Integral Subunit Research Articles

Basis of gene-specific transcription regulation by the Integrator complex

The Integrator complex attenuates gene expression via the premature termination of RNA polymerase II (RNAP2) at promoter-proximal pausing sites. It is required for stimulus response, cell differentiation, and neurodevelopment, but how gene-specific and adaptive regulation by Integrator is achieved remains unclear. Here, we identify two sites on human Integrator subunits 13/14 that serve as binding hubs for sequence-specific transcription factors (TFs) and other transcription effector complexes. When Integrator is attached to paused RNAP2, these hubs are positioned upstream of the transcription bubble, consistent with simultaneous TF-promoter tethering. The TFs co-localize with Integrator genome-wide, increase Integrator abundance on target genes, and co-regulate responsive transcriptional programs. For instance, sensory cilia formation induced by glucose starvation depends on Integrator-TF contacts. Our data suggest TF-mediated promoter recruitment of Integrator as a widespread mechanism for targeted transcription regulation.

A role for the C. elegans Argonaute protein CSR-1 in small nuclear RNA 3' processing.

The Integrator is a multi-subunit protein complex that catalyzes the maturation of snRNA transcripts via 3' cleavage, a step required for snRNA incorporation with snRNP for spliceosome biogenesis. Here we developed a GFP based in vivo snRNA misprocessing reporter as a readout of Integrator function and performed a genome-wide RNAi screen for Integrator regulators. We found that loss of the Argonaute encoding csr-1 gene resulted in widespread 3' misprocessing of snRNA transcripts that is accompanied by a significant increase in alternative splicing. Loss of the csr-1 gene down-regulates the germline expression of Integrator subunits 4 and 6 and is accompanied by a reduced protein translation efficiency of multiple Integrator catalytic and non-catalytic subunits. Through isoform and motif mutant analysis, we determined that CSR-1's effect on snRNA processing is dependent on its catalytic slicer activity but does not involve the CSR-1a isoform. Moreover, mRNA-sequencing revealed high similarity in the transcriptome profile between csr-1 and Integrator subunit knockdown via RNAi. Together, our findings reveal CSR-1 as a new regulator of the Integrator complex and implicate a novel role of this Argonaute protein in snRNA 3' processing.

Comprehensive analysis of INTS family related to expression, prognosis, diagnosis and immune features in hepatocellular carcinoma

PurposeThe integrator subunit (INTS) family, a group exclusive to metazoans, participates in various biologic processes. However, their roles in hepatocellular carcinoma (HCC) remain largely unexplored. MethodsPublic databases were utilized to investigate the transcriptional and protein expression, and clinical relevance of the INTS family in HCC. Meanwhile, the effects of INTS13 knockdown and overexpression on cell proliferation and apoptosis were studied using HCC cell lines. ResultsThe mRNA expression of most INTSs were higher in tumor than normal tissues. Higher expression of INTS1/2/3/4/7/8/9/11/12/13 were correlated with poorer overall survival (OS) in Kaplan-Meier Survival Analysis. Multivariate analysis revealed higher level of INTS13 was an independent prognostic factor for shorter OS. Furthermore, genetic alteration of INTS3/6/7/8/9/10 were found in HCC patients and was associated with shorter disease-free survival and progression-free survival. INTS1/2/3/5/7/11/13/14 were associated with activation of tumor-induced immune response and immune infiltration in HCC. Knockdown of INTS13 inhibited cell proliferation and induced apoptosis in HCC cell lines, while overexpression of INTS13 had the opposite effect. ConclusionOur results indicate that INTS13 is an independent prognostic biomarker in HCC. Furthermore, INTS13 enhances cell proliferation and decreases cell apoptosis in HCC cell lines leading to a poorer OS in HCC patients.

Primary Cilium in Neural Crest Cells Crucial for Anterior Segment Development and Corneal Avascularity.

