The Hippo pathway in disease and therapy: cancer and beyond

Targeting the Hippo Pathway in Cutaneous Melanoma

Melanoma is the most aggressive form of skin cancer. In the advanced stage of development, it is resistant to currently available therapeutic modalities. Increased invasiveness and metastatic potential depend on several proteins involved in various signal transduction pathways. Hippo signaling plays a vital role in malignant transformation. Dysfunctions of the Hippo pathway initiate the expression of tumor growth factors and are associated with tumor growth and metastasis formation. This review summarizes the recent achievements in studying the role of the Hippo pathway in melanoma pathogenesis and points to the potential specific targets for anti-melanoma therapy.

Neurofibromin 2 modulates Mammalian Ste2-like kinases1/2 and large tumor suppressor gene1 expression in A549 lung cancer cell line

AIM

To explore the impact of up- or down-regulation of Neurofibromin 2 (NF2) on the expression of downstream Hippo pathway genes, large tumor suppressor gene1 (LATS1), and phosphorylation of Mammalian Ste2-like kinases1/2 (MST1/2), in lung cancer cells.

METHODS

A549 lung cancer cells were used. The NF2 was down-regulated by si-RNA interference and upregulated by lentiviral vector mediated overexpression. The LATS1 and MST1/2 expressions were evaluated by real-time PCR and western blot.

RESULTS

Down-regulation of NF2 decreased LATS1 and MST1/2 level (P<0.05). Overexpression of NF2 increased LATS1 (P<0.05) and Mammalian Ste2-like kinases1 (MST1) (P<0.05), suggesting LATS1 and MST1 are modulated by NF2 in a lung cancer cell line.

CONCLUSIONS

NF2 mediates the downstream LATS1 and MST1/2 expressions in a lung cancer cell line.

Clinicopathological Significance of DUB3 Expression in Non-small Cell Lung Cancer and Relationship Between DUB3 Expression and LATS1 Expression

BACKGROUND/AIM

Deubiquitinating enzyme 3 (DUB3) is a member of the ubiquitin-specific proteases family involved in regulating cell proliferation, invasion, and apoptosis. However, the biological role and clinicopathological significance of DUB3 expression have not been elucidated in non-small cell lung cancer (NSCLC).

PATIENTS AND METHODS

We evaluated the expression of DUB3 by immunohistochemistry using tissue microarrays and assessed the clinicopathologic significance of DUB3 expression levels in 187 patients with NSCLC, including its two major subtypes (93 cases of adenocarcinoma and 72 cases of squamous cell carcinoma).

RESULTS

In adenocarcinoma, we observed that DUB3 expression had an effect on tumor size (p=0.030), vessel invasion (p=0.038), T stage (p=0.014), and tumor recurrence (p=0.002). Kaplan-Meier curves with log-rank test showed that high DUB3 expression was correlated with significantly more favorable clinical outcomes compared to those of the low expression group in adenocarcinoma (p=0.013). Multivariate analysis of disease-free survival also demonstrated that DUB3 expression is an independent prognostic factor in lung adenocarcinoma (p=0.017). Additionally, we identified the correlation between DUB3 and the expression of large tumor suppressor kinase 1 expression, a core protein of the Hippo pathway.

CONCLUSION

DUB3 could function as a tumor suppressor by regulating the Hippo pathway in lung adenocarcinoma and can be considered a powerful predictive factor and therapeutic target.

Novel Biomarkers for Inflammatory Bowel Disease and Colorectal Cancer: An Interplay between Metabolic Dysregulation and Excessive Inflammation

Persistent inflammation can trigger altered epigenetic, inflammatory, and bioenergetic states. Inflammatory bowel disease (IBD) is an idiopathic disease characterized by chronic inflammation of the gastrointestinal tract, with evidence of subsequent metabolic syndrome disorder. Studies have demonstrated that as many as 42% of patients with ulcerative colitis (UC) who are found to have high-grade dysplasia, either already had colorectal cancer (CRC) or develop it within a short time. The presence of low-grade dysplasia is also predictive of CRC. Many signaling pathways are shared among IBD and CRC, including cell survival, cell proliferation, angiogenesis, and inflammatory signaling pathways. Current IBD therapeutics target a small subset of molecular drivers of IBD, with many focused on the inflammatory aspect of the pathways. Thus, there is a great need to identify biomarkers of both IBD and CRC, that can be predictive of therapeutic efficacy, disease severity, and predisposition to CRC. In this study, we explored the changes in biomarkers specific for inflammatory, metabolic, and proliferative pathways, to help determine the relevance to both IBD and CRC. Our analysis demonstrated, for the first time in IBD, the loss of the tumor suppressor protein Ras associated family protein 1A (RASSF1A), via epigenetic changes, the hyperactivation of the obligate kinase of the NOD2 pathogen recognition receptor (receptor interacting protein kinase 2 [RIPK2]), the loss of activation of the metabolic kinase, AMP activated protein kinase (AMPKα1), and, lastly, the activation of the transcription factor and kinase Yes associated protein (YAP) kinase, that is involved in proliferation of cells. The expression and activation status of these four elements are mirrored in IBD, CRC, and IBD-CRC patients and, importantly, in matched blood and biopsy samples. The latter would suggest that biomarker analysis can be performed non-invasively, to understand IBD and CRC, without the need for invasive and costly endoscopic analysis. This study, for the first time, illustrates the need to understand IBD or CRC beyond an inflammatory perspective and the value of therapeutics directed to reset altered proliferative and metabolic states within the colon. The use of such therapeutics may truly drive patients into remission.

Identification of a Yorkie homolog from Litopenaeus vannamei as a negative regulator in anti-WSSV immune response

Hippo signaling pathway is a serine threonine kinase cascade that is evolutionary conserved with well-established roles in organ size control, development, tumorigenesis and immunity. As its core molecule, Yorkie also plays an important role against pathogen. In this study, we cloned and characterized a Yorkie homolog from Litopenaeus vannamei, designed as LvYKI, which has a 1650 bp open reading frame. It has the characterized domains of Yokie family, and displayed to be close to the insects and crustacean. Quantitative Real-time PCR showed that LvYKI had different regulatory mechanisms in different tissues. The transcriptional level of Lvyki was down-regulated in gill, while up-regulated in hepatopancreas post white spot syndrome virus (WSSV) infection. Moreover, the expression and phosphorylation of LvYKI was reduced upon WSSV infection, which indicated that LvYKI was involved in WSSV infection. Furthermore, RNAi was performed to evaluate the role of LvYKI in shrimp immune responses. Knocking down of Lvyki resulted in inhibition of the transcription of WSSV gene ie1 and vp28, and delayed mortality of shrimp post WSSV infection. Meanwhile, the apoptosis of hemocyte was increased as well. All results suggested that shrimp can promote apoptosis to resist WSSV infection mediated by down-regulation of LvYKI. In addition, it was found that LvYKI could interact with Lvβ-catenin, which cross-linked the Wnt and Hippo signaling pathway in innate immunity. Conclusively, our study provided clues that LvYKI plays an important role in the interaction between shrimp and virus. It will promote our understanding of the molecular mechanism in innate immunity.

Molecular Alterations in Malignant Pleural Mesothelioma: A Hope for Effective Treatment by Targeting YAP

Malignant pleural mesothelioma is a rare and aggressive neoplasm, which has primarily been attributed to the exposure to asbestos fibers (83% of cases); yet, despite a ban of using asbestos in many countries, the incidence of malignant pleural mesothelioma failed to decline worldwide. While little progress has been made in malignant pleural mesothelioma diagnosis, bevacizumab at first, then followed by double immunotherapy (nivolumab plus ipilumumab), were all shown to improve survival in large phase III randomized trials. The morphological analysis of the histological subtyping remains the primary indicator for therapeutic decision making at an advanced disease stage, while a platinum-based chemotherapy regimen combined with pemetrexed, either with or without bevacizumab, is still the main treatment option. Consequently, malignant pleural mesothelioma still represents a significant health concern owing to poor median survival (12-18 months). Given this context, both diagnosis and therapy improvements require better knowledge of the molecular mechanisms underlying malignant pleural mesothelioma's carcinogenesis and progression. Hence, the Hippo pathway in malignant pleural mesothelioma initiation and progression has recently received increasing attention, as the aberrant expression of its core components may be closely related to patient prognosis. The purpose of this review was to provide a critical analysis of our current knowledge on these topics, the main focus being on the available evidence concerning the role of each Hippo pathway's member as a promising biomarker, enabling detection of the disease at earlier stages and thus improving prognosis.

How Phosphofructokinase-1 Promotes PI3K and YAP/TAZ in Cancer: Therapeutic Perspectives

Simple Summary

We propose that PFK1 promotes a positive feedback loop with PI3K/AKT and YAP/TAZ signaling pathways in cancer cells. Therefore, targeting PFK1 (or its product F-1,6-BP) could improve the efficacy of PI3K and YAP/TAZ inhibitors currently tested in clinical trials. To this aim, we suggest the use of citrate, which is a physiologic and potent inhibitor of PFK1.

