The role of uncoupling protein-2 (UCP-2) in beta -cells is presently unclear. We have tested the notion that UCP-2 participates in beta -cell defense against oxidants. Expression of the UCP-2 gene in clonal beta -cells (INS-1) was decreased by 45% after 48 h of culture with vitamin E and selenite. When INS-1 cells were exposed to 200 muM H2O2 for 5 min, the cell viability (MTT assay) decreased to 85 +/- 1, 61 +/-1, 40 +/- 2, and 39 +/- 2% of control when measured respectively 30 min, 2 h, 6 h, and 16 h after H2O2 exposure. At corresponding time points UCP-2 mRNA levels were 1.01 +/- 0.09, 1.53 +/- 0.15 (P < 0.05), 1.44 +/- 0.18 (P = 0.06), and 1.12 +/- 0,09 fold of control, i.e., transiently increased. We next tested whether overexpression of UCP-2 could enhance resistance of -cells toward H2O2 toxicity. A cotransfection method using EGFP as a suitable marker and a human cDNA UCP-2 construct was used for transient overexpression of UCP-2, Transfected cells expressed the gene about 30-fold more than normal cells. After exposure to H2O2 (200 mum, 5 min), the survival of UCP-2 overexpressing cells was measured 30-45 min later by flow cytometry. Survival was 13 +/- 0.05% higher than control (EGFP only) cells, P < 0.004 for difference. The results indicate that oxidative stress induces UCP-2 expression in -cells, and that UCP-2 serves a role in beta -cell defense against oxidative stress.