A requirement for p120-catenin in the metastasis of invasive ductal breast cancer

We report here the effects of targeted p120-catenin (encoded by CTNND1; hereafter denoted p120) knockout (KO) in a PyMT mouse model of invasive ductal (mammary) cancer (IDC). Mosaic p120 ablation had little effect on primary tumor growth but caused significant pro-metastatic alterations in the tumor microenvironment, ultimately leading to a marked increase in the number and size of pulmonary metastases. Surprisingly, although early effects of p120-ablation included decreased cell-cell adhesion and increased invasiveness, cells lacking p120 were almost entirely unable to colonized distant metastatic sites in vivo The relevance of this observation to human IDC was established by analysis of a large clinical dataset of 1126 IDCs. As reported by others, p120 downregulation in primary IDC predicted worse overall survival. However, as in the mice, distant metastases were almost invariably p120 positive, even in matched cases where the primary tumors were p120 negative. Collectively, our results demonstrate a strong positive role for p120 (and presumably E-cadherin) during metastatic colonization of distant sites. On the other hand, downregulation of p120 in the primary tumor enhanced metastatic dissemination indirectly via pro-metastatic conditioning of the tumor microenvironment.

Kaiso is required for MTG16-dependent effects on colitis-associated carcinoma

The myeloid translocation gene family member MTG16 is a transcriptional corepressor that relies on the DNA-binding ability of other proteins to determine specificity. One such protein is the ZBTB family member Kaiso, and the MTG16:Kaiso interaction is necessary for repression of Kaiso target genes such as matrix metalloproteinase-7. Using the azoxymethane and dextran sodium sulfate (AOM/DSS) murine model of colitis-associated carcinoma, we previously determined that MTG16 loss accelerates tumorigenesis and inflammation. However, it was unknown whether this effect was modified by Kaiso-dependent transcriptional repression. To test for a genetic interaction between MTG16 and Kaiso in inflammatory carcinogenesis, we subjected single and double knockout (DKO) mice to the AOM/DSS protocol. Mtg16^−/− mice demonstrated increased colitis and tumor burden; in contrast, disease severity in Kaiso^−/− mice was equivalent to wild type controls. Surprisingly, Kaiso deficiency in the context of MTG16 loss reversed injury and pro-tumorigenic responses in the intestinal epithelium following AOM/DSS treatment, and tumor numbers were returned to near to wild type levels. Transcriptomic analysis of non-tumor colon tissue demonstrated that changes induced by MTG16 loss were widely mitigated by concurrent Kaiso loss, and DKO mice demonstrated downregulation of metabolism and cytokine-associated gene sets with concurrent activation of DNA damage checkpoint pathways as compared with Mtg16^−/−. Further, Kaiso knockdown in intestinal enteroids reduced stem- and WNT-associated phenotypes, thus abrogating the induction of these pathways observed in Mtg16^−/− samples. Together, these data suggest that Kaiso modifies MTG16-driven inflammation and tumorigenesis and suggests that Kaiso deregulation contributes to MTG16-dependent colitis and CAC phenotypes.

p120ctn-Mediated Organ Patterning Precedes and Determines Pancreatic Progenitor Fate

The mechanism of how organ shape emerges and specifies cell fate is not understood. Pancreatic duct and endocrine lineages arise in a spatially distinct domain from the acinar lineage. Whether these lineages are pre-determined or settle once these niches have been established remains unknown. Here, we reconcile these two apparently opposing models, demonstrating that pancreatic progenitors re-localize to establish the niche that will determine their ultimate fate. We identify a p120ctn-regulated mechanism for coordination of organ architecture and cellular fate mediated by differential E-cadherin based cell sorting. Reduced p120ctn expression is necessary and sufficient to re-localize a subset of progenitors to the peripheral tip domain, where they acquire an acinar fate. The same mechanism is used re-iteratively during endocrine specification, where it balances the choice between the alpha and beta cell fates. In conclusion, organ patterning is regulated by p120ctn-mediated cellular positioning, which precedes and determines pancreatic progenitor fate.

