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DEAD Box Protein 5 Inhibits Liver Tumorigenesis by Stimulating Autophagy via Interaction with p62/SQSTM1.

In hepatocellular carcinoma (HCC), dysregulated expression of DDX5 (DEAD box protein 5) and impaired autophagy have been reported separately. However, the relationship between them has not been explored. Here we present evidence to show that, by interacting with autophagic receptor p62, DDX5 promotes autophagy and suppresses tumorigenesis. DDX5 inversely correlated with p62/sequestosome 1 (SQSTM1) expression in HBV-associated and non-HBV associated HCCs. Patients with low DDX5 expression showed poor prognosis after tumor resection. We found that DDX5 overexpression induced, while DDX5 knockdown attenuated autophagic flux in HepG2 and Huh7 cells. DDX5 promoted p62 degradation and markedly reduced the half-life of p62. Moreover, DDX5 overexpression dramatically reduced while DDX5 knockdown promoted cancer cell growth and tumorigenesis in vitro and in vivo. We found that DDX5 bound to p62 and interfered with p62/TRAF6 (TNF receptor associated factor 6) interaction. Further findings revealed that the N-terminal domain of DDX5, involved in the interaction with p62, was sufficient to induce autophagy independent of its RNA binding and helicase activity. DDX5 overexpression decreased p62/TRAF6 mediated lysine 63-linked ubiquitination of mTOR, and subsequently inhibited the mTOR signaling pathway. Knockdown of TRAF6 blocked DDX5-induced autophagy. Furthermore, we showed that the miR-17-5p downregulated DDX5 and impaired autophagy. Inhibition of miR-17-5p promoted autophagic flux and suppressed tumor growth in HCC xenograft models.

CONCLUSION: Our findings define a non-canonical pathway that links miR-17-5p, DDX5, p62/TRAF6, autophagy and HCC. These findings open a new avenue for the treatment of HCC. This article is protected by copyright. All rights reserved.

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