Relationship of cAMP and calcium messenger systems in prostaglandin-stimulated UMR-106 cells.
The effect of prostaglandins (PG) on free cytosolic calcium concentrations [( Ca2+]i) and cAMP levels was studied in the osteosarcoma cell line UMR-106. PGF2 alpha and PGE2, but not 6-keto-PGF1 alpha, induced an increase in [Ca2+]i which was mainly due to Ca2+ release from intracellular stores. The EC50 for PGF2 alpha was approximately 7 nM, whereas that for PGE2 was approximately 1.8 microM. Maximal doses of PGF2 alpha increased [Ca2+]i to higher levels than PGE2. Both active PGs also stimulated phosphatidylinositol turnover in UMR-106 cells. The effects of the two PGs were independent of each other and appear to involve separate receptors for each PG. PGE2 was a very potent stimulator of cAMP production and increased cAMP by approximately 80-fold with an EC50 of 0.073 microM. PGF2 alpha was a very poor stimulator of cAMP production; 25 microM PGF2 alpha increased cAMP by 5-fold. The increase in cellular cAMP levels activated a plasma membrane Ca2+ channel which resulted in a secondary, slow increase in [Ca2+]i. High concentrations of both PGs (10-50 microM) inhibited this channel independent of their effect on cAMP levels. Pretreatment of the cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate inhibited the PG-mediated increase in phosphatidylinositol turnover and the increase in [Ca2+]i. However, pretreatment with 12-O-tetradecanoyl-13-acetate had no effect on the PGE2-mediated increase in cAMP. The latter finding, together with the dose responses for PGE2-mediated increases in [Ca2+]i and cAMP levels, suggests the presence of two subclasses of PGE2 receptors: one coupled to adenylate cyclase and the other to phospholipase C. With respect to osteoblast function, the cAMP signaling system is antiproliferative, whereas the Ca2+ messenger system, although having no proliferative effect by itself, tempers cAMP's antiproliferative effect.
Yamaguchi
D T
DT
Research and Medical Services, Veterans Administration Center, West Los Angeles, California 90073.
Hahn
T J
TJ
Beeker
T G
TG
Kleeman
C R
CR
Muallem
S
S
D015121:6-Ketoprostaglandin F1 alpha / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D015237:Dinoprost; D015232:Dinoprostone; D004987:Ethers / Q000494:pharmacology; D015759:Ionomycin; D007700:Kinetics; D012516:Osteosarcoma; D011453:Prostaglandins / Q000494:pharmacology*; D011458:Prostaglandins E / Q000494:pharmacology; D011460:Prostaglandins F / Q000494:pharmacology
D004987:Ethers; D011453:Prostaglandins; D011458:Prostaglandins E; D011460:Prostaglandins F; D015759:Ionomycin; D015121:6-Ketoprostaglandin F1 alpha; D015237:Dinoprost; D000242:Cyclic AMP; D015232:Dinoprostone; D002118:Calcium