The MOZ-BRPF1 acetyltransferase complex in epigenetic crosstalk linked to gene regulation, development, and human diseases

The Phenotypic and Genotypic Spectrum of BRPF1-Related Disorder: 29 New Patients and Literature Review

Intellectual Developmental Disorder with Dysmorphic Facies and Ptosis (IDDDFP) is a rare autosomal dominant syndrome caused by pathogenic variants in the BRPF1 gene, which is critical for chromatin regulation. This study expands the clinical and molecular spectrum of IDDDFP by analysing 29 new patients from 20 families with confirmed BRPF1 variants. Our cohort presented with a wide range of clinical features including developmental delay, intellectual disability (ID) and characteristic dysmorphic facial features such as ptosis, blepharophimosis and a broad nasal bridge. New phenotypic features identified include palpebral oedema, laterally elongated eyebrows, low hanging columella and hypertrichosis. Neuropsychological assessment reveals a predominance of mild to moderate ID, with cognitive profiles showing variability in verbal and visual processing. Structural abnormalities such as agenesis of the corpus callosum and ocular defects were noted, consistent with previous studies but with some differences. Familial analysis revealed variability in clinical expression. Our findings highlight the diverse clinical manifestations of BRPF1-related disorders and suggest that comprehensive ophthalmological evaluation is essential for the management of these patients.

BRPF1 inhibition reduces migration and invasion of metastatic ovarian cancer cells, representing a potential therapeutic target

Ovarian Cancer (OC) is the most lethal gynecological malignancy, characterized by peritoneal metastasis, directly linked to most OC-related deaths. Here, by interrogating CRISPR-Cas9 loss-of-function genetic screen data, we identified a list of genes essential for metastatic OC, including several well-known oncogenes (PAX8, CCNE1, WWTR1, WT1, KAT6A, MECOM, and SOX17) and others whose roles in OC have not yet been explored. Protein-protein interaction analysis of the selected genes revealed the presence of a protein network participating in the epigenetic regulation of gene expression. For one of the network components, BRPF1, we found that its increased expression correlates with OC progression and a poor prognosis for OC patients. Functional assays demonstrated that BRPF1 inhibition significantly reduces cellular migration and invasion, supporting its role in metastatic progression. Pharmacological blockade of BRPF1 using small molecule inhibitors resulted in reduced proliferation of high-grade serous OC cells through mechanisms involving the activation of programmed cell death, cell cycle deregulation, and enhanced DNA damage. Furthermore, analysis of transcriptional changes induced by BRPF1 targeting showed that the growth inhibitory effects may be mediated by the deregulation of PPARα signaling. The obtained results indicate that BRPF1 represents a novel potential therapeutic target for metastatic OC treatment.

KAT6B overexpression rescues embryonic lethality in homozygous null KAT6A mice restoring vitality and normal lifespan

Closely related genes typically display common essential functions but also functional diversification, ensuring retention of both genes throughout evolution. The histone lysine acetyltransferases KAT6A (MOZ) and KAT6B (QKF/MORF), sharing identical protein domain structure, are mutually exclusive catalytic subunits of a multiprotein complex. Mutations in either KAT6A or KAT6B result in congenital intellectual disability disorders in human patients. In mice, loss of function of either gene results in distinct, severe phenotypic consequences. Here we show that, surprisingly, 4-fold overexpression of Kat6b rescues all previously described developmental defects in Kat6a mutant mice, including rescuing the absence of hematopoietic stem cells. Kat6b restores acetylation at histone H3 lysines 9 and 23 and reverses critical gene expression anomalies in Kat6a mutant mice. Our data suggest that the target gene specificity of KAT6A can be substituted by the related paralogue KAT6B, despite differences in amino acid sequence, if KAT6B is expressed at sufficiently high levels.

Targeting lysine acetylation readers and writers

Lysine acetylation is a major post-translational modification in histones and other proteins that is catalysed by the 'writer' lysine acetyltransferases (KATs) and mediates interactions with bromodomains (BrDs) and other 'reader' proteins. KATs and BrDs play key roles in regulating gene expression, cell growth, chromatin structure, and epigenetics and are often dysregulated in disease states, including cancer. There have been accelerating efforts to identify potent and selective small molecules that can target individual KATs and BrDs with the goal of developing new therapeutics, and some of these agents are in clinical trials. Here, we summarize the different families of KATs and BrDs, discuss their functions and structures, and highlight key advances in the design and development of chemical agents that show promise in blocking the action of these chromatin proteins for disease treatment.

