THE EFFECT OF INTERLEUKIN-1 ON C-REACTIVE PROTEIN EXPRESSION IN HEP3BCELLS IS EXERTED AT THE TRANSCRIPTIONAL LEVEL

The combination of interleukin 6 (IL-6) and interleukin 1 (IL-1) syner gistically induces the human acute-phase reactant, C-reactive protein (CRP) in Hep3B cells. While previous studies have indicated that IL-6 induces transcription of CRP, the mode of action of IL-1 has not been clearly defined. It has been suggested that the effect of IL-1 might b e post-transcriptional, exerted through the 5'-untranslated region (5' -UTR). To evaluate the role of IL-1 in CRP gene expression, we studied the effects of interleukin-6 (IL-6) and interleukin-1 beta (IL-1 beta ) on both the endogenous CRP gene and on transfected CRP-CAT construct s in Hep3B cells. In kinetic studies of the endogenous CRP gene, IL-1 beta alone had no effect on CRP mRNA levels, but when added to IL-6, s ynergistically enhanced both CRP mRNA levels and transcription, as det ermined by Northern-blot analyses and nuclear run-on studies. IL-6 alo ne and the combination of [IL-1 beta + IL-6] each induced increases in mRNA levels roughly comparable with observed increases in transcripti on. These findings indicate that the effect of IL-1 beta on CRP expres sion is exerted largely at the transcriptional level in this system. T his conclusion was confirmed by studies in Hep3B cells transiently tra nsfected with CRP-CAT constructs, each containing 157 bp of the CRP 5' -flanking region but differing in the length of the 5'-UTR from 104 bp to 3 bp. All constructs responded in the same way; IL-6, but not IL-1 beta, induced significant chloramphenicol acetyltransferase (CAT) exp ression which was synergistically enhanced 2- to 3-fold by IL-1 beta. These results indicate that IL-1 beta stimulates transcriptional event s in the presence of IL-6 and that the upstream 157 bases of the CRP p romoter contain elements capable of both IL-6 induction and the synerg istic effect of IL-1 beta on transcription.