The Myb-MuvB Complex Is Required for YAP-Dependent Transcription of Mitotic Genes

FOXM1 expression reverts aging chromatin profiles through repression of the senescence-associated pioneer factor AP-1

Aging is characterized by changes in gene expression, some of which can drive deleterious cellular phenotypes and senescence. The transcriptional activation of senescence genes has been mainly attributed to epigenetic shifts, but the changes in chromatin accessibility and its underlying mechanisms remain largely elusive in natural aging. Here, we profiled chromatin accessibility in human dermal fibroblasts (HDFs) from individuals with ages ranging from neonatal to octogenarian. We found that AP-1 binding motifs are prevalent in elderly-specific accessible chromatin regions while neonatal-specific regions are highly enriched for TEAD binding motifs. We further show that TEAD4 and FOXM1 share a conserved transcriptional regulatory landscape controlled by a not previously described and age-dependent enhancer that loses accessibility with aging and whose deletion drives senescence. Finally, we demonstrate that FOXM1 ectopic expression in elderly cells partially resets chromatin accessibility to a youthful state due to FOXM1's repressive function on several members of the AP-1 complex, which is known to trigger the senescence transcriptional program. These results place FOXM1 at a top hierarchical level in chromatin remodeling required to prevent senescence.

The SETDB1-PC4-UPF1 post-transcriptional machinery controls periodic degradation of CENPF mRNA and maintains mitotic progression

Numerous genes exhibit periodic oscillations in mRNA expression, essential for orderly cell division. Mitosis-related mRNAs fluctuate cyclically from the G2 to M phase, primarily regulated by transcription factors. However, the role of post-transcriptional regulation in this process remains unclear. Here, we demonstrated a decrease in mRNA levels of centromere protein F (CENPF) from the early to late G2 phase. SETDB1-PC4-UPF1 serves as a crucial post-transcriptional machinery, orchestrating the periodic degradation of CENPF mRNA, ensuring balanced CENP expression, proper spindle assembly, and successful mitosis. In early G2, newly synthesized CENPF mRNAs accumulate and bind to PC4, leading to SETDB1-mediated PC4 dimethylation at K35. In late G2, dimethylated PC4 interacts with UPF1 to promote deadenylation-dependent degradation of CENPF mRNAs, forming a regulatory loop for CENP homeostasis. Elevated PC4 dimethylation in hepatocellular carcinoma, coupled with increased sensitivity to taxanes upon its inhibition, suggests promising therapeutic avenues. These findings suggest a post-transcriptional quality control mechanism regulating cyclic mitotic mRNA fluctuations, providing comprehensive insights into cell cycle gene regulation dynamics.

MYBL2 promotes proliferation of clear cell renal cell carcinoma by regulating TOP2A and activating AKT/mTOR signaling pathway

Renal cell carcinoma (RCC) is one of the most common malignancies in the urinary system, and clear cell renal cell carcinoma (ccRCC) is the most common subtype. MYBL2 has been reported to be overexpressed in various tumors and associated with poor prognosis in patients, but its biological role in ccRCC remains unclear. In this study, we investigated the mRNA and protein expression levels of MYBL2 in ccRCC samples and evaluated the prognostic value of MYBL2 using TCGA dataset. In vitro functional assays were performed using CCK-8, EdU, colony formation, cell scratch, and transwell assays, as well as in vivo tumorigenesis assays to investigate the biological functions of MYBL2 in ccRCC. Additionally, gene set enrichment analysis (GSEA) was used to explore the downstream pathways of MYBL2, which were further validated. Finally, we predicted the target genes of MYBL2 using bioinformatics and validated them using ChIP and dual-luciferase reporter gene assays. MYBL2 expression was significantly higher in ccRCC than in adjacent normal tissues and was associated with poor prognosis. MYBL2 expression was positively correlated with the pathological tumor grade and clinical TNM stage of ccRCC patients. Knockdown of MYBL2 significantly inhibited the proliferation of renal cancer cells in vitro and in vivo, and knockdown of MYBL2 could inhibit cell invasion and migration, while overexpression of MYBL2 had the opposite effect. GSEA revealed that MYBL2 was associated with the mTOR signaling pathway and cell cycle pathway, which was confirmed by our study. Finally, we found that TOP2A was a target gene of MYBL2, and MYBL2 could bind to the TOP2A promoter to regulate its transcriptional activity, promoting the proliferation of clear cell renal cell carcinoma cells. MYBL2 emerges as a highly expressed factor that significantly correlates with adverse patient prognosis in ccRCC. Mechanistically, MYBL2 transcriptionally upregulates TOP2A, thereby modulating the proliferation of ccRCC cells. Furthermore, MYBL2 activates the mTOR signaling pathway, a critical node in the progression of ccRCC. Collectively, these findings position MYBL2 as a promising candidate for both a biological marker and a therapeutic target in the management of ccRCC.

Emerging Role of the DREAM Complex in Cancer and Therapeutic Opportunities

The DREAM (dimerization partner, RB-like, E2F, and multi-vulval class B) complex is an evolutionarily conserved transcriptional repression complex that coordinates nearly one thousand target genes, primarily associated with the cell cycle processes. The formation of the DREAM complex consequently inhibits cell cycle progression and induces cellular quiescence. Given its unique role in cell cycle control, the DREAM complex has gained significant interest across various physiological and pathological contexts, particularly in conditions marked by dysregulated cell cycles, such as cancer. However, the specific cancer types most significantly affected by alterations in the DREAM complex are yet to be determined. Moreover, the possibility of restoring or pharmacologically targeting the DREAM complex as a therapeutic intervention against cancer remains a relatively unexplored area of research and is currently under active investigation. In this review, we provide an overview of the latest advances in understanding the DREAM complex, focusing on its role in cancer. We also explore strategies for targeting the DREAM complex as a potential approach for cancer therapeutics. Advances in understanding the precise role of the DREAM complex in cancer, combined with ongoing efforts to develop targeted therapies, may pave the way for new options in cancer therapy.

YAP/TAZ Signalling Controls Epidermal Keratinocyte Fate

The paralogues Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) control cell proliferation and cell fate determination from embryogenesis to ageing. In the skin epidermis, these proteins are involved in both homeostatic cell renewal and injury-induced regeneration and also drive carcinogenesis and other pathologies. YAP and TAZ are usually considered downstream of the Hippo pathway. However, they are the central integrating link for the signalling microenvironment since they are involved in the interplay with signalling cascades induced by growth factors, cytokines, and physical parameters of the extracellular matrix. In this review, we summarise the evidence on how YAP and TAZ are activated in epidermal keratinocytes; how YAP/TAZ-mediated signalling cooperates with other signalling molecules at the plasma membrane, cytoplasmic, and nuclear levels; and how YAP/TAZ ultimately controls transcription programmes, defining epidermal cell fate.

