Dietary intake of fish, ω‐3 and ω‐6 fatty acids and risk of colorectal cancer: A prospective study in U.S. men and women

The association between fish, ω‐3 and ω‐6 polyunsaturated fatty acid (PUFA) intake and risk of colorectal cancer (CRC) remains inconclusive. Recent prospective studies suggest that the relationship may vary by gender, subsite and duration of follow‐up. We followed 123,529 US adults (76,386 women and 47,143 men) without a history of cancer at baseline for 24 to 26 years. Fish and PUFA intake was assessed at baseline and updated every 4 years by using a validated food‐frequency questionnaire. We found no overall association between fish, ω‐3 and ω‐6 PUFA intake and CRC risk with hazard ratio (HR) of 1.03 [95% confidence interval (CI): 0.89–1.20] comparing marine ω‐3 intake of ≥0.30 g/d versus <0.15 g/d among women and 1.05 (95% CI: 0.85–1.30) comparing intake of ≥0.41 g/d versus <0.16 g/d among men. However, fish and marine ω‐3 PUFA intake appeared to be positively associated with risk of distal colon cancer in both men and women and inversely with risk of rectal cancer in men. In an analysis based on a limited number of cases, marine ω‐3 PUFA intake assessed 12–16 years before diagnosis tended to be inversely associated with CRC risk in men (HR: 0.76; 95% CI: 0.52–1.10). In conclusion, although no overall association between fish, ω‐3 or ω‐6 PUFA intake was observed with CRC risk, marine ω‐3 PUFA may be differentially associated with risk of distal colon and rectal cancers and a long latency may be needed for its protection against CRC in men.     

Association between activation of atypical NF‐κB1 p105 signaling pathway and nuclear β‐catenin accumulation in colorectal carcinoma

Recent studies have demonstrated that increased expression of coding region determinant‐binding protein (CRD‐BP) in response to β‐catenin signaling leads to the stabilization of β‐TrCP1, a substrate‐specific component of SCF E3 ubiquitin ligase complex, resulting in an accelerated degradation of IκBα and activation of canonical nuclear factor‐κB (NF‐κB) pathway. Here, we show that the noncanonical NF‐κB1 p105 pathway is constitutively activated in colorectal carcinoma specimens, being particularly associated with β‐catenin‐mediated increased expression of CRD‐BP and β‐TrCP1. In the carcinoma tissues exhibiting high levels of nuclear β‐catenin the phospho‐p105 levels were increased and total p105 amounts were decreased in comparison to that of normal tissue indicating an activation of this NF‐κB pathway. Knockdown of CRD‐BP in colorectal cancer cell line SW620 resulted in significantly higher basal levels of both NF‐κB inhibitory proteins, p105 and IκBα. Furthermore decreased NF‐κB binding activity was observed in CRD‐BP siRNA‐transfected SW620 cells as compared with those transfected with control siRNA. Altogether, our findings suggest that activation of NF‐κB1 p105 signaling in colorectal carcinoma might be attributed to β‐catenin‐mediated induction of CRD‐BP and β‐TrCP1. © 2009 Wiley‐Liss, Inc.     

HBx mutations promote hepatoma cell migration through the Wnt/β‐catenin signaling pathway

HBx mutations (T1753V, A1762T, G1764A, and T1768A) are frequently observed in hepatitis B virus (HBV)‐related hepatocellular carcinoma (HCC). Aberrant activation of the Wnt/β‐catenin signaling pathway is involved in the development of HCC. However, activation of the Wnt/β‐catenin signaling pathway by HBx mutants has not been studied in hepatoma cells or HBV‐associated HCC samples. In this study, we examined the effects of HBx mutants on the migration and proliferation of HCC cells and evaluated the activation of Wnt/β‐catenin signaling in HBx‐transfected HCC cells and HBV‐related HCC tissues. We found that HBx mutants (T, A, TA, and Combo) promoted the migration and proliferation of hepatoma cells. The HBx Combo mutant potentiated TOP‐luc activity and increased nuclear translocation of β‐catenin. Moreover, the HBx Combo mutant increased and stabilized β‐catenin levels through inactivation of glycogen synthase kinase‐3β, resulting in upregulation of downstream target genes such as c‐Myc, CTGF, and WISP2. Enhanced activation of Wnt/β‐catenin was found in HCC tissues with HBx TA and Combo mutations. Knockdown of β‐catenin effectively abrogated cell migration and proliferation stimulated by the HBx TA and Combo mutants. Our results indicate that HBx mutants, especially the Combo mutant, allow constitutive activation of the Wnt signaling pathway and may play a pivotal role in HBV‐associated hepatocarcinogenesis.     

