SAT178 EZH2 Upregulation And Lysine 27 Trimethylation at Histone 3 Is Associated With Severe Sporadic Primary Hyperparathyroidism

Abstract Disclosure: P. Kumari: None. A.K. Arya: None. D. Dahiya: None. N. Sachdeva: None. J. Kaur: None. U.N. Saikia: None. S. Bhadada: None. S.D. Rao: None. Introduction: The enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that regulates gene activity through histone modifications of lysine (K) at H3 histone and has a crucial role in tumor development. However, the level of methylation at H3 histone and its association with EZH2 expression in sporadic primary hyperparathyroidism (PHPT) are not known. This study was designed to investigate how global levels of histone methylation were associated with altered expression of EZH2 in promoting parathyroid tumorigenesis. Methodology: A total of 30 parathyroid tumors (15 non-severe, 15 severe, and 5 normal parathyroid tissues) were collected during 2020-2021. The global histone methylation of major methylation sites at lysine (K) K4, K9, K27, K36, and K79 was evaluated from blood and tissue samples using a calorimetric ELISA (H3 global modification kit, Epegentek, USA). Gene and protein expression of EZH2 were performed by quantitative real-time PCR and immunohistochemistry respectively. Histone methylation and expression data were correlated with indices of disease severity. Results: We found that the global levels of H3K27me1 and me3 were significantly upregulated, whereas, H3K4me3 and H3K36me2 were significantly downregulated in tumors from patients with severe PHPT compared to tumors from non-severe PHPT and controls. Moreover, H3K27me3 showed the highest upregulation (8-fold) in severe PHPT. Additionally, EZH2 gene expression was significantly upregulated in severe PHPT [Mean ± S.E; (9.1 ± 1.6 vs. 1.2 ± 0.3, p = 0.005), but not in non-severe (4.2 ± 2.7 vs. 1.2 ± 0.3, p = 0.4) PHPT, compared to normal parathyroid tissues. Furthermore, the protein expression was also consistent with the gene expression, with 86% (n= 13/15) nuclear positivity for EZH2 in tumors from severe PHPT and 40% (6 of 15) in tumors from non-severe PHPT compared to normal parathyroid tissue (negative staining). Correlation analysis revealed that EZH2 gene expression is positively related with S.Ca (r = 0.44, p = 0.003), PTH (r = 0.59, p = 0.000), tumor weight (r = 0.455, p = 0.002), EZH2 protein expression (r = 0.7, p = 0.000), and Ki67 proliferative marker (r = 0.66, p = 0.002). Conclusions: Increased global trimethylation of K27 at histone 3 (H3K27me3) was associated with increased EZH2 expression in sporadic PHPT and was predictive of a more severe clinical phenotype. Sources of research support: (ICMR), New Delhi Extramural Research Grant 2020. Presentation: Saturday, June 17, 2023