Preferential cytoplasmic localization of p34cdc2 in recurrent human squamous cell carcinoma after radiotherapy.

Duration of the G2-phase delay and arrest after exposure to ionizing radiation is thought to influence radiosensitivity. The kinase activity of the p34cdc2-cyclin B complex and the p34cdc2-cyclin A complex is implicated in G2- to M-phase transition and in G2-phase arrest after exposure to ionizing radiation. We analyzed the expression level and the subcellular location of p34cdc2, cyclin A and cyclin B in head and neck squamous cell carcinoma (SCC) tumors; samples were obtained from patients with locally nonrecurrent and recurrent tumors that had been treated by surgery and radiotherapy. No significant difference was noticed in cyclin A, cyclin B and p34cdc2 expression. However, we noted a significant preferential cytoplasmic location of p34cdc2 in recurring tumors compared to the nonrecurring ones (P < 0.001). This abnormal location of p34cdc2 occurs even in primary tumors in patients with recurring tumors, suggesting that a default in the activation of p34cdc2 kinase could be implicated in clinical radioresistance.