Some characteristics of cancer-testis gene expression regulation in colorectal cancer.

Abstract

e14233 Background: Cancer-testis antigens (CTA) can be used in immunotherapy and for early detection of cancer. Despite numerous studies of the CTA expression in different tumors, their transcriptional activity and its regulation in colorectal cancer (CRC) remain poorly understood. The purpose of the study was to analyze the expression of cancer-testis genes (CT-genes) and mechanisms of its regulation in CRC. Methods: Tumor and intact tissues of the colon were studied in 60 patients. RNAs were isolated using the method described by Chomczynski and Sacchi (2006). The REVERTA-L reagent kit was used for the cDNA synthesis. Expression of 16 CT-genes (MAGE-A1, -A2, -A3, -A4, MAGE-B1, -B2, GAGE-1, -3, -4, MAGEC1, BAGE, XAGE3, NYESO1, SSX2, SCP1, PRAME1) and expression and copy number of 3 DNA methyltransferase genes (DNMT1, DNMT3A, DNMT3B) were determined by Real-Time qPCR (GAPDH and GUSB - reference genes). For the cluster analysis, we used our R scripts. Differences were assessed by the Mann-Whitney test, and correlations – by the Spearman's rank correlation coefficient (r). Results: The expression of 2 CT genes, SSX2 and PRAME1, was increased (p < 0.05) by 1.8 and 2.9 times, respectively, and the BAGE expression was decreased by 2.4 times in tumor tissues, compared to the normal tissues. The expression and copy number of DNMT3A in tumor tissues was 1.5 and 2 times higher (p < 0.05), and that of DNMT3B – 2 times lower (p < 0.005), compared to normal tissues. The copy number and expression of the DNMT1 gene did not change. A strong positive correlation (r = 0.996) between the expression and copy number of DNA methyltransferase genes was observed. Using cluster analysis (Hierarchical Clustering, Euclidean distance), we detected two clusters of CRC samples different in the expression of CT-genes and methyltransferases. Cluster 1 showed increased expression of DNMT1, DNMT3A and DNMT3B and decreased expression of BAGE, SSX2 and PRAME1; cluster 2 – decreased expression of DNMT1, DNMT3A and DNMT3B and increased expression of BAGE, SSX2 and PRAME1. Conclusions: The detected aberrant expression of the CT-genes BAGE, SSX2, PRAME1 in CRC depends on the expression of DNMT1, DNMT3A, DNMT3B, which in its turn depends on the copy number of the corresponding DNA methyltransferase genes.