Figure 3.
Activation of Ins-R/PI3K/Akt pathway occurs 2 min after insulin stimulation and requires caveolin-3 expression. Control (A, B, C) and caveolin-3 null (B, C) skeletal muscle cells were differentiated for 5 days and treated with or without insulin (160 nM) for 2, 5, and 20 min. Cell lysates were immunoprecipitated with anti-insulin receptor-β IgGs (A) and IRS-1 IgGs (B), and immunoprecipitates were subjected to immunoblot analysis using specific antibody probes against phospho-tyrosine proteins (A), and p85 (B). In addition, total cell lysates were separated by SDS-PAGE and subjected to Western blotting analysis using anti-phospho-Akt and Akt IgGs (C). Total IRS-1 and p85 protein expression was not affected by insulin (data not shown). Moreover, total cell lysates from control and caveolin-3 null myotubes were subjected to immunoblot analysis with anti-Ins-Rβ IgGs (D). Finally, control and caveolin-3 null myotubes were left untreated or treated with 10 μM pervanadate for 15 min, and cell lysates subjected to immunoblot analysis using anti-phospho-Akt and Akt IgGs (E).