To directly test whether ATM function is compromised in radiosensitive HPV+ HNSCC cells, we assessed ATM-mediated signal transduction after irradiation in three ATM target proteins: Chk2 (T68), KAP1 (S824), and ATM itself (autophosphorylation at S1981). The gene discussed is ATM; the disease is head and neck squamous cell carcinoma.