ERG Activates the YAP1 Transcriptional Program and Induces the Development of Age-Related Prostate Tumors

Disrupting prostate cancer research: Challenge accepted; report from the 2023 Coffey-Holden Prostate Cancer Academy Meeting

INTRODUCTION

The 2023 Coffey-Holden Prostate Cancer Academy (CHPCA) Meeting, themed "Disrupting Prostate Cancer Research: Challenge Accepted," was convened at the University of California, Los Angeles, Luskin Conference Center, in Los Angeles, CA, from June 22 to 25, 2023.

METHODS

The 2023 marked the 10th Annual CHPCA Meeting, a discussion-oriented scientific think-tank conference convened annually by the Prostate Cancer Foundation, which centers on innovative and emerging research topics deemed pivotal for advancing critical unmet needs in prostate cancer research and clinical care. The 2023 CHPCA Meeting was attended by 81 academic investigators and included 40 talks across 8 sessions.

RESULTS

The central topic areas covered at the meeting included: targeting transcription factor neo-enhancesomes in cancer, AR as a pro-differentiation and oncogenic transcription factor, why few are cured with androgen deprivation therapy and how to change dogma to cure metastatic prostate cancer without castration, reducing prostate cancer morbidity and mortality with genetics, opportunities for radiation to enhance therapeutic benefit in oligometastatic prostate cancer, novel immunotherapeutic approaches, and the new era of artificial intelligence-driven precision medicine.

DISCUSSION

This article provides an overview of the scientific presentations delivered at the 2023 CHPCA Meeting, such that this knowledge can help in facilitating the advancement of prostate cancer research worldwide.

Mitogen signaling strength and duration can control cell cycle decisions

Decades ago, mitogen-promoted signaling duration and strength were observed to be sensed by the cell and to be critical for its decisions: to proliferate or differentiate. Landmark publications established the importance of mitogen signaling not only in the G1 cell cycle phase but also through the S and the G2/M transition. Despite these early milestones, how mitogen signal duration and strength, short and strong or weaker and sustained, control cell fate has been largely unheeded. Here, we center on cardinal signaling-related questions, including (i) how fluctuating mitogenic signals are converted into cell proliferation-differentiation decisions and (ii) why extended duration of weak signaling is associated with differentiation, while bursts of strong and short induce proliferation but, if too strong and long, induce irreversible senescence. Our innovative broad outlook harnesses cell biology and protein conformational ensembles, helping us to define signaling strength, clarify cell cycle decisions, and thus cell fate.

Hippo signaling modulation and its biological implications in urological malignancies

Although cancer diagnosis and treatment have rapidly advanced in recent decades, urological malignancies, which have high morbidity and mortality rates, are among the most difficult diseases to treat. The Hippo signaling is an evolutionarily conserved pathway in organ size control and tissue homeostasis maintenance. Its downstream effectors, Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), are key modulators of numerous physiological and pathological processes. Recent work clearly indicates that Hippo signaling is frequently altered in human urological malignancies. In this review, we discuss the disparate viewpoints on the upstream regulators of YAP/TAZ and their downstream targets and systematically summarize the biological implications. More importantly, we highlight the molecular mechanisms involved in Hippo-YAP signaling to improve our understanding of its role in every stage of prostate cancer, bladder cancer and kidney cancer progression. A better understanding of the biological outcomes of YAP/TAZ modulation will contribute to the establishment of future therapeutic approaches.

Anticancer drugs: How to select small molecule combinations?

Small molecules are at the forefront of anticancer therapies. Successive treatments with single molecules incur drug resistance, calling for combination. Here, we explore the tough choices oncologists face - not just which drugs to use but also the best treatment plans, based on factors such as target proteins, pathways, and gene expression. We consider the reality of cancer's disruption of normal cellular processes, highlighting why it's crucial to understand the ins and outs of current treatment methods. The discussion on using combination drug therapies to target multiple pathways sheds light on a promising approach while also acknowledging the hurdles that come with it, such as dealing with pathway crosstalk. We review options and provide examples and the mechanistic basis, altogether providing the first comprehensive guide to combinatorial therapy selection.

Hippo-YAP/TAZ signaling in breast cancer: Reciprocal regulation of microRNAs and implications in precision medicine

Breast cancer is a molecularly heterogeneous disease and the most common female malignancy. In recent years, therapy approaches have evolved to accommodate molecular diversity, with a focus on more biologically based therapies to minimize negative consequences. To regulate cell fate in human breast cells, the Hippo signaling pathway has been associated with the alpha subtype of estrogen receptors. This pathway regulates tissue size, regeneration, and healing, as well as the survival of tissue-specific stem cells, proliferation, and apoptosis in a variety of organs, allowing for cell differentiation. Hippo signaling is mediated by the kinases MST1, MST2, LATS1, and LATS2, as well as the adaptor proteins SAV1 and MOB. These kinases phosphorylate the downstream effectors of the Hippo pathway, yes-associated protein (YAP), and transcriptional coactivator with PDZ-binding motif (TAZ), suppressing the expression of their downstream target genes. The Hippo signaling pathway kinase cascade plays a significant role in all cancers. Understanding the principles of this kinase cascade would prevent the occurrence of breast cancer. In recent years, small noncoding RNAs, or microRNAs, have been implicated in the development of several malignancies, including breast cancer. The interconnections between miRNAs and Hippo signaling pathway core proteins in the breast, on the other hand, remain poorly understood. In this review, we focused on highlighting the Hippo signaling system, its key parts, its importance in breast cancer, and its regulation by miRNAs and other related pathways.

ENO1 promotes liver carcinogenesis through YAP1-dependent arachidonic acid metabolism

Enolase 1 (ENO1) is a glycolytic enzyme that plays essential roles in various pathological activities including cancer development. However, the mechanisms underlying ENO1-contributed tumorigenesis are not well explained. Here, we uncover that ENO1, as an RNA-binding protein, binds to the cytosine-uracil-guanine-rich elements of YAP1 messenger RNA to promote its translation. ENO1 and YAP1 positively regulate alternative arachidonic acid (AA) metabolism by inverse regulation of PLCB1 and HPGD (15-hydroxyprostaglandin dehydrogenase). The YAP1/PLCB1/HPGD axis-mediated activation of AA metabolism and subsequent accumulation of prostaglandin E2 (PGE2) are responsible for ENO1-mediated cancer progression, which can be retarded by aspirin. Finally, aberrant activation of ENO1/YAP1/PLCB1 and decreased HPGD expression in clinical hepatocellular carcinoma samples indicate a potential correlation between ENO1-regulated AA metabolism and cancer development. These findings underline a new function of ENO1 in regulating AA metabolism and tumorigenesis, suggesting a therapeutic potential for aspirin in patients with liver cancer with aberrant expression of ENO1 or YAP1.

SND1 binds to ERG and promotes tumor growth in genetic mouse models of prostate cancer

SND1 and MTDH are known to promote cancer and therapy resistance, but their mechanisms and interactions with other oncogenes remain unclear. Here, we show that oncoprotein ERG interacts with SND1/MTDH complex through SND1's Tudor domain. ERG, an ETS-domain transcription factor, is overexpressed in many prostate cancers. Knocking down SND1 in human prostate epithelial cells, especially those overexpressing ERG, negatively impacts cell proliferation. Transcriptional analysis shows substantial overlap in genes regulated by ERG and SND1. Mechanistically, we show that ERG promotes nuclear localization of SND1/MTDH. Forced nuclear localization of SND1 prominently increases its growth promoting function irrespective of ERG expression. In mice, prostate-specific Snd1 deletion reduces cancer growth and tumor burden in a prostate cancer model (PB-Cre/Ptenflox/flox/ERG mice), Moreover, we find a significant overlap between prostate transcriptional signatures of ERG and SND1. These findings highlight SND1's crucial role in prostate tumorigenesis, suggesting SND1 as a potential therapeutic target in prostate cancer.

