Folic acid reduces nuclear translocation of beta-catenin in rectal mucosal crypts of patients with colorectal adenomas

Folic Acid Reduces Tau Phosphorylation by Regulating PP2A Methylation in Streptozotocin-Induced Diabetic Mice

High incidence rate of Alzheimer’s disease (AD) is observed in patients with type 2 diabetes. Aggregated β-amyloid (Aβ) and hyperphosphorylated tau are the hallmarks of AD. Hyperphosphorylated tau has been detected in diabetic animals as well as in diabetic patients. Folates mediate the transfer of one carbon unit, required in various biochemical reactions. The effect of folate on tau phosphorylation in diabetic models still remains unknown. In this study, we investigated the effect and mechanism of folic acid on hyperphosphorylation of tau in streptozotocin (STZ)-induced diabetic mice. Diabetic mice induced by STZ, at the age of 10 weeks, were administered with three levels of folic acid: folic acid-deficient diet, diet with normal folic acid content, and 120 μg/kg folic acid diet for 8 weeks. Levels of serum folate and blood glucose were monitored. Tau phosphorylation, protein phosphatase 2A (PP2A) methylation, and Glycogen synthase kinase 3β (GSK-3β) phosphorylation were detected using Western blot. The S-adenosyl methionine:S-adenosyl homocysteine ratio (SAM:SAH) in brain tissues was also determined. DNA methyltransferase (DNMT) mRNA expression levels were detected using real-time PCR. Folic acid reduced tau hyperphosphorylation at Ser396 in the brain of diabetes mellitus (DM) mice. In addition, PP2A methylation and DNMT1 mRNA expression were significantly increased in DM mice post folic acid treatment. GSK-3β phosphorylation was not regulated by folic acid administration. Folic acid can reduce tau phosphorylation by regulating PP2A methylation in diabetic mice. These results support that folic acid can serve as a multitarget neuronal therapeutic agent for treating diabetes-associated cognitive dysfunction.

DDX17 nucleocytoplasmic shuttling promotes acquired gefitinib resistance in non-small cell lung cancer cells via activation of β-catenin

Although epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are effective for non-small cell lung cancer (NSCLC) patients with EGFR mutations, almost all these patients will eventually develop acquired resistance to EGFR-TKI. However, the molecular mechanisms responsible for gefitinib resistance remain still not fully understood. Here, we report that elevated DDX17 levels are observed in gefitinib-resistant NSCLC cells than gefitinib-sensitive cells. Upregulation of DDX17 enhances the gefitinib resistance, whereas DDX17-silenced cells partially restore gefitinib sensitivity. Mechanistically, we demonstrate that DDX17 disassociates the E-cadherin/β-catenin complex, resulting in β-catenin nuclear translocation and subsequently augmenting the transcription of β-catenin target genes. Moreover, we identify two nuclear localization signal (NLS) and four nuclear export signal (NES) sequences mediated DDX17 nucleocytoplasmic shuttling via an exportin/importin-dependent pathways. Interruption of dynamic nucleocytoplasmic shuttling of DDX17 impairs DDX17-mediating the activation of β-catenin and acquired resistance in NSCLC cells. In conclusion, our findings reveal a novel and important mechanism by which DDX17 contributes to acquired gefitinib resistance through exportin/importin-dependent cytoplasmic shuttling and followed by activation of β-catenin, and DDX17 inhibition may be a promising strategy to overcome acquired resistance of gefitinib in NSCLC patients.

People with low serum folate levels have higher risk of colorectal adenoma/advanced colorectal adenoma occurrence and recurrence in China

Objective

To investigate the potential association between serum folate levels and colorectal adenoma (CRA) occurrence and recurrence.

Methods

This prospective study measured baseline serum folate levels in outpatients who were screened for CRA using colonoscopy. Participants were then randomly selected to produce one group with CRA and one without CRA. These two subgroups underwent further follow-up observations of colonoscopy to determine the occurrence of new and recurrent CRA.

