The Torsin Activator LULL1 Is Required for Efficient Growth of Herpes Simplex Virus 1

Abstract

TorsinA is a membrane-tethered AAA؉ ATPase implicated in nuclear envelope dynamics as well as the nuclear egress of herpes simplex virus 1 (HSV-1). The activity of TorsinA and the related ATPase TorsinB strictly depends on LAP1 and LULL1, type II transmembrane proteins that are integral parts of the Torsin/cofactor AAA ring, forming a composite, membrane-spanning assembly. Here, we use CRISPR/Cas9-mediated genome engineering to create single-and double knockout (KO) cell lines of TorA and TorB as well as their activators, LAP1 and LULL1, to investigate the effect on HSV-1 production. Consistent with LULL1 being the more potent Torsin activator, a LULL1 KO reduces HSV-1 growth by one order of magnitude, while the deletion of other components of the Torsin system in combination causes subtle defects. Notably, LULL1 deficiency leads to a 10-fold decrease in the number of viral genomes per host cell without affecting viral protein production, allowing us to tentatively assign LULL1 to an unexpected role that precedes HSV-1 nuclear egress. IMPORTANCEIn this study, we conduct the first comprehensive genetic and phenotypic analysis of the Torsin/cofactor system in the context of HSV-1 infection, establishing LULL1 as the most important component of the Torsin system with respect to viral production. Herpesviruses are enveloped, double-stranded DNA viruses that enter the host cell by fusing with the plasma membrane. Following the microtubule-dependent transport of the nucleocapsid to the nuclear pore complex, the linear herpesvirus genome is ejected into the nucleus of the host cell, where it is transcribed and replicated. Viral genome replication (1), transcription of viral genes, and assembly and packaging of new viral particles take place in designated replication compartments located at the periphery of the nucleus (2).After the viral capsids are assembled and packaged, they must exit the nucleus to undergo further maturation in the cytoplasm. Herpesviruses undergo nuclear egress via a nuclear membrane budding mechanism in which the viral capsid first buds through the inner nuclear membrane (INM) to form an enveloped intermediate within the perinuclear space, which then fuses with the outer nuclear membrane (ONM) to release the deenveloped capsid into the cytosol (3, 4).Several viral proteins are required for efficient nuclear egress. Viral kinase U S 3 and the virally manipulated host cell protein kinase C phosphorylate and locally disassemble the nuclear lamina, which represents a physical barrier between the viral capsid and the INM (5-7). Additionally, the soluble phosphoprotein U L 31 and the type II inner nuclear membrane phosphoprotein U L 34, which together constitute the viral nuclear egress complex, accumulate at the INM to facilitate capsid envelopment (8-10). Both U L 31 and U L 34 are essential for herpesvirus growth (11), and their coexpression without viral infection is sufficient to cause vesicle formation (12,13). While the viral factors involved in nuclear egress are well characterized, muc...

HIV–host interactome revealed directly from infected cells

“…This effect is specific for the HIV-1 and SIV Envs, but without effect on HIV-1 Env − virus pseudotyped with VSV-G, suggesting that Tor3A acts against HIV-1 during a late phase of the viral life cycle, perhaps modulating the folding/oligomerization of this large, highly glycosylated protein. In contrast, compared with its progenitor cell line, virus produced in CRISPR/Cas9 TOR1AIP2/LULL1 knockout cells 22 increased the infectivity of WT HIV-1 (Fig. 5c and Supplementary Fig.…”

“…11a), suggesting that HIV-1 Env maturation and therefore function may be constrained by Tor3A and LULL1. Interestingly, TOR1AIP2 was recently shown to be required for efficient growth of HSV-1 as deletion of TOR1AIP2 affected a late step of the viral life cycle preceding viral egress but not earlier steps of viral entry, transcription or protein production 22 .…”

Torsins: not your typical AAA+ ATPases

“…However, LULL1 depletion does decrease the formation of ER-derived sinusoidal membrane structures upon TorsinB overexpression (Rose et al, 2014), indicating a potential role for LULL1 in ER morphology. Recently, it has been found that LULL1 knockout in HeLa cells decreases the formation of infectious HSV-1 particles by an order of magnitude, while a LAP1B knockout has no effect (Turner et al, 2015). This again suggests that these proteins have different functions, which is consistent with their distinct subcellular localization.…”

Fantastic nuclear envelope herniations and where to find them

“…For example, herpesvirus exits the nucleus by budding through the NE lumen/PNS[91,92](Figure 3). While the molecular machinery that drives herpesvirus egress is encoded by the viral genome (the nuclear egress complex/NEC) and is thus distinct from NPC biogenesis, there is nonetheless evidence for the involvement of ESCRTs[93,94] and Torsin A[95] (and LULL1[96]) in the viral lifecycle hinting at a functional relationship with host nuclear membrane remodeling pathways. Further, Torsin A has been implicated in an egress pathway for so-called “Mega” RNPs that functions in the cells of Drosophila neuromuscular junctions[70,97] and in sea urchin embryos[98].…”