Glucocorticoid-induced gene tripartite motif-containing 63 (TRIM63) promotes differentiation of osteoblastic cells

Glucocorticoids exert their function by regulating glucocorticoid-responsive genes through interaction with glucocorticoid receptor alpha (GRalpha), a nuclear receptor. Glucocorticoids also affect bone metabolism; this is evidenced by the fact that GRalpha is expressed in several kinds of cells in bone tissue, including osteoblasts, osteocytes, osteoclasts, mononuclear cells in bone marrow, and hypertrophic chondrocytes. Glucocorticoids are known to induce osteoblastic differentiation and bone formation. However, this effect of glucocorticoids on bone tissue is still controversial since long-term use of glucocorticoids results in osteoporosis in vivo. To identify glucocorticoid-regulated genes in human osteoblastic cells, SaOS2 cells were treated with dexamethasone (10(-8) M) for 6 hours, and were then subjected to microarray analysis. Genes such as C/EBPdelta, DUSP1, Per1 and TRIM63 were found to be induced by dexamethasone. The induction of mRNAs of these genes by dexamethasone (10(-8) M, 10(-7) M, and 10(-6) M) was confirmed by quantitative real-time polymerase chain reaction (PCR). TRIM63, also called muscle-specific ring finger protein 1 (MuRF1), was reported to be an E3 ubiquitin ligase expressed mainly in muscular tissue. SaOS2 cells overexpressing exogenous TRIM63 showed increased expression of an osteoblastic differentiation marker gene, alkaline phosphatase, with reduced proliferation. These results suggest that TRIM63 is a candidate for genes mediating the glucocorticoid-induced promotion of osteoblastic differentiation.