HUMAN CYTOMEGALOVIRUS INDUCED CHANGES IN LOW-DENSITY LIPOPROTEIN RECEPTOR EXPRESSION AND TRAFFICKING

Abstract

Human cytomegalovirus (HCMV) is a beta-herpesvirus that establishes a lifelong latent infection in its host. It then reactivates based upon environmental cues and stressors, causing disease in those who are immunocompromised. It has a broad cell tropism allowing it to infect a wide variety of cells and manipulate numerous cellular pathways to establish a successful infection. In unpublished data collected by the Goodrum lab, low-density lipoprotein receptor (LDLR) was found to be strongly downregulated in HCMV infection in fibroblasts. LDLR is a cell surface receptor responsible for the uptake of cholesterol-rich ligands. Using immunoblotting, immunofluorescence, and siRNA knockdowns, we gain insight into how LDLR is trafficked in a latent versus replicative infection, and why those changes may affect HCMV replication. In a latent infection, there is no change in LDLR levels between mock and WT infected cells. However, in a replicative infection in fibroblasts, mature LDLR (mLDLR) is driven to the lysosome for degradation, and immature iLDLR (iLDLR) accumulates in the ER and is targeted for ER-associated protein degradation (ERAD). A knockdown of LDLR increases viral protein levels and the cleavage of SREBP2, a transcription factor for lipogenic proteins. This may indicate that downregulating LDLR helps the virus increase cholesterol biosynthesis, providing a potential reason for the virus to degrade and block the formation of LDLR. Future experiments are needed to further understand the workings of the mechanism, and the implications and consequences of HCMV manipulating ERAD to degrade host proteins.