Loss of JAK1 Function Causes G2–M Cell-Cycle Defects Vulnerable to KIF18A Inhibition

Therapeutic resistance to DNA damage is a significant challenge in oncology. To gain insight into the biological mechanisms that cause DNA damage resistance and to inform strategies for achieving synergy with therapeutic radiation, we performed parallel pooled genetic CRISPR-Cas9 screening for survival in high-risk head and neck squamous cell carcinoma (HNSCC) subtypes. Surprisingly, in addition to known mediators of radiotherapy response, including ATM, DNA-PK, and NF-κB signaling, the loss of JAK1 was identified as a driver of tumor cell radioresistance. Knockout (KO) of JAK1 in HNSCC increased cell survival by enhancing the DNA damage-dependent G2-M cell-cycle arrest and delaying progression to radiation-induced mitotic catastrophe. In line with this finding, both JAK1 KO and kinase inhibition with abrocitinib prevented the subsequent formation of radiation-induced micronuclei. Loss of JAK1 function did not affect canonical cyclin-dependent kinase 1 signaling but instead reduced activation of polo-like kinase 1 and aurora kinase A, two kinases with auxiliary roles in the regulation of G2- and M-phase progression. Correspondingly, using both EdU labeling and live cell imaging techniques, JAK1 loss was found to cause prolonged metaphase, mitotic slippage, and progression to tetraploidy. Targeting the mitotic kinesin KIF18A with the small-molecule sovilnesib exacerbated mitotic stress and enhanced the efficacy of radiation. These studies establish KIF18A inhibition as a strategy to counteract the protective G2-M cell-cycle arrest induced by DNA damage and thus enhance tumor cell sensitivity to radiotherapy. SIGNIFICANCE: Loss of JAK1 promotes radioresistance in head and neck cancer through altered G2-M cell-cycle progression that can be reversed with KIF18A inhibition, supporting a potential strategy to restore radiosensitivity.