Tracing Quiescent Cancer Cells In Vivo

QCCs have long gained significant interest as potential "seeds" for recurrent cancers. Clinical evidence suggests that a subset of cancer cells exits the cell cycle and enters a quiescent state following anti-cancer treatment. These microscopic-residual QCCs are extremely challenging to trace and detect within patients. Additionally, QCCs resist conventional anti-cancer therapies due to the lack of cell activity. Notably, upon the unknown environmental cues in unknown time points, sometimes decades later, QCCs can reactivate, triggering cancer relapse at primary or secondary sites. Currently, no targeted therapies or diagnostic tools exist for QCCs, and their molecular regulatory mechanisms remain largely unknown. The major challenge in understanding QCCs lies in the limited availability of human-relevant pre-clinical models that trace and collect QCCs in vivo. This review provides an overview of existing QCC tracing systems and analyzes their limitations. It also cautiously proposes potential improvements for tracing QCCs in vivo based on recent advancements in QCC studies and lineage-tracing techniques. Developing human-relevant and easily accessible in vivo tracing systems will be a crucial step in advancing QCC diagnostics and therapeutic strategies.

FOXM1 Transcriptionally Co-Upregulates Centrosome Amplification and Clustering Genes and Is a Biomarker for Poor Prognosis in Androgen Receptor-Low Triple-Negative Breast Cancer

There are currently no approved targeted treatments for quadruple-negative breast cancer [QNBC; ER-/PR-/HER2-/androgen receptor (AR)-], a subtype of triple-negative breast cancer (TNBC). AR-low TNBC is more proliferative and clinically aggressive than AR-high TNBC. Centrosome amplification (CA), a cancer hallmark, is rampant in TNBC, where it induces spindle multipolarity-mediated cell death unless centrosome clustering pathways are co-upregulated to avert these sequelae. We recently showed that genes that confer CA and centrosome clustering are strongly overexpressed in AR-low TNBCs relative to AR-high TNBCs. However, the molecular mechanisms that index centrosome clustering to the levels of CA are undefined. We argue that FOXM1, a cell cycle-regulated oncogene, links the expression of genes that drive CA to the expression of genes that act at kinetochores and along microtubules to facilitate centrosome clustering. We provide compelling evidence that upregulation of the FOXM1-E2F1-ATAD2 oncogene triad in AR-low TNBC is accompanied by CA and the co-upregulation of centrosome clustering proteins such as KIFC1, AURKB, BIRC5, and CDCA8, conferring profound dysregulation of cell cycle controls. Targeting FOXM1 in AR-low TNBC may render cancer cells incapable of clustering their centrosomes and impair their ability to generate excess centrosomes. Hence, our review illuminates FOXM1 as a potential actionable target for AR-low TNBC.

A-MYB substitutes for B-MYB in activating cell cycle genes and in stimulating proliferation

A-MYB (MYBL1) is a transcription factor with a role in meiosis in spermatocytes. The related B-MYB protein is a key oncogene and a master regulator activating late cell cycle genes. To activate genes, B-MYB forms a complex with MuvB and is recruited indirectly to cell cycle genes homology region (CHR) promoter sites of target genes. Activation through the B-MYB-MuvB (MMB) complex is essential for successful mitosis. Here, we discover that A-MYB has a function in transcriptional regulation of the mitotic cell cycle and can substitute for B-MYB. Knockdown experiments in cells not related to spermatogenesis show that B-MYB loss alone merely delays cell cycle progression. Only dual knockdown of B-MYB and A-MYB causes G2/M cell cycle arrest, endoreduplication, and apoptosis. A-MYB can substitute for B-MYB in binding to MuvB. The resulting A-MYB-MuvB complex activates genes through CHR sites. We find that A-MYB activates the same target genes as B-MYB. Many of the corresponding proteins are central regulators of the cell division cycle. In summary, we demonstrate that A-MYB is an activator of the mitotic cell cycle by activating late cell cycle genes.

Targeting the Hippo pathway to prevent radioresistance brain metastases from the lung (Review)

The prognosis for patients with non‑small cell lung cancer (NSCLC), a cancer type which represents 85% of all lung cancers, is poor with a 5‑year survival rate of 19%, mainly because NSCLC is diagnosed at an advanced and metastatic stage. Despite recent therapeutic advancements, ~50% of patients with NSCLC will develop brain metastases (BMs). Either surgical BM treatment alone for symptomatic patients and patients with single cerebral metastases, or in combination with stereotactic radiotherapy (RT) for patients who are not suitable for surgery or presenting with fewer than four cerebral lesions with a diameter range of 5‑30 mm, or whole‑brain RT for numerous or large BMs can be administered. However, radioresistance (RR) invariably prevents the action of RT. Several mechanisms of RR have been described including hypoxia, cellular stress, presence of cancer stem cells, dysregulation of apoptosis and/or autophagy, dysregulation of the cell cycle, changes in cellular metabolism, epithelial‑to‑mesenchymal transition, overexpression of programmed cell death‑ligand 1 and activation several signaling pathways; however, the role of the Hippo signaling pathway in RR is unclear. Dysregulation of the Hippo pathway in NSCLC confers metastatic properties, and inhibitors targeting this pathway are currently in development. It is therefore essential to evaluate the effect of inhibiting the Hippo pathway, particularly the effector yes‑associated protein‑1, on cerebral metastases originating from lung cancer.

DREAM a little dREAM of DRM: Model organisms and conservation of DREAM-like complexes: Model organisms uncover the mechanisms of DREAM-mediated transcription regulation

DREAM complexes are transcriptional regulators that control the expression of hundreds to thousands of target genes involved in the cell cycle, quiescence, differentiation, and apoptosis. These complexes contain many subunits that can vary according to the considered target genes. Depending on their composition and the nature of the partners they recruit, DREAM complexes control gene expression through diverse mechanisms, including chromatin remodeling, transcription cofactor and factor recruitment at various genomic binding sites. This complexity is particularly high in mammals. Since the discovery of the first dREAM complex (drosophila Rb, E2F, and Myb) in Drosophila melanogaster, model organisms such as Caenorhabditis elegans, and plants allowed a deeper understanding of the processes regulated by DREAM-like complexes. Here, we review the conservation of these complexes. We discuss the contribution of model organisms to the study of DREAM-mediated transcriptional regulatory mechanisms and their relevance in characterizing novel activities of DREAM complexes.

Inhibition of the YAP-MMB interaction and targeting NEK2 as potential therapeutic strategies for YAP-driven cancers

YAP activation in cancer is linked to poor outcomes, making it an attractive therapeutic target. Previous research focused on blocking the interaction of YAP with TEAD transcription factors. Here, we took a different approach by disrupting YAP's binding to the transcription factor B-MYB using MY-COMP, a fragment of B-MYB containing the YAP binding domain fused to a nuclear localization signal. MY-COMP induced cell cycle defects, nuclear abnormalities, and polyploidization. In an AKT and YAP-driven liver cancer model, MY-COMP significantly reduced liver tumorigenesis, highlighting the importance of the YAP-B-MYB interaction in tumor development. MY-COMP also perturbed the cell cycle progression of YAP-dependent uveal melanoma cells but not of YAP-independent cutaneous melanoma cell lines. It counteracted YAP-dependent expression of MMB-regulated cell cycle genes, explaining the observed effects. We also identified NIMA-related kinase (NEK2) as a downstream target of YAP and B-MYB, promoting YAP-driven transformation by facilitating centrosome clustering and inhibiting multipolar mitosis.

