Abstract
The aim of our work was to evaluate mechanisms leading to radiosensitization of MOLT-4 leukemia cells following valproic acid (VA) treatment. Cells were pretreated with 2 mM VA for 24 h followed by irradiation with a dose of 0.5 or 1 Gy.
The effect of both noxae, alone and combined, was detected 1 and 24 hours after the irradiation. Induction of apoptosis was evaluated by a flow cytometry.
The extent of DNA damage was further determined by phosphorylation of histone H2AX using confocal microscopy. Changes in protein expression were identified by SDS-PAGE/immunoblotting.
Two millimolar VA increased apoptosis induction after irradiation as well as phosphorylation of H2AX and provokes an increase in the level of p53 and its phosphorylation at Ser392 in 4 h postirradiation. Likewise, p21 protein reached its maximal expression in 4 h after the irradiation of VA treated cells.
Twenty four hours later, only the p53 phosphorylated at Ser15 was detected. At the same time, the protein mdm2 (negative regulator of p53) was maximally activated.
The 24 hour treatment of MOLT-4 leukemia cells with 2 mM VA results in radiosensitizing, increases apoptosis induction, H2AX phosphorylation, and also p53 and p21 activation.