Localization of vitamin D3-responsive alkaline phosphatase in cultured chondrocytes.
Alkaline phosphatase activity appears to be altered when chondrocyte cultures are incubated with 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). This study examined whether the hormone-responsive enzyme activity is associated with alkaline phosphatase-enriched extracellular membrane organelles called matrix vesicles. Confluent, third passage cultures of rat costochondral growth cartilage (GC) or resting zone chondrocytes (RC) were incubated with 1,25-(OH)2D3 or 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3) and enzyme specific activity was assayed in the cell layer or in isolated matrix vesicle and plasma membrane fractions. Alkaline phosphatase-specific activity in the matrix vesicles was enriched at least 2-fold over that of the plasma membrane and 10-fold over that of the cell layer. Matrix vesicle alkaline phosphatase was stimulated by 1,25-(OH)2D3 in GC cultures and by 24,25-(OH)2D3 in RC cultures. The cell layer failed to reveal these subtle differences. 1,25-(OH)2D3 increased GC enzyme activity but the effect was one-half that observed in the matrix vesicles alone. No effect of 1,25-(OH)2D3 on enzyme activity of the RC cell layer or of 24,25-(OH)2D3 on either GC or RC cell layers was detected. Thus, response to the metabolites is dependent on chondrocytic differentiation and is site specific: the matrix vesicle fraction is targeted and not the cells per se.
Schwartz
Z
Z
Department of Periodontics, University of Texas Health Science Center, San Antonio 78284.
Knight
G
G
Swain
L D
LD
Boyan
B D
BD
D015650:24,25-Dihydroxyvitamin D 3; D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002356:Cartilage / Q000201:enzymology*; D002478:Cells, Cultured; D004100:Dihydroxycholecalciferols / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D004100:Dihydroxycholecalciferols; D015650:24,25-Dihydroxyvitamin D 3; D000469:Alkaline Phosphatase; D002117:Calcitriol