Identification of a novel FAS/ER-alpha fusion transcript expressed in human cancer cells

Gallic acid for cancer therapy: Molecular mechanisms and boosting efficacy by nanoscopical delivery

Cancer is the second leading cause of death worldwide. Majority of recent research efforts in the field aim to address why cancer resistance to therapy develops and how to overcome or prevent it. In line with this, novel anti-cancer compounds are desperately needed for chemoresistant cancer cells. Phytochemicals, in view of their pharmacological activities and capacity to target various molecular pathways, are of great interest in the development of therapeutics against cancer. Plant-derived-natural products have poor bioavailability which restricts their anti-tumor activity. Gallic acid (GA) is a phenolic acid exclusively found in natural sources such as gallnut, sumac, tea leaves, and oak bark. In this review, we report on the most recent research related to anti-tumor activities of GA in various cancers with a focus on its underlying molecular mechanisms and cellular pathwaysthat that lead to apoptosis and migration of cancer cells. GA down-regulates the expression of molecular pathways involved in cancer progression such as PI3K/Akt. The co-administration of GA with chemotherapeutic agents shows improvements in suppressing cancer malignancy. Various nano-vehicles such as organic- and inorganic nano-materials have been developed for targeted delivery of GA at the tumor site. Here, we suggest that nano-vehicles improve GA bioavailability and its ability for tumor suppression.

EMT Factors and Metabolic Pathways in Cancer

The epithelial-mesenchymal transition (EMT) represents a biological program during which epithelial cells lose their cell identity and acquire a mesenchymal phenotype. EMT is normally observed during organismal development, wound healing and tissue fibrosis. However, this process can be hijacked by cancer cells and is often associated with resistance to apoptosis, acquisition of tissue invasiveness, cancer stem cell characteristics, and cancer treatment resistance. It is becoming evident that EMT is a complex, multifactorial spectrum, often involving episodic, transient or partial events. Multiple factors have been causally implicated in EMT including transcription factors (e.g., SNAIL, TWIST, ZEB), epigenetic modifications, microRNAs (e.g., miR-200 family) and more recently, long non-coding RNAs. However, the relevance of metabolic pathways in EMT is only recently being recognized. Importantly, alterations in key metabolic pathways affect cancer development and progression. In this review, we report the roles of key EMT factors and describe their interactions and interconnectedness. We introduce metabolic pathways that are involved in EMT, including glycolysis, the TCA cycle, lipid and amino acid metabolism, and characterize the relationship between EMT factors and cancer metabolism. Finally, we present therapeutic opportunities involving EMT, with particular focus on cancer metabolic pathways.

Transcriptional-Readthrough RNAs Reflect the Phenomenon of "A Gene Contains Gene(s)" or "Gene(s) within a Gene" in the Human Genome, and Thus Are Not Chimeric RNAs

Tens of thousands of chimeric RNAs, i.e., RNAs with sequences of two genes, have been identified in human cells. Most of them are formed by two neighboring genes on the same chromosome and are considered to be derived via transcriptional readthrough, but a true readthrough event still awaits more evidence and trans-splicing that joins two transcripts together remains as a possible mechanism. We regard those genomic loci that are transcriptionally read through as unannotated genes, because their transcriptional and posttranscriptional regulations are the same as those of already-annotated genes, including fusion genes formed due to genetic alterations. Therefore, readthrough RNAs and fusion-gene-derived RNAs are not chimeras. Only those two-gene RNAs formed at the RNA level, likely via trans-splicing, without corresponding genes as genomic parents, should be regarded as authentic chimeric RNAs. However, since in human cells, procedural and mechanistic details of trans-splicing have never been disclosed, we doubt the existence of trans-splicing. Therefore, there are probably no authentic chimeras in humans, after readthrough and fusion-gene derived RNAs are all put back into the group of ordinary RNAs. Therefore, it should be further determined whether in human cells all two-neighboring-gene RNAs are derived from transcriptional readthrough and whether trans-splicing truly exists.

