[Effects of Sinopodophyllum hexundrum on apoptosis in K562 cells].

OBJECTIVE: To investigate the effects of Sinopodophyllum hexundrum on apoptosis in K562 cells. METHODS: K562 cells were treated with Sinopodophyllum hexundrum at different concentrations and for different lengths of time to determine the optimal conditions of SinoPodophyllum hexandrum treatment for K562 cells using CCK8 assay. The cell apoptotic rate was detected by flow cytometry, and the cell morphology and nuclear morphology of K562 cells were observed with Wright staining and DPAI staining, respectively. The protein expressions of BCR/ABL, p-BCR/ABL, STAT5, p-STAT5 and the apoptosis-related proteins PARP, caspase-3 and cleaved-caspase-3 were determined with Western blotting. RESULTS: The cell proliferation was inhibited in a concentration-and time-dependent manner by 1, 2, and 3 µg/mL Sinopodophyllum hexundrum. The treatment was optimal with a Sinopodophyllum hexundrum concentration of 2 µg/mL a treatment time of 48 h, and the cell apoptotic rate increased in a time-dependent manner and significantly increased at 48 h (P<0.001). The expression of apoptosis-related proteins PARP, caspase-3 and cleaved-caspase-3 were also activated in a time-dependent manner. The cells showed typical apoptotic changes after treatment with 2 µg/mL Sinopodophyllum hexundrum for 48 h with significantly reduced expressions of BCR/ABL, p-BCR/ABL, STAT5, AND p-STAT5. CONCLUSION: Sinopodophyllum hexundrum promotes K562 cell apoptosis possibly by inhibiting BCR/ABL-STAT5 survival signal pathways and activating the mitochondrion-associated apoptotic pathways.

Heat shock protein-70 neutralizes apoptosis inducing factor in Bcr/Abl expressing cells.

Bcr/Abl fusion protein is a hallmark of human chronic myeloid leukemia (CML). The protein can activate various signaling pathways to make normal cells transform malignantly and thus to facilitate tumorigenesis. It has been reported that heat shock protein-70 (HSP-70) can be served as an anti-apoptotic protein that suppresses Bax and Apo-2L/TRAIL. But it is unclear whether HSP-70 affects AIF-initiated apoptosis in Bcr/Abl expressing cells considering that HSP-70 is coincidentally over-regulated in these cells. Our findings supported that abundant HSP-70 in Bcr/Abl cells neutralizes AIF by segregating it from nucleus via direct interaction, leading to the failure of AIF initiating cell death and the silence of caspase-independent apoptotic pathway upon apoptotic induction. Moderate inhibition of HSP-70 expression by siRNA leads to Vp-16 triggered re-distribution of AIF in nucleus. In addition, AIF bears a HSP-70 binding domain allowing association with HSP-70. Therefore, disruption of the association using an AIF mutant lacking this domain can restore the potential of AIF importing into nucleus, and finally triggers cell death in a time dependent manner.