Fuel and hormone regulation of phospholipase C beta 1 and delta 1 overexpressed in RINm5F pancreatic beta cells.
The mechanism by which glucose and other fuels stimulate phosphoinositide-specific phospholipase C (PLC) in pancreatic islet beta cells is not known. Previous studies have suggested that glucose may couple to PLC beta 1 and PLC delta 1. To determine directly if fuels activate these PLC isozymes, clones stably overexpressing PLC beta 1 or PLC delta 1 were generated in the fuel-sensitive beta cell line RINm5F, and secretagogue regulation of these PLC isoforms was determined. Overexpression of PLC beta 1 or PLC delta 1 significantly increased PLC activity in isolated cell fractions, consistent with overexpression of active PLC isoforms in these clones. In paired experiments, stimulation of inositol phosphate (IP) accumulation by the fuel glyceraldehyde was enhanced in clones overexpressing PLC beta 1, in parallel with the G-protein alpha subunit activator, AlF(4)(-), suggesting a coupling between glyceraldehyde and this PLC isoform. In contrast, overexpression of PLC delta 1 had no effect on glyceraldehyde- or AlF(4)(-)-stimulated IP accumulation. Similarly, IP accumulation stimulated by ionomycin was enhanced in PLC beta 1, but not PLC delta 1 clones, indicating that increases in intracellular free calcium [Ca(2+)](i) can regulate PLC beta 1 but not PLC delta 1 overexpressed in this cell line. Interestingly, [Arg(8)] vasopressin-stimulated, but not carbachol-stimulated, IP accumulation was significantly increased in clones overexpressing either PLC beta 1 or PLC delta 1. These studies illustrate unique pathways coupling diverse secretagogues to specific PLC isoforms in islet beta cells, and demonstrate that glyceraldehyde can activate PLC beta 1 but not PLC delta 1; whereas, vasopressin, but not carbachol, can stimulate either isoform.
Kelley
G G
GG
Department of Medicine, SUNY Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA. kelleyg@mail.upstate.edu
Ondrako
J M
JM
Reks
S E
SE
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D005985:Glyceraldehyde / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000201:enzymology*; D007527:Isoenzymes / Q000187:drug effects / Q000378:metabolism*; D054799:Phospholipase C beta; D054803:Phospholipase C delta; D051381:Rats; D014162:Transfection; D010738:Type C Phospholipases / Q000187:drug effects / Q000378:metabolism*; D014667:Vasopressins / Q000494:pharmacology*
D007295:Inositol Phosphates; D007328:Insulin; D007527:Isoenzymes; D014667:Vasopressins; D005985:Glyceraldehyde; D002217:Carbachol; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D054803:Phospholipase C delta; C518035:Plcb1 protein, rat; C518026:Plcd1 protein, rat