YAP Nuclear Localization Research Articles

The PDZ-binding motif of Yes-associated protein is required for its co-activation of TEAD-mediated CTGF transcription and oncogenic cell transforming activity

YAP is a transcriptional co-activator that acts downstream of the Hippo signaling pathway and regulates multiple cellular processes, including proliferation. Hippo pathway-dependent phosphorylation of YAP negatively regulates its function. Conversely, attenuation of Hippo-mediated phosphorylation of YAP increases its ability to stimulate proliferation and eventually induces oncogenic transformation. The C-terminus of YAP contains a highly conserved PDZ-binding motif that regulates YAP’s functions in multiple ways. However, to date, the importance of the PDZ-binding motif to the oncogenic cell transforming activity of YAP has not been determined. In this study, we disrupted the PDZ-binding motif in the YAP (5SA) protein, in which the sites normally targeted by Hippo pathway-dependent phosphorylation are mutated. We found that loss of the PDZ-binding motif significantly inhibited the oncogenic transformation of cultured cells induced by YAP (5SA). In addition, the increased nuclear localization of YAP (5SA) and its enhanced activation of TEAD-dependent transcription of the cell proliferation gene CTGF were strongly reduced when the PDZ-binding motif was deleted. Similarly, in mouse liver, deletion of the PDZ-binding motif suppressed nuclear localization of YAP (5SA) and YAP (5SA)-induced CTGF expression. Taken together, our results indicate that the PDZ-binding motif of YAP is critical for YAP-mediated oncogenesis, and that this effect is mediated by YAP’s co-activation of TEAD-mediated CTGF transcription.

Abstract 769: Integrin-Linked Kinase (ILK) breaks Merlin's spell to inhibit the Hippo tumor suppressor pathway and activate the YAP oncogene.

Abstract The Hippo signalling pathway is gaining recognition as an important player in tumor progression. Components of the pathway, which include transcriptional co-activators YAP/TAZ, are dysregulated in a significant fraction of human cancers, and YAP activation has recently been shown to promote Epithelial to Mesenchymal Transition (EMT) and metastasis. However, how Hippo signalling is dysregulated in tumors remains unclear. Here, we demonstrate that Integrin-Linked Kinase (ILK), an actin-interacting, focal adhesion adaptor and serine/threonine protein kinase whose expression is also significantly upregulated in many types of cancers, inhibits the Hippo tumor suppressor pathway by stimulating the phosphorylation, and inhibiting the activity of Merlin, via the protein phosphatase inhibitor, CPI-17, an established target of ILK, and an inhibitor of Merlin (Deng JT et al. Biochem J 2002; Huang J et al. Biochem J 2006). We have assessed the pathway in human breast and prostate cancer cell lines, in which the Hippo pathway is switched OFF, as determined by the phosphorylation status of Merlin, MST1/2, LATS1/2, and YAP, and the nuclear YAP localization. We demonstrate that inhibition of ILK expression, or inhibition of its activity in these cells turns the Hippo pathway ON, resulting in the stimulation of YAP phosphorylation, sequestration in the cytoplasm, and inhibition of TEAD transcriptional activity. In addition, we have determined that YAP/TAZ protein expression is significantly upregulated in vivo in ErbB2 induced mammary tumors from transgenic mice, and that deletion of ILK from these tumors, which significantly delays tumor growth and inhibits metastasis, dramatically suppresses the expression of these transcription co-activators. Finally, we demonstrate that ILK plays a critical role in the suppression of the Hippo pathway by TGF-b, EGF and LPA. Treatment of human breast and prostate epithelial cells with these growth factors results in dephosphorylation of LATS 1/2, and YAP, and nuclear localization of YAP. However, inhibiting ILK activity under these conditions results in the stimulation of phosphorylation of LATS1/2 and YAP, as well as in the sequestration of YAP/TAZ in the cytoplasm. These novel data demonstrate that ILK inhibits the Hippo tumor suppressor pathway leading to nuclear activation of YAP/TAZ, thereby contributing to tumor progression and metastasis. Citation Format: Isabel Serrano, William J. Muller, Shoukat Dedhar. Integrin-Linked Kinase (ILK) breaks Merlin's spell to inhibit the Hippo tumor suppressor pathway and activate the YAP oncogene. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 769. doi:10.1158/1538-7445.AM2013-769

The Hippo Size Control Pathway—Ever Expanding

An important regulator of organ size and tumorigenesis is the Hippo pathway. Recent studies have unveiled increasing complexity in regulation of Hippo pathway activity at the level of the oncoprotein Yes-associated protein (YAP). The protein tyrosine phosphatase 14 (PTPN14, known as Pez in Drosophila) was identified as a protein that antagonizes the function of the key Hippo pathway protein YAP by promoting its cytoplasmic localization under high cell density conditions. In Drosophila, Pez was identified as a repressor of epithelial proliferation in vivo. Studies in mammalian cells showed that a family of G protein-coupled receptors, the protease-activated receptors, functioned as activators of YAP. These studies shed light on the intricate regulation of the Hippo pathway and also highlight the importance of investigating these newly discovered regulatory links in physiological and pathological settings to fully appreciate their importance.