Gallic acid inhibits bladder cancer cell proliferation and migration via regulating fatty acid synthase (FAS)

Bladder cancer is known as the world’s ninth most prevalent cancer in 2012. New cytotoxic drugs have created considerable progress in the treatment. Gallic acid (GA) has been shown to inhibit carcinogenesis in animal models and various cancer cell lines. The aim of the present study was to evaluate the effect of GA on proliferation and migration inhibition of a bladder cancer cell line. The results showed that GA inhibited fatty acid synthase (FAS) activity and increased ER alpha level of TSGH-8301 bladder cancer cell. GA regulated the cell proliferation via the PI3K/AKT and MAPK/ERK pathway. Immunoprecipitation assay demonstrated that GA decreased Skp2 protein level and attenuated Skp2-p27 association. It was suggested that GA acted upstream of the proteasome to control p27 levels and ultimately inhibited G2/M phase transition. Further, transwell chambers assay showed that GA suppressed bladder cancer cell invasion and migration through p-AKT/MMP-2 signaling pathway. The finding indicated that GA inhibited TSGH-8301 bladder cancer cell growth, invasion and migration through inhibition of fatty acid synthase.

Fatty acid synthase regulates estrogen receptor-α signaling in breast cancer cells

Fatty acid synthase (FASN), the key enzyme for endogenous synthesis of fatty acids, is overexpressed and hyperactivated in a biologically aggressive subset of sex steroid-related tumors, including breast carcinomas. Using pharmacological and genetic approaches, we assessed the molecular relationship between FASN signaling and estrogen receptor alpha (ERα) signaling in breast cancer. The small compound C75, a synthetic slow-binding inhibitor of FASN activity, induced a dramatic augmentation of estradiol (E₂)-stimulated, ERα-driven transcription. FASN and ERα were both necessary for the synergistic activation of ERα transcriptional activity that occurred following co-exposure to C75 and E₂: first, knockdown of FASN expression using RNAi (RNA interference) drastically lowered (>100 fold) the amount of E₂ required for optimal activation of ERα-mediated transcriptional activity; second, FASN blockade synergistically increased E₂-stimulated ERα-mediated transcriptional activity in ERα-negative breast cancer cells stably transfected with ERα, but not in ERα-negative parental cells. Non-genomic, E₂-regulated cross-talk between the ERα and MAPK pathways participated in these phenomena. Thus, treatment with the pure antiestrogen ICI 182 780 or the potent and specific inhibitor of MEK/ERK, U0126, was sufficient to abolish the synergistic nature of the interaction between FASN blockade and E₂-stimulated ERα transactivation. FASN inhibition suppressed E₂-stimulated breast cancer cell proliferation and anchorage-independent colony formation while promoting the reduction of ERα protein. FASN blockade resulted in the increased expression and nuclear accumulation of the cyclin-dependent kinase inhibitors p21^WAF1/CIP1 and p27^Kip1, two critical mediators of the therapeutic effects of antiestrogen in breast cancer, while inactivating AKT, a key mediator of E₂-promoted anchorage-independent growth. The ability of FASN to regulate E₂/ERα signaling may represent a promising strategy for anticancer treatment involving a new generation of FASN inhibitors.

Hypothesis: Artifacts, Including Spurious Chimeric RNAs with a Short Homologous Sequence, Caused by Consecutive Reverse Transcriptions and Endogenous Random Primers

Recent RNA-sequencing technology and associated bioinformatics have led to identification of tens of thousands of putative human chimeric RNAs, i.e. RNAs containing sequences from two different genes, most of which are derived from neighboring genes on the same chromosome. In this essay, we redefine "two neighboring genes" as those producing individual transcripts, and point out two known mechanisms for chimeric RNA formation, i.e. transcription from a fusion gene or trans-splicing of two RNAs. By our definition, most putative RNA chimeras derived from canonically-defined neighboring genes may either be technical artifacts or be cis-splicing products of 5'- or 3'-extended RNA of either partner that is redefined herein as an unannotated gene, whereas trans-splicing events are rare in human cells. Therefore, most authentic chimeric RNAs result from fusion genes, about 1,000 of which have been identified hitherto. We propose a hypothesis of "consecutive reverse transcriptions (RTs)", i.e. another RT reaction following the previous one, for how most spurious chimeric RNAs, especially those containing a short homologous sequence, may be generated during RT, especially in RNA-sequencing wherein RNAs are fragmented. We also point out that RNA samples contain numerous RNA and DNA shreds that can serve as endogenous random primers for RT and ensuing polymerase chain reactions (PCR), creating artifacts in RT-PCR.

