A comprehensive assessment of p53-responsive genes following adenoviral-p53 gene transfer in Bcl-2-expressing prostate cancer cells

Flaxseed Lignans as Important Dietary Polyphenols for Cancer Prevention and Treatment: Chemistry, Pharmacokinetics, and Molecular Targets

Cancer causes considerable morbidity and mortality across the world. Socioeconomic, environmental, and lifestyle factors contribute to the increasing cancer prevalence, bespeaking a need for effective prevention and treatment strategies. Phytochemicals like plant polyphenols are generally considered to have anticancer, anti-inflammatory, antiviral, antimicrobial, and immunomodulatory effects, which explain their promotion for human health. The past several decades have contributed to a growing evidence base in the literature that demonstrate ability of polyphenols to modulate multiple targets of carcinogenesis linking models of cancer characteristics (i.e., hallmarks and nutraceutical-based targeting of cancer) via direct or indirect interaction or modulation of cellular and molecular targets. This evidence is particularly relevant for the lignans, an ubiquitous, important class of dietary polyphenols present in high levels in food sources such as flaxseed. Literature evidence on lignans suggests potential benefit in cancer prevention and treatment. This review summarizes the relevant chemical and pharmacokinetic properties of dietary polyphenols and specifically focuses on the biological targets of flaxseed lignans. The consolidation of the considerable body of data on the diverse targets of the lignans will aid continued research into their potential for use in combination with other cancer chemotherapies, utilizing flaxseed lignan-enriched natural products.

Silencing overexpression of FXYD3 protein in breast cancer cells amplifies effects of doxorubicin and γ-radiation on Na(+)/K(+)-ATPase and cell survival

FXYD3, also known as mammary tumor protein 8, is overexpressed in several common cancers, including in many breast cancers. We examined if such overexpression might protect Na(+)/K(+)-ATPase and cancer cells against the high levels of oxidative stress characteristic of many tumors and often induced by cancer treatments. We measured FXYD3 expression, Na(+)/K(+)-ATPase activity and glutathionylation of the β1 subunit of Na(+)/K(+)-ATPase, a reversible oxidative modification that inhibits the ATPase, in MCF-7 and MDA-MB-468 cells. Expression of FXYD3 was suppressed by transfection with FXYD3 siRNA. A colorimetric end-point assay was used to estimate cell viability. Apoptosis was estimated by caspase 3/7 (DEVDase) activation using a Caspase fluorogenic substrate kit. Expression of FXYD3 in MCF-7 breast cancer cells was ~eightfold and ~twofold higher than in non-cancer MCF-10A cells and MDA-MB-468 cancer cells, respectively. A ~50 % reduction in FXYD3 expression increased glutathionylation of the β1 Na(+)/K(+)-ATPase subunit and reduced Na(+)/K(+)-ATPase activity by ~50 %, consistent with the role of FXYD3 to facilitate reversal of glutathionylation of the β1 subunit of Na(+)/K(+)-ATPase and glutathionylation-induced inhibition of Na(+)/K(+)-ATPase. Treatment of MCF-7 and MDA-MB- 468 cells with doxorubicin or γ-radiation decreased cell viability and induced apoptosis. The treatments upregulated FXYD3 expression in MCF-7 but not in MDA-MB-468 cells and suppression of FXYD3 in MCF-7 but not in MDA-MB-468 cells amplified effects of treatments on Na(+)/K(+)-ATPase activity and treatment-induced cell death and apoptosis. Overexpression of FXYD3 may be a marker of resistance to cancer treatments and a potentially important therapeutic target.

PI3 Kinase inhibition on TRAIL-induced apoptosis correlates with androgen-sensitivity and p21 expression in prostate cancer cells

