Human placental cells transformed by tsA mutants of simian virus 40: a model system for the study of placental functions.

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Abstract
Human placental cells were transformed with wild-type SV-40 and temperature-sensitive SV-40 mutants of the A and B classes. Four criteria for transformation were used: decreased generation time, increased saturation density, increased efficiency of growth on plastic and ability to overgrow a nontransformed monolayer. Cell lines transformed by tsA mutants lost the transformed phenotype at the restrictive temperature (40.degree. C); therefore, the A function of SV-40 is required for the maintenance of the transformed phenotype in human placental cells. A decrease in alkaline phosphatase activity, an inhibition of human chorionic gonadotropin synthesis and an increase in thymidine kinase activity were seen when human placental cells transformed by wild-type or tsB mutants of SV-40 were grown at 33.degree. or 40.degree. C and when tsA transformants were grown to 40.degree. C, alkaline phosphatase activity and human chorionic gonadotropin synthesis were greatly stimulated and thymidine kinase activity was greatly reduced, approximating their levels in the placenta.