Project description:Tissue homeostasis requires lineage fidelity of stem cells. Dysregulation of cell fate specification and differentiation leads to various diseases, yet the cellular and molecular processes remain elusive. We demonstrate that YAP/TAZ activation reprograms airway secretory cells to lose cellular identity and acquire squamous alveolar type 1 (AT1) fate in the lungs. Significantly, this cell fate conversion is mediated via distinctive transitional cell states of Damage-Associated Transient Progenitors (DATPs), recently known to emerge during injury repair, in mouse and human lungs. Further, YAP/TAZ signaling is identified to realign the amino acid metabolism by modulating mTORC1-ATF4 activity, which is integral to fate conversion of secretory cells into AT1 fate. We observed aberrant activation of the YAP/TAZ-mTORC1-ATF4 axis in the altered airway epithelium of human pulmonary fibrosis where the emergence of DATPs and A1 cells is prominent. Finally, genetic and pharmacologic inhibition of mTORC1 activity restores lineage alteration and subepithelial fibrosis driven by YAP/TAZ activation, proposing a potential therapeutic target for human fibrotic lung diseases.
Project description:Pancreas volume or mass varies more than 3-fold among adult humans. The heterogeneity is likely the result of genetics, diseases, and nutrition. Dietary protein intake and blood amino acid levels are known to affect pancreas mass, but the underlying mechanism is not well understood. The goal of this study is to determine how increased blood amino acid level (hyperaminoacidemia) induces pancreas expansion.Multiple complementary mouse and zebrafish models were used to study the impact of hyperaminoacidemia on pancreatic mass, acinar cell size and proliferation. Blood amino acid levels were manipulated by dietary protein content, or by pharmacologic or genetic interruption of glucagon signaling (IGS). The activation of mammalian target of rapamycin complex 1 (mTORC1) and Yes-associated protein 1 (YAP) were determined by pS6 and YAP staining. Sirolimus administration in mice and knockdown of solute carrier family 38 member 5b (slc38a5b) and yap/taz in zebrafish were used to determine the role of mTORC1, SLC38A5 and YAP/TAZ in acinar cell proliferation and pancreas expansion. We found that the IGS-induced pancreas expansion was the result of acinar cell proliferation and hypertrophy. Hyperaminoacidemia was the likely mediator as pancreas expansion was blunted by a low protein diet in mice and by knocking down the most highly expressed amino acid transporter gene, slc38a5b, in zebrafish lacking both glucagon receptor genes (gcgr-/-). In GCGR-Ab treated mice, inhibition of mTORC1 attenuated both hyperplasia and hypertrophy of acinar cells. There was a gene expression signature of YAP activation in acinar cells, consistent with increased YAP-expressing acinar cells in GCGR-Ab treated mice and increased fraction of acinar cells with nuclear YAP1 in gcgr-/- zebrafish. Knocking down yap1 or taz decreased mTORC1 activity and acinar cell hyperplasia and hypertrophy in gcgr-/- zebrafish. Hyperaminoacidemia leads to acinar cell proliferation and hypertrophy via activation of both mTORC1 and YAP pathways. The study discovered a previously unrecognized role of the YAP/Taz pathway in hyperaminoacidemia-induced acinar cell hypertrophy and hyperplasia.
Project description:Angiogenesis, the process by which endothelial cells (ECs) form new blood vessels from existing ones, is intimately linked to the tissue's metabolic milieu and often occurs at nutrient-deficient sites. However, ECs rely on sufficient metabolic resources to support growth and proliferation. How endothelial nutrient acquisition and usage are regulated is unknown. Here we show that these processes are dictated by YAP/TAZ-TEAD – a transcriptional module whose function is highly responsive to changes in the tissue environment. ECs lacking YAP/TAZ or their transcriptional partners, TEAD1, 2, and 4 fail to divide, resulting in stunted vascular growth in mice. Conversely, activation of TAZ, the more abundant paralogue in ECs, boosts proliferation, leading to vascular hyperplasia. We find that YAP/TAZ promote angiogenesis by fueling nutrient mTORC1 signaling. By orchestrating the transcription of a repertoire of cell-surface transporters, YAP/TAZ-TEAD stimulate the import of amino acids and other essential nutrients, thereby enabling mTORC1 pathway activation. Dissociating mTORC1 from these nutrient inputs – elicited by the loss of Rag GTPases – inhibits mTORC1 activity and prevents YAP/TAZ-dependent vascular growth. These findings define a pivotal role for YAP/TAZ-TEAD in steering endothelial mTORC1 and illustrate the essentiality of coordinated nutrient fluxes in the vasculature.
