Glucagon-like peptide-1 regulates proliferation and apoptosis via activation of protein kinase B in pancreatic INS-1 beta cells.
OBJECTIVE
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 (3)H-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 Balpha 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
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.
Wang
Q
Q
Department of Physiology, University of Toronto, Toronto, Ontario, Canada.|Department of Medicine, Division of Endocrinology and Metabolism, University of Toronto, Toronto, Ontario, Canada.|St Michael's Hospital, University of Toronto, Toronto, Ontario, Canada.
Li
L
L
Department of Physiology, University of Toronto, Toronto, Ontario, Canada.
Xu
E
E
Department of Physiology, University of Toronto, Toronto, Ontario, Canada.|St Michael's Hospital, University of Toronto, Toronto, Ontario, Canada.
Wong
V
V
Department of Physiology, University of Toronto, Toronto, Ontario, Canada.
Rhodes
C
C
Pacific Northwest Research Institute, Seattle, Washington, USA.
Brubaker
P L
PL
Department of Physiology, University of Toronto, Toronto, Ontario, Canada. p.brubaker@utoronto.ca.|Department of Medicine, Division of Endocrinology and Metabolism, University of Toronto, Toronto, Ontario, Canada. p.brubaker@utoronto.ca.|Room 3366, Medical Sciences Building, University of Toronto, Toronto, Ontario, M5S 1A8, Canada. p.brubaker@utoronto.ca.
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D007328:Insulin / Q000032:analysis / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D010446:Peptide Fragments / Q000494:pharmacology*; D011498:Protein Precursors / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019311:Staurosporine / Q000494:pharmacology
D007328:Insulin; D010446:Peptide Fragments; D011498:Protein Precursors; D011518:Proto-Oncogene Proteins; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019311:Staurosporine