Significance of epithelial-mesenchymal transition in colorectal cancerogenesis

ABSTRACT: The development of colorectal carcinoma (CRC) is divided in several stages, from normal mucosa to adenoma and invasive carcinoma. In routine diagnostic work, the correct diagnosis of colorectal adenoma, adenoma with epithelial misplacement and CRC is of utmost importance, enabling to choose the optimal treatment. Endoscopic removal is the treatment of choice for adenomas and adenomas with epithelial misplacement, since these lesions do not metastasize and additional surgical treatment is not necessary. In contrast, CRC including early stages (malignant adenomas) are capable to metastasize. It is important to make the correct diagnosis and to evaluate the risk for metastases and additionally treat these patients with surgical removal of the colon if needed. Despite meticulous microscopic investigation of histological slides, it is not always possible to distinguish between various lesions. Epithelial-mesenchymal transition (EMT) has emerged as a possible mechanism in the development of CRC, but the information on EMT particularly in early stages of CRC development is missing. Previous studies have demonstrated some micro RNAs (e.g., miR141, miR-200a/b/c and miR-429) to be good markers of EMT. Our study included formalin-fixed paraffin-embedded biopsy samples of 62 patients (10 adenomas and 30 cases of CRC with corresponding normal mucosa, 10 malignant adenomas, and 12 adenomas with pseudoinvasion). Expression of miR-141, miR-200a/b/c and miR-429 and their target genes (CDKN1B, ONECUT2, PTPN13, RND3, SOX2, TGFB2 and ZEB2) was analysed using quantitative real-time PCR. Expression of E-cadherin was analysed using immunohistochemistry. All miRNAs were down-regulated and their target genes showed the opposite expression in CRC compared to adenoma. Down-regulation of the miR-200 family at the invasive front in comparison to the central part of tumour was observed as well as a correlation of expression of the miR200b, CDKN1B, ONECUT2 and ZEB2 to nodal metastases. Expression of the miR200 family and SOX2 also correlated with E-cadherin staining. In addition, down-regulation of the miR-200 family and PTPN13 and upregulation of CDKN1B in early carcinoma compared to adenomas and adenomas with epithelial misplacement was observed. These results suggest that the miR-200 family and their target genes contribute to progression of adenoma to CRC, invasive properties and development of metastases. Our results strongly support the postulated hypotheses of partial EMT and intra-tumour heterogeneity during CRC cancerogenesis