RESUMEN
MicroRNAs (miRNAs) are small noncoding RNAs that control diverse cellular and developmental events through repression of large sets of target mRNAs. miRNAs expressions were mainly regulated at two levels: transcriptional and post-transcriptional. Transcriptional regulation of miRNA-encoding genes produce specific expression patterns of individual miRNA. However, the mechanism of post-transcriptional regulation of miRNAs remains largely unknown. The present study was aimed to clarify whether HuR, an evolutionary conserved AU-rich binding protein, could regulate miRNAs expressions. By means of a computational screen for AUUUA motifs within pri-miRNAs, we found that the downstream of hsa-let-7c but not hsa-miR-21 was enriched of AUUUA motifs. Then we transfected HuR and mutant HuR lacking RNA recognition motif 3 (RRM3) respectively into HEK293T cells. And HuR protein and miRNAs expressions were detected by Western blot and real-time PCR, respectively. The results showed that the overexpression of HuR promoted mature hsa-let-7c expression but not hsa-miR-21 expression. Furthermore, overexpression of HuR deletion mutant lacking RRM3 did not promote hsa-let-7c expression. These results suggest that RRM3 is crucial for HuR mediating mature hsa-let-7c expression. Collectively, these findings proposed a novel role of HuR in biogenesis of miRNAs, possibly by way of post-transcriptional regulation of miRNAs.