Essential Coactivator Research Articles

The epigenetic regulators EP300/CREBBP represent promising therapeutic targets in MLL-rearranged acute myeloid leukemia

Acute myeloid leukemia (AML) with mixed-lineage leukemia (MLL) gene rearrangements (MLL-r) is an aggressive subtype of blood cancer with dismal prognosis, underscoring the urgent need for novel therapeutic strategies. E1A-binding protein (EP300) and CREB-binding protein (CREBBP) function as essential transcriptional coactivators and acetyltransferases, governing leukemogenesis through diverse mechanisms. Targeting EP300/CREBBP holds great promise for treating leukemia with some certain cytogenetic abnormalities. Here, we demonstrated that EP300 and CREBBP are core epigenetic regulators in the pathogenesis of MLL-r AML through assaying the transposase-accessible chromatin with high-throughput sequencing (ATAC-seq). Knocking-out EP300/CREBBP and inhibitor (A-485) treatment depressed the MLL-r cells proliferation, while the MLL wild-type cells remained uninfluenced. We found that the CDK4/RB/E2F axis was downregulated specifically in MLL-r AML cell after A-485 treatment by RNA-seq, western blot and cut-tag analyses. EP300/CREBBP inhibitor selectively exerted potent anti-leukemia activity through blocking the MLL-r-BET complex binding to H3K27Ac modification on critical genes loci, distinct from global histone acetylation. Collectively, our study identified EP300/CREBBP as a critical epigenetic driver of MLL-r leukemia and validated their therapeutic potential through targeting inhibition, offering a promising avenue for improving clinical outcomes in this aggressive leukemia.

ABHD5 as a friend or an enemy in cancer biology?

Alpha beta hydrolase domain containing 5 (ABHD5) is an essential coactivator of adipose triglyceride lipase (ATGL), a rate-limiting enzyme in various cell types that promotes the hydrolysis of triacylglycerol (TG) into diacylglycerol (DG) and fatty acid (FA). It acts as a critical regulatory factor in cellular lipid metabolism. The reprogramming of lipid metabolism is one of the hallmarks of cancer, suggesting that altering lipid metabolism could become a new strategy for tumor treatment. Research has revealed a close association between ABHD5 and the development and progression of malignancies. This review summarizes the role of ABHD5 in various malignant tumors and explores the different signaling pathways and metabolic routes that may be involved, providing a comprehensive mechanistic understanding of ABHD5.

Kindlin-2 regulates colonic cancer stem-like cells survival and self-renewal via Wnt/β-catenin mediated pathway

BackgroundCancer Stem Cells (CSCs) have emerged as a critical mediator in recurrence and resistance in cancers. Kindlin-isoform (1 and 2) binds with cytoplasmic β-tail of integrin and are essential co-activators of integrin function. Given their important function in regulating cancer hallmarks such as cell proliferation, invasion, migration, and metastasis, we hypothesize that it might play a critical role in CSC growth, survival, and self-renewal of colon cancer. Materials and methodsUsing knockdown approaches, we inhibited Kindlin-2 expression in HCT116 and HT29 colon cancer cells. Extreme limiting dilution and self-renewal assay were performed to measure the role of Kindlin in colonic CSC. Standard methods such as qRT-PCR and western blotting were carried out to understand the signaling cascade by which Kindlin regulates CSC marker expression and downstream targets. ResultsOur data show isoform-specific upregulation of Kindlin-2 in colonic CSCs. The silencing of Kindlin-2 reduces colonosphere formation, decreases CSC size, and self-renewal marker genes such as CD-133, CXCR-4, LGR-5, and C-MYC. Kindlin-2 silencing reduces colonosphere proliferation, invasion, and migration of colonic CSCs. Mechanistically, Kindlin-2 silencing reduces the expression, and nuclear localization of β-catenin, and decreases β-catenin target genes such as C-MYC, cyclin D1, DKK-1, and Snail-1. ConclusionOur study delineates the isoform-specific activity of Kindlin-2 in regulating Colonic CSC. Isoform-specific targeting of Kindlin-2 may be a novel strategy to tackle this devastating disease.

Evolutionary diversity of the control of the azole response by Tra1 across yeast species.