Intraflagellar transport 46 (IFT46) is an integral subunit of the IFT-B complex, playing a key role in the assembly and maintenance of primary cilia responsible for transducing signaling pathways. Despite its predominant expression in the basal body of cilia, the precise role of Ift46 in ocular development remains undetermined. This study aimed to elucidate the impact of neural crest (NC)-specific deletion of Ift46 on ocular development. NC-specific conditional knockout mice for Ift46 (NC-Ift46F/F) were generated by crossing Ift46F mice with Wnt1-Cre2 mice, enabling the specific deletion of Ift46 in NC-derived cells (NCCs). Sonic Hedgehog (Shh) and Notch signaling activities in NC-Ift46F/F mice were evaluated using Gli1lacZ and CBF:H2B-Venus reporter mice, respectively. Cell fate mapping was conducted using ROSAmTmG reporter mice. The deletion of Ift46 in NCCs resulted in a spectrum of ocular abnormalities, including thickened corneal stroma, hypoplasia of the anterior chamber, irregular iris morphology, and corneal neovascularization. Notably, this deletion led to reduced Shh signal activity in the periocular mesenchyme, sustained expression of key transcription factors Foxc1, Foxc2 and Pitx2, along with persistent cell proliferation. Additionally, it induced increased Notch signaling activity and the development of ectopic neovascularization within the corneal stroma. The absence of primary cilia due to Ift46 deficiency in NCCs is associated with anterior segment dysgenesis (ASD) and corneal neovascularization, suggesting a potential link to Axenfeld-Rieger syndrome, a disorder characterized by ASD. This underscores the pivotal role of primary cilia in ensuring proper anterior segment development and maintaining an avascular cornea.

Abstract 5712: Functional dissection of CDK7 in transcription using a highly selective CDK7 inhibitor Q901

Abstract CDK7 is a well-known regulator of both the cell cycle and transcription and plays a crucial role in cell cycle progression by catalyzing T-loop phosphorylation of other CDKs. CDK7 is also an integral subunit of the general transcription factor, TFIIH and regulates transcription through phosphorylation of RNA Polymerase II (Pol II) at CTD Ser5 and CDK9. We used Q901, a highly selective CDK7 inhibitor to further investigate the molecular function of CDK7 in the transcriptional process. Q901 is currently being evaluated in a phase 1 clinical study for selected advanced solid tumors. Compared to previously reported CDK7 inhibitors, Q901 has increased specificity and efficacy, but the impact on transcription have not been studied in detail. In our study, we combined RNA Pol II (pan, Ser5P, Ser2P) ChIP-seq and PRO-seq techniques in the MCF7 breast cancer cell line. The findings demonstrated that the Q901 effectively altered transcription and the RNA Pol II profile in a subset of genes, leading to a significant reduction in Ser5 phosphorylation levels in RNA Pol II. The downregulated genes were associated with critical pathways including downstream of oncogenic genes (MYC and E2F), DNA damage repair, cell cycle checkpoint, and gene expression. To verify whether these genes were the direct targets of CDK7, we performed CDK7 ChIP-seq analysis. CDK7 binding exclusively to the genes that were downregulated by Q901, without any detectable binding to upregulated genes. Despite the universal role of general transcription machinery in transcription, the data demonstrated that the highly selective inhibition of CDK7 in transcription of various oncogenic pathways underlies the potent in vitro and in vivo anti-cancer efficacy of this specific CDK7 inhibitor. Citation Format: Hyerim Jung, Dahun Um, Yoonji Lee, Donghoon Yu, Dayoung Lee, Jiye Ahn, Jeongjun Kim, Seung-Joo Lee, Jaeseung Kim, Kiyean Nam, Tae-Kyung Kim. Functional dissection of CDK7 in transcription using a highly selective CDK7 inhibitor Q901 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5712.

IntS6 and the Integrator phosphatase module tune the efficiency of select premature transcription termination events

The metazoan-specific Integrator complex catalyzes 3' end processing of small nuclear RNAs (snRNAs) and premature termination that attenuates the transcription of many protein-coding genes. Integrator has RNA endonuclease and protein phosphatase activities, but it remains unclear if both are required for complex function. Here, we show IntS6 (Integrator subunit 6) over-expression blocks Integrator function at a subset of Drosophila protein-coding genes, although having no effect on snRNAs or attenuation of other loci. Over-expressed IntS6 titrates protein phosphatase 2A (PP2A) subunits, thereby only affecting gene loci where phosphatase activity is necessary for Integrator function. IntS6 functions analogous to a PP2A regulatory B subunit as over-expression of canonical B subunits, which do not bind Integrator, is also sufficient toinhibit Integrator activity. These results show that the phosphatase module is critical at only a subset of Integrator-regulated genes and point to PP2A recruitment as a tunable step that modulates transcription termination efficiency.

