CIDEB RNAi program

Excessive accumulation of long‐chain fatty acids in the pancreatic islets is associated with beta cell dysfunction and ultimately contributes to the pathogenesis of type 2 diabetes. It has been well proved that the cell death‐inducing DFF45‐like effector b (Cideb) is involved in cell apoptosis and lipid metabolism. However, the expression and function of Cideb in endocrine pancreas remain to be investigated.

By using reverse transcript polymerase chain reaction, immunohistochemistry and Western blot, we observed the expression of Cideb in pancreas tissues and clonal beta‐cell lines. The physiological role of Cideb was examined under the free fatty acid (FFA) administration and Cideb ribonucleic acid interference, and further analysis on apoptosis was measured by terminal deoxynucleotidyl transferase‐mediated deoxyuridine triphosphate nick end labelling assay and caspase‐3 activity. Nile red staining and quantitative evaluation of triglyceride were used to detect the lipid accumulation. The changes in esterification of FFA were traced by radiolabelled palmitate.

Cideb was abundantly expressed in pancreas and mainly localized in beta cells. FFAs, especially palmitate, induced an obvious increase of Cideb expression in beta cell lines. Adenoviral‐mediated overexpression of Cideb increased the apoptosis, whereas ribonucleic acid interference‐based Cideb depletion in beta‐TC3 cells had no effect on apoptosis in normal condition. Palmitate supplementation led to beta cell lipoapoptosis, and Cideb silencing exacerbated the apoptosis induced by palmitate, reduced intracellular triglyceride content and aggravated FFA overload in beta cells.

The present results suggest that increased Cideb expression upon palmitate exposure may be involved in beta cell lipoapoptosis through its influence on conversion of FFAs to lipid esters in lipid droplets. Copyright © 2011 John Wiley & Sons, Ltd.

DFF45 is a subunit of the DNA fragmentation factor (DFF) that is cleaved by caspase-3 during apoptosis. However, the mechanism by which DFF45 regulates apoptotic cell death remains poorly understood. Here we report the identification and characterization of two mammalian genes, CIDE-A and CIDE-B, encoding highly related proteins with homology to the N-terminal region of DFF45. CIDE-A and CIDE-B were found to activate apoptosis in mammalian cells, which was inhibited by DFF45 but not by caspase inhibitors. Expression of CIDE-A induced DNA fragmentation in 293T cells, which was inhibited by DFF45, further suggesting that DFF45 inhibits the apoptotic activities of CIDEs. In addition to mammalian CIDE-A and CIDE-B, we identified DREP-1, a Drosophila melanogaster homolog of DFF45 that could inhibit CIDE-A-mediated apoptosis. Mutant analysis revealed that the C-terminal region of CIDE-A was necessary and sufficient for killing whereas the region with homology to DFF45 located in the N-terminus was required for DFF45 to inhibit CIDE-A-induced apoptosis. CD95/Fas-mediated apoptosis was enhanced by CIDEs but inhibited by DFF45. These studies suggest that DFF45 is evolutionarily conserved and implicate CIDEs as DFF45-inhibitable effectors that promote cell death and DNA fragmentation.