Tra1 is an essential coactivator protein of the yeast SAGA and NuA4 acetyltransferase complexes that regulate gene expression through multiple mechanisms including the acetylation of histone proteins. Tra1 is a pseudokinase of the PIKK family characterized by a C-terminal PI3K domain with no known kinase activity. However, mutations of specific arginine residues to glutamine in the PI3K domains (an allele termed tra1Q3) result in reduced growth and increased sensitivity to multiple stresses. In the opportunistic fungal pathogen Candida albicans, the tra1Q3 allele reduces pathogenicity and increases sensitivity to the echinocandin antifungal drug caspofungin, which disrupts the fungal cell wall. Here, we found that compromised Tra1 function, in contrast to what is seen with caspofungin, increases tolerance to the azole class of antifungal drugs, which inhibits ergosterol synthesis. In C. albicans, tra1Q3 increases the expression of genes linked to azole resistance, such as ERG11 and CDR1. CDR1 encodes a multidrug ABC transporter associated with efflux of multiple xenobiotics, including azoles. Consequently, cells carrying tra1Q3 show reduced intracellular accumulation of fluconazole. In contrast, a tra1Q3 Saccharomyces cerevisiae strain displayed opposite phenotypes: decreased tolerance to azole, decreased expression of the efflux pump PDR5, and increased intracellular accumulation of fluconazole. Therefore, our data provide evidence that Tra1 differentially regulates the antifungal response across yeast species.

PGC-1α Inhibits Schwann Cell Dedifferentiation and Delays Peripheral Nerve Degeneration by Targeting PON1.

PPARγ coactivator-1 alpha (PGC-1α) is an essential transcription factor co-activator that regulates gene transcription and neural regeneration. Schwann cells, which are unique glial cells in peripheral nerves that dedifferentiate after peripheral nerve injury (PNI) and are released from degenerative nerves. Wallerian degeneration is a series of stereotypical events that occurs in response to nerve fibers after PNI. The role of PGC-1α in Schwann cell dedifferentiation and Wallerian degeneration is not yet clear. As Wallerian degeneration plays a crucial role in PNI, we conducted a study to determine whether PGC-1α has an effect on peripheral nerve degeneration after injury. We examined the expression of PGC-1α after sciatic nerve crush or transection using Western blotting and found that PGC-1α expression increased after PNI. Then we utilized ex vivo and in vitro models to investigate the effects of PGC-1α inhibition and activation on Schwann cell dedifferentiation and nerve degeneration. Our findings indicate that PGC-1α negatively regulates Schwann cell dedifferentiation and nerve degeneration. Through the use of RNA-seq, siRNA/plasmid transfection and reversal experiments, we identified that PGC-1α targets inhibit the expression of paraoxonase 1 (PON1) during Schwann cell dedifferentiation in degenerated nerves. In summary, PGC-1α plays a crucial role in preventing Schwann cell dedifferentiation and its activation can reduce peripheral nerve degeneration by targeting PON1. PGC-1α inhibits Schwann cell dedifferentiation and peripheral nerve degeneration. PGC-1α negatively regulates Schwann cell dedifferentiation and peripheral nerve degeneration after injury by targeting PON1.

Wnt7b expressed by hypertrophic chondrocytes is a stimulatory factor for endochondral ossification that is regulated by Smad4 activity.

Endochondral ossification contributes to longitudinal skeletal growth. Osteoblasts, which are bone-forming cells, appear close to terminally differentiated hypertrophic chondrocytes during endochondral ossification. We established mice with conditional knockout (cKO) of Smad4, an essential co-activator for transforming growth factor β family signaling. The mice showed a marked increase in bone volume in the metaphysis as a result of increased bone formation by osteoblasts, in which β-catenin, an effector of canonical Wnt signaling, accumulated. We identified Wnt7b as a factor with increased expression in growth plate cartilage in Smad4 cKO mice. Wnt7b mRNA was expressed in differentiated chondrocytes and suppressed by BMP4 stimulation. Ablation of Wnt7b blunted the increase in bone in adult Smad4 cKO mice and reduced skeletal growth in juvenile mice. Overall, we conclude that Wnt7b is a crucial factor secreted from hypertrophic chondrocytes to initiate endochondral ossification. These results suggest that Smad4-dependent BMP signaling regulates the Wnt7b-β-catenin axis during endochondral ossification.

New mutant alleles for Spargel/dPGC-1 highlights the function of Spargel RRM domain in oogenesis and expands the role of Spargel in embryogenesis and intracellular transport.

