Survivin Is a Central Mediator of Cell Proliferation in HPV-Negative Head and Neck Squamous Cell Carcinoma

Background/Objectives: HNSCC is a highly aggressive malignancy marked by the dysregulation of the cell cycle. In HPV− HNSCC, mutations in the CDKN2A gene frequently result in the loss of the p16 protein, a key inhibitor of the cyclin D1/CDK4/6 complex. This loss results in unchecked G1/S phase progression. The CDK4/6 inhibitor palbociclib has shown therapeutic potential in HPV− HNSCC by inducing G1 phase arrest and reducing cell viability. In this study, we investigated the molecular mechanisms by which palbociclib affects cell viability in HPV− HNSCC. Methods: Four HPV− HNSCC cell lines were treated with palbociclib, and RNA sequencing was performed to assess changes in gene expression. Cell viability was measured using the MTT assay. To further investigate protein localization, interactions, and function, we used immunofluorescence staining, co-immunoprecipitation, small molecule inhibitors, and siRNA-mediated knockdown. Results: We demonstrate that palbociclib downregulates survivin, a protein that plays dual roles in mitosis and apoptosis, thereby inhibiting cell proliferation. We also found that survivin is overexpressed in HPV− HNSCC. Inhibiting survivin dimerization using the compound LQZ-7i significantly reduces cell viability and promotes its export from the nucleus to the cytoplasm. Additionally, we identified USP1, a deubiquitinase, as both a downstream target of CDK4/6 and a key regulator of survivin stability. Inhibiting USP1 activity or silencing its expression significantly reduces survivin levels. Conclusions: Our findings highlight survivin as a critical mediator of cell proliferation in HPV− HNSCC and suggest that targeting the CDK4/6-USP1-survivin axis may offer a promising therapeutic strategy.