Histone post-translational modifications (PTMs) play an important role in the regulation of the expression of genes, including those involved in cancer development and progression. However, our knowledge of PTM patterns in human tumours is limited.

Epithelial tissues achieve a highly organized structure due to cell‑cell junction complexes. Carcinogenesis is accompanied by changes in cell interactions and tissue morphology, which appear in the early stages of benign tumors and progress along with invasive potential. The aim of the present study was to analyze the changes in expression levels of genes encoding intercellular junction proteins that have been previously identified to be differentially expressed in colorectal tumors compared with normal mucosa samples (fold change, >2.5) in genome‑wide expression profiling. The expression of 20 selected genes was assessed using quantitative reverse transcription polymerase chain reaction in 26 colorectal cancer, 42 adenoma and 24 normal mucosa samples. Between these tissue types, differences were observed in the mRNA levels of genes encoding adherens junction proteins (upregulation of CDH3 and CDH11, and downregulation of CDH19 and PTPRF), tight junction proteins (upregulation of CLDN1 and CLDN2, and downregulation of CLDN5, CLDN8, CLDN23, CLDN15, JAM2 and CGN) and desmosomes (upregulation of DSC3 and DSG3, and downregulation of DSC2), in addition to a decrease in the expression of certain other genes involved in intercellular connections: PCDHB14, PCDH7, MUPCDH and NEO1. The differences between tissue types were statistically significant, and separate clustering of normal adenoma and carcinoma samples was observed in a hierarchical clustering analysis. These results indicate that the morphological changes in neoplastic colon tissue that occur during the ‘adenoma‑carcinoma sequence’ are accompanied by specific changes in the expression of multiple genes encoding the majority of cell‑cell junction complexes. The particular differential expression patterns appear to be consistent among patients with cancer and adenoma, in addition to normal mucosa samples.

Objective: Pituitary corticotroph adenomas commonly cause Cushing’s disease (CD) but part of these tumours are hormonally inactive (silent corticotroph adenomas, SCA). USP8 mutations are well-known driver mutations in corticotrophinomas. Differences in transcriptomic profiles between functioning and silent tumours or tumours with different USP8 status have not been investigated. Design and methods: Forty-eight patients (28 CD, 20 SCA) were screened for USP8 mutations with Sanger sequencing. Twenty-four patients were included in transcriptomic profiling with Ampliseq Transcriptome Human Gene Expression Core Panel. The entire patients group was included in qRT-PCR analysis of selected genes expression. Immunohistochemistry was used for visualization of selected protein. Results: We found USP8 mutation in 15 patients with CD and 4 SCAs. USP8 mutations determine molecular profile of the tumours as showed by hierarchical clustering and identification of 1648 genes differentially expressed in USP8-mutated and USP8-wild-type tumours. Mutations affect many molecular pathways as observed in Gene Set Enrichment analysis. USP8-mutated adenomas showed higher level of POMC, CDC25A, MAPK4 but lower level of CCND2, CDK6, CDKN1B than USP8-wt tumours. Eighty-seven genes differentially expressed between CD-related adenomas and SCAs were found, including those involved in cell signalling (GLI2, DLC1, TBX2, RASSF6), cell adhesion (GJA1, CDH6), ion transport (KCNN4, KCNJ5) and GABA signalling (GABBR2, GABRD). Conclusion: USP8 mutations occur in functioning and silent corticotrophinomas. They have pleiotropic effect, not limited to EGFR signalling, and affect expression levels of many genes involved in different pathways. Expression of GABA-related genes GABBR2, GNAL, GABARD and KCNJ5 correspond to functional status of the tumours.

Altered epigenetic mechanisms, similar to gene mutations, contribute to the pathogenesis and molecular heterogeneity of neoplasms, including colorectal cancer (CRC). Enhancer of zeste 2 (EZH2) is a histone methyltransferase, which is involved in epigenetic gene silencing and is aberrantly expressed in CRC. Therefore, the identification of the genes regulated by EZH2 in CRC is important to improve current understanding of its role in cancer epigenetics. The present study used chromatin immunoprecipitation (ChIP) followed by deep sequencing to assess genome-wide EZH2‑DNA interactions in healthy or CRC mucosa samples. In total, 86.9/61.6 and 92.5/62.6 million tags were sequenced/mapped in healthy and CRC mucosa samples, respectively. The EZH2-binding densities were correlated with transcriptomic datasets and this demonstrated that the claudin-23 (CLDN23) gene, which encodes a component of cell-cell adhesion structures, was occupied by EZH2 and significantly silenced in CRC tissue. The measurement of DNA methylation at the CLDN23 promoter using pyrosequencing excluded the possibility that silencing of this gene in CRC patient samples was a result of DNA hypermethylation. Following treatment of the Colo205 and HT-29 CRC cell lines, with the EZH2 inhibitor, GSK126, the level of histone H3 lysine 27 trimethylation (H3K27me3) was reduced and the mRNA and protein expression levels of CLDN23 were increased. ChIP analysis confirmed that the level of H3K27m3 along the CLDN23 gene was decreased in the GSK126-treated cell lines. Furthermore, ChIP analysis of these samples detected histone H3 lysine 4 trimethylation (H3K4me3) at the CLDN23 promoter, demonstrating that the balance between H3K27me3 and H3K4me3 may underlie the regulation of the expression of CLDN23. The present study demonstrated an epigenetic link between the activity of the EZH2 methyltransferase at the CLDN23 locus and the expression of CLDN23 in CRC tissue.