Extracellular 5′‐nucleotidase (CD73) promotes human breast cancer cells growth through AKT/GSK‐3β/β‐catenin/cyclinD1 signaling pathway

To identify the role and to explore the mechanism of extracellular 5′‐nucleotidase (CD73) in human breast cancer growth, CD73 expression was measured firstly in breast cancer tissues and cell lines, and then interfered with or over‐expressed by recombinant lentivirus in cell lines. Impacts of CD73 on breast cancer cell proliferation and cell cycle were investigated with colony formation assay, CCK‐8 and flow cytometry. The relationship between CD73 and AKT/GSK‐3β/β‐catenin pathway was assessed with adenosine, adenosine 2A receptor antagonist (SCH‐58261), adenosine 2A receptor agonist (NECA), CD73 enzyme inhibitor (APCP) and Akt inhibitor (MK‐2206). Moreover, the effect of CD73 on breast cancer growth in vivo was examined with human breast cancer transplanting model of nude mice. The results showed that the expression of CD73 was high in breast cancer tissues and increased with advanced tumor grades and lympho‐node status. CD73 expression was higher in more malignant cells, and CD73 overexpression promoted breast cancer cell proliferation in both in vivo and in vitro. It activated AKT/GSK‐3β/β‐catenin/cyclinD1 signaling pathway through CD73 enzyme activity and other mechanism.     

HBO1 promotes cell proliferation in bladder cancer via activation of Wnt/β‐catenin signaling

Histone acetyltransferase binding to ORC1 (HBO1), a histone acetyltransferase, was recently identified as an oncoprotein; however, its role in bladder cancer remains unknown. In this study, we showed that HBO1 was highly expressed at both the mRNA and the protein levels in bladder cancer. HBO1 expression was associated with the clinical features of human bladder cancer, including tumor size (P = 0.018) and T (P = 0.007) classifications. Patients with higher HBO1 expression had shorter recurrence‐free survival time, whereas patients with lower HBO1 expression had better survival time. Moreover, we found that ectopic overexpression of HBO1 promoted, whereas HBO1 silencing inhibited tumor growth in bladder cancer cells both in vitro and in vivo. We further demonstrated that upregulation of HBO1 activated the Wnt/β‐catenin signaling pathway and led to nuclear localization of β‐catenin and upregulation of downstream targets of of Wnt/β‐catenin signaling. These findings suggest that HBO1 plays a key role in the progression of bladder cancer via the Wnt/β‐catenin pathway, and may serve as a potential therapeutic target for the treatment of bladder cancer.     

Targeting IL‐13Rα2 in human pancreatic ductal adenocarcinoma with combination therapy of IL‐13‐PE and gemcitabine

Pancreatic cancer is an aggressive disease with only limited therapeutic options available. We have identified that 71% pancreatic ductal adenocarcinoma (PDA) express high levels of IL‐13Rα2, a high‐affinity receptor for IL‐13. To target IL‐13Rα2, we have developed a recombinant immunotoxin, which is a fusion of IL‐13 and Pseudomonas exotoxin (IL‐13‐PE). Since IL‐13‐PE and a commonly used cytotoxic drug gemcitabine act by a different mechanism, we hypothesized that they synergize in mediating antitumor response. Both IL‐13‐PE and gemcitabine‐mediated cytotoxicity to two pancreatic cancer cell lines and when combined synergistic cytotoxicity was observed. This synergism was also demonstrated in vivo in an orthotopic mouse model of human PDA. IL‐13‐PE and gemcitabine showed complete eradiation of tumors as assessed by whole body imaging of GFP‐transfected tumors in 57% of mice in an early cancer model resulting into prolongation of survival. In contrast, monotherapy with either agent did not produce complete eradiation, but tumor volumes were significantly decreased. In advanced PDA model, combination therapy also produced dramatic reduction in tumor growth and enhanced survival compared to animals treated with either agent alone. When IL‐13Rα2 was knocked‐down by RNAi prior to tumor implantation, IL‐13‐PE and gemcitabine did not synergize indicating that IL‐13Rα2 is essential. Mechanistically, gemcitabine increased IL‐13Rα2 expression in vitro and in vivo, which resulted in a synergism of combination therapy. Interestingly, PDA cancer stem cells were resistant to gemcitabine, but not to IL‐13‐PE. These results suggest that combination therapy with IL‐13‐PE and gemcitabine may be a useful strategy for PDA therapy.     

Retinoid X receptor α enhances human cholangiocarcinoma growth through simultaneous activation of Wnt/β‐catenin and nuclear factor‐κB pathways

Retinoid X receptor α (RXRα) plays important roles in the malignancy of several cancers such as human prostate tumor, breast cancer, and thyroid tumor. However, its exact functions and molecular mechanisms in cholangiocarcinoma (CCA), a chemoresistant carcinoma with poor prognosis, remain unclear. In this study we found that RXRα was frequently overexpressed in human CCA tissues and CCA cell lines. Downregulation of RXRα led to decreased expression of mitosis‐promoting factors including cyclin D1and cyclin E, and the proliferating cell nuclear antigen, as well as increased expression of cell cycle inhibitor p21, resulting in inhibition of CCA cell proliferation. Furthermore, RXRα knockdown attenuated the expression of cyclin D1 through suppression of Wnt/β‐catenin signaling. Retinoid X receptor α upregulated proliferating cell nuclear antigen expression through nuclear factor‐κB (NF‐κB) pathways, paralleled with downregulation of p21. Thus, the Wnt/β‐catenin and NF‐κB pathways account for the inhibition of CCA cell growth induced by RXRα downregulation. Retinoid X receptor α plays an important role in proliferation of CCA through simultaneous activation of Wnt/β‐catenin and NF‐κB pathways, indicating that RXRα might serve as a potential molecular target for CCA treatment.     

