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Regulation of the 1b Isoform of the Plasma Membrane Calcium Pump by 1,25‐Dihydroxyvitamin D 3 in Rat Osteoblast‐Like Cells
Author(s) -
Glendenning Paul,
Ratajczak Thomas,
Dick Ian M.,
Prince Richard L.
Publication year - 2001
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.2001.16.3.525
Subject(s) - messenger rna , gene isoform , osteoblast , biology , medicine , endocrinology , gene expression , alternative splicing , calcium , microbiology and biotechnology , biochemistry , gene , in vitro
The first isogene of the plasma membrane calcium pump (PMCA1) is expressed on the apical plasma membrane of osteoblasts, but its regulation by 1,25‐dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] has not been studied in this cell type. We studied 1,25(OH) 2 D 3 effects on PMCA1 function, protein, messenger RNA (mRNA), and isoform expression in osteoblasts. Of seven rat and human immortalized osteoblast‐like cell lines studied, PMCA1 mRNA expression was confirmed in all. Only ROS 17/2.8 cells expressed measurable PMCA1 protein by Western analysis. Immunocytochemistry indicated that PMCA1 was expressed predominantly on the plasma membrane of ROS 17/2.8 cells. The 1,25(OH) 2 D 3 but not 24,25‐dihydroxyvitamin D 3 [24,25(OH) 2 D 3 ] treatment of confluent ROS 17/2.8 cells resulted in an approximate 3‐ to 5‐fold dose‐dependent increase in PMCA1 expression of message and protein as assessed by Western and Northern analysis and vesicular 45 Ca uptake of membrane vesicles. 1,25(OH) 2 D 3 had no effect on PMCA1 posttranscriptional splicing. The 1b isoform of PMCA was expressed under all experimental conditions. 1,25(OH) 2 D 3 favored increased expression of the 5.5 kilobases (kb) over the 7.5‐kb PMCA1b transcript, with a 2‐fold proportional increase in the smaller transcript relative to the larger transcript evident at the highest dose of 1,25(OH) 2 D 3 studied. The resultant proportional increase in the smaller 5.5‐kb transcript may increase mRNA stability and account for the increase in PMCA1b protein and function with 1,25(OH) 2 D 3 . These data provide evidence for the role of 1,25(OH) 2 D 3 and PMCA1b in the regulation of calcium transport in bone cells.