Conserved cAMP responsive element and core promoter complex are critical for specificity of the distal T-cell receptor beta chain enhancer for its native promoter

The co-activator p300 associates physically with and can mediate the action of the distal enhancer of the FGF-4 gene

Distal enhancers commonly regulate gene expression. However, the mechanisms of transcriptional mediation by distal enhancers remain largely unknown. To better understand distal enhancer-mediated transcription, we examined the regulation of the FGF-4 gene. The FGF-4 gene is regulated during early development by a powerful distal enhancer located downstream of the promoter in exon 3. Sox-2 and Oct-3 bind to the enhancer and are required for the activation of the FGF-4 gene. Previously, we implicated the co-activator p300 as a mediator of Sox-2/Oct-3 synergistic activation of a heterologous promoter, suggesting that p300 may play a role in mediating enhancer activation of the FGF-4 gene. In this study, we provide both functional and physical evidence that p300 plays an important role in the action of the FGF-4 enhancer. Specifically, we show that E1a, but not a mutant form of E1a that is unable to bind p300, inhibits enhancer activation of the FGF-4 promoter. We also demonstrate that Gal4/p300 fusion proteins can stimulate the FGF-4 promoter when bound to the FGF-4 enhancer. Additionally, we present evidence that p300 mediation of the FGF-4 enhancer requires acetyltransferase activity. Importantly, we also show that Sox-2 and p300 are physically associated with the endogenous FGF-4 enhancer but weakly associated with the endogenous FGF-4 promoter. These results are consistent with a model of transitory interaction between the distal enhancer and the FGF-4 promoter. Our results also suggest that intragenic distal enhancers may use mechanisms that differ from extragenic distal enhancers.

Differential regulation between gene expression and histone H3 acetylation in the variable regions of the TCRbeta locus

Histone acetylation is suggested to regulate gene expression in the TCR loci. Using R2CD3 mouse model, we previously showed that germline transcription of the TCRbeta chain gene is discrete between 5' Vbeta regions and Dbeta-Jbeta-Cbeta clusters plus Vbeta14 region. In this study, we investigated a role of histone H3 acetylation in transcriptional regulation of the TCRbeta locus. Our results showed that DN-DP transition is accompanied by significant promotion of histone H3 acetylation in both Dbeta-Jbeta-Cbeta cluster and Vbeta14 region, correlating with up-regulation of germline transcription. Surprisingly, termination of germline transcription of the 5' Vbeta regions was inversely correlated with histone H3 hyperacetylation. Moreover, histone H3 acetylation showed equivalent level in both functionally rearranged Vbeta region with active transcription and unrearranged Vbeta region without transcription in mature T cells. These results suggest that histone acetylation is not a sole limiting factor in both terminating germline Vbeta transcription during DN-DP transition and maintaining functionally rearranged Vbeta gene expression.

The synergistic activity of thyroid transcription factor 1 and Pax 8 relies on the promoter/enhancer interplay

The transcription factors, thyroid transcription factor 1 (TTF-1) and Pax 8, play a pivotal role in the transcriptional regulation of the thyroid differentiation marker genes and in the differentiation of the thyroid follicular cells. They have a very restricted tissue distribution, and the thyrocyte is the only cell type with the simultaneous expression of these factors. Here we show that TTF-1 and Pax 8 cooperatively activate their target genes and that their synergistic activity requires the cross-talk between enhancer and gene promoter. We have characterized the cis and trans requirements of the TTF1/Pax 8 synergistic activity on the thyroperoxidase gene. We show that their synergy is also important for thyroglobulin gene transcription.