Convergent signaling in the regulation of connective tissue growth factor in malignant mesothelioma: TGFβ signaling and defects in the Hippo signaling cascade

Advances and Challenges in Targeting TGF-β Isoforms for Therapeutic Intervention of Cancer: A Mechanism-Based Perspective

The TGF-β family is a group of 25 kDa secretory cytokines, in mammals consisting of three dimeric isoforms (TGF-βs 1, 2, and 3), each encoded on a separate gene with unique regulatory elements. Each isoform plays unique, diverse, and pivotal roles in cell growth, survival, immune response, and differentiation. However, many researchers in the TGF-β field often mistakenly assume a uniform functionality among all three isoforms. Although TGF-βs are essential for normal development and many cellular and physiological processes, their dysregulated expression contributes significantly to various diseases. Notably, they drive conditions like fibrosis and tumor metastasis/progression. To counter these pathologies, extensive efforts have been directed towards targeting TGF-βs, resulting in the development of a range of TGF-β inhibitors. Despite some clinical success, these agents have yet to reach their full potential in the treatment of cancers. A significant challenge rests in effectively targeting TGF-βs' pathological functions while preserving their physiological roles. Many existing approaches collectively target all three isoforms, failing to target just the specific deregulated ones. Additionally, most strategies tackle the entire TGF-β signaling pathway instead of focusing on disease-specific components or preferentially targeting tumors. This review gives a unique historical overview of the TGF-β field often missed in other reviews and provides a current landscape of TGF-β research, emphasizing isoform-specific functions and disease implications. The review then delves into ongoing therapeutic strategies in cancer, stressing the need for more tools that target specific isoforms and disease-related pathway components, advocating mechanism-based and refined approaches to enhance the effectiveness of TGF-β-targeted cancer therapies.

Multifaceted TGF-β signaling, a master regulator: From bench-to-bedside, intricacies, and complexities

Physiological embryogenesis and adult tissue homeostasis are regulated by transforming growth factor-β (TGF-β), an evolutionarily conserved family of secreted polypeptide factors, acting in an autocrine and paracrine manner. The role of TGF-β in inflammation, fibrosis, and cancer is complex and sometimes even contradictory, exhibiting either inhibitory or promoting effects depending on the stage of the disease. Under pathological conditions, especially fibrosis and cancer, overexpressed TGF-β causes extracellular matrix deposition, epithelial-mesenchymal transition, cancer-associated fibroblast formation, and/or angiogenesis. In this review article, we have tried to dive deep into the mechanism of action of TGF-β in inflammation, fibrosis, and carcinogenesis. As TGF-β and its downstream signaling mechanism are implicated in fibrosis and carcinogenesis blocking this signaling mechanism appears to be a promising avenue. However, targeting TGF-β carries substantial risk as this pathway is implicated in multiple homeostatic processes and is also known to have tumor-suppressor functions. There is a need for careful dosing of TGF-β drugs for therapeutic use and patient selection.

Understanding the Role of Yes-Associated Protein (YAP) Signaling in the Transformation of Lens Epithelial Cells (EMT) and Fibrosis

Fibrotic cataracts, posterior capsular opacification (PCO), and anterior subcapsular cataracts (ASC) are mainly attributed to the transforming growth factor-β (TGFβ)-induced epithelial-to-mesenchymal transition (EMT) of lens epithelial cells (LECs). Previous investigations from our laboratory have shown the novel role of non-canonical TGFβ signaling in the progression of EMT in LECs. In this study, we have identified YAP as a critical signaling molecule involved in lens fibrosis. The observed increase in nuclear YAP in capsules of human ASC patients points toward the involvement of YAP in lens fibrosis. In addition, the immunohistochemical (IHC) analyses on ocular sections from mice that overexpress TGFβ in the lens (TGFβtg) showed a co-expression of YAP and α-SMA in the fibrotic plaques when compared to wild-type littermate lenses, which do not. The incubation of rat lens explants with verteporfin, a YAP inhibitor, prevented a TGFβ-induced fiber-like phenotype, α-SMA, and fibronectin expression, as well as delocalization of E-cadherin and β-catenin. Finally, LECs co-incubated with TGFβ and YAP inhibitor did not exhibit an induction in matrix metalloproteinase 2 compared to those LECs treated with TGFβ alone. In conclusion, these data demonstrate that YAP is required for TGFβ-mediated lens EMT and fibrosis.

The circadian clock protein Cryptochrome 1 is a direct target and feedback regulator of the Hippo pathway

Circadian clock controls daily behavior and physiology. The activity of various signaling pathways affects clock gene expression. Here, we show that the core circadian clock gene CRY1 is a direct target of the Hippo pathway effector YAP. YAP binds to TEADs and occupies the proximal promoter regions of CRY1, positively regulating its transcription. Interestingly, we further identified that CRY1 acts in a feedback loop to fine-tune Hippo pathway activation by modulating the expression of YAP and MOB1. Indeed, loss of CRY1 results in enhanced YAP activation. Consistently, we found that YAP levels and activity control clock gene expression and oscillation in synchronized cells. Furthermore, in breast cancer cells, CRY1 downregulation causes YAP/TAZ hyperactivation and enhanced DNA damage. Together, our findings provide a direct mechanistic link between the Hippo pathway and the circadian clock, where CRY1 and Hippo components form an orchestrated signaling network that influences cell growth and circadian rhythm.

Chronic Inflammation, Oxidative Stress and Metabolic Plasticity: Three Players Driving the Pro-Tumorigenic Microenvironment in Malignant Mesothelioma

Malignant pleural mesothelioma (MPM) is a lethal and rare cancer, even if its incidence has continuously increased all over the world. Asbestos exposure leads to the development of mesothelioma through multiple mechanisms, including chronic inflammation, oxidative stress with reactive oxygen species (ROS) generation, and persistent aberrant signaling. Together, these processes, over the years, force normal mesothelial cells' transformation. Chronic inflammation supported by "frustrated" macrophages exposed to asbestos fibers is also boosted by the release of pro-inflammatory cytokines, chemokines, growth factors, damage-associated molecular proteins (DAMPs), and the generation of ROS. In addition, the hypoxic microenvironment influences MPM and immune cells' features, leading to a significant rewiring of metabolism and phenotypic plasticity, thereby supporting tumor aggressiveness and modulating infiltrating immune cell responses. This review provides an overview of the complex tumor-host interactions within the MPM tumor microenvironment at different levels, i.e., soluble factors, metabolic crosstalk, and oxidative stress, and explains how these players supporting tumor transformation and progression may become potential and novel therapeutic targets in MPM.

