Project description:The functions of the paralogous transcriptional coactivators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) in bone are controversial. Each has been observed to promote or inhibit osteogenesis in vitro, with reports of both equivalent and divergent functions. Their combinatorial roles in bone physiology are unknown. We report that combinatorial YAP/TAZ deletion from skeletal lineage cells, using Osterix-Cre, caused an osteogenesis imperfecta-like phenotype with severity dependent on allele dose and greater phenotypic expressivity with homozygous TAZ vs. YAP ablation. YAP/TAZ deletion decreased bone accrual and reduced intrinsic bone material properties through impaired collagen content and organization. These structural and material defects produced spontaneous fractures, particularly in mice with homozygous TAZ deletion and caused neonatal lethality in dual homozygous knockouts. At the cellular level in vivo, YAP/TAZ ablation reduced osteoblast activity and increased osteoclast activity, in an allele dose-dependent manner, impairing bone accrual and remodeling. Transcriptionally, YAP/TAZ deletion and small-molecule inhibition of YAP/TAZ interaction with the transcriptional coeffector TEAD reduced osteogenic and collagen-related gene expression, both in vivo and in vitro. These data demonstrate that YAP and TAZ combinatorially promote bone development through regulation of osteoblast activity, matrix quality, and osteoclastic remodeling.-Kegelman, C. D., Mason, D. E., Dawahare, J. H., Horan, D. J., Vigil, G. D., Howard, S. S., Robling, A. G., Bellido, T. M., Boerckel, J. D. Skeletal cell YAP and TAZ combinatorially promote bone development.
Project description:Alveolar epithelium plays a pivotal role in protecting the lungs from inhaled infectious agents. Therefore, the regenerative capacity of the alveolar epithelium is critical for recovery from these insults in order to rebuild the epithelial barrier and restore pulmonary functions. Here, we show that sublethal infection of mice with Streptococcus pneumoniae, the most common pathogen of community-acquired pneumonia, led to exclusive damage in lung alveoli, followed by alveolar epithelial regeneration and resolution of lung inflammation. We show that surfactant protein C-expressing (SPC-expressing) alveolar epithelial type II cells (AECIIs) underwent proliferation and differentiation after infection, which contributed to the newly formed alveolar epithelium. This increase in AECII activities was correlated with increased nuclear expression of Yap and Taz, the mediators of the Hippo pathway. Mice that lacked Yap/Taz in AECIIs exhibited prolonged inflammatory responses in the lung and were delayed in alveolar epithelial regeneration during bacterial pneumonia. This impaired alveolar epithelial regeneration was paralleled by a failure to upregulate IκBa, the molecule that terminates NF-κB-mediated inflammatory responses. These results demonstrate that signals governing resolution of lung inflammation were altered in Yap/Taz mutant mice, which prevented the development of a proper regenerative niche, delaying repair and regeneration of alveolar epithelium during bacterial pneumonia.
Project description:Proper lung function relies on the precise balance of specialized epithelial cells that coordinate to maintain homeostasis. Herein, we describe essential roles for the transcriptional regulators YAP/TAZ in maintaining lung epithelial homeostasis, reporting that conditional deletion of Yap and Wwtr1/Taz in the lung epithelium of adult mice results in severe defects, including alveolar disorganization and the development of airway mucin hypersecretion. Through in vivo lineage tracing and in vitro molecular experiments, we reveal that reduced YAP/TAZ activity promotes intrinsic goblet transdifferentiation of secretory airway epithelial cells. Global gene expression and chromatin immunoprecipitation sequencing (ChIP-seq) analyses suggest that YAP/TAZ act cooperatively with TEA domain (TEAD) transcription factors and the NuRD complex to suppress the goblet cell fate program, directly repressing the SPDEF gene. Collectively, our study identifies YAP/TAZ as critical factors in lung epithelial homeostasis and offers molecular insight into the mechanisms promoting goblet cell differentiation, which is a hallmark of many lung diseases.
Project description:Lung cancer is the leading cause of cancer death in the world and there is no current treatment able to efficiently treat the disease as the tumor is often diagnosed at an advanced stage. Moreover, cancer cells are often resistant or acquire resistance to the treatment. Further knowledge of the mechanisms driving lung tumorigenesis, aggressiveness, metastasization, and resistance to treatments could provide new tools for detecting the disease at an earlier stage and for a better response to therapy. In this scenario, Yes Associated Protein (YAP) and Trascriptional Coactivator with PDZ-binding motif (TAZ), the final effectors of the Hippo signaling transduction pathway, are emerging as promising therapeutic targets. Here, we will discuss the most recent advances made in YAP and TAZ biology in lung cancer and, more importantly, on the newly discovered mechanisms of YAP and TAZ inhibition in lung cancer as well as their clinical implications.