Abstract P2-02-02: The receptor tyrosine kinase EphA2 promotes glutamine metabolism in tumors by activating the transcriptional coactivators YAP and TAZ

Malignant tumors reprogram cellular metabolism to support cancer cell proliferation and survival. Although most cancers depend on a high rate of aerobic glycolysis, many cancer cells also display addiction to glutamine. Glutamine transporters and glutaminase activity are critical for glutamine metabolism in tumor cells, and upstream regulatory signaling pathways may represent a novel mechanism for targeted therapies in glutamine-addicted breast tumors such as Her2-overexpressing and triple-negative breast cancers (TNBC). We have found that the receptor tyrosine kinase EphA2 activated the transcriptional coactivators YAP and TAZ (YAP/TAZ), likely in a ligand-independent manner, to promote glutamine metabolism in cells and mouse models of breast cancer. Overexpression of EphA2 induced the nuclear accumulation of YAP and TAZ and increased the expression of YAP/TAZ target genes. Inhibition of the GTPase Rho or the kinase ROCK abolished EphA2-dependent YAP/TAZ nuclear localization. Silencing YAP or TAZ reduced the amount of intracellular glutamate through decreased expression of SLC1A5 and GLS, respectively, genes that encode proteins that promote glutamine uptake and metabolism. The regulatory DNA elements of both SLC1A5 and GLS contain the consensus sequence of the TEAD family of transcription factors that are closely associated with YAP/TAZ and were bound by TEAD4 in an EphA2-dependent manner. In patient breast cancer tissues, EphA2 expression positively correlated with that of YAP and TAZ, as well as that of GLS and SLC1A5. Although high expression of EphA2 predicted enhanced metastatic potential and poor patient survival, it also rendered breast cancer cells more sensitive to glutaminase inhibition. The findings define a previously unknown mechanism of EphA2-mediated glutaminolysis through YAP/TAZ activation in breast cancer and identify potential therapeutic targets in patients.

Citation Format: Edwards DN, Ngwa VM, Wang S, Shiuan E, Brantley-Sieders DM, Kim LC, Reynolds AB, Chen J. The receptor tyrosine kinase EphA2 promotes glutamine metabolism in tumors by activating the transcriptional coactivators YAP and TAZ [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-02-02.

Regulation of Epithelial Plasticity Determines Metastatic Organotropism in Pancreatic Cancer

The regulation of metastatic organotropism in pancreatic ductal a denocarcinoma (PDAC) remains poorly understood. We demonstrate, using multiple mouse models, that liver and lung metastatic organotropism is dependent upon p120catenin (p120ctn)-mediated epithelial identity. Mono-allelic p120ctn loss accelerates Kras^G12D-driven pancreatic cancer formation and liver metastasis. Importantly, one p120ctn allele is sufficient for E-CADHERIN-mediated cell adhesion. By contrast, cells with bi-allelic p120ctn loss demonstrate marked lung organotropism; however, rescue with p120ctn isoform 1A restores liver metastasis. In a p120ctn-independent PDAC model, mosaic loss of E-CADHERIN expression reveals selective pressure for E-CADHERIN-positive liver metastasis and E-CADHERIN-negative lung metastasis. Furthermore, human PDAC and liver metastases support the premise that liver metastases exhibit predominantly epithelial characteristics. RNA-seq demonstrates differential induction of pathways associated with metastasis and epithelial-to-mesenchymal transition in p120ctn-deficient versus p120ctn-wild-type cells. Taken together, P120CTN and E-CADHERIN mediated epithelial plasticity is an addition to the conceptual framework underlying metastatic organotropism in pancreatic cancer.

Abstract 1452: The receptor tyrosine kinase EphA2 promotes glutamine metabolism in tumors by activating the transcriptional coactivators YAP and TAZ