Abstract

PI3K/AKT is one of the most frequently altered signaling pathways in human cancers, supporting the activation of many proteins sustaining cell metabolism, proliferation, and aggressiveness. Another important pathway frequently altered in cancer cells is the one regulating the YAP/TAZ transcriptional coactivators, which promote the expression of genes sustaining aerobic glycolysis (such as WNT, MYC, HIF-1), EMT, and drug resistance. Of note, the PI3K/AKT pathway can also regulate the YAP/TAZ one. Unfortunately, although PI3K and YAP inhibitors are currently tested in highly resistant cancers (both solid and hematologic ones), several resistance mechanisms may arise. Resistance mechanisms to PI3K inhibitors may involve the stimulation of alternative pathways (such as RAS, HER, IGFR/AKT), the inactivation of PTEN (the physiologic inhibitor of PI3K), and the expression of anti-apoptotic Bcl-xL and MCL1 proteins. Therefore, it is important to improve current therapeutic strategies to overcome these limitations. Here, we want to highlight how the glycolytic enzyme PFK1 (and its product F-1,6-BP) promotes the activation of both PI3K/AKT and YAP/TAZ pathways by several direct and indirect mechanisms. In turn, PI3K/AKT and YAP/TAZ can promote PFK1 activity and F-1,6-BP production in a positive feedback loop, thus sustaining the Warburg effect and drug resistance. Thus, we propose that the inhibition of PFK1 (and of its key activator PFK2/PFKFB3) could potentiate the sensitivity to PI3K and YAP inhibitors currently tested. Awaiting the development of non-toxic inhibitors of these enzymes, we propose to test the administration of citrate at a high dosage, because citrate is a physiologic inhibitor of both PFK1 and PFK2/PFKFB3. Consistently, in various cultured cancer cells (including melanoma, sarcoma, hematologic, and epithelial cancer cells), this “citrate strategy” efficiently inhibits the IGFR1/AKT pathway, promotes PTEN activity, reduces Bcl-xL and MCL1 expression, and increases sensitivity to standard chemotherapy. It also inhibits the development of sarcoma, pancreatic, mammary HER⁺ and lung RAS-driven tumors in mice without apparent toxicities.

Noncanonical HIPPO/MST Signaling via BUB3 and FOXO Drives Pulmonary Vascular Cell Growth and Survival

RATIONALE

The MSTs (mammalian Ste20-like kinases) 1/2 are members of the HIPPO pathway that act as growth suppressors in adult proliferative diseases. Pulmonary arterial hypertension (PAH) manifests by increased proliferation and survival of pulmonary vascular cells in small PAs, pulmonary vascular remodeling, and the rise of pulmonary arterial pressure. The role of MST1/2 in PAH is currently unknown.

OBJECTIVE

To investigate the roles and mechanisms of the action of MST1 and MST2 in PAH.

METHODS AND RESULTS

Using early-passage pulmonary vascular cells from PAH and nondiseased lungs and mice with smooth muscle-specific tamoxifen-inducible Mst1/2 knockdown, we found that, in contrast to canonical antiproliferative/proapoptotic roles, MST1/2 act as proproliferative/prosurvival molecules in human PAH pulmonary arterial vascular smooth muscle cells and pulmonary arterial adventitial fibroblasts and support established pulmonary vascular remodeling and pulmonary hypertension in mice with SU5416/hypoxia-induced pulmonary hypertension. By using unbiased proteomic analysis, gain- and loss-of function approaches, and pharmacological inhibition of MST1/2 kinase activity by XMU-MP-1, we next evaluated mechanisms of regulation and function of MST1/2 in PAH pulmonary vascular cells. We found that, in PAH pulmonary arterial adventitial fibroblasts, the proproliferative function of MST1/2 is caused by IL-6-dependent MST1/2 overexpression, which induces PSMC6-dependent downregulation of forkhead homeobox type O 3 and hyperproliferation. In PAH pulmonary arterial vascular smooth muscle cells, MST1/2 acted via forming a disease-specific interaction with BUB3 and supported ECM (extracellular matrix)- and USP10-dependent BUB3 accumulation, upregulation of Akt-mTORC1, cell proliferation, and survival. Supporting our in vitro observations, smooth muscle-specific Mst1/2 knockdown halted upregulation of Akt-mTORC1 in small muscular PAs of mice with SU5416/hypoxia-induced pulmonary hypertension.

CONCLUSIONS

Together, this study describes a novel proproliferative/prosurvival role of MST1/2 in PAH pulmonary vasculature, provides a novel mechanistic link from MST1/2 via BUB3 and forkhead homeobox type O to the abnormal proliferation and survival of pulmonary arterial vascular smooth muscle cells and pulmonary arterial adventitial fibroblasts, remodeling and pulmonary hypertension, and suggests new target pathways for therapeutic intervention.

SEPT6_TRIM33 Gene Fusion and Mutated TP53 Pathway Associate With Unfavorable Prognosis in Patients With B-Cell Lymphomas

Background

Mounting studies have sought to identify novel mutation biomarkers having diagnostic and prognostic potentials. Nevertheless, the understanding of the mutated pathways related to development and prognosis of B-cell lymphoma is still lacking. We aimed to comprehensively analyze the mutation alterations in genes of canonical signaling pathways and their impacts on the clinic outcomes of patients with B-cell lymphoma.

Methods

Circulating cell-free DNA (cfDNA) samples from 79 patients with B-cell lymphomas were used for targeted sequencing with a 560-gene panel for depicting mutation landscapes and identifying gene fusion events. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analyses of mutated genes were performed. The associations of mutation status of genes and seven canonical oncogenic pathways with progression-free survival (PFS) were assessed using Kaplan-Meier test and multivariate Cox analysis. The variant allele frequencies (VAFs) of genes in TP53 and Hippo pathways in paired baseline and post-treatment samples from 18 B-cell lymphoma patients were compared. Finally, the associations of identified fusion genes, mutated genes, and pathways with treatment response were evaluated based on objective response rates (ORRs) comparisons of groups.

Results

We identified 666 mutations from 262 genes in baseline cfDNAs from 79 B-cell lymphoma patients, and found some genes were preferentially mutated in our cohort such as GNAQ, GNAS, H3F3A, DNMT3A, HLA-A, and HLA-B. These frequently mutated genes were significantly associated with negative "regulation of gene expression, epigenetic" and virus infections such as cytomegalovirus, Epstein-Barr virus, human immunodeficiency virus 1 infections. We detected five fusion genes in at least two patients with B-cell lymphoma, and among them, TCF7L2_WT1 gene fusion was most frequently detected in 30.4% of patients (24 of 79 cases). SEPT6_TRIM33 gene fusion, mutated TP53 and Hippo pathways were significantly associated with poor PFS, and SEPT6_TRIM33 fusion gene and mutated TP53 pathway were independent prognostic factors for B-cell lymphoma. A decreased VAF of TP53 p.Y88C and LATS2 p.F972L was detected in patients with complete response to treatments. Moreover, a significant difference in ORR was observed in patients with NPM1_NR4A3 and SEPT6_TRIM33 fusions.

Conclusions

SEPT6_TRIM33 gene fusion and mutated TP53 and Hippo pathways may serve as prognostic makers for B-cell lymphoma patients.

Hippo Signaling Pathway in Pancreas Development

The Hippo signaling pathway is a vital regulator of pancreatic development and homeostasis, directing cell fate decisions, morphogenesis, and adult pancreatic cellular plasticity. Through loss-of-function research, Hippo signaling has been found to play key roles in maintaining the proper balance between progenitor cell renewal, proliferation, and differentiation in pancreatic organogenesis. Other studies suggest that overactivation of YAP, a downstream effector of the pathway, promotes ductal cell development and suppresses endocrine cell fate specification via repression of Ngn3. After birth, disruptions in Hippo signaling have been found to lead to de-differentiation of acinar cells and pancreatitis-like phenotype. Further, Hippo signaling directs pancreatic morphogenesis by ensuring proper cell polarization and branching. Despite these findings, the mechanisms through which Hippo governs cell differentiation and pancreatic architecture are yet to be fully understood. Here, we review recent studies of Hippo functions in pancreatic development, including its crosstalk with NOTCH, WNT/β-catenin, and PI3K/Akt/mTOR signaling pathways.

