The 3′-untranslated region of human interleukin-8 mRNA suppresses IL-8 gene expression

Although adenosine/uridine (AU)-rich sequences in the 3′-untranslated region (UTR) of the interleukin-8 (IL-8) gene have been suggested to contribute to its post-transcriptional regulation, the molecular basis whereby this occurs still needs to be understood. To investigate the role of the 3′-UTR on human IL-8 gene regulation, chimeric reporter genes were generated by adding full length or differentially deleted 3′-UTR of the IL-8 gene to chloramphenicol acetyltransferase (CAT). Addition of the entire IL-8 3′-UTR markedly reduced CAT mRNA and protein expression in COS 7 cells. In a reporter gene study, IL-8 3′-UTR destabilized CAT mRNA, which was dependent on active transcription in COS 7 cells. A 357-base sequence (nucleotides (nt) 2387–2743 of genomic DNA) within 3′-UTR, designated e, suppressed CAT gene expression by accelerating CAT mRNA turnover. A 26-base AU-rich sequence (nt 2552–2577) within e, containing four AUUUA pentamers that form two UAUUUAUU and one UUAUUUAU octamers, did not suppress CAT gene expression. However, deletion of the AU-rich sequences attenuated the inhibitory effect of e on CAT gene expression. Elimination of the first 100 bases (nt 2386–2486) attenuated the potency of fragment e, but much weaker than elimination of the first 146 bases (nt 2387–2533). This study gives new insights in unravelling the molecular mechanisms involved in the post-transcriptional regulation of the IL-8 gene