Malignant tumors reprogram cellular metabolism to support cancer cell proliferation and survival. Although most cancers depend on a high rate of aerobic glycolysis, many cancer cells also display addiction to glutamine. Glutamine transporters and glutaminase activity are critical for glutamine metabolism in tumor cells. We found that the receptor tyrosine kinase EphA2 activated the TEAD family transcriptional coactivators YAP and TAZ (YAP/TAZ), likely in a ligand-independent manner, to promote glutamine metabolism in cells and mouse models of HER2-positive breast cancer. Overexpression of EphA2 induced the nuclear accumulation of YAP and TAZ and increased the expression of YAP/TAZ target genes. Inhibition of the GTPase Rho or the kinase ROCK abolished EphA2-dependent YAP/TAZ nuclear localization. Silencing YAP or TAZ substantially reduced the amount of intracellular glutamate through decreased expression of SLC1A5 and GLS, respectively, genes that encode proteins that promote glutamine uptake and metabolism. The regulatory DNA elements of both SLC1A5 and GLS contain TEAD binding sites and were bound by TEAD4 in an EphA2-dependent manner. In patient breast cancer tissues, EphA2 expression positively correlated with that of YAP and TAZ, as well as that of GLS and SLC1A5. Although high expression or EphA2 predicted enhanced metastatic potential and poor patient survival, it also rendered HER2-positive breast cancer cells more sensitive to glutaminase inhibition. The findings define a previously unknown mechanism of EphA2-mediated glutaminolysis through YAP/TAZ activation in HER2-positive breast cancer and identify therapeutic targets in patients.

Citation Format: Deanna N. Edwards, Verra M. Ngwa, Shan Wang, Eileen Shiuan, Dana Brantley-Sieders, Laura Kim, Albert B. Reynolds, Jin Chen. The receptor tyrosine kinase EphA2 promotes glutamine metabolism in tumors by activating the transcriptional coactivators YAP and TAZ [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1452.

The receptor tyrosine kinase EphA2 promotes glutamine metabolism in tumors by activating the transcriptional coactivators YAP and TAZ

Malignant tumors reprogram cellular metabolism to support cancer cell proliferation and survival. Although most cancers depend on a high rate of aerobic glycolysis, many cancer cells also display addiction to glutamine. Glutamine transporters and glutaminase activity are critical for glutamine metabolism in tumor cells. We found that the receptor tyrosine kinase EphA2 activated the TEAD family transcriptional coactivators YAP and TAZ (YAP/TAZ), likely in a ligand-independent manner, to promote glutamine metabolism in cells and mouse models of HER2-positive breast cancer. Overexpression of EphA2 induced the nuclear accumulation of YAP and TAZ and increased the expression of YAP/TAZ target genes. Inhibition of the GTPase Rho or the kinase ROCK abolished EphA2-dependent YAP/TAZ nuclear localization. Silencing YAP or TAZ substantially reduced the amount of intracellular glutamate through decreased expression of SLC1A5 and GLS, respectively, genes that encode proteins that promote glutamine uptake and metabolism. The regulatory DNA elements of both SLC1A5 and GLS contain TEAD binding sites and were bound by TEAD4 in an EphA2-dependent manner. In patient breast cancer tissues, EphA2 expression positively correlated with that of YAP and TAZ, as well as that of GLS and SLC1A5 Although high expression of EphA2 predicted enhanced metastatic potential and poor patient survival, it also rendered HER2-positive breast cancer cells more sensitive to glutaminase inhibition. The findings define a previously unknown mechanism of EphA2-mediated glutaminolysis through YAP/TAZ activation in HER2-positive breast cancer and identify potential therapeutic targets in patients.

p120-Catenin is an obligate haploinsufficient tumor suppressor in intestinal neoplasia

p120-Catenin (p120) functions as a tumor suppressor in intestinal cancer, but the mechanism is unclear. Here, using conditional p120 knockout in Apc-sensitized mouse models of intestinal cancer, we have identified p120 as an "obligatory" haploinsufficient tumor suppressor. Whereas monoallelic loss of p120 was associated with a significant increase in tumor multiplicity, loss of both alleles was never observed in tumors from these mice. Moreover, forced ablation of the second allele did not further enhance tumorigenesis, but instead induced synthetic lethality in combination with Apc loss of heterozygosity. In tumor-derived organoid cultures, elimination of both p120 alleles resulted in caspase-3-dependent apoptosis that was blocked by inhibition of Rho kinase (ROCK). With ROCK inhibition, however, p120-ablated organoids exhibited a branching phenotype and a substantial increase in cell proliferation. Access to data from Sleeping Beauty mutagenesis screens afforded an opportunity to directly assess the tumorigenic impact of p120 haploinsufficiency relative to other candidate drivers. Remarkably, p120 ranked third among the 919 drivers identified. Cofactors α-catenin and epithelial cadherin (E-cadherin) were also among the highest scoring candidates, indicating a mechanism at the level of the intact complex that may play an important role at very early stages of of intestinal tumorigenesis while simultaneously restricting outright loss via synthetic lethality.

