Chromatin is an arrangement of DNA and proteins which form chromosomes. Chromatin is formed from nucleosomes, which are comprised of a set of four histone proteins (H2A, H2B, H3, H4) wrapped with DNA. Chromatin is very dynamic, where post-translational modifications can regulate DNA to be copied, transcribed, or repaired.
Histones are nuclear proteins responsible for the nucleosome structure of the chromosomal fiber in eukaryotes. Changes in chromatin structure play a large role in the regulation of transcription. The chromatin fibers are compacted through the interaction of a linker histone, H1, with the DNA between the nucleosomes to form higher order chromatin structures.
Common histone modifications include methylation of lysine and arginine, acetylation of lysine, phosphorylation of threonine and serine, and sumoylation, biotinylation, and ubiquitylation of lysine. Posttranslational modifications such as acetylation of core histones regulates gene expression, thus altering protein function and regulation (1). Histone H3 is primarily acetylated at lysines 9, 14, 18, and 23 and have a theoretical molecular weight of 15 kDa. Acetylation at lysine 9 and 14 appears to control histone deposition, chromatin assembly and active transcription. Methylation of arginine residues within histone H3 has also been linked to transcription regulation. Histone H3 has been linked to various types of cancer as a biomarker through the aberrant expression of histone deacetylase (HDAC) enzymes and changes to chromatins (2-4).
1. Zhang, Y. X., Akumuo, R. C., Espana, R. A., Yan, C. X., Gao, W. J., & Li, Y. C. (2018). The histone demethylase KDM6B in the medial prefrontal cortex epigenetically regulates cocaine reward memory. Neuropharmacology, 141, 113-125. doi:10.1016/j.neuropharm.2018.08.030
2. Nandakumar, V., Hansen, N., Glenn, H. L., Han, J. H., Helland, S., Hernandez, K,...Meldrum, D. R. (2016). Vorinostat differentially alters 3D nuclear structure of cancer and non-cancerous esophageal cells. Sci Rep, 6, 30593. doi:10.1038/srep30593
3. Zhou, M., Li, Y., Lin, S., Chen, Y., Qian, Y., Zhao, Z., & Fan, H. (2019). H3K9me3, H3K36me3, and H4K20me3 Expression Correlates with Patient Outcome in Esophageal Squamous Cell Carcinoma as Epigenetic Markers. Dig Dis Sci, 64(8), 2147-2157. doi:10.1007/s10620-019-05529-2
4. Li, Y., Guo, D., Sun, R., Chen, P., Qian, Q., & Fan, H. (2019). Methylation Patterns of Lys9 and Lys27 on Histone H3 Correlate with Patient Outcome in Gastric Cancer. Dig Dis Sci, 64(2), 439-446. doi:10.1007/s10620-018-5341-8