Abstract
Krüppel-like factor 5 (KLF5) is frequently deleted and inactivated in prostate cancer, and exerts tumor-suppressing function in prostate cancer cells. However, the function of KLF5 in the apoptosis of prostate cancer cells remains unclear. In the present study, the effect of KLF5 on phorbol 12-myristate 13-acetate (PMA)-induced apoptosis was investigated in prostate cancer LNCaP cells. It was demonstrated that PMA induced the expression of KLF5 at the mRNA and protein level. To identify whether KLF5 regulates the activity of the downstream pathway, stable KLF5 knockdown or overexpression cell lines were constructed with lentivirus harboring shRNA targeting KLF5 or full-length KLF5 in LNCaP cells. Knockdown of KLF5 significantly decreased PMA-induced apoptosis, while cell apoptosis was significantly increased following KLF5 overexpression compared with the corresponding control groups. Consistently, expression of cleaved poly(ADP-ribose) polymerase and caspase-3 induced by PMA was decreased following KLF5 knockdown and increased following KLF5 overexpression. Using the control medium from cells treated with PMA, it was demonstrated that KLF5 is required for the control medium to induce apoptosis. c-Jun N-terminal kinase (JNK) activity is essential for the apoptosis induced by PMA. It was revealed that knockdown of KLF5 decreased, while overexpression of KLF5 increased the phosphorylation of JNK induced by PMA and control medium treatment. Furthermore, inhibition of tumor necrosis factor α (TNFα) decreased KLF5 expression and significantly decreased cell apoptosis induced by PMA, and control medium. This data indicates that KLF5 is essential for the apoptosis induced by PMA in LNCaP prostate cancer cells. Furthermore, KLF5 is essential for activity of the autocrine factor TNFα, which is secreted by cells treated with PMA and mediates the function of PMA-induced apoptosis through regulating the activity of JNK signaling pathway. These results provide novel insights into the complexity of the signaling pathways regulating apoptosis in prostate cancer cells, which could aid in the development of novel treatments for patients with prostate cancer.