Exendin-4 Stimulation of Cyclin A2 in β-Cell Proliferation

Abstract

OBJECTIVE-␤-Cell proliferation is an important mechanism underlying ␤-cell mass adaptation to metabolic demands. We have examined effects, in particular those mediated through intracellular cAMP signaling, of the incretin hormone analog exendin-4 on cell cycle regulation in ␤-cells.RESEARCH DESIGN AND METHODS-Changes in islet protein levels of cyclins and of two critical cell cycle regulators cyclin kinase inhibitor p27 and S-phase kinase-associated protein 2 (Skp2) were assessed in mice treated with exendin-4 and in a mouse model with specific upregulation of nuclear cAMP signaling exhibiting increased ␤-cell proliferation (CBP-S436A mouse). Because cyclin A2 was stimulated by cAMP, we assessed the role of cylcin A2 in cell cycle progression in Min6 and isolated islet ␤-cells.RESULTS-Mice treated with exendin-4 showed increased ␤-cell proliferation, elevated islet protein levels of cyclin A2 with unchanged D-type cyclins, elevated PDX-1 and Skp2 levels, and reduced p27 levels. Exendin-4 stimulated cyclin A2 promoter activity via the cAMP-cAMP response element binding protein pathway. CBP-S436A islets exhibited elevated cyclin A2, reduced p27, and no changes in D-type cyclins, PDX-1, or Skp2. In cultured islets, exendin-4 increased cyclin A2 and Skp2 and reduced p27. Cyclin A2 overexpression in primary islets increased proliferation and reduced p27. In Min6 cells, cyclin A2 knockdown prevented exendin-4 -stimulated proliferation. PDX-1 knockdown reduced exendin-4 -stimulated cAMP synthesis and cyclin A2 transcription.CONCLUSIONS-Cyclin A2 is required for ␤-cell proliferation, exendin-4 stimulates cyclin A2 expression via the cAMP pathway, and exendin-4 stimulation of cAMP requires PDX-1. Diabetes 57:2371-2381, 2008 P ancreatic ␤-cell mass is dynamic and responds to variations in metabolic demand on insulin production. The inability of the endocrine pancreas to adapt to changing insulin demand (inadequate ␤-cell mass) is found both in type 1 and type 2 diabetes. Increasing ␤-cell mass by regeneration may ameliorate or correct both type 1 and 2 diabetes (1). Within the pancreas, ␤-cells regenerate predominantly by ␤-cell replication (2,3). In this context, insight into the mechanisms underlying ␤-cell proliferation and cell cycle regulation, may provide potential targets for therapy in situations of inadequate ␤-cell mass.The incretin hormone glucagon-like peptide-1 (GLP-1) and its long-acting peptide analog exendin-4 stimulate ␤-cell proliferation in vitro and in vivo (4), leading to increased ␤-cell mass in rodents and amelioration of glucose metabolism in diabetic animal models and human diabetic subjects (4). Downstream effectors of the GLP-1 signaling to the cell nucleus include 1) the epidermal growth factor receptor-phosphoinositol 3-kinase (PI 3-kinase)-protein kinase B (PKB/Akt)-forkhead box transcription factor O1 (FoxO1) pathway (5) and 2) the cAMP-protein kinase A (PKA)-cAMP response element binding protein (CREB) pathway (4). Activation of the PI 3-kinase pathway results in phosphorylation and nuclear...

iPSC-derived β cells model diabetes due to glucokinase deficiency

“…To further improve differentiation conditions from pancreatic progenitor to β cells, exendin-4, a glucagon-like peptide-1 agonist, and SB431542, a TGF-β signaling inhibitor, were added to stage 3 progenitor cells. Both of these additions enhanced the differentiation efficiency of β cells to 4.6% and 8.2% (C-peptide + ), respectively, consistent with previous observations (21)(22)(23). A combination of exendin-4 and SB431542 treatment from day 9 to day 12 produced the highest percentage of β cells (15%) ( Figure 2D).…”

Nupr1 deletion protects against glucose intolerance by increasing beta cell mass

“…This conclusion is further supported by our demonstration that transient overexpression of NUPR1 reduced the rate of MIN6 beta cell proliferation in parallel with inhibiting expression of the cell cycle regulators Ccna2 and Tcf19 through effects to suppress their promoter activities in beta cells. The Ccna2 gene regulates progression at both the G1/S and G2/M checkpoints of the cell cycle [27,28] and lentiviral-mediated infection of islets to overexpress Ccna2 stimulates beta cell self-replication [20]. The TCF19 protein contains a sequence exhibiting characteristics of transcription factors and its expression is regulated in the late stages of the cell cycle [21], consistent with it playing a regulatory role in the expression of genes necessary for cell cycle progression.…”

“…Given the increased islet mass with Nupr1 deletion, attention was focused on genes known to regulate the cell cycle. Messenger RNAs for cyclin A2, which has been identified as a target in the regulation of beta cell mass [20], and TCF19, which has been implicated in regulating genes involved in the later stages of cell cycle progression [21], emerged as possible candidates. Our array analysis indicated that Ccna2 and Tcf19 mRNAs were increased by 1.6-fold (p <0.0004) and 1.9-fold (p =0.00002), respectively, in Nupr1 −/− islets.…”

Exendin-4 stimulates islet cell replication via the IGF1 receptor activation of mTORC1/S6K1

“…Previous studies have implicated both cAMP- (Buteau et al 2003, Song et al 2008) and b-arrestin (Talbot et al 2012)-dependent mechanisms in the proliferative effects of GLP1 on pancreatic b-cells. In addition, it has been reported that the proliferative action of GLP1 is mediated by the transactivation of epidermal growth factor receptor (EGFR; Buteau et al 2003) or the increased expression and activation of the insulin-like growth factor 1 receptor (IGF1R) (Cornu et al 2010) both of which result in the activation of the PI3K/protein kinase B (PKB) pathway.…”