Expression of cell cycle regulator genes in KB, a human squamous cell carcinoma cell line, after irradiation

DNA damage induced by irradiation causes overexpression of the p53 gene, an d subsequently the upregulation of p53 downstream genes involved in cell cy cle modification. Irradiated malignant cells which possess wild-type p53 ha ve been known to undergo G(1) arrest due to p21/Cip1/Waf1 upregulation. Oth er p53 downstream genes related to the modification of the cell cycle such as gadd45 may cause G(2) arrest. Many of the genes which regulate the cell cycle progression have been identified, including the G(1) phase specific i nk4 family of cyclin-dependent kinase inhibitors (CDK-I), another group of CDK-Is, which affect the cyclin-CDK complexes ubiquitously, and S/G(2) acce lerator genes. The sequential changes in these cell cycle regulator genes a fter irradiation has not been clarified. We analyzed the appearance of the apoptotic fraction and cell cycle perturbation after irradiation using KB, a human squamous cell carcinoma line derived from oral floor, and examined the alteration of gene expression for cell cycle regulator genes. The KB ce lls proceeded to undergo apoptosis in a time and dose dependent manner afte r irradiation and showed G(2) arrest accompanied by upregulation of p53, ub iquitous CDK-Is, and S and G(2) accelerator genes.