Fig. 3.

Phosphorylation of IRS-1 at Ser-1101 depends on nutrient availability. Serum-deprived L6 muscle cells, 3T3-L1 adipocytes, or Fao hepatoma cells were incubated either in an amino acid-containing or amino acid-deprived medium for 1 h and stimulated or not with 100 nM insulin as indicated, and then 0.01% DMSO vehicle or 25 nM rapamycin was added during the 1-h incubation. Phosphorylation of IRS-1 and S6K1 was determined by using antibodies that recognized IRS-1 and S6K1 only when phosphorylated at Ser-1101 and Thr-389, respectively. Stripped membranes were reprobed for total IRS-1 and S6K1. Results are of one representative experiment repeated at least three times.