OBJECTIVETo investigate the effect of meisoindigo on bcr-abl signaling pathway and to explore the mechanism of meisoindigo inducing apoptosis in K562 cells.

METHODSApoptosis and mitochondria membrane potential (MMP) were evaluated by flow cytometry. In K562 cells, the expression level of Bcl-2 family members, cleaved caspase members, bcr-abl, STAT5 and CRKL were determined by Western blot and bcr-abl mRNA expression level was measured by RT-PCR before and after meisoindigo treatment. The DNA binding potential of STAT3 and STAT5 was checked by electronic mobility shift assay (EMSA).

RESULTSDown-regulation of total and phosphorylated bcr-abl protein level in K562 cells was observed when treated with 20 micromol/L meisoindigo, but its mRNA level was not changed. The expression level of phosphorylated STAT5 and CRKL was decreased and the DNA binding potential of STAT3 and STAT5 were inhibited in K562 cell after exposure to meisoindigo. Exposure to 5 - 20 micromol/L meisoindigo induced apoptosis accompanied with activating of caspase 3, 8, 9 and decreasing of MMP in K562 cells in a dose-dependent manner. The apoptosis was blocked by 50 micromol/L z-DEVD-fmk, z-IETD-cho, z-LETD-fmk, the specific inhibitors of caspase 3, 8, 9, respectively. No change in Bcl-2, Bax and Bid protein expression levels were observed before and after meisoindigo inducing apoptosis.

CONCLUSIONMeisoindigo can inhibit the proliferation of K562 cells by affecting the bcr-abl signaling transduction pathway. Meisoindigo induces K562 cell apoptosis through a novel caspase dependent pathway in addition to the contribution of mitochondria. The Bcl-2 family members are not involved in the apoptosis induction by meisoindigo in K562 cells.