Induction of apoptosis in human leukemia cells by grape seed extract occurs via activation of c-Jun NH ₂-terminal kinase

Purpose: To characterize the functional role of c-Jun NH ₂-terminal kinase (JNK) and other apoptottc pathways in grape seed extract (GSE)-induced apoptosis in human leukemia cells by using pharmacologic and genetic approaches. Experimental Design: Jurkat cells were treated with various concentrations of GSE for 12 and 24 h or with 50 μg/mL GSE for various time intervals, after which apoptosis, caspase activation, and cell signaling pathways were evaluated. Parallel studies were done in U937 and HL-60 human leukemia cells. Results: Exposure of Jurkat cells to GSE resulted in dose- and time-dependent increase in apoptosis and caspase activation, events associated with the pronounced increase in Cip1/p21 protein level. Furthermore, treatment of Jurkat cells with GSE resulted in marked increase in levels of phospho-JNK. Conversely, interruption of the JNK pathway by pharmacologic inhibitor (e.g., SP600125) or genetic (e.g., small interfering RNA) approaches displayed significant protection against GSE-mediated lethality in Jurkat cells. Conclusions: The result of the present study showed that GSE induces apoptosis in Jurkat cells through a process that involves sustained JNK activation and Cip1/p21 up-regulation, culminating in caspase activation.