Evidence that protein kinase Cδ is not required for palmitate-induced cytotoxicity in BRIN-BD11 β-cells

Abstract

Chronic exposure of pancreatic β-cells to saturated fatty acids leads to loss of viability, an effect that has been implicated in the process of β-cell 'lipotoxicity' associated with the progression of type 2 diabetes. The mechanisms involved are unknown but recent evidence has implicated the δ isoform of protein kinase C (PKCδ) in mediating fatty acid toxicity. We have investigated this proposition in the clonal insulin-secreting cell line, BRIN-BD11. BRIN-BD11 cells were found to undergo apoptosis when exposed to palmitate and this response was attenuated by the purportedly selective inhibitor of PKCδ, rottlerin. However, activation of PKCδ with the phorbol ester, phorbol-12-myristate-13-acetate (PMA), failed to promote cell death and down-regulation of PKCδ did not prevent the cytotoxic effects of palmitate. Moreover, rottlerin remained effective as a blocker of the palmitate response in cells depleted of PKCδ. Since rottlerin can inhibit various other kinases in addition to PKCδ, a range of additional kinase inhibitors was also tested. Of these, only the putative Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) inhibitor, KN-62, was found to inhibit palmitate-induced cell death. However, this effect was not reproduced by a more selective pseudo-substrate inhibitor of CaM kinase II. Therefore, the present results reveal that palmitate induces cell death in BRIN-BD11 cells and suggest that this may involve the activation of a rottlerin (and KN-62 -sensitive kinase. However, it is clear that PKCδ is not required for this response. © 2004 Society for Endocrinology.