BMP and activin membrane-bound inhibitor regulate connective tissue growth factor controlling mesothelioma cell proliferation

Background

Malignant mesothelioma (MM) is an aggressive mesothelial cell cancer type linked mainly to asbestos inhalation. MM characterizes by rapid progression and resistance to standard therapeutic modalities such as surgery, chemotherapy, and radiotherapy. Our previous studies have suggested that tumor cell-derived connective tissue growth factor (CTGF) regulates the proliferation of MM cells as well as the tumor growth in mouse xenograft models.

Methods

In this study, we knock downed the bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) and CTGF in MM cells and investigated the relationship between both and their impact on the cell cycle and cell proliferation.

Results

The knockdown of CTGF or BAMBI reduced MM cell proliferation. In contrast to CTGF knockdown which decreased BAMBI, knockdown of BAMBI increased CTGF levels. Knockdown of either BAMBI or CTGF reduced expression of the cell cycle regulators; cyclin D3, cyclin-dependent kinase (CDK)2, and CDK4. Further, in silico analysis revealed that higher BAMBI expression was associated with shorter overall survival rates among MM patients.

Conclusions

Our findings suggest that BAMBI is regulated by CTGF promoting mesothelioma growth by driving cell cycle progression. Therefore, the crosstalk between BAMBI and CTGF may be an effective therapeutic target for MM treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10080-x.

Incidence and Risk Factors of Chest Wall Metastasis at Biopsy Sites in Patients with Malignant Pleural Mesothelioma

To investigate the incidence and risk factors of chest wall metastasis (CWM) at biopsy sites in patients with malignant pleural mesothelioma (MPM). This retrospective cohort study was conducted in 262 consecutive MPM patients who underwent multimodal treatment in which including neoadjuvant chemotherapy (NAC) and curative-intent surgery, from August 2009 to March 2021. CWM was evaluated radiologically (r-CWM) and pathologically (p-CWM). We also investigated the risk factors of p-CWM and the consistency between r-CWM and p-CWM. Of 262 patients, 25 patients were excluded from analysis due to missing data or impossibility of evaluation. Of the eligible 237 patients, pleural biopsy was performed via video-assisted thoracoscopic surgery in 197 (83.1%) and medical thoracoscopy in 40 (16.9%). Pleurodesis was performed after pleural biopsy in 74 patients (31.2%). All patients received NAC followed by curative-intent surgery. Radiological examination showed r-CWM in 43 patients (18.1%), while pathological examination showed p-CWM in 135 patients (57.0%). The incidence of p-CWM was significantly higher in the patients who received pleurodesis after pleural biopsy (77.0% vs. 47.9%, <0.001). Multivariate logistic regression analysis for p-CWM revealed that pleurodesis is an independent risk factor of p-CWM (adjusted hazard ratio, 3.46; 95% confidence interval, 1.84−6.52, <0.001). CWM at the biopsy site was pathologically proven in more than half of the patients (57.0%) who received NAC followed by curative-intent surgery, which was higher than the numbers diagnosed by radiological examinations (p-CWM: 57.0% vs. r-CWM: 18.1%). Pleurodesis after pleural biopsy is an independent risk factor of p-CWM.

Origin and Therapies of Osteosarcoma

Simple Summary

Osteosarcoma is the most common malignant bone tumor in children, with a 5-year survival rate ranging from 70% to 20% depending on the aggressiveness of the disease. The current treatments have not evolved over the past four decades due in part to the genetic complexity of the disease and its heterogeneity. This review will summarize the current knowledge of OS origin, diagnosis and therapies.

Abstract

Osteosarcoma (OS) is the most frequent primary bone tumor, mainly affecting children and young adults. Despite therapeutic advances, the 5-year survival rate is 70% but drastically decreases to 20–30% for poor responders to therapies or for patients with metastasis. No real evolution of the survival rates has been observed for four decades, explained by poor knowledge of the origin, difficulties related to diagnosis and the lack of targeted therapies for this pediatric tumor. This review will describe a non-exhaustive overview of osteosarcoma disease from a clinical and biological point of view, describing the origin, diagnosis and therapies.

Hybrid molecule between platanic acid and LCL-161 as a yes-associated protein (YAP) degrader

Dysregulated Yes-associated protein (YAP) is involved in several malignant cancers. However, discovering a druggable YAP inhibitor(s) is difficult because YAP itself does not have any enzymatic activity. In such cases, targeted protein degradation strategies based on hybrid molecules that bind to the target protein and an E3 ubiquitin ligase are useful for suppressing proteins that exhibit aberrant activation and/or excessive expression. Upon screening YAP-interacting small compounds, we identified HK13, a platanic acid, as a novel compound that interacts with YAP. Next, we synthesized hybrid compounds of platanic acid and LCL-161, which reportedly shows a high affinity to for cIAP, one of E3 ubiquitin ligases. Among these compounds, HK24 possessed the ability to inhibit the growth of YAP overexpressing NCI-H290 cells. This inhibitory activity may be mediated by YAP degradation, although HK24 exhibited weak YAP degradation. Furthermore, we confirmed involvement of proteasome pathway in HK24-dependent YAP degradation by culturing NCI-H290 cells in the presence of a proteasome inhibitor. Therefore, it is possible that platanic acid is a potential candidate for molecular medicine targeting YAP.

Involvement of the TGF-β Signaling Pathway in the Development of YAP-Driven Osteosarcoma Lung Metastasis

Background

The poor survival rate of patients with osteosarcoma (OS), specifically with metastases at diagnosis, undergoes the urgency to develop new therapeutic strategies. Although we recently demonstrated the key role of YAP/TEAD signaling in the growth of OS primary tumor, the molecular mechanisms by which YAP regulates metastases development remain poorly understood.

Methods

The molecular mechanisms by which YAP regulates metastases development were studied using an overexpression of mutated forms of YAP able or not able to interact with TEAD. Molecular signatures were identified using RNA-sequencing analysis and gene set enrichment. Interactions between YAP and Smad3 were studied using proximity ligation assay (PLA), immunoprecipitation, and promoter/specific gene assays. The involvement of the TGF-β pathway in the ability of YAP to stimulate metastatic development in vivo was studied using an inhibitor of the TGF-β cascade in a preclinical model of OS and in vitro on the ability of OS cells to migrate and invade.

Results

Our work shows that a high YAP expression is associated with the presence of lung metastases which predicts a poor prognosis. Molecular analysis indicates that TGF-β signaling is involved in YAP-driven osteosarcoma cell pro-migratory phenotype, epithelial mesenchymal transition, cell migration, and in vivo lung metastasis development. Regardless of its ability to bind to TEAD, YAP interacts with Smad3 and stimulates the transcriptional activity of TGF-β/Smad3, thereby enhancing the ability of TGF-β to stimulate lung metastasis development.