Chlamydial YAP activation in host endocervical epithelial cells mediates pro-fibrotic paracrine stimulation of fibroblasts

IMPORTANCE

Chronic or repeated infection of the female upper genital tract by C. trachomatis can lead to severe fibrotic sequelae, including tubal factor infertility and ectopic pregnancy. However, the molecular mechanisms underlying this effect are unclear. In this report, we define a transcriptional program specific to C. trachomatis infection of the upper genital tract, identifying tissue-specific induction of host YAP-a pro-fibrotic transcriptional cofactor-as a potential driver of infection-mediated fibrotic gene expression. Furthermore, we show that infected endocervical epithelial cells stimulate collagen production by fibroblasts and implicate chlamydial induction of YAP in this effect. Our results define a mechanism by which infection mediates tissue-level fibrotic pathology via paracrine signaling and identify YAP as a potential therapeutic target for the prevention of Chlamydia-associated scarring of the female genital tract.

RHOAL57V drives the development of diffuse gastric cancer through IGF1R-PAK1-YAP1 signaling

Cancer-associated mutations in the guanosine triphosphatase (GTPase) RHOA are found at different locations from the mutational hotspots in the structurally and biochemically related RAS. Tyr42-to-Cys (Y42C) and Leu57-to-Val (L57V) substitutions are the two most prevalent RHOA mutations in diffuse gastric cancer (DGC). RHOAY42C exhibits a gain-of-function phenotype and is an oncogenic driver in DGC. Here, we determined how RHOAL57V promotes DGC growth. In mouse gastric organoids with deletion of Cdh1, which encodes the cell adhesion protein E-cadherin, the expression of RHOAL57V, but not of wild-type RHOA, induced an abnormal morphology similar to that of patient-derived DGC organoids. RHOAL57V also exhibited a gain-of-function phenotype and promoted F-actin stress fiber formation and cell migration. RHOAL57V retained interaction with effectors but exhibited impaired RHOA-intrinsic and GAP-catalyzed GTP hydrolysis, which favored formation of the active GTP-bound state. Introduction of missense mutations at KRAS residues analogous to Tyr42 and Leu57 in RHOA did not activate KRAS oncogenic potential, indicating distinct functional effects in otherwise highly related GTPases. Both RHOA mutants stimulated the transcriptional co-activator YAP1 through actin dynamics to promote DGC progression; however, RHOAL57V additionally did so by activating the kinases IGF1R and PAK1, distinct from the FAK-mediated mechanism induced by RHOAY42C. Our results reveal that RHOAL57V and RHOAY42C drive the development of DGC through distinct biochemical and signaling mechanisms.

Keratin 17 Impacts Global Gene Expression and Controls G2/M Cell Cycle Transition in Ionizing Radiation-Induced Skin Damage

Keratin 17 (K17) is a cytoskeletal protein that is part of the intermediate filaments in epidermal keratinocytes. In K17-/- mice, ionizing radiation induced more severe hair follicle damage, whereas the epidermal inflammatory response was attenuated compared with that in wild-type mice. Both p53 and K17 have a major impact on global gene expression because over 70% of the differentially expressed genes in the skin of wild-type mice showed no expression change in p53-/- or K17-/- skin after ionizing radiation. K17 does not interfere with the dynamics of p53 activation; rather, global p53 binding in the genome is altered in K17-/- mice. The absence of K17 leads to aberrant cell cycle progression and mitotic catastrophe in epidermal keratinocytes, which is due to nuclear retention, thus reducing the degradation of B-Myb, a key regulator of the G2/M cell cycle transition. These results expand our understanding of the role of K17 in regulating global gene expression and ionizing radiation-induced skin damage.

Nrg1 Regulates Cardiomyocyte Migration and Cell Cycle in Ventricular Development

BACKGROUND

Cardiac ventricles provide the contractile force of the beating heart throughout life. How the primitive endocardium-layered myocardial projections called trabeculae form and mature into the adult ventricles is of great interest for biology and regenerative medicine. Trabeculation is dependent on the signaling protein Nrg1 (neuregulin-1). However, the mechanism of action of Nrg1 and its role in ventricular wall maturation are poorly understood.

METHODS

We investigated the functions and downstream mechanisms of Nrg1 signaling during ventricular chamber development using confocal imaging, transcriptomics, and biochemical approaches in mice with cardiac-specific inactivation or overexpression of Nrg1.

RESULTS

Analysis of cardiac-specific Nrg1 mutant mice showed that the transcriptional program underlying cardiomyocyte-oriented cell division and trabeculae formation depends on endocardial Nrg1 to myocardial ErbB2 (erb-b2 receptor tyrosine kinase 2) signaling and phospho-Erk (phosphorylated extracellular signal-regulated kinase; pErk) activation. Early endothelial loss of Nrg1 and reduced pErk activation diminished cardiomyocyte Pard3 and Crumbs2 (Crumbs Cell Polarity Complex Component 2) protein and altered cytoskeletal gene expression and organization. These alterations are associated with abnormal gene expression related to mitotic spindle organization and a shift in cardiomyocyte division orientation. Nrg1 is crucial for trabecular growth and ventricular wall thickening by regulating an epithelial-to-mesenchymal transition-like process in cardiomyocytes involving migration, adhesion, cytoskeletal actin turnover, and timely progression through the cell cycle G2/M phase. Ectopic cardiac Nrg1 overexpression and high pErk signaling caused S-phase arrest, sustained high epithelial-to-mesenchymal transition-like gene expression, and prolonged trabeculation, blocking compact myocardium maturation. Myocardial trabecular patterning alterations resulting from above- or below-normal Nrg1-dependent pErk activation were concomitant with sarcomere actin cytoskeleton disorganization. The Nrg1 loss- and gain-of-function transcriptomes were enriched for Yap1 (yes-associated protein-1) gene signatures, identifying Yap1 as a potential downstream effector. Furthermore, biochemical and imaging data reveal that Nrg1 influences pErk activation and Yap1 nuclear-cytoplasmic distribution during trabeculation.

CONCLUSIONS

These data establish the Nrg1-ErbB2/ErbB4-Erk axis as a crucial regulator of cardiomyocyte cell cycle progression and migration during ventricular development.

Genetic and Pharmacological YAP Activation Induces Proliferation and Improves Survival in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Cardiomyocyte loss following myocardial infarction cannot be addressed with current clinical therapies. Cell therapy with induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) is a potential approach to replace cardiomyocyte loss. However, engraftment rates in pre-clinical studies have been low, highlighting a need to refine current iPSC-CM technology. In this study, we demonstrated that inducing Yes-associated protein (YAP) by genetic and pharmacological approaches resulted in increased iPSC-CM proliferation and reduced apoptosis in response to oxidative stress. Interestingly, iPSC-CM maturation was differently affected by each strategy, with genetic activation of YAP resulting in a more immature cardiomyocyte-like phenotype not witnessed upon pharmacological YAP activation. Overall, we conclude that YAP activation in iPSC-CMs enhances cell survival and proliferative capacity. Therefore, strategies targeting YAP, or its upstream regulator the Hippo signalling pathway, could potentially be used to improve the efficacy of iPSC-CM technology for use as a future regenerative therapy in myocardial infarction.

