DIFFERENTIAL ACUTE-PHASE RESPONSE OF RAT KININOGEN GENES INVOLVES TYPE-I AND TYPE-II INTERLEUKIN-6 RESPONSE ELEMENTS

The serum concentration of rat T1 kininogen increases 20-30-fold in re sponse to acute inflammation. This increase, induced in the liver, is regulated primarily at the transcriptional level. In contrast, synthes is of a homologous K kininogen is not induced. In this study, we furth er analyzed a 321-base pair interleukin (IL)-6 response element in the T1 kininogen promoter and showed that it consists of at least three f unctionally distinct sequences (A, B, and C boxes). All three sequence s were required for full promoter activity. The B box, a strong C/EBP- binding site, was crucial for T1 kininogen's basal expression, whereas A and C boxes resembled the type II IL-6 response elements and were c ritical for the cytokine response. C/EBPalpha, -beta, and -delta inter acted with the B box sequence; however, upon IL-6 stimulation, C/EBPde lta binding activity was dramatically induced and became the predomina nt factor binding to this site. Consistent with these binding studies were the cotransfection experiments, revealing that C/EBPdelta was the most potent transactivator under induced conditions and that its tran sactivation on the T1 kininogen promoter required an intact B box. The se findings substantiated the importance of the B box in eliciting the full acute-phase response. A sequence comparison showed the K kininog en promoter contained identical A and B boxes but differed from the T1 kininogen promoter by two nucleotides at the C box. This divergence r educed the IL-6 response by approximately 4-fold, thus contributing to the differential inflammatory response. Our studies demonstrate that evolutionary divergence of a few nucleotides at a critical sequence in the promoter regions can profoundly alter the expression patterns of downstream genes.