Glucose increases MafA protein levels via O-GlcNAcylation by OGT. A, Western blot analysis of MafA protein levels in MIN6 cells cultured overnight with 25 mm glucose, 1 mm glucose, or 1 mm glucose and 100 μm PUGNAc. B, OGT protein levels were knocked down within MIN6 cells using predesigned siRNA as described under “Experimental Procedures.” After OGT knockdown, MIN6 cells were cultured overnight on 25 mm glucose, after which time MafA and OGT protein levels were analyzed by Western blotting. β-Actin was used as a loading control. The blot shown is representative of two independent experiments.