YY1 REPRESSES RAT SERUM AMYLOID AL GENE-TRANSCRIPTION AND IS ANTAGONIZED BY NF-KAPPA-B DURING ACUTE-PHASE RESPONSE

Serum amyloid A (SAA), one of the major acute-phase proteins, increase s several hundredfold in concentration in plasma following acute infla mmation, primarily as a result of a 200-fold increase in its transcrip tional rate. Functional analysis of the rat SAA1 promoter has identifi ed a 65-bp cytokine response unit (CRU; positions -135 to -71) that co uld confer cytokine responsiveness on a heterologous promoter. Within this CRU, two cis-regulatory elements, corresponding to NF-kappa B- an d C/EBP-binding sites, mere found to be functionally important and exe rted synergistic effects on induced SAA1 expression. In this report, w e show that a third transcription factor interacts with the CRU throug h a region located between the NF-kappa B- and C/EBP-binding sites. On the basis of its gel mobility shift patterns, ubiquitous binding acti vity, sequence specificity of DNA binding, zinc dependent binding acti vity, and gel mobility supershift by specific antibodies, me concluded that this factor is identical to YY1. Methylation interference studie s revealed that YY1 binding sequences overlapped with those of NF-kapp a B, and gel mobility studies showed that NF-kappa B binding to the CR U was effectively inhibited by YY1. Consistent with its presumed antag onistic role to NF-kappa B, YY1 exerted a negative effect on SAA1 expr ession, whereas disruption of its binding in the promoter elevated bas al and cytokine-induced activities. Furthermore, overexpression of YY1 trans-repressed SAA1 promoter activity. Thus, our results demonstrate that SAA1 expression is tightly regulated by an on-off switch of acti vators and repressors, presumably to ensure that it is expressed only under appropriate physiological conditions.