Hidden biochemical action of Ethanol on colon carcinoma cell models

Colorectal cancer (CRC) is one of the most widespread cancers in the world. Numerous risk factors have been correlated with the development of CRC, including genetic factors, inflammation, intestinal microflora composition, as well as lifestyle factors, such as smoking, high consumption of red meats and alcohol intake. Epidemiological studies support the conclusion that chronic and heavy alcohol consumption increases the risk to develop CRC as well as favors the progression of this form of cancer. However, the biochemical mechanisms responsible for these events have not yet been fully clarified. The aim of my doctoral project was to study the effects of ethanol in human colorectal carcinoma cells in culture and to evaluate its molecular action mechanism. In particular, my research focused on the identification of one or more molecules involved both in the survival of the tumor cells and, especially, in tumor progression and invasiveness. To this end, I investigated the effect of high doses of ethanol on survival and progression of three different colon cancer cells (HCT116 , HT29 and Caco2 cells). The results demonstrated that ethanol promotes oxidative and ER stress in colon cancer cells as demonstrated by ROS increase and upregulation of ER markers Grp78 and CHOP. Despite the activation of stress, colon cancer cells did not present sign of toxicity because they are able to activate an autophagic survival mechanism. Moreover, in response to oxidative stress, ethanol promoted nuclear translocation of Nrf2 and upregulated the level of the antioxidant enzymes SOD, catalase and heme-oxygenase (HO-1). Silencing Nrf2 in HCT116 cells abrogated the effect of ethanol on upregulation of SOD and HO-1, thereby suggesting that the induction of antioxidant enzymes is dependent on Nrf2 activation. Interestingly, ethanol also promoted HO-1 nuclear translocation. Preventing HO-1 nuclear translocation by addition of E64d, the activation of antioxidant response by Nrf2 was reduced. Finally, the results demonstrated that the activation of Nrf2/HO-1 axis induced by ethanol is also responsible for the induction of MMP-2 and VEGF, two well known factors favoring cellular invasiveness.