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Evidence that a 90 kilodalton phosphoprotein an associated kinase and a specific phosphatase are involved in the regulation of cloudman melanoma cell proliferation by insulin


Proceedings of the National Academy of Sciences of the United States of America 82(4): 1007-1011
Evidence that a 90 kilodalton phosphoprotein an associated kinase and a specific phosphatase are involved in the regulation of cloudman melanoma cell proliferation by insulin
Proliferation of wild-type Cloudman S91 melanoma cells is inhibited when insulin is included in the culture medium. Using growth inhibition as a selective marker, variant cell lines were isolated that are either resistant to insulin or dependent upon insulin for growth. The effects of insulin on proliferation were studied by using combined genetic and biochemical approaches. Through a series of genetic hybridization analyses, 3 complementation groups were identified and in general, insulin-sensitivity is dominant to insulin-resistance. Through analyses of in vitro protein phosphorylation reactions, a protein of .simeq. 90 kDa [kilodalton] (pp90) was identified whose phosphorylation is a function of at least one of the complementation groups. Although pp90 is not phosphorylated in extracts of insulin-resistant variants, it is phosphorylated in extracts of insulin-sensitive hybrids formed between complementing resistant variants. Insulin itself exhibits little or no regulation over the phosphorylation of pp90; rather, the ability to phosphorylate pp90 correlates with the ability of cells to respond to insulin. Migration in NaDodSO4[sodium dodecyl sulfate]/polyacrylamide gels, solubility characteristics and divalent cation requirements indicate that pp90 is distinct from the 95-kDa .beta.-subunit of the insulin receptor. Both pp90 and its associated phosphoprotein kinase are found in 30,000 .times. g pellets of sonicated cell lysates, whereas a specific pp90 phosphoprotein phosphatase activity is found in 30,000 .times. g supernatant fractions. Phosphorylation of pp90 occurs at tyrosine and serine residues. Apparently the state of phosphorylation of pp90 is an important determinant in the regulation of cellular proliferation by insulin.


Accession: 005411971



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