Targeted protein kinase A and PP-2B regulate insulin secretion through reversible phosphorylation.
Protein kinases and phosphatases play key roles in integrating signals from various insulin secretagogues. In this study, we show that the activities of the cAMP-dependent protein kinase (PKA) and the calcium/calmodulin-dependent phosphatase, PP-2B are coordinated resulting in the regulation of insulin secretion. Transient inhibition of PP-2B, using the immunosuppressant FK506, increased forskolin stimulated insulin secretion by 2.5-fold +/- 0.3 (n = 6) in rat islets and RINm5F cells. Surprisingly, forskolin treatment resulted in the dephosphorylation of the vesicle-associated protein synapsin 1 and increased PP-2B activity by 2.98 +/- 0.97-fold (n = 4). One potential explanation for the observed coordination of PKA and PP-2B activity is their colocalization through a mutual anchoring protein, AKAP79/150. Accordingly, RINm5F cells expressing AKAP79 exhibited decreased insulin secretion, reduced PP-2B activity and were insensitive to FK506. This suggests that AKAP targeting of PKA and PP-2B maintains a signal transduction complex that may regulate reversible phosphorylation events involved in insulin secretion.
Lester
L B
LB
Division of Endocrinology , Oregon Health Sciences University, Portland, Oregon 97201, USA. lesterl@ohsu.edu
Faux
M C
MC
Nauert
J B
JB
Scott
J D
JD
D000818:Animals; D019703:Calcineurin / Q000502:physiology*; D065095:Calcineurin Inhibitors; D002352:Carrier Proteins / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D016572:Cyclosporine / Q000494:pharmacology; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000201:enzymology / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism; D016704:Synapsins / Q000378:metabolism; D016559:Tacrolimus / Q000494:pharmacology
D065095:Calcineurin Inhibitors; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D007328:Insulin; D016704:Synapsins; D016572:Cyclosporine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019703:Calcineurin; D016559:Tacrolimus