Notes: Growth of Immortal Simian Virus 40 tsA-Transformed Human Fibroblasts Is Temperature Dependent

Abstract

Simian virus 40 (SV40)-mediated transformation of human fibroblasts offers an experimental system for studying both carcinogenesis and cellular aging, since such transformants show the typical features of altered cellular growth but still have a limited life span in culture and undergo senescence. We have previously demonstrated (D. S. Neufeld, S. Ripley, A. Henderson, and H. L. Ozer, Mol. Cell. Biol. 7:2794-2802, 1987) that transformants generated with origin-defective mutants of SV40 show an increased frequency of overcoming senescence and becoming immortal. To clarify further the role of large T antigen, we have generated immortalized transformants by using origin-defective mutants of SV40 encoding a heat-labile large T antigen (tsA58 transformants). At a temperature permissive for large-T-antigen function (35 degrees C), the cell line AR5 had properties resembling those of cell lines transformed with wild-type SV40. However, the AR5 cells were unable to proliferate or form colonies at temperatures restrictive for large-T-antigen function (39 degrees C), demonstrating a continuous need for large T antigen even in immortalized human fibroblasts. Such immortal temperature-dependent transformants should be useful cell lines for the identification of other cellular or viral gene products that induce cell proliferation in human cells.

Mutation or not, what directly establishes a neoplastic state, namely cellular immortality and autonomy, still remains unknown and should be prioritized in our research

“…However, for different research needs, many systems of "conditional immortality" or "conditional transformation" have also been created [600][601][602][603][604][605], including transgenic animals [606]. Accordingly, many conditional cell lines have been established [589,[606][607][608][609][610][611][612][613][614][615], like the temperaturecontrolled ones [612,616], which show controllable immortalization or neoplastic transformation [612,615,617]. The words "conditional" and "controllable" already proclaim the nature of swift reversibility and accentuate that the immortality or the neoplastic transformation so created is not authentic because the cells are still mortal.…”