HCV infection induces ubiquitin-dependent degradation of LATS1, inactivating the Hippo pathway and upregulating transcription of the CYR61 and CTGF genes

Abstract

Hepatitis C virus (HCV) is often associated with chronic liver diseases and significant alterations in host cellular signaling. However, the molecular mechanisms underlying HCV- related liver pathogenesis remain to be elucidated. The Hippo signaling pathway, a key regulator of cell proliferation and survival, plays a critical role in maintaining liver homeostasis. Here we investigated the role of the Hippo pathway in HCV-related pathogenesis. We demonstrated that HCV infection induces degradation of LATS1, a key regulator of the Hippo pathway. Degradation of LATS1 protein was restored by a proteasomal inhibitor, but not a lysosome inhibitor, indicating that HCV promotes proteasomal degradation of LATS1 protein. HCV-induced degradation of LATS1 protein was suppressed in si-Itch-transfected Huh-7.5 cells. These results suggest that Itch ubiquitin ligase is involved in ubiquitin-dependent degradation of LATS1 protein. Cell fractionation assays and immunofluorescence staining revealed that HCV infection promoted nuclear translocation of YAP1 protein, suggesting that HCV infection suppresses the Hippo pathway. Furthermore, the transcription of YAP1 target genes, CYR61 and CTGF, that are involved in tissue remodeling and proliferation, was upregulated in HCV-infected Huh-7.5 cells and in HCV-infected patients. Taken together, we propose that HCV promotes the ubiquitin-dependent proteasomal degradation of LATS1 protein, leading to suppression of the Hippo pathway, thereby upregulating transcription of CYR61 and CTGF genes. DATA SUMMARYAll data are presented in the main figures. Raw sequencing data, microscopy images, materials, and sequence information are available upon request. Correspondence and requests for materials should be addressed to Professor Ikuo Shoji. The data that support the findings of this study is available at bioRxiv (https://www.biorxiv.org/). IMPACT STATEMENTWe demonstrate evidence suggesting that HCV infection promotes the Itch-mediated ubiquitin-dependent degradation of LATS1 protein, a key factor for the Hippo pathway. HCV-induced ubiquitin-dependent degradation of LATS1 protein promotes inactivation of the Hippo pathway and nuclear translocation of YAP1 protein, thereby upregulating transcription of CYR61 and CTGF genes. We propose a novel molecular mechanism in which HCV infection promotes degradation of LATS1 protein, leading to inactivation of the Hippo pathway. Understanding HCV-induced inactivation of the Hippo pathway may lead to developing new strategies for preventing or treating HCV-related pathogenesis.