FIG. 6.

SUMOylation and deSUMOylation enzymes modulate glucose enhancement of exocytosis in mouse and human β-cells. A: Cells were preincubated at 1 mmol/L glucose for 4 h prior to a 15-min exposure to either 1 or 10 mmol/L glucose, after which exocytosis was measured as the whole-cell capacitance response to a series of membrane depolarizations (arrow). B: Exocytosis in mouse β-cells was blunted at 1 mmol/L (●), and enhanced at 10 mmol/L (○) glucose in cells dialyzed with GST. Dialysis of SENP1 peptide at 1 mmol/L glucose recapitulated the effect of glucose stimulation (■), but had no further effect at 10 mmol/L glucose (□). The total capacitance response under these conditions (right). C: Same as in B but human β-cells by overexpression rather than acute dialysis. Also, expression of the SUMO ligase, Ubc9, prevented glucose enhancement of exocytosis in these cells (△). **P < 0.01; ***P < 0.001 vs. 1 mmol/L glucose control.