Insulin‐induced mitogenesis associated with transformation by the SV40 large T antigen

Abstract

Simian virus 40 (SV40) large T antigen‐transformed cells typically show a markedly reduced serum requirement for growth and the inability to growth arrest and differentiate. An SV40 large T antigen‐transformed 3T3 T cell line, CSV3‐1, that can growth arrest and differentiate into adipocytes with high efficiency has, however, recently been described (Scott et al: Proc. Natl. Acad. Sci. U.S.A. 86: 1652–1656, 1989; Estervig et al: J. Virol. 63: 2718–2725, 1989; J. Cell. Physiol. 142:552–558, 1990). The results of the current studies using these cells show that whereas quiescent 3T3 T cells show no mitogenic response to insulin, quiescent CSV3‐1 cells show a highly significant insulin‐induced mitogenic responsiveness in the absence of other added growth factors. Maximum mito‐genesis was observed at an insulin concentration of 1 μg/ml, which induced 40–70% of the cells to undergo DNA synthesis within 48 hours. The half maximum response was achieved with 1–10 ng/ml of insulin. Insulin's mitogenic effect on CSV3‐1 cells was evident under several different culture conditions that induce quiescence and was not mediated by any detectable autocrine growth factors that might make CSV3‐1 cells competent to respond to insulin. In CSV3‐1 cells insulin appears to act on its own receptor rather than on the IGF‐1 receptor, because at comparable dosages IGF‐1 is 10‐to 100‐fold less effective than insulin. Insulin also is shown to be a mitogen for another SV40‐transformed cell line, CSV3–35, which can be growth arrested; in contrast insulin has no mitogenic effect on two control cell lines that are stably transfected with pSV2neo, a plasmid containing SV40 early promoter/enhancer but lacking large T antigen gene. These results suggest a significant relationship between SV40 T antigen‐associated transformation and the expression of mitogenic responsiveness to insulin.