Loss of TIP60 (KAT5) abolishes H2AZ lysine 7 acetylation and causes p53, INK4A, and ARF-independent cell cycle arrest

Histone acetyltransferases as promising therapeutic targets in glioblastoma resistance

Glioblastoma (GBM) is a fatal adult brain tumor with an extremely poor prognosis. GBM poses significant challenges for targeted therapies due to its intra- and inter-tumoral heterogeneity, a highly immunosuppressive microenvironment, diffuse infiltration into normal brain parenchyma, protection by the blood-brain barrier and acquisition of therapeutic resistance. Recent studies have implicated epigenetic modifiers as key players driving tumorigenesis, resistance, and progression of GBM. While the vast majority of GBM research on epigenetic modifiers thus far has focused predominantly on elucidating the functional roles and targeting of DNA methyltransferases and histone deacetylases, emerging evidence indicates that histone acetyltransferases (HATs) also play a key role in mediating plasticity and therapeutic resistance in GBM. Here, we will provide an overview of HATs, their dual roles and functions in cancer as both tumor suppressors and oncogenes and focus specifically on their implications in GBM resistance. We also discuss the technical challenges in developing selective HAT inhibitors and highlight their promise as potential anti-cancer therapeutics for treating intractable cancers such as GBM.

Structural insights into the human NuA4/TIP60 acetyltransferase and chromatin remodeling complex

The human nucleosome acetyltransferase of histone H4 (NuA4)/Tat-interactive protein, 60 kilodalton (TIP60) coactivator complex, a fusion of the yeast switch/sucrose nonfermentable related 1 (SWR1) and NuA4 complexes, both incorporates the histone variant H2A.Z into nucleosomes and acetylates histones H4, H2A, and H2A.Z to regulate gene expression and maintain genome stability. Our cryo-electron microscopy studies show that, within the NuA4/TIP60 complex, the E1A binding protein P400 (EP400) subunit serves as a scaffold holding the different functional modules in specific positions, creating a distinct arrangement of the actin-related protein (ARP) module. EP400 interacts with the transformation/transcription domain-associated protein (TRRAP) subunit by using a footprint that overlaps with that of the Spt-Ada-Gcn5 acetyltransferase (SAGA) complex, preventing the formation of a hybrid complex. Loss of the TRRAP subunit leads to mislocalization of NuA4/TIP60, resulting in the redistribution of H2A.Z and its acetylation across the genome, emphasizing the dual functionality of NuA4/TIP60 as a single macromolecular assembly.

Multifunctional histone variants in genome function

Histones are integral components of eukaryotic chromatin that have a pivotal role in the organization and function of the genome. The dynamic regulation of chromatin involves the incorporation of histone variants, which can dramatically alter its structural and functional properties. Contrary to an earlier view that limited individual histone variants to specific genomic functions, new insights have revealed that histone variants exert multifaceted roles involving all aspects of genome function, from governing patterns of gene expression at precise genomic loci to participating in genome replication, repair and maintenance. This conceptual change has led to a new understanding of the intricate interplay between chromatin and DNA-dependent processes and how this connection translates into normal and abnormal cellular functions.

Structures of H2A.Z-associated human chromatin remodelers SRCAP and TIP60 reveal divergent mechanisms of chromatin engagement

H2A.Z is a conserved histone variant that is localized to specific genomic regions where it plays important roles in transcription, DNA repair, and replication. Central to the biochemistry of human H2A.Z are the SRCAP and TIP60 chromatin remodelers, homologs of yeast SWR1 which catalyzes ATP-dependent H2A.Z exchange. Here, we use cryo-electron microscopy to resolve six structural states of the native SRCAP complex, uncovering conformational intermediates interpreted as a stepwise path to full nucleosome engagement. We also resolve the structure of the native TIP60 complex which consists of a structured core from which flexibly tethered chromatin binding domains emerge. Despite the shared subunit composition, the core of TIP60 displays divergent architectures from SRCAP that structurally disfavor nucleosome engagement, suggesting a distinct biochemical function.