Results

A total of 1310 participants were screened at baseline: 888 were healthy subjects without CRA; and 422 had CRA. Two subgroups were randomly selected (n = 200 per group) for follow-up. In the overall population, baseline serum folate levels were significantly lower in patients with CRA or advanced CRA (A-CRA) compared with healthy participants without CRA. Similar findings were shown for the follow-up study in terms of the association between CRA and A-CRA occurrence and recurrence and baseline serum folate levels. After controlling for confounders, increased serum folate was associated with a reduced risk of occurrence of CRA (odds ratio [OR] 0.993, 95% confidence interval [CI] 0.924, 1.066) and recurrence of CRA (OR 0.749, 95% CI 0.322, 1.742).

Conclusions

Higher serum folate levels may be protective against CRA and/or A-CRA.

Luteolin inhibits cell proliferation during Azoxymethane-induced experimental colon carcinogenesis via Wnt/ β-catenin pathway

The protective role of Luteolin (LUT) against Azoxymethane (AOM)-induced mouse colon carcinogenesis has been documented earlier. The aim of this study is to investigate on the mechanism of chemopreventive action exhibited by LUT employing AOM-induced colon carcinogenesis in mice as an experimental model. LUT inhibited AOM-induced colon tumorigenesis by decreasing tumor incidence and size. LUT reduced the cell proliferation by decreasing the number of Argyrophillic nucleolar organizer region (AgNOR)/nucleus and Proliferating Cell Nuclear Antigen (PCNA) index. It was known that β-catenin is a key effector in Wingless and Int (Wnt) signaling pathway and 90% of colon tumors arise from mutations in this pathway. In this study, we show evidence that LUT inhibited colon carcinogenesis by decreasing AOM-induced cell proliferation through the involvement of β-catenin, Glycogen synthase kinase (GSK)-3β and cyclin D1, the key components in Wnt signaling pathway. In conclusion, the protective effect of LUT could be attributed to inhibition of AOM-induced cellular proliferation probably through the involvement of β-catenin, GSK-3β and cyclin D1.

A lentivirus-mediated genetic screen identifies dihydrofolate reductase (DHFR) as a modulator of beta-catenin/GSK3 signaling

The multi-protein beta-catenin destruction complex tightly regulates beta-catenin protein levels by shuttling beta-catenin to the proteasome. Glycogen synthase kinase 3beta (GSK3beta), a key serine/threonine kinase in the destruction complex, is responsible for several phosphorylation events that mark beta-catenin for ubiquitination and subsequent degradation. Because modulation of both beta-catenin and GSK3beta activity may have important implications for treating disease, a complete understanding of the mechanisms that regulate the beta-catenin/GSK3beta interaction is warranted. We screened an arrayed lentivirus library expressing small hairpin RNAs (shRNAs) targeting 5,201 human druggable genes for silencing events that activate a beta-catenin pathway reporter (BAR) in synergy with 6-bromoindirubin-3'oxime (BIO), a specific inhibitor of GSK3beta. Top screen hits included shRNAs targeting dihydrofolate reductase (DHFR), the target of the anti-inflammatory compound methotrexate. Exposure of cells to BIO plus methotrexate resulted in potent synergistic activation of BAR activity, reduction of beta-catenin phosphorylation at GSK3-specific sites, and accumulation of nuclear beta-catenin. Furthermore, the observed synergy correlated with inhibitory phosphorylation of GSK3beta and was neutralized upon inhibition of phosphatidyl inositol 3-kinase (PI3K). Linking these observations to inflammation, we also observed synergistic inhibition of lipopolysaccharide (LPS)-induced production of pro-inflammatory cytokines (TNFalpha, IL-6, and IL-12), and increased production of the anti-inflammatory cytokine IL-10 in peripheral blood mononuclear cells exposed to GSK3 inhibitors and methotrexate. Our data establish DHFR as a novel modulator of beta-catenin and GSK3 signaling and raise several implications for clinical use of combined methotrexate and GSK3 inhibitors as treatment for inflammatory disease.

Folic acid supplementation inhibits recurrence of colorectal adenomas: A randomized chemoprevention trial

AIM: To determine whether folic acid supplementation will reduce the recurrence of colorectal adenomas, the precursors of colorectal cancer, we performed a double-blind placebo-controlled trial in patients with adenomatous polyps.