Structure of a membrane-bound menaquinol:organohalide oxidoreductase

Organohalide-respiring bacteria are key organisms for the bioremediation of soils and aquifers contaminated with halogenated organic compounds. The major players in this process are respiratory reductive dehalogenases, corrinoid enzymes that use organohalides as substrates and contribute to energy conservation. Here, we present the structure of a menaquinol:organohalide oxidoreductase obtained by cryo-EM. The membrane-bound protein was isolated from Desulfitobacterium hafniense strain TCE1 as a PceA2B2 complex catalysing the dechlorination of tetrachloroethene. Two catalytic PceA subunits are anchored to the membrane by two small integral membrane PceB subunits. The structure reveals two menaquinone molecules bound at the interface of the two different subunits, which are the starting point of a chain of redox cofactors for electron transfer to the active site. In this work, the structure elucidates how energy is conserved during organohalide respiration in menaquinone-dependent organohalide-respiring bacteria.

The Integrator Complex Is Essential for Erythropoiesis

Erythropoiesis is a finely orchestrated process that involves the generation of a ~2.5 million red blood cells per second to maintain homeostasis and prevent anemia. During terminal maturation, erythroid precursors upregulate erythroid-specific genes while silencing non-erythroid genes in the setting of a cell that is rapidly dividing, and nucleus that is condensing in preparation for enucleation. Our group has shown that regulation of RNAPII activity is an essential determinant of erythroid cell function. During terminal erythroid maturation, RNA polymerase II (RNAPII) levels decline dramatically, becoming a scarce resource allocated to erythroid genes, such as alpha and beta globin (Murphy Blood 2021). The mechanism(s) by which RNAPII is removed from genes unnecessary to erythroid differentiation and shunted to produce mRNA essential for red blood cell function are unknown. The Integrator Complex (INT) is a modular and multi-subunit machinery that binds to paused RNAPII and promotes promoter-proximal termination. INT is highly expressed in maturing erythroid cells, although little is known about the function of INT during erythropoiesis. We hypothesize that INT facilitates promoter-proximal termination at non-erythroid genes to maintain RNAPII availability during terminal erythroid maturation. The balance between kinase and phosphatase activity is a key regulator of RNAPII activity. Phosphorylation of the c-terminal domain of RNAPII by pTEFb facilitates RNAPII pause release, and promotes active transcription. Alternatively, subunit 8 of INT (INTS8) can dephosphorylate the c-terminal domain of RNAPII through association with protein phosphatase 2a (PP2A) (Huang Mol Cell 2020), enforcing RNAPII pausing and antagonizing pTEFb activity. Integrator subunit 11 then cleaves the nascent RNA causing promoter-proximal transcriptional termination (Wu PNAS 2017). To gain insights into the function of INT in erythropoiesis, we utilized the RNP method of Crispr/Cas 9 genome editing (Gundry Cell Reports 2016) to delete INTS8 from CD34+ HSPCs, and then subjected them to erythroid differentiation and colony forming assays. Disruption of INTS8 significantly impaired erythroid proliferation and viability. It also delayed erythroid maturation, evident by delayed GPA expression, less mature morphology, and lower rates of benzidine positivity. Moreover, INTS8 disruption led to a decline in erythroid colony-forming ability and decreased expression of alpha and beta globin. Together these data indicate that INT function is essential for erythropoiesis. Integrator subunit 1 (INTS1) serves as a molecular scaffold for the complex, and can be used as an indicator of INT levels and occupancy. Western blotting demonstrated that INTS1 protein increased after CD36 selection and remained high throughout terminal erythroid maturation. To delineate the genomic targets of INT we performed CUT&RUN for INTS1 on day 7 and day 9 of erythroid culture following CD36 selection (as described in Gautier, Cell Reports 2016), corresponding to the basophilic and polychromatic stages of erythroid maturation. Approximately 50% of sites of INT occupancy were located at transcription start sites at both time points. Motif analyses of sites of INTS1 occupancy were enriched for transcription factors involved in signaling, including STAT5 (p1e-189) and SMAD2 (p1e-170), and INTS1 was present at several known STAT5 target genes including MYC and CCNB1. Interestingly, ~74% of genes with stably paused RNAPII, as indicated by a pausing index (PI) >4, were occupied by INTS1. Further, the level of INTS1 occupancy was significantly higher at genes with a PI >4 than genes with PI <4. The genomic occupancy of INTS increased from day 7 to day 9. Transcription start sites that gained INTS1 occupancy during maturation lost RNPII, suggesting a role for INT in promoting RNAPII eviction at these loci. Collectively, our findings identify a critical role for INT in governing erythroid maturation and gene expression, and provide novel insights into the transcriptional regulation of erythropoiesis.

