A temporal requirement for Hippo signaling in mammary gland differentiation, growth, and tumorigenesis

YAP increases response to Trastuzumab in HER2-positive Breast Cancer by enhancing P73-induced apoptosis

The role of the Yes-associated protein (YAP) in oncogenesis and progression of breast cancer remains controversial. Meanwhile, development of therapeutic resistance to trastuzumab, a common breast cancer treatment administered after chemotherapy, is a significant challenge in the treatment of HER2-positive breast cancer. We, therefore, analyzed the role of YAP in trastuzumab resistance in HER2-positive-breast carcinoma cells in vitro and evaluated the status of YAP and related proteins in patient-derived breast carcinoma tissues by immunohistochemistry. YAP expression was observed in both BT474-TS (trastuzumab-sensitive) and BT474-TR (trastuzumab-resistant) cells. Treatment with trastuzumab increased expression of nuclear-YAP (N-YAP) in BT474-TS cells, whereas BT474-TR cells showed a decrease in N-YAP expression following trastuzumab treatment. YAP silencing significantly reduced trastuzumab-induced inhibitory effects in BT474-TS cells. YAP-silenced cells also showed decreased apoptosis and significantly lower p73 levels following trastuzumab treatment. Combined protein kinase B (AKT) inhibitor-trastuzumab treatment significantly inhibited BT474-TR cell proliferation, resulting in increased N-YAP and p73 expression, as well as apoptosis. In both paclitaxel, doxorubicin and cyclophosphamide (TAC)-treated, and docetaxel, carboplatin, and trastuzumab (TCbH)-treated groups; the pathological complete response (pCR) ratios were inversely correlated with p-AKT status in biopsy specimens, while YAP and p73 status were positively correlated with the pCR ratio in the biopsy specimens of the TCbH group. Our results show that YAP is involved in trastuzumab resistance in HER2-positive breast carcinoma cells and that YAP and AKT may be developed as prognostic markers of neoadjuvant trastuzumab therapy in patients with HER2-positive breast cancer.

YAP and TAZ Are Not Identical Twins

Yes-associated protein (YAP) and TAZ (WW domain containing transcription regulator 1, or WWTR1) are paralog transcriptional regulators, able to integrate mechanical, metabolic, and signaling inputs to regulate cell growth and differentiation during development and neoplastic progression. YAP and TAZ hold common and distinctive structural features, reflecting only partially overlapping regulatory mechanisms. The two paralogs interact with both shared and specific transcriptional partners and control nonidentical transcriptional programs. Although most of the available literature considers YAP and TAZ as functionally redundant, they play distinctive or even contrasting roles in different contexts. The issue of their divergent roles is currently underexplored but holds fundamental implications for mechanistic and translational studies. Here, we aim to review the available literature on the biological functions of YAP and TAZ, highlighting differential roles that distinguish these two paralogues.

Network-based multi-task learning models for biomarker selection and cancer outcome prediction

MOTIVATION

Detecting cancer gene expression and transcriptome changes with mRNA-sequencing or array-based data are important for understanding the molecular mechanisms underlying carcinogenesis and cellular events during cancer progression. In previous studies, the differentially expressed genes were detected across patients in one cancer type. These studies ignored the role of mRNA expression changes in driving tumorigenic mechanisms that are either universal or specific in different tumor types. To address the problem, we introduce two network-based multi-task learning frameworks, NetML and NetSML, to discover common differentially expressed genes shared across different cancer types as well as differentially expressed genes specific to each cancer type. The proposed frameworks consider the common latent gene co-expression modules and gene-sample biclusters underlying the multiple cancer datasets to learn the knowledge crossing different tumor types.

RESULTS

Large-scale experiments on simulations and real cancer high-throughput datasets validate that the proposed network-based multi-task learning frameworks perform better sample classification compared with the models without the knowledge sharing across different cancer types. The common and cancer-specific molecular signatures detected by multi-task learning frameworks on The Cancer Genome Atlas ovarian, breast and prostate cancer datasets are correlated with the known marker genes and enriched in cancer-relevant Kyoto Encyclopedia of Genes and Genome pathways and gene ontology terms.

AVAILABILITY AND IMPLEMENTATION

Source code is available at: https://github.com/compbiolabucf/NetML.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Determination of the migration effect and molecular docking of verteporfin in different subtypes of breast cancer cells

Breast cancer is one of the most aggressive malignant tumors in women. According to the expression differences of estrogen receptor, progesterone receptor, human epidermal growth factor receptor-2 (HER-2) and cell proliferation antigen Ki-67, breast cancer can be divided into four molecular subtypes: Luminal A, Luminal B, HER-2 overexpression and Basal-like. Yes-associated protein (YAP), a downstream effector of the Hippo pathway, is overexpressed in human cancers and is associated with proliferation, apoptosis, migration, invasion and resistance to chemotherapy drugs in breast cancer cells. Verteporfin (VP) is used as a photosensitizer in the treatment of neovascular macular degeneration. VP is also identified as an inhibitor of YAP/TEA domain transcription factor (TEAD) interaction in the absence of light activation. However, detailed structural information about VP and YAP interactions is relatively scarce and VP research targeting YAP in different molecular subtypes of breast cancer cells is also rare. The aims of the present study were to structurally describe the VP binding site in the YAP crystal structure and to verify the non-photoreactive VP effect targeting YAP on the migration of different molecular subtypes of breast cancer cells. The crystal structure of VP and YAP was calculated by AutoDock 4.2 and the result was illustrated using PyMOL. The non-photoactivated VP effect on the migration of Luminal A MCF-7, Luminal B BT-474 and triple-negative breast cancer BT-549 breast cancer cells was evaluated by wound healing and Transwell migration experiments. Results from molecular docking experiments demonstrated that VP could interact through hydrogen bonds and hydrophobic interactions with important YAP residues involved in TEADs binding (Gln82, Val84, Met86 and Arg89). Migration experiments revealed that the non-photoinduced VP could inhibit the migration of different molecular subtypes of breast cancer cells. The results of the present study indicated that VP may be a novel repositioned drug for breast cancer treatment in the future.

Therapeutic Targeting of Signaling Pathways Related to Cancer Stemness

The theory of cancer stem cells (CSCs) proposes that the different cells within a tumor, as well as metastasis deriving from it, are originated from a single subpopulation of cells with self-renewal and differentiation capacities. These cancer stem cells are supposed to be critical for tumor expansion and metastasis, tumor relapse and resistance to conventional therapies, such as chemo- and radiotherapy. The acquisition of these abilities has been attributed to the activation of alternative pathways, for instance, WNT, NOTCH, SHH, PI3K, Hippo, or NF-κB pathways, that regulate detoxification mechanisms; increase the metabolic rate; induce resistance to apoptotic, autophagic, and senescence pathways; promote the overexpression of drug transporter proteins; and activate specific stem cell transcription factors. The elimination of CSCs is an important goal in cancer therapeutic approaches because it could decrease relapses and metastatic dissemination, which are main causes of mortality in oncology patients. In this work, we discuss the role of these signaling pathways in CSCs along with their therapeutic potential.

