Insulin stimulates the phosphorylation of ribosomal protein S6 in a cell-free system derived from 3T3-L1 adipocytes.

Physiological concentrations of insulin stimulate the incorporation of 32P into ribosomal protein S6 in intact 3T3-L1 adipocytes (Smith, C. J., Wejksnora, P. J., Warner, J. B., Rubin, C. S., and Rosen, O. M. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 2725-2729). Extracts from cells treated with insulin also exhibit an increased ability to incorporate 32P from [gamma-32P]ATP into protein S6 in vitro (Smith, C. J., Rubin, C. S., and Rosen, O. M. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 2641-2645). We now report that the direct addition of insulin to particulate preparations containing high affinity insulin receptors and ribosomes derived from insulin-sensitive cells (not previously exposed to insulin) stimulates incorporation of 32P from [gamma-32P]ATP into ribosomal protein S6 1.5- to 3.0-fold. The stimulation occurs at the same concentrations of insulin (0.1-1.0 nM) and within the same period of time as it does in intact cells.