Effects of overexpression of pancreatic derived factor (FAM3B) in isolated mouse islets and insulin-secreting βTC3 cells

Abstract

PANcreatic DERived factor (PANDER, FAM3B) is a recently discovered islet-specific cytokine. We have previously shown that, in vitro, truncated recombinant PANDER isoforms (20 and 21 kDa) are cytotoxic to β-cell lines but the effects of full-length PANDER on islet biology remain unclear. In this study, we used adenovirus (Ad-PANDER) to overexpress full-length cDNA of PANDER in islets and βTC3 cells. βTC3 cells were infected with Ad-PANDER or control vector. After 48 h, cell viability was significantly decreased as evaluated by MTT assay. The number of dead cells was significantly increased as indicated by the fluorescent intensity of the propidium iodide-stained cells (160 ± 13 vs. control 100 ± 7%, P = 0.001). Flow cytometric Tunel assay showed that overexpressing PANDER induced a significant fourfold increase in β-cell apoptosis (19.4 ± 6.3 vs. control 4.1 ± 0.8%, P < 0.05). There was a significant increase in the number of annexin V-positive (apoptotic) cells and propidium iodide-positive (dead) cells in mouse islets infected with Ad-PANDER compared with control cells infected with Ad-LacZ. Addition of 4 nM recombinant PANDER protein to βTC3 cells or infection of Ad-PANDER did not affect Akt and STAT1 phosphorylation, Bcl-2, Fas, and NF-κB protein levels. However, activation of caspase-3 was observed in βTC3 and islets infected with Ad-PANDER. Overexpression of PANDER in mouse islets or addition of recombinant PANDER decreased insulin secretion induced by carbachol plus glucose or high potassium but not that by glucose alone. Culture with recombinant PANDER did not affect glucose-induced NAD(P)H elevation in mouse islets. In conclusion, Ad-PANDER infection is as effective as truncated recombinant PANDER to induce βTC3 cell and mouse islet apoptosis.