en Genetics & Disease Genetics & Disease Original Article Original Article <div style="text-align: justify;">Inorganic arsenicals are worldwide environmental contaminants that affect molecular characteristics in biological systems and lead to genomic and epigenomic instability as well as epithelial mesenchymal transition (EMT). In this study, we aimed to investigate whether low levels of sodium arsenite (iAsIII) can influence EMT and genomic instability through microsatellite analysis. We have also determined epigenomic instability by investigating the methylation status of <em>SEPT9 </em>tumor marker in colorectal cancer (CRC) cell lines, Caco2 and HCT116, which were treated with iAsIII to assess IC50s. Short-term and long-term exposure to low concentrations (1 &micro;M and 0.1 &micro;M) of iAsIII in two separate experiments was implemented to analyze EMT, microsatellite status and the methylation pattern of <em>SEPT9</em> promoter. As expected, after 20 days of exposure to iAsIII, the expression of <em>CDH1 </em>was significantly decreased while the expression of <em>CDH2</em>, <em>FIB1</em> and <em>VIM </em>was increased in Caco2 and HCT116, a finding that confirmed EMT induction. However, there was no detectable alteration in the size of microsatellites. As for the methylation pattern, <em>SEPT9</em> promoter was hypomethylated as a result of long-term exposure to 0.1 &micro;M iAsIII in Caco2. Long-term exposure of HCT116 to both concentrations could induce hypomethylation of <em>SEPT9</em> promoter. Our findings indicate no linkage between EMT induction and microsatellite status in iAsIII-treated CRC cell lines. For the first time, the current study has shown that the induction of EMT by iAsIII is linked with <em>SEPT9</em> promoter hypomethylation in Caco2 and HCT116 in a concentration- and time-dependent pattern.</div> Arsenic, colorectal cancer, eEpithelial-mMesenchymal transition, microsatellite instability, SEPT9, methylation 130 140 http://ijmcmed.org/browse.php?a_code=A-10-1923-1&slc_lang=en&sid=1 Gholamreza Rafiei shahgen@gmail.com 100319475328460015589 100319475328460015589 No Department of Medical Genetics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Reza Shirkoohi rshirkoohi@tums.ac.ir 100319475328460015590 100319475328460015590 No Cancer Biology Research Center, Cancer Institute of Iran, Tehran University of Medical Sciences, Tehran, Iran. Mojtaba Saffari saffari_mojtaba@yahoo.com 100319475328460015591 100319475328460015591 No Department of Medical Genetics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Pouya Salehipour p-salehipour@razi.tums.ac.ir 100319475328460015592 100319475328460015592 No Department of Medical Genetics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Hossein Modarressi modaresi@tums.ac.ir 100319475328460015593 100319475328460015593 Yes Department of Medical Genetics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.