Cellular network perturbations by disease-associated variants

Interactomics of CXXC proteins involved in epigenetic regulation of gene expression

Regulation of gene expression is an extremely complex and multicomponent biological phenomenon. Proteins containing the CXXC-domain “zinc fingers” (CXXC-proteins) are master regulators of expression of many genes and have conserved functions of methylation of DNA bases and histone proteins. CXXC proteins function as a part of multiprotein complexes, which indicates the fundamental importance of studying post-translational regulation through modulation of the protein-protein interaction spectrum (PPI) in both normal and pathological conditions. In this paper we discuss general aspects of the involvement of CXXC proteins and their protein partners in neoplastic processes, both from the literature data and our own studies. Special attention is paid to recent data on the particular interactomics of the CFP1 protein encoded by the CXXC1 gene located on the human chromosome 18. CFP1 is devoid of enzymatic activity and implements epigenetic regulation of expression through binding to chromatin and a certain spectrum of PPIs.

Protective C allele of the single-nucleotide polymorphism rs1335532 is associated with strong binding of Ascl2 transcription factor and elevated CD58 expression in B-cells

CD58 is expressed on the surface of antigen-presenting cells, including B-cells, and provides co-stimulation to regulatory T-cells (Treg) through CD2 receptor binding. Tregs appear to be essential suppressors of tissue-specific autoimmune responses. Thereby, CD58 plays protective role in multiple sclerosis (MS) and CD58 was identified among several loci associated with MS susceptibility. Minor (C) variant of the single-nucleotide polymorphism (SNP) rs1335532 is associated with lower MS risk according to genome-wide association studies (GWAS) and its presence correlates with higher CD58 mRNA levels in MS patients. We found that genomic region containing rs1335532 has enhancer properties and can significantly boost the CD58 promoter activity in lymphoblast cells. Using bioinformatics and pull-down assay we found that the protective (C) rs1335532 allele created functional binding site for ASCL2 transcription factor, a target of the Wnt signaling pathway. Both in B-lymphoblastoid cell lines and in primary B-cells, as well as in a monocytic cell line, activation of Wnt signaling resulted in an increased CD58 promoter activity in the presence of the protective but not the risk allele of rs1335532, whereas ASCL2 knockdown abrogated this effect. In summary, our results suggest that ASCL2 mediates the protective function of rs1335532 minor (C) allele in MS.

Identification of Single Nucleotide Non-coding Driver Mutations in Cancer

Recent whole-genome sequencing studies have identified millions of somatic variants present in tumor samples. Most of these variants reside in non-coding regions of the genome potentially affecting transcriptional and post-transcriptional gene regulation. Although a few hallmark examples of driver mutations in non-coding regions have been reported, the functional role of the vast majority of somatic non-coding variants remains to be determined. This is because the few driver variants in each sample must be distinguished from the thousands of passenger variants and because the logic of regulatory element function has not yet been fully elucidated. Thus, variants prioritized based on mutational burden and location within regulatory elements need to be validated experimentally. This is generally achieved by combining assays that measure physical binding, such as chromatin immunoprecipitation, with those that determine regulatory activity, such as luciferase reporter assays. Here, we present an overview of in silico approaches used to prioritize somatic non-coding variants and the experimental methods used for functional validation and characterization.