Phosphoproteome Remodeling upon CDK1 Inhibition Restricts HSV-1 IE Gene Transcription and Replication

Cyclin-dependent kinase 1 (CDK1) regulates multiple cellular processes that HSV-1 can exploit to promote its own replication, particularly during the early steps of lytic infection. We investigated whether CDK1 inhibition disrupts immediate-early (IE) gene expression and analyzed the host phosphoproteome early in infection to identify putative host factors and mechanisms that facilitate HSV-1 IE gene expression and are controlled by CDK1. Human foreskin fibroblasts (HFFs) were pre-treated with a CDK1 inhibitor and showed a 1000-fold reduction in HSV-1 replication and significant reductions in IE mRNAs and protein levels at 4 hpi. We characterized cells after CDK1 inhibition and HSV-1 infection at 3 hpi by tandem mass spectrometry and identified >5500 phosphopetides (~2600 proteins), analyzing differential phosphorylation and protein-protein interactions. We validated CDK1 inhibition by detecting phosphorylation-specific decreases in known CDK1 substrates, as well as Robust Kinase Activity Inference. Rank- and network-based analyses of our dataset highlighted several candidate proteins, linking their CDK-directed phosphorylation to HSV-1 IE gene expression. Notably, the C-terminal domain of the large subunit of RNA polymerase II (RNAPII), POLR2A, is extensively phosphorylated, and its phosphorylation is significantly reduced upon CDK1 inhibition during viral infection. Taken together, these data support a model in which CDK1 activity maintains a transcriptionally permissive cellular state required for efficient HSV-1 IE gene expression. Our data suggest that when CDK1 is pharmacologically inhibited, key transcriptional facilitators are dysregulated, impairing viral transcription and replication.