Chlamydial YAP activation in host endocervical epithelial cells mediates pro-fibrotic paracrine stimulation of fibroblasts

Infection of the female genital tract by Chlamydia trachomatis can produce severe fibrotic sequelae, including tubal factor infertility and ectopic pregnancy. While infection demonstrably mediates a pro-fibrotic response in host cells, it remains unclear if intrinsic properties of the upper genital tract exacerbate chlamydial fibrosis. The relatively sterile environment of the upper genital tract is primed for a pro-inflammatory response to infection, potentially enhancing fibrosis - however, subclinical C. trachomatis infections still develop fibrosis-related sequelae. Here, we compare infection-associated and steady-state gene expression of primary human cervical and vaginal epithelial cells. In the former, we observe enhanced baseline expression and infection-mediated induction of fibrosis-associated signal factors (e.g. TGFA , IL6 , IL8 , IL20 ), implying predisposition to Chlamydia -associated pro-fibrotic signaling. Transcription factor enrichment analysis identified regulatory targets of YAP, a transcriptional cofactor induced by infection of cervical epithelial cells, but not vaginal epithelial cells. YAP target genes induced by infection include secreted fibroblast-activating signal factors; therefore, we developed an in vitro model involving coculture of infected endocervical epithelial cells with uninfected fibroblasts. Coculture enhanced fibroblast expression of type I collagen, as well as prompting reproducible (albeit statistically insignificant) induction of α-smooth muscle actin. Fibroblast collagen induction was sensitive to siRNA-mediated YAP knockdown in infected epithelial cells, implicating chlamydial YAP activation in this effect. Collectively, our results present a novel mechanism of fibrosis initiated by Chlamydia, wherein infection-mediated induction of host YAP facilitates pro-fibrotic intercellular communication. Chlamydial YAP activation in cervical epithelial cells is thus a determinant of this tissue's susceptibility to fibrosis.

Importance

Chronic or repeated infection of the female upper genital tract by C. trachomatis can lead to severe fibrotic sequelae, including tubal factor infertility and ectopic pregnancy. However, the molecular mechanisms underlying this effect are unclear. In this report, we define a transcriptional program specific to C. trachomatis infection of the upper genital tract, identifying tissue-specific induction of host YAP - a pro-fibrotic transcriptional cofactor - as a potential driver of infection-mediated fibrotic gene expression. Further, we show that infected endocervical epithelial cells stimulate collagen production by fibroblasts, and implicate chlamydial induction of YAP in this effect. Our results define a mechanism by which infection mediates tissue-level fibrotic pathology via paracrine signaling, and identify YAP as a potential therapeutic target for prevention of Chlamydia -associated scarring of the female genital tract.

YAP1 and WWTR1 expression inversely correlates with neuroendocrine markers in Merkel cell carcinoma

BackgroundMerkel cell carcinoma (MCC) is an aggressive neuroendocrine (NE) skin cancer caused by severe UV-induced mutations or expression of Merkel cell polyomavirus (MCPyV) large and small T antigens (LT and ST). Despite deep genetic differences between MCPyV-positive and -negative subtypes, current clinical diagnostic markers are indistinguishable, and the expression profile of MCC tumors is, to our knowledge, unexplored.MethodsHere, we leveraged bulk and single-cell RNA-Seq of patient-derived tumor biopsies and cell lines to explore the underlying transcriptional environment of MCC.ResultsStrikingly, MCC samples could be separated into transcriptional subtypes that were independent of MCPyV status. Instead, we observed an inverse correlation between a NE gene signature and the Hippo pathway transcription factors Yes1-associated transcriptional regulator (YAP1) and WW domain-containing transcriptional regulator 1 (WWTR1). This inverse correlation was broadly present at the transcript and protein levels in the tumor biopsies as well as in established and patient-derived cell lines. Mechanistically, expression of YAP1 or WWTR1 in a MCPyV-positive MCC cell line induced cell-cycle arrest at least in part through TEA domain-dependent (TEAD-dependent) transcriptional repression of MCPyV LT.ConclusionThese findings identify what we believe to be a previously unrecognized heterogeneity in NE gene expression within MCC and support a model of YAP1/WWTR1 silencing as essential for the development of MCPyV-positive MCC.FundingUS Public Health Service grants R35CA232128, P01CA203655, and P30CA06516.

The oncogenic roles and clinical implications of YAP/TAZ in breast cancer

Breast cancer (BC) is the most commonly diagnosed form of cancer and a leading cause of cancer-related deaths among women worldwide. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are homologous transcriptional coactivators and downstream effectors of Hippo signalling. YAP/TAZ activation has been revealed to play essential roles in multiple events of BC development, including tumour initiation, progression, metastasis, drug resistance and stemness regulations. In this review, we will first give an overview of YAP/TAZ-mediated oncogenesis in BC, and then systematically summarise the oncogenic roles of YAP/TAZ in various BC subtypes, BC stem cells (BCSCs) and tumour microenvironments (TMEs). Based on these findings, we will further discuss the clinical implications of YAP/TAZ-based targeted therapies in BC and the potential future direction.

Coordinating gene expression during the cell cycle

Cell cycle-dependent gene transcription is tightly controlled by the retinoblastoma (RB):E2F and DREAM complexes, which repress all cell cycle genes during quiescence. Cyclin-dependent kinase (CDK) phosphorylation of RB and DREAM allows for the expression of two gene sets. The first set of genes, with peak expression in G1/S, is activated by E2F transcription factors (TFs) and is required for DNA synthesis. The second set, with maximum expression during G2/M, is required for mitosis and is coordinated by the MuvB complex, together with B-MYB and Forkhead box M1 (FOXM1). In this review, we summarize the key findings that established the distinct control mechanisms regulating G1/S and G2/M gene expression in mammals and discuss recent advances in the understanding of the temporal control of these genes.

A calpain-6/YAP axis in sarcoma stem cells that drives the outgrowth of tumors and metastases

Sarcomas include cancer stem cells, but how these cells contribute to local and metastatic relapse is largely unknown. We previously showed the pro-tumor functions of calpain-6 in sarcoma stem cells. Here, we use an osteosarcoma cell model, osteosarcoma tissues and transcriptomic data from human tumors to study gene patterns associated with calpain-6 expression or suppression. Calpain-6 modulates the expression of Hippo pathway genes and stabilizes the hippo effector YAP. It also modulates the vesicular trafficking of β-catenin degradation complexes. Calpain-6 expression is associated with genes of the G2M phase of the cell cycle, supports G2M-related YAP activities and up-regulated genes controlling mitosis in sarcoma stem cells and tissues. In mouse models of bone sarcoma, most tumor cells expressed calpain-6 during the early steps of tumor out-growth. YAP inhibition prevented the neoformation of primary tumors and metastases but had no effect on already developed tumors. It could even accelerate lung metastasis associated with large bone tumors by affecting tumor-associated inflammation in the host tissues. Our results highlight a specific mechanism involving YAP transcriptional activity in cancer stem cells that is crucial during the early steps of tumor and metastasis outgrowth and that could be targeted to prevent sarcoma relapse.

