Fig. 4.

Both IRS1 and IRS2 are involved in insulin-induced insulin gene transcription in β-cells. (A) The currently proposed mechanism of JNK action, IRS1 Ser-307 phosphorylation, decreases the affinity of the IRS1 PTB domain for activated InsR, thereby decreasing its tyrosine phosphorylation and ability to activate various effector functions. IRS2 may compensate for loss of IRS1 function. (B) IRS1 and IRS2 are required for insulin-induced AKT phosphorylation in β-cells. Cultured mouse islets were infected or not with Ad-shIRS1, Ad-shIRS2, or an Ad-GFP control virus as indicated. After 24 h, the cells were treated with insulin (200 microunits/ml) for 5 min. AKT phosphorylation and IRS1 and IRS2 expression were analyzed by immunoblotting. (C) IRS1 and IRS2 are required for insulin-induced insulin gene expression. Islets were treated as above, and insulin mRNA abundance was examined 2 h after insulin addition. Relative insulin mRNA levels are indicated above the panel.