MicroRNA-Independent Modulation of DICER1 Expression by hAgo2

ABSTRACT

Many proteins, including DICER1 and hAgo2, are involved in the biogenesis of microRNAs (miRNAs). Whether hAgo2 regulates DICER1 expression is unknown. Exogenously overexpressed hAgo2 suppressed DICER1 expression at the levels of both protein and mRNA, and the reduction in hAgo2 expression enhanced DICER1 expression. Precursor miRNA processing mediated by DICER1 was also modulated by hAgo2. However, hAgo2 protein did not suppress DICER1 promoter activity. Therefore, hAgo2 protein probably regulates DICER1 expression at the posttranscriptional level. Indeed, hAgo2 protein inhibited the reporter assay of the DICER1 mRNA 3′ untranslated region (3′-UTR). Previous reports have demonstrated that miRNAs (e.g., let-7 and miR-103/107) inhibited DICER1 expression posttranscriptionally. However, hAgo2 still suppressed DICER1 expression in the cells depleted of these miRNAs. Moreover, the reporter activities of the DICER1 mRNA 3′-UTR without these miRNA binding sites were still suppressed by hAgo2. Therefore, in addition to an miRNA-dependent pathway, hAgo2 can also modulate DICER1 expression through an miRNA-independent mechanism. Downregulation of DICER1 expression was further proven to be dependent on both hAgo2 and AUF1 proteins. Interactions of hAgo2 and AUF1 proteins were demonstrated by the coimmunoprecipitation assay. As expected, hAgo2 could not suppress the DICER1 mRNA 3′-UTR reporter with a mutation in the potential AUF1-binding site. Thus, downregulation of DICER1 expression through the 3′-UTR requires both hAgo2 and AUF1.

KEYWORDS:

• knockdown
• knockout
• posttranscriptional level
• luciferase reporter assay
• coimmunoprecipitation

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SUPPLEMENTAL MATERIAL

Supplemental material is available online only.

ACKNOWLEDGMENTS

We thank G. J. Hannon, D. Bartel, and D. Fisher for providing the expression plasmids. The RNAi reagents were obtained from the National RNAi Core Facility, located at the Institute of Molecular Biology/Genomic Research Center, Academia Sinica, which is supported by grants from the NSC National Research Program for Genomic Medicine (NSC 94-3112-B-001-003 and NSC 94-3112-B-001-018-Y).

This work was supported by grants from the Ministry of Science and Technology, Republic of China (MOST 106-2320-B-320-009-MY3), to Shih-Yen Lo and from the Tzu Chi University to Shih-Yen Lo (TCIRP106001-04Y1) and to Hui-Chun Li (TCIRP106001-02Y1).

We have no competing interests to declare.

Authors made the following contributions: designed research, S.-Y.L.; performed research, C.-H.Y., T.-S.K., C.-H.W. and K.-C.S.; analyzed data, H.-C.L. and S.-Y.L.; wrote the paper, H.-C.L. and S.-Y.L.