CROSS-TALK BETWEEN TRANSCRIPTION FACTORS NF-KAPPA-B AND C EBP IN THE TRANSCRIPTIONAL REGULATION OF GENES/

The study of the acute phase response has attracted substantial intere st, not only for its medical implication, but also its provision as an excellent system with which to elucidate the molecular mechanisms inv olved in the modulation of gene expression, Our previous data suggest that the synergistic induction of the major acute phase reactant serum amyloid A2 (SAA2) expression by interleukin-1 (IL-1) and interleukin- 6 (IL-6) is mediated by two families of transcription factors, namely NF-kappa B and C/EBP, To understand the molecular mechanisms of this s ynergy, we have undertaken a molecular dissection of the factors invol ved in the formation of the regulatory complex, Electrophoretic mobili ty shift analysis indicates that NF-kappa B p65 (RelA) and p50, but no t p52 or c-Rel, bind specifically to the NF-kappa B site of the SAA2 p romoter in response to IL-I stimulation, In addition, C/EBP beta and C /EBP delta, but not C/EBP alpha, bind specifically to the C/EBP site o f SAA2 in response to IL-6 stimulation, Transient co-transfection anal ysis indicates that co-operative association of NF-kappa B p65 with C/ EBP beta and, in particular, with C/EBP delta, results in synergistic transcriptional activation of the SAA2 promoter, When incubated togeth er, NF-kappa B p65 and C/EBP beta form a ternary complex by direct pro tein/protein interaction, Mutational analysis demonstrates that the C- terminus region of the Rel homology domain (RHD) and the C-terminus of the activation domain of p65 are important for its interaction with C /EBP beta, These results suggest the NF-kappa B and C/EBP may form a n ew complex of transcription factors that mediates the synergistic indu ction of SAA2 by IL-1 and IL-6, (C) 1997 Elsevier Science Ltd, All rig hts reserved.