Organotypic culture assays for murine and human primary and metastatic-site tumors

Cancer invasion and metastasis are challenging to study in vivo since they occur deep inside the body over extended time periods. Organotypic 3D culture of fresh tumor tissue enables convenient real-time imaging, genetic and microenvironmental manipulation and molecular analysis. Here, we provide detailed protocols to isolate and culture heterogenous organoids from murine and human primary and metastatic site tumors. The time required to isolate organoids can vary based on the tissue and organ type but typically takes <7 h. We describe a suite of assays that model specific aspects of metastasis, including proliferation, survival, invasion, dissemination and colony formation. We also specify comprehensive protocols for downstream applications of organotypic cultures that will allow users to (i) test the role of specific genes in regulating various cellular processes, (ii) distinguish the contributions of several microenvironmental factors and (iii) test the effects of novel therapeutics.

Yes‑associated protein protects and rescues SH‑SY5Y cells from ketamine‑induced apoptosis

Ketamine is a widely used intravenous anesthetic; however, basic and clinical studies have demonstrated that prolonged exposure can cause irreversible injury to the immature human brain. Yes-associated protein (YAP) is the main effector of the Hippo signaling pathway, which serves an important role in regulating tissue homeostasis and organ size during development. However, whether YAP mediates ketamine-induced apoptosis is not completely understood. Based on the functions of YAP during apoptosis resistance and cell self-renewal regulation, the present study hypothesized that YAP serves a role during ketamine-induced apoptosis. An in vitro model was utilized to investigate the effects of ketamine on neurotoxicity and to further investigate the role of YAP in ketamine-induced apoptosis using techniques including CCK-8 assay, flow cytometry and western blotting. The present study assessed the effects of YAP overexpression and knockdown on the expression of typical apoptotic markers in SH-SY5Y cells. Ketamine induced apoptosis in a dose-dependent manner, which was regulated by YAP. Following YAP overexpression, ketamine-treated SH-SY5Y cells displayed increased activity and viability, whereas expression levels of the apoptotic markers were decreased compared with the negative control group. By contrast, ketamine-induced apoptosis was enhanced following YAP knockdown. Collectively, the results of the present study indicated that YAP may serve an important role during ketamine-induced neurotoxicity, and alterations to YAP signaling may counteract ketamine-induced apoptosis. The neuroprotective effect of YAP activation may serve as a novel pharmacological target for the treatment of ketamine-induced neurotoxicity via neurogenesis normalization.

The Hippo pathway oncoprotein YAP promotes melanoma cell invasion and spontaneous metastasis

Melanoma is a deadly form of skin cancer that accounts for a disproportionally large proportion of cancer-related deaths in younger people. Compared with most other skin cancers, a feature of melanoma is its high metastatic capacity, although the mechanisms that confer this are not well understood. The Hippo pathway is a key regulator of organ growth and cell fate that is deregulated in many cancers. To analyse the Hippo pathway in cutaneous melanoma, we generated a transcriptional signature of melanoma cells that overexpressed YAP, the key downstream Hippo pathway oncoprotein. YAP-mediated transcriptional activity varied in melanoma cell lines but did not cluster with known genetic drivers of melanomagenesis such as BRAF and NRAS mutations. Instead, it correlated strongly with published gene expression profiles linked to melanoma cell invasiveness and varied throughout the metastatic cascade in melanoma patient tumours. Consistent with this, YAP was both necessary and sufficient for melanoma cell invasion in vitro. In vivo, YAP promoted spontaneous melanoma metastasis, whilst the growth of YAP-expressing primary tumours was impeded. Finally, we identified the YAP target genes AXL, THBS1 and CYR61 as key mediators of YAP-induced melanoma cell invasion. These data suggest that YAP is a critical regulator of melanoma metastasis.

A Potential Role of YAP/TAZ in the Interplay Between Metastasis and Metabolic Alterations

Yes-Associated Protein (YAP) and Transcriptional Co-activator with PDZ-binding Motif (TAZ) are the downstream effectors of the Hippo signaling pathway that play a crucial role in various aspects of cancer progression including metastasis. Metastasis is the multistep process of disseminating cancer cells in a body and responsible for the majority of cancer-related death. Emerging evidence has shown that cancer cells reprogram their metabolism to gain proliferation, invasion, migration, and anti-apoptotic abilities and adapt to various environment during metastasis. Moreover, it has increasingly been recognized that YAP/TAZ regulates cellular metabolism that is associated with the phenotypic changes, and recent studies suggest that the YAP/TAZ-mediated metabolic alterations contribute to metastasis. In this review, we will introduce the latest knowledge of YAP/TAZ regulation and function in cancer metastasis and metabolism, and discuss possible links between the YAP/TAZ-mediated metabolic reprogramming and metastasis.

Regulation and functions of the Hippo pathway in stemness and differentiation

The Hippo pathway plays important roles in organ development, tissue regeneration, and human diseases, such as cancer. In the canonical Hippo pathway, the MST1/2-LATS1/2 kinase cascade phosphorylates and inhibits transcription coactivators Yes-associated protein and transcription coactivator with PDZ-binding motif and thus regulates transcription of genes important for cell proliferation and apoptosis. However, recent studies have depicted a much more complicate picture of the Hippo pathway with many new components and regulatory stimuli involving both chemical and mechanical signals. Furthermore, accumulating evidence indicates that the Hippo pathway also plays important roles in the determination of cell fates, such as self-renewal and differentiation. Here, we review regulations of the Hippo pathway and its functions in stemness and differentiation emphasizing recent discoveries.

IGF-1/IGF-1R/FAK/YAP Transduction Signaling Prompts Growth Effects in Triple-Negative Breast Cancer (TNBC) Cells

Triple-negative breast cancer (TNBC) is an aggressive breast tumor subtype that currently lacks targeted treatment options. The role played by the insulin-like growth factor-1 (IGF-1) and its cognate receptor IGF-1R in TNBC has been reported. Nevertheless, the molecular mechanisms by which the IGF-1/IGF-1R system may contribute to TNBC progression still remains to be fully understood. By computational analysis of the vast cancer genomics information in public databases (TCGA and METABRIC), we obtained evidence that high IGF-1 or IGF-1R levels correlate with a worse clinical outcome in TNBC patients. Further bioinformatics analysis revealed that both the focal adhesion and the Hippo pathways are enriched in TNBC harboring an elevated expression of IGF-1 or IGF-1R. Mechanistically, we found that in TNBC cells, the IGF-1/IGF-1R system promotes the activation of the FAK signal transduction pathway, which in turn regulates the nuclear accumulation of YAP (yes-associated protein/yes-related protein) and the expression of its target genes. At the biological level, we found that the IGF-1/IGF-1R-FAK-YAP network cascade triggers the growth potential of TNBC cells, as evaluated in different experimental systems. Overall, our results suggest that the IGF-1/IGF-1R/FAK/YAP axis may contribute to the progression of the aggressive TNBC subtype.

