Oleuropein Induced Apoptosis in HeLa Cells via a Mitochondrial Apoptotic Cascade Associated With Activation of the c-Jun NH2-Terminal Kinase

Oleuropein could inhibit growth and/or induce apoptosis in several cancer cell lines. In this study, we investigate how oleuropein strongly induces apoptotic cell death in HeLa human cervical carcinoma cells. Oleuropein induced HeLa cells apoptosis as demonstrated by induction of a sub-G1 peak in flow cytometry and apoptosis-related morphological changes observed by fluorescence microscopy after being stained by Hoechst 33324. The results also showed that 150 – 200 μM oleuropein–treated HeLa cells were arrested at the G2/M phase. Western blot analysis revealed that the phosphorylated ATF-2, c-Jun NH2-terminal kinase (JNK) protein, p53, p21, Bax, and cytochrome c protein in the cytoplasm significantly increased in a dose-dependent manner after treatment of oleuropein for 24 h. Additionally, increasing levels of Bax in response to JNK/SPAK signaling, which formed mitochondrial membrane channels, accounted for releasing of cytochrome c and activation of caspase-9 and -3. SP600125 (20 μM), a JNK1/2 inhibitor, markedly suppressed the formation of apoptotic bodies and JNK activation induced by oleuropein at 200 μM. Thus, oleuropein-induced apoptosis was activated by the JNK/SPAK signal pathway. The result shows that oleuropein holds promise as a potential chemotherapeutic agent for the treatment of HeLa cells.