| AIM To study the effects of an autophagy/Cathepain L activation mechanisms on Curcumin-induced death of K562 cells.METHODS After treatment with Curcumin , the growth inhibition of K562 cells was assessed by MTT colorimetric assay. MDC staining and Hoechst 33258 were used to examine autophagy and apoptosis induced by Curcumin in K562 cells. To examine the involvement of Cathepsin L in Curcumin-induced death of K562 cells, the Cathepsin L inhibitor Z-FY-DMK was added with Curcumin and the cytotoxicity of Curcumin was measured by MTT colorimetric assay. Immunohistochemistry, flow cytometry and Western blot analysis were used to study the apoptotic and autophagic mechanisms involved in death of K562 cells.RESULTS The proliferation of K562 cells was significantly inhibited in a dose- and time-dependent manner after Curcumin treatment. Autophagy and apoptosis were induced in K562 cells as detected by MDC and Hoechst staining; Immunofluorescence and western blot demonstrated that expression of LC3 and cathepsin L increased after Curcumin treatment. The expression of Bid increased, mitochondrial membrane potential collapsed, Bcl-2 reduced was induced and caspase-3 activation accelerated during death of K562 cells. The Cathepsin L inhibitor Z-FY-DMK exerted opposite effects on Curcumin-induced death of K562 cells. Moreover, pretreatment with Z-FY-DMK prior to Curcumin inhibited LC3 and Beclin 1 protein, but it amplified above-mentioned apoptotic signaling pathways.CONCLUSION The increase of autophagosomes and the activation of Cathepsin L may be involved in the toxicity induced by Curcumin. The Cathepsin L inhibitor Z-FY-DMK attenuated the toxicity induced by Curcumin. Cathepsin L enhanced autophagy, but it may be inhibited apoptotic process in curcumin-induced death of K562 cells. In terms of the overall cells, Z-FY-DMK inhibited autophagy is much larger than it promoted apoptosis, thus speculated autophagy is the form of death of K562 cells induced by curcumin and it is a major way.
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