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PubMed2025

Chromatin remodeling activity of EP400 safeguards chromosomal stability by preventing CENP-A mislocalization.

The mislocalization of CENP-A to non-centromeric regions contributes to chromosomal instability (CIN). The NuA4 histone acetyltransferase complex members EP400 and KAT5 regulate histone H2A.Z-H2B exchange and acetylation of histones, respectively. Overexpression of CENP-A and mutations in NuA4 components are observed in cancers. Here, we define a role for the chromatin remodeling activity of EP400, a top hit in RNAi screens for increased nuclear levels of CENP-A, in preventing CENP-A mislocalization and CIN. Mechanistically, we demonstrate a defect in the extraction of CENP-A from chromatin in cells expressing the EP400K1085G mutant, which lacks ATPase activity for histone exchange. Consistent with these results, EP400K1085G cells show increased CENP-A enrichment in chromatin and mislocalization to non-centromeric regions. Importantly, EP400K1085G cells exhibit CIN phenotypes in stable, near-diploid RPE1 cells with wild-type p53. In summary, our findings expand the role of EP400 from nucleosome destabilization for histone exchange to preventing the stable association of CENP-A with non-centromeric regions and CIN.

Humans↗
PubMed2025

Uterine Sarcomas With Recurrent KDM2B Gene Fusions: Three Cases of a Possible Novel Subtype of High-Grade Endometrial Stromal Sarcoma.

The advent of widespread genomic testing of uterine mesenchymal tumors has led to novel insights into the biology of these diverse tumors, and many genomically defined entities have been described in recent years. During a larger study of endometrial stromal sarcomas and unclassified uterine sarcomas, we identified 3 tumors harboring KDM2B gene fusions. Patients were 32, 61, and 67 years old, and all initially underwent incomplete sampling via laparoscopic myomectomy (n = 1), laparoscopic biopsy (n = 1), or hysteroscopic myomectomy (n = 1). One patient's tumor was densely adherent to the pelvic sidewall; she was treated with chemotherapy and died of widely metastatic disease at 29 weeks. Another underwent a subsequent recent hysterectomy with the tumor confined to the uterus and minimal follow-up to date. The final patient refused further treatment and was alive at 28 weeks, although the status of the disease progression was unknown. On microscopic examination, 2 tumors showed infiltrative borders, whereas interface with the myometrium was not present in the third. The tumors were variably cellular with alternating hypercellular and hypocellular zones in a myxoid to loosely collagenous stroma. The hypercellular areas contained round to ovoid cells in diffuse (n = 3) and sex cord-like arrangements, including cords (n = 3), nests (n = 2), and tubules (n = 1); 2 also contained occasional spindled cells arranged in vague fascicles. These cells showed moderate atypia with open chromatin, numerous mitoses (8, 24, and 25 per 10 high-power fields), and frequent apoptosis. The hypocellular areas contained sparse, ovoid-to-spindled cells with minimal atypia. All tumors were diffusely positive for cyclin D1, whereas BCL6 corepressor was diffusely positive in 1 and negative in 2; desmin and caldesmon were negative in all 3 neoplasms. All harbored KDM2B gene fusions; partner genes included EPC1, EP400, and CITED1. MDM2 amplification was also noted in 2. Clustering analysis based on RNA expression profiling revealed tight clustering of all 3 tumors within the broad group of high-grade endometrial stromal sarcomas. Based on the overall clinicopathologic and genomic features, we suggest that these tumors may represent a novel subtype of uterine sarcoma and may be best classified as high-grade endometrial stromal sarcoma, although additional confirmatory studies are needed.

Humans↗
PubMed2025

Functions of TIP60/NuA4 Complex Subunits in Cell Differentiation.

The TIP60/NuA4 complex is a large, multifunctional histone acetyltransferase assembly of ~1.7 megadaltons, composed of 17-20 subunits, which plays a central role in epigenetic regulation. Through recognition of H3K4me3 by the ING3 reader, TIP60/NuA4 is recruited to sites of active transcription, where it remodels chromatin to regulate gene expression. Its activities include histone acetylation, histone variant exchange, transcriptional co-activation, and regulation of the cell cycle and apoptosis. In this review, we examine how altered subunit levels or mutations impact the chromatin structure and transcriptional activity, and how these changes influence differentiation across diverse cell types. We emphasize the molecular mechanisms by which TIP60/NuA4 shapes lineage specification, including histone H2A and H4 acetylation by the KAT5 catalytic subunit, H2A.Z incorporation by EP400, and interactions with transcription factors such as MyoD, PPARγ, and Myc. By integrating mechanistic and functional insights, we highlight how TIP60/NuA4 acts as a central epigenetic hub in differentiation and contributes to proper developmental transitions.

Humans↗