Abstract
Regenerating gene (Reg) family protein Reg3α is normally expressed in pancreatic acinar and endocrine cells. In order to explore its effect on islet β-cell replication, insulinoma MIN6 cells were stably transfected with murine Reg3α cDNA. Determined using real-time PCR and Western blots, the levels of Reg3α mRNA and protein in Reg3α-transfected clones were increased 10- and 6-fold, respectively. Western blots also revealed that the protein was released into the culture medium, consistent with an endocrine effect. In MTT cell proliferation assay, Reg3α-overexpressing cells exhibited a 2-fold increase in the rate of cell growth. In order to investigate the intracellular mechanism, we studied cell cycle regulatory proteins. In Reg3α-expressing cells, we detected 2.2- and 2.5-fold increased levels of cyclin D1 and CDK4, respectively, which paralleled a 1.8-fold increase in the rate of Akt phosphorylation. It is established that β-cell replication is associated with increased cyclin D1 and CDK4 levels; deficiency in CDK4 or cyclin D2 results in reduced β-cell mass and diabetes. Our results suggest that Reg3α stimulates β-cell replication, by activating Akt kinase and increasing the levels of cyclin D1/CDK4.