Abstract 2884: Role of Kaiso in intestinal tumorigenesis

p120-catenin is a master regulator of classical cadherin stability and essential for epithelial homeostasis. p120 physically interacts with transcription factor Kaiso (ZBTB33) suggesting a direct or indirect role in transcription, but its precise function with respect to Kaiso is largely unknown. Kaiso belongs to the ZBTB family of transcription factors, most of which have important roles in development and/or cancer. Interestingly, Kaiso is strongly expressed in the intestinal crypt and abruptly downregulated as the cells move up onto the villus and terminally differentiate. Kaiso is constitutively upregulated in nascent adenomas initiated by loss of the tumor suppressor APC, suggesting a link between canonical Wnt signaling, Kaiso upregulation and intestinal tumorigenesis. Here, using ChipSeq and proteomics we describe several candidate Kaiso interactions with a group of proteins that include the tumor suppressor BRCA1, CHD2 (a chromatin remodifier) and the Ets1 oncoprotein, along with preliminary evidence for functional significance relevant to intestinal tumorigenesis.

Citation Format: Manish K. Tripathi, Albert B. Reynolds. Role of Kaiso in intestinal tumorigenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2884.

p120 Catenin Suppresses Basal Epithelial Cell Extrusion in Invasive Pancreatic Neoplasia

Aberrant regulation of cellular extrusion can promote invasion and metastasis. Here, we identify molecular requirements for early cellular invasion using a premalignant mouse model of pancreatic cancer with conditional knockout of p120 catenin (Ctnnd1). Mice with biallelic loss of p120 catenin progressively develop high-grade pancreatic intraepithelial neoplasia (PanIN) lesions and neoplasia accompanied by prominent acute and chronic inflammatory processes, which is mediated, in part, through NF-κB signaling. Loss of p120 catenin in the context of oncogenic Kras also promotes remarkable apical and basal epithelial cell extrusion. Abundant single epithelial cells exit PanIN epithelium basally, retain epithelial morphology, survive, and display features of malignancy. Similar extrusion defects are observed following p120 catenin knockdown in vitro, and these effects are completely abrogated by the activation of S1P/S1pr2 signaling. In the context of oncogenic Kras, p120 catenin loss significantly reduces expression of genes mediating S1P/S1pr2 signaling in vivo and in vitro, and this effect is mediated at least, in part, through activation of NF-κB. These results provide insight into mechanisms controlling early events in the metastatic process and suggest that p120 catenin and S1P/S1pr2 signaling enhance cancer progression by regulating epithelial cell invasion. Cancer Res; 76(11); 3351-63. ©2016 AACR.

p120-catenin controls contractility along the vertical axis of epithelial lateral membranes

In vertebrate epithelia, p120-catenin (hereafter referred to as p120; also known as CTNND1) mediates E-cadherin stability and suppression of RhoA. Genetic ablation of p120 in various epithelial tissues typically causes striking alterations in tissue function and morphology. Although these effects could very well involve p120's activity towards Rho, ascertaining the impact of this relationship has been complicated by the fact that p120 is also required for cell-cell adhesion. Here, we have molecularly uncoupled p120's cadherin-stabilizing and RhoA-suppressing activites. Unexpectedly, removing p120's Rho-suppressing activity dramatically disrupted the integrity of the apical surface, irrespective of E-cadherin stability. The physical defect was tracked to excessive actomyosin contractility along the vertical axis of lateral membranes. Thus, we suggest that p120's distinct activities towards E-cadherin and Rho are molecularly and functionally coupled and this, in turn, enables the maintenance of cell shape in the larger context of an epithelial monolayer. Importantly, local suppression of contractility by cadherin-bound p120 appears to go beyond regulating cell shape, as loss of this activity also leads to major defects in epithelial lumenogenesis.

Abstract PR05: p120 catenin mediated epithelial-to-mesenchymal plasticity determines the metastatic potential of pancreatic ductal adenocarcinoma

Introduction: The majority of pancreatic ductal adenocarcinoma (PDAC) patients present with metastases and nearly all will succumb to disease within 6-12 months of clinical presentation (Hidalgo, 2010). Recently, p120catenin (p120) was identified as a “cancer candidate gene” in sleeping beauty-induced PDAC and p120 loss is associated with poor patient survival (Mann et al, 2012). P120 is critical in stabilizing E-cadherin (E-cad) at the adherens junctions. In this study, we wished to unravel new roles for p120 in the context of PDAC initiation and progression (epithelial-mesenchymal transition or EMT), as well as metastasis.