SRCAP complex promotes lung cancer progression by reprograming the oncogenic transcription of Hippo-YAP/TAZ signaling pathway

The activation of YAP/TAZ, a pair of paralogs of transcriptional coactivators, initiates a dysregulated transcription program, which is a key feature of human cancer cells. However, it is not fully understood how YAP/TAZ promote dysregulated transcription for tumor progression. In this study, we employed the BioID method to identify the interactome of YAP/TAZ and discovered that YAP/TAZ interact with multiple components of SRCAP complex, a finding that was further validated through endogenous and exogenous co-immunoprecipitation, as well as immunofluorescence experiments. CUT&Tag analysis revealed that SRCAP complex facilitates the deposition of histone variant H2A.Z at target promoters. The depletion of SRCAP complex resulted in a decrease in H2A.Z occupancy and the oncogenic transcription of YAP/TAZ target genes. Additionally, the blockade of SRCAP complex suppressed YAP-driven tumor growth. In a genetically engineered lung adenocarcinoma mouse model and non-small cell lung cancer patients, SRCAP complex and H2A.Z deposition were found to be upregulated. This upregulation was statistically correlated with YAP expression, pathological stages, and poor survival in lung cancer patients. Together, our study uncovers that SRCAP complex plays a critical role in YAP/TAZ oncogenic transcription by coordinating H2A.Z deposition during cancer progression, providing potential targets for cancer diagnosis and prevention.

Global identification of SWI/SNF targets reveals compensation by EP400

Mammalian SWI/SNF chromatin remodeling complexes move and evict nucleosomes at gene promoters and enhancers to modulate DNA access. Although SWI/SNF subunits are commonly mutated in disease, therapeutic options are limited by our inability to predict SWI/SNF gene targets and conflicting studies on functional significance. Here, we leverage a fast-acting inhibitor of SWI/SNF remodeling to elucidate direct targets and effects of SWI/SNF. Blocking SWI/SNF activity causes a rapid and global loss of chromatin accessibility and transcription. Whereas repression persists at most enhancers, we uncover a compensatory role for the EP400/TIP60 remodeler, which reestablishes accessibility at most promoters during prolonged loss of SWI/SNF. Indeed, we observe synthetic lethality between EP400 and SWI/SNF in cancer cell lines and human cancer patient data. Our data define a set of molecular genomic features that accurately predict gene sensitivity to SWI/SNF inhibition in diverse cancer cell lines, thereby improving the therapeutic potential of SWI/SNF inhibitors.

Transcriptional regulation by the NSL complex enables diversification of IFT functions in ciliated versus nonciliated cells

Members of the NSL histone acetyltransferase complex are involved in multiorgan developmental syndromes. While the NSL complex is known for its importance in early development, its role in fully differentiated cells remains enigmatic. Using a kidney-specific model, we discovered that deletion of NSL complex members KANSL2 or KANSL3 in postmitotic podocytes led to catastrophic kidney dysfunction. Systematic comparison of two primary differentiated cell types reveals the NSL complex as a master regulator of intraciliary transport genes in both dividing and nondividing cells. NSL complex ablation led to loss of cilia and impaired sonic hedgehog pathway in ciliated fibroblasts. By contrast, nonciliated podocytes responded with altered microtubule dynamics and obliterated podocyte functions. Finally, overexpression of wild-type but not a double zinc finger (ZF-ZF) domain mutant of KANSL2 rescued the transcriptional defects, revealing a critical function of this domain in NSL complex assembly and function. Thus, the NSL complex exhibits bifurcation of functions to enable diversity of specialized outcomes in differentiated cells.

The effect of silencing the Tip60 gene on the response to radiotherapy in breast cancer cells

Since patients with triple-negative breast cancer do not respond to hormone therapy, the main treatment method is the combination of chemotherapy and radiotherapy. Because the DNA of the tumor cell is the target in both some chemotherapeutics and radiotherapy, problems may occur in individuals with a high DNA repair pathway. It is suggested that high expression of the Tip60 gene, which has an important role in repairing DNA damage, will increase the repair of DNA double-strand breaks in tumor cells, especially during radiotherapy treatment, thus reducing the response to treatment and adversely affecting treatment. In this study, for the first time, the role of the silenced and active Tip60 gene in response to radiotherapy in MDA-MB-231 and MCF-7 cells was investigated. For this purpose, the Tip60 gene was silenced by applying siRNA to the cell lines and UV was applied. In the study, cytotoxicity and DNA breaks were measured by MTT and COMET methods, and mRNA and protein expression values were measured by PCR and Raman spectrophotometer in silenced, unsilenced, UV-treated, and non-UV-treated cell lines. According to the results of the study, increased DNA damage was observed in MCF-7 cell lines in which the Tip60 gene was silenced, and radiotherapy was applied, compared to the cell lines with the Tip60 gene active. It was observed that DNA damage in MDA-MB-231 cell lines was less than in cell lines with the active Tip60 gene.

