p53-dependent G2 arrest associated with a decrease in cyclins A2 and B1 levels in a human carcinoma cell line

In vivo transfer of wild-type (wt) p53 gene via a recombinant adenovirus ha s been proposed to induce apoptosis and increase radiosensitivity in severa l human carcinoma models. In the context of combining p53 gene transfer and irradiation, we investigated the consequences of adenoviral-mediated wtp53 gene transfer on the cell cycle and radiosensitivity of a human head and n eck squamous cell carcinoma line (SCC97) with a p53 mutated phenotype. We s howed that ectopic expression of wtp53 in SCC97 cells resulted in a prolong ed G1 arrest, associated with an increased expression of the cyclin-depende nt kinase inhibitor WAF1/p21 target gene, A transient arrest in G2 but not in G1 was observed after irradiation. This G2 arrest was permanent when exp onentially growing cells were transduced by Ad5CMV-p53 (RPR/INGN201) immedi ately after irradiation with 5 or 10 Gy. Moreover, levels of cyclins A2 and B1, which are known to regulate the G2/M transition, dramatically decrease d as cells arrived in G2, whereas maximal levels of expression were observe d in the absence of wtp53. In conclusion, adenoviral mediated transfer of w tp53 in irradiated SCC97 cells, which are mutated for p53, appeared to incr ease WAF1/p21 expression and decrease levels of the mitotic cyclins A2 and B1. These observations suggest that the G2 arrest resulted from a p53-depen dent premature inactivation of the mitosis promoting factor. (C) 2000 Cance r Research Campaign.