Histone deacetylase inhibitor MS-275 stimulates bone formation in part by enhancing Dhx36-mediated TNAP transcription

Histone deacetylases (HDACs) deacetylate both histones and nonhistone proteins and play a key role in the regulation of physiologic and aberrant gene expression. Inhibition of HDACs has emerged as a promising therapeutic target for cancer and neurologic diseases. In this study we investigated the osteogenic effect and mechanism of action of MS-275, a class I HDAC inhibitor with preference for HDAC1. Both local and systemic administration of MS-275 stimulated bone regeneration in animal models. MS-275 stimulated mRNA expression and activity of the early osteogenic marker tissue-nonspecific alkaline phosphatase (TNAP) in bone tissue and osteogenic cells. By using a series of TNAP promoter deletion constructs and a DNA affinity precipitation assay, we identified DExH-box helicase Dhx36 as a factor that binds to the MS-275 response element in the TNAP promoter. We also found that Dhx36 binding to the MS-275 response element is crucial for MS-275 induction of TNAP transcription. Dhx36 physically interacted with a subset of HDACs (HDAC1 and -4) whose protein levels were downregulated by MS-275, and forced expression of these HDACs blunted the stimulatory effects of MS-275 by a deacetylase activity-independent mechanism(s). Taken together, the results of our study show that MS-275 induces TNAP transcription by decreasing the interaction of HDAC1/4 with Dhx36, which can at least in part contribute to the bone anabolic effects of MS-275.