Cyclin D1 activation through ATF-2 in Reg-induced pancreatic β-cell regeneration

Regenerating gene product (Reg) is induced in pancreatic β-cells and acts as an autocrine/paracrine growth factor for regeneration via a cell surface Reg receptor. However, the manner by which Reg induces β-cell regeneration was unknown. In the present study, we found that Reg increased phospho-ATF-2, which binds to −57 to −52 of the cyclin D1 gene to activate the promoter. The Reg/ATF-2-induced cyclin D1 promoter activation was attenuated by PI(3)K inhibitors such as LY294002 and wortmannin. In Reg knockout mouse islets, the levels of phospho-ATF-2, cyclin D1, and phospho-Rb were greatly decreased. These results indicate that the Reg–Reg receptor system stimulates the PI(3)K/ATF-2/cyclin D1 signaling pathway to induce β-cell regeneration.