Exendin-4 stimulation of cyclin A2 in beta-cell proliferation.
OBJECTIVE
Beta-cell proliferation is an important mechanism underlying beta-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 beta-cells.


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 beta-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 beta-cells.


RESULTS
Mice treated with exendin-4 showed increased beta-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 beta-cell proliferation, exendin-4 stimulates cyclin A2 expression via the cAMP pathway, and exendin-4 stimulation of cAMP requires PDX-1.
Metabolism Division, Departments of Pediatrics and Medicine, Johns Hopkins University, Baltimore, Maryland, USA.
Woo-Jin
WJ
Song
Weston E
WE
Schreiber
Enhong
E
Zhong
Fei-Fei
FF
Liu
Benjamin D
BD
Kornfeld
Fredric E
FE
Wondisford
Mehboob A
MA
Hussain
D000818:Animals; D050882:CREB-Binding Protein / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D019925:Cyclin A / Q000235:genetics / Q000378:metabolism*; D056751:Cyclin A2; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D000077270:Exenatide; D018398:Homeodomain Proteins / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D016086:Lentivirus / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D010455:Peptides / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000502:physiology; D044786:S-Phase Kinase-Associated Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D014688:Venoms / Q000494:pharmacology*
C508184:CCNA2 protein, mouse; D019925:Cyclin A; D056751:Cyclin A2; D018398:Homeodomain Proteins; D007004:Hypoglycemic Agents; D010455:Peptides; D044786:S-Phase Kinase-Associated Proteins; D015534:Trans-Activators; D014688:Venoms; C084010:pancreatic and duodenal homeobox 1 protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000077270:Exenatide; D000242:Cyclic AMP; D050882:CREB-Binding Protein; C494364:Crebbp protein, mouse; D019869:Phosphatidylinositol 3-Kinases