The Hippo pathway: key interaction and catalytic domains in organ growth control, stem cell self-renewal and tissue regeneration

The Interaction Between SMAD1 and YAP1 Is Correlated with Increased Resistance of Gastric Cancer Cells to Cisplatin

Drug resistance is a major obstacle leading to treating failure and poor outcome in gastric cancer (GC). This study explores the interaction between SMAD family member 1 (SMAD1) and Yes1-associated transcriptional regulator (YAP1) and their roles in cisplatin (DDP) resistance in GC. Transcriptome analysis predicted that SMAD1 is highly expressed in DDP-resistant cells. Elevated SMAD1 expression was detected in GC tissue and cells, especially in DDP-resistant cells (MKN-45/DDP and AGS/DDP). SMAD1 downregulation in cells decreased 50% inhibition value of DDP, reduced proliferation, migration, and invasion, and promoted cell cycle arrest and apoptosis. A protein-protein interaction network suggested a possible SMAD1 and YAP1 interaction in GC. The SMAD1 and YAP1 interaction was validated by chromatin immunoprecipitation (ChIP), co-immunoprecipitation (Co-IP), and luciferase assays. SMAD1 bound to YAP1 and activated its transcription. SMAD1 formed complexes with YAP1 in nucleus, and YAP1 upregulation enhanced SMAD1 activity as well. Upregulation of YAP1 restored the malignant behaviors of GC cells suppressed by SMAD1 silencing. In vivo, SMAD1 silencing suppressed growth and DDP resistance of xenograft tumors in nude mice, and this suppression was blocked by YAP1 overexpression again. In conclusion, this study demonstrates that SMAD1 can interact with YAP1 to enhance the DDP resistance of GC cells.

The investigation of hippo signaling pathway in mouse uterus during peri-implantation period

PURPOSE

Events in the uterus during the peri-implantation period include embryo development, acquisition of uterine receptivity, implantation and decidualization. Hippo signaling pathway regulates cell proliferation, apoptosis and differentiation. We aimed to determine localization and expressions of pYAP (Phospho Yes-associated protein), YAP (Yes-associated protein), TEAD1 (TEA domain family member 1) and CTGF (Connective tissue growth factor), members of the Hippo signaling pathway, in the mouse uterus during the peri-implantation period.

METHODS

Pregnant mice were randomly separated into 5 groups: 1st, 4th, 5th, 6th, and 8th days of pregnancy groups. Non-pregnant female mice in estrous phase were included in the estrous group. Uteri and implantation sites were collected. Also, inter-implantation sites were collected from the 5th day of pregnancy group. pYAP, YAP, TEAD-1 and CTGF were detected by immunohistochemistry and Western blotting.

RESULTS

We observed that the expressions of YAP, TEAD-1 and CTGF were increased in the luminal and glandular epithelium on the 1st and 4th days of pregnancy when epithelial proliferation occurred. pYAP expression was high, and YAP and CTGF expressions were low in the luminal epithelium of the implantation sites on the 5th day of pregnancy, when epithelial differentiation occurred. pYAP expression was low, YAP and CTGF expressions were high at implantation sites on the 6th and 8th days of pregnancy, where decidua was formed.

CONCLUSION

Our findings suggest that the Hippo signaling pathway might be involved in implantation and decidualization. Our findings will guide further studies and may help to elucidate underlying causes of implantation failure and pregnancy loss.

PTEN lipid phosphatase inactivation links the hippo and PI3K/Akt pathways to induce gastric tumorigenesis

Background

Phosphatase and tensin homolog (PTEN) is an important tumor suppressor gene, and its encoded protein has activities of both a protein phosphatase and a lipid phosphatase. However, the substitution effect of protein phosphatase activity remains unclear. PI3K/Akt is the most common pathway negatively regulated by PTEN. The Hippo and PI3K/Akt pathways have a joint effect in regulating cell proliferation and apoptosis. Therefore, how PTEN lipid phosphatase inactivation contributes to the occurrence and development of gastric cancer and the potential role of the Hippo and PI3K/Akt pathways in PTEN lipid phosphatase inactivation mediated gastric tumorigenesis remain to be explored.

Methods

Immunohistochemical staining was performed to detect the expression of p-PTEN and YAP in a gastric cancer tissue microarray. Stable cell lines expressing a wild-type or dominant-negative mutant PTEN were established. The proliferation and migration of stable cells were detected by MTT, BrdU, and colony-formation, transwell assay and high content analysis in vitro, and tumor growth differences were observed in xenograft nude mice. Changes in the expression of key molecules in the Hippo and Akt signaling pathways were detected by western blot. Nuclear-cytoplasm separation, immunofluorescence and coimmunoprecipitation analyses were conducted to explore the dysregulation of Hippo in the stable cell lines.

Results

PTEN lipid phosphatase inactivation strongly promoted the proliferation and migration of gastric cancer cells in vitro and tumor growth in vivo. A immunohistochemical analysis of gastric cancer tissues revealed a significant correlation between phosphorylated PTEN and nuclear YAP expression, and both were determined to be independent prognostic factors for gastric cancer. Mechanistically, PTEN lipid phosphatase inactivation abolished the MOB1-LATS1/2 interaction, decreased YAP phosphorylation and finally promoted YAP nuclear translocation, which enhanced the synergistic effect of YAP-TEAD, thus inducing cell proliferation and migration. Moreover, PTEN lipid phosphatase inactivation promoted the PI3K/Akt pathway, and disruption of YAP-TEAD-driven transcription decreased the activation of Akt in a dose-dependent manner.