Energy metabolism in vertebrates is controlled by three members of the PGC-1 (PPAR γ- coactivator 1) family, transcriptional coactivators that shape responses to physiological stimuli by interacting with the nuclear receptors and other transcription factors. Multiple evidence now supports that Spargel protein found in insects and ascidians is the ancestral form of vertebrate PGC-1's. Here, we undertook functional analysis of srl gene in Drosophila, asking about the requirement of Spargel per se during embryogenesis and its RNA binding domains. CRISPR- engineered srl gene deletion turned out to be an amorphic allele that is late embryonic/early larval lethal and Spargel protein missing its RNA binding domain (SrlΔRRM) negatively affects female fertility. Overexpression of wild-type Spargel in transgenic flies expedited the growth of egg chambers. On the other hand, oogenesis is blocked in a dominant-negative fashion in the presence of excess Spargel lacking its RRM domains. Finally, we observed aggregation of Notch proteins in egg chambers of srl mutant flies, suggesting that Spargel is involved in intracellular transport of Notch proteins. Taken together, we claim that these new mutant alleles of spargel are emerging powerful tools for revealing new biological functions for Spargel, an essential transcription coactivator in both Drosophila and mammals.

Microfibrillar-associated protein 5 suppresses adipogenesis by inhibiting essential coactivator of PPARγ

Femoral head necrosis is responsible for severe pain and its incidence is increasing. Abnormal adipogenic differentiation and fat cell hypertrophy of bone marrow mesenchymal stem cells increase intramedullary cavity pressure, leading to osteonecrosis. By analyzing gene expression before and after adipogenic differentiation, we found that Microfibril-Associated Protein 5 (MFAP5) is significantly down-regulated in adipogenesis whilst the mechanism of MFAP5 in regulating the differentiation of bone marrow mesenchymal stem cells is unknown. The purpose of this study was to clarify the role of MAFP5 in adipogenesis and therefore provide a theoretical basis for future therapeutic options of osteonecrosis. By knockdown or overexpression of MFAP5 in C3H10 and 3T3-L1 cells, we found that MFAP5 was significantly down-regulated as a key regulator of adipogenic differentiation, and identified the underlying downstream molecular mechanism. MFAP5 directly bound to and inhibited the expression of Staphylococcal Nuclease And Tudor Domain Containing 1, an essential coactivator of PPARγ, exerting an important regulatory role in adipogenesis.

Abstract OT1-02-02: A phase 1/2 study to evaluate the safety and efficacy of EP0062, an oral Selective Androgen Receptor Modulator (SARM), for the treatment of AR+/HER2-/ER+ advanced breast cancer