Bi-allelic variants in INTS11 are associated with a complex neurological disorder

The Integrator complex is a multi-subunit protein complex that regulates the processing of nascent RNAs transcribed by RNA polymerase II (RNAPII), including small nuclear RNAs, enhancer RNAs, telomeric RNAs, viral RNAs, and protein-coding mRNAs. Integrator subunit 11 (INTS11) is the catalytic subunit that cleaves nascent RNAs, but, to date, mutations in this subunit have not been linked to human disease. Here, we describe 15 individuals from 10 unrelated families with bi-allelic variants in INTS11 who present with global developmental and language delay, intellectual disability, impaired motor development, and brain atrophy. Consistent with human observations, we find that the fly ortholog of INTS11, dIntS11, is essential and expressed in the central nervous systems in a subset of neurons and most glia in larval and adult stages. Using Drosophila as a model, we investigated the effect of seven variants. We found that two (p.Arg17Leu and p.His414Tyr) fail to rescue the lethality of null mutants, indicating that they are strong loss-of-function variants. Furthermore, we found that five variants (p.Gly55Ser, p.Leu138Phe, p.Lys396Glu, p.Val517Met, and p.Ile553Glu) rescue lethality but cause a shortened lifespan and bang sensitivity and affect locomotor activity, indicating that they are partial loss-of-function variants. Altogether, our results provide compelling evidence that integrity of the Integrator RNA endonuclease is critical for brain development.

A combinatorial approach to uncover an additional Integrator subunit

RNA polymerase II (RNAPII) controls expression of all protein-coding genes and most noncoding loci in higher eukaryotes. Calibrating RNAPII activity requires an assortment of polymerase-associated factors that are recruited at sites of active transcription. The Integrator complex is one of the most elusive transcriptional regulators in metazoans, deemed to be recruited after initiation to help establish and modulate paused RNAPII. Integrator is known to be composed of 14 subunits that assemble and operate in a modular fashion. We employed proteomics and machine-learning structure prediction (AlphaFold2) to identify an additional Integrator subunit, INTS15. We report that INTS15 assembles primarily with the INTS13/14/10 module and interfaces with the Int-PP2A module. Functional genomics analysis further reveals a role for INTS15 in modulating RNAPII pausing at a subset of genes. Our study shows that omics approaches combined with AlphaFold2-based predictions provide additional insights into the molecular architecture of large and dynamic multiprotein complexes.

The Integrator complex desensitizes cellular response to TGF-β/BMP signaling

Maintenance of stem cells requires the concerted actions of niche-derived signals and stem cell-intrinsic factors. Although Decapentaplegic (Dpp), a Drosophila bone morphogenetic protein (BMP) molecule, can act as a long-range morphogen, its function is spatially limited to the germline stem cell niche in the germarium. We show here that Integrator, a complex known to be involved in RNA polymerase II (RNAPII)-mediated transcriptional regulation in the nucleus, promotes germline differentiation by restricting niche-derived Dpp/BMP activity in the cytoplasm. Further results show that Integrator works in various developmental contexts to desensitize the cellular response to Dpp/BMP signaling during Drosophila development. Mechanistically, our results show that Integrator forms a multi-subunit complex with the type I receptor Thickveins (Tkv) and other Dpp/BMP signaling components and acts in a negative feedback loop to promote Tkv turnover independent of its transcriptional activity. Similarly, human Integrator subunits bind transforming growth factor β (TGF-β)/BMP signaling components and antagonize their activity, suggesting a conserved role of Integrator across metazoans.

