Neurotropic herpesvirus envelopment and microtubule-mediated transport

The Alphaherpesvirinae include pathogens of the nervous system such as herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) and the swine virus pseudorabies virus (PRV). Initial infection is commonly at mucosal epithelia such as the oral and anogenital mucosa for HSV, and nasal and oropharyngeal mucosa for PRV. Following replication in these tissues, progeny viral particles are released and infect the termini of adjacent sensory neurons. They then travel by microtubule-directed retrograde traffic along the axon to the neuronal cell body. The viral genome is ultimately delivered to the nucleus and persists as a circular dsDNA episome during ensuing latency in the trigeminal ganglia of humans (HSV-1) and swine (PRV). Periodic reactivation from latency is followed by viral gene expression, DNA replication and assembly of new capsids. These become packaged with the viral genome, emerge from the nucleus and bud into cytoplasmic organelles to generate enveloped, infectious viral particles in the organellar lumen. How and where these transport and envelopment events occur in alphaherpesvirus-infected neurons is poorly understood. Maturing alphaherpesvirus particles are transported from the neuronal cell body into and along the axon by microtubule-directed anterograde transport using kinesin motors. Infectious mature viral particles accumulate at the nerve terminal then are released to infect adjacent mucosal epithelia, leading to subsequent rounds of viral replication and spread. The identity of the kinesin motors utilized at each stage, the machinery used to recruit kinesins to trafficking virions and even the structure of the viral particle that traffics down the axon, whether non-enveloped capsids or capsids that have acquired envelopes in the neuronal cell body, are key questions that we address in this application. In Specific Aim 1 we investigate the function of the gE/gI-US9p membrane protein complex in recruitment of the kinesin motors KIF1A and KIF5 to HSV-1 and PRV. We also test an innovative hypothesis concerning the role of the large tegument protein UL36p in assembly of KIF5 onto trafficking virions. In Specific Aim 2 we use a novel “envelopment trap” to address the controversial question of where HSV-1 acquires its envelope, whether in the cell body or nerve terminal (the Married and Separate mechanisms, respectively) in a range of neuronal cell lines, human iPSC-derived Trigeminal Ganglia and explanted sensory neurons. We also test key questions concerning the mechanisms of kinesin recruitment during egress of HSV-1 and PRV via the Married and Separate pathways. This proposal is therefore focused on the three major events that underlie alphaherpesvirus transmission from the nervous system to mucosal surfaces following reactivation from latency: capsid envelopment, microtubule-directed trafficking, and anterograde axonal transport. The specific aims exploit the complementary in vitro and in vivo expertise of the two principal investigators, and our common interests and experience with the gE/gI-US9p complex and UL36p, to dissect the molecular mechanisms supporting recrudescent disease caused by these viruses.