Phosphorylation-mediated control of chromatin organization and transcriptional activity of the tissue-specific osteocalcin gene

We have analyzed the linkage of protein phosphorylation to the remodeling o f chromatin structure that accompanies transcriptional activity of the rat osteocalcin (OC) gene in bone-derived cells. Short incubations with okadaic acid, an inhibitor of protein phosphatases 1 and 2A, induced marked change s in the chromatin organization of the OC gene promoter. These changes were reflected by loss of the two DNase I hypersensitive sites normally present in bone-derived cells expressing this gene. These hypersensitive sites inc lude the elements that control basal tissue-specific expression, as well as steroid hormone regulation. Indeed, the absence of hypersensitivity was ac companied by inhibition of basal and Vitamin D-dependent enhancement of OC gene transcription. The effects of okadaic acid on OC chromatin structure a nd gene activity were specific and reversible. Staurosporine, a protein kin ase C inhibitor, did not significantly affect transcriptional activity or D Nase I hypersensitivity of the OC gene. We conclude that cellular phosphory lation-dephosphorylation events distinct from protein kinase C-dependent re actions are required for both chromatin remodeling and transcriptional acti vity of the OC gene in osseous cells. J. Cell. Biochem. 72:586-594, 1999. ( C) 1999 Wiley-Liss, Inc.