Conclusions

We demonstrated the crucial involvement of the TGF-β/Smad3 signaling pathway in YAP-driven lung metastasis development in OS.

Anti-fibrotic effect of 6-bromo-indirubin-3'-oxime (6-BIO) via regulation of activator protein-1 (AP-1) and specificity protein-1 (SP-1) transcription factors in kidney cells

PAI-1 and CTGF are overexpressed in kidney diseases and cause fibrosis of the lungs, liver, and kidneys. We used a rat model of unilateral ureteral obstruction (UUO) to investigate whether 6-BIO, a glycogen synthase kinase-3β inhibitor, attenuated fibrosis by inhibiting PAI-1 and CTGF in vivo. Additionally, TGFβ-induced cellular fibrosis was observed in vitro using the human kidney proximal tubular epithelial cells (HK-2), and rat interstitial fibroblasts (NRK49F). Expression of fibrosis-related proteins and signaling molecules such as PAI-1, CTGF, TGFβ, αSMA, SMAD, and MAPK were determined in HK-2 and NRK49F cells using immunoblotting. To identify the transcription factors that regulate the expression of PAI-1 and CTGF the promoter activities of AP-1 and SP-1 were analyzed using luciferase assays. Confocal microscopy was used to observe the co-localization of AP-1 and SP-1 to PAI-1 and CTGF. Expression of PAI-1, CTGF, TGFβ, and α-SMA increased in UUO model as well as in TGFβ-treated HK-2 and NRK49F cells. Furthermore, UUO and TGFβ treatment induced the activation of P-SMAD2/3, SMAD4, P-ERK 1/2, P-P38, and P-JNK MAPK signaling pathways. PAI-1, CTGF, AP-1 and SP-1 promoter activity increased in response to TGFβ treatment. However, treatment with 6-BIO decreased the expression of proteins and signaling pathways associated with fibrosis in UUO model as well as in TGFβ-treated HK-2 and NRK49F cells. Moreover, 6-BIO treatment attenuated the expression of PAI-1 and CTGF as well as the promoter activities of AP-1 and SP-1, thereby regulating the SMAD and MAPK signaling pathways, and subsequently exerting anti-fibrotic effects on kidney cells.

Transforming Growth Factor-β: An Agent of Change in the Tumor Microenvironment

Transforming Growth Factor-β (TGF-β) is a key regulator of embryonic development, adult tissue homeostasis, and lesion repair. In tumors, TGF-β is a potent inhibitor of early stage tumorigenesis and promotes late stage tumor progression and metastasis. Here, we review the roles of TGF-β as well as components of its signaling pathways in tumorigenesis. We will discuss how a core property of TGF-β, namely its ability to change cell differentiation, leads to the transition of epithelial cells, endothelial cells and fibroblasts to a myofibroblastoid phenotype, changes differentiation and polarization of immune cells, and induces metabolic reprogramming of cells, all of which contribute to the progression of epithelial tumors.

Concurrent YAP/TAZ and SMAD signaling mediate vocal fold fibrosis

Vocal fold (VF) fibrosis is a major cause of intractable voice-related disability and reduced quality of life. Excision of fibrotic regions is suboptimal and associated with scar recurrence and/or further iatrogenic damage. Non-surgical interventions are limited, putatively related to limited insight regarding biochemical events underlying fibrosis, and downstream, the lack of therapeutic targets. YAP/TAZ integrates diverse cell signaling events and interacts with signaling pathways related to fibrosis, including the TGF-β/SMAD pathway. We investigated the expression of YAP/TAZ following vocal fold injury in vivo as well as the effects of TGF-β1 on YAP/TAZ activity in human vocal fold fibroblasts, fibroblast-myofibroblast transition, and TGF-β/SMAD signaling. Iatrogenic injury increased nuclear localization of YAP and TAZ in fibrotic rat vocal folds. In vitro, TGF-β1 activated YAP and TAZ in human VF fibroblasts, and inhibition of YAP/TAZ reversed TGF-β1-stimulated fibroplastic gene upregulation. Additionally, TGF-β1 induced localization of YAP and TAZ in close proximity to SMAD2/3, and nuclear accumulation of SMAD2/3 was inhibited by a YAP/TAZ inhibitor. Collectively, YAP and TAZ were synergistically activated with the TGF-β/SMAD pathway, and likely essential for the fibroplastic phenotypic shift in VF fibroblasts. Based on these data, YAP/TAZ may evolve as an attractive therapeutic target for VF fibrosis.

Hippo/YAP Signaling Pathway: A Promising Therapeutic Target in Bone Paediatric Cancers?

Osteosarcoma and Ewing sarcoma are the most prevalent bone pediatric tumors. Despite intensive basic and medical research studies to discover new therapeutics and to improve current treatments, almost 40% of osteosarcoma and Ewing sarcoma patients succumb to the disease. Patients with poor prognosis are related to either the presence of metastases at diagnosis or resistance to chemotherapy. Over the past ten years, considerable interest for the Hippo/YAP signaling pathway has taken place within the cancer research community. This signaling pathway operates at different steps of tumor progression: Primary tumor growth, angiogenesis, epithelial to mesenchymal transition, and metastatic dissemination. This review discusses the current knowledge about the involvement of the Hippo signaling pathway in cancer and specifically in paediatric bone sarcoma progression.

TGF-β in fibrosis by acting as a conductor for contractile properties of myofibroblasts

Myofibroblasts are non-muscle contractile cells that play a key physiologically role in organs such as the stem villi of the human placenta during physiological pregnancy. They are able to contract and relax in response to changes in the volume of the intervillous chamber. Myofibroblasts have also been observed in several diseases and are involved in wound healing and the fibrotic processes affecting several organs, such as the liver, lungs, kidneys and heart. During the fibrotic process, tissue retraction rather than contraction is correlated with collagen synthesis in the extracellular matrix, leading to irreversible fibrosis and, finally, apoptosis of myofibroblasts. The molecular motor of myofibroblasts is the non-muscle type IIA and B myosin (NMMIIA and NMMIIB). Fibroblast differentiation into myofibroblasts is largely governed by the transforming growth factor-β1 (TGF-β1). This system controls the canonical WNT/β-catenin pathway in a positive manner, and PPARγ in a negative manner. The WNT/β-catenin pathway promotes fibrosis, while PPARγ prevents it. This review focuses on the contractile properties of myofibroblasts and the conductor, TGF-β1, which together control the opposing interplay between PPARγ and the canonical WNT/β-catenin pathway.

