Cbx5, also known as chromobox homolog 5 or HP1α, is a transcriptional repressor that plays a crucial role in maintaining chromatin state. It is involved in multiple biological processes such as chromatin packing, epigenetic gene regulation, and is associated with pathways like histone 3 lysine 9 methylation (H3K9me) [4,6]. Cbx5 is important for normal cellular function and its dysregulation is linked to various diseases, making genetic models valuable for its study.

In myeloid leukemia, the RNA binding proteins RBMX and RBMXL1 directly bind to mRNAs, affect transcription of multiple loci including Cbx5, and control its nascent transcription. Forced Cbx5 expression can rescue the effects of RBMX/L1 depletion on cell growth and apoptosis, suggesting Cbx5 as a potential therapeutic target in myeloid malignancies [1]. In lung cancer, loss of Cbx5 drives EGFR inhibitor resistance. Cbx5 loss leads to increased E2F1 expression, which upregulates the anti-apoptotic gene BIRC5, attenuating apoptosis induction following EGFRi treatment [2]. In periodontitis, Porphyromonas gingivalis OMVs-derived msRNA sRNA45033 targets Cbx5, and Cbx5 regulates apoptosis through the methylation of p53 DNA [3]. In lung fibrosis, Cbx5, along with histone methyltransferase G9a, is essential for fibroblast activation through epigenetic repression of PPARGC1A. Inhibition of the Cbx5/G9a pathway reduces collagen accumulation in the lungs [4]. Loss of mesenchymal Cbx5 attenuates fibrosis development in idiopathic pulmonary fibrosis (IPF), accompanied by changes in pathogenic fibroblast and metabolic genes. Silencing Cbx5 in IPF fibroblasts inhibits glycolysis and enhances mitochondrial metabolism [5]. In glioma, LINC02381 can interact with CEBPβ to transcriptionally enhance Cbx5, promoting cell proliferation and hindering apoptosis [7].

In conclusion, Cbx5 is a key epigenetic regulator involved in chromatin-related functions. Model-based research, especially through gene knockout (KO) or conditional knockout (CKO) mouse models, has revealed its role in diseases such as myeloid malignancies, lung cancer, periodontitis, and lung fibrosis. Understanding Cbx5's functions provides potential therapeutic opportunities for these disease areas.

References:

1. Prieto, Camila, Nguyen, Diu T T, Liu, Zhaoqi, Rabadan, Raul, Kharas, Michael G. 2021. Transcriptional control of CBX5 by the RNA binding proteins RBMX and RBMXL1 maintains chromatin state in myeloid leukemia. In Nature cancer, 2, 741-757. doi:10.1038/s43018-021-00220-w. https://pubmed.ncbi.nlm.nih.gov/34458856/

2. Bugide, Suresh, Edwards, Yvonne J K, Gupta, Romi, Green, Michael R, Wajapeyee, Narendra. 2023. CBX5 loss drives EGFR inhibitor resistance and results in therapeutically actionable vulnerabilities in lung cancer. In Proceedings of the National Academy of Sciences of the United States of America, 120, e2218118120. doi:10.1073/pnas.2218118120. https://pubmed.ncbi.nlm.nih.gov/36652476/

3. Fan, Ruyi, Zhou, Yi, Chen, Xu, Wang, Xiaoqian, Xu, Yan. 2023. Porphyromonas gingivalis Outer Membrane Vesicles Promote Apoptosis via msRNA-Regulated DNA Methylation in Periodontitis. In Microbiology spectrum, 11, e0328822. doi:10.1128/spectrum.03288-22. https://pubmed.ncbi.nlm.nih.gov/36629433/

4. Ligresti, Giovanni, Caporarello, Nunzia, Meridew, Jeffrey A, Urrutia, Raul A, Tschumperlin, Daniel J. 2019. CBX5/G9a/H3K9me-mediated gene repression is essential to fibroblast activation during lung fibrosis. In JCI insight, 5, . doi:10.1172/jci.insight.127111. https://pubmed.ncbi.nlm.nih.gov/31095524/

5. Hong, Jeongmin, Pham, Tho X, Lee, Jisu, Huang, Steven K, Ligresti, Giovanni. 2024. Targeting the Epigenetic Regulator CBX5 Promotes Fibroblast Metabolic Reprogramming and Inhibits Lung Fibrosis. In American journal of respiratory cell and molecular biology, , . doi:10.1165/rcmb.2024-0255OC. https://pubmed.ncbi.nlm.nih.gov/39642371/

6. van Wijnen, Andre J, Bagheri, Leila, Badreldin, Amr A, Paradise, Christopher R, Wu, Zhong. 2020. Biological functions of chromobox (CBX) proteins in stem cell self-renewal, lineage-commitment, cancer and development. In Bone, 143, 115659. doi:10.1016/j.bone.2020.115659. https://pubmed.ncbi.nlm.nih.gov/32979540/

7. Sun, Yong, Wang, Xinjun, Bu, Xingyao. 2021. LINC02381 contributes to cell proliferation and hinders cell apoptosis in glioma by transcriptionally enhancing CBX5. In Brain research bulletin, 176, 121-129. doi:10.1016/j.brainresbull.2021.07.009. https://pubmed.ncbi.nlm.nih.gov/34274429/