
authors: VB
authors: Lokeshwar
authors: S S
authors: SS
authors: Huang
authors: J S
authors: JS
authors: Huang
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002472:Cell Transformation, Viral; D003593:Cytoplasm / Q000378:metabolism; D004705:Endocytosis; D006023:Glycoproteins / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000494:pharmacology; D006596:Hexosaminidases / Q000494:pharmacology; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D051379:Mice; D008970:Molecular Weight; D008985:Monensin / Q000494:pharmacology; D020575:Oncogene Proteins v-sis; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D017479:Receptors, Platelet-Derived Growth Factor; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism*; D015301:Retroviruses, Simian / Q000235:genetics*; D012842:Sarcoma Virus, Woolly Monkey / Q000235:genetics*; D013498:Suramin / Q000494:pharmacology; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D006023:Glycoproteins; D020575:Oncogene Proteins v-sis; D011956:Receptors, Cell Surface; D015682:Retroviridae Proteins, Oncogenic; D000643:Ammonium Chloride; D014415:Tunicamycin; D013498:Suramin; D008985:Monensin; D017479:Receptors, Platelet-Derived Growth Factor; D006026:Glycoside Hydrolases; D006596:Hexosaminidases; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase