AbstractImmune and radiation resistance of cancer cells to cytotoxicity mediated by TNFα is promoted by the transcription factor NF-κB in several cancers, including head and neck squamous cell carcinoma (HNSCC). Genomic alterations that converge on the TNFα/NF-κB signal axis were found in ∼40% of HNSCCs by The Cancer Genome Atlas. However, identification of therapeutic targets that contribute to aberrant TNFα/NF-κB activation and resistance has been challenging. Here, we conducted a functional RNAi screen to identify regulators of TNFα-induced NF-κB activation and cell viability, using parallel NF-κB β−lactamase reporter and cell viability assays in a HNSCC cell line which harbors expression and genomic alterations typically found in human papillomavirus–negative HNSCC. Besides multiple components of canonical TNFα/NF-κB signaling, we identified components of the WNT, NOTCH, and TGFβ pathways that we previously showed contribute to noncanonical activation of NF-κB. Unexpectedly, we also observed that multiple G2/M cell-cycle kinases [Aurora kinase A, polo-like kinase 1, WEE1, and threonine tyrosine kinase (TTK)], and structural kinetochore/microtubule components (NDC80 and NUF2), modulate TNFα-induced NF-κB activation and cell viability. Several of these targets inhibit TNF-induced nuclear translocation of RELA, consistent with prior reports linking NF-κB activation to G2/M kinases or microtubule assembly. Further investigation of an understudied mitotic kinase, TTK/monopolar spindle 1, shows that its inhibition or depletion attenuates TNFα-induced RELA nuclear translocation, promoting cell death, DNA damage, polyploidy, and mitotic catastrophe, leading to radiosensitization. Together, our RNAi screening identifies a critical linkage between the G2/M cell-cycle checkpoint/kinetochore components and NF-κB activity, as well as targets that can sensitize HNSCC cells to TNFα or radiation.Significance:Here, RNAi library screening reveals that multiple G2/M and kinetochore components, including TTK/monopolar spindle 1, modulate TNFα-induced NF-κB activation, cell survival, and genotoxicity, underscoring their potential importance as therapeutic targets in HNSCC.