Novel Insights into the Global Proteome Responses of Insulin-Producing INS-1E Cells To Different Degrees of Endoplasmic Reticulum Stress

Exposure of insulin-secreting beta-cells to inflammatory cytokines or high concentrations of free fatty acids, factors involved in the pathogenesis of type 1 and type 2 diabetes, leads to endoplasmic reticulum (ER) stress, beta-cell dysfunction, and eventually apoptotic beta-cell death. The aim of this study was to investigate the impact of ER stress on beta-cells at the protein level to evaluate the contribution of post-transcriptional and post-translational changes in ER stress-induced beta-cell damage. INS-1E cells were exposed in vitro to the ER-stress inducer cyclopiazonic acid (CPA) at two concentrations, and protein changes were evaluated using 2D-DIGE. CPA, 25 mu M, led to massive apoptosis, accompanied by a near complete protein translation shut-down. CPA, 6.25 mu M, led to adaptation of the beta-cells to ER stress. Identification of the differentially expressed proteins in the two conditions led to the discovery of a clear pattern of defense pathways, with post-translational modifications playing a crucial role. Key alterations included inhibition of insulin translation and post-translational modifications in ER chaperones HYOU1 and HSPA5. Also, a central role for 14-3-3 proteins is suggested. In conclusion, INS-1E cells are highly sensitive to ER stress, leading to important post-transcriptional and post-translational modifications that may contribute to beta-cell dysfunction and death.