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Stimulation of 1,25‐dihydroxyvitamin D 3 receptor gene expression in cultured cells by serum and growth factors
Author(s) -
Krishnan Aruna V.,
Feldman David
Publication year - 1991
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 - 10.1002/jbmr.5650061011
Subject(s) - calcitriol receptor , cycloheximide , endocrinology , medicine , stimulation , biology , receptor , downregulation and upregulation , cell growth , growth factor , gene expression , cell culture , northern blot , microbiology and biotechnology , gene , protein biosynthesis , vitamin d and neurology , biochemistry , genetics
The abundance of 1,25‐dihydroxyvitamin D 3 receptors (VDR) in bone cells has been shown to vary in direct relation to the rate of cell proliferation. In this study we further explored this upregulation of VDR as it relates to the mitogenic response using NIH‐3T3 mouse fibroblasts and MCF‐7 human breast cancer cells as model systems. Serum and growth factors, such as EGF, high concentrations of insulin (2 μM), and IGF‐I, were mitogenic and stimulated the proliferation of both cells types. These factors also caused significant increases in VDR levels as measured by ligand binding assays, which preceded the rise in cell proliferation rate measured by [ 3 H]thymidine incorporation. Serum and growth factors increased the abundance of VDR but did not affect the concentrations of other steroid receptors in MCF‐7 cells. Mouse cells have been reported to have several VDR mRNA transcripts. Our northern blot analysis revealed three mRNA species at approximately 7.5, 4.4, and 3 kb of which the 4.4 kb species was the most prominent and the 7.5 kb the least. Serum and growth factor stimulation of quiescent 3T3 cells led to significant increases in all the transcripts, suggesting that the upregulation occurs at the level of VDR mRNA expression. A time course analysis of serum stimulation in 3T3 cells showed that the mRNA species reached peak levels 4 h after serum addition. When serum stimulation was carried out in the presence of the protein synthesis inhibitor cycloheximide, the 3 kb transcript as well as the 7.5 kb transcript were superinduced but the stimulation of the 4.4 kb transcript was inhibited. Hydroxyurea (an inhibitor of DNA synthesis) and colchicine (a microtubule disruptive agent) had no effect on serum stimulation of the mRNA species, indicating that the enhanced expression of the VDR gene is not dependent upon the S , G 2 , or M phase of the cell cycle. The results suggest that the VDR gene appears to be one of a set of early genes activated when quiescent cells are stimulated by a mitogenic signal.