REGULATION OF HUMAN T-CELL RECEPTOR-BETA GENE-EXPRESSION BY ETS-1

Expression of the human TcRbeta gene is controlled by an enhancer located 6kb 3' to the Cbeta2 gene segment. The activity of this enhancer has been shown to be inducible with phorbol esters. Within the enhancer the betaE2 element is responsible for the major part of the inducibility, multimerised betaE2 alone is also highly phorbol ester inducible. The betaE2 element contains a consensus ets-binding site as well as a core motif, and we have shown that the betaE2 ets site binds both Ets-1 and Ets-2 in vitro and that purified core binding factor (CBF) can bind the core site present in betaE2. Mutations which specifically disrupt Ets-1 and Ets-2 binding abolish inducibility as well as reducing activity, whereas mutants which cannot bind CBF have only reduced basal activity. In Jurkat, which has a high level of endogenous Ets-1, multimerized betaE2 was inactive unless treated with PMA. However when tranfected into cells with no detectable Ets-I the betaE2 multimer was highly active in the absence of PMA. Co-transfection of an Ets-1 expression construct with the full enhancer into Jurkat cells led to a repression of enhancer activity, suggesting a repressive role for Ets-1. Co-transfection of Ets-I was also able to repress strongly the activity of the betaE2 multimer. Repression of activity from both the full enhancer construct and the betaE2 multimer was most dramatic in the presence of PMA, suggesting that Ets-1 could block TcRbeta activation. The Ets-I expression construct used transactivated the HTLV-1 LTR which has also been shown to bind Ets-1. The repression of betaE2 activity by Ets-I appears therefore to be specific. In conclusion, the combination of ets and core sites in betaE2 constitutes a novel inducible element, which is specifically transrepressed by Ets-1.