Downregulation of PD-L1 via amide analogues of brefelamide: Alternatives to antibody-based cancer immunotherapy

The therapeutic blockade of immune checkpoint has emerged as an effective treatment option for a broad range of tumors. However, the objective tumor response is still limited to a small number of cases and tumor types. The full utility of monoclonal antibody (mAb)-based treatment is hindered by several inherent limitations. Thus, there is an urgent requirement to explore alternative modalities targeting the same pathways. In the present study, two amide analogues of brefelamide, TPFS-201 and TPFS-202, were identified as small molecular immune checkpoint inhibitors, as they downregulated PD-L1 expression in tumor cells. PD-L1 was suppressed in cancer cells treated with TPFD compounds at both mRNA and protein levels, as detected by reverse transcription quantitative PCR and flow cytometric analysis, respectively. Reporter assays using a PD-L1 promoter luciferase construct confirmed the transcriptional inhibition of PD-L1 by TPFS compunds. TPFS compound-mediated PD-L1 downregulation in cancer cells consequently restored T cell activity, as identified by the reduction of apoptosis and an increase in interleukin-2 promoter activity in Jurkat T cells, which were co-cultured with TPFS compound-treated A549 cells. TPFS compound-mediated PD-L1 inhibition was partially abolished by the disruption of the putative transcriptional co-activator with PDZ (TAZ)/TEA domain (TEAD)-binding motif in the PD-L1 promoter. The inhibitory effect of TPFS compounds on PD-L1 was markedly inhibited in mouse cell lines, which is consistent with previous research demonstrating that PD-L1 regulation by TAZ is not conserved in mice due to distinct promoter sequences flanking the TAZ/TEAD-binding motif. Together, the data of the current study indicated the potential utility of the brefelamide amide analogues as small molecule immune checkpoint inhibitors, thereby providing therapeutic alternatives, which could be used as monotherapy or in combination with mAbs-based treatment.

Multiple roles and context-specific mechanisms underlying YAP and TAZ-mediated resistance to anti-cancer therapy

Understanding the molecular mechanisms driving resistance to anti-cancer drugs is both a crucial step to define markers of response to therapy and a clinical need in many cancer settings. YAP and TAZ transcriptional cofactors behave as oncogenes in different cancer types. Deregulation of YAP/TAZ expression or alterations in components of the multiple signaling pathways converging on these factors are important mechanisms of resistance to chemotherapy, target therapy and hormone therapy. Moreover, response to immunotherapy may also be affected by YAP/TAZ activities in both tumor and microenvironment cells. For these reasons, various compounds inhibiting YAP/TAZ function by different direct and indirect mechanisms have been proposed as a mean to counter-act drug resistance in cancer. A particularly promising approach may be to simultaneously target both YAP/TAZ expression and their transcriptional activity through BET inhibitors.

Loss of ANCO1 repression at AIB1/YAP targets drives breast cancer progression

Transcription factors critical for the transition of normal breast epithelium to ductal carcinoma in situ (DCIS) and invasive breast cancer are not clearly defined. Here, we report that the expression of a subset of YAP-activated and YAP-repressed genes in normal mammary and early-stage breast cancer cells is dependent on the nuclear co-activator AIB1. Gene expression, sequential ChIP, and ChIP-seq analyses show that AIB1 and YAP converge upon TEAD for transcriptional activation and repression. We find that AIB1-YAP repression of genes at the 1q21.3 locus is mediated by AIB1-dependent recruitment of ANCO1, a tumor suppressor whose expression is progressively lost during breast cancer progression. Reducing ANCO1 reverts AIB1-YAP-dependent repression, increases cell size, and enhances YAP-driven aberrant 3D growth. Loss of endogenous ANCO1 occurs during DCIS xenograft progression, a pattern associated with poor prognosis in human breast cancer. We conclude that increased expression of AIB1-YAP co-activated targets coupled with a loss of normal ANCO1 repression is critical to patterns of gene expression that mediate malignant progression of early-stage breast cancer.

Hippo-YAP/TAZ signalling in organ regeneration and regenerative medicine

The Hippo pathway and its downstream effectors, the transcriptional co-activators Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), regulate organ growth and cell plasticity during animal development and regeneration. Remarkably, experimental activation of YAP/TAZ in the mouse can promote regeneration in organs with poor or compromised regenerative capacity, such as the adult heart and the liver and intestine of old or diseased mice. However, therapeutic YAP/TAZ activation may cause serious side effects. Most notably, YAP/TAZ are hyperactivated in human cancers, and prolonged activation of YAP/TAZ triggers cancer development in mice. Thus, can the power of YAP/TAZ to promote regeneration be harnessed in a safe way? Here, we review the role of Hippo signalling in animal regeneration, examine the promises and risks of YAP/TAZ activation for regenerative medicine and discuss strategies to activate YAP/TAZ for regenerative therapy while minimizing adverse side effects.

Hippo Pathway and YAP Signaling Alterations in Squamous Cancer of the Head and Neck

Head and neck cancer affects the upper aerodigestive tract and is the sixth leading cancer worldwide by incidence and the seventh by cause of death. Despite significant advances in surgery and chemotherapy, molecularly targeted therapeutic options for this type of cancer are scarce and long term survival rates remain low. Recently, comprehensive genomic studies have highlighted the most commonly altered genes and signaling pathways in this cancer. The Hippo-YAP pathway has been identified as a key oncogenic pathway in multiple tumors. Expression of genes controlled by the Hippo downstream transcriptional coactivators YAP (Yes-associated protein 1) and TAZ (WWTR1, WW domain containing transcription regulator 1) is widely deregulated in human cancer including head and neck squamous cell carcinoma (HNSCC). Interestingly, YAP/TAZ signaling might not be as essential for the normal homeostasis of adult tissues as for oncogenic growth, altogether making the pathway an amenable therapeutic target in cancer. Recent advances in the role of Hippo-YAP pathway in HNSCC have provided evidence that genetic alterations frequent in this type of cancer such as PIK3CA (phosphatidylinositide 3-kinase catalytic subunit alpha) overexpression or FAT1 (FAT atypical cadherin 1) functional loss can result in YAP activation. We discuss current therapeutic options targeting this pathway which are currently in use for other tumor types.

Initiation of human mammary cell tumorigenesis by mutant KRAS requires YAP inactivation

High YAP activity is associated with poor prognosis human breast cancers, but its role during the initial stage of mammary cell transformation is unknown. To address this question, we designed experiments that exploit the ability of KRAS^G12D-transduced subsets of freshly isolated normal human mammary cells to form invasive tumors rapidly and efficiently when transplanted into immunodeficient mice. Initial examination of the newly developing tumors thus generated revealed a consistent marked loss of nuclear YAP, independent of the initial primary human mammary cell type transduced. Conversely, co-transduction of the same subsets of primary human mammary cells with KRAS^G12D plus the constitutively active YAP^S127A prevented tumor formation. These findings contrast with the enhanced display of transformed properties obtained when the immortalized, but non-tumorigenic MCF10A cells are transduced just with YAP^S127A. In addition, we show that YAP^S127A-transduction of the human MDA-MB-231 breast cancer cell line (that carry a similar KRAS mutation) enhances their metastatic activity in vivo. We also discover that the KRAS^G12D-induced early loss of YAP in primary human mammary cells is associated with their induced secretion of amphiregulin. Collectively, these findings suggest that YAP can differentially affect the acquisition of malignant properties by human mammary cells at different stages of their transformation.