Chromatin-bound RB targets promoters, enhancers, and CTCF-bound loci and is redistributed by cell-cycle progression

The interaction of RB with chromatin is key to understanding its molecular functions. Here, for first time, we identify the full spectrum of chromatin-bound RB. Rather than exclusively binding promoters, as is often described, RB targets three fundamentally different types of loci (promoters, enhancers, and insulators), which are largely distinguishable by the mutually exclusive presence of E2F1, c-Jun, and CTCF. While E2F/DP facilitates RB association with promoters, AP-1 recruits RB to enhancers. Although phosphorylation in CDK sites is often portrayed as releasing RB from chromatin, we show that the cell cycle redistributes RB so that it enriches at promoters in G1 and at non-promoter sites in cycling cells. RB-bound promoters include the classic E2F-targets and are similar between lineages, but RB-bound enhancers associate with different categories of genes and vary between cell types. Thus, RB has a well-preserved role controlling E2F in G1, and it targets cell-type-specific enhancers and CTCF sites when cells enter S-phase.

Structure of a nucleosome-bound MuvB transcription factor complex reveals DNA remodelling

Genes encoding the core cell cycle machinery are transcriptionally regulated by the MuvB family of protein complexes in a cell cycle-specific manner. Complexes of MuvB with the transcription factors B-MYB and FOXM1 activate mitotic genes during cell proliferation. The mechanisms of transcriptional regulation by these complexes are still poorly characterised. Here, we combine biochemical analysis and in vitro reconstitution, with structural analysis by cryo-electron microscopy and cross-linking mass spectrometry, to functionally examine these complexes. We find that the MuvB:B-MYB complex binds and remodels nucleosomes, thereby exposing nucleosomal DNA. This remodelling activity is supported by B-MYB which directly binds the remodelled DNA. Given the remodelling activity on the nucleosome, we propose that the MuvB:B-MYB complex functions as a pioneer transcription factor complex. In this work, we rationalise prior biochemical and cellular studies and provide a molecular framework of interactions on a protein complex that is key for cell cycle regulation.

Structure and function of MuvB complexes

Proper progression through the cell-division cycle is critical to normal development and homeostasis and is necessarily misregulated in cancer. The key to cell-cycle regulation is the control of two waves of transcription that occur at the onset of DNA replication (S phase) and mitosis (M phase). MuvB complexes play a central role in the regulation of these genes. When cells are not actively dividing, the MuvB complex DREAM represses G1/S and G2/M genes. Remarkably, MuvB also forms activator complexes together with the oncogenic transcription factors B-MYB and FOXM1 that are required for the expression of the mitotic genes in G2/M. Despite this essential role in the control of cell division and the relationship to cancer, it has been unclear how MuvB complexes inhibit and stimulate gene expression. Here we review recent discoveries of MuvB structure and molecular interactions, including with nucleosomes and other chromatin-binding proteins, which have led to the first mechanistic models for the biochemical function of MuvB complexes.

Context-dependent transcriptional regulations of YAP/TAZ in stem cell and differentiation

Hippo pathway is initially identified as a master regulator for cell proliferation and organ size control, and the subsequent researches show this pathway is also involved in development, tissue regeneration and homeostasis, inflammation, immunity and cancer. YAP/TAZ, the downstream effectors of Hippo pathway, usually act as coactivators and are dependent on other transcription factors to mediate their transcriptional outputs. In this review, we will first provide an overview on the core components and regulations of Hippo pathway in mammals, and then systematically summarize the identified transcriptional factors or partners that are responsible for the transcriptional output of YAP/TAZ in stem cell and differentiation. More than that, we will discuss the potential applications and future directions based on these findings.

LncRNA lncAY is upregulated by sulfatide via Myb/MEF2C acetylation to promote the tumorigenicity of hepatocellular carcinoma cells

LncRNA (long noncoding RNA) is often dysregulated in tumors especially hepatocellular carcinoma (HCC). However, the dysregulation mechanism of lncRNAs is largely unknown. Here, we showed that lncRNA lncAY expression was stimulated in HCC by either endogenous or exogenous sulfatide. Elevated lncAY promoted HCC cell migration or angiogenesis, whereas lncAY silence suppressed HCC cell migration and proliferation. Interestingly, the activity of lncAY gene promoter was enhanced by sulfatide. Then Myb and MEF2C were identified as the transcription factors responsible for the stimulation of lncAY promoter activity and transcription by sulfatide. Both Myb and MEF2C enrichment on lncAY promoter was further confirmed, and their occupancy on lncAY promoter was strengthened by sulfatide for Myb or MEF2C was acetylated. Mutant Myb-K456A exhibited reduced acetylation and weak stimulation for lncAY transcription. However, Myb mutation K456/503A prevented Myb from acetylation induced by sulfatide. The mutant Myb K456/503A further was unable to occupy lncAY promoter and enhance lncAY transcription. In conclusion, this study demonstrated lncAY transcription was abnormally upregulated by sulfatide in HCC through Myb/MEF2C to promote HCC progression.

The Hippo Signaling Pathway in Cancer: A Cell Cycle Perspective

Simple Summary

Cancer is increasingly viewed as a cell cycle disease in that the dysregulation of the cell cycle machinery is a common feature in cancer. The Hippo signaling pathway consists of a core kinase cascade as well as extended regulators, which together control organ size and tissue homeostasis. The aberrant expression of cell cycle regulators and/or Hippo pathway components contributes to cancer development, and for this reason, we specifically focus on delineating the roles of the Hippo pathway in the cell cycle. Improving our understanding of the Hippo pathway from a cell cycle perspective could be used as a powerful weapon in the cancer battlefield.

Abstract

Cell cycle progression is an elaborate process that requires stringent control for normal cellular function. Defects in cell cycle control, however, contribute to genomic instability and have become a characteristic phenomenon in cancers. Over the years, advancement in the understanding of disrupted cell cycle regulation in tumors has led to the development of powerful anti-cancer drugs. Therefore, an in-depth exploration of cell cycle dysregulation in cancers could provide therapeutic avenues for cancer treatment. The Hippo pathway is an evolutionarily conserved regulator network that controls organ size, and its dysregulation is implicated in various types of cancers. Although the role of the Hippo pathway in oncogenesis has been widely investigated, its role in cell cycle regulation has not been comprehensively scrutinized. Here, we specifically focus on delineating the involvement of the Hippo pathway in cell cycle regulation. To that end, we first compare the structural as well as functional conservation of the core Hippo pathway in yeasts, flies, and mammals. Then, we detail the multi-faceted aspects in which the core components of the mammalian Hippo pathway and their regulators affect the cell cycle, particularly with regard to the regulation of E2F activity, the G1 tetraploidy checkpoint, DNA synthesis, DNA damage checkpoint, centrosome dynamics, and mitosis. Finally, we briefly discuss how a collective understanding of cell cycle regulation and the Hippo pathway could be weaponized in combating cancer.

DREAM On: Cell Cycle Control in Development and Disease

Perfectly orchestrated periodic gene expression during cell cycle progression is essential for maintaining genome integrity and ensuring that cell proliferation can be stopped by environmental signals. Genetic and proteomic studies during the past two decades revealed remarkable evolutionary conservation of the key mechanisms that control cell cycle-regulated gene expression, including multisubunit DNA-binding DREAM complexes. DREAM complexes containing a retinoblastoma family member, an E2F transcription factor and its dimerization partner, and five proteins related to products of Caenorhabditis elegans multivulva (Muv) class B genes lin-9, lin-37, lin-52, lin-53, and lin-54 (comprising the MuvB core) have been described in diverse organisms, from worms to humans. This review summarizes the current knowledge of the structure, function, and regulation of DREAM complexes in different organisms, as well as the role of DREAM in human disease. Expected final online publication date for the Annual Review of Genetics, Volume 55 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Emerging Principles in the Transcriptional Control by YAP and TAZ

Simple Summary

YAP and TAZ are transcriptional cofactors that integrate several upstream signals to generate context-dependent transcriptional responses. This requires extensive integration with epigenetic regulators and other transcription factors. The molecular and genomic characterization of YAP and TAZ nuclear function has broad implications both in physiological and pathological settings.

