Abstract

The aim of this study was to investigate the relationships between the gadd genes expression and an apoptosis induction in two different growing cell types after treatments with cisplatin and methylmethan sulfonate (MMS). We have examined the kinetics and specificity of gadd45 and gadd153 expression following cisplatin and MMS treatments to HL-60 cells and primary cultured human kidney (HKN) cells. We have also determined an induction time of apoptosis by DNA fragmentation analysis and the presence of the cell cycle arrest by a flow cytometric measurement. The results were as follows. In non-adherent HL-60 cells, a typical ladder pattern was observed within 4 hours after treatments of 20 micrometer of cisplatin and 100 microgram/ml of MMS. At the same time while adherent HKN cells failed to exhibit a ladder pattern at even higher doses of genotoxic agents. Since HL-60 cells do not have p53 gene, these findings suggest the presence of a p53-independent apoptotic pathway. The increasing patterns of the mRNA levels of gadd45 and gadd153 varied with the type of genotoxic agents. In the case of MMS treatment, the induction was rapid and transient, regardless of the cell types. The mRNA level peaked at 4 hours after MMS treatment and markedly decreased after 12 hours. On the other hand, cisplatin-induced transcriptions of gadd45 and gadd153 continued to increase for at least 24 hours and reached a peak level at 48 hours after cisplatin treatment, regardless of the cell types. HL-60 cells revealed G2 arrest following 24 hours after cisplatin and MMS treatments. These findings suggest that the regulation mechanism of apoptosis between adherent and non-adherent cells, might be different and that gadd45 and gadd153 might have an important role in DNA repair rather than apoptosis. Also, the findings suggest that an expression pattern of gadd45 and gadd153 might be different according to the type of genotoxic agents.

• Keywords: p53, gadd;Cell cycle delay;Apoptosis;DNA damage