Role for p300 in Pax 8 induction of thyroperoxidase gene expression

The nuclear p300 protein functions as a co-activator of gene transcription. Here we show that p300 works as a ca-activator of the transcription factor Pax 8 on the thyroperoxidase gene promoter. Consistent with its role as co -activator, p300 potentiates Pax 8-activated transcription. Furthermore, we provide evidence supporting the formation of a complex between both factor s in vitro and in vitro. This interaction involves the aminoterminal and CH 3 domains of p300 and the trans-activation domain of Pax 8 at its carboxyl- terminal end. We show that the CH3 domain is crucial for the co-activator r ole of p300 on the thyroperoxidase gene promoter. In agreement with our fin ding and with the ability of the adenoviral protein E1A to bind p300, we sh ow that EIA down-regulates Pax 8 activity.