TNF-related apoptosis-inducing ligand (TRAIL) can induce apoptosis in many types of cancer cells. TRAIL is considered a therapeutic target, therefore, it was of interest to examine molecular mechanisms that may modulate sensitivity to TRAIL signaling in prostate cancer cells. LNCaP cells were found to be relatively resistant to TRAIL induced cell death while PC3 cells were sensitive. PI3-kinase (PI3 K) inhibitors were able to render LNCaP cells sensitive to TRAIL but conferred resistance to PC3 cells. PI3 K inhibitors were associated with an increase in p21(waf1, cip1) expression in PC3 cells where as p21 decreases in LNCaP cells suggesting that p21 may impart TRAIL resistance. Since androgen receptor (AR) signaling can be modulated by AKT, and p21 is an AR responsive gene, the impact of PI3 K inhibition on TRAIL sensitivity was evaluated in AR transfected PC3 cells (PC3AR). The expression of AR was significantly downregulated by PI3 K inhibition in LNCaP cells, which have an intact AR signaling axis. PC3AR cells expressed higher levels of p21 protein and were relatively resistant to TRAIL compared to control cells. Finally, using adenoviral p21 gene transfer we directly demonstrated that p21 can confer resistance to TRAIL-induced cell death. These results suggest that TRAIL resistance is not regulated simply by a PI3 K/AKT survival pathway associated with inactivating PTEN mutations but may also be modulated by downstream AR responsive targets such as p21. These findings may have significant clinical implications for the utility of TRAIL in the management of prostate cancer.

A resource for discovering specific and universal biomarkers for distributed stem cells

Specific and universal biomarkers for distributed stem cells (DSCs) have been elusive. A major barrier to discovery of such ideal DSC biomarkers is difficulty in obtaining DSCs in sufficient quantity and purity. To solve this problem, we used cell lines genetically engineered for conditional asymmetric self-renewal, the defining DSC property. In gene microarray analyses, we identified 85 genes whose expression is tightly asymmetric self-renewal associated (ASRA). The ASRA gene signature prescribed DSCs to undergo asymmetric self-renewal to a greater extent than committed progenitor cells, embryonic stem cells, or induced pluripotent stem cells. This delineation has several significant implications. These include: 1) providing experimental evidence that DSCs in vivo undergo asymmetric self-renewal as individual cells; 2) providing an explanation why earlier attempts to define a common gene expression signature for DSCs were unsuccessful; and 3) predicting that some ASRA proteins may be ideal biomarkers for DSCs. Indeed, two ASRA proteins, CXCR6 and BTG2, and two other related self-renewal pattern associated (SRPA) proteins identified in this gene resource, LGR5 and H2A.Z, display unique asymmetric patterns of expression that have a high potential for universal and specific DSC identification.

The p53 tumor suppressor network in cancer and the therapeutic modulation of cell death

The molecular subversion of cell death is acknowledged as a principal contributor to the development and progression of cancer. The p53 tumor suppressor protein is among the most commonly altered proteins in human cancer. The p53 protein mediates critical functions within cells including the response to genotoxic stress, differentiation, senescence, and cell death. Loss of p53 function can result in enhanced rates of cell proliferation, resistance to cell death stimuli, genomic instability, and metastasis. The community of cancer scientists is now in possession of a vast repository of information regarding the frequency, specific mechanisms, and clinical context of cell death deregulation in cancer. This information has enabled the design of therapeutic agents to target proteins, including p53. The feasibility and impact of targeting cell death signaling proteins has been established in preclinical models of human cancer. The appropriate application of these targeted agents is now being established in clinical trials.

The adenoviral E1B 55-kilodalton protein controls expression of immune response genes but not p53-dependent transcription

The human adenovirus type 5 (Ad5) E1B 55-kDa protein modulates several cellular processes, including activation of the tumor suppressor p53. Binding of the E1B protein to the activation domain of p53 inhibits p53-dependent transcription. This activity has been correlated with the transforming activity of the E1B protein, but its contribution to viral replication is not well understood. To address this issue, we used microarray hybridization methods to examine cellular gene expression in normal human fibroblasts (HFFs) infected by Ad5, the E1B 55-kDa-protein-null mutant Hr6, or a mutant carrying substitutions that impair repression of p53-dependent transcription. Comparison of the changes in cellular gene expression observed in these and our previous experiments (D. L. Miller et al., Genome Biol. 8:R58, 2007) by significance analysis of microarrays indicated excellent reproducibility. Furthermore, we again observed that Ad5 infection led to efficient reversal of the p53-dependent transcriptional program. As this same response was also induced in cells infected by the two mutants, we conclude that the E1B 55-kDa protein is not necessary to block activation of p53 in Ad5-infected cells. However, groups of cellular genes that were altered in expression specifically in the absence of the E1B protein were identified by consensus k-means clustering of the hybridization data. Statistical analysis of the enrichment of genes associated with specific functions in these clusters established that the E1B 55-kDa protein is necessary for repression of genes encoding proteins that mediate antiviral and immune defenses.

