title: Modulation by retinoic acid of 1,25-dihydroxyvitamin D3 effects on alkaline phosphatase activity and parathyroid hormone responsiveness in an osteoblast-like osteosarcoma cell line.
abstract: Based on the finding that retinoic acid (RA) increases 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] receptor number in ROS 17/2 cells, we investigated the effects of RA on the ability of 1,25-(OH)2D3 to regulate alkaline phosphatase activity and PTH-responsive adenylate cyclase in these cells. A maximally effective dose of 1,25-(OH)2D3 (10(-8) M) caused a 75-80% increase in alkaline phosphatase activity and an approximately 70-75% attenuation of the cAMP response to PTH, while RA (10(-6) M) decreased alkaline phosphatase activity by 30-45% and decreased PTH-stimulated cAMP levels by approximately 20%. Preincubation with RA did not enhance the 1,25-(OH)2D3-induced increases in alkaline phosphatase activity. The ED50 values for control and RA-treated cultures were approximately 8 X 10(-10) M and 6 X 10(-10) M, respectively. With regard to PTH responsiveness, the effects of RA preincubation on the 1,25-(OH)2D3 attenuation of cAMP response varied with the concentration of 1,25-(OH)2D3. At low doses (less than 10(-9) M), the effects of 1,25-(OH)2D3 and RA were additive. At higher doses of 1,25-(OH)2D3, the effects of RA and 1,25-(OH)2D3 were not additive, and there were no differences between control- and RA-treated cultures. The ED50 values for control- and RA-treated cultures were 10(-10) M and 3 X 10(-11) M, respectively. None of the above effects were observed using equimolar doses of the vitamin D3 metabolites 24,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3. The data show that pretreating ROS 17/2A cells with RA to increase 1,25-(OH)2D3 receptors does not correspond with a concomitant increase in the cellular responsiveness to 1,25-(OH)2D3, as measured by increases in alkaline phosphatase activity and decreases in PTH-responsive adenylate cyclase.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002117:Calcitriol / Q000378:metabolism / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D007700:Kinetics; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology; D012516:Osteosarcoma / Q000201:enzymology*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D051381:Rats; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D010281:Parathyroid Hormone; D014212:Tretinoin; D000242:Cyclic AMP; D000469:Alkaline Phosphatase; D000262:Adenylyl Cyclases; D002117:Calcitriol