Thapsigargin-induced apoptosis of K562 cells and its mechanism / 中国实验血液学杂志

ABSTRACT

The aim was to study the apoptotic induction effect of thapsigargin on leukemia cell line K562 and its possible mechanism. After the treatment of leukemia cell line K562 by thapsigargin, morphological change of apoptotic cells was investigated by AO/EB fluorescent staining under fluorescent microscope; apoptosis rate was determined with annexin V-FITC/PI double staining by flow cytometry; intracellular calcium concentrations ([Ca(2+)]i) were measured by fluorescence spectrophotometer with calcium sensitive fluorescence indicator Fura-2/AM; mitochondrial transmembrance potentials (Delta Psi m) was detected on flow cytometry through staining of Rhodamine (Rh123); the changes of caspase-3, -7, -9, -12, cytochrome C, GRP78 proteins were detected by Western blot. The results showed that K562 cells cultured in 4 micromol/L thapsigargin for 48 hours exhibited typical morphological changes of apoptotic cells under fluorescent microscope, including shrinkage of cell, condensation of chromatin, breakage of nuclear, formation of apoptotic bodies, fluorescence of yellow green and pellet observed in early apoptoyic cells and hyacinth fluorescence of chromatin showed in late apoptotic cells. 24 and 48 hours after exposure to 1, 2, 4, 8 micromol/L thapsigargin, the apoptotic rates of K562 were respectively 7.51%, 11.65%, 23.22%, 30.56% and 12.85%, 20.27%, 31.51%, 44.16%, in dose-dependent manner, and were statistically significant when compared with the controls (P < 0.05). The apoptotic rate of K562 was dose- and time-dependent in experiment range. The enhancement of [Ca(2+)]i and the decrease of the Delta Psi m in K562 cells were induced by thapsigargin and were dose-dependent in experiment range, compared with control, P < 0.05. Western blot results indicated that cleavage and activation of caspase-3, -7, -9, -12, releasing of cytochrome C from mitochondria, upregulation of GRP78 expression at the endoplasmic reticulum were induced in K562 cells after 24 hours exposure of 4 micromol/L thapsigargin. It is concluded that thapsigargin induces endoplasmic reticulum stress-induced apoptosis in K562 cells. Endoplasmic reticulum is a novel important initiatory site of apoptosis in cells; the cleavage and activation of caspase-3, -7, -9, -12 play very important role in endoplasmic reticulum stress-induced apoptosis of K562 cells and is one of the important mechanisms for thapsigargin-induced apoptosis. Thapsigargin-induced apoptosis in K562 cells is associated closely with the disruption of the Delta Psi m and the release of cytochrome C from mitochondria, mitochondria participates in endoplasmic reticulum stress-induced apoptosis in K562 cells.