Fenofibrate in cancer: mechanisms involved in anticancer activity

Objective: To review the mechanisms of anti-cancer activity of fenofibrate (FF) and other Peroxisome Proliferator Activator Receptor α (PPARα) agonists based on evidences reported in the published literature.Methods: We extensively reviewed the literature concerning FF as an off target anti-cancer drug. Controversies regarding conflicting findings were also addressed.Results: The main mechanism involved in anti-cancer activity is anti-angiogenesis through down-regulation of  Vascular Endothelial Growth Factor (VEGF), Vascular Endothelial Growth Factor Receptor (VEGFR) and Hypoxia Inducible factor-1 α (HIF-1α), inhibition of endothelial cell migration, up-regulation of endostatin and thrombospondin-1, but there are many other contributing mechanisms like apoptosis and cell cycle arrest, down-regulation of Nuclear Factor Kappa B (NF-kB) and Protein kinase B (Akt) and decrease of cellular energy by impairing mitochondrial function. Growth impairment is related to down-regulation of Phospho-Inositol 3 Kinase (PI3K)/Akt axis and down-regulation of the p38 map kinase (MAPK) cascade. A possible role should be assigned to FF stimulated over-expression of Tribbles Homolog-3 (TRIB3) which inhibits Akt phosphorylation. Important anti-cancer and anti-metastatic activities are due to down-regulation of MCP-1 (monocyte chemotactic protein-1), decreased Metalloprotease-9 (MMP-9) production, weak down-regulation of adhesion molecules like E selectin, intercellular adhesion molecules (ICAM) and Vascular Endothelial Adhesion Molecules (VCAM), and decreased secretion of chemokines like Interleukin-6 (IL-6), and down-regulation of cyclin D-1. There is no direct link between FF activity in lipid metabolism and anticancer activity, except for the fact that many anticancer actions are dependent from PPARα agonism. FF exhibits also PPARα independent anti-cancer activities.Conclusions: There are strong evidences indicating that FF can disrupt growth-related activities in many different cancers, due to anti-angiogenesis and anti-inflammatory effects. Therefore FF may be useful as a complementary adjunct treatment of cancer, particularly included in anti-angiogenic protocols like those currently increasingly used in glioblastoma. There are sound reasons to initiate well planned phase II clinical trials for FF as a complementary adjunct treatment of cancer.

Chimeric RNAs as potential biomarkers for tumor diagnosis

Cancers claim millions of lives each year. Early detection that can enable a higher chance of cure is of paramount importance to cancer patients. However, diagnostic tools for many forms of tumors have been lacking. Over the last few years, studies of chimeric RNAs as biomarkers have emerged. Numerous reports using bioinformatics and screening methodologies have described more than 30,000 expressed sequence tags (EST) or cDNA sequences as putative chimeric RNAs. While cancer cells have been well known to contain fusion genes derived from chromosomal translocations, rearrangements or deletions, recent studies suggest that trans-splicing in cells may be another source of chimeric RNA production. Unlike cis-splicing, trans-splicing takes place between two pre-mRNA molecules, which are in most cases derived from two different genes, generating a chimeric non-co-linear RNA. It is possible that trans-splicing occurs in normal cells at high frequencies but the resulting chimeric RNAs exist only at low levels. However the levels of certain RNA chimeras may be elevated in cancers, leading to the formation of fusion genes. In light of the fact that chimeric RNAs have been shown to be overrepresented in various tumors, studies of the mechanisms that produce chimeric RNAs and identification of signature RNA chimeras as biomarkers present an opportunity for the development of diagnoses for early tumor detection.

Short rare hTERT-VNTR2-2nd alleles are associated with prostate cancer susceptibility and influence gene expression

Background

The hTERT (human telomerase reverse transcriptase) gene contains five variable number tandem repeats (VNTR) and previous studies have described polymorphisms for hTERT-VNTR2-2^nd. We investigated how allelic variation in hTERT-VNTR2-2^nd may affect susceptibility to prostate cancer.

Methods

A case-control study was performed using DNA from 421 cancer-free male controls and 329 patients with prostate cancer. In addition, to determine whether the VNTR polymorphisms have a functional consequence, we examined the transcriptional levels of a reporter gene linked to these VNTRs and driven by the hTERT promoter in cell lines.

