Abstract
Neuroblastoma is a childhood tumor that arises from immature neuroblasts of the sympathetic nervous system. Krüpple-like factor 4 (KLF4) is a transcription factor, the precise function of which in neuroblastoma is unclear. We examined the effects of KLF4 overexpression and apigenin (APG) treatment in human malignant neuroblastoma SK-N-DZ and IMR-32 cell lines. KLF4 overexpression in both SK-N-DZ and IMR-32 cell lines was confirmed by laser scanning immunofluorescent confocal microscopy and Western blotting. We found that 100 nM KLF4 plasmid and 25 μM APG synergistically inhibited the growth of SK-N-DZ and IMR-32 cells. We also found increase in KLF4 expression in response to treatment with various concentrations of APG. Combination of KLF4 plasmid and APG treatment significantly increased the amounts of apoptosis in both cell lines when compared with control vector or single treatment. We also noticed that the combination therapy decreased expression of the anti-apoptotic proteins Bcl-2 and Mcl-1, increased expression of the pro-apoptotic proteins Bax, Noxa, and Puma, upregulated p53, and caused activation of caspase-3 for cleavage of the inhibitor of caspase-activated DNase (ICAD) leading to completion of apoptosis machinery. Further, combination of KLF4 overexpression and APG treatment was highly effective in inhibiting migration of both neuroblastoma cell lines and was associated with down regulation of matrix metalloproteinases (MMPs) such as MMP-2 and MMP-9. Collectively, our results from this investigation strongly suggest that KLF4 functions as a tumor suppressor and potentiates the anti-cancer activities of APG in two different human malignant neuroblastoma cell lines.