Mutations in the non-coding RNU4ATAC gene affect the homeostasis and function of the Integrator complex.

Various genetic diseases associated with microcephaly and developmental defects are due to pathogenic variants in the U4atac small nuclear RNA (snRNA), a component of the minor spliceosome essential for the removal of U12-type introns from eukaryotic mRNAs. While it has been shown that a few RNU4ATAC mutations result in impaired binding of essential protein components, the molecular defects of the vast majority of variants are still unknown. Here, we used lymphoblastoid cells derived from RNU4ATAC compound heterozygous (g.108_126del;g.111G>A) twin patients with MOPD1 phenotypes to analyze the molecular consequences of the mutations on small nuclear ribonucleoproteins (snRNPs)formation and on splicing. We found that the U4atac108_126del mutant is unstable and that the U4atac111G>A mutant as well as the minor di- and tri-snRNPs are present at reduced levels. Our results also reveal the existence of 3'-extended snRNA transcripts in patients' cells. Moreover, we show that the mutant cells have alterations in splicing of INTS7 and INTS10 minor introns, contain lower levels of the INTS7 and INTS10 proteins and display changes in the assembly of Integrator subunits. Altogether, our results show that compound heterozygous g.108_126del;g.111G>A mutations induce splicing defects and affect the homeostasis and function of the Integrator complex.

Pleiotropy of PP2A Phosphatases in Cancer with a Focus on Glioblastoma IDH Wildtype.

Serine/Threonine protein phosphatase 2A (PP2A) is a heterotrimeric (or occasionally, heterodimeric) phosphatase with pleiotropic functions and ubiquitous expression. Despite the fact that they all contribute to protein dephosphorylation, multiple PP2A complexes exist which differ considerably by their subcellular localization and their substrate specificity, suggesting diverse PP2A functions. PP2A complex formation is tightly regulated by means of gene expression regulation by transcription factors, microRNAs, and post-translational modifications. Furthermore, a constant competition between PP2A regulatory subunits is taking place dynamically and depending on the spatiotemporal circumstance; many of the integral subunits can outcompete the rest, subjecting them to proteolysis. PP2A modulation is especially important in the context of brain tumors due to its ability to modulate distinct glioma-promoting signal transduction pathways, such as PI3K/Akt, Wnt, Ras, NF-κb, etc. Furthermore, PP2A is also implicated in DNA repair and survival pathways that are activated upon treatment of glioma cells with chemo-radiation. Depending on the cancer cell type, preclinical studies have shown some promise in utilising PP2A activator or PP2A inhibitors to overcome therapy resistance. This review has a special focus on "glioblastoma, IDH wild-type" (GBM) tumors, for which the therapy options have limited efficacy, and tumor relapse is inevitable.

PARP1's Involvement in RNA Polymerase II Elongation: Pausing and Releasing Regulation through the Integrator and Super Elongation Complex.

RNA polymerase elongation along the gene body is tightly regulated to ensure proper transcription and alternative splicing events. Understanding the mechanism and factors critical in regulating the rate of RNA polymerase II elongation and processivity is clearly important. Recently we showed that PARP1, a well-known DNA repair protein, when bound to chromatin, regulates RNA polymerase II elongation. However, the mechanism by which it does so is not known. In the current study, we aimed to tease out how PARP1 regulates RNAPII elongation. We show, both in vivo and in vitro, that PARP1 binds directly to the Integrator subunit 3 (IntS3), a member of the elongation Integrator complex. The association between the two proteins is mediated via the C-terminal domain of PARP1 to the C-terminal domain of IntS3. Interestingly, the occupancy of IntS3 along two PARP1 target genes mimicked that of PARP1, suggesting a role in its recruitment/assembly of elongation factors. Indeed, the knockdown of PARP1 resulted in differential chromatin association and gene occupancy of IntS3 and other key elongation factors. Most of these PARP1-mediated effects were due to the physical presence of PARP1 rather than its PARylation activity. These studies argue that PARP1 controls the progressive RNAPII elongation complexes. In summary, we present a platform to begin to decipher PARP1′s role in recruiting/scaffolding elongation factors along the gene body regions during RNA polymerase II elongation and gene regulation.