Recent Advances of the Hippo/YAP Signaling Pathway in Brain Development and Glioma

The Hippo signaling pathway is highly conserved from Drosophila melanogaster to mammals and plays a crucial role in organ size control, tissue regeneration, and tumor suppression. The Yes-associated protein (YAP) is an important transcriptional co-activator that is negatively regulated by the Hippo signaling pathway. The Hippo signaling pathway is also regulated by various upstream regulators, such as cell polarity, adhesion proteins, and other signaling pathways (the Wnt/β-catenin, Notch, and MAPK pathways). Recently, accumulated evidence suggests that the Hippo/YAP signaling pathway plays important roles in central nervous system development and brain tumor, including glioma. In this review, we summarize the results of recent studies on the physiological effect of the Hippo/YAP signaling pathway in neural stem cells, neural progenitor cells, and glial cells. In particular, we also focus on the expression of MST1/2, LATS1/2, and the downstream effector YAP, in glioma, and offer a review of the latest research of the Hippo/YAP signaling pathway in glioma pathogenesis. Finally, we also present future research directions and potential therapeutic strategies for targeting the Hippo/YAP signaling in glioma.

Fry Is Required for Mammary Gland Development During Pregnant Periods and Affects the Morphology and Growth of Breast Cancer Cells

The Fry gene, located on chromosome 13, is an evolutionarily conserved large protein from yeast to human. Our previous study genetically linked the Fry gene with differential susceptibility to mammary carcinogenesis, but whether Fry affects mammary gland development and function, as well as the growth of breast cancer cells, is largely unknown. To define the consequences of Fry loss in the mammary glands, we have generated mice conditionally deficient of the Fry gene in the mammary glands using the Cre-loxP recombination system. We examined multiple phenotypes with male and female homozygous Fry conditional knockout mice (Mfry) and control mice (WT), including body weight, preliminary observations (health and neurological flexes), open field locomotion, sensory abilities, auditory threshold, and glucose metabolism. The loss of Fry in the mammary glands didn't cause a significant difference in these genotypes between Mfry and WT mice. However, our data showed that Fry was required during pregnancy, while it was functionally dispensable in virgin mammary gland development. Loss of Fry led to more lateral buds, and the lobuloalveoli were smaller and showed undistended morphology in mammary glands during late pregnancy. in vitro experiment, ectopic expression of FRY could alter the morphology and significantly suppress the growth and proliferation of the breast cancer cell lines, MDA-MB-231 (ER-/PR-/HER2-, Basal-like) and BT474 (ER+/PR+/HER2+, Luminal B). The following genome-wide transcriptomic analysis of these cells suggested that FRY interacted with protein kinases relevant signaling pathways and induced massive changes in gene expression, including the activation of the Hippo/Yap pathway. Together, our data suggest that the FRY is required for mammary glands developments during pregnant periods, and affects breast cancer cell growth and proliferation.

Mask family proteins ANKHD1 and ANKRD17 regulate YAP nuclear import and stability

Mask family proteins were discovered in Drosophila to promote the activity of the transcriptional coactivator Yorkie (Yki), the sole fly homolog of mammalian YAP (YAP1) and TAZ (WWTR1). The molecular function of Mask, or its mammalian homologs Mask1 (ANKHD1) and Mask2 (ANKRD17), remains unclear. Mask family proteins contain two ankyrin repeat domains that bind Yki/YAP as well as a conserved nuclear localisation sequence (NLS) and nuclear export sequence (NES), suggesting a role in nucleo-cytoplasmic transport. Here we show that Mask acts to promote nuclear import of Yki, and that addition of an ectopic NLS to Yki is sufficient to bypass the requirement for Mask in Yki-driven tissue growth. Mammalian Mask1/2 proteins also promote nuclear import of YAP, as well as stabilising YAP and driving formation of liquid droplets. Mask1/2 and YAP normally colocalise in a granular fashion in both nucleus and cytoplasm, and are co-regulated during mechanotransduction.

High-Dimensional Phenotyping Identifies Age-Emergent Cells in Human Mammary Epithelia

Aging is associated with tissue-level changes in cellular composition that are correlated with increased susceptibility to disease. Aging human mammary tissue shows skewed progenitor cell potency, resulting in diminished tumor-suppressive cell types and the accumulation of defective epithelial progenitors. Quantitative characterization of these age-emergent human cell subpopulations is lacking, impeding our understanding of the relationship between age and cancer susceptibility. We conducted single-cell resolution proteomic phenotyping of healthy breast epithelia from 57 women, aged 16–91 years, using mass cytometry. Remarkable heterogeneity was quantified within the two mammary epithelial lineages. Population partitioning identified a subset of aberrant basal-like luminal cells that accumulate with age and originate from age-altered progenitors. Quantification of age-emergent phenotypes enabled robust classification of breast tissues by age in healthy women. This high-resolution mapping highlighted specific epithelial subpopulations that change with age in a manner consistent with increased susceptibility to breast cancer.

•

CyTOF analysis reveals human mammary epithelial heterogeneity with age

•

Age-emergent luminal cells share phenotypes with candidate breast cancer cells of origin

•

Classification models correctly assign tissue samples to their age group

•

Age-related changes are conserved between mammary epithelial tissue and primary cells

Hippo signalling during development

The Hippo signalling pathway and its transcriptional co-activator targets Yorkie/YAP/TAZ first came to attention because of their role in tissue growth control. Over the past 15 years, it has become clear that, like other developmental pathways (e.g. the Wnt, Hedgehog and TGFβ pathways), Hippo signalling is a 'jack of all trades' that is reiteratively used to mediate a range of cellular decision-making processes from proliferation, death and morphogenesis to cell fate determination. Here, and in the accompanying poster, we briefly outline the core pathway and its regulation, and describe the breadth of its roles in animal development.

CCT3 acts upstream of YAP and TFCP2 as a potential target and tumour biomarker in liver cancer

Although Yes-associated protein (YAP) is very important to liver cancer, its nuclear localisation prevents consideration as a promising therapeutic target and a diagnostic biomarker. Recently, we reported that the protumourigenic roles of YAP in liver cancer are indispensable for transcription factor CP2 (TFCP2) in a Hippo-independent manner; however, proteins that act upstream to simultaneously control YAP and TFCP2 remain unclear. The aim of this study was to uncover such proteins and evaluate whether they are potential YAP-associated therapeutic targets and diagnostic biomarkers. Mass spectrometry revealed that chaperonin containing TCP1 subunit 3 (CCT3) co-interact with YAP and TFCP2, and notably, CCT3 is a non-nuclear protein. CCT3 was elevated in liver cancer, and its higher expression was associated with poorer overall survival. Inhibiting CCT3 resulted in a suppressed transformative phenotype in liver cancer cells, suggesting that CCT3 might be a potential therapeutic target. CCT3 prolonged half-life of YAP and TFCP2 by blocking their ubiquitination caused by poly(rC) binding protein 2 (PCBP2) in a beta-transducin repeat containing E3 ubiquitin protein ligase (βTrCP)-independent manner. Interestingly, PCBP2 directly interacted with YAP via a WB motif-WW domain interaction, whereas indirectly interacted with TFCP2 via the aid of YAP. Furthermore, CCT3 was capable of separating PCBP2-YAP interactions, thereby preventing YAP and TFCP2 from PCBP2-induced ubiquitination. Moreover, YAP and TFCP2 were downstream of CCT3 to positively control tumourigenesis, yet such effects were inhibited by PCBP2. Clinically, CCT3 was positively correlated with YAP and TFCP2, and elevated levels of the CCT3-YAP-TFCP2 axis might be critical for liver malignancy. In addition, seral-CCT3 was proven to be a potential biomarker, and its diagnostic capacity was better than that of alpha fetoprotein (AFP) to a certain extent. Together, CCT3 acts as a trigger of YAP and TFCP2 to affect tumourigenesis and serves as a potential therapeutic target and biomarker in liver cancer.