Modulation of the Tumor Microenvironment by Ellagic Acid in Rat Model for Hepatocellular Carcinoma: A Potential Target against Hepatic Cancer Stem Cells

The resistance to therapy and relapse in hepatocellular carcinoma (HCC) is highly attributed to hepatic cancer stem cells (HCSCs). HCSCs are under microenvironment control. This work aimed to assess the systemic effect of ellagic acid (EA) on the HCC microenvironment to decline HCSCs. Fifty Wistar rats were divided into six groups: negative control (CON), groups 2 and 3 for solvents (DMSO), and (OVO). Group 4 was administered EA only. The (HCC-M) group, utilized as an HCC model, administered CCL4 (0.5 mL/kg in OVO) 1:1 v/v, i.p) for 16 weeks. HCC-M rats were treated orally with EA (EA + HCC) 50 mg/kg bw for five weeks. Biochemical, morphological, histopathological, and immunohistochemical studies, and gene analysis using qRT-PCR were applied. Results revealed elevated liver injury biomarkers ALT, AST, ALP, and tumor biomarkers AFP and GGT, and marked nodularity of livers of HCC-M. EA effectively reduced the biomarkers and restored the altered structure of the livers. At the mRNA level, EA downregulated the expression of TGF-α, TGF-β, and VEGF, and restored p53 expression. This induced an increase in apoptotic cells immunostained with caspase3 and decreased the CD44 immunostained HCSCs. EA could modulate the tumor microenvironment in the HCC rat model and ultimately target the HCSCs.

YAP is required for prostate development, regeneration, and prostate stem cell function

Prostate development and regeneration depend on prostate stem cell function, the delicate balance of stem cell self-renewal and differentiation. However, mechanisms modulating prostate stem cell function remain poorly identified. Here, we explored the roles of Yes-associated protein 1 (YAP) in prostate stem cells, prostate development and regeneration. Using YAPfl/fl, CD133-CreER mice, we found that stem cell-specific YAP-deficient mice had compromised branching morphogenesis and epithelial differentiation, resulting in damaged prostate development. YAP inhibition also significantly affected the regeneration process of mice prostate, leading to impaired regenerated prostate. Furthermore, YAP ablation in prostate stem cells significantly reduced its self-renewal activity in vitro, and attenuated prostate regeneration of prostate grafts in vivo. Further analysis revealed a decrease in Notch and Hedgehog pathways expression in YAP inhibition cells, and treatment with exogenous Shh partially restored the self-renewal ability of prostate sphere cells. Taken together, our results revealed the roles of YAP in prostate stem cell function and prostate development and regeneration through regulation of the Notch and Hedgehog signaling pathways.

Pre-Clinical Models to Study Human Prostate Cancer

Prostate cancer is a common cancer among men and typically progresses slowly for several decades before becoming aggressive and spreading to other organs, leaving few treatment options. While large animals have been studied, the dog's prostate is anatomically similar to humans and has been used to study spontaneous prostate cancer. However, most research currently focuses on the mouse as a model organism due to the ability to genetically modify their prostatic tissues for molecular analysis. One milestone in this research was the identification of the prostate-specific promoter Probasin, which allowed for the prostate-specific expression of transgenes. This has led to the generation of mice with aggressive prostatic tumors through overexpression of the SV40 oncogene. The Probasin promoter is also used to drive Cre expression and has allowed researchers to generate prostate-specific loss-of-function studies. Another landmark moment in the process of modeling prostate cancer in mice was the orthoptic delivery of viral particles. This technology allows the selective overexpression of oncogenes from lentivirus or the use of CRISPR to generate complex loss-of-function studies. These genetically modified models are complemented by classical xenografts of human prostate tumor cells in immune-deficient mice. Overall, pre-clinical models have provided a portfolio of model systems to study and address complex mechanisms in prostate cancer for improved treatment options. This review will focus on the advances in each technique.

Gain-of-function mutant p53 together with ERG proto-oncogene drive prostate cancer by beta-catenin activation and pyrimidine synthesis

Whether TMPRSS2-ERG fusion and TP53 gene alteration coordinately promote prostate cancer (PCa) remains unclear. Here we demonstrate that TMPRSS2-ERG fusion and TP53 mutation / deletion co-occur in PCa patient specimens and this co-occurrence accelerates prostatic oncogenesis. p53 gain-of-function (GOF) mutants are now shown to bind to a unique DNA sequence in the CTNNB1 gene promoter and transactivate its expression. ERG and β-Catenin co-occupy sites at pyrimidine synthesis gene (PSG) loci and promote PSG expression, pyrimidine synthesis and PCa growth. β-Catenin inhibition by small molecule inhibitors or oligonucleotide-based PROTAC suppresses TMPRSS2-ERG- and p53 mutant-positive PCa cell growth in vitro and in mice. Our study identifies a gene transactivation function of GOF mutant p53 and reveals β-Catenin as a transcriptional target gene of p53 GOF mutants and a driver and therapeutic target of TMPRSS2-ERG- and p53 GOF mutant-positive PCa.

Targeting Prostate Cancer, the 'Tousled Way'

Androgen deprivation therapy (ADT) has been the mainstay of prostate cancer (PCa) treatment, with success in developing more effective inhibitors of androgen synthesis and antiandrogens in clinical practice. However, hormone deprivation and AR ablation have caused an increase in ADT-insensitive PCas associated with a poor prognosis. Resistance to ADT arises through various mechanisms, and most castration-resistant PCas still rely on the androgen axis, while others become truly androgen receptor (AR)-independent. Our research identified the human tousled-like kinase 1 (TLK1) as a crucial early mediator of PCa cell adaptation to ADT, promoting androgen-independent growth, inhibiting apoptosis, and facilitating cell motility and metastasis. Although explicit, the growing role of TLK1 biology in PCa has remained underrepresented and elusive. In this review, we aim to highlight the diverse functions of TLK1 in PCa, shed light on the molecular mechanisms underlying the transition from androgen-sensitive (AS) to an androgen-insensitive (AI) disease mediated by TLK1, and explore potential strategies to counteract this process. Targeting TLK1 and its associated signaling could prevent PCa progression to the incurable metastatic castration-resistant PCa (mCRPC) stage and provide a promising approach to treating PCa.

ETV4 mediates dosage-dependent prostate tumor initiation and cooperates with p53 loss to generate prostate cancer

The mechanisms underlying ETS-driven prostate cancer initiation and progression remain poorly understood due to a lack of model systems that recapitulate this phenotype. We generated a genetically engineered mouse with prostate-specific expression of the ETS factor, ETV4, at lower and higher protein dosage through mutation of its degron. Lower-level expression of ETV4 caused mild luminal cell expansion without histologic abnormalities, and higher-level expression of stabilized ETV4 caused prostatic intraepithelial neoplasia (mPIN) with 100% penetrance within 1 week. Tumor progression was limited by p53-mediated senescence and Trp53 deletion cooperated with stabilized ETV4. The neoplastic cells expressed differentiation markers such as Nkx3.1 recapitulating luminal gene expression features of untreated human prostate cancer. Single-cell and bulk RNA sequencing showed that stabilized ETV4 induced a previously unidentified luminal-derived expression cluster with signatures of cell cycle, senescence, and epithelial-to-mesenchymal transition. These data suggest that ETS overexpression alone, at sufficient dosage, can initiate prostate neoplasia.