The direct p53 target gene, FLJ11259/DRAM, is a member of a novel family of transmembrane proteins

The tumor suppressor p53 regulates diverse biological processes primarily via activation of downstream target genes. Even though many p53 target genes have been described, the precise mechanisms of p53 biological actions are uncertain. In previous work we identified by microarray analysis a candidate p53 target gene, FLJ11259/DRAM. In this report we have identified three uncharacterized human proteins with sequence homology to FLJ11259, suggesting that FLJ11259 is a member of a novel family of proteins with six transmembrane domains. Several lines of investigation confirm FLJ11259 is a direct p53 target gene. p53 siRNA prevented cisplatin-mediated up-regulation of FLJ11259 in NT2/D1 cells. Likewise in HCT116 p53+/+ cells and MCF10A cells, FLJ11259 is induced by cisplatin treatment but to a much lesser extent in isogenic p53-suppressed cells. A functional p53 response element was identified 22.3 kb upstream of the first coding exon of FLJ11259 and is shown to be active in reporter assays. In addition, chromatin immunoprecipitation assays indicate that p53 binds directly to this element in vivo and that binding is enhanced following cisplatin treatment. Confocal microscopy showed that an FLJ-GFP fusion protein localizes mainly in a punctate pattern in the cytoplasm. Overexpression studies in Cos-7, Saos2, and NT2/D1 cells suggest that FLJ11259 is associated with increased clonal survival. In summary, we have identified FLJ11259/DRAM as a p53-inducible member of a novel family of transmembrane proteins. FLJ11259/DRAM may be an important modulator of p53 responses in diverse tumor types.

Dissecting functional roles of p53 N-terminal transactivation domains by microarray expression analysis

The p53 protein exerts its tumor suppressive function mainly by acting as a transcription activator. Two transactivation domains (TADs) located at the amino-terminus of p53 are required for transcription activation, and the activity of TADs is tightly regulated by post-translational modifications, such as phosphorylation. We attempted to dissect the functions of the two TADs and phosphorylation within the TADs by analyzing p53 target genes induced by full-length p53 (FL-p53), N-terminally deleted p53 isoform lacking the first TAD (Delta1stTAD) and p53 carrying point mutations at all serine residues within the two TADs (TAD-S/A). By performing a comprehensive survey by employing microarray expression analysis, the induction of target genes by FL-p53, Delta1stTAD and TAD-S/A was analyzed. All p53s showed different target gene induction patterns, suggesting the importance of the two TADs and phosphorylation within the TADs in target gene induction. Although Delta1stTAD showed a marked decrease in the ability to induce genes induced by FL-p53, Delta1stTAD induced many apoptosis-related genes that were not induced by FL-p53, suggesting the roles of these Delta1stTAD-induced genes in Delta1stTAD-dependent apoptosis. Approximately 80% of genes induced by FL-p53 were not induced by TAD-S/A, including 29 previously reported p53 target genes such as Hdm2 and Bax, emphasizing the importance of phosphorylation within the TADs. These results demonstrate the significance of the regulation and differential roles of the N-terminal TADs in p53 transcriptional activity.

Identification of cell cycle regulatory genes as principal targets of p53-mediated transcriptional repression

