Mediation of γ-Hexachlorocyclohexane-induced DNA Fragmentation in HL-60 Cells through Intracellular Ca2+ Release Pathway

The cytotoxicity of γ-hexachlorcyclohexane (γ-HCC) was evaluated in HL-60 cells. γ-HCC dose-dependently induced cytotoxicity of HL-60 with an IC50 value of 60±5 μm. The γ-HCC treated cells showed some characteristic changes of apoptosis, including blebbing of the membrane, condensation of the nuclear chromatin, vacuolation of cytoplasm and internucleosomal DNA fragmentation. γ-HCC induced DNA fragmentation of HL-60 cells in a dose-, time- and Ca2+-dependent manner. The DNA fragmentation induced was inhibited by intracellular Ca2+ chelator, calmodulin antagonist and Ca2+ sensitive endonuclease inhibitor. γ-HCC caused a steady increase in the cytosolic free Ca2+ concentration due to release from intracellular stores. Neither the DNA fragmentation nor the increase of intracellular Ca2+ induced by γ-HCC was inhibited by the removal of extracellular Ca2+. These data suggested that the cytotoxicity of γ-HCC in HL-60 cells is mediated by the increase of intracellular Ca2+ concentration and the activation of Ca2+-dependent endonuclease, which triggers apoptosis in a Ca2+ and calmodulin-dependent manner.