Results: We have introduced a floxed p120 allele into the Pdx1cre;LSL-KrasG12D;R26YFP (KCY) PDAC mouse model. Mice with homozygous p120 deletion in the context of a LSL-KrasG12D allele (KCYp120fl/fl) are not viable. However, mice with heterozygous p120 loss (KCYp120fl/wt) are born according to Mendelian ratios. At 20 weeks of age, KCYp120fl/wt mice show a remarkable acceleration of the Kras-driven phenotype. KCYp120fl/wt mice (n=21) harbor the entire spectrum of precursor lesions, including PanINs (1-3), mucinous cystic neoplasms (MCN) and intraductal papillary mucinous neoplasms (IPMN) and metastatic PDAC. The phenotype in control KCYp120wt/wt mice (n=12) was restricted to early PanINs. We next asked whether the second allele of p120 is lost during metastatic dissemination. We demonstrated that the remaining p120 allele is expressed in liver metastases, indicating that p120 loss-of-heterozygosity did not occur. Of note, in liver metastases, p120 co-localizes with E-cad, thereby indicating that a single p120 allele is sufficient to stabilize E-cad. This raised the question of whether one p120 allele is required to establish epithelial integrity at the metastatic site. In order to address this mechanistically, and since KCYp120fl/fl are not viable, we performed three-dimensional (3D) culture experiments with pancreatic cells isolated from non-recombined LSL-KrasG12D/+;p120wt/wt;R26YFP (KYp120wt/wt), KYp120fl/wt and KYp120fl/fl mice. Cells were Cre-recombined in vitro. In 3D culture, KYp120wt/wt cells form round multicellular cysts. Monoallelic p120 loss only disrupts the symmetry of cysts while biallelic loss completely prevents cells from forming organized, cyctic structures. We next injected these cell lines orthotopically into the pancreata of immunodeficient mice. KYp120wt/wt cells form PanIN-like structures. Interestingly, KYp120fl/wt establish large cysts reminiscent of IPMN/MCN lesions. In the cysts, p120 is localized at the plasma membrane with E-cad. However, the invasive fronts of tumors show significantly less p120 expression. Finally, KYp120fl/fl cells form poorly differentiated tumors invading into the surrounding stroma. Given the fact that p120 stabilizes E-cad and that E-cad is critical in EMT and MET, we injected the KYp120wt/wt, KYp120fl/wt and KYp120fl/fl cell lines directly into the portal veins of these mice. KYp120fl/wt cells colonize the liver and retain the remaining p120 allele and display membranous E-cad localization. By contrast, although KYp120fl/fl cells are able to generate invasive primary pancreatic tumors when being injected orthotopically, these cells fail to colonize the liver.

Conclusions: Our findings demonstrate that monoallelic loss of p120 accelerates Kras-driven PDAC formation. However, one allele of p120 is required to establish epithelial integrity and metastases. Taken together, these results for the first time underscore the importance of p120-mediated EMT plasticity in order to complete the metastatic cascade in vivo. Furthermore, therapeutic strategies to prevent EMT alone may not be sufficient in light of our results but rather require novel approaches to target EMT plasticity so as to enhance survival in metastatic PDAC.

This abstract is also presented as Poster A63.

Citation Format: Maximilian Reichert, Basil S. Bakir, Christopher M. Hahn, Gregory P. Botta, Andrew D. Rhim, Robert H. Vonderheide, Albert B. Reynolds, Yingtao Bi, Ramana Davuluri, Burcu Saka, N. Volkan Adsay, Anil K. Rustgi. p120 catenin mediated epithelial-to-mesenchymal plasticity determines the metastatic potential of pancreatic ductal adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr PR05.

p120-catenin expressed in alveolar type II cells is essential for the regulation of lung innate immune response

