Monoamine Oxidase B Predicts Poor Prognosis in Colorectal Cancer Patients, and Its Expression Is Significantly Associated with Epithelial to Mesenchymal Transition

Abstract

Background: Monoamine oxidases (MAOs) are enzymes located on the outer membrane of mitochondria that catalyze monoamine oxidation. Recently, increased expression levels of MAOs have been shown in several cancer types. However, the possible roles of MAOs in the progression and prognosis of colorectal cancer have not yet been elucidated. Methods: We analyzed the role and importance of MAOs in colorectal cancer via an online database analysis and by using tumor tissue microarray. Findings: Several independent colorectal cancer cohorts indicated that high expression of monoamine oxidase B (MAOB) but not of MAOA correlated with worse disease stage and poorer survival. A tissue microarray of 203 cases of colorectal cancer underwent immunohistochemical staining for MAOs and the results were evaluated for the associations with clinicopathological parameters and patient outcomes. High expression of MAOB in primary tumor tissue was observed in 114 samples and was significantly correlated with poor prognosis in colorectal cancer patients (p = 0.002). Moreover, via multivariate analyses, overexpression of MAOB remained an independent prognostic factor for overall survival (p = 0.006) and disease-free survival (p = 0.009). However, the correlation between MAOA expression and these parameters was not significant in colorectal cancer patients. Interpretation: In this study, a significant positive correlation between MAOB and mesenchymal-type gene expression was also found. According to the highlighted characteristics of MAOB in colorectal cancer, MAOB can be used as an independent poor prognostic indicator for colorectal cancer. Funding: This study was supported by the Ministry of Science and Technology, Taiwan, R.O.C. Declaration of Interest: The authors have declared no conflicts of interest. Ethical Approval: The study was carried out with the approval of the Institutional Review Board of WanFang Hospital (Approval No. 99047) and permission from the ethics committees of the institution involved.