HBO1, a MYSTerious KAT and its links to cancer

The histone acetyltransferase HBO1, also known as KAT7, is a major chromatin modifying enzyme responsible for H3 and H4 acetylation. It is found within two distinct tetrameric complexes, the JADE subunit-containing complex and BRPF subunit-containing complex. The HBO1-JADE complex acetylates lysine 5, 8 and 12 of histone H4, and the HBO1-BRPF complex acetylates lysine 14 of histone H3. HBO1 regulates gene transcription, DNA replication, DNA damage repair, and centromere function. It is involved in diverse signaling pathways and plays crucial roles in development and stem cell biology. Recent work has established a strong relationship of HBO1 with the histone methyltransferase MLL/KMT2A in acute myeloid leukemia. Here, we discuss functional and pathological links of HBO1 to cancer, highlighting the underlying mechanisms that may pave the way to the development of novel anti-cancer therapies.

Essential gene screening identifies the bromodomain-containing protein BRPF1 as a new actionable target for endocrine therapy-resistant breast cancers

Identifying master epigenetic factors controlling proliferation and survival of cancer cells allows to discover new molecular targets exploitable to overcome resistance to current pharmacological regimens. In breast cancer (BC), resistance to endocrine therapy (ET) arises from aberrant Estrogen Receptor alpha (ERα) signaling caused by genetic and epigenetic events still mainly unknown. Targeting key upstream components of the ERα pathway provides a way to interfere with estrogen signaling in cancer cells independently from any other downstream event. By combining computational analysis of genome-wide 'drop-out' screenings with siRNA-mediated gene knock-down (kd), we identified a set of essential genes in luminal-like, ERα + BC that includes BRPF1, encoding a bromodomain-containing protein belonging to a family of epigenetic readers that act as chromatin remodelers to control gene transcription. To gather mechanistic insights into the role of BRPF1 in BC and ERα signaling, we applied chromatin and transcriptome profiling, gene ablation and targeted pharmacological inhibition coupled to cellular and functional assays. Results indicate that BRPF1 associates with ERα onto BC cell chromatin and its blockade inhibits cell cycle progression, reduces cell proliferation and mediates transcriptome changes through the modulation of chromatin accessibility. This effect is elicited by a widespread inhibition of estrogen signaling, consequent to ERα gene silencing, in antiestrogen (AE) -sensitive and -resistant BC cells and pre-clinical patient-derived models (PDOs). Characterization of the functional interplay of BRPF1 with ERα reveals a new regulator of estrogen-responsive BC cell survival and suggests that this epigenetic factor is a potential new target for treatment of these tumors.

A MOZ-TIF2 leukemia mouse model displays KAT6-dependent H3K23 propionylation and overexpression of a set of active developmental genes

Aberrant regulation of chromatin modifiers is a common occurrence across many cancer types, and a key priority is to determine how specific alterations of these proteins, often enzymes, can be targeted therapeutically. MOZ, a histone acyltransferase, is recurrently fused to coactivators CBP, p300, and TIF2 in cases of acute myeloid leukemia (AML). Using either pharmacological inhibition or targeted protein degradation in a mouse model for MOZ-TIF2-driven leukemia, we show that KAT6 (MOZ/MORF) enzymatic activity and the MOZ-TIF2 protein are necessary for indefinite proliferation in cell culture. MOZ-TIF2 directly regulates a small subset of genes encoding developmental transcription factors, augmenting their high expression. Furthermore, transcription levels in MOZ-TIF2 cells positively correlate with enrichment of histone H3 propionylation at lysine 23 (H3K23pr), a recently appreciated histone acylation associated with gene activation. Unexpectedly, we also show that MOZ-TIF2 and MLL-AF9 regulate transcription of unique gene sets, and their cellular models exhibit distinct sensitivities to multiple small-molecule inhibitors directed against AML pathways. This is despite the shared genetic pathways of wild-type MOZ and MLL. Overall, our data provide insight into how aberrant regulation of MOZ contributes to leukemogenesis. We anticipate that these experiments will inform future work identifying targeted therapies in the treatment of AML and other diseases involving MOZ-induced transcriptional dysregulation.

The role of histone acetylation in transcriptional regulation and seed development

Histone acetylation is highly conserved across eukaryotes and has been linked to gene activation since its discovery nearly 60 years ago. Over the past decades, histone acetylation has been evidenced to play crucial roles in plant development and response to various environmental cues. Emerging data indicate that histone acetylation is one of the defining features of "open chromatin," while the role of histone acetylation in transcription remains controversial. In this review, we briefly describe the discovery of histone acetylation, the mechanism of histone acetylation regulating transcription in yeast and mammals, and summarize the research progress of plant histone acetylation. Furthermore, we also emphasize the effect of histone acetylation on seed development and its potential use in plant breeding. A comprehensive knowledge of histone acetylation might provide new and more flexible research perspectives to enhance crop yield and stress resistance.