Figure 3.

Role of AMPK in HNF4α expression. A, effect of AMPK activators on HNF4α protein levels. MIN6 cells were cultured at the indicated concentration of AICAR or metformin for 24 h, and Western blotting was performed. B and C, isolated mouse islets were treated with 2 mm metformin for 24 h, and HNF4α protein levels were examined. D and E, MIN6 cells expressing the pMX empty vector or pMX-KD-AMPKα2 vector were treated with 2 mm metformin for 20 h, and HNF4α protein levels were examined (n = 3). F and G, an insulin secretion assay was performed (n = 4–5), and insulin concentration was determined by an insulin ELISA. Fold-change in glucose-stimulated insulin secretion (insulin level at 22 mm glucose divided by that at 2.2 mm glucose) is shown (n = 4–5). H, isolated mouse islets expressing either LacZ or KD-AMPKα2 were treated with 2 mm metformin for 20 h, and HNF4α protein levels were examined by Western blot analysis. I and J, islet insulin secretion was examined. Insulin levels are expressed as absolute values or as fold-change (n = 11–12). All data are presented as mean ± S.E. (error bars). N.S., not significant; *, p < 0.05; **, p < 0.01; ***, p < 0.001.