Protein kinase B/Akt signalling is required for palmitate-induced beta-cell lipotoxicity.
This study was conducted to clarify cell death and survival signals in pancreatic beta-cell lipotoxicity. Rat insulinoma INS-1 cells, with or without expression of dominant-negative mutant of Akt (K179M), were cultured with palmitate (C16:0) or oleate (C18:1) and cell numbers were determined by 0.2% eosin dye exclusion assay. The Akt activity was determined by anti-3'-phospho-inositide-dependent protein kinase (Akt)/protein kinase B (PKB) or anti-phospho-Akt (Serine 473) immunoblotting, and nuclear protein nuclear factor-kB (NF-kappaB)-binding activity was by supershift analysis. Twenty-four hours treatment with palmitate increased the INS-1 cell number at 0.1-0.2 mM but decreased the cell number at 0.5-1 mM. Oleate did not affect cell number at 0.1-1.0 mM. Palmitate dose-dependently increased phosphorylation of 473th serine in Akt/PKB. The K179M form of Akt/PKB abolished palmitate-induced cell proliferation at the low dose and death at the high dose. Nuclear protein NF-kappaB binding was enhanced at 0.2 and 0.5 mM of palmitate but decreased at 1.0 mM. Results suggest that Akt/PKB signalling is involved in palmitate-induced cell death and survival of pancreatic beta cell.