Identification of Serum-Derived Sphingosine-1-Phosphate as a Small Molecule Regulator of YAP

Hippo signaling represents a tumor suppressor pathway that regulates organ size and tumorigenesis through phosphorylation and inhibition of the transcription coactivator YAP. Here, we show that serum deprivation dramatically induces YAP Ser127 phosphorylation and cytoplasmic retention, independent of cell-cell contact. Through chemical isolation and activity profiling, we identified serum-derived sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA) as small molecule activators of YAP. S1P induces YAP nuclear localization through S1P(2) receptor, Rho GTPase activation, and F-actin polymerization, independent of the core Hippo pathway kinases. Bioinformatics studies also showed that S1P stimulation induces YAP target gene expression in mouse liver and human embryonic stem cells. These results revealed potent small molecule regulators of YAP and suggest that S1P and LPA might modulate cell proliferation and tumorigenesis through YAP activation.

Abstract P279: YAP, a Transcriptional Cofactor of the Hippo Pathway, Regulates Cardiomyocyte Growth, Survival, and Proliferation

Mst1 and Lats2, components of the mammalian Hippo pathway, stimulate apoptosis and inhibit hypertrophy of cardiomyocytes (CMs), thereby mediating reperfusion injury and heart failure. YAP, a transcription factor co-factor, is negatively regulated by the Hippo pathway, and controls cell survival, proliferation and tissue regeneration. The role of YAP in regulating growth and death of CMs is poorly understood. YAP overexpression in CMs induced cardiac hypertrophy, as indicated by increases in cell size (+1.2 fold, p<0.01), protein content (+1.1 fold, p<0.01) and ANF (luciferase reporter activity +1.7 fold, mRNA +2.2 fold, and staining +2.7 fold, p<0.01). Lats2 phosphorylates YAP at Serine 127, which induces cytoplasmic translocation of YAP, whereas YAP(S127A) is localized constitutively in the nucleus. Expression of YAP(S127A) enhanced hypertrophy in cultured CMs compared to that of wild type YAP (+1.87 fold ANF staining, p<0.05), suggesting that the Mst1/Hippo pathway negatively regulates cardiac hypertrophy through YAP. YAP inhibited cell death induced by H2O2 treatment, as evaluated with TUNEL staining (-65%, p<0.05) and CellTiter Blue assays (+34.9%, p<0.01), indicating that YAP plays an essential role in mediating CM survival. Interestingly, YAP also significantly increased Ki67 positive cells in cultured CMs compared to LacZ (+2.65 fold, p<0.05). We used a mouse model of chronic myocardial infarction (MI) to evaluate the function of YAP in the heart in vivo. Although YAP is diffusely localized both in the nucleus and cytosol in CMs in control hearts, CMs in the border zone of MI exhibited nuclear localization of YAP whereas YAP was excluded from the nucleus in CMs in the remodeling area four days after MI (+6.52 fold and +1.28 fold). Some of the YAP positive CMs in the border zone exhibited positive co-staining with Ki67, suggesting that YAP potentially induces CM proliferation. A significant increase in nuclear YAP and Ki67 positive CMs (+2.95 fold, p<0.01 and +2.18 fold, p<0.05) was also observed in neonatal rat hearts whose apex was surgically resected three days before euthanasia. These results suggest that YAP plays an important role in mediating not only hypertrophy and survival, but also proliferation of CMs in response to myocardial injury.

Differential Oxidant Tolerance Determined by the Key Transcription Factor Yap1 Is Controlled by Levels of the Yap1-binding Protein, Ybp1

The Saccharomyces cerevisiae transcription factor Yap1 is a central determinant of oxidative stress tolerance. This protein is found primarily in the cytoplasm in the absence of oxidative stress but, upon exposure to oxidants, rapidly translocates to the nucleus and activates expression of target genes. Although both diamide and H(2)O(2) have been used to impose oxidative stress on cells, these different oxidants trigger Yap1 nuclear localization in distinctly different ways. Diamide appears to oxidize particular cysteine residues on Yap1, leading to inhibition of association of Yap1 with the nuclear exportin Crm1. Crm1 would normally transport Yap1 out of the nucleus. H(2)O(2) activation of Yap1 nuclear localization requires the participation of the glutathione peroxidase Gpx3 and the Yap1-binding protein Ybp1. H(2)O(2) exposure triggers formation of a dual disulfide bonded Yap1 that is catalyzed by the presence of Gpx3 and Ybp1. In the current study, we have determined that two distinct pools of Yap1 exist in the cell. These pools are designated by the level of Ybp1. Ybp1 interacts directly with Yap1 and these proteins form a stable complex in vivo. Genetic and biochemical experiments indicate that Ybp1 is rate-limiting for Yap1 oxidative folding during H(2)O(2) stress. The fungal pathogen Candida glabrata expresses a protein homologous to Ybp1 called CgYbp1. Overproduction of CgYbp1 elevated H(2)O(2) tolerance in this pathogen indicating that the determinative role of Ybp1 in setting the level of H(2)O(2) resistance has been evolutionarily conserved.

Abstract 1015: Head and neck cancer expression of YAP65: A novel oncogene

Abstract Yes-associated protein (YAP), a transcription coactivator associated with maintaining tissue size, is reported as an oncogene in many types of cancer including ovarian, liver, lung, colon and prostate. However, the role of YAP in head and neck carcinomas is not known. Our objective was to explore the role of YAP in head and neck carcinomas. We found YAP overexpressed in the epithelial and stromal compartments of head and neck carcinomas compared to benign tissues in 140 samples. Interestingly, the squamous cell carcinomas, had elevated YAP expression in the epithelial cytoplasm in 36% of the patients. However, we observed both cytoplasmic and prominently nuclear localization of YAP in the adenocarcinomas. The tumor microenvironment is widely accepted as a promoter of tumor progression, where carcinoma-associated fibroblasts (CAFs) constitute the majority of cells. In the stroma, YAP was found to be expressed in endothelial cells and some heterogenously within the CAF population. As reported for prostate cancer, we found the transforming growth factor-beta (TGF-ß) receptor type II expression to be lost in the head and neck cancer-associated stromal cells. Since YAP has never been reported to be associated with CAFs, we performed in vitro experiment to determine the relationship of YAP and TGF-ß signaling in primary stromal cells associated with benign and head and neck cancer cells. We found TGF-ß1 can promote YAP expression and nuclear localization in normal fibroblasts. The oral human CAFs have differential expression of YAP and α-smooth muscle actin (α-SMA). Although CAFs are commonly characterized by their expression of α-SMA, YAP-expressing CAFs expressed less α-SMA and α-SMA-expressing CAFs expressed less YAP in seven independent CAF lines developed. However, all of these heterougenous head and neck CAF lines had the loss of TGF-ß receptor type II expression and concomitant upregulation of Wnt5a. Interestingly, those CAFs expressing YAP had 2-fold greater Wnt5a expression. In conclusion YAP expression is differentially expressed in adeno- and squamous cell carcinomas of head and neck carcinomas, and is heterogenously expressed in the associated CAF. YAP may regulate Wnt5a as a paracrine factor, reported to promote the progression of oral carcinomas, in a TGF-ß dependent and independent manner. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1015.

The Hippo Signaling Pathway Components Lats and Yap Pattern Tead4 Activity to Distinguish Mouse Trophectoderm from Inner Cell Mass

Outside cells of the preimplantation mouse embryo form the trophectoderm (TE), a process requiring the transcription factor Tead4. Here, we show that transcriptionally active Tead4 can induce Cdx2 and other trophoblast genes in parallel in embryonic stem cells. In embryos, the Tead4 coactivator protein Yap localizes to nuclei of outside cells, and modulation of Tead4 or Yap activity leads to changes in Cdx2 expression. In inside cells, Yap is phosphorylated and cytoplasmic, and this involves the Hippo signaling pathway component Lats. We propose that active Tead4 promotes TE development in outside cells, whereas Tead4 activity is suppressed in inside cells by cell contact- and Lats-mediated inhibition of nuclear Yap localization. Thus, differential signaling between inside and outside cell populations leads to changes in cell fate specification during TE formation.

