Fig. 3. Insulin-induced PKC activation regulates STAT3 association and phosphorylation. (A) Keratinocytes were untreated (–) or treated with insulin for 5 minutes (+). PKC immunoprecipitates were subjected to western blot analysis using antibodies against STAT3, anti-phosphotyrosine-705-STAT3 (p-tyr), anti-phosphoserine-727-STAT3 (p-ser) and anti-PKC. Relative optical densities of the blots are presented in arbitrary units. Relative optical density of four blots is presented in arbitrary units (mean ± s.d.). (B) Primary keratinocytes were either untreated or infected for 1 hour with isoform-specific PKC recombinant adenovirus, or with ß-galactosidase (ß-Gal) adenovirus as control. Control cells were either untreated (C) or stimulated with insulin for 5 minutes (Ins 5'). Cells were extracted and immunoprecipitated (IP) with isoform-specific PKC antibodies. The immunoprecipitates were subjected to western blot analysis using anti-PKCs, anti-STAT3 or anti-phosphoserine-727-STAT3 (STAT p-ser) antibodies. Experiments were repeated three times.