Accurate prediction of kinase-substrate networks using knowledge graphs

Phosphorylation of specific substrates by protein kinases is a key control mechanism for vital cell-fate decisions and other cellular processes. However, discovering specific kinase-substrate relationships is time-consuming and often rather serendipitous. Computational predictions alleviate these challenges, but the current approaches suffer from limitations like restricted kinome coverage and inaccuracy. They also typically utilise only local features without reflecting broader interaction context. To address these limitations, we have developed an alternative predictive model. It uses statistical relational learning on top of phosphorylation networks interpreted as knowledge graphs, a simple yet robust model for representing networked knowledge. Compared to a representative selection of six existing systems, our model has the highest kinome coverage and produces biologically valid high-confidence predictions not possible with the other tools. Specifically, we have experimentally validated predictions of previously unknown phosphorylations by the LATS1, AKT1, PKA and MST2 kinases in human. Thus, our tool is useful for focusing phosphoproteomic experiments, and facilitates the discovery of new phosphorylation reactions. Our model can be accessed publicly via an easy-to-use web interface (LinkPhinder).

LinkPhinder is a new approach to prediction of protein signalling networks based on kinase-substrate relationships that outperforms existing approaches. Phosphorylation networks govern virtually all fundamental biochemical processes in cells, and thus have moved into the centre of interest in biology, medicine and drug development. Fundamentally different from current approaches, LinkPhinder is inherently network-based and makes use of the most recent AI developments. We represent existing phosphorylation data as knowledge graphs, a format for large-scale and robust knowledge representation. Training a link prediction model on such a structure leads to novel, biologically valid phosphorylation network predictions that cannot be made with competing tools. Thus our new conceptual approach can lead to establishing a new niche of AI applications in computational biology.

Atorvastatin Augments Gemcitabine-Mediated Anti-Cancer Effects by Inhibiting Yes-Associated Protein in Human Cholangiocarcinoma Cells

Cholangiocarcinoma (CCA) is associated with high mortality rates because of its resistance to conventional gemcitabine-based chemotherapy. Hydroxy-methyl-glutaryl-coenzyme A reductase inhibitors (statins) reportedly exert anti-cancer effects in CCA and lower the risk of CCA; however, the underlying mechanism of these effects remains unclear. The proliferative and oncogenic activities of the transcriptional co-activator Yes-associated protein (YAP) are driven by its association with the TEA domain (TEAD) of transcription factors; thereby, upregulating genes that promote cell growth, inhibit apoptosis, and confer chemoresistance. This study investigated the effects of atorvastatin in combination with gemcitabine on the progression of human CCA associated with YAP oncogenic regulation. Both atorvastatin and gemcitabine concentration-dependently suppressed the proliferation of HuCCT-1 and KKU-M213 human CCA cells. Moreover, both agents induced cellular apoptosis by upregulating the pro-apoptotic marker BAX and downregulating the anti-apoptotic markers MCL1 and BCL2. Atorvastatin also significantly decreased the mRNA expression of the TEAD target genes CTGF, CYR61, ANKRD1, and MFAP5 in both CCA cell lines. A xenograft tumor growth assay indicated that atorvastatin and gemcitabine potently repressed human CCA cell-derived subcutaneous tumor growth by inhibiting YAP nuclear translocation and TEAD transcriptional activation. Notably, the anti-cancer effects of the individual agents were significantly enhanced in combination. These results indicate that gemcitabine plus atorvastatin could serve as a potential novel treatment option for CCA.

A Human Papillomavirus-Independent Cervical Cancer Animal Model Reveals Unconventional Mechanisms of Cervical Carcinogenesis

HPV infections are common in healthy women and only rarely cause cervical cancer, suggesting that individual genetic susceptibility may play a critical role in the establishment of persistent HPV infection and the development of cervical cancer. Here, we provide convincing in vitro and in vivo evidence showing that differential expression and activation of YAP1 oncogene determine individual susceptibility to HPV infection and cervical carcinogenesis. We found that hyperactivation of YAP1 in mouse cervical epithelium was sufficient to induce invasive cervical cancer. Cervical epithelial cell-specific HPV16 E6/E7 and YAP1 double-knockin mouse model demonstrated that high-risk HPV synergized with hyperactivated YAP1 to promote the initiation and progression of cervical cancer. Our mechanistic studies indicated that hyperactivation of YAP1 in cervical epithelial cells facilitated HPV infection by increasing the putative HPV receptor molecules and disrupting host cell innate immunity. Our finding reveals an unconventional mechanism for cervical carcinogenesis.

HPV infections are common in healthy women and only rarely cause cervical cancer. He et al. provide evidence that hyperactivation of the YAP1 oncogene can drive cervical cancer initiation and progression. YAP1 hyperactivation in cervical epithelial cells increases the HPV receptors and disrupts host cell innate immunity, facilitating HPV infection.

Robust organ size requires robust timing of initiation orchestrated by focused auxin and cytokinin signalling

Organ size and shape are precisely regulated to ensure proper function. The four sepals in each Arabidopsis thaliana flower must maintain the same size throughout their growth to continuously enclose and protect the developing bud. Here we show that DEVELOPMENT RELATED MYB-LIKE 1 (DRMY1) is required for both timing of organ initiation and proper growth, leading to robust sepal size in Arabidopsis. Within each drmy1 flower, the initiation of some sepals is variably delayed. Late-initiating sepals in drmy1 mutants remain smaller throughout development, resulting in variability in sepal size. DRMY1 focuses the spatiotemporal signalling patterns of the plant hormones auxin and cytokinin, which jointly control the timing of sepal initiation. Our findings demonstrate that timing of organ initiation, together with growth and maturation, contribute to robust organ size.

Targeting YAP Degradation by a Novel 1,2,4-Oxadiazole Derivative via Restoration of the Function of the Hippo Pathway

Recent evidence has linked the dysregulation of the Hippo pathway to tumorigenesis and cancer progression due to its pivotal role in regulating the stability of the oncoprotein YAP. Based on an unexpected finding from the SAR study of a recently reported oxadiazole-based EGFR/c-Met dual inhibitor (compound 1), we identified a closely related derivative, compound 2, which exhibited cogent antitumor activities while devoid of compound 1's ability to promote EGFR/c-Met degradation. Compound 2 acted, in part, by facilitating YAP degradation through activation of its upstream kinase LATS1. However, it did not alter the phosphorylation status of MST1/2, a LATS1 kinase, suggesting an alternative mechanism for LATS1 activation. Orally administered compound 2 was effective in suppressing MDA-MB-231 xenograft tumor growth while exhibiting a satisfactory safety profile. From a therapeutic perspective, compound 2 might help foster new therapeutic strategies for cancer treatment by restoring the Hippo pathway regulatory function to facilitate YAP degradation.

A case report of sinusoidal diffuse large B-cell lymphoma in a STK4 deficient patient

INTRODUCTION

Primary immunodeficiency diseases (PIDs), a rare group of gene defects with different manifestations, are at great risk of malignancy. The incidence of diffuse large B-cell lymphoma in the sinusoidal tract is quite rare with nasal congestion, stuffiness, and pain in maxillary sinus manifestation. Human serine-threonine kinase 4 (STK4) deficiency affects the immune system with recurrent bacterial and viral infections, mucocutaneous candidiasis, cutaneous warts, skin abscesses, T- and B-cell lymphopenia, and neutropenia.

PATIENT CONCERN

In this study we describe the infrequent incidence and successful treatment of sinusoidal diffuse large B-cell lymphoma in a STK4 deficient patient with clinical manifestation of severe intractable headaches, unilateral swelling of her face, nasal congestion, stuffiness, and pain in maxillary.

DIAGNOSIS

Clinical data including headaches, unilateral swelling of face, nasal congestion, stuffiness and pain in maxillary sinus with confirmed histopathology and magnetic resonance imaging finding confirmed sinusoidal diffuse large B cell lymphoma in a STK4 deficient patient.

INTERVENTION

Six cycles of R-CHOP (rituximab with cyclophosphamide, doxorubicin, vincristine, and prednisolone) were administered and after each cycle, G-CSF support was used. Chemotherapeutic drugs were administered with standard dose and no dose reduction was done during the treatment. IVIG treatment continued during the courses of chemotherapy.

OUTCOME

The index patient achieved complete response at the end of chemotherapy courses and was in remission for about 8 months afterward, prior to the date of the present report.

CONCLUSION

PID patient are often at increased risk of malignancies. Sinusoidal diffuse large B-cell lymphoma is quite rare and prognosis is variable. Early attention to patient's manifestation, suitable treatment, and monitoring manifestations caused by PID are critical.

The Hippo Pathway and Viral Infections

The Hippo signaling pathway is a novel tumor suppressor pathway, initially found in Drosophila. Recent studies have discovered that the Hippo signaling pathway plays a critical role in a wide range of biological processes, including organ size control, cell proliferation, cancer development, and virus-induced diseases. In this review, we summarize the current understanding of the biological feature and pathological role of the Hippo pathway, focusing particularly on current findings in the function of the Hippo pathway in virus infection and pathogenesis.

Inhibition of cyclin-dependent kinase 7 down-regulates yes-associated protein expression in mesothelioma cells

Cyclin-dependent kinase 7 (CDK7) is a protein kinase that plays a major role in transcription initiation. Yes-associated protein (YAP) is a main effector of the Hippo/YAP signalling pathway. Here, we investigated the role of CDK7 on YAP regulation in human malignant pleural mesothelioma (MPM). We found that in microarray samples of human MPM tissue, immunohistochemistry staining showed correlation between the expression level of CDK7 and YAP (n = 70, r = .513). In MPM cells, CDK7 expression level was significantly correlated with GTIIC reporter activity (r = .886, P = .019). Inhibition of CDK7 by siRNA decreased the YAP protein level and the GTIIC reporter activity in the MPM cell lines 211H, H290 and H2052. Degradation of the YAP protein was accelerated after CDK7 knockdown in 211H, H290 and H2052 cells. Inhibition of CDK7 reduced tumour cell migration and invasion, as well as tumorsphere formation ability. Restoration of the CDK7 gene rescued the YAP protein level and GTIIC reporter activity after siRNA knockdown in 211H and H2052 cells. Finally, we performed a co-immunoprecipitation analysis using an anti-YAP antibody and captured the CDK7 protein in 211H cells. Our results suggest that CDK7 inhibition reduces the YAP protein level by promoting its degradation and suppresses the migration and invasion of MPM cells. Cyclin-dependent kinase 7 may be a promising therapeutic target for MPM.

Down-regulation of interferon regulatory factor 2 binding protein 2 suppresses gastric cancer progression by negatively regulating connective tissue growth factor

Interferon regulatory factor 2 binding protein 2 (IRF2BP2) is a transcriptional repressor involved in regulating gene expression and other biological processes, including tumorigenesis. However, the clinical significance and roles of IRF2BP2 in human gastric cancer (GC) remain uncertain. Clinical GC tissues were obtained from GC patients at the First Affiliated Hospital of Nanchang University. Immunohistochemistry (IHC) was conducted to detect the IRF2BP2 protein in clinical paraffin specimens. Cell proliferation, migration and invasion were evaluated by MTT, colony formation assays and transwell assays. Co-immunoprecipitation was conducted to detect the interaction between TEA domain family members 4 (TEAD4) and vestigial-like family member 4 (VGLL4) or Yes-associated protein 1 (YAP1). Dual-luciferase reporter assay was used to confirm the binding of miR-101-3p to the 3'-UTR. The expression of IRF2BP2 was significantly higher in GC tissues than in normal tissues. Patients with higher IRF2BP2 protein expression had lower survival. IRF2BP2 knockdown inhibited proliferation, migration, invasion and epithelial-mesenchymal transition in GC cells. IRF2BP2 knockdown decreased the mRNA and protein levels of connective tissue growth factor (CTGF). The interaction between IRF2BP2 and VGLL4 increased the binding of TEAD4 to YAP1, resulting in the transcriptional coactivation of CTGF. In addition, miR-101-3p suppressed the expression of CTGF by directly targeting the 3'-UTR of IRF2BP2. Taken together, these findings provide a model for the role of miR-101-3p-IRF2BP2-CTGF signalling axis in GC and a novel insight into the mechanism of GC progression and metastasis.

Yes-associated protein expression in germ cells is dispensable for spermatogenesis in mice

Yes-associated protein (YAP), a key effector of the Hippo signaling pathway, is expressed in the nucleus of spermatogonia in mice, suggesting a potential role in spermatogenesis. Here, we report the generation of a conditional knockout mouse model (Yap^flox/flox ; Ddx4^cre/+ ) that specifically inactivates Yap in the germ cells. The inactivation of Yap in spermatogonia was found to be highly efficient in this model. The loss of Yap in the germ cells had no observable effect on spermatogenesis in vivo. Histological examination of the testes showed no structural differences between mutant animals and age-matched Yap^flox/flox controls, nor was any differences detected in gonadosomatic index, expression of germ cell markers or sperm counts. Cluster-forming assay using undifferentiated spermatogonia, including spermatogonial stem cells (SSCs), also showed that YAP is dispensable for SSC cluster formation in vitro. However, an increase in the expression of spermatogenesis and oogenesis basic helix-loop-helix 1 (Sohlh1) and neurogenin 3 (Ngn3) was observed in clusters derived from Yap^flox/flox ; Ddx4^cre/+ animals. Taken together, these results suggest that YAP fine-tunes the expression of genes associated with spermatogonial fate commitment, but that its loss is not sufficient to alter spermatogenesis in vivo.

Cell-intrinsic PD-1 promotes proliferation in pancreatic cancer by targeting CYR61/CTGF via the hippo pathway

Pancreatic ductal adenocarcinoma (PDAC) remains a refractory disease. Programmed cell death protein-1 (PD-1) monotherapy has shown strong performance in targeting several malignancies. However, the effect and mechanism of intrinsic PD-1 in pancreatic cancer cells is still unknown. In this study, associations between clinicopathological characteristics and stained tissue microarrays of PDAC specimens were analyzed along with profiling and functional analyses. The results showed that cell-intrinsic PD-1 was significantly correlated with overall survival (OS). Independently of adaptive immunity, intrinsic PD-1 promoted tumor growth in PDAC. Concomitantly, the overexpression of intrinsic PD-1 enhanced cancer proliferation and inhibited cell apoptosis in vitro and in vivo. Mechanistically, PD-1 binds to the downstream MOB1, thereby inhibiting its phosphorylation. Moreover, greater synergistic tumor suppression in vitro resulted from combining Hippo inhibitors with anti-PD-1 treatment compared with the suppression achieved by either single agent alone. Additionally, Hippo downstream targets, CYR61 (CCN1) and CTGF (CCN2), were directly affected by PD-1 mediated Hippo signaling activation in concert with survival outcomes. Finally, the formulated nomogram showed superior predictive accuracy for OS in comparison with the TNM stage alone. Therefore, PD-1 immunotherapy in combination with Hippo pathway inhibitors may optimize the anti-tumor efficacy in PDAC patients via targeting cell-intrinsic PD-1.

Knockdown of lncRNA LEF1-AS1 inhibited the progression of oral squamous cell carcinoma (OSCC) via Hippo signaling pathway

It is verified that long non-coding RNAs (lncRNAs) play crucial roles in various cancers. LncRNA LEF1-AS1 is a reported oncogene in colorectal cancer and glioblastoma. In this study, we unveiled that LEF1-AS1 markedly increased in oral squamous cell carcinoma (OSCC) tissues and cell lines. Besides, OSCC patients with high levels of LEF1-AS1 were apt to poor prognosis. Functionally, LEF1-AS1 knockdown inhibited cell survival, proliferation and migration, whereas enhanced cell apoptosis and induced G0/G1 cell cycle arrest in vitro. Consistently, LEF1-AS1 silence hindered tumor growth in vivo. Moreover, LEF1-AS1 inhibition stimulated the activation of Hippo signaling pathway through directly interacting with LATS1. Furtherly, we disclosed that LEF1-AS1 silence abolished the interaction of LEF1-AS1 with LATS1 while enhanced the binding of LATS1 to MOB, therefore promoting YAP phosphorylation but impairing YAP1 nuclear translocation. Additionally, we demonstrated that LEF1-AS1 regulated YAP1 translocation via a LATS1-dependent manner. Furthermore, we also uncovered that YAP1 overexpression abolished the suppressive impact of LEF1-AS1 repression on the biological processes of OSCC cells. In a word, we concluded that LEF1-AS1 served an oncogenic part in OSCC through suppressing Hippo signaling pathway by interacting with LATS1, suggesting the therapeutic and prognostic potential of LEF1-AS1 in OSCC.

Integrative genomic analysis of peritoneal malignant mesothelioma: understanding a case with extraordinary chemotherapy response

Peritoneal malignant mesothelioma is a rare disease with a generally poor prognosis and poor response to chemotherapy. To improve survival there is a need for increased molecular understanding of the disease, including chemotherapy sensitivity and resistance. We here present an unusual case concerning a young woman with extensive peritoneal mesothelioma who had a remarkable response to palliative chemotherapy (platinum/pemetrexed). Tumor samples collected at surgery before and after treatment were analyzed on the genomic and transcriptional levels (exome sequencing, RNA-seq, and smallRNA-seq). Integrative analysis of single nucleotide and copy-number variants, mutational signatures, and gene expression was performed to provide a comprehensive picture of the disease. LATS1/2 were identified as the main mutational drivers together with homozygous loss of BAP1 and PBRM1, which also may have contributed to the extraordinary chemotherapy response. The presence of the S3 mutational signature is consistent with homologous recombination DNA repair defects due to BAP1 loss. Up-regulation of the PI3K/AKT/mTOR pathway after treatment, supported by deactivated PTEN through miRNA regulation, is associated with cancer progression and could explain chemotherapy resistance. The molecular profile suggests potential benefit from experimental targeting of PARP, EZH2, the PI3K/AKT/mTOR pathway and possibly also from immune checkpoint inhibition. In addition to providing the molecular background for this unusual case of peritoneal mesothelioma, the results show the potential value of integrative genomic analysis in precision medicine.

Immunofluorescence Study of Endogenous YAP in Mammalian Cells

Immunocytochemistry enables determination of cellular localization and relative abundance of proteins. This protocol describes a rapid and cost-effective approach to study the cellular localization of YAP (and TAZ), the transcriptional co activators of the Hippo pathway, in mammalian cells. Cells are seeded onto coated cover slips, cultivated and treated as required. Subsequently, they are chemically fixed, and cellular proteins are fluorescently labeled by means of specific antibodies. Multiplexing antibodies enables ascertaining the subcellular localization of YAP and TAZ and thereby also the activation state of the Hippo pathway in various cell types.

The Hippo Pathway Regulates Caveolae Expression and Mediates Flow Response via Caveolae

The Hippo pathway plays major roles in development, regeneration, and cancer. Its activity is tightly regulated by both diffusible chemical ligands and mechanical stimuli. The pathway consists of a series of kinases that can control the sub-cellular localization and stability of YAP or TAZ, homologous transcriptional co-factors. Caveolae, small (60–100 nm) bulb-like invaginations of the plasma membrane, are comprised predominantly of caveolin and cavin proteins and can respond to mechanical stimuli. Here, we show that YAP/TAZ, the major transcriptional mediators of the Hippo pathway, are critical for expression of caveolae components and therefore caveolae formation in both mammalian cells and zebrafish. In essence, without YAP/TAZ, the cell loses an entire organelle. CAVEOLIN1 and CAVIN1, the two essential caveolar genes, are direct target genes of YAP/TAZ, regulated via TEA domain (TEAD) transcription factors. Notably, YAP/TAZ become nuclear enriched and facilitate target gene transcription in cells with diminished levels of caveolae. Furthermore, caveolar-mediated shear stress response activates YAP/TAZ. These data link caveolae to Hippo signaling in the context of cellular responses to mechanical stimuli and suggest activity-based feedback regulation between components of caveolae and the outputs of the Hippo pathway.

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YAP/TAZ are critical for CAVIN1 and CAVEOLIN1 expression and caveolae formation

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The essential caveolar genes CAVIN1 and CAVEOLIN1 are direct YAP/TAZ-TEAD target genes

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YAP/TAZ are hyperactivated in caveolae-deficient cells

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Caveolae facilitate YAP/TAZ-mediated shear stress response

The MST4-MOB4 complex disrupts the MST1-MOB1 complex in the Hippo-YAP pathway and plays a pro-oncogenic role in pancreatic cancer

The mammalian STE20-like protein kinase 1 (MST1)-MOB kinase activator 1 (MOB1) complex has been shown to suppress the oncogenic activity of Yes-associated protein (YAP) in the mammalian Hippo pathway, which is involved in the development of multiple tumors, including pancreatic cancer (PC). However, it remains unclear whether other MST-MOB complexes are also involved in regulating Hippo-YAP signaling and have potential roles in PC. Here, we report that mammalian STE20-like kinase 4 (MST4), a distantly related ortholog of the MST1 kinase, forms a complex with MOB4 in a phosphorylation-dependent manner. We found that the overall structure of the MST4-MOB4 complex resembles that of the MST1-MOB1 complex, even though the two complexes exhibited opposite biological functions in PC. In contrast to the tumor-suppressor effect of the MST1-MOB1 complex, the MST4-MOB4 complex promoted growth and migration of PANC-1 cells. Moreover, expression levels of MST4 and MOB4 were elevated in PC and were positively correlated with each other, whereas MST1 expression was down-regulated. Because of divergent evolution of key interface residues, MST4 and MOB4 could disrupt assembly of the MST1-MOB1 complex through alternative pairing and thereby increased YAP activity. Collectively, these findings identify the MST4-MOB4 complex as a noncanonical regulator of the Hippo-YAP pathway with an oncogenic role in PC. Our findings highlight that although MST-MOB complexes display some structural conservation, they functionally diverged during their evolution.

Reconstruction of the genome-scale co-expression network for the Hippo signaling pathway in colorectal cancer

The Hippo signaling pathway (HSP) has been identified as an essential and complex signaling pathway for tumor suppression that coordinates proliferation, differentiation, cell death, cell growth and stemness. In the present study, we conducted a genome-scale co-expression analysis to reconstruct the HSP in colorectal cancer (CRC). Five key modules were detected through network clustering, and a detailed discussion of two modules containing respectively 18 and 13 over and down-regulated members of HSP was provided. Our results suggest new potential regulatory factors in the HSP. The detected modules also suggest novel genes contributing to CRC. Moreover, differential expression analysis confirmed the differential expression pattern of HSP members and new suggested regulatory factors between tumor and normal samples. These findings can further reveal the importance of HSP in CRC.

Yes-associated protein and WW-containing transcription regulator 1 regulate the expression of sex-determining genes in Sertoli cells, but their inactivation does not cause sex reversal

Yes-associated protein (YAP) and WW-containing transcription regulator 1 (WWTR1) are two functionally redundant transcriptional regulators that are downstream effectors of the Hippo signaling pathway, and that act as major regulators of cell growth and differentiation. To elucidate their role in Sertoli cells, primary Sertoli cell culture from Yapflox/flox; Wwtr1flox/flox animals were infected with a Cre recombinase-expressing adenovirus. Concomitant inactivation of Yap and Wwtr1 resulted in a decrease in the mRNA levels of the male sex differentiation genes Dhh, Dmrt1, Sox9, and Wt1, whereas those of genes involved in female differentiation (Wnt4, Rspo1, and Foxl2) were induced. SOX9, FOXL2, and WNT4 proteins were regulated in the same manner as their mRNAs in response to loss of YAP and WWTR1. To further characterize the role of YAP and WWTR1 in Sertoli cells, we generated a mouse model (Yapflox/flox; Wwtr1flox/flox; Amhcre/+) in which Yap and Wwtr1 were conditionally deleted in Sertoli cells. An increase in the number of apoptotic cells was observed in the seminiferous tubules of 4 dpp mutant mice, leading to a reduction in testis weights and a decrease in the number of Sertoli cells in adult animals. Gene expression analyses of testes from 4 dpp Yapflox/flox; Wwtr1flox/flox; Amhcre/+ mice showed that Sertoli cell differentiation is initially altered, as Dhh, Dmrt1, and Sox9 mRNA levels were downregulated, whereas Wnt4 mRNA levels were increased. However, expression of these genes was not changed in older animals. Together, these results suggest a novel role of the Hippo signaling pathway in the mechanisms of sex differentiation.

YAP/TAZ Activation as a Target for Treating Metastatic Cancer

Yes-Associated Protein (YAP) and Transcriptional Co-activator with PDZ-binding Motif (TAZ) have both emerged as important drivers of cancer progression and metastasis. YAP and TAZ are often upregulated or nuclear localized in aggressive human cancers. There is abundant experimental evidence demonstrating that YAP or TAZ activation promotes cancer formation, tumor progression, and metastasis. In this review we summarize the evidence linking YAP/TAZ activation to metastasis, and discuss the roles of YAP and TAZ during each step of the metastatic cascade. Collectively, this evidence strongly suggests that inappropriate YAP or TAZ activity plays a causal role in cancer, and that targeting aberrant YAP/TAZ activation is a promising strategy for the treatment of metastatic disease. To this end, we also discuss several potential strategies for inhibiting YAP/TAZ activation in cancer and the challenges each strategy poses.

Targeted Disruption of YAP and TAZ Impairs the Maintenance of the Adrenal Cortex

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are functionally redundant transcriptional regulators that are downstream effectors of the Hippo signaling pathway. They act as major regulators of stem cell maintenance, cell growth, and differentiation. To characterize their roles in the adrenal cortex, we generated a mouse model in which Yap and Taz were conditionally deleted in steroidogenic cells (Yapflox/flox;Tazflox/flox;Nr5a1cre/+). Male Yapflox/flox;Tazflox/flox;Nr5a1cre/+ mice were characterized by an age-dependent degeneration of the adrenal cortex associated with an increase in apoptosis and a progressive reduction in the expression levels of steroidogenic genes. Evaluation of the expression levels of stem and progenitor cell population markers in the adrenal glands of Yapflox/flox;Tazflox/flox;Nr5a1cre/+ mice also showed the downregulation of sonic hedgehog (Shh), a marker of the subcapsular progenitor cell population. Gross degenerative changes were not observed in the adrenal glands of Yapflox/flox;Tazflox/flox;Nr5a1cre/+ females, although steroidogenic capacity and Shh expression were reduced, suggesting that mechanisms of adrenocortical maintenance are sex specific. These results define a crucial role for YAP and TAZ in the maintenance of the postnatal adrenal cortex.

Targeting YAP in malignant pleural mesothelioma

Malignant mesothelioma is an aggressive cancer that is resistant to current therapy. The poor prognosis of mesothelioma has been associated with elevated Yes-associated protein (YAP) activity. In this study, we evaluated the effect of targeting YAP in mesothelioma. First, we comprehensively studied YAP activity in five mesothelioma cell lines (211H, H2052, H290, MS-1 and H2452) and one normal mesothelial cell line (LP9). We found decreased phospho-YAP to YAP protein ratio and consistently increased GTIIC reporter activity in 211H, H2052 and H290 compared to LP9. The same three cell lines (IC50 s < 1 μM) were more sensitive than LP9 (IC50 = 3.5 μM) to the YAP/TEAD inhibitor verteporfin. We also found that verteporfin significantly reduced YAP protein level, mRNA levels of YAP downstream genes and GTIIC reporter activity in the same three cell lines, indicating inhibition of YAP signaling by verteporfin. Verteporfin also impaired invasion and tumoursphere formation ability of H2052 and H290. To validate the effect of specific targeting YAP in mesothelioma cells, we down-regulated YAP by siRNA. We found siYAP significantly decreased YAP transcriptional activity and impaired invasion and tumoursphere formation ability of H2052 and H290. Furthermore, forced overexpression of YAP rescued GTIIC reporter activity and cell viability after siYAP targeting 3'UTR of YAP. Finally, we found concurrent immunohistochemistry staining of ROCK2 and YAP (P < 0.05). Inhibition of ROCK2 decreased GTIIC reporter activity in H2052 and 211H suggesting that Rho/ROCK signaling also contributed to YAP activation in mesothelioma cells. Our results indicate that YAP may be a potential therapeutic target in mesothelioma.

Mapping the STK4/Hippo signaling network in prostate cancer cell

Dysregulation of MST1/STK4, a key kinase component of the Hippo-YAP pathway, is linked to the etiology of many cancers with poor prognosis. However, how STK4 restricts the emergence of aggressive cancer remains elusive. Here, we investigated the effects of STK4, primarily localized in the cytoplasm, lipid raft, and nucleus, on cell growth and gene expression in aggressive prostate cancer. We demonstrated that lipid raft and nuclear STK4 had superior suppressive effects on cell growth in vitro and in vivo compared with cytoplasmic STK4. Using RNA sequencing and bioinformatics analysis, we identified several differentially expressed (DE) genes that responded to ectopic STK4 in all three subcellular compartments. We noted that the number of DE genes observed in lipid raft and nuclear STK4 cells were much greater than cytoplasmic STK4. Our functional annotation clustering showed that these DE genes were commonly associated with oncogenic pathways such as AR, PI3K/AKT, BMP/SMAD, GPCR, WNT, and RAS as well as unique pathways such as JAK/STAT, which emerged only in nuclear STK4 cells. These findings indicate that MST1/STK4/Hippo signaling restricts aggressive tumor cell growth by intersecting with multiple molecular pathways, suggesting that targeting of the STK4/Hippo pathway may have important therapeutic implications for cancer.

In Vitro Validation of the Hippo Pathway as a Pharmacological Target for Canine Mammary Gland Tumors

Canine mammary tumors (CMTs) are the most common neoplasms in intact female dogs. Some clinical and molecular similarities between certain CMT subtypes and breast cancer make them a potential model for the study of the human disease. As misregulated Hippo signaling is thought to play an important role in breast cancer development and also occurs in CMTs, we sought to determine if Hippo represents a valid pharmacological target for the treatment of CMTs. Six CMT cell lines were assessed for their expression of the Hippo pathway effectors YAP and TAZ and for their sensitivity to verteporfin, an inhibitor of YAP-mediated transcriptional coactivation. Four cell lines that expressed YAP (CMT-9, -12, -28, -47) were found to be very sensitive to verteporfin treatment, which killed the cells through induction of apoptosis with ED50 values of 14-79 nM. Conversely, two YAP-negative cell lines (CF-35, CMT-25) were an order of magnitude more resistant to verteporfin. Verteporfin suppressed the expression of YAP/TAZ target genes, particularly CYR61 and CTGF, which play important roles in breast cancer development. Verteporfin was also able to inhibit cell migration and anchorage-independent growth. Likewise, verteporfin efficiently suppressed tumor cell invasiveness in the CMT-28 and -47 lines, but not in CF-35 cells. Together, our findings provide proof of principle that pharmacological targeting of the Hippo pathway compromises the viability and attenuates the malignant behavior of CMT cells. These results will serve as the basis for the development of novel chemotherapeutic approaches for CMTs that could translate to human medicine.

Association between YAP expression in neoplastic and non-neoplastic breast tissue with arsenic urinary levels

The Hippo pathway regulates cell proliferation and apoptosis and it has been noted that loss of critical components of this pathway can lead to uncontrolled cell growth. Yes-associated protein (YAP) is an important component of this Hippo pathway because YAP is the nuclear effector of the Hippo tumor suppressor pathway and it is crucial for the response to oxidative stress induced by cellular process and by different xenobiotics, including arsenic. It has been proposed that YAP dysregulation can contribute to a malignant cellular phenotype acting as both a tumor suppressor and an oncogene. The aim of the study was to assess and compare the expression of YAP in neoplastic and non-neoplastic breast tissue of women chronically exposed to arsenic through drinking water. YAP expression was assessed by immunohistochemistry in 120 breast biopsies from women with breast cancer and from women with other non-neoplastic breast pathologies. Arsenic concentration was quantified in urine. The results disclosed a significant lower percentage of cytoplasm YAP expression in cases and that YAP high-intensity staining in the cytoplasm but not in the nucleus decreases the risk for breast cancer. In conclusion, our overall data suggest that YAP may act as a tumor suppressor protein because their reduced expression in cases, which can induce an environment favorable for inhibition of apoptosis and promoting cellular proliferation by increasing genetic instability of cells, which might contribute to the pathogenesis of cancer. Copyright © 2017 John Wiley & Sons, Ltd.

Spatial regulation of ARAF controls the MST2-Hippo pathway

The RAF-MAPK signaling pathway regulates several very diverse cellular processes such as proliferation, differentiation, apoptosis, and transformation. While the canonical function of RAF kinases within the MAPK pathway is the activation of MEK, our group could demonstrate an important crosstalk between RAF signaling and the pro-apoptotic mammalian sterile 20-like kinase (MST2) tumor suppressor pathway in several cancer entities, including head and neck, colon, and breast. Here, the RAF kinases CRAF and ARAF sequester and inhibit the pro-apoptotic kinase MST2 independently of their own kinase activity. In our recent study, we showed that the ARAF-MST2 complex is regulated by subcellular compartmentalization during epithelial differentiation. Proliferating cells of the basal cell layer in squamous epithelia and tumor cells express ARAF at the mitochondria thus allowing for efficient sequestration of MST2. In contrast, non-malignant squamous epithelia have ARAF localized at the plasma membrane, where the control of MST2-mediated apoptosis is compromised. This re-distribution is regulated by the scaffold protein kinase suppressor of Ras 2 (KSR2). Here, we summarize how spatial and temporal regulation of RAF signaling complexes affect cellular signaling and functions.

miR-285-Yki/Mask double-negative feedback loop mediates blood-brain barrier integrity in Drosophila

The Hippo signaling pathway is highly conserved from Drosophila to mammals and plays a central role in maintaining organ size and tissue homeostasis. The blood-brain barrier (BBB) physiologically isolates the brain from circulating blood or the hemolymph system, and its integrity is strictly maintained to perform sophisticated neuronal functions. Until now, the underlying mechanisms of subperineurial glia (SPG) growth and BBB maintenance during development are not clear. Here, we report an miR-285-Yorkie (Yki)/Multiple Ankyrin repeats Single KH domain (Mask) double-negative feedback loop that regulates SPG growth and BBB integrity. Flies with a loss of miR-285 have a defective BBB with increased SPG ploidy and disruptive septate junctions. Mechanistically, miR-285 directly targets the Yki cofactor Mask to suppress Yki activity and down-regulates the expression of its downstream target cyclin E, a key regulator of cell cycle. Disturbance of cyclin E expression in SPG causes abnormal endoreplication, which leads to aberrant DNA ploidy and defective septate junctions. Moreover, the expression of miR-285 is increased by knockdown of yki or mask and is decreased with yki overexpression, thus forming a double-negative feedback loop. This regulatory loop is crucial for sustaining an appropriate Yki/Mask activity and cyclin E level to maintain SPG ploidy and BBB integrity. Perturbation of this signaling loop, either by dysregulated miR-285 expression or Yki activity, causes irregular SPG ploidy and BBB disruption. Furthermore, ectopic expression of miR-285 promotes canonical Hippo pathway-mediated apoptosis independent of the p53 or JNK pathway. Collectively, these results reveal an exquisite regulatory mechanism for BBB maintenance through an miR-285-Yki/Mask regulatory circuit.

