Egan, Laurence J.

Abstract Inflammatory bowel disease is characterized by chronic inflammation which predisposes to colorectal cancer. The mechanisms by which inflammation promotes tumorigenesis are not fully known. We aimed to investigate the links between colonic inflammation and tumorigenesis via epigenetic gene silencing. Colon cancer specimens were assessed for the expression of DNA methyltransferase-1 (DNMT-1) using immunohistochemistry. Colorectal carcinoma cell lines were assessed for DNMT1 expression, methylcytosine content, promoter methylation, gene expression, and tumorigenesis in response to interleukin (IL)-6. DNMT1 was expressed at higher levels in both the peritumoral stroma and tumor in inflammatory bowel disease–associated cancers compared with sporadic colon cancers. IL-6 treatment of colon cancer cells resulted in an increase in DNMT1 expression, independent of de novo gene expression. IL-6 increased the methylation of promoter regions of genes associated with tumor suppression, adhesion, and apoptosis resistance. Expression of a subset of these genes was downregulated by IL-6, an effect that was prevented by preincubation with 5-azadeoxycytidine, a DNMT1 inhibitor. Anchorage-independent growth and migration of colon cancer cells was also increased by IL-6 in a 5-azadeoxycytidine–sensitive manner. Our results indicate that DNMT-mediated gene silencing may play a role in inflammation-associated colon tumorigenesis. Mol Cancer Res; 8(4); 471–81. ©2010 AACR.

Endothelial cell-based angiogenesis requires activation of survival signals that generate resistance to external apoptotic stimuli, such as tumor necrosis factor-alpha (TNF-α), during pathobiologic settings. Mechanisms by which this is achieved are not fully defined. Here, we use a model in which the multifunctional cytokine nitric oxide counterbalances TNF-α-induced apoptosis, to define a role for membrane trafficking in the process of endothelial cell survival signaling. By perturbing dynamin GTPase function, we identify a key role of dynamin for ensuing downstream endothelial cell survival signals and vascular tube formation. Furthermore, nitric oxide is directly demonstrated to promote dynamin function through specific cysteine residue nitrosylation, which promotes endocytosis and endothelial cell survival signaling. Thus, these studies identify a novel role for dynamin as a survival factor in endothelial cells, through a mechanism by which dynamin S-nitrosylation regulates the counterbalances of TNF-α-induced apoptosis and nitric oxide-dependent survival signals, with implications highly relevant to angiogenesis.

Acute injury to the intestinal mucosa is a major dose-limiting complication of abdominal radiation therapy. We studied the role of the transcription factor NF-κB in protection against radiation-induced apoptosis in the intestinal epithelium in vivo . We use mice in which NF-κB signaling through IκB-kinase (IKK)-β is selectively ablated in intestinal epithelial cells to show that failure to activate epithelial cell NF-κB in vivo results in a significant increase in radiation-induced epithelial cell apoptosis. Furthermore, bacterial lipopolysaccharide, which is normally a radioprotective agent, is radiosensitizing in IKKβ-deficient intestinal epithelial cells. Increased apoptosis in IKKβ-deficient intestinal epithelial cells was accompanied by increased expression and activation of the tumor suppressor p53 and decreased expression of antiapoptotic Bcl-2 family proteins. These results demonstrate the physiological importance of the NF-κB system in protection against radiation-induced death in the intestinal epithelium in vivo and identify IKKβ as a key molecular target for radioprotection in the intestine. Selective preactivation of NF-κB through IKKβ in intestinal epithelial cells could provide a therapeutic modality that allows higher doses of radiation to be tolerated during cancer radiotherapy.