Historically, most studies attribute p53 function to the transactivation of target genes. That p53 can selectively repress genes to affect a cellular response is less widely appreciated. Available evidence suggests that repression is important for p53-induced apoptosis and cell cycle arrest. To better establish the scope of p53-repressed target genes and the cellular processes they may affect, a global expression profiling strategy was used to identify p53-responsive genes following adenoviral p53 gene transfer (Ad-p53) in PC3 prostate cancer cells. A total of 111 genes, 0.77% of the 14,500 genes represented on the Affymetrix U133A microarray, were repressed more than 2-fold (p < or = 0.05). Validation of the array data, using reverse transcription-PCR of 20 randomly selected genes, yielded a confirmation rate of >95.5% for the complete data set. Functional over-representation analysis revealed that cell cycle regulatory genes exhibited a highly significant enrichment (p < or = 5 x 10(-28)) within the transrepressed targets. 41% of the repressed targets are cell cycle regulators. A subset of these genes exhibited repression following DNA damage, preceding cell cycle arrest, in LNCaP cells. The use of a p53 small interfering RNA strategy in LNCaP cells and the use of p53-null cell lines demonstrated that this repression is p53-dependent. These findings identify a set of genes not known previously to be down-regulated by p53 and indicate that p53-induced cell cycle arrest is a function of not only the transactivation of cell cycle inhibitors (e.g. p21) but also the repression of targets that regulate proliferation at several distinct phases of the cell cycle.

Up-regulation of Skp2 after prostate cancer cell adhesion to basement membranes results in BRCA2 degradation and cell proliferation

Aberrant interaction of carcinoma cells with basement membranes (BM) is a fundamental pathophysiological process that initiates a series of events resulting in cancer cell invasion and metastasis. In this report, we describe the results of our investigations pertaining to the events triggered by the adhesion of normal (PNT1A) and highly metastatic (PC-3) prostate cells onto BM proteins. Unlike PNT1A, PC-3 cells adhered avidly to Matrigel BM matrix as well as to isolated collagen type IV, laminin, and heparan sulfate proteoglycan perlecan, main BM components. This aberrantly increased cancer cell adhesion resulted in sustained BRCA2 protein depletion and vigorous cell proliferation, a cascade triggered by beta1 integrin-mediated phosphatidylinositol 3-kinase activation leading to BRCA2 degradation in the proteasome. This latter effect was orchestrated by phosphatidylinositol 3-kinase-dependent up-regulation of Skp2, a subunit of the Skp1-Cul1-F-box protein ubiquitin complex that directly associates with BRCA2 as demonstrated by coimmunoprecipitation assays, determines its ubiquitination, and ultimately targets it for proteasomal degradation. Inhibition of Skp2 expression by small interference RNA prevented BRCA2 depletion and inhibited the trophic effect upon cell proliferation. These results provide additional evidence on the role of BRCA2 as a modulator of cancer cell growth and elucidate the molecular mechanisms involved in its down-regulation in cancer cells when interacting with BM, a crucial step in the biology of metastasis. Furthering the understanding of this molecular pathway may prove valuable in designing new therapeutic strategies aimed at modifying the natural history of prostate carcinoma.

Down-regulation of BRCA2 expression by collagen type I promotes prostate cancer cell proliferation

BRCA2 is a tumor suppressor gene that when mutated confers an increased susceptibility to developing breast and prostate carcinoma. Besides its role in mediating DNA repair, new evidence suggests that BRCA2 may also play a role in suppressing cancer cell growth. Because altered interactions between neoplastic cells and the surrounding extracellular matrix (ECM) play a pivotal role in unchecked cancer cell proliferation and metastatic progression, we hypothesized that the ECM may have an effect in BRCA2 expression. By using normal and prostate carcinoma cell lines, we demonstrated that although normal cells transiently increase BRCA2 protein levels when adhering to the ECM protein collagen type I (COL1), carcinoma cells exhibit a significant reduction in BRCA2 protein. This aberrant effect is independent from de novo protein synthesis and results from COL1-beta(1) integrin signaling through phosphatidylinositol (PI) 3-kinase leading to BRCA2 ubiquitination and degradation in the proteasome. BRCA2 protein depletion after cancer cell adhesion to COL1 or in small RNA interference assays triggers new DNA synthesis, a trophic effect that is abrogated by recombinant BRCA2 expression. Blocking or inhibiting beta(1) integrin, PI 3-kinase, or proteasome activity all have a negative effect on COL1-mediated DNA synthesis in cancer cells. In normal cells, the transient increase in BRCA2 expression is independent from beta(1) integrin or PI 3-kinase and has no effect in cell proliferation. In summary, these results unravel a novel mechanism whereby prostate carcinoma cell proliferation is enhanced by the down-regulation of BRCA2 expression when interacting with COL1, a major component of the ECM at osseous metastatic sites.