Phosphatidylethanol Accumulation Promotes Intestinal Hyperplasia by Inducing ZONAB-Mediated Cell Density Increase in Response to Chronic Ethanol Exposure

Abstract

Chronic alcohol consumption is associated with increased risk of gastrointestinal cancer. High concentrations of ethanol trigger mucosal hyperregeneration, disrupt cell adhesion, and increase the sensitivity to carcinogens. Most of these effects are thought to be mediated by acetaldehyde, a genotoxic metabolite produced from ethanol by alcohol dehydrogenases. Here, we studied the role of low ethanol concentrations, more likely to mimic those found in the intestine in vivo, and used intestinal cells lacking alcohol dehydrogenase to identify the acetaldehyde-independent biological effects of ethanol. Under these conditions, ethanol did not stimulate the proliferation of nonconfluent cells, but significantly increased maximal cell density. Incorporation of phosphatidylethanol, produced from ethanol by phospholipase D, was instrumental to this effect. Phosphatidylethanol accumulation induced claudin-1 endocytosis and disrupted the claudin-1/ZO-1 association. The resulting nuclear translocation of ZONAB was shown to mediate the cell density increase in ethanol-treated cells. In vivo, incorporation of phosphatidylethanol and nuclear translocation of ZONAB correlated with increased proliferation in the colonic epithelium of ethanol-fed mice and in adenomas of chronic alcoholics. Our results show that phosphatidylethanol accumulation after chronic ethanol exposure disrupts signals that normally restrict proliferation in highly confluent intestinal cells, thus facilitating abnormal intestinal cell proliferation.

Stress- and Rho-activated ZO-1–associated nucleic acid binding protein binding to p21 mRNA mediates stabilization, translation, and cell survival

“…The ZONAB-dependent survival pathway thus provides a possible therapeutic opportunity to target ZONAB to induce cell death in cancer cells. This survival pathway seems up-regulated in different types of carcinomas because ZONAB has been reported to be upregulated in cancers form different tissues (14)(15)(16)(17)(18)(19)(20). Therapeutic targeting of ZONAB might also improve the effectiveness of existing therapies, because depletion enhanced cell death in response to Taxol (Fig.…”

“…ZONAB is activated in different types of cancers (14)(15)(16)(17)(18)(19)(20); hence, it would be important to know whether and how ZONAB promotes cell survival in response to cytotoxic stress and proinflammatory signals because targeting such survival pathways offers therapeutic benefits.…”

A sideways glance. Alcoholic breakdown of barriers: how ethanol can initiate a landslide towards disease

“…Phosphatidylethanol accumulation following chronic ethanol treatment of intestinal Caco-2 cells was shown to produce detachment of ZONAB from the TJ protein ZO-1 and its migration to the nucleus, resulting in transcriptional activation of genes involved in the initiation of cell proliferation. In addition, phosphatidylethanol accumulation and mislocalization of ZO-1 and ZONAB were confirmed both in colonic mucosa of ethanol-fed rats and in human colon adenomas of chronic alcohol-consumers, whereas adenomas from non-drinkers did not exhibit such changes [15]. Therefore, the disruption of ZONAB-mediated physiological signals originating from TJ complexes to stop proliferation of confluent epithelial cells might, in addition, facilitate the stimulatory role of other ethanol metabolites, such as acetaldehyde, on the proliferation of cells within intestinal crypts, thereby contributing to the well established co-carcinogenic role of alcohol consumption in the colon-rectum.…”

“…2). Recently, chronic low-dose ethanol exposure was shown both in vivo and in vitro to be associated with increased production of phosphatidylethanol through the enzymatic activity of phospholipase D (PLD) in intestinal epithelial cells, resulting in changes in the localization of the TJ proteins claudin 1 and ZO-1 and of the ZO-1-associated transcription factor ZONAB, even in the absence of marked changes to TJs permeability [15]. ZONAB is a Y-box transcription factor [22] that shuttles between the TJs (where it binds to the scaffolding protein ZO-1), and the nucleus (where it participates in the regulation of gene expression).…”

“…Low density proliferating epithelial cells in culture were shown to express low levels of ZO-1 and high levels of ZONAB accumulating in the nucleus and in TJs. Conversely, high density post-mitotic cells expressed high levels of ZO-1 that sequestered the low levels of ZONAB at the junction [15]. ZO-1 and ZONAB are involved in the control of cell proliferation by at least two mechanisms: ZONAB interaction with CDK4, a regulator of G1/S phase transition which also co-localizes with ZO-1 at TJs, and direct regulation of cell cycle genes by ZONAB acting as transcription factor [2].…”