Human saliva contains thousands of mRNAs, some of which have translational value as diagnostic markers for human diseases. We have found that more than 30% of the mRNAs detected in human saliva contain AU-rich elements (ARE) in their 3′ untranslated regions (3′UTR). Since AREs are known to contribute to RNA turnover by forming complexes with ARE-binding proteins, we hypothesized that salivary mRNA stability is mediated by ARE-binding proteins in human saliva. To test this hypothesis, we monitored the in vitro degradation of a radiolabeled ARE-containing salivary mRNA (IL-8) in salivary protein extracts. The degradation of IL-8 mRNA was accelerated by competition for saliva ARE-binding proteins through the addition of excess unlabeled IL-8 mRNA fragments containing 4 tandem AREs. UV cross-linking and immunoprecipitation experiments revealed 2 ARE-binding proteins, AUF1 and HuR, associated with IL-8 mRNA in saliva. These results demonstrate that ARE-binding proteins contribute to the stability of ARE mRNAs in human saliva.
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