ABSTRACT
<p><b>OBJECTIVE</b>To investigate the apoptosis inducing effects of ponicidin (PON) on leukemic K562 cells and its mechanisms of action.</p><p><b>METHOD</b>K562 cells in culture medium in vitro were given different concentrations of PON (10-50 micromol x L(-1)) for 24, 48 and 72 h. The inhibitory rate of the cells was measured by MTT assay, cell apoptotic rates were detected by flow cytometry (FCM) using Annexin V staining after K562 cells were treated with different concentrations of PON for 72 hours, and cell morphology was observed by Wright-Giemsa staining. Western blot was used to detect caspase-3 and poly(ADP-ribose) polymerase (PARP) expression, and the protein levels in mitogen-activated protein kinase signaling pathways (MAPKs, p-P38, p-ERK and p-JNK) as well as p-AKT and p-P85 in PI3K/AKT signaling pathways were also detected.</p><p><b>RESULT</b>PON (over 30 micromol x L(-1)) could inhibit the growth of K562 cells in both time- and dose-dependent manner. FCM analysis revealed that apoptotic cells were gradually increased in a dose-dependent manner after treatment for 72 hours, and that marked morphological changes of cell apoptosis such as condensation of chromatin was clearly observed by Wright-Giemsa staining after treatment by 50 micromol x L(-1) PON. Western blot showed cleavage of the caspase-3 zymogen protein (32 kD), with the appearance of its 17 kD subunit, and a cleaved 89 kD fragment of 116 kD PARP was also found. Furthermore, Western blotting also showed that expression of p-AKT and p-P85 in PI3K/AKT signaling pathways was downregulated dramatically whereas the expression of p-P38 as well as p-ERK and p-JNK remained unchanged after the cells were treated by PON for 48 h.</p><p><b>CONCLUSION</b>The results demonstrate that PON exhibits in vitro anti-leukemia effect by induction of apoptosis in K562 cells, and that PON induced apoptosis in K562 cells mainly related to activation of caspase-3 as well as inactivation of PI3K/AKT signaling pathway via down regulation of the expression of p-AKT and p-P85 protein levels. These results provide strong laboratory evidence for further anti-leukemia trials of PON.</p>