The Tip60/Ep400 chromatin remodeling complex impacts basic cellular functions in cranial neural crest-derived tissue during early orofacial development

The cranial neural crest plays a fundamental role in orofacial development and morphogenesis. Accordingly, mutations with impact on the cranial neural crest and its development lead to orofacial malformations such as cleft lip and palate. As a pluripotent and dynamic cell population, the cranial neural crest undergoes vast transcriptional and epigenomic alterations throughout the formation of facial structures pointing to an essential role of factors regulating chromatin state or transcription levels. Using CRISPR/Cas9-guided genome editing and conditional mutagenesis in the mouse, we here show that inactivation of Kat5 or Ep400 as the two essential enzymatic subunits of the Tip60/Ep400 chromatin remodeling complex severely affects carbohydrate and amino acid metabolism in cranial neural crest cells. The resulting decrease in protein synthesis, proliferation and survival leads to a drastic reduction of cranial neural crest cells early in fetal development and a loss of most facial structures in the absence of either protein. Following heterozygous loss of Kat5 in neural crest cells palatogenesis was impaired. These findings point to a decisive role of the Tip60/Ep400 chromatin remodeling complex in facial morphogenesis and lead us to conclude that the orofacial clefting observed in patients with heterozygous KAT5 missense mutations is at least in part due to disturbances in the cranial neural crest.

Tip60/KAT5 Histone Acetyltransferase Is Required for Maintenance and Neurogenesis of Embryonic Neural Stem Cells

Epigenetic regulation via epigenetic factors in collaboration with tissue-specific transcription factors is curtail for establishing functional organ systems during development. Brain development is tightly regulated by epigenetic factors, which are coordinately activated or inactivated during processes, and their dysregulation is linked to brain abnormalities and intellectual disability. However, the precise mechanism of epigenetic regulation in brain development and neurogenesis remains largely unknown. Here, we show that Tip60/KAT5 deletion in neural stem/progenitor cells (NSCs) in mice results in multiple abnormalities of brain development. Tip60-deficient embryonic brain led to microcephaly, and proliferating cells in the developing brain were reduced by Tip60 deficiency. In addition, neural differentiation and neuronal migration were severely affected in Tip60-deficient brains. Following neurogenesis in developing brains, gliogenesis started from the earlier stage of development in Tip60-deficient brains, indicating that Tip60 is involved in switching from neurogenesis to gliogenesis during brain development. It was also confirmed in vitro that poor neurosphere formation, proliferation defects, neural differentiation defects, and accelerated astrocytic differentiation in mutant NSCs are derived from Tip60-deficient embryonic brains. This study uncovers the critical role of Tip60 in brain development and NSC maintenance and function in vivo and in vitro.

Tip60-mediated H2A.Z acetylation promotes neuronal fate specification and bivalent gene activation

Cell lineage specification is accomplished by a concerted action of chromatin remodeling and tissue-specific transcription factors. However, the mechanisms that induce and maintain appropriate lineage-specific gene expression remain elusive. Here, we used an unbiased proteomics approach to characterize chromatin regulators that mediate the induction of neuronal cell fate. We found that Tip60 acetyltransferase is essential to establish neuronal cell identity partly via acetylation of the histone variant H2A.Z. Despite its tight correlation with gene expression and active chromatin, loss of H2A.Z acetylation had little effect on chromatin accessibility or transcription. Instead, loss of Tip60 and acetyl-H2A.Z interfered with H3K4me3 deposition and activation of a unique subset of silent, lineage-restricted genes characterized by a bivalent chromatin configuration at their promoters. Altogether, our results illuminate the mechanisms underlying bivalent chromatin activation and reveal that H2A.Z acetylation regulates neuronal fate specification by establishing epigenetic competence for bivalent gene activation and cell lineage transition.