Abstract

Yes-associated protein (YAP) and TAZ are transcriptional cofactors that sit at the crossroad of several signaling pathways involved in cell growth and differentiation. As such, they play essential functions during embryonic development, regeneration, and, once deregulated, in cancer progression. In this review, we will revise the current literature and provide an overview of how YAP/TAZ control transcription. We will focus on data concerning the modulation of the basal transcriptional machinery, their ability to epigenetically remodel the enhancer–promoter landscape, and the mechanisms used to integrate transcriptional cues from multiple pathways. This reveals how YAP/TAZ activation in cancer cells leads to extensive transcriptional control that spans several hallmarks of cancer. The definition of the molecular mechanism of transcriptional control and the identification of the pathways regulated by YAP/TAZ may provide therapeutic opportunities for the effective treatment of YAP/TAZ-driven tumors.

Nuclear translocation of MTL5 from cytoplasm requires its direct interaction with LIN9 and is essential for male meiosis and fertility

Meiosis is essential for the generation of gametes and sexual reproduction, yet the factors and underlying mechanisms regulating meiotic progression remain largely unknown. Here, we showed that MTL5 translocates into nuclei of spermatocytes during zygotene-pachytene transition and ensures meiosis advances beyond pachytene stage. MTL5 shows strong interactions with MuvB core complex components, a well-known transcriptional complex regulating mitotic progression, and the zygotene-pachytene transition of MTL5 is mediated by its direct interaction with the component LIN9, through MTL5 C-terminal 443–475 residues. Male Mtl5^c-mu/c-mu mice expressing the truncated MTL5 (p.Ser445Arg fs*3) that lacks the interaction with LIN9 and is detained in cytoplasm showed male infertility and spermatogenic arrest at pachytene stage, same as that of Mtl5 knockout mice, indicating that the interaction with LIN9 is essential for the nuclear translocation and function of MTL5 during meiosis. Our data demonstrated MTL5 translocates into nuclei during the zygotene-pachytene transition to initiate its function along with the MuvB core complex in pachytene spermatocytes, highlighting a new mechanism regulating the progression of male meiosis.

Meiosis is essential for spermatogenesis and male fertility. However, the factors regulating the progression of meiosis remain largely unknown. We reported the testis specific protein MTL5 translocated into the nuclei of spermatocytes at the zygotene-pachytene transition by direct interaction with LIN9, which is an essential component of MuvB core complex, to promote meiotic progression beyond the pachytene stage. We also showed that MTL5 pulls down MYBL1 and all of the MuvB core complex (except LIN54) in spermatocytes. Given the known role of the MuvB core complex as a cell cycle regulator in mitotic cells, we suggested that MTL5 promotes meiotic progression along with the MuvB core complex to ensure male fertility. Our results indicated a novel function of the MuvB complex in male meiosis and also shed light on the master regulator proteins that control meiotic progression at the pachytene stage. MTL5 is a novel and germ-cell specific regulator of cell cycle progression to function at a specific stage by nuclear translocation in meiosis.

Cellular feedback dynamics and multilevel regulation driven by the hippo pathway

The Hippo pathway is a dynamic cellular signalling nexus that regulates differentiation and controls cell proliferation and death. If the Hippo pathway is not precisely regulated, the functionality of the upstream kinase module is impaired, which increases nuclear localisation and activity of the central effectors, the transcriptional co-regulators YAP and TAZ. Pathological YAP and TAZ hyperactivity consequently cause cancer, fibrosis and developmental defects. The Hippo pathway controls an array of fundamental cellular processes, including adhesion, migration, mitosis, polarity and secretion of a range of biologically active components. Recent studies highlight that spatio-temporal regulation of Hippo pathway components are central to precisely controlling its context-dependent dynamic activity. Several levels of feedback are integrated into the Hippo pathway, which is further synergized with interactors outside of the pathway that directly regulate specific Hippo pathway components. Likewise, Hippo core kinases also ‘moonlight’ by phosphorylating multiple substrates beyond the Hippo pathway and thereby integrates further flexibility and robustness in the cellular decision-making process. This topic is still in its infancy but promises to reveal new fundamental insights into the cellular regulation of this therapeutically important pathway. We here highlight recent advances emphasising feedback dynamics and multilevel regulation of the Hippo pathway with a focus on mitosis and cell migration, as well as discuss potential productive future research avenues that might reveal novel insights into the overall dynamics of the pathway.

IQGAP3, a YAP Target, Is Required for Proper Cell-Cycle Progression and Genome Stability

Controlling cell proliferation is critical for organism development, tissue homeostasis, disease, and regeneration. IQGAP3 has been shown to be required for proper cell proliferation and migration, and is associated to a number of cancers. Moreover, its expression is inversely correlated with the overall survival rate in the majority of cancers. Here, we show that IQGAP3 expression is elevated in cervical cancer and that in these cancers IQGAP3 high expression is correlated with an increased lethality. Furthermore, we demonstrate that IQGAP3 is a target of YAP, a regulator of cell cycle gene expression. IQGAP3 knockdown resulted in an increased percentage of HeLa cells in S phase, delayed progression through mitosis, and caused multipolar spindle formation and consequentially aneuploidy. Protein-protein interaction studies revealed that IQGAP3 interacts with MMS19, which is known in Drosophila to permit, by competitive binding to Xpd, Cdk7 to be fully active as a Cdk-activating kinase (CAK). Notably, IQGAP3 knockdown caused decreased MMS19 protein levels and XPD knockdown partially rescued the reduced proliferation rate upon IQGAP3 knockdown. This suggests that IQGAP3 modulates the cell cycle via the MMS19/XPD/CAK axis. Thus, in addition to governing proliferation and migration, IQGAP3 is a critical regulator of mitotic progression and genome stability. IMPLICATIONS: Our data indicate that, while IQGAP3 inhibition might be initially effective in decreasing cancer cell proliferation, this approach harbors the risk to promote aneuploidy and, therefore, the formation of more aggressive cancers.