Safety Considerations in the Development of Hippo Pathway Inhibitors in Cancers

The Hippo pathway is a critical regulator of cell and organ growth and has emerged as a target for therapeutic intervention in cancers. Its signaling is thought to play an important role in various physiological processes including homeostasis and tissue regeneration. To date there has been limited information about potential pharmacology-related (on-target) safety liabilities of Hippo pathway inhibitors in the context of cancer indications. Herein, we review data from human genetic disorders and genetically engineered rodent models to gain insight into safety liabilities that may emerge from the inhibition of Hippo pathway. Germline systemic deletion of murine Hippo pathway effectors (Yap, Taz, and Teads) resulted in embryonic lethality or developmental phenotypes. Mouse models with tissue-specific deletion (or mutant overexpression) of the key effectors in Hippo pathways have indicated that, at least in some tissues, Hippo signaling may be dispensable for physiological homeostasis; and appears to be critical for regeneration upon tissue damage, indicating that patients with underlying comorbidities and/or insults caused by therapeutic agents and/or comedications may have a higher risk. Caution should be taken in interpreting phenotypes from tissue-specific transgenic animal models since some tissue-specific promoters are turned on during development. In addition, therapeutic agents may result in systemic effects not well-predicted by animal models with tissue-specific gene deletion. Therefore, the development of models that allows for systemic deletion of Yap and/or Taz in adult animals will be key in evaluating the potential safety liabilities of Hippo pathway modulation. In this review, we focus on potential challenges and strategies for targeting the Hippo pathway in cancers.

The Hippo Signaling Pathway in Development and Disease

The Hippo signaling pathway regulates diverse physiological processes, and its dysfunction has been implicated in an increasing number of human diseases, including cancer. Here, we provide an updated review of the Hippo pathway; discuss its roles in development, homeostasis, regeneration, and diseases; and highlight outstanding questions for future investigation and opportunities for Hippo-targeted therapies.

YAP and TAZ: a signalling hub of the tumour microenvironment

YAP and TAZ are transcriptional activators pervasively induced in several human solid tumours and their functions in cancer cells are the focus of intense investigation. These studies established that YAP and TAZ are essential to trigger numerous cell-autonomous responses, such as sustained proliferation, cell plasticity, therapy resistance and metastasis. Yet tumours are complex entities, wherein cancer cells are just one of the components of a composite "tumour tissue". The other component, the tumour stroma, is composed of an extracellular matrix with aberrant mechanical properties and other cell types, including cancer-associated fibroblasts and immune cells. The stroma entertains multiple and bidirectional interactions with tumour cells, establishing dependencies essential to unleash tumorigenesis. The molecular players of such interplay remain partially understood. Here, we review the emerging role of YAP and TAZ in choreographing tumour-stromal interactions. YAP and TAZ act within tumour cells to orchestrate responses in stromal cells. Vice versa, YAP and TAZ in stromal cells trigger effects that positively feed back on the growth of tumour cells. Recognizing YAP and TAZ as a hub of the network of signals exchanged within the tumour microenvironment provides a fresh perspective on the molecular principles of tumour self-organization, promising to unveil numerous new vulnerabilities.

Mammary stem cells and progenitors: targeting the roots of breast cancer for prevention

Breast cancer prevention is daunting, yet not an unsurmountable goal. Mammary stem and progenitors have been proposed as the cells-of-origin in breast cancer. Here, we present the concept of limiting these breast cancer precursors as a risk reduction approach in high-risk women. A wealth of information now exists for phenotypic and functional characterization of mammary stem and progenitor cells in mouse and human. Recent work has also revealed the hormonal regulation of stem/progenitor dynamics as well as intrinsic lineage distinctions between mammary epithelial populations. Leveraging these insights, molecular marker-guided chemoprevention is an achievable reality.

Transcriptional regulation of normal human mammary cell heterogeneity and its perturbation in breast cancer

The mammary gland in adult women consists of biologically distinct cell types that differ in their surface phenotypes. Isolation and molecular characterization of these subpopulations of mammary cells have provided extensive insights into their different transcriptional programs and regulation. This information is now serving as a baseline for interpreting the heterogeneous features of human breast cancers. Examination of breast cancer mutational profiles further indicates that most have undergone a complex evolutionary process even before being detected. The consequent intra-tumoral as well as inter-tumoral heterogeneity of these cancers thus poses major challenges to deriving information from early and hence likely pervasive changes in potential therapeutic interest. Recently described reproducible and efficient methods for generating human breast cancers de novo in immunodeficient mice transplanted with genetically altered primary cells now offer a promising alternative to investigate initial stages of human breast cancer development. In this review, we summarize current knowledge about key transcriptional regulatory processes operative in these partially characterized subpopulations of normal human mammary cells and effects of disrupting these processes in experimentally produced human breast cancers.

The posttranslational modifications of Hippo-YAP pathway in cancer

BACKGROUND

Yes-associated protein (YAP) is a key effector of the Hippo pathway and is frequently dysregulated in aggressive human cancers. Aberrant YAP activation has emerged as an important driver of tumorigenesis, chemoresistance and metastasis. Since posttranslational modifications (PTMs) are pivotal modifiers that determine protein activation or subcellular localization, the malfunction of YAP due to dysregulated PTMs has been linked to various cancers. Collectively, although YAP has long been considered an "undruggable" transcription cofactor, its PTMs may be its "Achilles' heel". To provide theoretical support for developing small molecule inhibitors based on PTMs, in this review article, we summarize the current understanding of the impact of PTMs in regulating the Hippo-YAP pathway and further discuss potential therapeutic intervention.

SCOPE OF REVIEW

In our review, we summarize the known posttranslational modifications (PTMs) of YAP that dictate its protein stability, transcriptional activity and subcellular localization at different stages. Here, we clearly summarize the specific enzymes and sites involved in YAP PTMs and place additional focus on the consequences of PTM-modulated YAP activity and translocation.

MAIN CONCLUSION

PTMs of YAP play fundamental roles in controlling the protein abundance and function. Therefore, interfering with PTMs of YAP may contribute to solving the "undruggable" problem in YAP inhibition, thus providing new approaches for YAP-based cancer therapy.

GENERAL SIGNIFICANCE

Future studies that target corresponding PTM-related kinases/enzymes will provide new strategies for cancer therapy, particularly in tumors with YAP dysregulation.

Regulation of the Hippo signaling pathway by deubiquitinating enzymes in cancer

Regulation of the Hippo signaling pathway is essential for normal organ growth and tissue homeostasis. The proteins that act to regulate this pathway are important for ensuring proper function and cellular location. Deubiquitinases (DUBs) are a family of proteases that act upon many proteins. While ubiquitinases add ubiquitin and target proteins for degradation, DUBs act by removing ubiquitin (Ub) moieties. Changes in ubiquitin chain topology results in the stabilization of proteins, membrane trafficking, and the alteration of cellular localization. While the roles of these proteins have been well established in a cancer setting, their convergence in cancer is still under investigation. In this review, we discuss the roles that DUBs play in the regulation of the Hippo signaling pathway for homeostasis and disease.