Abstract There is growing interest in targeting the androgen receptor (AR) in advanced/metastatic breast cancer. It has been recently demonstrated preclinically that AR activation, rather than AR suppression, exerts potent antitumor activity across a number of ER+/AR+ breast tumors, including those resistant to standard-of-care endocrine therapy and CDK4/6 inhibitors (Hickey et al, Nature Medicine 2021 27: 310-320). Mechanistically, agonist activation of AR altered the genomic distribution of ER and essential co-activators resulting in repression of ER-regulated cell cycle genes and upregulation of AR target genes, including known tumor suppressors. EP0062 is an oral, non-steroidal, SARM currently being developed for the treatment of AR+/HER2-/ER+ advanced breast cancer. The efficacy and safety of EP0062 has previously been investigated in a Phase 1 clinical trial of AR+/HER2–/ER+ advanced breast cancer, and demonstrated that EP0062 has acceptable tolerability with evidence of clinical efficacy (LoRusso et al. Clinical Breast Cancer 2022 22;1 67-77). This new study is designed to further extend the evaluation of EP0062 as a potential therapy for AR+/HER2–/ER+ advanced breast cancer. The primary aim of the study is to assess tolerability and identify an optimal RP2D dose. The study will also explore the relationship between efficacy of EP0062 and AR expression, to establish a threshold for future patient selection, and undertake an initial evaluation of the safety and efficacy of EP0062 in combination with established standard of care therapies. The study will recruit up to 128 patients with AR+/HER2-/ER+ advanced breast cancer. Module A is a dose finding cohort to investigate safety, tolerability, PK and PD and to define the maximum tolerated dose (MTD) and/or Recommended Phase II Dose (RP2D). Dose finding will be based on a 3+3 design and is expected to recruit up to 32 patients. Once potential recommended doses are identified, approximately 60 evaluable patients will be randomised to two different dose cohorts in Module B in order to further optimise the RP2D dose, by further evaluation of safety and tolerability, as well as prospectively evaluate the relationship between efficacy and AR expression. In Module C, EP0062 will be combined with select standard of care targeted therapies in patients with relapsed AR+/HER2-/ER+ advanced breast cancer to confirm safety and explore efficacy. This will include approximately 36 patients across a number of single arm expansion cohorts. The key inclusion criteria are as follows: • Post-menopausal women, ≥18 years • ECOG performance status of 0 to 1 • Locally advanced or metastatic breast cancer • ER+, HER2- as per ASCO CAP guidelines • AR+, as defined as ≥ 10% AR nuclei staining by IHC • Endocrine-sensitive defined as greater than 3 years endocrine treatment prior to recurrence if recurrence occurred in the adjuvant setting, or ≥ 6 months treatment and response if recurrence occurred from primary treatment in the advanced setting • Relapsed, defined as clear and documented evidence of disease progression following ≥ 1 lines and ≤2 prior lines of previous endocrine therapy and ≤ 2 lines of chemotherapy in the advanced/metastatic setting • Measurable disease defined by RECIST version 1.1, or measurable bone-only disease EP0062 will be dosed to progression. Endpoints include incidence of DLTs during Cycle 1 of EP0062 treatment (28 days), MTD, RP2D (Module A), incidence and severity of AEs and SAEs, plasma PK parameters, Clinical Benefit Rate (complete response, partial response, or stable disease) at 24 weeks, ORR, duration of response, PFS, OS and quality of life. Clinic follow-up will be at 2 and 4 weeks, then every 4 weeks until disease progression. Recruitment is scheduled to initiate in Q4 2022. Citation Format: Elgene Lim, Erika Hamilton, Carlo Palmieri, Hendrik-Tobias Arkenau, Sue Brook, Geoff Fisher, Andrew Mazur. A phase 1/2 study to evaluate the safety and efficacy of EP0062, an oral Selective Androgen Receptor Modulator (SARM), for the treatment of AR+/HER2-/ER+ advanced breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT1-02-02.

NARF is a hypoxia-induced coactivator for OCT4-mediated breast cancer stem cell specification.

Hypoxia is a key characteristic of the breast cancer microenvironment that promotes expression of the transcriptional activator hypoxia-inducible factor 1 (HIF-1) and is associated with poor patient outcome. HIF-1 increases the expression or activity of stem cell pluripotency factors, which control breast cancer stem cell (BCSC) specification and are required for cancer metastasis. Here, we identify nuclear prelamin A recognition factor (NARF) as a hypoxia-inducible, HIF-1 target gene in human breast cancer cells. NARF functions as an essential coactivator by recruiting the histone demethylase KDM6A to OCT4 bound to genes encoding the pluripotency factors NANOG, KLF4, and SOX2, leading to demethylation of histone H3 trimethylated at lysine-27 (H3K27me3), thereby increasing the expression of NANOG, KLF4, and SOX2, which, together with OCT4, mediate BCSC specification. Knockdown of NARF significantly decreased the BCSC population in vitro and markedly impaired tumor initiation capacity and lung metastasis in orthotopic mouse models.

METTL4-mediated nuclear N6-deoxyadenosine methylation promotes metastasis through activating multiple metastasis-inducing targets

BackgroundDNA N6-methyldeoxyadenosine (6mA) is rarely present in mammalian cells and its nuclear role remains elusive.ResultsHere we show that hypoxia induces nuclear 6mA modification through a DNA methyltransferase, METTL4, in hypoxia-induced epithelial-mesenchymal transition (EMT) and tumor metastasis. Co-expression of METTL4 and 6mA represents a prognosis marker for upper tract urothelial cancer patients. By RNA sequencing and 6mA chromatin immunoprecipitation-exonuclease digestion followed by sequencing, we identify lncRNA RP11-390F4.3 and one novel HIF-1α co-activator, ZMIZ1, that are co-regulated by hypoxia and METTL4. Other genes involved in hypoxia-mediated phenotypes are also regulated by 6mA modification. Quantitative chromatin isolation by RNA purification assay shows the occupancy of lncRNA RP11-390F4.3 on the promoters of multiple EMT regulators, indicating lncRNA-chromatin interaction. Knockdown of lncRNA RP11-390F4.3 abolishes METTL4-mediated tumor metastasis. We demonstrate that ZMIZ1 is an essential co-activator of HIF-1α.ConclusionsWe show that hypoxia results in enriched 6mA levels in mammalian tumor cells through METTL4. This METTL4-mediated nuclear 6mA deposition induces tumor metastasis through activating multiple metastasis-inducing genes. METTL4 is characterized as a potential therapeutic target in hypoxic tumors.