YAP inactivation in estrogen receptor alpha-positive hepatocellular carcinoma with less aggressive behavior

The expression of estrogen receptor alpha (ERα, encoded by ESR1) has been shown to be associated with the prognostic outcomes of patients in various cancers; however, its prognostic and mechanistic significance in hepatocellular carcinoma (HCC) remain unclear. Here, we evaluated the expression of ERα and its association with clinicopathological features in 339 HCC patients. ERα was expressed in 9.4% (32/339) of HCCs and was related to better overall survival (OS; hazard ratio [HR] = 0.11, p = 0.009, 95% C.I. = 0.016–0.82) and disease-free survival (DFS, HR = 0.4, p = 0.013, 95% C.I. = 0.18–0.85). ERα expression was also associated with features related to more favorable prognosis, such as older age, lower serum alpha-fetoprotein level, and less microvascular invasion (p < 0.05). In addition, to obtain mechanistic insights into the role of ERα in HCC progression, we performed integrative transcriptome data analyses, which revealed that yes-associated protein (YAP) pathway was significantly suppressed in ESR1-expressing HCCs. By performing cell culture experiments, we validated that ERα expression enhanced YAP phosphorylation, attenuating its nuclear translocation, which in turn suppressed the downstream signaling pathways and cancer cell growth. In conclusion, we suggest that ERα expression is an indicator of more favorable prognosis in HCC and that this effect is mediated by inactivation of YAP signaling. Our results provide new clinical and pathobiological insights into ERα and YAP signaling in HCC.

Estrogen receptor signaling can act as a brake preventing the progression of an often deadly form of liver cancer. Studies have shown that women are at a lower risk of developing and succumbing to hepatocellular carcinoma (HCC) than men, suggesting a potential role for sex hormones. Researchers in South Korea led by Hyun Goo Woo of the Ajou University School of Medicine, Suwon, and Young Nyun Park of Yonsei University College of Medicine, Seoul, have now shown that expression of the estrogen receptor α is a strong prognostic predictor for HCC. In a survey of patient tumor samples, they found that expression of this hormone receptor is associated with nearly a tenfold increased likelihood of survival. The researchers identified a mechanism by which estrogen receptor α signaling impedes cancerous growth, revealing potential new drug targets.

Heterozygous Loss of Yap1 in Mice Causes Progressive Cataracts

Purpose

Yap1 encodes an evolutionarily conserved transcriptional coactivator and functions as a down-stream effector of the Hippo signaling pathway that controls tissue size and cell growth. Yap1 contributes to lens epithelial development. However, the effect of Yap1 haplodeficiency on the lens epithelium and its role in the development of cataracts has not been reported. The aim of the current study is to investigate Yap1 function and its regulatory mechanisms in lens epithelial cells (LECs).

Methods

Lens phenotypes were investigated in Yap1 heterozygous mutant mice by visual observation and histological and biochemical methods. Primary LEC cultures were used to study regulatory molecular mechanism.

Results

The heterozygous inactivation of Yap1 in mice caused cataracts during adulthood with defective LEC phenotypes. Despite a normal early development of the eye including the lens, the majority of Yap1 heterozygotes developed cataracts in the first six months of age. Cataract was preceded by multiple morphological defects in the lens epithelium, including decreased cell density and abnormal cell junctions. The low LEC density was coincident with reduced LEC proliferation. In addition, expression of the Yap1 target gene Crim1 was reduced in the Yap1^+/− LEC, and overexpression of Crim1 restored Yap1^+/− LEC cell proliferation in vitro.

Conclusions

Homozygosity of the Yap1 gene was critical for adequate Crim1 expression needed to maintain the constant proliferation of LEC and to maintain a normal-sized lens. Yap1 haplodeficiency leads to cataracts.

MYBL2 and ATM suppress replication stress in pluripotent stem cells

Replication stress, a major cause of genome instability in cycling cells, is mainly prevented by the ATR-dependent replication stress response pathway in somatic cells. However, the replication stress response pathway in embryonic stem cells (ESCs) may be different due to alterations in cell cycle phase length. The transcription factor MYBL2, which is implicated in cell cycle regulation, is expressed a hundred to a thousand-fold more in ESCs compared with somatic cells. Here we show that MYBL2 activates ATM and suppresses replication stress in ESCs. Consequently, loss of MYBL2 or inhibition of ATM or Mre11 in ESCs results in replication fork slowing, increased fork stalling and elevated origin firing. Additionally, we demonstrate that inhibition of CDC7 activity rescues replication stress induced by MYBL2 loss and ATM inhibition, suggesting that uncontrolled new origin firing may underlie the replication stress phenotype resulting from loss/inhibition of MYBL2 and ATM. Overall, our study proposes that in addition to ATR, a MYBL2-MRN-ATM replication stress response pathway functions in ESCs to control DNA replication initiation and prevent genome instability.

Aberrant transcriptional and post-transcriptional regulation of SPAG5, a YAP-TAZ-TEAD downstream effector, fuels breast cancer cell proliferation

Sperm-associated antigen 5 (SPAG5) is an important driver of the cell mitotic spindle required for chromosome segregation and progression into anaphase. SPAG5 has been identified as an important proliferation marker and chemotherapy-sensitivity predictor, especially in estrogen receptor-negative breast cancer subtypes. Here, we report that SPAG5 is a direct target of miR-10b-3p, and its aberrantly high expression associates with poor disease-free survival in two large cohorts of breast cancer patients. SPAG5 depletion strongly impaired cancer cell cycle progression, proliferation, and migration. Interestingly, high expression of SPAG5 pairs with a YAP/TAZ-activated signature in breast cancer patients. Reassuringly, the depletion of YAP, TAZ, and TEAD strongly reduced SPAG5 expression and diminished its oncogenic effects. YAP, TAZ coactivators, and TEAD transcription factors are key components of the Hippo signaling pathway involved in tumor initiation, progression, and metastasis. Furthermore, we report that SPAG5 is a direct transcriptional target of TEAD/YAP/TAZ, and pharmacological targeting of YAP and TAZ severely reduces SPAG5 expression. Collectively, our data uncover an oncogenic feedback loop, comprising miR-10b-3p, SPAG5, and YAP/TAZ/TEAD, which fuels the aberrant proliferation of breast cancer.

MYBL2 disrupts the Hippo-YAP pathway and confers castration resistance and metastatic potential in prostate cancer

Rationale: Resistance to androgen-deprivation therapy (ADT) associated with metastatic progression remains a challenging clinical task in prostate cancer (PCa) treatment. Current targeted therapies for castration-resistant prostate cancer (CRPC) are not durable. The exact molecular mechanisms mediating resistance to castration therapy that lead to CRPC progression remain obscure. Methods: The expression of MYB proto-oncogene like 2 (MYBL2) was evaluated in PCa samples. The effect of MYBL2 on the response to ADT was determined by in vitro and in vivo experiments. The survival of patients with PCa was analyzed using clinical specimens (n = 132) and data from The Cancer Genome Atlas (n = 450). The mechanistic model of MYBL2 in regulating gene expression was further detected by subcellular fractionation, western blotting, quantitative real-time PCR, chromatin immunoprecipitation, and luciferase reporter assays. Results: MYBL2 expression was significantly upregulated in CRPC tissues and cell lines. Overexpression of MYBL2 could facilitate castration-resistant growth and metastatic capacity in androgen-dependent PCa cells by promoting YAP1 transcriptional activity via modulating the activity of the Rho GTPases RhoA and LATS1 kinase. Importantly, targeting MYBL2, or treatment with either the YAP/TAZ inhibitor Verteporfin or the RhoA inhibitor Simvastatin, reversed the resistance to ADT and blocked bone metastasis in CRPC cells. Finally, high MYBL2 levels were positively associated with TNM stage, total PSA level, and Gleason score and predicted a higher risk of metastatic relapse and poor prognosis in patients with PCa. Conclusions: Our results reveal a novel molecular mechanism conferring resistance to ADT and provide a strong rationale for potential therapeutic strategies against CRPC.