The a subunit isoforms of vacuolar-type proton ATPase exhibit differential distribution in mouse perigastrulation embryos

Vacuolar-type H+-ATPases (V-ATPases) are large multi-subunit complexes that play critical roles in the acidification of a variety of intracellular or extracellular compartments. Mammalian cells contain four isoforms of the membrane integral subunit a (a1–a4); these isoforms contain the information necessary to target the enzyme to different cellular destinations. They are also involved in regulating the efficiency of ATP hydrolysis and proton transport. Previously, we showed that early embryogenesis requires V-ATPase function, and the luminal acidic endocytic and lysosomal compartments in the visceral endoderm of mouse embryos at the pre-gastrulation stage (E6.5) are essential for both nutrition and signal transduction during early embryogenesis. In this study, we examined the expression and distribution of a subunit isoforms in mouse embryos at E6.5. We found that all four isoforms expressed and exhibited differential distribution in the E6.5 embryo. At this developmental stage, the embryos establish highly elaborate endocytic compartments called apical vacuoles, on which the a3 isoform specifically accumulated.

Subtle sequence differences between two interacting σ54 -dependent regulators lead to different activation mechanisms.

In the strictly anaerobic nitrate reducing bacterium Aromatoleum anaerobium, degradation of 1,3-dihydroxybenzene (1,3-DHB, resorcinol) is controlled by two bacterial enhancer-binding proteins (bEBPs), RedR1 and RedR2, which regulate the transcription of three σ54 -dependent promoters controlling expression of the pathway. RedR1 and RedR2 are identical over their length except for their N-terminal tail which differ in sequence and length (six and eight residues, respectively), a single change in their N-terminal domain (NTD), and nine non-identical residues in their C-terminal domain (CTD). Their NTD is composed of a GAF and a PAS domain connected by a linker helix. We show that each regulator is controlled by a different mechanism: whilst RedR1 responds to the classical NTD-mediated negative regulation that is released by the presence of its effector, RedR2 activity is constitutive and controlled through interaction with BtdS, an integral membrane subunit of hydroxyhydroquinone dehydrogenase carrying out the second step in 1,3-DHB degradation. BtdS sequesters the RedR2 regulator to the membrane through its NTD, where a four-Ile track in the PAS domain, interrupted by a Thr in RedR1, and the N-terminal tail are involved. The presence of 1,3-DHB, which is metabolized to hydroxybenzoquinone, releases RedR2 from the membrane. Most bEBPs assemble into homohexamers to activate transcription; we show that hetero-oligomer formation between RedR1 and RedR2 is favoured over homo-oligomers. However, either an NTD-truncated version of RedR1 or a full-length RedR2 are capable of promoter activation on their own, suggesting they should assemble into homohexamers in vivo. We show that promoter DNA behaves as an allosteric effector through binding the CTD to control ΔNTD-RedR1 multimerization and activity. Overall, the regulation of the 1,3-DHB anaerobic degradation pathway can be described as a novel mode of bEBP activation and assembly.

Role of chromatin modulator Dpy30 in osteoclast differentiation and function.

Osteoclasts are the principal bone resorption cells crucial for homeostatic bone remodeling and pathological bone destruction. Increasing data demonstrate a vital role of histone methylation in osteoclastogenesis. As an integral core subunit of H3K4 methyltransferases, Dpy30 is notal as a key chromatin regulator for cell growth and differentiation and stem cell fate determination, particularly in the hematopoietic system. However, its role in osteoclastogenesis is currently unknown. Herein, we generated Dpy30F/F; LysM-Cre+/+ mice, which deletes Dpy30 in myeloid cells, to characterize its involvement in osteoclast differentiation and function. Dpy30F/F; LysM-Cre+/+ mice showed increased bone mass, evident by impaired osteoclastogenesis and defective osteoclast activity, but no alteration of osteoblast numbers and bone formation. Additionally, our ex vivo analysis showed that the loss of Dpy30 significantly impedes osteoclast differentiation and suppresses osteoclast-related gene expression. Moreover, Dpy30 deficiency significantly decreased the enrichment of H3K4me3 on the promoter region of NFATc1. Thus, we revealed a novel role for Dpy30 in osteoclastogenesis through epigenetic mechanisms, and that it could potentially be a therapeutic target for bone destruction diseases.

SMARCE1 deficiency generates a targetable mSWI/SNF dependency in clear cell meningioma.