Repression of SLC22A3 by the AR-V7/YAP1/TAZ axis in enzalutamide-resistant castration-resistant prostate cancer

Metastatic castration-resistant prostate cancer (mCRPC) is an aggressive and fatal disease, with most patients succumbing within 1-2 years despite undergoing multiple treatments. Androgen-receptor (AR) inhibitors, including enzalutamide (ENZ), are used for the treatment of mCRPC; however, most patients develop resistance to ENZ. Herein, we propose that the repression of SLC22A3 by AR-V7/YAP1/TAZ conferred ENZ resistance in mCRPC. SLC22A3 expression is specifically downregulated in the ENZ-resistant C4-2B MDVR cells, and when YAP1/TAZ is hyperactivated by AR full-length or AR-V7, these proteins interact with DNMT1 to repress SLC22A3 expression. We observed low SLC22A3 expression and high levels of TAZ or YAP1 in mCRPC patient tissues harbouring AR-V7 and the opposite expression patterns in normal patient tissues. Our findings suggest a mechanism underlying ENZ resistance by providing evidence that the AR-V7/YAP1/TAZ axis represses SLC22A3, which could be a potential treatment target in prostate cancer.

The roles of ETS transcription factors in liver fibrosis

E26 transformation specific or E twenty-six (ETS) protein family consists of 28 transcription factors, five of which, named ETS1/2, PU.1, ERG and EHF, are known to involve in the development of liver fibrosis, and are expected to become diagnostic markers or therapeutic targets of liver fibrosis. In recent years, some small molecule inhibitors of ETS protein family have been discovered, which might open up a new path for the liver fibrosis therapy targeting ETS. This article reviews the research progress of ETS family members in the development liver fibrosis as well as their prospect of clinical application.

NEK1-Mediated Phosphorylation of YAP1 Is Key to Prostate Cancer Progression

The key to preventing mCRPC progression is understanding how androgen-dependent PCa cells progress to independence and modify their transcriptional repertoire accordingly. We recently identified a novel axis of the Hippo pathway characterized by the sequential kinase cascade induced by androgen deprivation, AR−>TLK1B>NEK1>pYAP1-Y407, leading to CRPC adaptation. Phosphorylation of YAP1-Y407 increases upon ADT or induction of DNA damage, correlated with the known increase in NEK1 expression/activity, and this is suppressed in the Y407F mutant. Dominant expression of YAP1-Y407F in Hek293 cells reprograms the YAP1-mediated transcriptome to reduce TEAD- and p73-regulated gene expression and mediates sensitivity to MMC. NEK1 haploinsufficient TRAMP mice display reduced YAP1 expression and, if castrated, fail to progress to overt prostate carcinomas, even while displaying reduced E-Cadherin (E-Cad) expression in hyperplastic ductules. YAP1 overexpression, but not the Y407F mutant, transforms LNCaP cells to androgen-independent growth with a mesenchymal morphology. Immunohistochemical examination of prostate cancer biopsies revealed that the pYAP1-Y407 nuclear signal is low in samples of low-grade cancer but elevated in high GS specimens. We also found that J54, a pharmacological inhibitor of the TLK1>NEK1>YAP1 nexus leading to degradation of YAP1, can suppress the transcriptional reprogramming of LNCaP cells to androgen-independent growth and EMT progression, even when YAP1-WT is overexpressed.

TPM2 attenuates progression of prostate cancer by blocking PDLIM7-mediated nuclear translocation of YAP1

BACKGROUND

Prostate cancer (PCa) is a common malignant tumor of the genitourinary system. Clinical intervention in advanced PCa remains challenging. Tropomyosins 2 (TPM2) are actin-binding proteins and have been found as a biomarker candidate for certain cancers. However, no studies have explored the role of TPM2 in PCa and its regulatory mechanism.

METHODS

TPM2 expression was assessed in Gene Expression Omnibus (GEO) and the Cancer Genome Atlas (TCGA) PCa patient dataset. The effect of TPM2 on PCa progression was assessed in vitro and in vivo by quantifying proliferation, migration, invasion and tumor growth assays, and the mechanism of TPM2 in PCa progression was gradually revealed by Western blotting, immunoprecipitation, and immunofluorescence staining arrays.

RESULTS

TPM2 was found to be severely downregulated in tumor tissues of PCa patients compared with tumor-adjacent normal tissues. In vitro experiments revealed that TPM2 overexpression inhibited PCa cell proliferation, invasion and androgen-independent proliferation. Moreover, TPM2 overexpression inhibited the growth of subcutaneous xenograft tumors in vivo. Mechanistically, this effect was noted to be dependent on PDZ-binding motif of TPM2. TPM2 competed with YAP1 for binding to PDLIM7 through the PDZ-binding motif. The binding of TPM2 to PDLIM7 subsequently inhibited the nuclear transport function of PDLIM7 for YAP1. YAP1 sequestered in the cytoplasm phosphorylated at S127, resulting in its inactivation or degradation which in turn inhibited the expression of YAP1 downstream target genes.

CONCLUSIONS

This study investigated the role of TPM2, PDLIM7, and YAP1 in PCa progression and castration resistance. TPM2 attenuates progression of PCa by blocking PDLIM7-mediated nuclear translocation of YAP1. Accordingly, targeting the expression or functional modulation of TPM2, PDLIM7, or YAP1 has the potential to be an effective therapeutic approach to reduce PCa proliferation and prevent the progression of castration-resistant prostate cancer (CRPC).

Genetic Alterations and Deregulation of Hippo Pathway as a Pathogenetic Mechanism in Bone and Soft Tissue Sarcoma

The Hippo pathway is an evolutionarily conserved modulator of developmental biology with a key role in tissue and organ size regulation under homeostatic conditions. Like other signaling pathways with a significant role in embryonic development, the deregulation of Hippo signaling contributes to oncogenesis. Central to the Hippo pathway is a conserved cascade of adaptor proteins and inhibitory kinases that converge and regulate the activity of the oncoproteins YAP and TAZ, the final transducers of the pathway. Elevated levels and aberrant activation of YAP and TAZ have been described in many cancers. Though most of the studies describe their pervasive activation in epithelial neoplasms, there is increasing evidence pointing out its relevance in mesenchymal malignancies as well. Interestingly, somatic or germline mutations in genes of the Hippo pathway are scarce compared to other signaling pathways that are frequently disrupted in cancer. However, in the case of sarcomas, several examples of genetic alteration of Hippo members, including gene fusions, have been described during the last few years. Here, we review the current knowledge of Hippo pathway implication in sarcoma, describing mechanistic hints recently reported in specific histological entities and how these alterations represent an opportunity for targeted therapy in this heterogeneous group of neoplasm.

Emerging Role of YAP and the Hippo Pathway in Prostate Cancer

The Hippo pathway regulates and contributes to several hallmarks of prostate cancer (PCa). Although the elucidation of YAP function in PCa is in its infancy, emerging studies have shed light on the role of aberrant Hippo pathway signaling in PCa development and progression. YAP overexpression and nuclear localization has been linked to poor prognosis and resistance to treatment, highlighting a therapeutic potential that may suggest innovative strategies to treat cancer. This review aimed to summarize available data on the biological function of the dysregulated Hippo pathway in PCa and identify knowledge gaps that need to be addressed for optimizing the development of YAP-targeted treatment strategies in patients likely to benefit.

Interplay of Developmental Hippo-Notch Signaling Pathways with the DNA Damage Response in Prostate Cancer

Prostate cancer belongs in the class of hormone-dependent cancers, representing a major cause of cancer incidence in men worldwide. Since upon disease onset almost all prostate cancers are androgen-dependent and require active androgen receptor (AR) signaling for their survival, the primary treatment approach has for decades relied on inhibition of the AR pathway via androgen deprivation therapy (ADT). However, following this line of treatment, cancer cell pools often become resistant to therapy, contributing to disease progression towards the significantly more aggressive castration-resistant prostate cancer (CRPC) form, characterized by poor prognosis. It is, therefore, of critical importance to elucidate the molecular mechanisms and signaling pathways underlying the progression of early-stage prostate cancer towards CRPC. In this review, we aim to shed light on the role of major signaling pathways including the DNA damage response (DDR) and the developmental Hippo and Notch pathways in prostate tumorigenesis. We recapitulate key evidence demonstrating the crosstalk of those pathways as well as with pivotal prostate cancer-related 'hubs' such as AR signaling, and evaluate the clinical impact of those interactions. Moreover, we attempt to identify molecules of the complex DDR-Hippo-Notch interplay comprising potentially novel therapeutic targets in the battle against prostate tumorigenesis.

Past, Current, and Future Strategies to Target ERG Fusion-Positive Prostate Cancer

Simple Summary

In addition to its role in development and in the vascular and hematopoietic systems, ERG plays a central role in prostate cancer. Approximately 40–50% of prostate cancer cases are characterized by ERG gene fusions, which lead to ERG overexpression. Importantly, inhibition of ERG activity in prostate cancer cells decreases their viability. Therefore, inhibiting ERG might represent an important step to improve treatment efficacy for patients with ERG-positive prostate tumors. Here, we summarize the attempts made over the past years to repress ERG activity, the current use of ERG fusion detection and the strategies that might be utilized in the future to treat ERG fusion-positive tumors.

Abstract

The ETS family member ERG is a transcription factor with physiological roles during development and in the vascular and hematopoietic systems. ERG oncogenic activity characterizes several malignancies, including Ewing’s sarcoma, leukemia and prostate cancer (PCa). In PCa, ERG rearrangements with androgen-regulated genes—mostly TMPRSS2—characterize a large subset of patients across disease progression and result in androgen receptor (AR)-mediated overexpression of ERG in the prostate cells. Importantly, PCa cells overexpressing ERG are dependent on ERG activity for survival, further highlighting its therapeutic potential. Here, we review the current understanding of the role of ERG and its partners in PCa. We discuss the strategies developed in recent years to inhibit ERG activity, the current therapeutic utility of ERG fusion detection in PCa patients, and the possible future approaches to target ERG fusion-positive tumors.

How do phosphodiesterase-5 inhibitors affect cancer? A focus on glioblastoma multiforme

Since the discovery of phosphodiesterase-5 (PDE5) enzyme overexpression in the central nervous system (CNS) malignancies, investigations have explored the potential capacity of current PDE5 inhibitor drugs for repositioning in the treatment of brain tumors, notably glioblastoma multiforme (GBM). It has now been recognized that these drugs increase brain tumors permeability and enhance standard chemotherapeutics effectiveness. More importantly, studies have highlighted the promising antitumor functions of PDE5 inhibitors, e.g., triggering apoptosis, suppressing tumor cell growth and invasion, and reversing tumor microenvironment (TME) immunosuppression in the brain. However, contradictory reports have suggested a pro-oncogenic role for neuronal cyclic guanosine monophosphate (cGMP), indicating the beneficial function of PDE5 in the brain of GBM patients. Unfortunately, due to the inconsistent preclinical findings, only a few clinical trials are evaluating the therapeutic value of PDE5 inhibitors in GBM treatment. Accordingly, additional studies should be conducted to shed light on the precise effect of PDE5 inhibitors in GBM biology regarding the existing molecular heterogeneities among individuals. Here, we highlighted and discussed the previously investigated mechanisms underlying the impacts of PDE5 inhibitors in cancers, focusing on GBM to provide an overview of current knowledge necessary for future studies.

ETS factors in prostate cancer

The ETS family of proteins consists of 28 transcription factors, many of which play critical roles in both normal tissue development and homeostasis and have been implicated in development and progression of a variety of cancers. In prostate cancer, gene fusion and overexpression of ETS factors ERG, FLI1, ETV1, ETV4 and ETV5 have been found in half of prostate cancer patients in Caucasian men and define the largest genetic subtype of prostate cancer. This review summarizes the data on the discovery, modeling, molecular taxonomy, lineage plasticity and therapeutic targeting of ETS family members in prostate cancer.

Reciprocal YAP1 loss and INSM1 expression in neuroendocrine prostate cancer

Neuroendocrine prostate cancer (NEPC) is a rare but aggressive histologic variant of prostate cancer that responds poorly to androgen deprivation therapy. Hybrid NEPC-adenocarcinoma (AdCa) tumors are common, often eluding accurate pathologic diagnosis and requiring ancillary markers for classification. We recently performed an outlier-based meta-analysis across a number of independent gene expression microarray datasets to identify novel markers that differentiate NEPC from AdCa, including up-regulation of insulinoma-associated protein 1 (INSM1) and loss of Yes-associated protein 1 (YAP1). Here, using diverse cancer gene expression datasets, we show that Hippo pathway-related genes, including YAP1, are among the top down-regulated gene sets with expression of the neuroendocrine transcription factors, including INSM1. In prostate cancer cell lines, transgenic mouse models, and human prostate tumor cohorts, we confirm that YAP1 RNA and YAP1 protein expression are silenced in NEPC and demonstrate that the inverse correlation of INSM1 and YAP1 expression helps to distinguish AdCa from NEPC. Mechanistically, we find that YAP1 loss in NEPC may help to maintain INSM1 expression in prostate cancer cell lines and we further demonstrate that YAP1 silencing likely occurs epigenetically, via CpG hypermethylation near its transcriptional start site. Taken together, these data nominate two additional markers to distinguish NEPC from AdCa and add to data from other tumor types suggesting that Hippo signaling is tightly reciprocally regulated with neuroendocrine transcription factor expression. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

P4HA2-induced prolyl hydroxylation suppresses YAP1-mediated prostate cancer cell migration, invasion, and metastasis

Yes-associated protein 1 (YAP1), a key player in the Hippo pathway, has been shown to play a critical role in tumor progression. However, the role of YAP1 in prostate cancer cell invasion, migration, and metastasis is not well defined. Through functional, transcriptomic, epigenomic, and proteomic analyses, we showed that prolyl hydroxylation of YAP1 plays a critical role in the suppression of cell migration, invasion, and metastasis in prostate cancer. Knockdown (KD) or knockout (KO) of YAP1 led to an increase in cell migration, invasion, and metastasis in prostate cancer cells. Microarray analysis showed that the EMT pathway was activated in Yap1-KD cells. ChIP-seq analysis showed that YAP1 target genes are enriched in pathways regulating cell migration. Mass spectrometry analysis identified P4H prolyl hydroxylase in the YAP1 complex and YAP1 was hydroxylated at multiple proline residues. Proline-to-alanine mutations of YAP1 isoform 3 identified proline 174 as a critical residue, and its hydroxylation suppressed cell migration, invasion, and metastasis. KO of P4ha2 led to an increase in cell migration and invasion, which was reversed upon Yap1 KD. Our study identified a novel regulatory mechanism of YAP1 by which P4HA2-dependent prolyl hydroxylation of YAP1 determines its transcriptional activities and its function in prostate cancer metastasis.

LncRNA coordinates Hippo and mTORC1 pathway activation in cancer

The Hippo and mammalian target of rapamycin complex 1 (mTORC1) pathways are the two predominant pathways that regulate tumour growth and metastasis. Therefore, we explored the potential crosstalk between these two functionally relevant pathways to coordinate their tumour growth-control functions. We found that a Hippo pathway-related long noncoding RNA, HPR, directly interacts with Raptor, an essential component of mTORC1, to upregulate mTORC1 activation by impairing the phosphorylation of Raptor by AMPK. Knockdown or knockout of HPR in breast cancer and cholangiocarcinoma cells led to a reduction in tumour growth. Compared with HPR WT cells, HPR-overexpressing cells exhibited nuclear accumulation of YAP1, and significantly blocked the downregulation of mTORC1 signalling induced by energy stress. Thus, our study reveals a direct link between the Hippo and mTORC1 pathways in the control of tumour growth.

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.

Ras/ERK and PI3K/AKT signaling differentially regulate oncogenic ERG mediated transcription in prostate cells

The TMPRSS2/ERG gene rearrangement occurs in 50% of prostate tumors and results in expression of the transcription factor ERG, which is normally silent in prostate cells. ERG expression promotes prostate tumor formation and luminal epithelial cell fates when combined with PI3K/AKT pathway activation, however the mechanism of synergy is not known. In contrast to luminal fates, expression of ERG alone in immortalized normal prostate epithelial cells promotes cell migration and epithelial to mesenchymal transition (EMT). Migration requires ERG serine 96 phosphorylation via endogenous Ras/ERK signaling. We found that a phosphomimetic mutant, S96E ERG, drove tumor formation and clonogenic survival without activated AKT. S96 was only phosphorylated on nuclear ERG, and differential recruitment of ERK to a subset of ERG-bound chromatin associated with ERG-activated, but not ERG-repressed genes. S96E did not alter ERG genomic binding, but caused a loss of ERG-mediated repression, EZH2 binding and H3K27 methylation. In contrast, AKT activation altered the ERG cistrome and promoted expression of luminal cell fate genes. These data suggest that, depending on AKT status, ERG can promote either luminal or EMT transcription programs, but ERG can promote tumorigenesis independent of these cell fates and tumorigenesis requires only the transcriptional activation function.

ERG is the most common oncogene in prostate cancer. The ERG protein can bind DNA and can activate some genes and repress others. Previous studies indicated that ERG cannot promote cancer by itself, but that ERG works together with mutations that activate the protein AKT. In this study we found that activation of AKT changes the genes that ERG regulates, leading to luminal epithelial differentiation, which is a hallmark of most prostate tumors. However, we also found that a mutant version of ERG that can activate, but cannot repress genes, can drive prostate tumorigenesis without activation of AKT, but this mutant ERG cannot promote luminal differentiation. Our findings suggest that ERG mediated tumorigenesis only requires ERG’s activation function and can occur independent of luminal cell differentiation.

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.

YAP1 overexpression contributes to the development of enzalutamide resistance by induction of cancer stemness and lipid metabolism in prostate cancer

Metastatic castration-resistant prostate cancer (mCRPC) is a malignant and lethal disease caused by relapse after androgen-deprivation (ADT) therapy. Since enzalutamide is innovated and approved by US FDA as a new treatment option for mCRPC patients, drug resistance for enzalutamide is a critical issue during clinical usage. Although several underlying mechanisms causing enzalutamide resistance were previously identified, most of them revealed that drug resistant cells are still highly addicted to androgen and AR functions. Due to the numerous physical functions of AR in men, innovated AR-independent therapy might alleviate enzalutamide resistance and prevent production of adverse side effects. Here, we have identified that yes-associated protein 1 (YAP1) is overexpressed in enzalutamide-resistant (EnzaR) cells. Furthermore, enzalutamide-induced YAP1 expression is mediated through the function of chicken ovalbumin upstream promoter transcription factor 2 (COUP-TFII) at the transcriptional and the post-transcriptional levels. Functional analyses reveal that YAP1 positively regulates numerous genes related to cancer stemness and lipid metabolism and interacts with COUP-TFII to form a transcriptional complex. More importantly, YAP1 inhibitor attenuates the growth and cancer stemness of EnzaR cells in vitro and in vivo. Finally, YAP1, COUP-TFII, and miR-21 are detected in the extracellular vesicles (EVs) isolated from EnzaR cells and sera of patients. In addition, treatment with EnzaR-EVs induces the abilities of cancer stemness, lipid metabolism and enzalutamide resistance in its parental cells. Taken together, these results suggest that YAP1 might be a crucial factor involved in the development of enzalutamide resistance and can be an alternative therapeutic target in prostate cancer.

Narciclasine is a novel YAP inhibitor that disturbs interaction between YAP and TEAD4

Yes-associated protein (YAP) is involved in development, cell growth, cell size, and homeostasis and plays a key role in the progression of various cancers. Among them, constitutive activation of YAP can often be observed in malignant mesothelioma, which arises in the pleura, peritoneum, and pericardium because of inactivation of the Hippo pathway. To date, however, only less-effective treatments such as chemotherapy, radiation therapy, and surgery are available for patients with malignant mesothelioma. In this study, we identified narciclasine as a novel YAP inhibitor that prevents YAP from interacting with TEAD4 because it competes with TEAD4 for binding to YAP. Furthermore, narciclasine could perturb the cell growth and colony formation of malignant mesothelioma NCI-H290 cells in addition to inhibiting their growth in nude mice. Therefore, narciclasine might be a potential seed for a novel antitumor drug against malignant mesothelioma and other cancers in which hyperactivation and/or overexpression of YAP are observed.

NEK1 Phosphorylation of YAP Promotes Its Stabilization and Transcriptional Output

Simple Summary

We earlier described the involvement of the TLK1>NEK1>ATR>Chk1 axis as a key determinant of cell cycle arrest in androgen-dependent prostate cancer (PCa) cells after androgen deprivation. We now report that the TLK1>NEK1 axis is also involved in stabilization of yes-associated protein 1 (YAP1), the transcriptional co-activator in the Hippo pathway, presumably facilitating reprogramming of the cells toward castration-resistant PCa (CRPC). NEK1 interacts with YAP1 physically resulting in its phosphorylation of 6 residues, which enhance its stability and activity. Analyses of cancer Protein Atlas and TCGA expression panels revealed a link between activated NEK1 and YAP1 expression and several YAP transcription targets.

Abstract

Most prostate cancer (PCa) deaths result from progressive failure in standard androgen deprivation therapy (ADT), leading to metastatic castration-resistant PCa (mCRPC); however, the mechanism and key players leading to this are not fully understood. While studying the role of tousled-like kinase 1 (TLK1) and never in mitosis gene A (NIMA)-related kinase 1 (NEK1) in a DNA damage response (DDR)-mediated cell cycle arrest in LNCaP cells treated with bicalutamide, we uncovered that overexpression of wt-NEK1 resulted in a rapid conversion to androgen-independent (AI) growth, analogous to what has been observed when YAP1 is overexpressed. We now report that overexpression of wt-NEK1 results in accumulation of YAP1, suggesting the existence of a TLK1>NEK1>YAP1 axis that leads to adaptation to AI growth. Further, YAP1 is co-immunoprecipitated with NEK1. Importantly, NEK1 was able to phosphorylate YAP1 on six residues in vitro, which we believe are important for stabilization of the protein, possibly by increasing its interaction with transcriptional partners. In fact, knockout (KO) of NEK1 in NT1 PCa cells resulted in a parallel decrease of YAP1 level and reduced expression of typical YAP-regulated target genes. In terms of cancer potential implications, the expression of NEK1 and YAP1 proteins was found to be increased and correlated in several cancers. These include PCa stages according to Gleason score, head and neck squamous cell carcinoma, and glioblastoma, suggesting that this co-regulation is imparted by increased YAP1 stability when NEK1 is overexpressed or activated by TLK1, and not through transcriptional co-expression. We propose that the TLK1>NEK1>YAP1 axis is a key determinant for cancer progression, particularly during the process of androgen-sensitive to -independent conversion during progression to mCRPC.

Characterization of the genomic landscape and actionable mutations in Chinese breast cancers by clinical sequencing

The remarkable advances in next-generation sequencing technology have enabled the wide usage of sequencing as a clinical tool. To promote the advance of precision oncology for breast cancer in China, here we report a large-scale prospective clinical sequencing program using the Fudan-BC panel, and comprehensively analyze the clinical and genomic characteristics of Chinese breast cancer. The mutational landscape of 1,134 breast cancers reveals that the most significant differences between Chinese and Western patients occurred in the hormone receptor positive, human epidermal growth factor receptor 2 negative breast cancer subtype. Mutations in p53 and Hippo signaling pathways are more prevalent, and 2 mutually exclusive and 9 co-occurring patterns exist among 9 oncogenic pathways in our cohort. Further preclinical investigation partially suggests that NF2 loss-of-function mutations can be sensitive to a Hippo-targeted strategy. We establish a public database (Fudan Portal) and a precision medicine knowledge base for data exchange and interpretation. Collectively, our study presents a leading approach to Chinese precision oncology treatment and reveals potentially actionable mutations in breast cancer.

Chinese breast cancer patients have not been well represented in clinical sequencing studies. Here the authors analyse the mutational landscape of 1,134 Chinese breast cancer patients, finding actionable targets and a higher prevalence of p53 and Hippo pathway mutations compared to Western cohorts.

The mevalonate pathway promotes the metastasis of osteosarcoma by regulating YAP1 activity via RhoA

Osteosarcoma is the most common malignant bone tumour, and the metastasis of osteosarcoma is an important cause of death. Evidence has shown that the mevalonate pathway is highly activated and is expected to be a new target for tumour therapy. In this study, we investigated the effect of mevalonate signalling on osteosarcoma metastasis and its molecular mechanism. First, we found that the key rate-limiting enzyme of mevalonate signalling, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), was highly expressed in osteosarcoma cells, and inhibition of HMGCR with simvastatin significantly inhibited the motility of 143B cells. Next, we found that YAP1 activity was significantly upregulated in osteosarcoma cells and that YAP1 knockdown inhibited the motility of 143B cells. We also found that the mevalonate pathway regulated the motility of 143B cells by modulating YAP1 phosphorylation and cellular localization. Moreover, we found that the activity of YAP1 was regulated by the mevalonate pathway by modulating the cell membrane localization of RhoA. Finally, we demonstrated that inhibition of the mevalonate pathway notably reduced the lung metastasis of 143B cells, as reflected by the decreased incidence and number of metastatic nodules and the increased survival time of the nude mice. Taken together, our findings suggest that the mevalonate pathway can promote the metastasis of osteosarcoma by activating YAP1 via RhoA. Inhibition of the mevalonate pathway may be a promising therapeutic strategy for osteosarcoma metastasis.

Schwannoma development is mediated by Hippo pathway dysregulation and modified by RAS/MAPK signaling

Schwannomas are tumors of the Schwann cells that cause chronic pain, numbness, and potentially life-threatening impairment of vital organs. Despite the identification of causative genes, including NF2 (Merlin), INI1/SMARCB1, and LZTR1, the exact molecular mechanism of schwannoma development is still poorly understood. Several studies have identified Merlin as a key regulator of the Hippo, MAPK, and PI3K signaling pathways; however, definitive evidence demonstrating the importance of these pathways in schwannoma pathogenesis is absent. Here, we provide direct genetic evidence that dysregulation of the Hippo pathway in the Schwann cell lineage causes development of multiple schwannomas in mice. We found that canonical Hippo signaling through the effectors YAP/TAZ is required for schwannomagenesis and that MAPK signaling modifies schwannoma formation. Furthermore, cotargeting YAP/TAZ transcriptional activity and MAPK signaling demonstrated a synergistic therapeutic effect on schwannomas. Our new model provides a tractable platform to dissect the molecular mechanisms underpinning schwannoma formation and the role of combinatorial targeted therapy in schwannoma treatment.

Canonical Hippo signaling through the effectors YAP/TAZ is required for the development of peripheral nervous system tumors of Schwann cells, and MAPK signaling modifies schwannoma formation.

Rearranged ERG confers robustness to prostate cancer cells by subverting the function of p53

OBJECTIVE

ERG rearrangements are frequent and early events in prostate cancer. The functional role of rearranged ERG, however, is still incompletely understood. ERG rearrangements are maintained during prostate cancer progression suggesting that they may confer a selective advantage. The molecular basis of this notion is the subject of this study.

METHODS

A variety of immunological methods were used to characterize the effects of rearranged ERG on p53. Consequences of an overexpression of N-terminally deleted ERG on p53 function were interrogated by measuring apoptosis and cellular senescence in the presence or absence of exogenous DNA damage. Effects of N-terminally deleted ERG on the transactivation function of p53 were analyzed by qRT-PCR.

RESULTS

We show that overexpression of ERG leads to an increased basal level of DNA damage and a stabilization of p53 that involves a sequestration of its E3 ubiquitin ligase, MDM2, into nucleoli. A higher p53 expression was also observed in vivo in an ERG-overexpressing prostatic intraepithelial neoplasia mouse model. The correlation between ERG and p53 expression was corroborated in 163 patients with prostate cancer. ERG overexpression was found to inhibit both apoptosis and cellular senescence induced by exogenous DNA damage. Mechanistically, this protective effect of ERG involved an abrogation of the DNA damage-induced expression of p53 target genes.

CONCLUSIONS

By protecting tumor cells from the antiproliferative consequences of genotoxic stress, ERG may allow the survival and proliferation of genomically unstable tumor cells. Targeting ERG may therefore represent a promising strategy to suppress such adverse features during prostate cancer progression.

Up regulation of the Hippo signalling effector YAP1 is linked to early biochemical recurrence in prostate cancers

The transcriptional coactivator YAP1 controls the balance between cell proliferation and apoptosis. YAP1 overexpression is linked to poor prognosis in many cancer types, yet its role in prostate cancer is unknown. Here, we applied YAP1 immunohistochemistry to a tissue microarray containing 17,747 clinical prostate cancer specimens. Cytoplasmic and nuclear YAP1 staining was seen in 81% and 63% of tumours. For both cytoplasmic and nuclear YAP1 staining, high levels were associated with advanced tumour stage, classical and quantitative Gleason grade, positive nodal stage, positive surgical margin, high KI67 labelling index, and early biochemical recurrence (p < 0.0001 each). The prognostic role of YAP1 staining was independent of established prognostic features in multivariate models (p < 0.001). Comparison with previously studied molecular markers identified associations between high YAP1 staining, TMPRSS2:ERG fusion (p < 0.0001), high androgen receptor (AR) expression (p < 0.0001), high Ki67 labelling index (p < 0.0001), and PTEN and 8p deletions (p < 0.0001 each). In conclusion, high YAP1 protein expression is an independent predictor of unfavourable disease course in prostate cancer. That cytoplasmic and nuclear YAP1 staining is equally linked to phenotype and prognosis fits well to a model where YAP1 activation during tumour progression includes up regulation, cytoplasmic accumulation and subsequent translocation to the nucleus.

Targeting Hippo coactivator YAP1 through BET bromodomain inhibition in esophageal adenocarcinoma

Hippo/YAP1 signaling is a major regulator of organ size, cancer stemness, and aggressive phenotype. Thus, targeting YAP1 may provide a novel therapeutic strategy for tumors with high YAP1 expression in esophageal cancer (EC). Chromatin immunoprecipitation (ChiP) and quantitative ChiP‐PCR were used to determine the regulation of the chromatin remodeling protein bromodomain‐containing protein 4 (BRD4) on YAP1. The role of the bromodomain and extraterminal motif (BET) inhibitor JQ1, an established BRD4 inhibitor, on inhibition of YAP1 in EC cells was dissected using western blot, immunofluorescence, qPCR, and transient transfection. The antitumor activities of BET inhibitor were further examined by variety of functional assays, cell proliferation (MTS), tumorsphere, and ALDH1+ labeling in vitro and in vivo. Here, we show that BRD4 regulates YAP1 expression and transcription. ChiP assays revealed that BRD4 directly occupies YAP1 promoter and that JQ1 robustly blocks BRD4 binding to the YAP1 promoter. Consequently, JQ1 strongly suppresses constitutive or induced YAP1 expression and transcription in EC cells and YAP1/Tead downstream transcriptional activity. Intriguingly, radiation‐resistant cells that acquire strong cancer stem cell traits and an aggressive phenotype can be effectively suppressed by JQ1 as assessed by cell proliferation, tumorsphere formation, and reduction in the ALDH1+ cells. Moreover, effects of JQ1 are synergistically amplified by the addition of docetaxel in vitro and in vivo. Our results demonstrate that BRD4 is a critical regulator of Hippo/YAP1 signaling and that BRD4 inhibitor JQ1 represents a new class of inhibitor of Hippo/YAP1 signaling, primarily targeting YAP1 high and therapy‐resistant cancer cells enriched with cancer stem cell properties.