The common YAP activation mediates corneal epithelial regeneration and repair with different-sized wounds

Regeneration/repair after injury can be endowed by adult stem cells (ASCs) or lineage restricted and even terminally differentiated cells. In corneal epithelium, regeneration after a large wound depends on ASCs (limbal epithelial stem cells, LESCs), whereas repair after a small wound is LESCs-independent. Here, using rat corneal epithelial wounds with different sizes, we show that YAP activation promotes the activation and expansion of LESCs after a large wound, as well as the reprogramming of local epithelial cells (repairing epithelial cells) after a small wound, which contributes to LESCs-dependent and -independent wound healing, respectively. Mechanically, we highlight that the reciprocal regulation of YAP activity and the assembly of cell junction and cortical F-actin cytoskeleton accelerates corneal epithelial healing with different-sized wounds. Together, the common YAP activation and the underlying regulatory mechanism are harnessed by LESCs and lineage-restricted epithelial cells to cope with corneal epithelial wounds with different sizes.

MYB oncoproteins: emerging players and potential therapeutic targets in human cancer

MYB transcription factors are highly conserved from plants to vertebrates, indicating that their functions embrace fundamental mechanisms in the biology of cells and organisms. In humans, the MYB gene family is composed of three members: MYB, MYBL1 and MYBL2, encoding the transcription factors MYB, MYBL1, and MYBL2 (also known as c-MYB, A-MYB, and B-MYB), respectively. A truncated version of MYB, the prototype member of the MYB family, was originally identified as the product of the retroviral oncogene v-myb, which causes leukaemia in birds. This led to the hypothesis that aberrant activation of vertebrate MYB could also cause cancer. Despite more than three decades have elapsed since the isolation of v-myb, only recently investigators were able to detect MYB genes rearrangements and mutations, smoking gun evidence of the involvement of MYB family members in human cancer. In this review, we will highlight studies linking the activity of MYB family members to human malignancies and experimental therapeutic interventions tailored for MYB-expressing cancers.

Cooperation Between MYC and β-Catenin in Liver Tumorigenesis Requires Yap/Taz

BACKGROUND AND AIMS

Activation of MYC and catenin beta-1 (CTNNB1, encoding β-catenin) can co-occur in liver cancer, but how these oncogenes cooperate in tumorigenesis remains unclear.

APPROACH AND RESULTS

We generated a mouse model allowing conditional activation of MYC and WNT/β-catenin signaling (through either β-catenin activation or loss of APC - adenomatous polyposis coli) upon expression of CRE recombinase in the liver and monitored their effects on hepatocyte proliferation, apoptosis, gene expression profiles, and tumorigenesis. Activation of WNT/β-catenin signaling strongly accelerated MYC-driven carcinogenesis in the liver. Both pathways also cooperated in promoting cellular transformation in vitro, demonstrating their cell-autonomous action. Short-term induction of MYC and β-catenin in hepatocytes, followed by RNA-sequencing profiling, allowed the identification of a "Myc/β-catenin signature," composed of a discrete set of Myc-activated genes whose expression increased in the presence of active β-catenin. Notably, this signature enriched for targets of Yes-associated protein (Yap) and transcriptional coactivator with PDZ-binding motif (Taz), two transcriptional coactivators known to be activated by WNT/β-catenin signaling and to cooperate with MYC in mitogenic activation and liver transformation. Consistent with these regulatory connections, Yap/Taz accumulated upon Myc/β-catenin activation and were required not only for the ensuing proliferative response, but also for tumor cell growth and survival. Finally, the Myc/β-catenin signature was enriched in a subset of human hepatocellular carcinomas characterized by comparatively poor prognosis.

CONCLUSIONS

Myc and β-catenin show a strong cooperative action in liver carcinogenesis, with Yap and Taz serving as mediators of this effect. These findings warrant efforts toward therapeutic targeting of Yap/Taz in aggressive liver tumors marked by elevated Myc/β-catenin activity.

Genome-wide CRISPR screens of oral squamous cell carcinoma reveal fitness genes in the Hippo pathway

New therapeutic targets for oral squamous cell carcinoma (OSCC) are urgently needed. We conducted genome-wide CRISPR-Cas9 screens in 21 OSCC cell lines, primarily derived from Asians, to identify genetic vulnerabilities that can be explored as therapeutic targets. We identify known and novel fitness genes and demonstrate that many previously identified OSCC-related cancer genes are non-essential and could have limited therapeutic value, while other fitness genes warrant further investigation for their potential as therapeutic targets. We validate a distinctive dependency on YAP1 and WWTR1 of the Hippo pathway, where the lost-of-fitness effect of one paralog can be compensated only in a subset of lines. We also discover that OSCCs with WWTR1 dependency signature are significantly associated with biomarkers of favorable response toward immunotherapy. In summary, we have delineated the genetic vulnerabilities of OSCC, enabling the prioritization of therapeutic targets for further exploration, including the targeting of YAP1 and WWTR1.

Interaction of YAP with the Myb-MuvB (MMB) complex defines a transcriptional program to promote the proliferation of cardiomyocytes

The Hippo signalling pathway and its central effector YAP regulate proliferation of cardiomyocytes and growth of the heart. Using genetic models in mice we show that the increased proliferation of embryonal and postnatal cardiomyocytes due to loss of the Hippo-signaling component SAV1 depends on the Myb-MuvB (MMB) complex. Similarly, proliferation of postnatal cardiomyocytes induced by constitutive active YAP requires MMB. Genome studies revealed that YAP and MMB regulate an overlapping set of cell cycle genes in cardiomyocytes. Protein-protein interaction studies in cell lines and with recombinant proteins showed that YAP binds directly to B-MYB, a subunit of MMB, in a manner dependent on the YAP WW domains and a PPXY motif in B-MYB. Disruption of the interaction by overexpression of the YAP binding domain of B-MYB strongly inhibits the proliferation of cardiomyocytes. Our results point to MMB as a critical downstream effector of YAP in the control of cardiomyocyte proliferation.

YAP, the major downstream transducer of the Hippo pathway, is a potent inducer of proliferation. Here we show that the Myb-MuvB complex (MMB) mediates cardiomyocyte proliferation by YAP. We find that YAP and MMB regulate an overlapping set of pro-proliferative genes which involves binding of MMB to the promoters of these genes. We also identified a direct interaction between the B-MYB subunit of MMB and YAP. Based on the binding studies, we created a tool called MY-COMP that interferes with the association YAP to B-MYB and strongly inhibits proliferation of cardiomyocytes. Together, our data suggests that the YAP-MMB interaction is essential for division of cardiomyocytes, underscoring the functional relevance of the crosstalk between these two pathways for proper heart development.

One way to rule them all: G2/M gene regulation by oncogenic YAP1 and B-MYB

The Hippo pathway plays a major role in regulating organ size during embryogenesis. Loss of Hippo signaling can cause cancer due to unrestricted cell proliferation. Recently we found that Yes-associated protein 1 (YAP1), the major downstream effector of Hippo, promotes mitotic gene expression and proliferation through binding and activating the Myb-MuvB (MMB) complex subunit MYB proto-oncogene like 2 (B-MYB).