Figure 3.

Direct gene regulatory effects of leptin on the rat insulin I promoter in INS-1 cells are independent from K_ATP channel activation. (A) DNA constructs of the rat insulin I gene promoter used for luciferase reporter gene assays. Major known regulatory elements are indicated. INS1A, INS1B, and INSTAT denote the location of the oligonucleotides used in electrophoretic mobility-shift analysis. (B) Indicated reporter gene constructs were transfected into INS-1 cells and cells treated with leptin (6.25 nM) or vehicle at 5.6 mM and 25 mM glucose. ∗, P < 0.05. (C) Indicated reporter gene constructs were transfected into INS-1 cells and cells treated with leptin (6.25 nM) or vehicle at 11.1 mM glucose in the presence and absence of 10 nM GLP-1. ∗, P < 0.05. (D) Representative Northern blot for rat preproinsulin mRNA in INS-1 cells treated with 6.25 nM leptin or vehicle at 25 mM glucose in the presence or absence of 100 μM diazoxide. The results shown are representative of three independently performed experiments. (E) −410rINS-1 was transfected into INS-1 cells and cells treated with leptin (6.25 nM) or vehicle at 5.6 mM and 25 mM glucose in the presence and absence of 100 μM diazoxide. Means ± SD.