Conclusions

Taken together, our findings indicate that PTEN lipid phosphatase inactivation links the Hippo and PI3K/Akt pathways to promote gastric tumorigenesis and cancer development.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0795-2) contains supplementary material, which is available to authorized users.

Claudin-18-mediated YAP activity regulates lung stem and progenitor cell homeostasis and tumorigenesis

Claudins, the integral tight junction (TJ) proteins that regulate paracellular permeability and cell polarity, are frequently dysregulated in cancer; however, their role in neoplastic progression is unclear. Here, we demonstrated that knockout of Cldn18, a claudin family member highly expressed in lung alveolar epithelium, leads to lung enlargement, parenchymal expansion, increased abundance and proliferation of known distal lung progenitors, the alveolar epithelial type II (AT2) cells, activation of Yes-associated protein (YAP), increased organ size, and tumorigenesis in mice. Inhibition of YAP decreased proliferation and colony-forming efficiency (CFE) of Cldn18-/- AT2 cells and prevented increased lung size, while CLDN18 overexpression decreased YAP nuclear localization, cell proliferation, CFE, and YAP transcriptional activity. CLDN18 and YAP interacted and colocalized at cell-cell contacts, while loss of CLDN18 decreased YAP interaction with Hippo kinases p-LATS1/2. Additionally, Cldn18-/- mice had increased propensity to develop lung adenocarcinomas (LuAd) with age, and human LuAd showed stage-dependent reduction of CLDN18.1. These results establish CLDN18 as a regulator of YAP activity that serves to restrict organ size, progenitor cell proliferation, and tumorigenesis, and suggest a mechanism whereby TJ disruption may promote progenitor proliferation to enhance repair following injury.

YAP mediated mechano-homeostasis - conditioning 3D animal body shape

Cells of terrestrial animals are constantly exposed to external forces including gravity. However, the complex 3D structure of the body and its organs form without being flattened. A century ago, the mathematical biologist D'Arcy Thompson predicted in 'On Growth and Form' that terrestrial animal body shapes are entirely conditioned by gravity [1], but the prediction remained to be proved due to the lack of an appropriate animal model. In this review, we outline a new mechanism of morphogenesis which ensures the generation of vertebrate 3D body shape that can withstand gravity and in which Hippo-YAP signaling acts as a mechano-effector controlling mechano-homeostasis. We will highlight the recent papers that advanced the field and discuss the impact of this previously unrecognized function of YAP-mediated signaling on the established concept of organogenesis, tissue homeostasis and disease.

Antagonistic regulation of p57kip2 by Hes/Hey downstream of Notch signaling and muscle regulatory factors regulates skeletal muscle growth arrest

A central question in development is to define how the equilibrium between cell proliferation and differentiation is temporally and spatially regulated during tissue formation. Here, we address how interactions between cyclin-dependent kinase inhibitors essential for myogenic growth arrest (p21(cip1) and p57(kip2)), the Notch pathway and myogenic regulatory factors (MRFs) orchestrate the proliferation, specification and differentiation of muscle progenitor cells. We first show that cell cycle exit and myogenic differentiation can be uncoupled. In addition, we establish that skeletal muscle progenitor cells require Notch signaling to maintain their cycling status. Using several mouse models combined with ex vivo studies, we demonstrate that Notch signaling is required to repress p21(cip1) and p57(kip2) expression in muscle progenitor cells. Finally, we identify a muscle-specific regulatory element of p57(kip2) directly activated by MRFs in myoblasts but repressed by the Notch targets Hes1/Hey1 in progenitor cells. We propose a molecular mechanism whereby information provided by Hes/Hey downstream of Notch as well as MRF activities are integrated at the level of the p57(kip2) enhancer to regulate the decision between progenitor cell maintenance and muscle differentiation.

The Hippo signaling pathway is required for salivary gland development and its dysregulation is associated with Sjogren's syndrome

Sjogren's syndrome (SS) is a complex autoimmune disease that primarily affects salivary and lacrimal glands and is associated with high morbidity. Although the prevailing dogma is that immune system pathology drives SS, increasing evidence points to structural defects, including defective E-cadherin adhesion, to be involved in its etiology. We have shown that E-cadherin has pivotal roles in the development of the mouse salivary submandibular gland (SMG) by organizing apical-basal polarity in acinar and ductal progenitors and by signaling survival for differentiating duct cells. Recently, E-cadherin junctions have been shown to interact with effectors of the Hippo signaling pathway, a core pathway regulating the organ size, cell proliferation, and differentiation. We now show that Hippo signaling is required for SMG-branching morphogenesis and is involved in the pathophysiology of SS. During SMG development, a Hippo pathway effector, TAZ, becomes increasingly phosphorylated and associated with E-cadherin and α-catenin, consistent with the activation of Hippo signaling. Inhibition of Lats2, an upstream kinase that promotes TAZ phosphorylation, results in dysmorphogenesis of the SMG and impaired duct formation. SMGs from non-obese diabetic mice, a mouse model for SS, phenocopy the Lats2-inhibited SMGs and exhibit a reduction in E-cadherin junctional components, including TAZ. Importantly, labial specimens from human SS patients display mislocalization of TAZ from junctional regions to the nucleus, coincident with accumulation of extracellular matrix components, fibronectin and connective tissue growth factor, known downstream targets of TAZ. Our studies show that Hippo signaling has a crucial role in SMG-branching morphogenesis and provide evidence that defects in this pathway are associated with SS in humans.