Gibson, J. E. | bioRxiv Science

bioRxiv2026

Selective effects of cyclin dependent kinase inhibitors in gammaherpesvirus reactivation from latency

Cell cycle manipulation is critical to oncogenesis, including cancers associated with oncogenic gammaherpesviruses, Epstein-Barr Virus and Kaposis Sarcoma-associated Herpesvirus. Infection with these viruses can result in various cancers, including lymphomas and carcinomas. In healthy individuals, gammaherpesvirus infections result in lifelong latent infections with occasional reactivation. The cell cycle plays a critical role in infection, particularly in reactivation from quiescent latency to lytic virus replication. A number of cyclin-dependent kinase (CDK) inhibitors are clinically available but with little investigation thus far for virus-associated cancers. Using the mouse gammaherpesvirus model, we assessed the impact of CDK inhibitors on virus reactivation. First, we tested chemical inducers of reactivation, and found that optimal reactivation occurred with a combination of PMA and sodium butyrate. Application of optimal reactivation triggers demonstrated distinct stage-specific outcomes of reactivation, distinguished using flow cytometry to measure expression of GFP (early reactivation) and vRCA, a late viral protein (late reactivation). Following chemical induction of reactivation, we used flow cytometry to demonstrate that the early effects of induction were unaffected by CDK inhibitors. However, all broad spectrum CDK inhibitors tested, Dinaciclib, Alvocidib, and Seliciclib, decreased both reactivation from latency and primary lytic replication. In contrast, the impact of targeted CDK 4/6 inhibitors, Palbociclib, Ribociclib, and Abemaciclib, was more nuanced, with decreased reactivation when given concurrently, but increased reactivation when administered prior to induction. These findings were consistent for both murine gammaherpesvirus and Epstein-Barr Virus. Overall, our data indicate that CDK inhibitors may be useful for targeted treatment of gammaherpesvirus-associated cancers, but optimal use of targeted CDK 4/6 inhibitors requires careful consideration of cell state and order of therapies.

microbiology↗

bioRxiv2019

The gammaherpesvirus 68 viral cyclin facilitates reactivation by promoting latent gene expression.

Gammaherpesviruses establish life-long infections within their host and have been shown to be the causative agents of devastating malignancies. Chronic infection within the host is mediated through cycles of transcriptionally quiescent stages of latency with periods of reactivation into more active lytic and productive infection. The mechanisms that regulate reactivation from latency remain poorly understood. Previously, we defined a critical role for the viral cyclin in promoting reactivation from latency. Disruption of the viral cyclin had no impact on the frequency of cells containing viral genome during latency, yet it remains unclear whether the viral cyclin influences latently infected cells in a qualitative manner. To define the impact of the viral cyclin on latent gene expression, we utilized a viral cyclin deficient variant expressing a LANA-beta-lactamase fusion protein (LANA::{beta}la), to enumerate both the cellular distribution and frequency of latent gene expression. Disruption of the viral cyclin did not affect the cellular distribution of latently infected cells, but did result in a significant decrease in the frequency of cells that expressed LANA::{beta}la across multiple tissues and in both immunocompetent and immunodeficient hosts. Strikingly, whereas the cyclin-deficient virus had a reactivation defect in bulk culture, sort purified cyclin-deficient LANA::{beta}la expressing cells were fully capable of reactivation. These data emphasize that the {gamma}HV68 latent reservoir is comprised of at least two distinct stages of infection characterized by differential latent gene expression, and that a primary function of the viral cyclin is to promote latent gene expression within infected cells in vivo.\n\nAUTHOR SUMMARYGammaherpesviruses are ubiquitous viruses with oncogenic potential that establish latency for the life of the host. These viruses can emerge from latency through reactivation, a process that is controlled by the immune system. Control of viral latency and reactivation is thought to be critical to prevent {gamma}HV-associated disease. This study focuses on a virally-encoded cyclin that is required for reactivation from latency. By characterizing how the viral cyclin influences latent infection in pure cell populations, we find that the viral cyclin has a vital role in promoting viral gene expression during latency. This work provides new insight into the function of a virally encoded cyclin in promoting reactivation from latency.

microbiology↗