Single-Cell Analysis of the Liver Epithelium Reveals Dynamic Heterogeneity and an Essential Role for YAP in Homeostasis and Regeneration

The liver can substantially regenerate after injury, with both main epithelial cell types, hepatocytes and biliary epithelial cells (BECs), playing important roles in parenchymal regeneration. Beyond metabolic functions, BECs exhibit substantial plasticity and in some contexts can drive hepatic repopulation. Here, we performed single-cell RNA sequencing to examine BEC and hepatocyte heterogeneity during homeostasis and after injury. Instead of evidence for a transcriptionally defined progenitor-like BEC cell, we found significant homeostatic BEC heterogeneity that reflects fluctuating activation of a YAP-dependent program. This transcriptional signature defines a dynamic cellular state during homeostasis and is highly responsive to injury. YAP signaling is induced by physiological bile acids (BAs), required for BEC survival in response to BA exposure, and is necessary for hepatocyte reprogramming into biliary progenitors upon injury. Together, these findings uncover molecular heterogeneity within the ductal epithelium and reveal YAP as a protective rheostat and regenerative regulator in the mammalian liver.

Role of cytoplasmic lncRNAs in regulating cancer signaling pathways

Cancer remains a serious healthcare problem despite significant improvements in early detection and treatment approaches in the past few decades. Novel biomarkers for diagnosis and therapeutic strategies are urgently needed. In recent years, long noncoding RNAs (lncRNAs) have been reported to be aberrantly expressed in tumors and show crosstalk with key cancer-related signaling pathways. In this review, we summarized the current progress of research on cytoplasmic lncRNAs and their roles in regulating cancer signaling and tumor progression, further characterization of which may lead to effective approaches for cancer prevention and therapy.

Analysis of the role of the Hippo pathway in cancer

Cancer is a serious health issue in the world due to a large body of cancer-related human deaths, and there is no current treatment available to efficiently treat the disease as the tumor is often diagnosed at a serious stage. Moreover, Cancer cells are often resistant to chemotherapy, radiotherapy, and molecular-targeted therapy. Upon further knowledge of mechanisms of tumorigenesis, aggressiveness, metastasis, and resistance to treatments, it is necessary to detect the disease at an earlier stage and for a better response to therapy. The hippo pathway possesses the unique capacity to lead to tumorigenesis. Mutations and altered expression of its core components (MST1/2, LATS1/2, YAP and TAZ) promote the migration, invasion, malignancy of cancer cells. The biological significance and deregulation of it have received a large body of interests in the past few years. Further understanding of hippo pathway will be responsible for cancer treatment. In this review, we try to discover the function of hippo pathway in different diversity of cancers, and discuss how Hippo pathway contributes to other cellular signaling pathways. Also, we try to describe how microRNAs, circRNAs, and ZNFs regulate hippo pathway in the process of cancer. It is necessary to find new therapy strategies for cancer.

YAP1-LATS2 feedback loop dictates senescent or malignant cell fate to maintain tissue homeostasis

Dysfunction of the homeostasis-maintaining systems in specific cell types or tissues renders the organism susceptible to a range of diseases, including cancers. One of the emerging mechanisms for maintaining tissue homeostasis is cellular senescence. Here, we report that the Hippo pathway plays a critical role in controlling the fate of ovarian cells. Hyperactivation of Yes-associated protein 1 (YAP1), the major effector of the Hippo pathway, induces senescence in cultured primary human ovarian surface epithelial cells (hOSEs). Large tumor suppressor 2 (LATS2), the primary upstream negative regulator of YAP1, is elevated in both YAP1-induced and natural replicative-triggered senescence. Deletion of LATS2 in hOSEs prevents these cells from natural replicative and YAP1-induced senescence. Most importantly, loss of LATS2 switches ovarian cells from YAP-induced senescence to malignant transformation. Our results demonstrate that LATS2 and YAP1, two major components of the Hippo/YAP signaling pathway, form a negative feedback loop to control YAP1 activity and prevent ovarian cells from malignant transformation. Human cancer genomic data extracted from TCGA datasets further confirm the clinical relevance of our finding.

Biophysical properties of cells for cancer diagnosis

Biophysical properties associated with the microenvironment of a tumor has been recognized as an important modulator for cell behaviour and function. Particularly, tissue rigidity is important during tumor carcinogenesis as it affects the tumor's ability to metastasis. Multiple downstream pathways are affected with a difference in rigidity of the extracellular matrix. The insight into tumor mechanosignalling represents a promising field that may lead to novel approaches for cancer diagnostics. Measurement of rigidity of the extracellular matrix or the tissue is a potential diagnostics approach for cancer detection. Altered extracellular matrix states persist for a long period of time and have lower heterogeneity compared to protein or genetic markers, therefore are more reliable as biomarkers. On the other hand, measurement of different kinase associated proteins or transcripts provide an early insight into potential transition of cells towards metastasis. Co-localization of transcriptional factors like YAP/TAZ provide an insight to determine if the cells are undergoing metastatic changes. This review explains the unique biophysical properties of the tumor microenvironment that present the potential targets for the diagnosis of cancer.

WW Domain-Containing Proteins YAP and TAZ in the Hippo Pathway as Key Regulators in Stemness Maintenance, Tissue Homeostasis, and Tumorigenesis

The Hippo pathway is a conserved signaling pathway originally defined in Drosophila melanogaster two decades ago. Deregulation of the Hippo pathway leads to significant overgrowth in phenotypes and ultimately initiation of tumorigenesis in various tissues. The major WW domain proteins in the Hippo pathway are YAP and TAZ, which regulate embryonic development, organ growth, tissue regeneration, stem cell pluripotency, and tumorigenesis. Recent reports reveal the novel roles of YAP/TAZ in establishing the precise balance of stem cell niches, promoting the production of induced pluripotent stem cells (iPSCs), and provoking signals for regeneration and cancer initiation. Activation of YAP/TAZ, for example, results in the expansion of progenitor cells, which promotes regeneration after tissue damage. YAP is highly expressed in self-renewing pluripotent stem cells. Overexpression of YAP halts stem cell differentiation and yet maintains the inherent stem cell properties. A success in reprograming iPSCs by the transfection of cells with Oct3/4, Sox2, and Yap expression constructs has recently been shown. In this review, we update the current knowledge and the latest progress in the WW domain proteins of the Hippo pathway in relevance to stem cell biology, and provide a thorough understanding in the tissue homeostasis and identification of potential targets to block tumor development. We also provide the regulatory role of tumor suppressor WWOX in the upstream of TGF-β, Hyal-2, and Wnt signaling that cross talks with the Hippo pathway.

p53 controls the plasticity of mammary luminal progenitor cells downstream of Met signaling

Background

The adult mammary epithelium is composed of basal and luminal cells. The luminal lineage comprises two major cell populations, positive and negative for estrogen and progesterone receptors (ER and PR, respectively), both containing clonogenic progenitor cells. Deregulated ER/PR⁻ luminal progenitor cells are suspected to be at the origin of basal-type triple-negative (TNBC) breast cancers, a subtype frequently associated with loss of P53 function and MET signaling hyperactivation. Using mouse models, we recently reported that p53 restricts luminal progenitor cell amplification whereas paracrine Met activation stimulates their growth and favors a luminal-to-basal switch. Here, we analyzed how these two critical pathways interact to control luminal progenitor function.

