Abstract
The double-edged role of p21 to command survival and apoptosis is emerging. The current investigation highlights ER stress-mediated JNK activation that plausibly triggers cell death by attenuating endogenous p21 level. Here, we demonstrated that ER stress activator 3-AWA diminishes the p21 levels in cancer cells by averting the senescent phenotype to commence G2/M arrest. In essence, the deceleration in p21 level occurs through ER stress/JNK/Caspase-3 axis via activation/induction of proapoptotic Par-4 and inhibition of AKT. The molecular dynamics studies identified important interactions, which may be responsible for the AKT inhibition and efficacy of 3-AWA towards AKT binding pocket. Interestingly, the p21 deceleration was rescued by incubating the cells with 3-AWA in the presence of an ER stress inhibitor, Salubrinal. Furthermore, we demonstrated that p21 expression decreases solitarily in Par-4+/+ MEFs; albeit, ER stress-induced JNK activation was observed in both Par-4+/+ and Par-4−/− MEFs. Par-4 knockdown or overexpression studies established that ectopic Par-4 along with ER stress are not sufficient to downregulate p21 in PC-3 cells but are adequate for DU-145 cells and that the ER stress inflicted activation of JNK, inhibition of AKT and Par-4 induction are all crucial to p21 downmodulation by 3-AWA. By using isogenic cell lines, such as HCT-116 p53+/+ and HCT-116 p53−/−, we found that deceleration in p21 expression due to ER stress is p53 independent. Moreover, in orthotopic carcinogen-induced rat colorectal carcinoma model, we found that 3-AWA inhibits colorectal tumor growth and formation of colorectal polyps at a tolerable dose, similar to the first-line drug for colorectal cancer-5-fluorouracil.
Highlights
The diverse biological functions of p21 are well known for its controversial role in predicting the prognosis of cancer patients. p21 levels are highly amplified in various cancers including prostate, cervical, colon, breast and squamous cell carcinomas. p21 activation directly correlates with tumor grade and invasiveness, the mechanisms remain vague
We demonstrate that pharmacological induction of ER stress by 3-Azido withaferin A (3-AWA) attenuates p21 levels, an effect that coincides with the activation of Jun N-terminal kinase (JNK)
We have provided evidence that Par-4, a major player contributing to cancer cell apoptosis, may be involved in the regulation of the cell cycle regulator p21 during ER stress facilitating the commitment of cells to a proapoptotic program
Summary
The diverse biological functions of p21 are well known for its controversial role in predicting the prognosis of cancer patients. p21 levels are highly amplified in various cancers including prostate, cervical, colon, breast and squamous cell carcinomas. p21 activation directly correlates with tumor grade and invasiveness, the mechanisms remain vague. Bcl2-Beclin 1 interaction through ER stress-mediated Par-4 reduced, Salubrinal could not prevent 3-AWA mediated caspase-3 induction in prostate cancer cells.15 3-Azido withaferin A activation but blocked the decline in XIAP expression This (3-AWA), a novel derivative of withaferin A, is a strong inducer of Par-4,16 and several lines of evidence incriminate the proapoptotic and anti-invasive role of Par-4 in cancer.[17] In provides an evidence that higher concentration of 3-AWA could promote apoptosis even in the presence of salubrinal through XIAP independent pathway.
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