A ROR1-HER3-lncRNA signalling axis modulates the Hippo-YAP pathway to regulate bone metastasis

Bone metastases remain as a serious health concern because of limited therapeutic options. Here, we report that crosstalk between ROR1-HER3 and the Hippo-YAP pathway promotes breast cancer bone metastasis in a long noncoding RNA-dependent fashion. Mechanistically, the orphan receptor tyrosine kinase ROR1 phosphorylates HER3 at a previously unidentified site Tyr1307, upon neuregulin stimulation, independently of other ErbB family members. p-HER3 Tyr1307 recruits the LLGL2-MAYA-NSUN6 RNA-protein complex to methylate Hippo/MST1 at Lys59. This methylation leads to MST1 inactivation and activation of YAP target genes in tumor cells, which elicits osteoclast differentiation and bone metastasis. Furthermore, increased ROR1, p-HER3 Tyr1307 and MAYA levels correlate with tumor metastasis and unfavorable outcomes. Our data provide insights into the mechanistic regulation and linkage of the ROR1-HER3 and Hippo-YAP pathway in cancer-specific context, and also imply valuable therapeutic targets for bone metastasis and possible therapy-resistant tumors.

ACTL6A Is Co-Amplified with p63 in Squamous Cell Carcinoma to Drive YAP Activation, Regenerative Proliferation, and Poor Prognosis

Loss-of-function mutations in SWI/SNF chromatin-remodeling subunit genes are observed in many cancers, but an oncogenic role for SWI/SNF is not well established. Here, we reveal that ACTL6A, encoding an SWI/SNF subunit linked to stem cell and progenitor cell function, is frequently co-amplified and highly expressed together with the p53 family member p63 in head and neck squamous cell carcinoma (HNSCC). ACTL6A and p63 physically interact, cooperatively controlling a transcriptional program that promotes proliferation and suppresses differentiation, in part through activation of the Hippo-YAP pathway via regulators including WWC1. Ectopic ACTL6A/p63 expression promotes tumorigenesis, while ACTL6A expression and YAP activation are highly correlated in primary HNSCC and predict poor patient survival. Thus, ACTL6A and p63 collaborate as oncogenic drivers in HNSCC.

HIPPO-Integrin-linked Kinase Cross-Talk Controls Self-Sustaining Proliferation and Survival in Pulmonary Hypertension

RATIONALE

Enhanced proliferation and impaired apoptosis of pulmonary arterial vascular smooth muscle cells (PAVSMCs) are key pathophysiologic components of pulmonary vascular remodeling in pulmonary arterial hypertension (PAH).

OBJECTIVES

To determine the role and therapeutic relevance of HIPPO signaling in PAVSMC proliferation/apoptosis imbalance in PAH.

METHODS

Primary distal PAVSMCs, lung tissue sections from unused donor (control) and idiopathic PAH lungs, and rat and mouse models of SU5416/hypoxia-induced pulmonary hypertension (PH) were used. Immunohistochemical, immunocytochemical, and immunoblot analyses and transfection, infection, DNA synthesis, apoptosis, migration, cell count, and protein activity assays were performed in this study.

MEASUREMENTS AND MAIN RESULTS

Immunohistochemical and immunoblot analyses demonstrated that the HIPPO central component large tumor suppressor 1 (LATS1) is inactivated in small remodeled pulmonary arteries (PAs) and distal PAVSMCs in idiopathic PAH. Molecular- and pharmacology-based analyses revealed that LATS1 inactivation and consequent up-regulation of its reciprocal effector Yes-associated protein (Yap) were required for activation of mammalian target of rapamycin (mTOR)-Akt, accumulation of HIF1α, Notch3 intracellular domain and β-catenin, deficiency of proapoptotic Bim, increased proliferation, and survival of human PAH PAVSMCs. LATS1 inactivation and up-regulation of Yap increased production and secretion of fibronectin that up-regulated integrin-linked kinase 1 (ILK1). ILK1 supported LATS1 inactivation, and its inhibition reactivated LATS1, down-regulated Yap, suppressed proliferation, and promoted apoptosis in PAH, but not control PAVSMCs. PAVSM in small remodeled PAs from rats and mice with SU5416/hypoxia-induced PH showed down-regulation of LATS1 and overexpression of ILK1. Treatment of mice with selective ILK inhibitor Cpd22 at Days 22-35 of SU5416/hypoxia exposure restored LATS1 signaling and reduced established pulmonary vascular remodeling and PH.

CONCLUSIONS

These data report inactivation of HIPPO/LATS1, self-supported via Yap-fibronectin-ILK1 signaling loop, as a novel mechanism of self-sustaining proliferation and apoptosis resistance of PAVSMCs in PAH and suggest a new potential target for therapeutic intervention.

Cartography of Pathway Signal Perturbations Identifies Distinct Molecular Pathomechanisms in Malignant and Chronic Lung Diseases

Lung diseases are described by a wide variety of developmental mechanisms and clinical manifestations. Accurate classification and diagnosis of lung diseases are the bases for development of effective treatments. While extensive studies are conducted toward characterization of various lung diseases at molecular level, no systematic approach has been developed so far. Here we have applied a methodology for pathway-centered mining of high throughput gene expression data to describe a wide range of lung diseases in the light of shared and specific pathway activity profiles. We have applied an algorithm combining a Pathway Signal Flow (PSF) algorithm for estimation of pathway activity deregulation states in lung diseases and malignancies, and a Self Organizing Maps algorithm for classification and clustering of the pathway activity profiles. The analysis results allowed clearly distinguish between cancer and non-cancer lung diseases. Lung cancers were characterized by pathways implicated in cell proliferation, metabolism, while non-malignant lung diseases were characterized by deregulations in pathways involved in immune/inflammatory response and fibrotic tissue remodeling. In contrast to lung malignancies, chronic lung diseases had relatively heterogeneous pathway deregulation profiles. We identified three groups of interstitial lung diseases and showed that the development of characteristic pathological processes, such as fibrosis, can be initiated by deregulations in different signaling pathways. In conclusion, this paper describes the pathobiology of lung diseases from systems viewpoint using pathway centered high-dimensional data mining approach. Our results contribute largely to current understanding of pathological events in lung cancers and non-malignant lung diseases. Moreover, this paper provides new insight into molecular mechanisms of a number of interstitial lung diseases that have been studied to a lesser extent.

Early protective role of MST1 knockdown in response to experimental diabetic nephropathy

Diabetic nephropathy (DN) is a progressive kidney disease caused by the damage of capillaries in kidney's glomeruli. Mammalian Sterile 20-like kinase 1 (MST1) has been reported to play an important role in many disease, such as diabetes, cardiac disease and ect. However, the potential role of MST1 pathway in DN has not been fully evaluated. In this study, we hypothesized that MST1 could be involved in DN, and MST1 knockdown would attenuate the DN injury in experimental diabetic nephropathy induced by streptozotocin (STZ). The sieving method was used to generate primary cultures of rat podocytes, and cultured according to the previous reports. The clinical data were analyzed for vein specimens from ESRD. Real-time quantitative PCR was used to examine the mRNA levels. Immuno-fluorescence assay was used for primary podocyte in vitro. Lectrophoretic mobility shift assay was used for DNA binding activity of NF-κB. HE staining for histological examination and western blot assay for protein expression were employed. The average GBM thickness (GBMT) was measured By using the electron microscopy. In vitro, MST1 level increased significantly in primary rat podocyte cultured in hyperglycemia condition. In vivo experiment, diabetes induced by a single STZ injection (50 mg/kg) in SD rats. Knockdown of MST1 expression by lentiviral mediated gene transfer partly reduced the proteinuria and the level of FASL, and improved the pathological changes of the diabetic kidney. In conclusion, the MST1 could be involved in DN pathogenesis and may serve as the target for development of new therapies for DN.

