Mediation of γ-Hexachlorocyclohexane-induced DNA fragmentation in HL- 60 cells through intracellular Ca²⁺ release pathway

Abstract - 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 trated cells showed some characteristics 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 tha activation of Ca²⁺-dependent endonuclease, which triggers apoptosis in a Ca²⁺ and calmodulin-dependent manner.