Chad Kuny, PhD

Research Title: The Contribution of UL97 Viral Cyclin-dependent Kinase Activity to HCMV Infection

Research Summary: Human Cytomegalovirus (HCMV) is a pathogen of worldwide importance, infecting the majority of the world’s population and causing diseases as varied as birth defects and atherosclerosis, with current research implicating HCMV for a contributory role in glioblastoma. One of the hallmarks of HCMV infection is the manipulation of the cell cycle into a “pseudo S-phase” such that S-phase genes are expressed in the absence of cellular DNA replication. Presumably, this allows the virus full access to the cellular DNA replication resources including Nucleotide Biosynthetic Enzymes (NBEs) that catalyze the de novo synthesis of nucleotides, and facilitates efficient replication of the viral genome. However, in order for HCMV to force the cell into the pseudo S-phase, the virus must inactivate the retinoblastoma tumor suppressor protein (Rb) that regulates the G1/S cell cycle transition. HCMV encodes a viral cyclin-dependent kinase (v-Cdk) named UL97 that phosphorylates and thus inactivates Rb, allowing for S-phase gene expression. Correspondingly, HCMV mutants that lack UL97 have reduced levels of DNA replication, among other defects. Trainee Chad Kuny discovered that the other Beta-Herpesviruses also encode v-Cdks that phosphorylate Rb (Kuny, et al., PLoS Pathogens 2010). Beta-Herpesviruses are notably lacking in NBEs when compared to other herpesviruses, leading Chad to hypothesize that HCMV was using UL97 to phosphorylate Rb primarily to allow for the expression of NBEs and therefore ensure an adequate supply of nucleotides for viral DNA replication. To test this hypothesis, he examined HCMV DNA replication in the presence of added deoxyribonucleosides, which can be imported into the cell and phosphorylated into deoxyribonucleotides (dNTPs) in the absence of S-phase gene expression. These experiments showed that dNTP availability is generally limiting for HCMV DNA replication, and is not a phenotype that can be specifically traced to the influence of UL97. However, in the process of performing these experiments, he also found evidence that HCMV can induce dNTP production through the DNA damage pathway, independent of Rb phosphorylation.

Dr. Kuny is continuing his training as a postdoctoral trainee at Penn State University’s Department of Biochemistry and Molecular Biology.