MDM2 as a target for ellagic acid­mediated suppression of prostate cancer cells in vitro.

Prostate cancer (PCa) is the most common cancer in men. Despite the available treatments for PCa, a significant number of patients relapse as the disease becomes hormonal­independent. p53 is a common tumor suppressor; however, its activity is diminished via the overexpression of murine double minute­2 (MDM2). The pomegranate, walnuts, and blueberries are widely consumed fruits and nuts that contain several polyphenolic compounds, mainly ellagic acid (EA). The present study focused on the influence of EA on the p53/MDM2 pathway in PCa cell lines. Three human PCa cell lines PCa LNCaP (p53+/+), 22RV1 (p53-/+), and PC3 (p53-/-) harboring different p53 genotypes were used in this research. We found that EA downregulated the gene and protein expression levels of MDM2 and increased the protein expression of p53 as determined by qPCR and western blot analyses. Moreover, by using western blot analysis, we determined that EA increased the protein expression of the p53 target proteins p21, p53 upregulated modulator of apoptosis (PUMA) [also known as Bcl­2­binding component 3 (BBC3)] and Phorbol­12­myristate­13­acetate­induced protein 1 (NOXA). Furthermore, we found that EA induced apoptosis in the absence of p53 by downregulating MDM2 and X­linked inhibitor of apoptosis protein (XIAP) protein expressions as determined by western blot analysis. We conclude that EA suppressed PCa cells in vitro partly by downregulating MDM2.

Urolithin A induces prostate cancer cell death in p53-dependent and in p53-independent manner.

PURPOSE: Pomegranate and walnuts are widely consumed dietary sources and contain several bioactive compounds, including the ellagitannins (ETs). ETs are polyphenols that are metabolized in the gut microbiota to urolithin A (UA). p53 is a tumor suppressor that lost its activity through MDM2 activation in about half cancers. The purpose of this study was to investigate the influence of UA on the p53-MDM2 interaction pathway in prostate cancer cell lines. METHODS: Three human prostate cancer cell lines were used that harbor different p53 genotypes; LNCaP (p53+/+), 22RV1(p53-/+) and PC3 (p53-/-). Cell viability was determined by CellTiter-Glo Luminescent assay. Apoptosis was confirmed by measuring annexin V by flow cytometry. The expression of p53, its target proteins, and apoptotic markers were measured by western blotting. Real-time qPCR was used to measure the gene expression of p21, a main target gene of p53. Co-immunoprecipitation-immunoblotting was used to assess the inhibition of interactions between p53 and MDM2 and to assess the effect of UA on MDM2-mediated p53 polyubiquitination. RESULTS: We found UA inhibited CaP cells' viability and induced apoptosis. For 22RV1 and LNCaP, we found UA increased p53 protein expression and its main target protein, p21, and MDM2, forming an autoregulatory feedback loop. In addition, UA increased the p53 proapoptotic proteins PUMA and NOXA. Moreover, UA inhibited the interaction between p53 and MDM2 and inhibited MDM2-mediated p53 polyubiquitination. UA downregulated MDM2 and XIAP protein expression in PC3 cells and upregulated p21 and p14ARF in a p53-independent manner. CONCLUSION: The influencing of UA on p53-MDM2 pathway may partly contribute to its anticancer effect.