HIF-1α promotes autophagic proteolysis of Dicer and enhances tumor metastasis
Hui-Huang Lai, … , Hiroshi I. Suzuki, Pai-Sheng Chen
Hui-Huang Lai, … , Hiroshi I. Suzuki, Pai-Sheng Chen
Published December 18, 2017
Citation Information: J Clin Invest. 2018;128(2):625-643. https://doi.org/10.1172/JCI89212.
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HIF-1α promotes autophagic proteolysis of Dicer and enhances tumor metastasis

Abstract

HIF-1α, one of the most extensively studied oncogenes, is activated by a variety of microenvironmental factors. The resulting biological effects are thought to depend on its transcriptional activity. The RNAse enzyme Dicer is frequently downregulated in human cancers, which has been functionally linked to enhanced metastatic properties; however, current knowledge of the upstream mechanisms regulating Dicer is limited. In the present study, we identified Dicer as a HIF-1α–interacting protein in multiple types of cancer cell lines and different human tumors. HIF-1α downregulated Dicer expression by facilitating its ubiquitination by the E3 ligase Parkin, thereby enhancing autophagy-mediated degradation of Dicer, which further suppressed the maturation of known tumor suppressors, such as the microRNA let-7 and microRNA-200b. Consequently, expression of HIF-1α facilitated epithelial-mesenchymal transition (EMT) and metastasis in tumor-bearing mice. Thus, this study uncovered a connection between oncogenic HIF-1α and the tumor-suppressive Dicer. This function of HIF-1α is transcription independent and occurs through previously unrecognized protein interaction–mediated ubiquitination and autophagic proteolysis.

Authors

Hui-Huang Lai, Jie-Ning Li, Ming-Yang Wang, Hsin-Yi Huang, Carlo M. Croce, Hui-Lung Sun, Yu-Jhen Lyu, Jui-Wen Kang, Ching-Feng Chiu, Mien-Chie Hung, Hiroshi I. Suzuki, Pai-Sheng Chen

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Figure 3

HIF-1α enhances proteolysis of Dicer through an autophagy-lysosomal pathway.

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HIF-1α enhances proteolysis of Dicer through an autophagy-lysosomal path...
(A) Effects of the nontranscriptional activity of HIF-1α on Dicer. WT HIF-1α or HLH-truncated HIF-1α was overexpressed in HCT116 cells for Western blot analysis to determine the expression of Dicer, PDK1, CA9, and PAI-1. The immunoblots presented were derived from replicate samples run on parallel gels. (B) HIF-1α enhances the protein degradation of Dicer. Cells were treated with CHX at the indicated times to block de novo protein synthesis. The expression of Dicer was determined by Western blot analysis and was further quantified by ImageJ (NIH). The relative levels of Dicer protein remaining at each time point were normalized to α-tubulin (right). Data are presented as mean ± SD, with at least n = 3 per group. **P < 0.01, 2-way ANOVA. All of the cell lysates were run on the same gel. (C–E) Effects of the proteolytic pathways on the HIF-1α–induced downregulation of Dicer. Cells were treated with MG132 to inhibit proteasomal degradation (C), ammonium chloride (NH4Cl) to inhibit lysosomal degradation (D), or 3-MA to inhibit autophagic degradation (E). The immunoblots presented were derived from replicate samples run on parallel gels. The ratios of Dicer/α-tubulin protein levels were quantified by using ImageJ. (F) Similar experiments were performed in cells in which ATG5 was genetically knocked down to inhibit autophagy. LC3 was detected for autophagic activation. (G and H) The associations between Dicer and the autophagy receptor p62 were analyzed in the presence of NH4Cl and CQ to block autophagy-lysosomal degradation in HIF-1α–overexpressing (G) or HIF-1α knockdown (H) HCT116 cells. The immunoblots presented were derived from replicate samples run on parallel gels (H).