Protein kinase A phosphorylates and regulates the osteogenic activity of Dlx5.

Dlx5 transcription factor plays important roles in osteoblast differentiation and its transcription is regulated by many osteogenic signals including BMP-2. Recent studies suggest that the function of Dlx5 is also regulated post-translationally by protein kinases such as p38 and CaMKII. Protein kinase A (PKA) is involved in several steps of osteoblast differentiation and its activity has been shown necessary, yet not sufficient, for BMP-induced osteoblast differentiation. PKA is a ubiquitous cellular kinase that phosphorylates serine and threonine residues(s) of target proteins. In this study, we investigated the potential regulation of Dlx5 function by PKA in osteoblast differentiation. We found that PKA phosphorylates Dlx5 and that PKA activation increases the protein stability, osteogenic activity and transcriptional activity of Dlx5. We also found that BMP-2 increases the protein level of Dlx5 in a PKA activity-dependent manner. These results suggest that PKA activity enhances the osteogenic function of Dlx5, at least in part, through protein stabilization and that BMP-2 regulates the osteogenic function of Dlx5, at least in part, through PKA.