Differential localization of A-Raf regulates MST2-mediated apoptosis during epithelial differentiation

A-Raf belongs to the family of oncogenic Raf kinases that are involved in mitogenic signaling by activating the MEK-ERK pathway. Low kinase activity of A-Raf toward MEK suggested that A-Raf might have alternative functions. We recently identified A-Raf as a potent inhibitor of the proapoptotic mammalian sterile 20-like kinase (MST2) tumor suppressor pathway in several cancer entities including head and neck, colon, and breast. Independent of kinase activity, A-Raf binds to MST2 thereby efficiently inhibiting apoptosis. Here, we show that the interaction of A-Raf with the MST2 pathway is regulated by subcellular compartmentalization. Although in proliferating normal cells and tumor cells A-Raf localizes to the mitochondria, differentiated non-carcinogenic cells of head and neck epithelia, which express A-Raf at the plasma membrane. The constitutive or induced re-localization of A-Raf to the plasma membrane compromises its ability to efficiently sequester and inactivate MST2, thus rendering cells susceptible to apoptosis. Physiologically, A-Raf re-localizes to the plasma membrane upon epithelial differentiation in vivo. This re-distribution is regulated by the scaffold protein kinase suppressor of Ras 2 (KSR2). Downregulation of KSR2 during mammary epithelial cell differentiation or siRNA-mediated knockdown re-localizes A-Raf to the plasma membrane causing the release of MST2. By using the MCF7 cell differentiation system, we could demonstrate that overexpression of A-Raf in MCF7 cells, which induces differentiation. Our findings offer a new paradigm to understand how differential localization of Raf complexes affects diverse signaling functions in normal cells and carcinomas.

Evaluation of LATS1 and LATS2 Promoter Methylation with the Risk of Pterygium Formation

Purpose. Pterygium is a serious eye problem in countries with high exposure to UV. However, despite numerous studies, the molecular etiology of pterygium is unclear. Recent studies have indicated that LATS1 and LATS2 genes are involved in DDR signaling pathways against continuous UV exposure. Our aim was to evaluate the LATS1 and LATS2 promoter methylation with the risk of pterygium formation. Methods. We evaluated the promoter methylation status of LATS1 and LATS2 using methylation-specific PCR technique. Also, mRNA expression of LATS1 and LATS2 was assessed in 14 cases of pterygium and 14 normal specimens by real-time PCR. Results. Promoter methylation of LATS1 and LATS2 was detected significantly between pterygium tissues and normal tissues [LATS1; OR = 4.9; 95% CI: 1.54 to 15.48, P = 0.003; LATS2; OR = 7.1; 95% CI: 1.53 to 33.19, P = 0.004]. The gene expression analysis showed a statistically significant difference between pterygium tissues and healthy controls for both LATS1 and LATS2 (P < 0.05). Conclusions. The data of this study is the first report regarding the effect of promoter methylation of the LATS1 and LATS2 in the pterygium. To confirm these data, doing further studies in various genetic populations with large sample sizes using advanced molecular techniques is proposed.

YAP promotes proliferation, chemoresistance, and angiogenesis in human cholangiocarcinoma through TEAD transcription factors

The Yes-associated protein (YAP)/Hippo pathway has been implicated in tissue development, regeneration, and tumorigenesis. However, its role in cholangiocarcinoma (CC) is not established. We show that YAP activation is a common feature in CC patient biopsies and human CC cell lines. Using microarray expression profiling of CC cells with overexpressed or down-regulated YAP, we show that YAP regulates genes involved in proliferation, apoptosis, and angiogenesis. YAP activity promotes CC growth in vitro and in vivo by functionally interacting with TEAD transcription factors (TEADs). YAP activity together with TEADs prevents apoptosis induced by cytotoxic drugs, whereas YAP knockdown sensitizes CC cells to drug-induced apoptosis. We further show that the proangiogenic microfibrillar-associated protein 5 (MFAP5) is a direct transcriptional target of YAP/TEAD in CC cells and that secreted MFAP5 promotes tube formation of human microvascular endothelial cells. High YAP activity in human CC xenografts and clinical samples correlates with increased MFAP5 expression and CD31(+) vasculature.

CONCLUSIONS

These findings establish YAP as a key regulator of proliferation and antiapoptotic mechanisms in CC and provide first evidence that YAP promotes angiogenesis by regulating the expression of secreted proangiogenic proteins.

Interaction of the EGF Receptor and the Hippo Pathway in the Diabetic Kidney

Activation of the EGF receptor (EGFR) or the Hippo signaling pathway can control cell proliferation, apoptosis, and differentiation, and the dysregulation of these pathways can contribute to tumorigenesis. Previous studies showed that activation of EGFR signaling in renal epithelial cells can exacerbate diabetic kidney injury. Moreover, EGFR has been implicated in regulating the Hippo signaling pathway in Drosophila; thus, we examined this potential interaction in mammalian diabetic kidney disease. Yes-associated protein (YAP) is a transcriptional regulator regulated by the Hippo signaling pathway. We found YAP protein expression and phosphorylation were upregulated in diabetic mouse renal proximal tubule epithelial cells, which were inhibited in diabetic proximal tubule EGFR-knockout mice (EGFR(ptKO)) or administration of an EGFR tyrosine kinase inhibitor erlotinib. Furthermore, activation of an EGFR-PI3K-Akt-CREB signaling pathway mediated YAP gene expression and YAP nuclear translocation and interaction with the TEA domain (TEAD) transcription factor complex, which led to upregulated expression of two TEAD-dependent genes, the connective tissue growth factor and amphiregulin genes. In a renal proximal tubule cell line, either pharmacologic or genetic inhibition of EGFR, Akt, or CREB blunted YAP expression in response to high-glucose treatment. Additionally, knocking down YAP expression by specific siRNA inhibited cell proliferation in response to high glucose or exogenous EGF. Therefore, these results link the Hippo pathway to EGFR-mediated renal epithelial injury in diabetes.

MST2-RASSF protein-protein interactions through SARAH domains

The detailed, atomistic-level understanding of molecular signaling along the tumor-suppressive Hippo signaling pathway that controls tissue homeostasis by balancing cell proliferation and death through apoptosis is a promising avenue for the discovery of novel anticancer drug targets. The activation of kinases such as Mammalian STE20-Like Protein Kinases 1 and 2 (MST1 and MST2)-modulated through both homo- and heterodimerization (e.g. interactions with Ras association domain family, RASSF, enzymes)-is a key upstream event in this pathway and remains poorly understood. On the other hand, RASSFs (such as RASSF1A or RASSF5) act as important apoptosis activators and tumor suppressors, although their exact regulatory roles are also unclear. We present recent molecular studies of signaling along the Ras-RASSF-MST pathway, which controls growth and apoptosis in eukaryotic cells, including a variety of modern molecular modeling and simulation techniques. Using recently available structural information, we discuss the complex regulatory scenario according to which RASSFs perform dual signaling functions, either preventing or promoting MST2 activation, and thus control cell apoptosis. Here, we focus on recent studies highlighting the special role being played by the specific interactions between the helical Salvador/RASSF/Hippo (SARAH) domains of MST2 and RASSF1a or RASSF5 enzymes. These studies are crucial for integrating atomistic-level mechanistic information about the structures and conformational dynamics of interacting proteins, with information available on their system-level functions in cellular signaling.

Hippo Component TAZ Functions as a Co-repressor and Negatively Regulates ΔNp63 Transcription through TEA Domain (TEAD) Transcription Factor

Transcriptional co-activator with a PDZ binding domain (TAZ) is a WW domain-containing transcriptional co-activator and a core component of an emerging Hippo signaling pathway that regulates organ size, tumorigenesis, metastasis, and drug resistance. TAZ regulates these biological functions by up-regulating downstream cellular genes through transactivation of transcription factors such as TEAD and TTF1. To understand the molecular mechanisms underlying TAZ-induced tumorigenesis, we have recently performed a gene expression profile analysis by overexpressing TAZ in mammary cells. In addition to the TAZ-up-regulated genes that were confirmed in our previous studies, we identified a large number of cellular genes that were down-regulated by TAZ. In this study, we have confirmed these down-regulated genes (including cytokines, chemokines, and p53 gene family members) as bona fide downstream transcriptional targets of TAZ. By using human breast and lung epithelial cells, we have further characterized ΔNp63, a p53 gene family member, and shown that TAZ suppresses ΔNp63 mRNA, protein expression, and promoter activity through interaction with the transcription factor TEAD. We also show that TEAD can inhibit ΔNp63 promoter activity and that TAZ can directly interact with ΔNp63 promoter-containing TEAD binding sites. Finally, we provide functional evidence that down-regulation of ΔNp63 by TAZ may play a role in regulating cell migration. Altogether, this study provides novel evidence that the Hippo component TAZ can function as a co-repressor and regulate biological functions by negatively regulating downstream cellular genes.

Roles of the Hippo pathway in lung development and tumorigenesis

Lung cancer is the most commonly diagnosed cancer and accounts for one fifth of all cancer deaths worldwide. Although significant progress has been made toward our understanding of the causes of lung cancer, the 5-year survival is still lower than 15%. Therefore, there is an urgent need for novel lung cancer biomarkers and drug targets. The Hippo signaling pathway is an emerging signaling pathway that regulates various biological processes. Recently, increasing evidence suggests that the Hippo pathway may play important roles in not only lung development but also lung tumorigenesis. In this review article, we will summarize the most recent advances and predict future directions on this new cancer research field.