Detection of TGF-β in pleural effusions for diagnosis and prognostic stratification of malignant pleural mesothelioma

OBJECTIVES

Malignant pleural mesothelioma (MPM) is an aggressive malignancy with dismal prognosis but variable course of disease. To support diagnosis and to risk stratify patients, more reliable biomarkers are warranted. Emerging evidence underlines a functional role of transforming growth factor-beta (TGF-β) in MPM tumorigenesis though its utility as a clinical biomarker remains unexplored.

MATERIALS AND METHODS

Corresponding pleural effusions and serum samples taken at primary diagnosis were analyzed for TGF-β by ELISA, and for mesothelin (SMRP) by chemiluminescence enzyme immunoassay. Tumor load was quantified in MPM patients by volumetric analysis of chest CT scans. All findings were correlated with clinicopathological characteristics.

RESULTS

In total 48 MPM patients, 24 patients with non-malignant pleural disease (NMPD) and 30 patients with stage IV lung cancer were enrolled in this study. Pleural effusions from MPM patients had significantly higher TGF-β levels than from NMPD or lung cancer patients (p < 0.0001; AUC for MPM vs NMPD: 0.78, p = 0.0001). Both epithelioid and non-epithelioid MPM were associated with higher TGF-β levels (epithelioid: p < 0.05; non-epithelioid: p < 0.0001) and levels of TGF-β correlated with disease stage (p = 0.003) and with tumor volume (p = 0.002). Interestingly, high TGF-β levels in pleural effusion, but not in serum, was significantly associated with inferior overall survival (TGF-beta ≥14.36 ng/mL: HR 3.45, p = 0.0001). This correlation was confirmed by multivariate analysis. In contrast, effusion SMRP levels were exclusively high in epithelioid MPM, negatively correlated with effusion TGF-β levels and did not provide prognostic information.

CONCLUSION

TGF-β levels determined in pleural effusion may be a promising biomarker for diagnosis and prognostic stratification of MPM.

Identification of Prolyl isomerase Pin1 as a novel positive regulator of YAP/TAZ in breast cancer cells

The Hippo signalling pathway plays very important roles in tumorigenesis, metastasis, organ size control, and drug resistance. Although, it has been shown that the two major components of Hippo pathway, YAP and TAZ, play very crucial role in tumorigenesis and drug resistance, the exact molecular mechanisms are still unknown. Recently, we have shown that the prolyl isomerase Pin1 regulates the activity of Hippo pathway through interaction with Hippo component LATS kinase. Thus we asked if Pin1 is also able to interact with other Hippo pathway components. Therefore, in order to investigate whether Pin1 can interacts with other components of the Hippo pathway, we performed GST-pull down and co-immunoprecipitation (Co-IP) assays and have identified two Hippo components YAP and TAZ oncoproteins as novel binding partner of Pin1. We found that Pin1 interacts with YAP/TAZ in a phosphorylation-independent manner and WW domain of Pin1 is necessary for this interaction. Moreover, by using real time qRT-PCR, Cycloheximide chase, luciferase reporter, cell viability and soft agar assays, we have shown that Pin1 increases the tumorigenic and drug-resistant activity of YAP/TAZ through stabilization of YAP/TAZ at protein levels. Together, we have identified Pin1 as a novel positive regulator of YAP/TAZ in tumorigenesis and drug resistance of breast cancer cells. These findings will provide a significant contribution for targeting the Pin1-YAP/TAZ signaling for the successful treatment of tumorigenesis and drug resistance of breast and other cancers in the future.

YAP and TAZ are distinct effectors of corneal myofibroblast transformation

PURPOSE

Transforming growth factor β1 (TGFβ1) is elevated in wounds after injury and promotes the transdifferentiation of quiescent cells in the stroma (keratocytes, to activated fibroblasts and subsequently myofibroblasts-KFM transformation). Coactivators of transcription, YAP (Yes-associated protein) and TAZ (Transcriptional coactivator with PDZ-binding motif), are mechanotransducers that intersect with the TGFβ pathway via interactions with Smad proteins. Here, we examined the distinct role of YAP and TAZ on TGFβ1 induced myofibroblast transformation of primary human corneal fibroblasts (HCFs).

METHODS

A knockdown approach was used to silence YAP and TAZ individually in HCFs. Forty-eight hours post siRNA transfection, cells were cultured in the presence or absence of 2 ng/ml TGFβ1 for 24h. The cells were subjected to nuclear and cytoplasmic fractionation. The expression of α-smooth muscle actin (αSMA), Smad 2, 3 and 4, CTGF and phospho-Smad2, 3, and 4 were assessed by qPCR and Western blotting.

RESULTS

TGFβ1 stimulation resulted in the decreased phosphorylation of YAP in the cytosol, and increased levels of phosphorylated TAZ and Smad2/3/4 in the nucleus. Knockdown of TAZ resulted in elevated YAP expression but not vice versa. Additionally, knockdown of TAZ but not YAP resulted in upregulation of αSMA expression in the presence and absence of TGFβ1. In the presence of TGFβ1 YAP knockdown increased Smad2/3/4 expression and Smad4 phosphorylation, while TAZ knockdown had no effect on Smad2/3/4 expression and phosphorylation. YAP knockdown inhibited CTGF expression while TAZ knockdown resulted in its increased expression. Finally, simultaneous knockdown of YAP and TAZ resulted in cell death.

CONCLUSION

Our findings suggest that YAP and TAZ function as distinct modulators of TGFβ1 induced myofibroblast transformation and have different roles in signalling. Specifically, TAZ limits YAP's ability to mediate KFM transformation via Smad proteins. The data also suggest that while having distinct effects, YAP and TAZ have redundant or combinatorial functions critical to cell survival. These results suggest that a loss of TAZ may help drive corneal haze and fibrosis and that the balance between YAP/TAZ is essential in controlling myofibroblast differentiation.

DNA binding partners of YAP/TAZ

Hippo signaling plays critical roles in regulation of tissue homeostasis, organ size, and tumorigenesis by inhibiting YES-associated protein (YAP) and PDZ-binding protein TAZ through MST1/2 and LATS1/2 pathway. It is also engaged in cross-talk with various other signaling pathways, including WNT, BMPs, Notch, GPCRs, and Hedgehog to further modulate activities of YAP/TAZ. Because YAP and TAZ are transcriptional coactivators that lack DNA-binding activity, both proteins must interact with DNA-binding transcription factors to regulate target gene’s expression. To activate target genes involved in cell proliferation, TEAD family members are major DNA-binding partners of YAP/TAZ. Accordingly, YAP/TAZ were originally classified as oncogenes. However, YAP might also play tumor-suppressing role. For example, YAP can bind to DNA-binding tumor suppressors including RUNXs and p73. Thus, YAP might act either as an oncogene or tumor suppressor depending on its binding partners. Here, we summarize roles of YAP depending on its DNA-binding partners and discuss context-dependent functions of YAP/TAZ.