METHODS: In the current double-blind, placebo-controlled trial at this VA Medical Center, patients with colorectal adenomas were randomly assigned to receive either a daily 5 mg dose of folic acid or a matched identical placebo for 3 years. All polyps were removed at baseline colonoscopy and each patient had a follow up colonoscopy at 3 years. The primary endpoint was a reduction in the number of recurrent adenomas at 3 years.

RESULTS: Of 137 subjects, who were eligible after confirmation of polyp histology and run-in period to conform compliance, 94 completed the study; 49 in folic acid group and 45 in placebo group. Recurrence of adenomas at 3-year was compared between the two groups. The mean number of recurrent polyps at 3-year was 0.36 (SD, 0.69) for folic acid treated patients compared to 0.82 (SD, 1.17) for placebo treated subjects, resulting in a 3-fold increase in polyp recurrence in the placebo group. Patients below 70 years of age and those with left-sided colonic adenomas or advanced adenomas responded better to folic acid supplementation.

CONCLUSION: High dose folic acid supplementation is associated with a significant reduction in the recurrence of colonic adenomas suggesting that folic acid may be an effective chemopreventive agent for colorectal neoplasia.

The Wnt-dependent signaling pathways as target in oncology drug discovery

Our current understanding of the Wnt-dependent signaling pathways is mainly based on studies performed in a number of model organisms including, Xenopus, Drosophila melanogaster, Caenorhabditis elegans and mammals. These studies clearly indicate that the Wnt-dependent signaling pathways are conserved through evolution and control many events during embryonic development. Wnt pathways have been shown to regulate cell proliferation, morphology, motility as well as cell fate. The increasing interest of the scientific community, over the last decade, in the Wnt-dependent signaling pathways is supported by the documented importance of these pathways in a broad range of physiological conditions and disease states. For instance, it has been shown that inappropriate regulation and activation of these pathways is associated with several pathological disorders including cancer, retinopathy, tetra-amelia and bone and cartilage disease such as arthritis. In addition, several components of the Wnt-dependent signaling pathways appear to play important roles in diseases such as Alzheimer’s disease, schizophrenia, bipolar disorder and in the emerging field of stem cell research. In this review, we wish to present a focused overview of the function of the Wnt-dependent signaling pathways and their role in oncogenesis and cancer development. We also want to provide information on a selection of potential drug targets within these pathways for oncology drug discovery, and summarize current data on approaches, including the development of small-molecule inhibitors, that have shown relevant effects on the Wnt-dependent signaling pathways.

Wnt signalling and prostate cancer

The Wnt signalling pathway plays a role in the direction of embryological development and maintenance of stem cell populations. Heritable alterations in genes encoding molecules of the Wnt pathway, including mutation and epigenetic events, have been demonstrated in a variety of cancers. It has been proposed that disruption of this pathway is a significant step in the development of many tumours. Interactions between beta-catenin--the effector molecule of the Wnt pathway--and the androgen receptor highlight the pathway's relevance to urological malignancy. Mutation or altered expression of Wnt genes in tumours may give prognostic information and treatments are being developed which target this pathway.

The nonsteroidal anti-inflammatory drug, nabumetone, differentially inhibits beta-catenin signaling in the MIN mouse and azoxymethane-treated rat models of colon carcinogenesis

The mechanisms through which beta-catenin signaling is inhibited during colorectal cancer chemoprevention by nonsteroidal anti-inflammatory agents is incompletely understood. We report that nabumetone decreased uninvolved intestinal mucosal beta-catenin levels in the MIN mouse with a concomitant increase in glycogen synthase kinase (GSK)-3beta levels, an enzyme that targets beta-catenin for destruction. However, in the azoxymethane-treated rat, where beta-catenin is frequently rendered GSK-3beta-insensitive, nabumetone failed to alter beta-catenin levels but did decrease beta-catenin nuclear localization and transcriptional activity as gauged by cyclin D1. In conclusion, we demonstrate that the differential mechanisms for beta-catenin suppression may be determined, at least partly, by GSK-3beta.