Overexpression of Reg3α increases cell growth and the levels of cyclin D1 and CDK4 in insulinoma cells

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; deficie...