Methods

We have (i) established and analyzed the gene expression profile of luminal progenitors isolated by ICAM-1, a robust surface marker we previously identified; (ii) purified luminal progenitors from p53-deficient and p53-proficient mouse mammary epithelium to compare their functional and molecular characteristics; and (iii) analyzed their response to HGF, the major Met ligand, in three-dimensional cultures.

Results

We found that luminal progenitors, compared to non-clonogenic luminal cells, overexpress Trp53 and numerous p53 target genes. In vivo, loss of Trp53 induced the expansion of luminal progenitors, affecting expression of several important p53 target genes including those encoding negative regulators of cell cycle progression. Consistently, p53-deficient luminal progenitors displayed increased proliferative and self-renewal activities in culture. However, they did not exhibit perturbed expression of luminal-specific markers and major regulators, such as Hey1, Elf5, and Gata3. Moreover, although expressing Met at higher level than p53-proficient luminal progenitors, p53-deficient luminal progenitors failed to acquire basal-specific features when stimulated by HGF, showing that p53 promotes the plastic behavior of luminal progenitors downstream of Met activation.

Conclusions

Our study reveals a crosstalk between Met- and p53-mediated signaling pathways in the regulation of luminal progenitor function. In particular, it shows that neither p53 loss alone nor p53 loss combined with Met signaling activation caused an early detectable cell fate alteration in luminal progenitors. Conceivably, additional events are required to confer basal-specific characteristics to luminal-derived TNBCs.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1101-8) contains supplementary material, which is available to authorized users.

RNA-binding protein QKI regulates contact inhibition via Yes-associate protein in ccRCC

Contact inhibition adjusts organ size to the proper size and ensures the cultured cells growing to a monolayer. By regulating the downstream coordinator YAP, the evolutionarily conserved Hippo transduction pathway attunes cell growth and death in response to cell contact inhibition, polarity, self-renewal, and differentiation. Dysregulation of this pathway is involved in various diseases such as cancer. RNA-binding protein QKI regulates cell proliferation, metabolism, division, and immunity in various cancer models, but its role in cancer cell contact inhibition remains unclear. In this study, we aimed to clarify the relationship between QKI and YAP, and the role of their interaction in cell contact inhibition. We found a lower QKI expression level in sparse condition, whereas a higher expression level in confluent condition by western blot analysis and immunofluorescence assay. QKI knockdown elevated cell proliferation and invasion both in vitro and in vivo. Strikingly, the results of CCK-8 assay, colony formation assay, and transwell assay showed that the phenomenon was in accord with the expression level of pYAP and reverse with YAP. Higher levels of Wnt3a and β-catenin were also found in xenografts of QKI-knockdown clear cell renal cell carcinoma (ccRCC) CAKI-1 cells by western blot analysis and immumohistochemical staining. Finally, a positive correlation between QKI and pYAP was found in clinical specimens by immunohistochemistry. Thus, as a negative regulator of YAP, QKI attuned the cell contact inhibition, leading to inhibition of cancer cell proliferation and invasion through Wnt and GPCR pathway.

Phenotypic Plasticity: Driver of Cancer Initiation, Progression, and Therapy Resistance

Our traditional understanding of phenotypic plasticity in adult somatic cells comprises dedifferentiation and transdifferentiation in the context of tissue regeneration or wound healing. Although dedifferentiation is central to tissue repair and stemness, this process inherently carries the risk of cancer initiation. Consequently, recent research suggests phenotypic plasticity as a new paradigm for understanding cancer initiation, progression, and resistance to therapy. Here, we discuss how cells acquire plasticity and the role of plasticity in initiating cancer, cancer progression, and metastasis and in developing therapy resistance. We also highlight the epithelial-to-mesenchymal transition (EMT) and known molecular mechanisms underlying plasticity and we consider potential therapeutic avenues.

WW-Domain Containing Protein Roles in Breast Tumorigenesis

Protein-protein interactions are key factors in executing protein function. These interactions are mediated through different protein domains or modules. An important domain found in many different types of proteins is WW domain. WW domain-containing proteins were shown to be involved in many human diseases including cancer. Some of these proteins function as either tumor suppressor genes or oncogenes, while others show dual identity. Some of these proteins act on their own and alter the function(s) of specific or multiple proteins implicated in cancer, others interact with their partners to compose WW domain modular pathway. In this review, we discuss the role of WW domain-containing proteins in breast tumorigenesis. We give examples of specific WW domain containing proteins that play roles in breast tumorigenesis and explain the mechanisms through which these proteins lead to breast cancer initiation and progression. We discuss also the possibility of using these proteins as biomarkers or therapeutic targets.

NUAK2 is a critical YAP target in liver cancer

The Hippo-YAP signaling pathway is a critical regulator of proliferation, apoptosis, and cell fate. The main downstream effector of this pathway, YAP, has been shown to be misregulated in human cancer and has emerged as an attractive target for therapeutics. A significant insufficiency in our understanding of the pathway is the identity of transcriptional targets of YAP that drive its potent growth phenotypes. Here, using liver cancer as a model, we identify NUAK2 as an essential mediator of YAP-driven hepatomegaly and tumorigenesis in vivo. By evaluating several human cancer cell lines we determine that NUAK2 is selectively required for YAP-driven growth. Mechanistically, we found that NUAK2 participates in a feedback loop to maximize YAP activity via promotion of actin polymerization and myosin activity. Additionally, pharmacological inactivation of NUAK2 suppresses YAP-dependent cancer cell proliferation and liver overgrowth. Importantly, our work here identifies a specific, potent, and actionable target for YAP-driven malignancies.

Hippo-YAP pathway plays an important role in cancers; however the in vivo relevance of YAP/TAZ target genes is unclear. Here, the authors show that NUAK2 is a target of YAP and participates in a feedback loop to maximize YAP activity. Inhibition of NUAK2 suppresses YAP-driven hepatomegaly and liver cancer growth, offering a new target for cancer therapy.

miR-205 Regulates Basal Cell Identity and Stem Cell Regenerative Potential During Mammary Reconstitution

Mammary gland development is fueled by stem cell self-renewal and differentiation. External cues from the microenvironment coupled with internal cues such as post-transcriptional regulation exerted by microRNAs regulate stem cell behavior and fate. Here, we have identified a miR-205 regulatory network required for mammary gland ductal development and stem cell regeneration following transplantation into the cleared mammary fat pad. In the postnatal mammary gland, miR-205 is predominantly expressed in the basal/stem cell enriched population. Conditional deletion of miR-205 in mammary epithelial cells impairs stem cell self-renewal and mammary regenerative potential in the in vitro mammosphere formation assay and in vivo mammary reconstitution. miR-205 null transplants display significant changes in basal cells, basement membrane, and stroma. NKD1 and PTPA, which inhibit the Wnt signaling pathway, and AMOT, which causes YAP cytoplasmic retention and inactivation were identified as miR-205 downstream mediators. These studies also confirmed that miR-205 is a direct ΔNp63 target gene that is critical for the regulation of basal cell identity. Stem Cells 2018;36:1875-15.

