The Role of AUF1 in AU-rich interleukin-6 mRNA regulation

The AU-rich elements (AREs) consisting of repeated AUUUA motifs confer rapid degradation to many cellular mRNAs when present in the 3' untranslated region (3'UTR). We have studied the instability of interleukin-6 mRNA by grafting its 3'UTR to a stable green fluorescent protein mRNA. Subsequent scanning mutagenesis identified two conserved elements, which taken together account for most of the instability. Destabilization of ARE-containing mRNAs is thought to involve ARE-binding proteins such as AUF1. We tested whether AUF1 binding to interleukin-6 mRNA correlates with decreased mRNA stability. Overexpression of myc-tagged p37AUF1 and p42AUF1 as well as suppression of all four AUF1 isoforms by RNA interference stabilized the interleukin-6 mRNA. Furthermore, the interleukin-6 mRNA co-immunoprecipitated specifically with myc-tagged p37AUF1 and p42AUF1 in cell extracts. These results indicate that AUF1 binds to the AU-rich element in vivo and promotes interleukin-6 mRNA degradation. The combination of mRNA co-immunoprecipitation with microarray technology revealed that at least 500 cellular mRNAs associate with AUF1.