Increasing GLP-1-induced β-cell proliferation by silencing the negative regulators of signaling cAMP response element modulator-α and DUSP14

OBJECTIVE-Glucagon-like peptide-1 (GLP-1) is a growth and differentiation factor for mature beta-cells and their precursors. However, the overall effect of GLP-1 on increasing beta-cell mass in both in vivo and in vitro conditions is relatively small, and augmenting this effect would be beneficial for the treatment or prevention of type 1 and type 2 diabetes. Here, we searched for cellular mechanisms that may limit the proliferative effect of GLP-1 and tested whether blocking them could increase P-cell proliferation. RESEARCH DESIGN AND METHODS-We examined GLP-1-regulated genes in beta TC-Tet cells by cDNA raicroarrays. To assess the effect of some of these gene on cell proliferation, we reduced their expression using small heterogenous RNA in P-cell lines and primary mouse islets and measured [H-3]thymidine or 5'-bromo-2'-deoxyuridine incorporation. RESULTS-We identified four negative regulators of intracellular signaling that were rapidly and strongly activated by GLP-1: the regulator of G-protein-signaling RGS2; the cAMP response element-binding protein (CREB) antagonists cAMP response element modulator (CREM)-alpha. and ICERI; and the dual specificity phosphatase DUSP14, a negative regulator of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase 1/2 (ERK1/2) pathway. We show that knockdown of CREM alpha or DUSP14 or expression of a dominant-negative form of DUSP14 increased P-cell line proliferation and enhanced the GLP-1-induced proliferation of primary beta-cells. CONCLUSIONS-Together, our data show that 1) the cAMP/ protein kinase A/CREB and MAPK/ERK1/2 pathways can additively control beta-cell proliferation, 2) beta-cells have evolved several mechanisms limiting GLP-1-induced cellular proliferation, and 3) blocking these mechanisms increases the positive effect of GLP-1 on beta-cell mass.