MOLECULAR CARCINOGENESIS OCT4 Spliced Variant OCT4B1 is Expressed in Human Colorectal Cancer Maria Gazouli, 1 * Maria G. Roubelakis, 1 George E. Theodoropoulos, 2 Joanna Papailiou, 2 Anna Vaiopoulou, 1 Kalliopi I. Pappa, 1,3 Nikolaos Nikiteas, 4 and Nicholas P. Anagnou 1 1 Laboratory of Biology, Department of Basic Medical Sciences, University of Athens School of Medicine and Cell and Gene Therapy Laboratory, Biomedical Research Foundation of the Academy of Athens, Athens, Greece 2 First Department of Propaedeutic Surgery, University of Athens School of Medicine, Hippocration Hospital, Athens, Greece 3 First Department of Obstetrics and Gynecology, University of Athens School of Medicine, Alexandra University Hospital, Athens, Greece 4 Second Propaedeutic Department of Surgery, Laikon Hospital, University of Athens School of Medicine, Athens, Greece OCT4, a POU-domain transcription factor is considered to be a key factor in maintaining the pluripotency of stem cells. Several OCT4 isoforms are differentially expressed in human pluripotent and non-pluripotent cells. Reactivation of OCT4 expression is postulated to occur in differentiated cells that have undergone tumorigenesis. To examine OCT4 expression in colorectal cancer (CRC) tissues, and to assess the efficacy of OCT4 as a potential biomarker for CRC, in this study, we investigated its expression in CRC tissues, evaluated its relationship to various clinicopathological parameters and defined the isoform of OCT4 that was found to be expressed in CRC cases. Primary tumor tissues and matching adjacent non-cancerous tissues were obtained from 84 CRC patients. OCT4 expression and isoform determi- nation were documented by reverse transcription-PCR and real-time PCR. OCT4, Sox-2, and NANOG localization were performed using immunohistochemistry. The isoforms expressed in the studied cases were confirmed by sequencing. Twenty biopsy specimens representing healthy tissues, retrieved from colonoscopy were studied in parallel as controls. OCT4 expression levels were higher in CRC tissues compared to matching, adjacent non-cancerous tissues, and healthy controls. Additionally, the levels of OCT4 expression in CRC tissues correlated with tumor stage. OCT4 and Sox-2 were localized in the nuclei and the cytoplasm of CRC cells. In all CRC cases, we found that the OCT4B1 isoform is expressed. Over-expression of OCT4B1 was found in poorly and moderately differentiated CRC tissues. In conclusion, the data imply that OCT4B1 isoform may represent a potential biomarker for the initiation, progression, and differentiation of CRC. ß 2011 Wiley-Liss, Inc. Key words: colorectal cancer; stem cells; cancer stem cells; OCT4; Sox-2 BACKGROUND Colorectal cancer (CRC) is a prevalent disease in the Western world. In Europe, there were an esti- mated 412,900 incident cases in 2006 and approxi- mately 207,400 deaths had occurred, constituting 12.2% of all cancer deaths [1]. A similar pattern is recorded for the USA [2]. Accordingly, CRC is rou- tinely listed as the second most common cause of cancer-related death in the developed world, behind lung cancer [1,2]. Consequently, understanding the principles of CRC initiation, progression, and metastasis is of paramount importance if the dis- ease is to be decisively combated and the mortality rate reduced. The long-held view of tumor development described in the stochastic model, is that every cancer cell is equally capable of initiating neoplas- tic growth. This theory is now challenged by the cancer stem cell (CSC) theory, which suggests that only a small proportion of cells within a tumor actually possess cancer-initiating potential and that these so-called CSCs are responsible for tumor development and sustain tumor growth [3,4]. CSCs are proposed to possess stem cell-like properties, including the ability for self-renewal and differen- tiation. Consequently, they can give rise to clo- nally heterogeneous tumors. Yet, by virtue of self- maintenance, their numbers and accordingly their aggressive properties are consistently retained within a tumor, facilitating tumor expansion and spread [4]. OCTamer-binding transcription factor 4 (OCT4), also known as OCT3 or POU5F1, is an embryonic transcription factor expressed in embryonic (ESCs) and adult stem cells, embryonic carcinoma cells (ECs) and oocytes, and belongs to the POU tran- scription factor family [5]. It plays a critical role for maintaining pluripotent and self-renewing state of Additional Supporting Information may be found in the online version of this article. *Correspondence to: Laboratory of Biology, School of Medicine, University of Athens, Michalakopoulou 176, 11527 Athens, Greece. Received 30 August 2010; Revised 11 February 2011; Accepted 1 March 2011 DOI 10.1002/mc.20773 Published online in Wiley Online Library (wileyonlinelibrary.com). ß 2011 WILEY-LISS, INC.