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Hormonal responses to 1,25‐dihydroxyvitamin D 3 in cultured mouse osteoblast‐like cells—modulation by changes in receptor level
Author(s) -
Chen Theresa L.,
Li Janet M.,
Van Ye Todd,
Cone Charlotte M.,
Feldman David
Publication year - 1986
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041260104
Subject(s) - receptor , medicine , endocrinology , osteoblast , dna synthesis , enzyme , biology , cell culture , cell growth , microbiology and biotechnology , chemistry , biochemistry , in vitro , genetics
The level of 1,25(OH) 2 D 3 receptors in cultured mouse osteoblast‐like (OB) cells is modulated by the rate of cell proliferation. We have studied two 1,25(OH) 2 D 3 ‐induced bioresponses to ascertain whether the changes in receptor levels during growth in culture alter cell responsiveness. Nuclear receptor levels were high (127 fmol/100 μgDNA) in rapidly dividing (log) cells and low (25 fmol/100 μg DNA) in quiescent (confluent) cells. The bioresponses we studied were induction of 25(OH)D 3 ‐24‐hydroxylase. activity (24‐hydroxylase) and inhibition of collagen synthesis. The basal levels of 24‐hydroxylase were low and similar in cells at log growth phase and confluence. At a maximal induction dose of 13 nM, 1,25(OH) 2 D 3 induced a three‐fold rise in enzyme activity at long growth phase, but only caused less than two‐fold rise at confluence. The half‐maximal dose (ED 50 ) was slightly shifted from 0.6 nM to 0.8 nM. Daily measurement of 1,25(OH) 2 D 3 receptor levels and maximal induction of 24‐hydroxylase activity throughout the culture cycle showed a strong correlation between receptor abundance and enzyme induction. The basal level of collagen synthesized by cells in log growth phase was ∼ 5% and increased to ∼ 8% at confluence. Maximal inhibition of collagen synthesis by 1,25(OH) 2 D 3 reached 80% of control levels in log cells, but was only 40% of control in confluent cells. The ED 50 was ∼ 0.1 nM in the log cells and increased to ∼ 1 nM at confluence. Daily assay of 1,25(OH) 2 D 3 receptor levels and 1,25(OH) 2 D 3 responses during the culture cycle indicated a correlation between changes in receptor level and the extent of inhibition of collagen synthesis. These changes in biore‐sponse at various growth phases did not occur in rat OB cells where the 1,25(OH) 2 D 3 receptor levels were independent of cell proliferation. The results indicate that cell proliferation rate, via change in receptor levels, determines the magnitude and sensitivity of the cellular responses to 1,25(OH) 2 D 3 .