Project description:Sarcomas encompass heterogenous, difficult to treat cancers, lacking common therapeutic targets. Phosphatidylinositol-3 kinase (PI3K) signaling is activated in sarcomas to a greater degree than previously appreciated due to phosphatase and tensin homolog (PTEN) loss, and could represent such a target. Targeting PI3K signaling has largely focused on targeting mTORC1, considered the main effector of PI3K signaling, but this has not translated to success in the clinic, suggesting that there may be other effectors downstream of PI3K. One gap in our understanding of the PI3K signaling pathway has been the absence of a known oncogenic transcription factor. Herein we implicate TAZ and YAP as additional transcriptional effectors downstream of PI3K signaling regulated by a LATS1/2 dependent mechanism. Using in vitro and in vivo approaches, we show that TAZ and YAP are central oncoproteins in PI3K driven oncogenesis along with mTORC1, providing a rationale for combination therapy. Leveraging these findings, we describe a therapeutic approach that builds upon pre-existing therapeutic strategies utilizing mTORC1 inhibitors and combines them with new TEAD inhibitors that target YAP and TAZ. Combination therapy using everolimus and IK-930, an inhibitor targeting autopalmitoylation of the TEADs, synergistically diminished proliferation and anchorage dependent growth of PI3K activated sarcoma cell lines at low, physiologically achievable doses. In vivo, this combination therapy showed a synergistic effect, contrasting with the lack of effect of the individual single agent therapies, suggesting that an integrated view of PI3K and Hippo signaling can be leveraged therapeutically in PI3K activated sarcomas.
Project description:The mammalian target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth that is commonly deregulated in human diseases. Here we find that mTORC1 controls a transcriptional program encoding amino acid transporters and metabolic enzymes through a mechanism also used to regulate protein synthesis. Bioinformatic analysis of mTORC1-responsive mRNAs identified a promoter element recognized by activating transcription factor 4 (ATF4), a key effector of the integrated stress response. ATF4 translation is normally induced by phosphorylation of eukaryotic initiation factor 2 alpha (eIF2α) through a mechanism that requires upstream open reading frames (uORFs) in the ATF4 5' UTR. mTORC1 also controls ATF4 translation through uORFs, but independent of changes in eIF2α phosphorylation. mTORC1 instead employs the 4E-binding protein (4E-BP) family of translation repressors. These results link mTORC1-regulated demand for protein synthesis with an ATF4-regulated transcriptional program that controls the supply of amino acids to the translation machinery.
Project description:The mechanistic target of rapamycin complex 1 (mTORC1) integrates inputs from growth factors and nutrients, but how mTORC1 autoregulates its activity remains unclear. The MiT/TFE transcription factors are phosphorylated and inactivated by mTORC1 following lysosomal recruitment by RagC/D GTPases in response to amino acid stimulation. We find that starvation-induced lysosomal localization of the RagC/D GAP complex, FLCN:FNIP2, is markedly impaired in a mTORC1-sensitive manner in cells with TSC2 loss, resulting in unexpected TFEB hypophosphorylation and activation upon feeding. TFEB phosphorylation in TSC2-null cells is partially restored by destabilization of the lysosomal folliculin complex (LFC) induced by FLCN mutants and is fully rescued by forced lysosomal localization of the FLCN:FNIP2 dimer. Our data indicate that a negative feedback loop constrains amino acid-induced, FLCN:FNIP2-mediated RagC activity in cells with constitutive mTORC1 signaling, and the resulting MiT/TFE hyperactivation may drive oncogenesis with loss of the TSC2 tumor suppressor.
Project description:The Hippo pathway downstream effectors YAP and TAZ display oncogenic potential via their transcriptional co-activator function, mediated primarily by binding to TEAD transcription factors. Many studies have focused on identifying YAP/TAZ-TEAD target genes, but their role in the regulation of protein synthesis has remained largely unexplored. Here we show that YAP activation is sufficient to overcome the global translation restriction of 5TOP-containing mRNAs, which is induced by serum deprivation and dependent on the inactivation of mTORC1. We found that YAP/TAZ repressed the expression of DDIT4, a negative regulator of mTORC1 whose expression is otherwise upregulated by serum deprivation. Forced expression of DDIT4 was sufficient to suppress translation and transformative potential of serum-unresponsive uveal melanoma cells, which harbor G protein mutations. Our findings highlight crosstalk between Hippo-YAP/TAZ and mTORC1 pathways in the regulation of translation and offer a new perspective towards understanding YAP/TAZ-driven malignancies.
Project description:The Hippo pathway downstream effectors YAP and TAZ display oncogenic potential via their transcriptional co-activator function, mediated primarily by binding to TEAD transcription factors. Many studies have focused on identifying YAP/TAZ-TEAD target genes, but their role in the regulation of protein synthesis has remained largely unexplored. Here we show that YAP activation is sufficient to overcome the global translation restriction of 5TOP-containing mRNAs, which is induced by serum deprivation and dependent on the inactivation of mTORC1. We found that YAP/TAZ repressed the expression of DDIT4, a negative regulator of mTORC1 whose expression is otherwise upregulated by serum deprivation. Forced expression of DDIT4 was sufficient to suppress translation and transformative potential of serum-unresponsive uveal melanoma cells, which harbor G protein mutations. Our findings highlight crosstalk between Hippo-YAP/TAZ and mTORC1 pathways in the regulation of translation and offer a new perspective towards understanding YAP/TAZ-driven malignancies.