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Antioxidant treatment promotes prostate epithelial proliferation in Nkx3.1 mutant mice.

ABSTRACT: Discordant results in preclinical and clinical trials have raised questions over the effectiveness of antioxidants in prostate cancer chemoprevention. Results from the large-scale Selenium and Vitamin E Cancer Prevention Trial (SELECT) showed that antioxidants failed to prevent, and in some cases promoted, prostate cancer formation in men without a history of the disease. One possible explanation for these alarming results is the notion that the effects of antioxidant treatment on the prostate are modified by specific, intrinsic genetic risk factors, causing some men to respond negatively to antioxidant treatment. Loss of expression of the homeobox transcription factor NKX3.1 in the prostate is frequently associated with human prostate cancer. Nkx3.1 mutant mice display prostatic hyperplasia and dysplasia and are used as a model of the early stages of prostate cancer initiation. While the mechanisms by which Nkx3.1 loss promotes prostate tumorigenicity are not completely understood, published data have suggested that elevated reactive oxygen species (ROS) associated with Nkx3.1 loss may be a causative factor. Here we have tested this hypothesis by treating Nkx3.1 mutant mice with the antioxidant N-acetylcysteine (NAC) for 13 weeks post-weaning. Surprisingly, while NAC treatment decreased ROS levels in Nkx3.1 mutant mouse prostates, it failed to reduce prostatic epithelial hyperplasia/dysplasia. Rather, NAC treatment increased epithelial cell proliferation and promoted the expression of a pro-proliferative gene signature. These results show that ROS do not promote proliferation in the Nkx3.1-null prostate, but instead inhibit proliferation, suggesting that antioxidant treatment may encourage prostate epithelial cell proliferation early in prostate tumorigenesis. Our findings provide new insight that may help explain the increased prostate cancer risk observed with vitamin E treatment in the SELECT trial and emphasize the need for preclinical studies using accurate models of cancer.

SUBMITTER: Martinez EE

PROVIDER: S-EPMC3471914 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Antioxidant treatment promotes prostate epithelial proliferation in Nkx3.1 mutant mice.

Martinez Erin E EE Anderson Philip D PD Logan Monica M Abdulkadir Sarki A SA

PloS one 20121015 10

Discordant results in preclinical and clinical trials have raised questions over the effectiveness of antioxidants in prostate cancer chemoprevention. Results from the large-scale Selenium and Vitamin E Cancer Prevention Trial (SELECT) showed that antioxidants failed to prevent, and in some cases promoted, prostate cancer formation in men without a history of the disease. One possible explanation for these alarming results is the notion that the effects of antioxidant treatment on the prostate a ...[more]

PMID: 23077524

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Project description:The E3 ubiquitin ligase adaptor speckle-type POZ protein (SPOP) is frequently dysregulated in prostate adenocarcinoma (PC), via either somatic mutations or mRNA downregulation, suggesting an important tumour suppressor function. To examine its physiologic role in the prostate epithelium in vivo, we generated mice with prostate-specific biallelic ablation of Spop. These mice exhibited increased prostate mass, prostate epithelial cell proliferation, and expression of c-MYC protein compared to littermate controls, and eventually developed prostatic intraepithelial neoplasia (PIN). We found that SPOPWT can physically interact with c-MYC protein and, upon exogenous expression in vitro, can promote c-MYC ubiquitination and degradation. This effect was attenuated in PC cells by introducing PC-associated SPOP mutants or upon knockdown of SPOP via short-hairpin-RNA, suggesting that SPOP inactivation directly increases c-MYC protein levels. Gene Set Enrichment Analysis revealed enrichment of Myc-induced genes in transcriptomic signatures associated with SPOPMT. Likewise, we observed strong inverse correlation between c-MYC activity and SPOP mRNA levels in two independent PC patient cohorts. The core SPOPMT;MYCHigh transcriptomic response, defined by the overlap between the SPOPMT and c-MYC transcriptomic programmes, was also associated with inferior clinical outcome in human PCs. Finally, the organoid-forming capacity of Spop-null murine prostate cells was more sensitive to c-MYC inhibition than that of Spop-WT cells, suggesting that c-MYC upregulation functionally contributes to the proliferative phenotype of Spop knock-out prostates. Taken together, our data highlight SPOP as an important regulator of luminal epithelial cell proliferation and c-MYC expression in prostate physiology, identify c-MYC as a novel bona fide SPOP substrate, and help explain the frequent inactivation of SPOP in human PC. We propose SPOPMT-induced stabilization of c-MYC protein as a novel mechanism that can increase total c-MYC levels in PC cells, in addition to amplification of c-MYC locus.

Project description:Key histological and growth progression characteristics of human prostate cancer are phenocopied in mouse models that have been subjected to androgen level depletion and engineered for hemizygosity of candidate prostate cancer tumor suppressor genes Nkx3.1 and Pten. To characterize their relative transcriptomes and identify a genomic basis for their relevance to human prostate cancers, we compared mouse prostate tumors expression profiles to those from a panel of human prostate cancer isolates and to normal and benign prostates. Human prostate cancers and mouse prostate tumor models both exhibit the activation of genes associated with growth, cell cycle control, and inhibition of differentiation (CDKN2A, CDKN2B, CDKN2C, CEBPB, CEBPG, CSF1, CTSS, DMBT1, EGFR, PLCG2, PXN, SPP1, TNFSF9), and conversely, diminished expression of genes associated with normal prostate differentiation and function. All tumors also exhibit dysregulated expression of genes associated with inflammation, the disruption of prostate-associated ER stress pathways, as well as with oxidative stress, energy metabolism, cell adhesion, and stress response. Immunoinflammatory and altered cell adhesion process-associated genes exhibited prominent expression in early stage tumors. In contrast, metastatic human prostate cancer samples eliminated the expression of most immunoinflammatory-associated transcripts. Cross-species comparisons of molecular programs that are shared or distinguishing of Nkx3.1; Pten mutant mouse models and human adenocarcinomas clearly delineate core tumorigenesis programs associated with cell cycle activation and loss of differentiation. Compared to locally spreading mouse and human tumors, metastatic prostate cancer exhibits greatly reduced expression of immunoinflammatory and adhesion genes, implying that immuno-inflammatory activation may enable first stages of tumorogenesis, but suppress metastasis. These results provide a novel framework to identify stage-specific biomarkers and candidate targets for combinatorial therapeutics. The complex role of inflammation suggests a need for additional caution in countering metastasis. Keywords: tumor stage

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Antioxidant treatment promotes prostate epithelial proliferation in Nkx3.1 mutant mice.

Publications

Antioxidant treatment promotes prostate epithelial proliferation in Nkx3.1 mutant mice.

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