Abstract LB197: Methylation patterns at adjacent CpG sites within enhancers are part of cell identity and are disrupted during malignant transformation
Authors: Taryma-Leśniak Olga , Bińkowski Jan , Przybylowicz Patrycja K. , Sokolowska Katarzyna E. , Borowski Konrad , Wojdacz Tomasz K. 
Published: April 2024

Abstract
Background: Following the principles of physiology of DNA methylation, it is generally accepted that methylation status of CpG sites spaced up to 50 bp is correlated and accumulation of locally disordered methylation at CpG sites is a part of neoplastic transformation, acting in similar way as stochastic accumulation of mutations during malignant transformation.
Methods: We developed a new algorithm allowing to analyze methylation status at the adjacent CpG sites. We then, used EPIC microarray data to analyze genome wide methylation patterns at the adjacent CpG sites in almost 600 samples, representing 12 healthy tissues and cell types as well as 572 cancer specimens. We also used bisulfite next generation sequencing data and Sanger sequencing to validate our findings.
Results: Our analysis, identified in human genome a subset of loci with adjacent CpG sites spaced less than 50bp (average 28bp), harboring one cytosine methylated and the other devoid of methyl group. These loci are enriched in enhancers that are targeted by families of transcription factors involved in cell differentiation. The methylation patterns at these loci can differ between alleles within a cell, what allows for remarkable level of heterogeneity of methylation patterns. However, our analysis also showed that, different types of specialized cells, acquire during differentiation only one specific and remarkably stable pattern of methylation at each of these loci and that pattern is to a large extent lost during neoplastic transformation.
Conclusions: Contrary to generally accepted principle of identical methylation status of the adjacent CpG sites being essential for regulatory function of DNA methylation. We have shown that methylation at a subset of adjacent CpG sites in human genome located within important functional genomic elements differs in healthy cells. These CpG sites acquire remarkably stable and tissue specific patterns of methylation during cell differentiation. Moreover, the methylation patterns at these CpG sites, are lost during malignant transformation suggesting the involvement of identified phenomenon in cancer pathology.
Funding: This work was funded by grant OPUS22 from Polish National Science Centre (grant number: 2021/43/B/NZ2/02979) and Polish National Agency for Academic Exchange (grant number: PPN/PPO/2018/1/00088/U).
Citation Format: Olga Taryma-Leśniak, Jan Bińkowski, Patrycja K. Przybylowicz, Katarzyna E. Sokolowska, Konrad Borowski, Tomasz K. Wojdacz. Methylation patterns at adjacent CpG sites within enhancers are part of cell identity and are disrupted during malignant transformation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB197.