Enhanced synthesis and stabilization of Mr 68,000 protein in transformed BALB/c-3T3 cells: candidate for restriction point control of cell growth.

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Abstract
Transformation of cells to tumorigenicity by chemical carcinogens may depend on stabilization of a protein responsible for growth regulation. Cell kinetic experiments in which normal and benzo[a]pyrene-transformed BALB/c-3T3 cells were pulsed with cycloheximide indicated that this protein should have a half-life of a few hours in normal cells and should be considerably more stable in transformed cells. A protein with these properties was not yet reported. Such a protein was sought using 2-dimensional electrophoresis to resolve proteins from cells labeled with [35S]methionine. Among .apprxeq. 1000 proteins that were resolved on these gels, one has a greater rate of synthesis and stability in benzo[a]pyrene-transformed than in untransformed cells. This result satisfies a necessary prediction of the labile protein hypothesis. This protein could be important in determining the loss of growth regulation in these tumor cells.