LATS1 and LATS2 suppress breast cancer progression by maintaining cell identity and metabolic state

In luminal B tumors LATS2 depletion results in metabolic rewiring whereas LATS1 depletion promotes the expression of basal-like features.

Deregulated activity of LArge Tumor Suppressor (LATS) tumor suppressors has broad implications on cellular and tissue homeostasis. We examined the consequences of down-regulation of either LATS1 or LATS2 in breast cancer. Consistent with their proposed tumor suppressive roles, expression of both paralogs was significantly down-regulated in human breast cancer, and loss of either paralog accelerated mammary tumorigenesis in mice. However, each paralog had a distinct impact on breast cancer. Thus, LATS2 depletion in luminal B tumors resulted in metabolic rewiring, with increased glycolysis and reduced peroxisome proliferator-activated receptor γ (PPARγ) signaling. Furthermore, pharmacological activation of PPARγ elicited LATS2-dependent death in luminal B-derived cells. In contrast, LATS1 depletion augmented cancer cell plasticity, skewing luminal B tumors towards increased expression of basal-like features, in association with increased resistance to hormone therapy. Hence, these two closely related paralogs play distinct roles in protection against breast cancer; tumors with reduced expression of either LATS1 or LATS2 may rewire signaling networks differently and thus respond differently to anticancer treatments.

Yap regulates glucose utilization and sustains nucleotide synthesis to enable organ growth

The Hippo pathway and its nuclear effector Yap regulate organ size and cancer formation. While many modulators of Hippo activity have been identified, little is known about the Yap target genes that mediate these growth effects. Here, we show that yap ^-/- mutant zebrafish exhibit defects in hepatic progenitor potential and liver growth due to impaired glucose transport and nucleotide biosynthesis. Transcriptomic and metabolomic analyses reveal that Yap regulates expression of glucose transporter glut1, causing decreased glucose uptake and use for nucleotide biosynthesis in yap ^-/- mutants, and impaired glucose tolerance in adults. Nucleotide supplementation improves Yap deficiency phenotypes, indicating functional importance of glucose-fueled nucleotide biosynthesis. Yap-regulated glut1 expression and glucose uptake are conserved in mammals, suggesting that stimulation of anabolic glucose metabolism is an evolutionarily conserved mechanism by which the Hippo pathway controls organ growth. Together, our results reveal a central role for Hippo signaling in glucose metabolic homeostasis.

Transcriptional addiction in cancer cells is mediated by YAP/TAZ through BRD4

Cancer cells rely on dysregulated gene expression. This establishes specific transcriptional addictions that may be therapeutically exploited. Yet, the mechanisms that are ultimately responsible for these addictions are poorly understood. Here, we investigated the transcriptional dependencies of transformed cells to the transcription factors YAP and TAZ. YAP/TAZ physically engage the general coactivator bromodomain-containing protein 4 (BRD4), dictating the genome-wide association of BRD4 to chromatin. YAP/TAZ flag a large set of enhancers with super-enhancer-like functional properties. YAP/TAZ-bound enhancers mediate the recruitment of BRD4 and RNA polymerase II at YAP/TAZ-regulated promoters, boosting the expression of a host of growth-regulating genes. Treatment with small-molecule inhibitors of BRD4 blunts YAP/TAZ pro-tumorigenic activity in several cell or tissue contexts, causes the regression of pre-established, YAP/TAZ-addicted neoplastic lesions and reverts drug resistance. This work sheds light on essential mediators, mechanisms and genome-wide regulatory elements that are responsible for transcriptional addiction in cancer and lays the groundwork for a rational use of BET inhibitors according to YAP/TAZ biology.

Expression of the Hippo signalling effectors YAP and TAZ in canine mammary gland hyperplasia and malignant transformation of mammary tumours

Canine mammary tumours (CMTs) are common neoplasms in dogs that feature many of the clinical, genetic and molecular characteristics of human breast cancer. Despite their high metastatic potential, few adjuvant chemotherapeutic treatment options exist for malignant CMTs, and the development of novel, targeted pharmacological approaches will require a better understanding of their pathogenesis. As recent evidence suggests that dysregulated Hippo signalling is involved in the development and progression of breast cancer, we sought to determine if this pathway could also play a role in CMT. The expression of the Hippo signalling effectors YAP and TAZ was analysed by immunoblotting and immunohistochemistry in samples including normal mammary gland, lobular hyperplasia, benign tumours and malignant tumours of all grades. We found a significant increase in TAZ (but not YAP) expression occurred in lobular hyperplasia relative to normal mammary gland, suggesting a role for TAZ in non-neoplastic epithelial proliferation. Nuclear expression of both TAZ and YAP were significantly higher in malignant tumours than in benign ones, suggesting that Hippo dysregulation could play a role in CMT malignant transformation. No differences in YAP or TAZ expression were detected between grades of malignant tumours. Together, our results indicate that alterations in Hippo signalling may play a role in the pathogenesis of CMT, in a manner similar to breast cancer. Hippo pathway components may therefore represent targets for the development of novel chemotherapeutic agents that could be useful for the treatment of both the human and canine diseases.

Mechanoregulation and pathology of YAP/TAZ via Hippo and non-Hippo mechanisms

Yes-associated protein (YAP) and its paralog WW domain containing transcription regulator 1 (TAZ) are important regulators of multiple cellular functions such as proliferation, differentiation, and survival. On the tissue level, YAP/TAZ are essential for embryonic development, organ size control and regeneration, while their deregulation leads to carcinogenesis or other diseases. As an underlying principle for YAP/TAZ-mediated regulation of biological functions, a growing body of research reveals that YAP/TAZ play a central role in delivering information of mechanical environments surrounding cells to the nucleus transcriptional machinery. In this review, we discuss mechanical cue-dependent regulatory mechanisms for YAP/TAZ functions, as well as their clinical significance in cancer progression and treatment.

Hippo pathway functions as a downstream effector of AKT signaling to regulate the activation of primordial follicles in mice

Clarifying the molecular mechanisms by which primordial follicles are initiated is crucial for the prevention and treatment of female infertility and ovarian dysfunction. The Hippo pathway has been proven to have a spatiotemporal correlation with the size of the primordial follicle pool in mice in our previous work. But the role and underlying mechanisms of the Hippo pathway in primordial follicle activation remain unclear. Here, the localization and expression of the core components were examined in primordial follicles before and after activation. And the effects of the Hippo pathway on primordial follicle activation were determined by genetically manipulating yes-associated protein 1 (Yap1), the key transcriptional effector. Furthermore, an AKT specific inhibitor (MK2206) was added to determine the interaction between the Hippo pathway and AKT, an important signaling regulator of ovarian function. Results showed that the core components of the Hippo pathway were localized in both primordial and primary follicles and the expression levels of them changed significantly during the initiation of primordial follicles. Yap1 knockdown suppressed primordial follicle activation, while its overexpression led to the opposite trend. MK2206 downregulated the ratio of P-MST/MST1 and upregulated the ratio of P-YAP1/YAP1 significantly, whereas Yap1-treatment had no influence on AKT. In addition, YAP1 upregulation partially rescued the suppression of the primordial follicle activation induced by MK2206. Our findings revealed that the Hippo-YAP1 regulates primordial follicular activation, which is mediated by AKT signaling in mice, thus providing direct and new evidence to highlight the role of Hippo signaling in regulating ovarian follicles development.