cAMP-regulated guanine nucleotide exchange factor II (Epac2) mediates Ca2+-induced Ca2+ release in INS-1 pancreatic beta-cells.
1. The signal transduction pathway responsible for cAMP-dependent Ca2+-induced Ca2+ release (CICR) from endoplasmic reticulum Ca2+ stores was assessed in the insulin-secreting cell line INS-1. 2. CICR was triggered by the GLP-1 receptor agonist exendin-4, an effect mimicked by caffeine, Sp-cAMPS or forskolin. CICR required influx of Ca2+ through L-type voltage-dependent Ca2+ channels, and was blocked by treatment with nimodipine, thapsigargin, or ryanodine, but not by the IP3 receptor antagonist xestospongin C. 3. Treatment with the cAMP antagonist 8-Br-Rp-cAMPS blocked CICR in response to exendin-4, whereas the PKA inhibitor H-89 was ineffective when tested at a concentration demonstrated to inhibit PKA-dependent gene expression. 4. RT-PCR of INS-1 cells demonstrated expression of mRNA coding for the type-II isoform of cAMP-regulated guanine nucleotide exchange factor (cAMP-GEF-II, Epac2). 5. CICR in response to forskolin was blocked by transient transfection and expression of a dominant negative mutant isoform of cAMP-GEF-II in which inactivating mutations were introduced into the exchange factor's two cAMP-binding domains. 6. It is concluded that CICR in INS-1 cells results from GLP-1 receptor-mediated sensitization of the intracellular Ca2+ release mechanism, a signal transduction pathway independent of PKA, but which requires cAMP-GEF-II.
Kang
G
G
Department of Physiology and Neuroscience, New York University School of Medicine, New York, NY 10016, USA.
Chepurny
O G
OG
Holz
G G
GG
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology; D000077270:Exenatide; D015870:Gene Expression / Q000502:physiology; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D007340:Insulinoma; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007515:Islets of Langerhans / Q000378:metabolism*; D010190:Pancreatic Neoplasms; D010455:Peptides / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D014688:Venoms
D020662:Guanine Nucleotide Exchange Factors; D010455:Peptides; D010726:Phosphodiesterase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D014688:Venoms; D005576:Colforsin; D002110:Caffeine; D000077270:Exenatide; D000242:Cyclic AMP; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium