CDK1 and head and neck squamous cell carcinoma: We found that CDK7 depletion led to reduced phosphorylation levels of the Carboxy-terminal domain (CTD) of RNA Polymerase II (Ser5), retinoblastoma protein (Rb) (Ser780), and CDK1 T-loop phosphorylation (Thr161) in the three HNSCC cell lines tested.