Traditional and systems biology based drug discovery for the rare tumor syndrome neurofibromatosis type 2

Neurofibromatosis 2 (NF2) is a rare tumor suppressor syndrome that manifests with multiple schwannomas and meningiomas. There are no effective drug therapies for these benign tumors and conventional therapies have limited efficacy. Various model systems have been created and several drug targets have been implicated in NF2-driven tumorigenesis based on known effects of the absence of merlin, the product of the NF2 gene. We tested priority compounds based on known biology with traditional dose-concentration studies in meningioma and schwann cell systems. Concurrently, we studied functional kinome and gene expression in these cells pre- and post-treatment to determine merlin deficient molecular phenotypes. Cell viability results showed that three agents (GSK2126458, Panobinostat, CUDC-907) had the greatest activity across schwannoma and meningioma cell systems, but merlin status did not significantly influence response. In vivo, drug effect was tumor specific with meningioma, but not schwannoma, showing response to GSK2126458 and Panobinostat. In culture, changes in both the transcriptome and kinome in response to treatment clustered predominantly based on tumor type. However, there were differences in both gene expression and functional kinome at baseline between meningioma and schwannoma cell systems that may form the basis for future selective therapies. This work has created an openly accessible resource (www.synapse.org/SynodosNF2) of fully characterized isogenic schwannoma and meningioma cell systems as well as a rich data source of kinome and transcriptome data from these assay systems before and after treatment that enables single and combination drug discovery based on molecular phenotype.

Stimulatory actions of IGF-I are mediated by IGF-IR cross-talk with GPER and DDR1 in mesothelioma and lung cancer cells

Insulin-like growth factor-I (IGF-I)/IGF-I receptor (IGF-IR) system has been largely involved in the pathogenesis and development of various tumors. We have previously demonstrated that IGF-IR cooperates with the G-protein estrogen receptor (GPER) and the collagen receptor discoidin domain 1 (DDR1) that are implicated in cancer progression. Here, we provide novel evidence regarding the molecular mechanisms through which IGF-I/IGF-IR signaling triggers a functional cross-talk with GPER and DDR1 in both mesothelioma and lung cancer cells. In particular, we show that IGF-I activates the transduction network mediated by IGF-IR leading to the up-regulation of GPER and its main target genes CTGF and EGR1 as well as the induction of DDR1 target genes like MATN-2, FBN-1, NOTCH 1 and HES-1. Of note, certain DDR1-mediated effects upon IGF-I stimulation required both IGF-IR and GPER as determined knocking-down the expression of these receptors. The aforementioned findings were nicely recapitulated in important biological outcomes like IGF-I promoted chemotaxis and migration of both mesothelioma and lung cancer cells. Overall, our data suggest that IGF-I/IGF-IR system triggers stimulatory actions through both GPER and DDR1 in aggressive tumors as mesothelioma and lung tumors. Hence, this novel signaling pathway may represent a further target in setting innovative anticancer strategies.

miR-375 is involved in Hippo pathway by targeting YAP1/TEAD4-CTGF axis in gastric carcinogenesis

miR-375 is a tumor-suppressive microRNA (miRNA) in gastric cancer (GC). However, its molecular mechanism remains unclear. The aim of this study is to comprehensively investigate how miR-375 is involved in Hippo pathway by targeting multiple oncogenes. miR-375 expression in gastric cancer cell lines and primary GC was investigated by qRT-PCR. The regulation of YAP1, TEAD4, and CTGF expression by miR-375 was evaluated by qRT-PCR, western blot, and luciferase reporter assays, respectively. The functional roles of the related genes were examined by siRNA-mediated knockdown or ectopic expression assays. The clinical significance and expression correlation analysis of miR-375, YAP1, and CTGF were performed in primary GCs. TCGA cohort was also used to analyze the expression correlation of YAP1, TEAD4, CTGF, and miR-375 in primary GCs. miR-375 was down-regulated in GC due to promoter methylation and histone deacetylation. miR-375 downregulation was associated with unfavorable outcome and lymph node metastasis. Ectopic expression of miR-375 inhibited tumor growth in vitro and in vivo. Three components of Hippo pathway, YAP1, TEAD4 and CTGF, were revealed to be direct targets of miR-375. The expression of three genes showed a negative correlation with miR-375 expression and YAP1 re-expression partly abolished the tumor-suppressive effect of miR-375. Furthermore, CTGF was confirmed to be the key downstream of Hippo-YAP1 cascade and its knockdown phenocopied siYAP1 or miR-375 overexpression. YAP1 nuclear accumulation was positively correlated with CTGF cytoplasmic expression in primary GC tissues. Verteporfin exerted an anti-oncogenic effect in GC cell lines by quenching CTGF expression through YAP1 degradation. In short, miR-375 was involved in the Hippo pathway by targeting YAP1-TEAD4-CTGF axis and enriched our knowledge on the miRNA dysregulation in gastric tumorigenesis.

Nuclear localization of TEF3-1 promotes cell cycle progression and angiogenesis in cancer

TEF3-1 (transcriptional enhancer factor 3 isoform 1), also known as TEAD4 (TEA domain family member 4), was recently revealed as an oncogenic character in cancer development. However, the underlying molecular pathogenic mechanisms remain undefined. In this paper, we investigated nuclear TEF3-1 could promote G1/S transition in HUVECs, and the expression levels of cyclins and CDKs were upregulated. Additionally, if TEF3-1 was knocked down, the expression of cyclins and CDKs was downregulated while the expression of P21, a negative regulator of the cell cycle, was upregulated. A microarray analysis also confirmed that TEF3-1 overexpression upregulates genes that are related to cell cycle progression and the promotion of angiogenesis. Moreover, we observed that nuclear TEF3-1 was highly expressed during the formation of vascular structures in gastric cancer (GC). Finally, tumor xenograft experiments indicated that, when TEF3-1 was knocked down, tumor growth and angiogenesis were also suppressed. Taken together, these results demonstrate for the first time that TEF3-1 localization to the nucleus stimulates the cell cycle progression in HUVECs and specifically contributes to tumor angiogenesis. Nuclear TEF3-1 in HUVECs may serve as an oncogenic biomarker, and the suppression of TEF3-1 may be a potential target in anti-tumor therapy.

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.

Targeting TGF-β Signaling for Therapeutic Gain

Transforming growth factor βs (TGF-βs) are closely related ligands that have pleiotropic activity on most cell types of the body. They act through common heterotetrameric TGF-β type II and type I transmembrane dual specificity kinase receptor complexes, and the outcome of signaling is context-dependent. In normal tissue, they serve a role in maintaining homeostasis. In many diseased states, particularly fibrosis and cancer, TGF-β ligands are overexpressed and the outcome of signaling is diverted toward disease progression. There has therefore been a concerted effort to develop drugs that block TGF-β signaling for therapeutic benefit. This review will cover the basics of TGF-β signaling and its biological activities relevant to oncology, present a summary of pharmacological TGF-β blockade strategies, and give an update on preclinical and clinical trials for TGF-β blockade in a variety of solid tumor types.

Targeting TGF-β Signaling for Therapeutic Gain

Transforming growth factor βs (TGF-βs) are closely related ligands that have pleiotropic activity on most cell types of the body. They act through common heterotetrameric TGF-β type II and type I transmembrane dual specificity kinase receptor complexes, and the outcome of signaling is context-dependent. In normal tissue, they serve a role in maintaining homeostasis. In many diseased states, particularly fibrosis and cancer, TGF-β ligands are overexpressed and the outcome of signaling is diverted toward disease progression. There has therefore been a concerted effort to develop drugs that block TGF-β signaling for therapeutic benefit. This review will cover the basics of TGF-β signaling and its biological activities relevant to oncology, present a summary of pharmacological TGF-β blockade strategies, and give an update on preclinical and clinical trials for TGF-β blockade in a variety of solid tumor types.

YAP-mediated mechanotransduction determines the podocyte's response to damage

Podocytes are terminally differentiated cells of the kidney filtration barrier. They are subjected to physiological filtration pressure and considerable mechanical strain, which can be further increased in various kidney diseases. When injury causes cytoskeletal reorganization and morphological alterations of these cells, the filtration barrier may become compromised and allow proteins to leak into the urine (a condition called proteinuria). Using time-resolved proteomics, we showed that podocyte injury stimulated the activity of the transcriptional coactivator YAP and the expression of YAP target genes in a rat model of glomerular disease before the development of proteinuria. Although the activities of YAP and its ortholog TAZ are activated by mechanical stress in most cell types, injury reduced YAP and TAZ activity in cultured human and mouse podocyte cell lines grown on stiff substrates. Culturing these cells on soft matrix or inhibiting stress fiber formation recapitulated the damage-induced YAP up-regulation observed in vivo, indicating a mechanotransduction-dependent mechanism of YAP activation in podocytes. YAP overexpression in cultured podocytes increased the abundance of extracellular matrix-related proteins that can contribute to fibrosis. YAP activity was increased in mouse models of diabetic nephropathy, and the YAP target CTGF was highly expressed in renal biopsies from glomerular disease patients. Although overexpression of human YAP in mice induced mild proteinuria, pharmacological inhibition of the interaction between YAP and its partner TEAD in rats ameliorated glomerular disease and reduced damage-induced mechanosignaling in the glomeruli. Thus, perturbation of YAP-dependent mechanosignaling is a potential therapeutic target for treating some glomerular diseases.

TAZ contributes to pulmonary fibrosis by activating profibrotic functions of lung fibroblasts

Transcriptional coactivator with PDZ-binding motif (TAZ) regulates a variety of biological processes. Nuclear translocation and activation of TAZ are regulated by multiple mechanisms, including actin cytoskeleton and mechanical forces. TAZ is involved in lung alveolarization during lung development and Taz-heterozygous mice are resistant to bleomycin-induced lung fibrosis. In this study, we explored the roles of TAZ in the pathogenesis of idiopathic pulmonary fibrosis (IPF) through histological analyses of human lung tissues and cell culture experiments. TAZ was highly expressed in the fibroblastic foci of lungs from patients with IPF. TAZ controlled myofibroblast marker expression, proliferation, migration, and matrix contraction in cultured lung fibroblasts. Importantly, actin stress fibers and nuclear accumulation of TAZ were more evident when cultured on a stiff matrix, suggesting a feedback mechanism to accelerate fibrotic responses. Gene expression profiling revealed TAZ-mediated regulation of connective tissue growth factor (CTGF) and type I collagen. Clinical relevance of TAZ-regulated gene signature was further assessed using publicly available transcriptome data. These findings suggest that TAZ is involved in the pathogenesis of IPF through multifaceted effects on lung fibroblasts.

Chronic sciatic nerve compression induces fibrosis in dorsal root ganglia

In the present study, pathological alterations in neurons of the dorsal root ganglia (DRG) were investigated in a rat model of chronic sciatic nerve compression. The rat model of chronic sciatic nerve compression was established by placing a 1 cm Silastic tube around the right sciatic nerve. Histological examination was performed via Masson's trichrome staining. DRG injury was assessed using Fluoro Ruby (FR) or Fluoro Gold (FG). The expression levels of target genes were examined using reverse transcription-quantitative polymerase chain reaction, western blot and immunohistochemical analyses. At 3 weeks post-compression, collagen fiber accumulation was observed in the ipsilateral area and, at 8 weeks, excessive collagen formation with muscle atrophy was observed. The collagen volume fraction gradually and significantly increased following sciatic nerve compression. In the model rats, the numbers of FR-labeled DRG neurons were significantly higher, relative to the sham-operated group, however, the numbers of FG-labeled neurons were similar. In the ipsilateral DRG neurons of the model group, the levels of transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF) were elevated and, surrounding the neurons, the levels of collagen type I were increased, compared with those in the contralateral DRG. In the ipsilateral DRG, chronic nerve compression was associated with significantly higher levels of phosphorylated (p)-extracellular signal-regulated kinase 1/2, and significantly lower levels of p-c-Jun N-terminal kinase and p-p38, compared with those in the contralateral DRGs. Chronic sciatic nerve compression likely induced DRG pathology by upregulating the expression levels of TGF-β1, CTGF and collagen type I, with involvement of the mitogen-activated protein kinase signaling pathway.