The Hippo Pathway Effectors YAP/TAZ Are Essential for Mineralized Tissue Homeostasis in the Alveolar Bone/Periodontal Complex.

YAP and TAZ are essential transcriptional co-activators and downstream effectors of the Hippo pathway, regulating cell proliferation, organ growth, and tissue homeostasis. To ask how the Hippo pathway affects mineralized tissue homeostasis in a tissue that is highly reliant on a tight homeostatic control of mineralized deposition and resorption, we determined the effects of YAP/TAZ dysregulation on the periodontal tissues alveolar bone, root cementum, and periodontal ligament. Loss of YAP/TAZ was associated with a reduction of mineralized tissue density in cellular cementum and alveolar bone, a downregulation in collagen I, alkaline phosphatase, and RUNX2 gene expression, an increase in the resorption markers TRAP and cathepsin K, and elevated numbers of TRAP-stained osteoclasts. Cyclic strain applied to periodontal ligament cells resulted in YAP nuclear localization, an effect that was abolished after blocking YAP. The rescue of YAP signaling with the heparan sulfate proteoglycan agrin resulted in a return of the nuclear YAP signal. Illustrating the key role of YAP on mineralization gene expression, the YAP inhibition-related downregulation of mineralization-associated genes was reversed by the extracellular matrix YAP activator agrin. Application of the unopposed mouse molar model to transform the periodontal ligament into an unloaded state and facilitate the distal drift of teeth resulted in an overall increase in mineralization-associated gene expression, an effect that was 10–20% diminished in Wnt1Cre/YAP/TAZ mutant mice. The unloaded state of the unopposed molar model in Wnt1Cre/YAP/TAZ mutant mice also caused a significant three-fold increase in osteoclast numbers, a substantial increase in bone/cementum resorption, pronounced periodontal ligament hyalinization, and thickened periodontal fiber bundles. Together, these data demonstrated that YAP/TAZ signaling is essential for the microarchitectural integrity of the periodontium by regulating mineralization gene expression and preventing excessive resorption during bodily movement of the dentoalveolar complex.

NuA4 and H2A.Z control environmental responses and autotrophic growth in Arabidopsis

Nucleosomal acetyltransferase of H4 (NuA4) is an essential transcriptional coactivator in eukaryotes, but remains poorly characterized in plants. Here, we describe Arabidopsis homologs of the NuA4 scaffold proteins Enhancer of Polycomb-Like 1 (AtEPL1) and Esa1-Associated Factor 1 (AtEAF1). Loss of AtEAF1 results in inhibition of growth and chloroplast development. These effects are stronger in the Atepl1 mutant and are further enhanced by loss of Golden2-Like (GLK) transcription factors, suggesting that NuA4 activates nuclear plastid genes alongside GLK. We demonstrate that AtEPL1 is necessary for nucleosomal acetylation of histones H4 and H2A.Z by NuA4 in vitro. These chromatin marks are diminished genome-wide in Atepl1, while another active chromatin mark, H3K9 acetylation (H3K9ac), is locally enhanced. Expression of many chloroplast-related genes depends on NuA4, as they are downregulated with loss of H4ac and H2A.Zac. Finally, we demonstrate that NuA4 promotes H2A.Z deposition and by doing so prevents spurious activation of stress response genes.

The Courage study: A first-in-human phase 1 study of the CBP/p300 inhibitor FT-7051 in men with metastatic castration-resistant prostate cancer.

