Human Cytomegalovirus Induces the Activity and Expression of Acetyl-Coenzyme A Carboxylase, a Fatty Acid Biosynthetic Enzyme Whose Inhibition Attenuates Viral Replication

Abstract

We have previously reported that human cytomegalovirus (HCMV) infection induces large-scale changes to host cell glycolytic, nucleic acid, and phospholipid metabolism. Here we explore the viral mechanisms involved in fatty acid biosynthetic activation. Our results indicate that HCMV targets ACC1, the rate-limiting enzyme of fatty acid biosynthesis, through multiple mechanisms. HCMV infection was found to activate ACC1 expression, increasing the abundance of both ACC1 mRNA and protein. Viral gene expression but not viral DNA replication was found to be necessary for HCMV-mediated induction of ACC1 levels. HCMV infection was also found to increase the proteolytic processing of SREBP-2, a transcription factor whose proteolytic cleavage is known to activate a variety of phospholipid metabolic genes. Processing of SREBP-2 was found to be dependent on mTOR activity; pharmaceutical inhibition of mTOR blocked HCMV-induced SREBP-2 processing and prevented the induction of fatty acid biosynthesis and ACC1 expression. Independent of the increases in ACC1 expression, HCMV infection also induced ACC1's enzymatic activity. Inhibition of ACC1 through either RNA interference (RNAi) or inhibitor treatment was found to attenuate HCMV replication, and HCMV replication was sensitive to ACC1 inhibition even at the later stages of infection, suggesting a late role for fatty acid biosynthesis during HCMV replication. These findings indicate that HCMV infection actively modulates numerous functional aspects of a key metabolic regulatory enzyme that is important for high-titer viral replication.For decades, numerous reports have indicated that infection with a wide variety of evolutionarily divergent viruses results in a general activation of host cell metabolism (7,15,16,26,29,39,42). This metabolic activation can be therapeutically useful; for example, increased or divergent nucleotide metabolism is often clinically targeted to treat various viral infections, such as hepatitis B virus, HIV, human cytomegalovirus (HCMV), and herpes simplex virus (3,13,18,28). Despite the successes of these antiviral strategies, relatively little is known about the specific metabolic activities induced by viral infection and the mechanisms responsible for their activation. Given the viral reliance on the host cell metabolic network for the production of viral progeny, elucidating the mechanisms of viral metabolic manipulation will likely highlight novel avenues for therapeutic development.HCMV is a widespread opportunistic pathogen that can cause severe disease in various immunosuppressed populations, including the elderly, cancer patients receiving immunosuppressive chemotherapy, transplant recipients, and AIDS patients (17,38). Additionally, congenital HCMV infection occurs in 1 to 2% of all live births (3) and can result in multiple organ system abnormalities, with central nervous system damage occurring in the majority of symptomatic newborns (11,38).HCMV is a large, double-stranded DNA virus that contains an ϳ240-kb genome encoding over 200 open re...

Differential Role for Host Translation Factors in Host and Viral Protein Synthesis during Human Cytomegalovirus Infection

“…As infection progresses, both total protein synthesis and virus replication become increasingly resistant to the effects of mTOR inhibitors, despite significant disruption of the eIF4F complex (19). This suggests that mTOR has additional eIF4F-independent roles in virus replication, perhaps in the metabolic remodeling of HCMV-infected cells (20). These data suggest that the eIF4F complex may not be required for viral mRNA translation during the later stages of infection.…”

“…Step gradients consisted of 10,20,30,40, and 50% sucrose steps, each prepared in polysome gradient buffer (20 mM TrisHCl [pH 7.4], 140 mM KCl, 5 mM MgCl 2 ) containing 100 g of cycloheximide/ml. Confluent serum-starved fibroblasts were infected at an MOI of 3 in serum-free media.…”

Human kinome profiling identifies a requirement for AMP-activated protein kinase during human cytomegalovirus infection

“…For example, active AMPK inhibits acetyl-CoA carboxylase (ACC), blocking fatty acid biosynthesis, and it activates the tuberous sclerosis protein complex (TSC1/2) to decrease mTOR signaling, disfavoring cell growth. Each of these alterations is exactly opposite to what is needed for HCMV replication (12,(34)(35)(36)(37)(38). How is active AMPK decoupled from some of its downstream substrates?…”

“…The HCMV pUL38 protein binds to TSC2 and prevents TSC1/2 from responding to AMPK phosphorylation (39). Although ACC is induced and required for HCMV replication (34), the mechanism by which it is protected from inactivation by AMPK after infection is unknown. It has been suggested that distinct thresholds of AMPK activity are required for activity toward each of its different substrates (40).…”

Recent advances in CMV tropism, latency, and diagnosis during aging

“…Amp-activated protein kinase (AMPK) and calmodulin-dependent kinase kinase (CAMKK) are important for changes in central carbon metabolism (McArdle et al 2012;McArdle et al 2011;Terry et al 2012). Viral changes to fatty acid metabolism involve mTOR signaling (Spencer et al 2011;Purdy et al 2015). Protein kinase RNA-like endoplasmic reticulum kinase (PERK), an ER stress-responsive factor, contributes to HCMV-induced lipid synthesis (Yu et al 2013).…”