The study may contribute to the understanding of the role of CD133 inactivation in the progression of colorectal cancers. Keywords: CD133, Promoter, Hypermethylation, ceritinib mechanism of action Colorectal cancer, Sodium bisulfite modification INTRODUCTION The cell surface antigen CD133 is a glycoprotein of 858-865 amino acids with a total molecular weight of 97-120 kDa and five transmembrane domains. Originally identified in neuroepithelial stem cells, CD133 has been detected in hematopoietic stem cells, endothelial progenitor cells, glioblastomas, neuronal and glial stem cells, and some other cell types[1,2]. As it has also been identified in cancer-initiating cells in several solid malignancies, it is regarded as one of the cancer stem cell (CSC) markers in colorectal carcinoma[3,4].

CD133 was the first identified member of a pentaspan membrane protein family in both humans and mice[1]. The glycoprotein specifically localizes in microvilli and protruding plasma membrane[5]. The CSC theory is a newly emerged concept of cancer initiation and development. According to this theory, only a small population of cells is clonogenic and contains tumor initiating potency, whereas the majority of the tumor cells have undergone differentiation and lost this potency. In colorectal cancer, these cells have been reported to express CD133 and a CD133-positive population of colon cancer cells was recently demonstrated to be highly enriched in tumor-initiating colon CSCs that have the ability to self-renew and to recapitulate the bulk tumor population[3,6-9]. The CD133 gene transcriptional regulation is rather complicated and poorly understood.

A possible involvement of five alternative TATA-less promoters has been suggested to explain the pattern of transcripts differing in the lengths and sequences of 5�� untranslated regions (UTRs). Two of these promoters, P1 and P2 (Figure (Figure1A),1A), are active in in vitro tests with a reporter gene. A common transcriptional initiation site was assigned to exons 1A and 1B (Figure (Figure1A),1A), and an mRNA transcribed from exon 1A or 1B was found to be the major transcript, with the choice between the transcription start sites depending on tissues. In particular, colon-expressed transcripts contain both exons 1A and 1B[10-12]. Figure 1 Schemes of Anacetrapib the promoter region of CD133. A: Schemes of the CD133 gene 5�� terminus; B: Distribution of CpG dinucleotides in a fragment of the CD133 gene harboring full P2 (250 bp) promoter and 5��-UTR exon 1B (The citation from Tabu et al[ … Changes in DNA methylation patterns are an important hallmark of tumor development and progression. Methylation of the C5 position of cytosine residues in DNA is one of the most fundamental epigenetic characteristics.