TPS5085 Background: Prostate cancer is the second leading cause of cancer-related death among men in the U.S., largely due to metastatic disease that progresses despite hormonal therapy (tx). The role for androgen receptor (AR) signaling in prostate cancer and hormone tx resistance is well-established. CBP/p300 are essential co-activators of AR-mediated transcription. FT-7051 is an oral, potent, and selective inhibitor of CBP/p300 with activity in preclinical models of prostate cancer including models resistant to currently used AR inhibitors like enzalutamide. The Courage Study (NCT04575766) is a first-in-human, multicenter, phase 1, open-label study examining the safety, pharmacokinetics (PK), preliminary anti-tumor activity, and pharmacodynamics (PD) of FT-7051 for the treatment of men with metastatic castration-resistant prostate cancer (mCRPC) who have progressed despite prior tx and have been treated with at least one approved androgen receptor pathway inhibitor. The study will enroll up to 45 men with mCRPC at ̃8-15 US sites. Methods: The study employs a Bayesian optimal interval (BOIN) design with an accelerated titration. Patients (pts) will initially be enrolled in a dose level cohort size of 1 until a Grade 2 or higher toxicity occurs that is considered related to FT-7051 or the highest dose level is reached. Upon completion of the accelerated titration phase, subsequent cohorts will enroll 3-5 pts. Treatment: FT-7051 capsules will be administered on a 28 d cycle (21 d on / 7 d off) with Dose Levels -1 to 7 assigned per protocol using the BOIN design. Key inclusion criteria: Diagnosis of mCRPC with either adenocarcinoma or mixed histology AND rising PSA; previously failed at least one approved androgen receptor pathway inhibitor; ≥ 18 yrs of age; prior taxane chemotherapy permitted. Key exclusion criteria: Previous solid organ transplant, prior anticancer tx including prior tx with small molecules within 4 wks of first dose of study treatment, prior radiation tx within 4 wks prior to initiation of study treatment, prior androgen antagonist tx within 2 wks, prior radium-223 tx within 6 wks. Endpoints: Primary endpoints are to define the recommended phase 2 monotherapy dose of FT-7051 through assessments of DLTs, SAEs, clinically relevant AEs, and clinically relevant safety laboratory values. Key secondary endpoints include: PSA at 12 wks, time to PSA progression, time to radiographic progression, overall response rate, and plasma PK parameters. PD assessments of CBP/p300 inhibition in surrogate tissue, biomarker assessments in CTCs (AR, AR-v7), and peripheral blood are included. Duration: Pts will remain on study treatment until they are deemed to be no longer clinically benefiting (NLCB) by the treating Investigator or until unacceptable toxicity. Pt may be followed for survival for up to 24 months from last dose of study treatment. The first pt was dosed January 2021. Clinical trial information: NCT04575766.

Inter‐modular interaction between the head and CDK8 modules of Mediator regulates a recruitment of TFIIH to the promoters

Mediator is an essential co-activator, which regulates RNA polymerase II (Pol II) transcription in eukaryotes. Mediator is a large multi-protein complex composed of four distinct sub-complexes termed Head, Middle, Tail, often termed core Mediator (cMed), as well as the CDK8 module (CKM), which is dissociable from core Mediator. While cMed regulates Pol II transcription by involving in formation and pre-initiation complex (PIC) via interaction with Pol II and general transcription factors (GTFs), the role of CKM still remains elusive. In higher eukaryotes, CKM appears to function as both in negative and positive regulator. In yeast Saccharomyces cerevisiae, CKM has been believed to function as a negative regulator. The one mode of inhibition by CKM comes from disruption of activators by triggering ubiquitin-mediated degradation by phosphorylation. However, overall the mode of transcription inhibition by CKM has not been fully understood. It is proposed that CKM inhibits transcription blocking cMed-Pol II interactions. However, genome-wide studies completely disputed this model. In this work, our structure-based functional study has led to a totally unexpected discovery that while Mediator head module facilitates recruitment of TFIIH, CKM appears to inhibit a process. In essence, the inter-modular interaction within the Mediator modules regulates conversion from initiation to elongation step of transcription by modulating a recruitment of a general transcription factor TFIIH.

Critical roles of transcriptional coactivator MED1 in the formation and function of mouse adipose tissues.

The MED1 subunit has been shown to mediate ligand-dependent binding of the Mediator coactivator complex to multiple nuclear receptors, including the adipogenic PPARγ, and to play an essential role in ectopic PPARγ-induced adipogenesis of mouse embryonic fibroblasts. However, the precise roles of MED1, and its various domains, at various stages of adipogenesis and in adipose tissue have been unclear. Here, after establishing requirements for MED1, including specific domains, for differentiation of 3T3L1 cells and both primary white and brown preadipocytes, we used multiple genetic approaches to assess requirements for MED1 in adipocyte formation, maintenance, and function in mice. We show that MED1 is indeed essential for the differentiation and/or function of both brown and white adipocytes, as its absence in these cells leads to, respectively, defective brown fat function and lipodystrophy. This work establishes MED1 as an essential transcriptional coactivator that ensures homeostatic functions of adipocytes.

