Hepatitis C virus NS5A protein promotes the lysosomal degradation of diacylglycerol O-acyltransferase 1 (DGAT1) via endosomal microautophagy.

Many viruses often use a protein degradation system (e.g., the ubiquitin-proteasome pathway or lysosome pathway) to modulate viral propagation and viral pathogenesis. We reported that hepatitis C virus (HCV) infection promotes the lysosomal degradation of hepatocyte nuclear factor-1α (HNF-1α) via chaperone-mediated autophagy (CMA) through an NS5A-mediated association of HNF-1α with cellular chaperone heat shock cognate 70 kDa (HSC70) protein. HSC70 binds to the pentapeptide KFERQ motif (also known as a CMA-targeting motif) on HNF-1α protein and promotes the lysosomal degradation of HNF-1α. The KFERQ motif plays a crucial role in the two lysosomal degradation pathways, CMA and endosomal microautophagy (eMI). Herein, we searched for a novel substrate of HCV-induced lysosomal degradation by examining the NS5A-interacting proteins that carry the KFERQ motif. We identified diacylglycerol O-acyltransferase 1 (DGAT1), which is a key factor for HCV particle formation, as a candidate substrate for HCV-induced lysosomal degradation pathway. The region spanning from amino acids 149-153 of DGAT1 protein matches the rule for the KFERQ motif. DGAT1 protein was co-immunoprecipitated with HSC70, whereas DGAT1 Q149A mutant was not co-immunoprecipitated with HSC70, suggesting that the KFERQ motif is responsible for the interaction between DGAT1 and HSC70. Knockdown of LAMP-2A protein in HCV J6/JFH1-infected cells did not recover DGAT1 protein, whereas knockdown of VPS4B recovered the level of DGAT1 protein, suggesting that DGAT1 is degraded via eMI. These findings lead us to propose that HCV NS5A protein facilitates the recruitment of HSC70 to DGAT1, thereby promoting the lysosomal degradation of DGAT1 via eMI.