Aims/hypothesis  

The incretin hormone glucagon-like peptide-1 augments islet cell mass in vivo by increasing proliferation and decreasing apoptosis of the beta cells. However, the signalling pathways that mediate these effects are mostly unknown. Using a clonal rat pancreatic beta cell line (INS-1), we examined the role of protein kinase B in mediating beta-cell growth and survival stimulated by glucagon-like peptide-1.

Methods  

Immunoblot analysis was used to detect active (phospho-) and total protein kinase B. Proliferation was assessed using ³H-thymidine incorporation, while apoptosis was quantitated using 4-6-diamidino-2-phenylindole staining and APO percentage apoptosis assay. Kinase-dead and wild-type protein kinase B was introduced into cells using adenoviral vectors.

Results  

Glucagon-like peptide-1 rapidly activated protein kinase B in INS-1 cells (by 2.7±0.7-fold, p<0.05). This effect was completely abrogated by inhibition, with wortmannin, of the upstream activator of protein kinase B, phosphatidylinositol-3-kinase. Glucagon-like peptide-1 also stimulated INS-1 cell proliferation in a dose-dependent manner (by 1.8±0.5-fold at 10^–7 mol/l, p<0.01), and inhibited staurosporine-induced apoptosis (by 69±12%, p<0.05). Both of these effects were also prevented by wortmannin treatment. Ablation of protein kinase B by adenovirus-mediated overexpression of the kinase-dead form of protein kinase B prevented protein kinase B phosphorylation and completely abrogated both cellular proliferation (p<0.05) and protection from drug-induced cellular death (p<0.01) induced by glucagon-like peptide-1.

Conclusions/interpretation  

These results identify protein kinase B as an essential mediator linking the glucagon-like peptide-1 signal to the intracellular machinery that modulates beta-cell growth and survival.