Mammalian SWI/SNF (mSWI/SNF) ATP-dependent chromatin remodeling complexes establish and maintain chromatin accessibility and gene expression, and are frequently perturbed in cancer. Clear cell meningioma (CCM), an aggressive tumor of the central nervous system, is uniformly driven by loss of SMARCE1, an integral subunit of the mSWI/SNF core. Here, we identify a structural role for SMARCE1 in selectively stabilizing the canonical BAF (cBAF) complex core-ATPase module interaction. In CCM, cBAF complexes fail to stabilize on chromatin, reducing enhancer accessibility, and residual core module components increase the formation of BRD9-containing non-canonical BAF (ncBAF) complexes. Combined attenuation of cBAF function and increased ncBAF complex activity generates the CCM-specific gene expression signature, which is distinct from that of NF2-mutated meningiomas. Importantly, SMARCE1-deficient cells exhibit heightened sensitivity to small-molecule inhibition of ncBAF complexes. These data inform the function of a previously elusive SWI/SNF subunit and suggest potential therapeutic approaches for intractable SMARCE1-deficient CCM tumors.

Development of a Method Combining Peptidiscs and Proteomics to Identify, Stabilize, and Purify a Detergent-Sensitive Membrane Protein Assembly.

The peptidisc membrane mimetic enables global reconstitution of the bacterial membrane proteome into water-soluble detergent-free particles, termed peptidisc libraries. We present here a method that combines peptidisc libraries and chromosomal-level gene tagging technology with affinity purification and mass spectrometry (AP/MS) to stabilize and identify fragile membrane protein complexes that exist at native expression levels. This method circumvents common artifacts caused by bait protein overproduction and protein complex dissociation due to lengthy exposure to detergents during protein isolation. Using the Escherichia coli Sec system as a case study, we identify an expanded version of the translocon, termed the HMD complex, consisting of nine different integral membrane subunits. This complex is stable in peptidiscs but dissociates in detergents. Guided by this native-level proteomic information, we design and validate a procedure that enables purification of the HMD complex with minimal protein dissociation. These results highlight the utility of peptidiscs and AP/MS to discover and stabilize fragile membrane protein assemblies. Data are available via ProteomeXchange with identifier PXD032315.

Telomerase holoenzymes

Telomerase is unusual genome replication machinery. The eukaryotic reverse transcriptase ribonucleoprotein (RNP) supplements telomeric simple‐sequence repeat tracts at chromosome ends by new repeat synthesis. Using each chromosome 3’ end as primer and an internal region of the integral telomerase RNA subunit as template, telomerase reiteratively reverse transcribes its short template into tandem single‐stranded telomeric repeats. Lagging‐strand DNA replication machinery and processing enzymes then create the functional telomere structure of duplex repeats with a 3’ overhang that can be single‐stranded, form alternative DNA structures such as G‐quadruplex, or invade the duplex region to form a displacment loop (D‐loop) of telomeric repeats termed the t‐loop.Two and a half decades of research in the Collins lab led the way to a resolution for several puzzles that were facing the telomere and telomerase field since soon after telomerase discovery by Carol Greider and Elizabeth Blackburn. How do telomerase reverse transcriptase protein (TERT) and telomerase RNA co‐fold in a hierarchical, complex process of cellular telomerase RNP biogenesis, and how does this drastically limit the amount of telomerase made by even the most strongly telomerase‐positive human cancer and stem cells? How can a precisely defined region within telomerase RNA be used as template? How does the template‐product duplex unpair and reform in a different template register to enable processive repeat synthesis? How is telomerase brought to telomeres and how does each telomere control telomerase activity according to its individual length to generate telomere length homeostasis?Human telomerase RNA (hTR) relies on proteins shared with H/ACA‐family small nucleolar RNAs for its processing, stability, and assembly with TERT. Inherited and spontaneous mutations in these H/ACA proteins cause disease syndromes by reducing telomerase function, as do subsequently identified mutations in hTR and TERT. Understanding of how these mutations compromise telomerase function has emerged from new high‐resolution structures of telomerase holoenzymes from the ciliate Tetrahymena thermophila and human cells, the two model systems of Collins lab research, and from understanding control of telomerase function at telomeres.