Stimulation of cholesterol efflux inhibits herpesvirus nuclear egress
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Cholesterol in herpesvirus envelopes and host membranes supports membrane fusion during virus entry. However, little is known about how cholesterol affects other aspects of the viral replication cycle. Here, using an infection model that begins with reactivation from latency, bypassing the entry step, we demonstrate that depleting intracellular cholesterol inhibits the production of infectious Kaposi’s sarcoma-associated herpesvirus (KSHV). Treatment of latently infected cells with the liver X receptor α (LXRα) agonist 22( R )-hydroxycholesterol (22OH) increased expression of sterol response genes, including the cholesterol efflux pump ATP binding cassette subfamily A member 1 (ABCA1), and reduced intracellular cholesterol. 22OH treatment initially enhanced lytic reactivation, but diminished viral protein accumulation during late replication, while altering accumulation of host proteins that regulate the cell cycle and innate immunity. Cholesterol efflux led to an increase in the proportion of capsids lacking viral genomes in the nucleus and a reduction in nucleocapsids accessing the cytoplasm. Next, we used a herpes simplex virus (HSV) infection model to explore if 22OH affected the conserved herpesvirus nuclear egress complex (NEC), comprised of two viral proteins that accumulate at the inner nuclear membrane and facilitate primary envelopment. We found that 22OH inhibited HSV-1 and HSV-2 replication and spread in plaque reduction assays and impaired localization of NEC proteins pUL31 and pUL34 to the nuclear periphery. These findings indicate that cholesterol efflux inhibits herpesvirus replication by interfering with the formation of nucleocapsids competent to complete nuclear egress.
IMPORTANCE
Cholesterol plays key roles in regulating the fluidity of cellular membranes and the trafficking and lateral diffusion of transmembrane proteins. Herpesviruses encode a variety of transmembrane proteins that traffic to different cellular compartments, while herpesvirus capsids and tegument proteins interact with nuclear and trans-Golgi network membranes throughout the primary and secondary envelopment process, respectively. This produces viral particles with cholesterol as an envelope component which is required to support membrane fusion during entry. Our discovery that cholesterol efflux inhibits KSHV nuclear egress suggests that cholesterol plays important supportive roles at this stage of lytic replication. Moreover, we observed that cholesterol efflux mediated by oxysterol treatment has widespread effects on host cell protein expression, resulting in a non-classical antiviral state. Cholesterol likely supports the proper trafficking of viral proteins to nuclear sites of virion assembly or is influencing the fluidity of nuclear membranes used for viral primary envelopment and de-envelopment during nuclear egress.
