EGFR phosphorylation of AGO2 under hypoxia inhibits tumor-suppressive miRNA maturation.

  • Major finding: EGFR phosphorylation of AGO2 under hypoxia inhibits tumor-suppressive miRNA maturation.

  • Mechanism: AGO2 Y393 phosphorylation reduces AGO2–DICER1 binding and loading of long-loop miRNA precursors.

  • Impact: AGO2 Y393 phosphorylation correlates with decreased overall survival in breast cancer.

MicroRNA (miRNA)-mediated reprogramming of gene expression plays an important role in the cellular response to stress and contributes to tumor progression. Processing of miRNAs from precursors to their mature form is controlled by the binding of argonaute 2 (AGO2), the catalytic component of the RNA-induced silencing complex (RISC), to DICER1, but how this complex is regulated in tumor cells in response to stress is unclear. Shen and colleagues found that AGO2 directly interacted with intracellular EGF receptor (EGFR) at late endosomes in cancer cells in response to hypoxic stress, which is known to promote EGFR activation. This interaction was triggered in part by stabilization of hypoxia-inducible factors, and resulted in impaired maturation of a specific cluster of miRNAs with tumor-suppressive characteristics and concomitant de-repression of their corresponding mRNA targets. EGFR-induced suppression of miRNA maturation was dependent on enhanced phosphorylation of AGO2 at tyrosine 393 (Y393) by EGFR under hypoxia; this modification disrupted the AGO2–DICER1 association and specifically decreased loading of miRNA precursors containing a long-loop structure, suggesting that this structure imparts selective regulation of miRNA maturation in response to stress. Indeed, AGO2 Y393 phosphorylation diminished the expression of long-loop miRNAs, and this long-loop structure was necessary and sufficient for phosphorylated-Y393 AGO2-mediated miRNA maturation. Consistent with downregulation of tumor-suppressive miRNAs, AGO2 Y393 phosphorylation was necessary for cell survival and promoted increased cell invasion under hypoxia. Furthermore, EGFR and phosphorylated-Y393 AGO2 were enriched in hypoxic areas of murine and primary human breast tumors, and elevated phosphorylated-Y393 AGO2 expression was correlated with reduced overall survival in patients with breast cancer. These results identify EGFR as a critical regulator of the miRNA machinery in response to stress and suggest that phosphorylated AGO2 may be a prognostic marker in breast cancer.

Shen J, Xia W, Khotskaya YB, Huo L, Nakanishi K, Lim SO, et al. EGFR modulates microRNA maturation in response to hypoxia through phosphorylation of AGO2. Nature 2013 May 1 [Epub ahead of print].