Inflammation associated with obesity may play a role in colorectal carcinogenesis, but the underlying mechanism remains unclear. This study investigated whether the Wnt pathway, an intracellular signaling cascade that plays a critical role in colorectal carcinogenesis, is activated by obesity-induced elevation of the inflammatory cytokine tumor necrosis factor-alpha (TNF-α). Animal studies were conducted on C57BL/6 mice, and obesity was induced by utilizing a high-fat diet (60% kcal). An inflammation-specific microarray was performed, and results were confirmed with real-time polymerase chain reaction. The array revealed that diet-induced obesity increased the expression of TNF-α in the colon by 72% (P=.004) and that of interleukin-18 by 41% (P=.023). The concentration of colonic TNF-α protein, determined by ex vivo culture assay, was nearly doubled in the obese animals (P=.002). The phosphorylation of glycogen synthase kinase 3 beta (GSK3β), an important intermediary inhibitor of Wnt signaling and a potential target of TNF-α, was quantitated by immunohistochemistry. The inactivated (phosphorylated) form of GSK3β was elevated in the colonic mucosa of obese mice (P<.02). Moreover, β-catenin, the key effector of canonical Wnt signaling, was elevated in the colons of obese mice (P<.05), as was the expression of a downstream target gene, c-myc (P<.05). These data demonstrate that diet-induced obesity produces an elevation in colonic TNF-α and instigates a number of alterations of key components within the Wnt signaling pathway that are protransformational in nature. Thus, these observations offer evidence for a biologically plausible avenue, the Wnt pathway, by which obesity increases the risk of colorectal cancer.

Objective Variations in the intake of folate are capable of modulating colorectal tumorigenesis; however, the outcome appears to be dependent on timing. This study sought to determine the effect of altering folate (and related B vitamin) availability during in-utero development and the suckling period on intestinal tumorigenesis. Design Female wildtype mice were fed diets either mildly deficient, replete or supplemented with vitamins B2, B6, B12 and folate for 4 weeks before mating to Apc1638N males. Females remained on their diet throughout pregnancy and until weaning. After weaning, all Apc1638N offspring were maintained on replete diets for 29 weeks. Results At 8 months of age tumour incidence was markedly lower among offspring of supplemented mothers (21%) compared with those of replete (59%) and deficient (55%) mothers (p=0.03). Furthermore, tumours in pups born to deficient dams were most likely to be invasive (p=0.03). The expression of Apc, Sfrp1, Wif1 and Wnt5a—all of which are negative regulatory elements of the Wnt signalling cascade—in the normal small intestinal mucosa of pups decreased with decreasing maternal B vitamin intake, and for Sfrp1 this was inversely related to promoter methylation. β-Catenin protein was elevated in offspring of deficient dams. Conclusions These changes indicate a de-repression of the Wnt pathway in pups of deficient dams and form a plausible mechanism by which maternal B vitamin intake modulates tumorigenesis in offspring. These data indicate that maternal B vitamin supplementation suppresses, while deficiency promotes, intestinal tumorigenesis in Apc1638N offspring.

The Wnt pathway is a pivotal signaling cascade in colorectal carcinogenesis. The purpose of this work is to determine whether depletion of folate and other metabolically related B vitamins induces in vivo activation of intestinal Wnt signaling and whether this occurs in parallel with increased tumorigenesis. A hybrid mouse was created by crossing a Wnt-reporter animal (BAT-LacZ) with a model of colorectal cancer (Apc1638N). A mild depletion of folate and vitamins B₂, B₆, and B₁₂ was induced over 16 wk, and the control animals in each instance were pair fed a diet containing the basal requirement of these nutrients. The multiplicity of macroscopic tumors and aberrant crypt foci both increased by ~50% in the hybrid mice fed the depletion diet (P<0.05). A 4-fold elevation in Wnt signaling was produced by the depletion diet (P<0.05) and was accompanied by significant changes in the expression of a number of Wnt-related genes in a pattern consistent with its activation. Proliferation and apoptosis of the colonic mucosa both changed in a protransformational direction (P<0.05). In summary, mild depletion of multiple B vitamins produces in vivo activation of colonic Wnt signaling, implicating it as a key pathway by which B-vitamin inadequacies enhance intestinal tumorigenesis.

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Background: p53 gene therapy has been examined in several clinical trials, however, the results of those trials have mostly been unsatisfactory due to the low efficacy of this therapy. Leptomycin B (LMB) is an antibiotic originally isolated from Streptomyces that has the ability to inhibit the export of proteins containing a nuclear export signal from the nucleus to the cytoplasm. Currently, it has been shown that p53 protein has a nuclear export signal. In this study, we assessed whether LMB augments the transduced p53 gene effect. Methods: Antiproliferative effect of LMB was assessed in human esophageal squamous cancer cell lines. Accumulation of p53 protein into the nucleus by LMB was observed by fluorescence microscopy. The combined effect of p53 and LMB was evaluated in in vitro experiments. Results: LMB induced cell death in a dose-dependent manner and p53 drastically accumulated in the nucleus after LMB treatment. The combinatory treatment of p53 gene and LMB significantly increases the efficiency compared to either agent alone. Conclusions: Our findings suggest that LMB has a potent ability to augment the effect of the tumor suppressor p53 in esophageal squamous cancer cell lines and that it is a promising component in p53 gene therapy.