Early Expression of Yeast Genes Affected by Chemical Stress

The variety of environmental stresses is probably the major challenge imposed on transcription activators and the transcriptional machinery. To precisely describe the very early genomic response developed by yeast to accommodate a chemical stress, we performed time course analyses of the modifications of the yeast gene expression program which immediately follows the addition of the antimitotic drug benomyl. Similar analyses were conducted with different isogenic yeast strains in which genes coding for relevant transcription factors were deleted and coupled with efficient bioinformatics tools. Yap1 and Pdr1, two well-known key mediators of stress tolerance, appeared to be responsible for the very rapid establishment of a transient transcriptional response encompassing 119 genes. Yap1, which plays a predominant role in this response, binds, in vivo, promoters of genes which are not automatically up-regulated. We proposed that Yap1 nuclear localization and DNA binding are necessary but not sufficient to elicit the specificity of the chemical stress response.

Pathways Linking Endocytosis and Actin Cytoskeleton in Mammalian Cells

Changes in cell morphology that involve alterations of the actin cytoskeleton are a hallmark of diseased renal tubular epithelial cells. While the impact of actin remodeling on gene expression has been analyzed in many model systems based on cell lines, this study investigated human primary tubular epithelial cells isolated from healthy parts of tumor nephrectomies.Latrunculin B (LatB) and cytochalasin D (CytoD) were used to modulate G-actin levels in a receptor-independent manner. Both compounds (at 0.5 μM) profoundly altered F-actin structures in a Rho kinase-dependent manner, but only CytoD strongly induced the pro-fibrotic factor CTGF (connective tissue growth factor). CTGF induction was dependent on YAP as shown by transient downregulation experiments. However, CytoD did not alter the nuclear localization of either YAP or TAZ, whereas LatB reduced nuclear levels particularly of TAZ. CytoD modified MKL1, a coactivator of serum response factor (SRF) regulating CTGF induction, and promoted its nuclear localization.TGFβ-1 is one of the major factors involved in tubulointerstitial disease and an inducer of CTGF. Preincubation with CytoD but not LatB synergistically enhanced the TGFβ-1-stimulated synthesis of CTGF, both in cells cultured on plastic dishes as well as in polarized epithelial cells. CytoD had no direct effect on the phosphorylation of Smad2/3, but facilitated their phosphorylation and thus activation by TGFβ-1.Our present findings provide evidence that morphological alterations have a strong impact on cellular signaling of one of the major pro-fibrotic factors, TGFβ-1. However, our data also indicate that changes in cell morphology per se cannot predict those interactions which are critically dependent on molecular fine tuning of actin reorganization.

Crm1 (XpoI) dependent nuclear export of the budding yeast transcription factor yAP-1 is sensitive to oxidative stress.

The yAP-1 transcription factor is crucial for the oxidative stress response of the budding yeast Saccharomyces cerevisiae; its activity is induced in response to oxidative stress, and as a consequence the expression of a number of target genes is enhanced. We have shown previously that yAP-1 is mainly found in the cytoplasm, but that upon the imposition of oxidative stress it localizes to the nucleus. In this study, we addressed the mechanism through which yAP-1 nuclear localization is regulated. Here we show that yAP-1 localization is mediated by active export from the nucleus, resulting from the activity of Crm1 (XpoI), a conserved protein that functions as an export receptor which recognizes the nuclear export signal (NES). When Crm1 expression was repressed, yAP-1 was localized in the nucleus and induced the expression of a yAP-1 dependent target gene. Our results also suggest that the cysteine rich domain (CRD), at the C-terminus of yAP-1, functions as an export recognition sequence. yAP-1 and Crm1 interact in vivo and this interaction is reduced in response to oxidative stress. These results suggest a novel regulatory mechanism of nucleocytoplasmic transport which is dependent upon a redox sensitive nuclear export pathway.

Regulation of yAP-1 nuclear localization in response to oxidative stress

The YAP1 gene of Saccharomyces cerevisiae encodes a bZIP-containing transcription factor that is essential for the normal response of cells to oxidative stress. Under stress conditions, the activity of yAP-1 is increased, leading to the induced expression of a number of target genes encoding protective enzymes or molecules. We have examined the mechanism of this activation. Upon imposition of oxidative stress, a small increase in the DNA-binding capacity of yAP-1 occurs. However, the major change is at the level of nuclear localization; upon induction the yAP-1 protein relocalizes from the cytoplasm to the nucleus. This regulated localization is mediated by a cysteine-rich domain (CRD) at the C-terminus, its removal resulting in constitutive nuclear localization and high level activity. Furthermore, the CRD of yAP-1 is sufficient to impose regulated nuclear localization of the GAL4 DNA-binding domain. Amino acid substitutions indicated that three conserved cysteine residues in the CRD are essential for the regulation. We suggest therefore, that these cysteine residues are important in sensing the redox state of the cell and hence regulating yAP-1 activity.