Chronic inflammation is known to promote cancer, suggesting that negative regulation of inflammation is likely to be tumor suppressive. We found that p53 is a general inhibitor of inflammation that acts as an antagonist of nuclear factor kappaB (NFkappaB). We first observed striking similarities in global gene expression profiles in human prostate cancer cells LNCaP transduced with p53 inhibitory genetic element or treated with TNF, suggesting that p53 inhibits transcription of TNF-inducible genes that are largely regulated by NFkappaB. Consistently, ectopically expressed p53 acts as an inhibitor of transcription of NFkappaB-dependent promoters. Furthermore, suppression of inflammatory response by p53 was observed in vivo in mice by comparing wild-type and p53 null animals at molecular (inhibition of transcription of genes encoding cytokines and chemokines, reducing accumulation of reactive oxygen species and protein oxidation products), cellular (activation of macrophages and neutrophil clearance) and organismal (high levels of metabolic markers of inflammation in tissues of p53-deficient mice and their hypersensitivity to LPS) levels. These observations indicate that p53, acting through suppression of NFkappaB, plays the role of a general "buffer" of innate immune response in vivo that is well consistent with its tumor suppressor function and frequent constitutive activation of NFkappaB in tumors.
p53 tumor suppressor gene controls cell response to a variety of stresses inducing growth arrest or apoptosis in damaged cells. It largely determines the sensitivity of tumor and normal cells to radiation and chemotherapy, and, therefore, de®nes both the ecacy and limitations of anti-cancer treatment. To determine molecular mechanisms of p53-dependent stress response in normal tissues we identi®ed and compared the spectra of radiation-responsive genes in cells of dierent origin and p53 status using a cDNA array hybridization technique. The majority of genes identi®ed were p53-dependent and cell type speci®c. Several of the new p53 responders encode known secreted growth inhibitory factors. This suggests that p53, in addition to its intrinsic antiproliferation activity, can cause`bystander eect' by inducing export of growth suppressive stimuli from damaged cells to neighboring cells. Consistently, a p53-dependent accumulation of factors, which causes growth inhibitory eects in a variety of cell lines, was found after gamma irradiation in the media from established and primary cell cultures and in the urine of irradiated mice. Moreover, p53-dependent factors released by normal human ®broblasts potentiated the cytotoxic eect of a chemotherapeutic drug on co-cultivated tumor cells. This suggests a previously unknown role for normal cells in chemo-and radiation therapy of cancer.
We investigated whether knocking down AR expression effects apoptosis after treatment with different apoptosis-inducing agents. We found that siRNA AR (si-AR) significantly decreased apoptosis induced by topoisomerase inhibitors doxorubicin (DOX) and camptothecin (Campt). It is known that DNA double-strand break inducing agents leads to activation (phosphorylation) of p53 that in turn regulates the expression of a variety of apoptosis-related genes including microRNA(miR)-34a and 34b/c. We found that DOX induced five phosphorylation sites of p53 (Ser15, 20, 37, 46 and 392); all of these sites were inhibited by si-AR. Subsequently we identified three kinases, SPAK, MDC1 and CaMKII that are under AR control and two of them, MDC1 and CaMKII, apparently participate in p53 upstream events that resulted in p53 inhibition. Using qPCR we showed that the level of miR-34a increased by 3-fold after DOX, but no increase was found with si-AR. MiR-34c expression increased 27 fold after DOX and only by 2.7 times with si-AR. It appears that AR-dependent inhibition of p53 resulted in suppression of miR-34a and -34c expression. Importantly, DOX did not induce miR-34 in LNCaP grown in an androgen free medium or in AR-negative prostate cancer cell lines, DU145 and PC3. To directly investigate the role of miR-34 in DOX-mediated apoptosis, we transfected cells with anti-miR-34 oligonucleotides or with miR-34. We found that inhibition of individual miR-34, either 34a or 34c, or forced overexpression of miR-34a or miR-34c did not modulate DOX-mediated apoptosis. Only simultaneous inhibition or forced overexpression of both miR-34 resulted in modulation of DOX-mediated apoptosis. Taken together, our data indicate that cooperation between miR-34a and 34c plays an important role in AR-dependent p53-mediated apoptosis in prostate cancer.
It has been suggested in many studies that combined treatment with chemotherapeutic agents and apoptosisinducing ligands belonging to TNFR family is a more effective strategy for cancer treatment. However, the role of androgen regulation of TNFR family-induced apoptosis in prostate cancer is poorly understood. In this study, we investigated the dose-dependent effects of androgen on TNF-a and TRAIL-mediated apoptosis in LNCaP. To investigate the interaction between the androgen receptor (AR) and the caspase-2 gene, chromatin immunoprecipitation analysis was used, and we are the first to identify that AR interacts in vivo with an androgen-responsive elements in intron 8 of caspase-2 gene. We have found that DHT inhibited apoptosis in dose-dependent manner. There is a direct, androgen-dependent correlation between the levels of activated Akt and caspase activation after treatment with TNF-a and TRAIL. We have also found that there are at least two different regulatory mechanisms of p53 expression by androgen: at the gene and protein levels. At the same time, the level of AR was found to be higher in LNCaP-si-p53 compared to LNCaP-mock cells. These data indicate that there is a mutual regulation of expression between p53 and AR. Our study suggests that androgen-dependent outcome of apoptotic treatment can occur, at least in part, via the caspase-2, Akt and p53-mediated pathways.
It has recently been shown that the androgen receptor (AR) is the main factor that required for prostate cancer cells survival. We show that knocking down AR expression by siRNA induces PI3K-independent activation of Akt, which was mediated by calcium/calmodulin-dependent kinase II (CaMKII). We further show, for the first time, that prostate cancer cells express beta,gamma and delta CaMKII genes, and the expression of these genes is under the control of AR activity: active AR in the presence of androgens inhibits CaMKII gene expression whereas inhibition of AR activity results in elevated level of kinase activity and in enhanced expression of CaMKII-beta and -gamma genes. Overexpression of CaMKII genes results in resistance to apoptosis induced by KN-93, a CaMKII inhibitor, or wortmanninn, a PI3K/Akt inhibitor, in combination with doxorubicin, thapsigargin and TRAIL. Moreover, overexpression of CaMKII increases secretion of prostate specific antigen and promotes cell growth of LNCaP in steroid-free condition. Our data show that there is cross-talk between AR- and CaMKII-mediated pathways. The results of this study suggest that CaMKII is an important player in prostate cancer cells ability to escape apoptosis under androgen ablation and facilitate the progression of prostate cancer cells to an androgen independent state.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.