Results

Three new rare alleles were detected from this study, two of which were identified only in cancer subjects. A statistically significant association between rare hTERT-VNTR2-2^nd alleles and risk of prostate cancer was observed [OR, 5.17; 95% confidence interval (CI), 1.09-24.43; P = 0.021]. Furthermore, the results indicated that these VNTRs inserted in the enhancer region could influence the expression of hTERT in prostate cancer cell lines.

Conclusions

This is the first study to report that rare hTERT VNTRs are associated with prostate cancer predisposition and that the VNTRs can induce enhanced levels of hTERT promoter activity in prostate cancer cell lines. Thus, the hTERT-VNTR2-2^nd locus may function as a modifier of prostate cancer risk by affecting gene expression.

Expression profiling by whole-genome microarray hybridization reveals differential gene expression in breast cancer cell lines after lycopene exposure

The correlation between diet and variation in gene-expression is an important field which could be considered to approach cancer pathways comprehension. We examined the effects of lycopene on breast cancer cell lines using pangenomic arrays. Lycopene is derived predominantly from tomatoes and tomato products and there is some epidemiologic evidence for a preventive role in breast cancer. Previously, we investigated lycopene in breast cancer using a dedicated breast cancer microarray. To confirm these results and explore pathways other than those implicated in breast cancer, for this study we used pangenomic arrays containing 25,000 oligonucleotides. This in vitro study assayed two human mammary cancer cell lines (MCF-7 and MDA-MB-231), and a fibrocystic breast cell line (MCF-10a) treated or not with 10 microM lycopene for 48 h. A competitive hybridization was performed between Cy3-labeled lycopene treated RNA and Cy5-labeled untreated RNA to define differentially expressed genes. Using t-test analysis, a subset of 391 genes was found to be differentially modulated by lycopene between estrogen-positive cells (MCF-7) and estrogen-negative cells (MDA-MB-231, MCF-10a). Hierarchical clustering revealed 726 discriminatory genes between breast cancer cell lines (MCF-7, MDA-MB-231) and the fibrocystic breast cell line (MCF-10a). Modified gene expression was observed in various molecular pathways, such as apoptosis, cell communication, MAPK and cell cycle as well as xenobiotic metabolism, fatty acid biosynthesis and gap junctional intercellular communication.

Stimulatory Cross-talk between NFAT3 and Estrogen Receptor in Breast Cancer Cells

Estrogen receptors (ERalpha and ERbeta) are ligand-regulated transcription factors that play critical roles in the development and progression of breast cancer by regulating target genes involved in cellular proliferation. The transcriptional activity of ERalpha and ERbeta is known to be modulated by cofactor proteins. We used a yeast two-hybrid system and identified NFAT3 as a novel ERbeta-binding protein. NFAT3 interacted with ERalpha and ERbeta both in vitro and in mammalian cells in a ligand-independent fashion. NFAT3 bound specifically to the ERbeta region containing the activation function-1 domain, a ligand-independent transactivation domain. Overexpression of NFAT3 enhanced both ERalpha and ERbeta transcriptional activities in a ligand-independent manner and up-regulated downstream estrogen-responsive genes including pS2 and cathepsin D. Reduction of endogenous NFAT3 with NFAT3 small interfering RNA or overexpression of NFAT3 deletion mutants that lack the ER-binding sites reduced the NFAT3 coactivation of ERalpha and ERbeta. NFAT3 increased binding of ERalpha to the estrogen-responsive element and was recruited to endogenous estrogen-responsive promoters. NFAT3 was expressed differentially in many breast cancer cell lines and overexpressed in a subset of breast cancer patients. Knockdown of endogenous NFAT3 reduced the growth of human breast cancer ZR75-1 cells in a ligand-independent manner. Taken together, these results suggest that NFAT3 may play important roles in ER signaling and represent a novel target for breast cancer therapy.

