Pseudosubstrate inhibition of cyclic AMP-dependent protein kinase in intact pancreatic islets: effects on cyclic AMP-dependent and glucose-dependent insulin secretion.
Synthetic peptides derived from the endogenous protein kinase A inhibitor (PKI) offer a specific means of inhibiting cyclic AMP-dependent protein kinase A (PKA), but their use in whole cells is restricted by the plasma membrane. We have now modified PKI sequences by N-terminal myristoylation to enhance their membrane permeability, and have used the myristoylated (myr) peptides to investigate the role of PKA activation in glucose-induced insulin secretion from intact pancreatic beta-cells. The myristoylated PKI peptides, myr PKI14-22 and myrPKI6-22, were effective inhibitors in vitro of PKA activity extracted from rat islets of Langerhans. In experiments using intact islets, myr PKI14-22 caused a concentration-dependent inhibition of insulin secretion in response to the PKA activators dibutyryl cyclic AMP and forskolin, suggesting that it gained access to the cytosolic compartment of intact beta-cells and inhibited PKA in situ. However, these concentrations of myr PKI14-22 did not inhibit insulin secretion in response to glucose suggesting that the activation of PKA is not required for the initiation of glucose-induced insulin secretion.
Harris
T E
TE
Biomedical Sciences Division, King's College London, United Kingdom.
Persaud
S J
SJ
Jones
P M
PM
D000818:Animals; D002352:Carrier Proteins / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D047908:Intracellular Signaling Peptides and Proteins; D007515:Islets of Langerhans / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity
D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; C094636:protein kinase inhibitor (6-22); D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D005947:Glucose