1,25(OH)2-vitamin D-3 stimulates phospholipase A2 activity via a guanine nucleotide-binding protein in chick myoblasts.
The steroid hormone 1,25(OH)2-vitamin D-3 [1,25(OH)2D3] stimulated phospholipase A2 (PLA2) activity in embryonic chick myoblasts releasing [3H]arachidonic acid from the sn-2 position of phospholipids. GTP-binding protein mediation of 1,25(OH)2D3-dependent PLA2 activity was investigated in cells prelabeled with [3H]arachidonic acid. AIF4-, a G-protein activator, mimicked 1,25(OH)2D3-stimulated arachidonic acid release from myoblasts in a dose-dependent manner. Consistent with the involvement of a G-protein in the activation of PLA2 by the hormone, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), a stable GTP analogue which activates G-protein mediated signals, strongly enhanced arachidonic acid release in myoblasts. Guanosine 5'-O-(2-thiodiphosphate) (GDP beta S), which competitively inhibits G-protein activation by GTP and its analogues, abolished 1,25(OH)2D3-dependent arachidonic acid release. Bordetella pertussis toxin pretreatment significantly suppressed the hormone action whereas cholera toxin had minor effects on 1,25(OH)2D3 action. Hormone-induced activation of PLA2 was mimicked by the Ca2+ ionophore A23187 and blocked by nifedipine, but was unaffected by neomycin, a phospholipase C inhibitor, ruling out the contribution of phosphoinositide metabolism to arachidonic acid release. These results suggest that 1,25(OH)2D3-stimulation of PLA2 activity in embryonic chick myoblasts is mediated by a pertussis toxin-sensitive GTP-binding protein coupled to influx of extracellular calcium.
De Boland
A R
AR
Departamento Biologia, Universidad Nacional del Sur, Bahia Blanca, Argentina.
Morelli
S
S
Boland
R
R
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002117:Calcitriol / Q000494:pharmacology*; D002478:Cells, Cultured; D002642:Chick Embryo; D002772:Cholera Toxin / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000201:enzymology*; D009543:Nifedipine / Q000494:pharmacology; D010539:Permeability; D037342:Pertussis Toxin; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D010743:Phospholipids / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D012503:Saponins / Q000494:pharmacology; D012969:Sodium Fluoride / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D010743:Phospholipids; D012503:Saponins; D010566:Virulence Factors, Bordetella; D016718:Arachidonic Acid; D000001:Calcimycin; D012969:Sodium Fluoride; D002772:Cholera Toxin; D037342:Pertussis Toxin; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D019204:GTP-Binding Proteins; D002117:Calcitriol; D009543:Nifedipine