Inhibition of tumor-associated fatty acid synthase activity antagonizes estradiol- and tamoxifen-induced agonist transactivation of estrogen receptor (ER) in human endometrial adenocarcinoma cells

Overexpression of the lipogenic enzyme fatty acid synthase (FAS) is a common molecular feature in subsets of sex-steroid-related tumors including endometrium and breast carcinomas that are associated with poor prognosis. Pharmacological inhibition of tumor-associated FAS hyperactivity is under investigation as a chemotherapeutic target. We examined the effects of the mycotoxin cerulenin (a covalent FAS inactivator), and the novel small compound C75 (a slow-binding FAS inhibitor) on estradiol (E2)- and tamoxifen (TAM)-stimulated ER-driven molecular responses in Ishikawa cells, an in vitro model of well-differentiated human endometrial carcinoma. We evaluated the effects of FAS inhibition on E2- and TAM-induced estrogen receptor (ER) transcriptional activity by using transient cotransfection assays with an estrogen-response element reporter construct (ERE-Luciferase). Antiestrogenic effects of cerulenin and C75 were observed by dose-dependent inhibition of E2-stimulated ERE-dependent transcription, whereas FAS inhibitors did not significantly increase the levels of ERE transcriptional activity in the absence of E2. Moreover, pharmacological blockade of FAS activity completely abolished TAM-stimulated ERE activity. To address the reliability of transient transfection assays, the effects of FAS inhibitors on E2-inducible gene products were evaluated. FAS blockade induced a dose-dependent decrease in E2-inducible alkaline phosphatase activity. E2-stimulated accumulation of progesterone receptor (PR) and HER-2/neu oncogene was abolished in the presence of FAS blockers. FAS inhibition also resulted in a marked downregulation of E2-stimulated ERalpha expression, and noticeably impaired E2-induced ERalpha nuclear accumulation. A dose-dependent decrease in cell proliferation and cell viability was observed after FAS blockade. A Cell Death ELISA, detecting DNA fragmentation, demonstrated that FAS inhibitors stimulated apoptosis of Ishikawa cells. The analysis of critical E2- and TAM-related cell cycle proteins revealed an increase of both the expression and the nuclear accumulation of cyclin-dependent kinase inhibitors p21WAF1/CIP1 and p27Kip1 following FAS inhibition. To rule out non-FAS cerulenin- and C75-related effects, we finally monitored ER signaling after silencing of FAS gene expression using the highly sequence-specific mechanism of RNA interference (RNAi). The concentrations of E2 and TAM inducing half-maximal ERE activity (EC50) dramatically increased (>100 times) in FAS RNAi-transfected Ishikawa cells. Moreover, depletion of FAS by RNAi also caused loss of ERalpha expression, downregulation of PR, and accumulation of p21WAF1/CIP1 and p27Kip1 in E2-stimulated Ishikawa cells. If chemically stable FAS inhibitors or cell-selective vector systems able to deliver RNAi targeting FAS gene demonstrate systemic anticancer effects in vivo, our results render FAS as a novel target for the prevention and treatment of endometrial carcinoma.

Ligand-independent activation of estrogen receptor alpha by XBP-1

The estrogen receptor (ER) is a member of a large superfamily of nuclear receptors that regulates the transcription of estrogen-responsive genes. Several recent studies have demonstrated that XBP-1 mRNA expression is associated with ERalpha status in breast tumors. However, the role of XBP-1 in ERalpha signaling remains to be elucidated. More recently, two forms of XBP-1 were identified due to its unconventional splicing. We refer to the spliced and unspliced forms of XBP-1 as XBP-1S and XBP-1U, respectively. Here, we report that XBP-1S and XBP-1U enhanced ERalpha-dependent transcriptional activity in a ligand-independent manner. XBP-1S had stronger activity than XBP-1U. The maximal effects of XBP-1S and XBP-1U on ERalpha transactivation were observed when they were co-expressed with full-length ERalpha. SRC-1, the p160 steroid receptor coactivator family member, synergized with XBP-1S or XBP-1U to potentiate ERalpha activity. XBP-1S and XBP-1U bound to the ERalpha both in vitro and in vivo in a ligand-independent fashion. XBP-1S and XBP-1U interacted with the ERalpha region containing the DNA-binding domain. The ERalpha-interacting regions on XBP-1S and XBP-1U have been mapped to two regions, including the N-terminal basic region leucine zipper domain (bZIP) and the C-terminal activation domain. The bZIP-deleted mutants of XBP-1S and XBP-1U completely abolished ERalpha transactivation by XBP-1S and XBP-1U. These findings suggest that XBP-1S and XBP-1U may directly modulate ERalpha signaling in both the absence and presence of estrogen and, therefore, may play important roles in the proliferation of normal and malignant estrogen-regulated tissues.