Thymoquinone (TQ) is the main constituent of black seed (Nigella sativa, spp) essential oil which shows promising in vitro and in vivo anti-neoplastic activities in different tumor cell lines. However, to date there are only a few reports regarding the apoptotic effects of TQ on cervical cancer cells. Here, we report that TQ stimulated distinct apoptotic pathways in two human cervical cell lines, Siha and C33A. TQ markedly induced apoptosis as demonstrated by cell cycle analysis in both cell lines. Moreover, quantitative PCR revealed that TQ induced apoptosis in Siha cells through p53-dependent pathway as shown by elevated level of p53-mediated apoptosis target genes, whereas apoptosis in C33A cells was mainly associated with the activation of caspase-3. These results support previous findings on TQ as a potential therapeutic agent for human cervical cancer.
ARID3A and ARID3B are transcriptional targets of p53. Recently, it has been reported that ARID3A plays a critical role in the transcriptional activation of pro-arrest p21 in response to DNA damage. However, the role of ARID3B in the p53 regulatory pathway remains poorly understood. Here we show that ARID3A and ARID3B specifically bind to putative ARID3-binding sites in p53 target genes in vitro and in vivo. ARID3B and, to a lesser extent, ARID3A silencing blocked transcriptional activation of pro-apoptotic p53 target genes, such as PUMA, PIG3, and p53. Furthermore, ectopic ARID3B, to a lesser extent, ARID3A expression activated the pro-apoptotic gene expression, and only ARID3B induced apoptosis. Finally, ARID3B but not ARID3A silencing blocked apoptosis induction following DNA damage. These results indicated that, although ARID3B and ARID3A share overlapping functions, ARID3B play a key role in the expression of pro-apoptotic p53-target genes and apoptosis.