From genomics to functions: preclinical mouse models for understanding oncogenic pathways in prostate cancer

Next-generation sequencing has revealed numerous genomic alterations that induce aberrant signaling activities in prostate cancer (PCa). Among them are pathways affecting multiple cancer types, including the PI3K/AKT/mTOR, p53, Rb, Ras/Raf/MAPK, Myc, FGF, and Wnt signaling pathways, as well as ones that are prominent in PCa, including alterations in genes of AR signaling, the ETS family, NKX3.1, and SPOP. Cross talk among the oncogenic pathways can confer PCa resistance to therapy, particularly in advanced tumors, which are castration-resistant or show neuroendocrine features. Various experimental models, such as cancer cell lines, animal models, and patient-derived xenografts and organoids have been utilized to dissect PCa progression mechanisms. Here, we review the current preclinical mouse models for studying the most commonly altered pathways in PCa, with an emphasis on their interplays. We highlight the power of genetically engineered mouse models (GEMMs) in translating genomic discoveries into understanding of the functions of these oncogenic events in vivo. Developing and analyzing PCa mouse models will undoubtedly continue to offer new insights into tumor biology and guide novel rationalized therapy.

The Hippo pathway in the heart: pivotal roles in development, disease, and regeneration

The Hippo-YAP (Yes-associated protein) pathway is an evolutionarily and functionally conserved regulator of organ size and growth with crucial roles in cell proliferation, apoptosis, and differentiation. This pathway has great potential for therapeutic manipulation in different disease states and to promote organ regeneration. In this Review, we summarize findings from the past decade revealing the function and regulation of the Hippo-YAP pathway in cardiac development, growth, homeostasis, disease, and regeneration. In particular, we highlight the roles of the Hippo-YAP pathway in endogenous heart muscle renewal, including the pivotal role of the Hippo-YAP pathway in regulating cardiomyocyte proliferation and differentiation, stress response, and mechanical signalling. The human heart lacks the capacity to self-repair; therefore, the loss of cardiomyocytes after injury such as myocardial infarction can result in heart failure and death. Despite substantial advances in the treatment of heart failure, an enormous unmet clinical need exists for alternative treatment options. Targeting the Hippo-YAP pathway has tremendous potential for developing therapeutic strategies for cardiac repair and regeneration for currently intractable cardiovascular diseases such as heart failure. The lessons learned from cardiac repair and regeneration studies will also bring new insights into the regeneration of other tissues with limited regenerative capacity.

STUB1 suppresseses tumorigenesis and chemoresistance through antagonizing YAP1 signaling

Yes-associated protein (YAP) is a component of the canonical Hippo signaling pathway that is known to play essential roles in modulating organ size, development, and tumorigenesis. Activation or upregulation of YAP1, which contributes to cancer cell survival and chemoresistance, has been verified in different types of human cancers. However, the molecular mechanism of YAP1 upregulation in cancer is still unclear. Here we report that the E3 ubiquitin ligase STUB1 ubiquitinates and destabilizes YAP1, thereby inhibiting cancer cell survival. Low levels of STUB1 expression were correlated with increased protein levels of YAP1 in human gastric cancer cell lines and patient samples. Moreover, we revealed that STUB1 ubiquitinates YAP1 at the K280 site by K48-linked polyubiquitination, which in turn increases YAP1 turnover and promotes cellular chemosensitivity. Overall, our study establishes YAP1 ubiquitination and degradation mediated by the E3 ligase STUB1 as an important regulatory mechanism in gastric cancer, and provides a rationale for potential therapeutic interventions.

EphA2-to-YAP pathway drives gastric cancer growth and therapy resistance

Yes-associated protein (YAP) is a transcriptional coactivator that promotes cell proliferation, stem cell maintenance and tissue homeostasis. The YAP activity is primarily regulated through an inhibitory phosphorylation by the serine/threonine kinases of Hippo pathway. Here, we show that receptor tyrosine kinase (RTK) erythropoietin-producing hepatocellular receptor A2 (EphA2) interacts with and phosphorylates YAP protein, leading to stabilization, nuclear translocation and activation of YAP in gastric cancer (GC) cells. EphA2 induces chemotherapy-resistance by increasing YAP stability and nuclear YAP protein. Knockdown of YAP blocks EphA2-induced tumor growth in GC xenograft mouse models. Importantly, the coactivation of EphA2 and YAP is manifested in clinical human GC, and is related to GC recurrence. Thus, our results establish a novel EphA2-to-YAP pathway that drives GC growth, progression and therapy-resistance, targeting this pathway would be an efficient way for the treatment of GC, particularly chemotherapy-resistant GC.

DLC1 deficiency and YAP signaling drive endothelial cell contact inhibition of growth and tumorigenesis

Deleted in Liver Cancer 1 (DLC1) is a tumor suppressor gene deleted in many cancers, including angiosarcoma, an aggressive malignancy of endothelial cell derivation. DLC1-deficiency in primary endothelial cells causes the loss of cell contact inhibition of growth through incompletely defined mechanisms. We report that DLC1 is a regulator of YAP, a transcriptional coactivator of proliferation-promoting and tumor-promoting genes; when confluent, active/nuclear YAP was significantly more abundant in DLC1-deficient endothelial cells compared with control cells. We also found that YAP is a required effector of the loss of cell contact inhibition of growth manifested by DLC1-deficient endothelial cells, as the silencing of YAP prevents this loss. Consistently, human angiosarcomas specimens contained a significantly greater proportion of DLC1^- tumor cells with nuclear YAP compared with the DLC1⁺ normal cells in the adjacent tissue. Verteporfin, an inhibitor of YAP, significantly reduced angiosarcoma growth in mice. These results identify YAP as a previously unrecognized effector of DLC1 deficiency-associated loss of cell contact growth inhibition in endothelial cells and a potential therapeutic target in angiosarcoma.

NR1B2 suppress kidney renal clear cell carcinoma (KIRC) progression by regulation of LATS 1/2-YAP signaling

BACKGROUND

Kidney Renal Clear Cell Carcinoma (KIRC) accounts for 75% of all renal cancers. Previous study had conflict evidences regarding NR1B2 role in cancer, and its expression and biological role in KIRC remained unclear. Our aims were to characterize the role of NR1B2 in KIRC.

METHODS

NR1B2 expression in TCGA database were analyzed. Clinical KIRC samples were examined by RT-PCR, western blot and tissue microarray (TMA). The relationship between NR1B2 expression and the clinical characteristics were evaluated. KIRC cell line were stably overexpressed NR1B2 or with an NR1B2 knocked down using lentivirus system. The cells were analyzed by migration and invasion assay, then injected into nude mice to assess tumor growth and metastasis. EMT marker expression and LATS 1/2-YAP pathway demonstration were detected by the TCGA database and western blot.

RESULTS

The expression of NR1B2 in KIRC was significantly down-regulated in the TCGA database and our clinical samples. Moreover, NR1B2 expression negatively correlated with tumor stage and positively correlated with overall and disease-free survival rate. Univariate and multivariate analyses indicated the expression level of NR1B2 could be used as an independent factor for predicting the prognosis of KIRC. Overexpression NR1B2 significantly inhibited and knockdown NR1B2 markedly promoted KIRC cell invasion and metastasis both in vitro and in vivo. Mechanistic investigations revealed that NR1B2 might be a tumor suppressor to inhibit EMT through the LATS1/2-YAP pathway.

