A Role for Myosin Va in Human Cytomegalovirus Nuclear Egress

Abstract

Herpesviruses replicate and package their genomes into capsids in replication compartments within the nuclear interior. Capsids then move to the inner nuclear membrane for envelopment and release into the cytoplasm in a process called nuclear egress. We previously found that nuclear F-actin is induced upon infection with the betaherpesvirus human cytomegalovirus (HCMV) and is important for nuclear egress and capsid localization away from replication compartment-like inclusions toward the nuclear rim. Despite these and related findings, it has not been shown that any specific motor protein is involved in herpesvirus nuclear egress. In this study, we have investigated whether the host motor protein, myosin Va, could be fulfilling this role. Using immunofluorescence microscopy and coimmunoprecipitation, we observed associations between a nuclear population of myosin Va and the viral major capsid protein, with both concentrating at the periphery of replication compartments. Immunoelectron microscopy showed that nearly 40% of assembled nuclear capsids associate with myosin Va. We also found that myosin Va and major capsid protein colocalize with nuclear F-actin. Importantly, antagonism of myosin Va with RNA interference or a dominant negative mutant revealed that myosin Va is important for the efficient production of infectious virus, capsid accumulation in the cytoplasm, and capsid localization away from replication compartment-like inclusions toward the nuclear rim. Our results lead us to suggest a working model whereby human cytomegalovirus capsids associate with myosin Va for movement from replication compartments to the nuclear periphery during nuclear egress. Little is known regarding how newly assembled and packaged herpesvirus capsids move from the nuclear interior to the periphery during nuclear egress. While it has been proposed that an actomyosin-based mechanism facilitates intranuclear movement of alphaherpesvirus capsids, a functional role for any specific myosin in nuclear egress has not been reported. Furthermore, the notion that an actomyosin-based mechanism facilitates intranuclear capsid movement is controversial. Here we show that human cytomegalovirus capsids associate with nuclear myosin Va and F-actin and that antagonism of myosin Va impairs capsid localization toward the nuclear rim and nuclear egress. Together with our previous results showing that nuclear F-actin is induced upon HCMV infection and is also important for these processes, our results lend support to the hypothesis that nascent human cytomegalovirus capsids migrate to the nuclear periphery via actomyosin-based movement. These results shed light on a poorly understood viral process and the cellular machinery involved.

A putative WAVE regulatory complex (WRC) interacting receptor sequence (WIRS) in the cytoplasmic tail of HSV-1 gE does not function in WRC recruitment or neuronal transport

“…Additionally, there was no evidence of colocalisation between gE and F-actin in both cell types, providing no evidence for an association of gE with F-actin. In studies of the betaherpesvirus human cytomegalovirus (HCMV), the association of myosin Va, the HCMV major capsid protein and F-actin within the nucleus suggests that actin motors are used for intranuclear HCMV capsid motility [ 70 ]. While nuclear actin filaments are also induced during PrV and HSV-1 infection [ 71 ] and actin is incorporated into mature HSV-1 virions [ 72 ] (suggesting a role in viral assembly), subsequent work by the same group demonstrated that siRNA-mediated knockdown of endogenous actin did not significantly impact HSV-1 virion production [ 73 ].…”

Nuclear myosins – roles for molecular transporters and anchors

“…Myosin Va has been shown to have a role in the transport of viral capsids during nuclear egress of the human cytomegalovirus (Wilkie et al, 2018). Here, nuclear myosin Va binds directly to the viral capsids, which are then found to be on filamentous actin that is directed towards the nuclear periphery (illustrated in Fig.…”

“…1). These myosins are involved in the following processes, which will form the basis of this reviewchromosome rearrangements (Chuang et al, 2006), DNA damage repair (Kulashreshtha et al, 2016), transcription (Zorca et al, 2015) and viral infections (Wilkie et al, 2018) (illustrated in Fig. 2).…”

Exploration of Binary Protein-Protein Interactions Between Tick-Borne Flaviviruses and Ixodes Ricinus

“…Myosin V is involved in short-range transport of diverse intracellular cargo -such as organelles, vesicles, protein complexes and mRNA -along actin laments [84]. To the best of our knowledge, no published report of a binary interaction between a viral protein and myosin V exists in the literature, although human myosin 5a has been shown to be important for early events during infection by Rhinovirus B14 [85], for transport of herpes simplex virus 1 from the trans-Golgi network toward the plasma membrane [86] and for nuclear egress of human cytomegalovirus [87]. Moreover, the myosin V paralog 5c has been implicated in the release of DENV [88].…”