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

Expression of the human TcRbeta gene is controlled by an enhancer loca ted 6kb 3' to the Cbeta2 gene segment. The activity of this enhancer h as been shown to be inducible with phorbol esters. Within the enhancer the betaE2 element is responsible for the major part of the inducibil ity, 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 dis rupt Ets-1 and Ets-2 binding abolish inducibility as well as reducing activity, whereas mutants which cannot bind CBF have only reduced basa l activity. In Jurkat, which has a high level of endogenous Ets-1, mul timerized betaE2 was inactive unless treated with PMA. However when tr anfected into cells with no detectable Ets-I the betaE2 multimer was h ighly active in the absence of PMA. Co-transfection of an Ets-1 expres sion construct with the full enhancer into Jurkat cells led to a repre ssion 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 enha ncer construct and the betaE2 multimer was most dramatic in the presen ce of PMA, suggesting that Ets-1 could block TcRbeta activation. The E ts-I expression construct used transactivated the HTLV-1 LTR which has also been shown to bind Ets-1. The repression of betaE2 activity by E ts-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.