Characterization of a new mastermind allele identified from somatic mosaic screen.

The Notch signaling pathway is highly conserved and regulates various fundamental development events. Activation of Notch signaling relies on production of the Notch intracellular domain (NICD), which assembles a transcription factor complex to turn on down-stream targets expression. The mastermind (mam) gene encodes an essential co-activator that permits NICD activity in the cell nucleus. During a somatic mosaic screen in Drosophila, an uncharacterized gene l(2)S9998 is identified as a positive regulator of the Notch signaling pathway. Genetic analysis demonstrates that l(2)S9998 functions at the level of transcriptional activation of Notch targets in the signal receiving cells. Whole genome sequencing reveals that l(2)S9998 is a novel allele of the mam gene, which is further confirmed by complementation tests. Along with three molecularly defined transposon insertions isolated from the screen, four mutants of mam are shown to modulate Notch signaling during fly wing development. Our analysis provides additional genetic resources for understanding mam function and Notch signaling regulation.

The androgen receptor is a tumor suppressor in estrogen receptor-positive breast cancer.

The role of the androgen receptor (AR) in estrogen receptor (ER)-α-positive breast cancer is controversial, constraining implementation of AR-directed therapies. Using a diverse, clinically relevant panel of cell-line and patient-derived models, we demonstrate that AR activation, not suppression, exerts potent antitumor activity in multiple disease contexts, including resistance to standard-of-care ER and CDK4/6 inhibitors. Notably, AR agonists combined with standard-of-care agents enhanced therapeutic responses. Mechanistically, agonist activation of AR altered the genomic distribution of ER and essential co-activators (p300, SRC-3), resulting in repression of ER-regulated cell cycle genes and upregulation of AR target genes, including known tumor suppressors. A gene signature of AR activity positively predicted disease survival in multiple clinical ER-positive breast cancer cohorts. These findings provide unambiguous evidence that AR has a tumor suppressor role in ER-positive breast cancer and support AR agonism as the optimal AR-directed treatment strategy, revealing a rational therapeutic opportunity.

ABHD5 suppresses cancer cell anabolism through lipolysis-dependent activation of the AMPK/mTORC1 pathway

ABHD5 is an essential coactivator of ATGL, the rate-limiting triglyceride (TG) lipase in many cell types. Importantly, ABHD5 also functions as a tumor suppressor, and ABHD5 mRNA expression levels correlate with patient survival for several cancers. Nevertheless, the mechanisms involved in ABHD5-dependent tumor suppression are not known. We found that overexpression of ABHD5 induces cell cycle arrest at the G1 phase and causes growth retardation in a panel of prostate cancer cells. Transcriptomic profiling and biochemical analysis revealed that genetic or pharmacological activation of lipolysis by ABHD5 potently inhibits mTORC1 signaling, leading to a significant downregulation of protein synthesis. Mechanistically, we found that ABHD5 elevates intracellular AMP content, which activates AMPK, leading to inhibition of mTORC1. Interestingly, ABHD5-dependent suppression of mTORC1 was abrogated by pharmacological inhibition of DGAT1 or DGAT2, isoenzymes that re-esterify fatty acids in a process that consumes ATP. Collectively, this study maps out a novel molecular pathway crucial for limiting cancer cell proliferation, in which ABHD5-mediated lipolysis creates an energy-consuming futile cycle between TG hydrolysis and resynthesis, leading to inhibition of mTORC1 and cancer cell growth arrest.

Transcriptional Activation of MYC-Induced Genes by GCN5 Promotes B-cell Lymphomagenesis.

Overexpression of the MYC oncoprotein is an initiating step in the formation of several cancers. MYC frequently recruits chromatin-modifying complexes to DNA to amplify the expression of cancer-promoting genes, including those regulating cell cycle, proliferation, and metabolism, yet the roles of specific modifiers in different cancer types are not well defined. Here, we show that GCN5 is an essential coactivator of cell-cycle gene expression driven by MYC overexpression and that deletion of Gcn5 delays or abrogates tumorigenesis in the Eμ-Myc mouse model of B-cell lymphoma. Our results demonstrate that Gcn5 loss impacts both expression and downstream functions of Myc. SIGNIFICANCE: Our results provide important proof of principle for Gcn5 functions in formation and progression of Myc-driven cancers, suggesting that GCN5 may be a viable target for development of new cancer therapies.