A PHORBOL ESTER RESPONSE ELEMENT WITHIN THE HUMAN T-CELL RECEPTOR BETA-CHAIN ENHANCER

The activity of the T-cell receptor beta-chain gene enhancer is increased by activators of the protein kinase C pathway during T-cell activation. Analysis of mutant enhancer constructs identified two elements, betaE2 and betaE3, conferring phorbol ester inducibility. Multimerized betaE2 acted in isolation as a phorbol ester-responsive element. Both betaE2 and betaE3, which contain a consensus Ets-binding site, were shown to bind directly to the product of the c-ets-1 protooncogene. Both regions also bound a second factor, core-binding factor. Mutation of the betaE2 Ets site abolished the inducibility of the betaE2 multimer. BetaE2 and betaE3 Ets site mutations also profoundly affected activity and inducibility of the enhancer. In contrast, enhancer activity but not its inducibility was affected by mutation of the betaE2 core-binding factor site. Cotransfection studies showed that Ets-1 specifically repressed activity of the multimerized betaE2 element and the complete T-cell receptor beta-chain enhancer. These data show that the T-cell receptor beta-chain enhancer responds to protein kinase C-mediated activation signals via a functional domain, composed of two elements, which contains binding sites for Ets transcription factors and which is negatively regulated by Ets-1.