High glucose, but not pyruvate, induces MafA expression. MIN6 and betaTC3 cells were cultured in the presence of 20 mm pyruvate (Pyr),1mm glucose, or 25 mm glucose overnight. A, Western blot analysis of MafA and Pdx-1 protein levels. B, real time RT-PCR analysis of MafA mRNA levels. MafA mRNA levels were normalized to β-actin mRNA levels, and -fold increases were calculated based on the levels of MafA mRNA present in cells grown on 20 mm pyruvate. The data shown represent averages of two independent samples ± S.D. C, Western blot analysis of MafA protein levels in betaTC3 cells.