Overexpressed nuclear factor-kappaB can participate in endogenous C-reactive protein induction, and enhances the effects of C/EBPbeta and signal transducer and activator of transcription-3.
C-reactive protein (CRP), the prototypical human acute phase protein, is produced primarily by hepatocytes. Its expression is modestly induced by interleukin (IL)-6 in Hep3B cells while IL-1, which alone has no effect, synergistically enhances the effects of IL-6. In previous studies of the proximal CRP promoter, we found that signal transducer and activator of transcription-3 (STAT3) and C/EBPbeta -mediated IL-6-induced transcription and that Rel p50 acted synergistically with C/EBPbeta, in the absence of p65, to enhance CRP transcription. Neither a requirement nor a binding site for the classic nuclear factor (NF)-kappaB heterodimer p50/p65 were found. The current studies were undertaken to determine whether similar novel transcription factor interactions might regulate the endogenous CRP gene. Transiently overexpressed p50 or p65 induced CRP mRNA accumulation in Hep3B cells. The heterodimer p50/p65 was markedly more effective than p50 or p65 homodimers. Co-overexpression of p50 or p65 with C/EBPbeta or STAT3 synergistically enhanced CRP expression. Maximal expression was observed with overexpression of all four transcription factors; comparable effects were observed with IL-1beta treatment of cells overexpressing STAT3 + C/EBPbeta. Data from the Human Genome Project revealed 13 potential kappaB sites in the first 4000 bases of the CRP promoter, only one of which, centred at -2652, bound nuclear p50/p65 heterodimer activated by IL-1beta. Our findings indicate that classical NF-kappaB activation can participate in endogenous CRP induction, and that activated NF-kappaB may synergistically enhance the effects of C/EBPbeta and STAT3. They raise the possibility, not as yet established, that NF-kappaB activation may be responsible for the synergistic effect of IL-1beta on IL-6-induced CRP expression.
Agrawal
Alok
A
Department of Biochemistry, Case Western Reserve University, Cleveland, OH, USA.
Cha-Molstad
Hyunjoo
H
Samols
David
D
Kushner
Irving
I
D002097:C-Reactive Protein / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D016328:NF-kappa B / Q000502:physiology*; D052002:NF-kappa B p50 Subunit; D012333:RNA, Messenger / Q000235:genetics; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000502:physiology*; D051996:Transcription Factor RelA; D014407:Tumor Cells, Cultured
D022782:CCAAT-Enhancer-Binding Protein-beta; D004268:DNA-Binding Proteins; D007375:Interleukin-1; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D051996:Transcription Factor RelA; D002097:C-Reactive Protein