Generation of nicotinic acid adenine dinucleotide phosphate and cyclic ADP-ribose by glucagon-like peptide-1 evokes Ca2+ signal that is essential for insulin secretion in mouse pancreatic islets.
OBJECTIVE
Glucagon-like peptide-1 (GLP-1) increases intracellular Ca(2+) concentrations ([Ca(2+)](i)), resulting in insulin secretion from pancreatic beta-cells. The molecular mechanism(s) of the GLP-1-mediated regulation of [Ca(2+)](i) was investigated.


METHODS
GLP-1-induced changes in [Ca(2+)](i) were measured in beta-cells isolated from Cd38(+/+) and Cd38(-/-) mice. Calcium-mobilizing second messengers were identified by measuring levels of nicotinic acid adenine dinucleotide phosphate (NAADP) and cyclic ADP-ribose (ADPR), using a cyclic enzymatic assay. To locate NAADP- and cyclic ADPR-producing enzyme(s), cellular organelles were separated using the sucrose gradient method.


RESULTS
A GLP-1-induced [Ca(2+)](i) increase showed a cooperative Ca(2+) signal, i.e., an initial [Ca(2+)](i) rise mediated by the action of NAADP that was produced in acidic organelles and a subsequent long-lasting increase of [Ca(2+)](i) by the action of cyclic ADPR that was produced in plasma membranes and secretory granules. GLP-1 sequentially stimulated production of NAADP and cyclic ADPR in the organelles through protein kinase A and cAMP-regulated guanine nucleotide exchange factor II. Furthermore, the results showed that NAADP production from acidic organelles governed overall Ca(2+) signals, including insulin secretion by GLP-1, and that in addition to CD38, enzymes capable of synthesizing NAADP and/or cyclic ADPR were present in beta-cells. These observations were supported by the study with Cd38(-/-) beta-cells, demonstrating production of NAADP, cyclic ADPR, and Ca(2+) signal with normal insulin secretion stimulated by GLP-1.


CONCLUSIONS
Our findings demonstrate that the GLP-1-mediated Ca(2+) signal for insulin secretion in pancreatic beta-cells is a cooperative action of NAADP and cyclic ADPR spatiotemporally formed by multiple enzymes.
Kim
Byung-Ju
BJ
Department of Biochemistry, Chonbuk National University Medical School, Keum-am dong, Jeonju, 561-182, Republic of Korea.
Park
Kwang-Hyun
KH
Yim
Chang-Yeol
CY
Takasawa
Shin
S
Okamoto
Hiroshi
H
Im
Mie-Jae
MJ
Kim
Uh-Hyun
UH
D051997:ADP-ribosyl Cyclase 1 / Q000172:deficiency / Q000235:genetics; D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D036563:Cyclic ADP-Ribose / Q000096:biosynthesis*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000502:physiology; D004917:Erythromycin / Q000031:analogs & derivatives / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1 / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008813:Mice, Inbred ICR; D018345:Mice, Knockout; D009249:NADP / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D007328:Insulin; D036563:Cyclic ADP-Ribose; D009249:NADP; C024376:NAADP; D004917:Erythromycin; C057513:erythromycin propionate-N-acetylcysteinate; D052216:Glucagon-Like Peptide 1; D051997:ADP-ribosyl Cyclase 1; D002118:Calcium; D000111:Acetylcysteine