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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Research Article Cell biology

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 2

HIF-1α downregulates Dicer protein expression.

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HIF-1α downregulates Dicer protein expression. (A) Effects of HIF-1α on ...
(A) Effects of HIF-1α on the expression of Dicer. The expression of Dicer was determined in HCT116 cells in which HIF-1α was overexpressed or knocked down by 2 specific shRNAs. The immunoblots presented were derived from replicate samples run on parallel gels. oxHIF-1α, overexpressed HIF-1α. (B) HIF-1α suppresses the protein expression of Dicer in multiple cancer cell lines. The cell lysates from Caco-2, MDA-MB-231, MDA-MB-453, Mia-PaCa-2, or PANC-1 with HIF-1α overexpression were subjected to Western blot analysis. The immunoblots presented were derived from replicate samples run on parallel gels (Caco-2). (C) HCT116 cells were treated with IGF or EGF and exposed to hypoxic conditions. The binding of Dicer with HIF-1α was determined through immunoprecipitation (left). (D–F) Similar experiments were performed in shHIF-1α–expressing HCT116 cells to study the functional roles of HIF-1α. The immunoblots presented were derived from replicate samples run on parallel gels (D). (G) Representative colon and breast cancer tissues showing the expression of either combined high HIF-1α and low Dicer or low HIF-1α and high Dicer. Each dot of fluorescence signal was generated from 2 closely contacted antibodies recognizing different epitopes of the same target protein (HIF-1α, orange; Dicer, green). Original magnification: ×600. (H and I) Dicer and HIF-1α scores were counted and calculated as PLA dots/cell for analyzing their expression correlation in colon (H) and breast (I) cancers. (J) The HIF-1α/Dicer ratio was used to study clinical associations with stage in both colon and breast cancers. Data are presented as mean ± SD, with at least n = 3 per group. Unpaired, independent groups of 2 were analyzed by 2-tailed Student’s t test.