TRANSCRIPTION FACTORS NF-IL6 AND CREB RECOGNIZE A COMMON ESSENTIAL SITE IN THE HUMAN PROINTERLEUKIN 1-BETA GENE

A site located between -2782 and -2729 of the human prointerleukin-1 b eta (IL1B) gene functions as a strong lipopolysaccharide (LPS)-respons ive enhancer independent of the previously identified enhancer located between -2896 and -2846 (F. Shirakawa, K. Saito, C.A. Bonagura, D. L. Galson, M. J. Fenton, A. C. Webb, and P. E. Auron, Mol. Cell. Biol. 1 3:1332-1344, 1993). Although these two enhancers appear to function co operatively in the native sequence context, they function independentl y as LPS-responsive elements upon removal of an interposed silencer se quence. The new enhancer is not induced by dibutyryl cyclic AMP (dbcAM P) alone but is superinduced by costimulation with LPS-dbcAMP. This pa ttern of induction depends upon the nature of the sequence, a composit e NF-IL6-cAMP response element (CRE) binding site. This pseudosymmetri cal sequence is shown to contrast with a classical symmetric CRE which responds to dbcAMP but not LPS. DNA binding studies using in vivo nuc lear extract, recombinant proteins, and specific antibodies show that LPS induces the formation of two different complexes at the enhancer: (i) an NF-IL6-CREB heterodimer and (ii) a heterodimer consisting of NF -IL6 and a non-CREB, CRE-binding protein. Cotransfection studies using NF-IL6 and CREB expression vectors show that NF-IL6 transactivates th e enhancer in the presence of LPS, whereas CREB acts either positively or negatively, depending upon its cAMP-regulated phosphorylation stat e. Our data demonstrate that the newly identified enhancer is a specia lized LPS responsive sequence which can be modulated by cAMP as a resu lt of the involvement of NF-IL6-CRE-binding protein heterodimers.