High expression of connective tissue growth factor accelerates dissemination of leukaemia

To improve treatment of acute lymphoblastic leukaemia (ALL), a better understanding of disease development is needed to tailor new therapies. Connective tissue growth factor (CTGF/CCN2) is highly expressed in leukaemia cells from the majority of paediatric patients with B-lineage ALL (pre-B ALL). CTGF is a matricellular protein and plays a role in aggressive cancers. Here we have genetically engineered leukaemia cells to modulate CTGF expression levels. Elevated CTGF levels accelerated disease dissemination and reduced survival in NOD/SCID mice. In vitro studies showed that CTGF protein induces stromal cell proliferation, promotes adhesion of leukaemia cells to stromal cells and leads to overexpression of genes associated with cell cycle and synthesis of extracellular matrix (ECM). Corresponding data from our leukaemia xenograft models demonstrated that CTGF leads to increased proliferation of non-leukaemia cells and deposition of ECM in the bone marrow. We document for the first time a functional role of CTGF in altering disease progression in a lymphoid malignancy. The findings provide support for targeting the bone marrow microenvironment in aggressive forms of leukaemia.

Role of YAP and TAZ in pancreatic ductal adenocarcinoma and in stellate cells associated with cancer and chronic pancreatitis

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a fibrotic and inflammatory microenvironment that is formed primarily by activated, myofibroblast-like, stellate cells. Although the stellate cells are thought to contribute to tumorigenesis, metastasis and drug resistance of PDAC, the signaling events involved in activation of the stellate cells are not well defined. Functioning as transcription co-factors, Yes-associated protein (YAP) and its homolog transcriptional co-activator with PDZ-binding motif (TAZ) modulate the expression of genes involved in various aspects of cellular functions, such as proliferation and mobility. Using human tissues we show that YAP and TAZ expression is restricted to the centroacinar and ductal cells of normal pancreas, but is elevated in cancer cells. In particular, YAP and TAZ are expressed at high levels in the activated stellate cells of both chronic pancreatitis and PDAC patients as well as in the islets of Langerhans in chronic pancreatitis tissues. Of note, YAP is up regulated in both acinar and ductal cells following induction of acute and chronic pancreatitis in mice. These findings indicate that YAP and TAZ may play a critical role in modulating pancreatic tissue regeneration, neoplastic transformation, and stellate cell functions in both PDAC and pancreatitis.

YAP1 Is a Driver of Myofibroblast Differentiation in Normal and Diseased Fibroblasts

Dupuytren disease is a fibrotic disorder characterized by contraction of myofibroblast-rich cords and nodules in the hands. The Hippo member Yes-associated protein 1 (YAP1) is activated by tissue stiffness and the profibrotic transforming growth factor-β1, but its role in cell fibrogenesis is yet unclear. We hypothesized that YAP1 regulates the differentiation of dermal fibroblasts into highly contractile myofibroblasts and that YAP1 governs the maintenance of a myofibroblast phenotype in primary Dupuytren cells. Knockdown of YAP1 in transforming growth factor-β1-stimulated dermal fibroblasts decreased the formation of contractile smooth muscle α-actin stress fibers and the deposition of collagen type I, which are hallmark features of myofibroblasts. Translating our findings to a clinically relevant model, we found that YAP1 deficiency in Dupuytren disease myofibroblasts resulted in decreased expression of ACTA2, COL1A1, and CCN2 mRNA, but this did not result in decreased protein levels. YAP1-deficient Dupuytren myofibroblasts showed decreased contraction of a collagen hydrogel. Finally, we showed that YAP1 levels and nuclear localization were elevated in affected Dupuytren disease tissue compared with matched control tissue and partly co-localized with smooth muscle α-actin-positive cells. In conclusion, our data show that YAP1 is a regulator of myofibroblast differentiation and contributes to the maintenance of a synthetic and contractile phenotype, in both transforming growth factor-β1-induced myofibroblast differentiation and primary Dupuytren myofibroblasts.

Signaling in Fibrosis: TGF-β, WNT, and YAP/TAZ Converge

Chronic organ injury leads to fibrosis and eventually organ failure. Fibrosis is characterized by excessive synthesis, remodeling, and contraction of extracellular matrix produced by myofibroblasts. Myofibroblasts are the key cells in the pathophysiology of fibrotic disorders and their differentiation can be triggered by multiple stimuli. To develop anti-fibrotic therapies, it is of paramount importance to understand the molecular basis of the signaling pathways contributing to the activation and maintenance of myofibroblasts. Several signal transduction pathways, such as transforming growth factor (TGF)-β, Wingless/Int (WNT), and more recently yes-associated protein 1 (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) signaling, have been linked to the pathophysiology of fibrosis. Activation of the TGF-β1-induced SMAD complex results in the upregulation of genes important for myofibroblast function. Similarly, WNT-stabilized β-catenin translocates to the nucleus and initiates transcription of its target genes. YAP and TAZ are two transcriptional co-activators from the Hippo signaling pathway that also rely on nuclear translocation for their functioning. These three signal transduction pathways have little molecular similarity but do share one principle: the cytosolic/nuclear regulation of its transcriptional activators. Past research on these pathways often focused on the isolated cascades without taking other signaling pathways into account. Recent developments show that parts of these pathways converge into an intricate network that governs the activation and maintenance of the myofibroblast phenotype. In this review, we discuss the current understanding on the signal integration between the TGF-β, WNT, and YAP/TAZ pathways in the development of organ fibrosis. Taking a network-wide view on signal transduction will provide a better understanding on the complex and versatile processes that underlie the pathophysiology of fibrotic disorders.

Signaling in Fibrosis: TGF-β, WNT, and YAP/TAZ Converge

Chronic organ injury leads to fibrosis and eventually organ failure. Fibrosis is characterized by excessive synthesis, remodeling, and contraction of extracellular matrix produced by myofibroblasts. Myofibroblasts are the key cells in the pathophysiology of fibrotic disorders and their differentiation can be triggered by multiple stimuli. To develop anti-fibrotic therapies, it is of paramount importance to understand the molecular basis of the signaling pathways contributing to the activation and maintenance of myofibroblasts. Several signal transduction pathways, such as transforming growth factor (TGF)-β, Wingless/Int (WNT), and more recently yes-associated protein 1 (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) signaling, have been linked to the pathophysiology of fibrosis. Activation of the TGF-β1-induced SMAD complex results in the upregulation of genes important for myofibroblast function. Similarly, WNT-stabilized β-catenin translocates to the nucleus and initiates transcription of its target genes. YAP and TAZ are two transcriptional co-activators from the Hippo signaling pathway that also rely on nuclear translocation for their functioning. These three signal transduction pathways have little molecular similarity but do share one principle: the cytosolic/nuclear regulation of its transcriptional activators. Past research on these pathways often focused on the isolated cascades without taking other signaling pathways into account. Recent developments show that parts of these pathways converge into an intricate network that governs the activation and maintenance of the myofibroblast phenotype. In this review, we discuss the current understanding on the signal integration between the TGF-β, WNT, and YAP/TAZ pathways in the development of organ fibrosis. Taking a network-wide view on signal transduction will provide a better understanding on the complex and versatile processes that underlie the pathophysiology of fibrotic disorders.