SH2B1 promotes epithelial‐mesenchymal transition through the IRS1/β‐catenin signaling axis in lung adenocarcinoma

Lung adenocarcinoma (LADC), the most prevalent type of human lung cancer, is characterized by many molecular abnormalities. SH2B1, a member of the SH2‐domain containing family, have recently been shown to act as tumor activators in multiple cancers, including LADC. However, the mechanisms underlying SH2B1 overexpression are not completely understood. Here, we reported that SH2B1 expression levels were significantly upregulated and positively associated with EMT markers and poor patient survival in LADC specimens. Modulation of SH2B1 levels had distinct effects on cell proliferation, cell cycle, migration, invasion, and morphology in A549 and H1299 cells in vitro and in vivo. At the molecular level, overexpression of SH2B1 resulted in the upregulation of the EMT markers, especially induced β‐catenin accumulation and activated β‐catenin signaling to promote LADC cell proliferation and metastasis, while silencing SH2B1 had the opposite effect. Furthermore, ectopic expression of SH2B1 in H1299 cells increased IRS1 expression level. Reduced expression of IRS1 considerably inhibited H1299 cell proliferation, migration, and invasion which were driven by SH2B1 overexpression. Collectively, these results provide unequivocal evidence to establish that SH2B1‐IRS1‐β‐catenin axis is required for promoting EMT, and might prove to be a promising strategy for restraining tumor progression in LADC patients.     

Tumor inhibition by sodium selenite is associated with activation of c‐Jun NH2‐terminal kinase 1 and suppression of β‐catenin signaling

Epidemiological and clinical studies suggest that an increased intake of dietary selenium significantly reduces overall cancer risk, but the anticancer mechanism of selenium is not clear. In this study, we fed intestinal cancer mouse model. Muc2/p21 double mutant mice with a selenium‐enriched (sodium selenite) diet for 12 or 24 weeks, and found that sodium selenite significantly inhibited intestinal tumor formation in these animals (p < 0.01), which was associated with phosphorylation of JNK1 and suppression of β‐catenin and COX2. In vitro studies showed that sodium selenite promoted cell apoptosis and inhibited cell proliferation in human colon cancer cell lines HCT116 and SW620. These effects were dose‐ and time course‐dependent, and were also linked to an increase of JNK1 phosphorylation and suppression of β‐catenin signaling. Reduced JNK1 expression by small RNA interference abrogated sufficient activation of JNK1 by sodium selenite, leading to reduced inhibition of the β‐catenin signaling, resulting in reduced efficacy of inhibiting cell proliferation. Taken together, our data demonstrate that sodium selenite inhibits intestinal carcinogenesis in vivo and in vitro through activating JNK1 and suppressing β‐catenin signaling, a novel anticancer mechanism of selenium.     

Epigenetic modulation of the retinoid X receptor α by green tea in the azoxymethane‐ApcMin/+ mouse model of intestinal cancer

We investigated the possible mechanisms of inhibition of colorectal carcinogenesis by green tea (GT) in azoxymethane‐treated (AOM) Apc^Min/+ mice. Mice received water or a 0.6% (w/v) solution of GT as the only source of beverage. GT treatment commenced at the 8th week of age and lasted for 8 wk. The treatment caused a statistically significant reduction in the number of newly formed tumors (28%, P < 0.05). Immunohistochemical analysis showed that GT decreased the levels of β‐catenin and its downstream target cyclin D1. To probe a mechanism, we further investigated the expression of retinoic X receptor alpha (RXRα) in AOM/Apc^Min/+ tumors. Our results show that RXRα is selectively downregulated in AOM/Apc^Min/+ mouse intestinal tumors. In contrast, other retinoic receptors including retinoic acid receptor alpha (RARα), RARβ, RXRβ, and RXRγ were all expressed in Apc^Min/+ adenomas. Furthermore, our results show that RXRα downregulation is an early event in colorectal carcinogenesis and is independent of β‐catenin expression. GT significantly increased the protein levels of RXRα. In addition, RT‐PCR analysis showed that GT induced a similar increase in the levels of RXRα mRNA. Genomic bisulfite treatment of colonic DNA followed by pyrosequencing of 24 CpG sites in the promoter region of RXRα gene showed a significant decrease in CpG methylation with GT treatment. The results suggest that a low concentration of GT is sufficient to desilence RXRα and inhibit intestinal tumorigenesis in the Apc^Min/+ mouse. Mol. Carcinog. © 2009 Wiley‐Liss, Inc.