Inhibition of Nrf1 activity is a relevant for the HCV-dependent dysregulation of host lipid metabolism

Abstract

BACKGROUNDDespite advances in knowledge and medicine, hepatitis C virus (HCV) infection remains a global challenge. The viral life cycle depends heavily on lipid metabolism; consequently, HCV infection is associated with significant alterations to host lipid homeostasis. One of the regulators maintaining this homeostasis is the transcription factor nuclear factor erythroid 2-related factor 1 (Nrf1). There are multiple Nrf1 proteoforms that differ in their capacity to act as a cholesterol sensor or to activate or inhibit gene expression. Previously, we identified that the amount of full-length Nrf1 protein in HCV-replicating cells is significantly reduced. In this study, we investigate whether HCV affects the formation and functionality of the different Nrf1 proteoforms, and whether this contributes to the HCV-dependent dysregulation of cellular lipid metabolism. METHODSThe HCV-Nrf1 crosstalk was characterized using robust methods including: Western blot, FRET Acceptor Photobleaching assay, reverse transcriptase-polymerase chain reaction and confocal laser scanning microscopy-based approaches. RESULTSHCV infection does not alter the onset of Nrf1 proteoforms generated through proteasomal cleavage of the protein. However, the amount of different Nrf1 proteoforms is significantly reduced in HCV-positive cells due to enhanced Nrf1 turnover. Furthermore, the Nrf1 proteoforms with transcriptional activator functions are prevented from translocation into the nucleus. Reduced Nrf1 activity contributes to elevated cholesterol levels and favors lipid droplets formation. Conversely, rescue of Nrf1 activity in HCV-replicating cells is associated with decreased intracellular cholesterol levels, reduced number of lipid droplets and impaired viral release reflected by intracellular accumulation of the core protein and intact viral particles. CONCLUSIONSOverall, our results identify Nrf1 as a significant factor in the deregulation of host lipid metabolism induced by HCV. The inhibition of Nrf1 functionality driven by HCV leads to intracellular cholesterol accumulation, resulting in enhanced lipid droplet formation that supports the HCV life cycle and contributes to HCV-associated pathogenesis.