Mechanisms of Glucose-induced Secretion of Pancreatic-derived Factor (PANDER or FAM3B) in Pancreatic Beta-cells

Pancreatic-derived factor (PANDER) is an islet-specific cytokine present in both pancreatic alpha- and beta-cells, which, in vitro, induces beta-cell apoptosis of primary islet and cell lines. In this study, we investigated whether PANDER is secreted by pancreatic alpha- and beta-cells and whether PANDER secretion is regulated by glucose and other insulin secretagogues. In mouse-derived insulin-secreting beta-TC3 cells, PANDER secretion in the presence of stimulatory concentrations of glucose was 2.8 +/- 0.4-fold higher (P < 0.05) than without glucose. Insulin secretion was similarly increased by glucose in the same cells. The total concentration of secreted PANDER in the medium was approximately 6-10 ng/ml (0.3-0.5 nmol/l) after a 24-h culture with glucose. L-Glucose failed to stimulate PANDER secretion in beta-TC3 cells. KCl stimulated PANDER secretion 2.1 +/- 0.1-fold compared with control without glucose. An L-type Ca2+ channel inhibitor, nifedipine, completely blocked both glucose- or KCl-induced insulin and PANDER secretion. In rat-derived INS-1 cells, glucose (20 mmol/l) stimulated PANDER secretion 4.4 +/- 0.9-fold, while leucine plus glutamine stimulated 4.4 +/- 0.7-fold compared with control without glucose. In mouse islets overexpressing PANDER, glucose (20 mmol/l) stimulated PANDER secretion 3.2 +/- 0.5-fold (P < 0.05) compared with basal (3 mmol/l glucose). PANDER was also secreted by alpha-TC3 cells but was not stimulated by glucose. Mutations of cysteine 229 or of cysteines 91 and 229 to serine, which may form one disulfide bond, and truncation of the COOH-terminus or NH2-terminus of PANDER all resulted in failure of PANDER secretion, even though these mutant or truncated PANDERs were highly expressed within the cells. In conclusion, we found that 1) PANDER is secreted from both pancreatic alpha- and beta-cells, 2) glucose stimulates PANDER secretion dose dependently in beta-cell lines and primary islets but not in alpha-cells, 3) PANDER is likely cosecreted with insulin via the same regulatory mechanisms, and 4) structure and conformation is vital for PANDER secretion.