Pronounced transcriptional regulation of apoptotic and TNF-NF-kappa-B signaling genes during the course of thymoquinone mediated apoptosis in HeLa cells

Thymoquinone (TQ) is the active ingredient extracted from the essential oil of Nigella sativa. A number of studies implicated TQ as an antitumor agent. In this study, cytotoxic effects of the oil of N. sativa and TQ were evaluated on human cervical cancer cell line, HeLa cells. IC50 value was similar to 0.125 mu l/ml for N. sativa oil preparations and 12.5 mu M for TQ. TQ strongly inhibited wound healing at all concentrations ranging from 12.5 to 100 mu M in a scratch wound healing assay. Additionally, induction of apoptosis by TQ was assessed by Giemsa staining and TQ was found to induce apoptosis in cancer cells especially at concentrations of 50 and 100 mu M. TQ-mediated transcriptional regulation of 84 genes involved in apoptosis was studied using a PCR array. At low dose (12.5 mu M), TQ was found to induce expression of four pro-apoptotic genes: BIK (similar to 22.7-fold), FASL (similar to 2.9-fold), BCL2L10 (similar to 2.1-fold), and CASP1 (similar to 2-fold). TQ was also found to reduce the expression of an anti-apoptotic gene implicated in NF-kappa-B signaling and cancer: RELA (similar to 8-fold). At high dose (100 mu M), TQ mediated the expression of 21 genes implicated directly in apoptosis (6 genes), TNF signaling (10 genes), and NF-kappa-B signaling (3 genes) such as BIK, BID, TNFRSF10A, TNFRSF10B, TNF, TRAF3, RELA, and RELB. In conclusion, this study implicates the role of TQ in the inhibition of cancer cell proliferation and migration. At the same time, our results strongly suggest that TQ intervenes with TNF and NF-kappa-B signaling during TQ-mediated induction of apoptosis in cancer cells.