Critical review about MDM2 in cancer: Possible role in malignant mesothelioma and implications for treatment

The tumor suppressor p53 regulates genes involved in DNA repair, metabolism, cell cycle arrest, apoptosis and senescence. p53 is mutated in about 50% of the human cancers, while in tumors with wild-type p53 gene, the protein function may be lost because of overexpression of Murine Double Minute 2 (MDM2). MDM2 targets p53 for ubiquitylation and proteasomal degradation. p53 reactivation through MDM2 inhibitors seems to be a promising strategy to sensitize p53 wild-type cancer cells to apoptosis. Moreover, additional p53-independent molecular functions of MDM2, such as neoangiogenesis promotion, have been suggested. Thus, MDM2 might be a target for anticancer treatment because of its antiapoptotic and proangiogenetic role. Malignant pleural mesothelioma (MPM) is an aggressive asbestos-related tumor where wild-type p53 might be present. The present review gives a complete landscape about the role of MDM2 in cancer pathogenesis, prognosis and treatment, with particular focus on Malignant Pleural Mesothelioma.

CTRP3 attenuates post-infarct cardiac fibrosis by targeting Smad3 activation and inhibiting myofibroblast differentiation

C1q/tumor necrosis factor-related protein-3 (CTRP3) is a novel adipokine with modulation effects on metabolism, inflammation, and cardiovascular system. This study aimed to investigate the effect of CTRP3 on cardiac fibrosis and its underlying mechanism. The myocardial expression of CTRP3 was significantly decreased after myocardial infarction (MI). Adenovirus-delivered CTRP3 supplement attenuated myocardial hypertrophy, improved cardiac function, inhibited interstitial fibrosis, and decreased the number of myofibroblasts post-MI. In cultured adult rat cardiac fibroblasts (CFs), CTRP3 attenuated cell proliferation; migration; and the expression of connective tissue growth factor, collagen I, and collagen III induced by transforming growth factor (TGF)-β1. Moreover, CTRP3 inhibited whereas CTRP3 small interfering RNA (siRNA) facilitated the expression of α-SMA and profibrotic molecules induced by TGF-β1. CTRP3 also attenuated TGF-β1-induced Smad3 phosphorylation, nuclear translocation, and interaction with p300. CTRP3 increased the phosphorylation of AMP-activated protein kinase (AMPK) and Akt in both rat hearts and CFs. Adenine 9-β-D-arabinofuranoside (AraA), an AMPK inhibitor, abolished the protective effect of CTRP3 against TGF-β1-induced profibrotic response and Smad3 activation. Taken together, CTRP3 attenuates cardiac fibrosis by inhibiting myofibroblast differentiation and the subsequent extracellular matrix production. AMPK is required for the anti-fibrotic effect of CTRP3 through targeting Smad3 activation and inhibiting myofibroblast differentiation.

KEY MESSAGE

CTRP3 alleviates cardiac fibrosis in a rat post-MI model and in cardiac fibroblasts. CTRP3 inhibits fibroblast-to-myofibroblast differentiation. CTRP3 exerts anti-fibrotic effect through targeting Smad3 activation. AMPK mediates the anti-fibrotic effect of CTRP3 by inhibition of Smad3 activation.

The mammalian Hippo pathway: regulation and function of YAP1 and TAZ

The Hippo pathway was originally identified as the signaling that controls organ size in Drosophila, with the core architecture conserved in mammals. In the mammalian Hippo pathway, mammalian Ste20-like kinases (MST1/2) and large tumor suppressor kinases (LATS1/2) regulate transcriptional co-activators, Yes-associated protein (YAP1) and Transcriptional co-activator with a PDZ-binding motif (TAZ). The Hippo pathway was initially thought to be quite straightforward; however, the identification of additional components has revealed its inherent complexity. Regulation of YAP1 and TAZ is not always dependent on MST1/2 and LATS1/2. MST1/2 and LATS1/2 play various YAP1/TAZ-independent roles, while YAP1 and TAZ cross-talk with other signaling pathways. In this review we focus on YAP1 and TAZ and discuss their regulation, function, and the consequences of their dysregulation.

c-Abl antagonizes the YAP oncogenic function

YES-associated protein (YAP) is a central transcription coactivator that functions as an oncogene in a number of experimental systems. However, under DNA damage, YAP activates pro-apoptotic genes in conjunction with p73. This program switching is mediated by c-Abl (Abelson murine leukemia viral oncogene) via phosphorylation of YAP at the Y357 residue (pY357). YAP as an oncogene coactivates the TEAD (transcriptional enhancer activator domain) family transcription factors. Here we asked whether c-Abl regulates the YAP-TEAD functional module. We found that DNA damage, through c-Abl activation, specifically depressed YAP-TEAD-induced transcription. Remarkably, c-Abl counteracts YAP-induced transformation by interfering with the YAP-TEAD transcriptional program. c-Abl induced TEAD1 phosphorylation, but the YAP-TEAD complex remained unaffected. In contrast, TEAD coactivation was compromised by phosphomimetic YAP Y357E mutation but not Y357F, as demonstrated at the level of reporter genes and endogenous TEAD target genes. Furthermore, YAP Y357E also severely compromised the role of YAP in cell transformation, migration, anchorage-independent growth, and epithelial-to-mesenchymal transition (EMT) in human mammary MCF10A cells. These results suggest that YAP pY357 lost TEAD transcription activation function. Our results demonstrate that YAP pY357 inactivates YAP oncogenic function and establish a role for YAP Y357 phosphorylation in cell-fate decision.

Deregulated expression of connective tissue growth factor (CTGF/CCN2) is linked to poor outcome in human cancer

Connective tissue growth factor (CTGF/CCN2) has long been associated with human cancers. The role it plays in these neoplasms is diverse and tumour specific. Recurring patterns in clinical outcome, histological desmoplasia and mechanisms of action have been found. When CTGF is overexpressed compared to low-expressing normal tissue or is underexpressed compared to high-expressing normal tissue, the functional outcome favours tumour survival and disease progression. CTGF acts by altering proliferation, drug resistance, angiogenesis, adhesion and migration contributing to metastasis. The pattern of CTGF expression and tumour response helps to clarify the role of this matricellular protein across a multitude of human cancers.