Combined BMP2 and cAMP signaling induces the catecholaminergic lineage in neural crest (NC) cultures by increasing expression of the proneural transcription factor Phox2a, in a cAMP response element (CRE)-binding protein (CREB)-mediated mechanism. To determine whether CREB acts directly on Phox2a transcription induced by BMP2؉cAMP-elevating agent IBMX, transient transfections of hPhox2a-reporter constructs were performed in avian NC cultures and murine, catecholaminergic CAD cells. Although BMP2؉IBMX increased endogenous Phox2a expression, the 7.5-kb hPhox2a reporters expressing either luciferase or DsRed1-E5 fluorescent protein were unresponsive to BMP2؉IBMX, but active in both cell types. Cell sorting of fluorescence-positive NC cells expressing the 7.5-kb hPhox2a fluorescent timer reporter differentiated to equal numbers of catecholaminergic cells as fluorescence-negative cells, suggesting inappropriate transcription from the transfected hPhox2a promoter. NC or CAD cells treated with histone deacetylase inhibitor trichostatin A and BMP2؉IBMX display increased endogenous Phox2a transcription and prolonged CREB phosphorylation, indicating Phox2a chromatin remodeling is linked to CREB activation. Chromatin immunoprecipitations employing CREB, CREB-binding protein, and acetylated H4 antibodies identified two CRE half-sites at ؊5.5 kb in the murine Phox2a promoter, which is also conserved in the human promoter. Proximal to the CRE half-sites, within a 170-bp region, are E-box and CCAAT binding sites, also conserved in mouse and human genes. This 170-bp promoter region confers cAMP, BMP2, and enhanced BMP2؉cAMP regulation to Phox2a-luciferase reporters. We conclude these CREs are functional, with CREB directly activating Phox2a transcription. Because the E-box binds bHLH proteins like ASH1 induced in NC cells by BMP2, we propose this novel 170-bp cis-acting element is a composite site, mediating the synergistic regulation by BMP2؉cAMP on Phox2a transcription.
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