Project description:Hepatoblastoma (HB) is the most common type of liver malignancy in children. Recent studies suggest that activation of Yes-associated protein (YAP) is a major molecular event in HB development, as activated YAP synergizes with mutant β-catenin to promote HB formation in mice (YAP/β-catenin). However, how YAP regulates HB development remains poorly defined. Similarly, de-regulation of mammalian target of rapamycin complex 1 (mTORC1) signaling has been implicated in multiple tumor types, but its functional role in HB development is scarcely understood. In the present study, we found that mTORC1 is activated in human HB cells and YAP/β-catenin-induced mouse HB tumor tissues. mTOR inhibitor MLN0128 significantly inhibits human HB cell growth in vitro. Furthermore, ablation of Raptor, the unique subunit of mTORC1, strongly delayed YAP/β-catenin-induced HB development in mice. At the molecular level, we found that expression of the amino acid transporter SLC38A1 is induced in mouse HB tissues, and amino acid deprivation leads to mTORC1 suppression in HB cell lines. Silencing of YAP and/or its paralog, transcriptional co-activator with PDZ binding motif (TAZ), decreased SLC38A1 expression as well as mTORC1 activation in HB cells. Furthermore, a frequent and concomitant upregulation of mTORC1 and SLC38A1 was detected in a collection of human HB specimens. Altogether, our study demonstrates the key role of mTORC1 in HB development. YAP and TAZ promote HB development via inducing SLC38A1 expression, whose upregulation leads to mTORC1 activation. Targeting mTOR pathway or amino acid transporters may represent novel therapeutic strategies for the treatment of human HB.
Project description:A hallmark of idiopathic pulmonary fibrosis (IPF) and other interstitial lung diseases is dysregulated repair of the alveolar epithelium. The Hippo pathway effector transcription factors YAP and TAZ are implicated as essential for type 1 and type 2 alveolar epithelial cell (AT1 and AT2) differentiation in the developing lung, yet aberrant activation of YAP/TAZ is a prominent feature of the dysregulated alveolar epithelium in IPF. In these studies, we sought to define the functional role of YAP/TAZ activity during alveolar regeneration. We demonstrated that Yap and Taz were normally activated in AT2 cells shortly after injury, and deletion of Yap/Taz in AT2 cells led to pathologic alveolar remodeling, failure of AT2-to-AT1 cell differentiation, increased collagen deposition, exaggerated neutrophilic inflammation, and increased mortality following injury induced by a single dose of bleomycin. Loss of Yap/Taz activity prior to an LPS injury prevented AT1 cell regeneration, led to intraalveolar collagen deposition, and resulted in persistent innate inflammation. These findings establish that AT2 cell Yap/Taz activity is essential for functional alveolar epithelial repair and prevention of fibrotic remodeling.
Project description:The lymphatic system consists of a vessel network lined by specialized lymphatic endothelial cells (LECs) that are responsible for tissue fluid homeostasis and immune cell trafficking. The mechanisms for organ-specific LEC responses to environmental cues are not well understood. We found robust lymphangiogenesis during influenza A virus infection in the adult mouse lung. We show that the number of LECs increases twofold at 7 days post-influenza infection (dpi) and threefold at 21 dpi, and that lymphangiogenesis is preceded by lymphatic dilation. We also show that the expanded lymphatic network enhances fluid drainage to mediastinal lymph nodes. Using EdU labeling, we found that a significantly higher number of pulmonary LECs are proliferating at 7 dpi compared to LECs in homeostatic conditions. Lineage tracing during influenza indicates that new pulmonary LECs are derived from preexisting LECs rather than non-LEC progenitors. Lastly, using a conditional LEC-specific YAP/TAZ knockout model, we established that lymphangiogenesis, fluid transport and the immune response to influenza are independent of YAP/TAZ activity in LECs. These findings were unexpected, as they indicate that YAP/TAZ signaling is not crucial for these processes.
Project description:Epithelioid hemangioendothelioma (EHE) is a vascular sarcoma that metastasizes early in its clinical course and lacks an effective medical therapy. The TAZ-CAMTA1 and YAP-TFE3 fusion proteins are chimeric transcription factors and initiating oncogenic drivers of EHE. A combined proteomic/genetic screen in human cell lines identified YEATS2 and ZZZ3, components of the Ada2a-containing histone acetyltransferase (ATAC) complex, as key interactors of both fusion proteins despite the dissimilarity of the C terminal fusion partners CAMTA1 and TFE3. Integrative next-generation sequencing approaches in human and murine cell lines showed that the fusion proteins drive a unique transcriptome by simultaneously hyperactivating a TEAD-based transcriptional program and modulating the chromatin environment via interaction with the ATAC complex. Interaction of the ATAC complex with both fusion proteins indicates that it is a key oncogenic driver and unifying enzymatic therapeutic target for this sarcoma. This study presents an approach to mechanistically dissect how chimeric transcription factors drive the formation of human cancers.
Project description:The transcriptional co-activators YAP and TAZ are key regulators of organ size and tissue homeostasis, and their dysregulation contributes to human cancer. Here, we discover YAP/TAZ as bona fide downstream effectors of the alternative Wnt signaling pathway. Wnt5a/b and Wnt3a induce YAP/TAZ activation independent of canonical Wnt/β-catenin signaling. Mechanistically, we delineate the "alternative Wnt-YAP/TAZ signaling axis" that consists of Wnt-FZD/ROR-Gα12/13-Rho GTPases-Lats1/2 to promote YAP/TAZ activation and TEAD-mediated transcription. YAP/TAZ mediate the biological functions of alternative Wnt signaling, including gene expression, osteogenic differentiation, cell migration, and antagonism of Wnt/β-catenin signaling. Together, our work establishes YAP/TAZ as critical mediators of alternative Wnt signaling.