Insulin-treated 3T3-L1 adipocytes and cell-free extracts derived from them incorporate 32P into ribosomal protein S6.

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Abstract
Differentiated [mouse] 3T3-L1 preadipocytes preincubated for 60 min with 32Pi incorporate 32P into ribosomal protein S6 within 5 min after exposure to 0.1-1.0 nM insulin [I]. Undifferentiated 3T3-L1 cells, which possess only 3-5% of the high-affinity cell surface I receptors present on the differentiated cells, are less sensitive to this stimulation. Under the same conditions used for I, epidermal growth factor, antibody to the I receptor, and a combination of isoproterenol and 1-methyl-3-isobutylxanthine also promote 32P incorporation into S6 in the differentiated cells although less effectively than I. Cell-free extracts derived from cells treated for 5-10 min with either physiological concentrations of I or epidermal growth factor (0.1 .mu.g/ml) reflect intact cells and catalyze the incorporation of 32P from exogenous [.gamma.-32P]ATP into ribosomal protein S6.