CONCLUSIONS

our results defined NR1B2 as a tumor suppressor in KIRC that restricted EMT by the LATS1/2-YAP pathway.

Helicobacter pylori-induced YAP1 nuclear translocation promotes gastric carcinogenesis by enhancing IL-1β expression

Gastric cancer (GC) is one of the most common and malignant pathologies, and a significant portion of GC incidences develops from Helicobacter pylori (Hp)-induced chronic gastritis. Although the exact mechanisms of GC are complex and poorly understood, gastric carcinogenesis is a good model to investigate how inflammation and infection collaboratively promote tumorigenesis. Yes-associated protein 1 (YAP1) is the key effector of the Hippo pathway, which is silenced in most human cancers. Herein, we verified the tumor-promoting effect of YAP1 in vitro, in vivo, and in human specimens. We revealed that YAP1 displays nuclear translocation and works with TEAD to activate transcription of the crucial inflammatory cytokine IL-1β in gastric cells infected with Hp. As IL-1ß accounts for inflammation-associated tumorigenesis, this process can lead to gastric carcinogenesis. Thus, in addition to activating proliferation genes, YAP1 also plays a major role in inflammation amplification by activating inflammatory cytokine genes. Excitingly, our research demonstrates that transfection of mutant plasmid YAP-5SA/S94A or addition of the drug verteporfin, both of which are thought to disrupt the YAP1-TEAD interaction, can arrest the carcinogenesis process. These findings can provide new approaches to GC treatment.

Implication for Cancer Stem Cells in Solid Cancer Chemo-Resistance: Promising Therapeutic Strategies Based on the Use of HDAC Inhibitors

Resistance to therapy in patients with solid cancers represents a daunting challenge that must be addressed. Indeed, current strategies are still not effective in the majority of patients; which has resulted in the need for novel therapeutic approaches. Cancer stem cells (CSCs), a subset of tumor cells that possess self-renewal and multilineage differentiation potential, are known to be intrinsically resistant to anticancer treatments. In this review, we analyzed the implications for CSCs in drug resistance and described that multiple alterations in morphogenetic pathways (i.e., Hippo, Wnt, JAK/STAT, TGF-β, Notch, Hedgehog pathways) were suggested to be critical for CSC plasticity. By interrogating The Cancer Genome Atlas (TCGA) datasets, we first analyzed the prevalence of morphogenetic pathways alterations in solid tumors with associated outcomes. Then, by highlighting epigenetic relevance in CSC development and maintenance, we selected histone deacetylase inhibitors (HDACi) as potential agents of interest to target this subpopulation based on the pleiotropic effects exerted specifically on altered morphogenetic pathways. In detail, we highlighted the role of HDACi in solid cancers and, specifically, in the CSC subpopulation and we pointed out some mechanisms by which HDACi are able to overcome drug resistance and to modulate stemness. Although, further clinical and preclinical investigations should be conducted to disclose the unclear mechanisms by which HDACi modulate several signaling pathways in different tumors. To date, several lines of evidence support the testing of novel combinatorial therapeutic strategies based on the combination of drugs commonly used in clinical practice and HDACi to improve therapeutic efficacy in solid cancer patients.

HNF4α and CDX2 Regulate Intestinal YAP1 Promoter Activity

The Hippo pathway is important for tissue homeostasis, regulation of organ size and growth in most tissues. The co-transcription factor yes-associated protein 1 (YAP1) serves as a main downstream effector of the Hippo pathway and its dysregulation increases cancer development and blocks colonic tissue repair. Nevertheless, little is known about the transcriptional regulation of YAP1 in intestinal cells. The aim of this study to identify gene control regions in the YAP1 gene and transcription factors important for intestinal expression. Bioinformatic analysis of caudal type homeobox 2 (CDX2) and hepatocyte nuclear factor 4 alpha (HNF4α) chromatin immunoprecipitated DNA from differentiated Caco-2 cells revealed potential intragenic enhancers in the YAP1 gene. Transfection of luciferase-expressing YAP1 promoter-reporter constructs containing the potential enhancer regions validated one potent enhancer of the YAP1 promoter activity in Caco-2 and T84 cells. Two potential CDX2 and one HNF4α binding sites were identified in the enhancer by in silico transcription factor binding site analysis and protein-DNA binding was confirmed in vitro using electrophoretic mobility shift assay. It was found by chromatin immunoprecipitation experiments that CDX2 and HNF4α bind to the YAP1 enhancer in Caco-2 cells. These results reveal a previously unknown enhancer of the YAP1 promoter activity in the YAP1 gene, with importance for high expression levels in intestinal epithelial cells. Additionally, CDX2 and HNF4α binding are important for the YAP1 enhancer activity in intestinal epithelial cells.

The Hippo Pathway in Prostate Cancer

Despite recent efforts, prostate cancer (PCa) remains one of the most common cancers in men. Currently, there is no effective treatment for castration-resistant prostate cancer (CRPC). There is, therefore, an urgent need to identify new therapeutic targets. The Hippo pathway and its downstream effectors—the transcriptional co-activators, Yes-associated protein (YAP) and its paralog, transcriptional co-activator with PDZ-binding motif (TAZ)—are foremost regulators of stem cells and cancer biology. Defective Hippo pathway signaling and YAP/TAZ hyperactivation are common across various cancers. Here, we draw on insights learned from other types of cancers and review the latest advances linking the Hippo pathway and YAP/TAZ to PCa onset and progression. We examine the regulatory interaction between Hippo-YAP/TAZ and the androgen receptor (AR), as main regulators of PCa development, and how uncontrolled expression of YAP/TAZ drives castration resistance by inducing cellular stemness. Finally, we survey the potential therapeutic targeting of the Hippo pathway and YAP/TAZ to overcome PCa.

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.

The hippo pathway effector Yes-associated protein promotes epithelial proliferation and remodeling in chronic rhinosinusitis with nasal polyps

BACKGROUND

Hippo-Yes-associated protein (YAP) pathway plays an important role in epithelial cell proliferation and development. However, its possible role in chronic rhinosinusitis with nasal polyps (CRSwNP) remains unknown. We aim to investigate it on nasal epithelial proliferation and remodeling in CRSwNP.

METHODS

The expressions of hippo pathway components as well as Ki-67 and E-cadherin in the sinonasal mucosa and nasal epithelial cells were analyzed in 14 controls, 14 eosinophilic CRSwNP, and 14 noneosinophilic CRSwNP. Nasal epithelial cells from 6 controls, 6 eosinophilic CRSwNP, and 6 noneosinophilic CRSwNP were cultured and treated with lipopolysaccharide (LPS), Poly(I:C), or a selective YAP inhibitor verteporfin (VP).

RESULTS

The hippo pathway components MST1, LATS1/2, YAP, and TEAD1 were increased in both eosinophilic and noneosinophilic CRSwNP, particularly in nasal epithelial cells, along with upregulation of Ki-67 and downregulation of E-cadherin. The mRNA levels of YAP positively correlated with the Ki-67 mRNA levels, and negatively associated with the E-cadherin mRNA levels in polyp tissues and epithelial cells from nasal polyps (NPECs). LPS and Poly(I:C) upregulated the YAP expression in nasal epithelial cells accompanied by increased TEAD1 and Ki-67 expression. Conversely, YAP inhibition by VP decreased TEAD1 and Ki-67 expression in NPECs.

CONCLUSIONS

Hippo pathway components are abnormally upregulated in NPECs, and its effector YAP promotes nasal epithelial cells proliferation and remodeling in CRSwNP. It provides a rationale to explore inhibition of YAP as a novel therapeutic strategy for reducing the epithelial proliferation and remodeling in CRSwNP.