The integrity of the lung alveolar epithelial barrier is required for the gas exchange and is important for immune regulation. Alveolar epithelial barrier is composed of flat type I cells, which make up approximately 95% of the gas-exchange surface, and cuboidal type II cells, which secrete surfactants and modulate lung immunity. p120-catenin (p120; gene symbol CTNND1) is an important component of adherens junctions of epithelial cells; however, its function in lung alveolar epithelial barrier has not been addressed in genetic models. Here, we created an inducible type II cell-specific p120-knockout mouse (p120EKO). The mutant lungs showed chronic inflammation, and the alveolar epithelial barrier was leaky to (125)I-albumin tracer compared to wild type. The mutant lungs also demonstrated marked infiltration of inflammatory cells and activation of NF-κB. Intracellular adhesion molecule 1, Toll-like receptor 4, and macrophage inflammatory protein 2 were all up-regulated. p120EKO lungs showed increased expression of the surfactant proteins Sp-B, Sp-C, and Sp-D, and displayed severe inflammation after pneumonia caused by Pseudomonas aeruginosa compared with wild type. In p120-deficient type II cell monolayers, we observed reduced transepithelial resistance compared to control, consistent with formation of defective adherens junctions. Thus, although type II cells constitute only 5% of the alveolar surface area, p120 expressed in these cells plays a critical role in regulating the innate immunity of the entire lung.

p120 Catenin is required for normal tubulogenesis but not epithelial integrity in developing mouse pancreas

The intracellular protein p120 catenin aids in maintenance of cell-cell adhesion by regulating E-cadherin stability in epithelial cells. In an effort to understand the biology of p120 catenin in pancreas development, we ablated p120 catenin in mouse pancreatic progenitor cells, which resulted in deletion of p120 catenin in all epithelial lineages of the developing mouse pancreas: islet, acinar, centroacinar, and ductal. Loss of p120 catenin resulted in formation of dilated epithelial tubules, expansion of ductal epithelia, loss of acinar cells, and the induction of pancreatic inflammation. Aberrant branching morphogenesis and tubulogenesis were also observed. Throughout development, the phenotype became more severe, ultimately resulting in an abnormal pancreas comprised primarily of duct-like epithelium expressing early progenitor markers. In pancreatic tissue lacking p120 catenin, overall epithelial architecture remained intact; however, actin cytoskeleton organization was disrupted, an observation associated with increased cytoplasmic PKCζ. Although we observed reduced expression of adherens junction proteins E-cadherin, β-catenin, and α-catenin, p120 catenin family members p0071, ARVCF, and δ-catenin remained present at cell membranes in homozygous p120(f/f) pancreases, potentially providing stability for maintenance of epithelial integrity during development. Adult mice homozygous for deletion of p120 catenin displayed dilated main pancreatic ducts, chronic pancreatitis, acinar to ductal metaplasia (ADM), and mucinous metaplasia that resembles PanIN1a. Taken together, our data demonstrate an essential role for p120 catenin in pancreas development.

KAISO, a critical regulator of p53-mediated transcription of CDKN1A and apoptotic genes

An unresolved issue in genotoxic stress response is identification of induced regulatory proteins and how these activate tumor suppressor p53 to determine appropriate cell responses. Transcription factor KAISO was previously described to repress transcription following binding to methylated DNA. In this study, we show that KAISO is induced by DNA damage in p53-expressing cells and then interacts with the p53-p300 complex to increase acetylation of p53 K320 and K382 residues, although decreasing K381 acetylation. Moreover, the p53 with this particular acetylation pattern shows increased DNA binding and potently induces cell cycle arrest and apoptosis by activating transcription of CDKN1A (cyclin-dependent kinase inhibitor 1) and various apoptotic genes. Analogously, in Kaiso KO mouse embryonic fibroblast cells, p53-to-promoter binding and up-regulation of p21 and apoptosis gene expression is significantly compromised. KAISO may therefore be a critical regulator of p53-mediated cell cycle arrest and apoptosis in response to various genotoxic stresses in mammalian cells.

p120-catenin-dependent junctional recruitment of Shroom3 is required for apical constriction during lens pit morphogenesis

Apical constriction (AC) is a widely utilized mechanism of cell shape change whereby epithelial cells transform from a cylindrical to conical shape, which can facilitate morphogenetic movements during embryonic development. Invertebrate epithelial cells undergoing AC depend on the contraction of apical cortex-spanning actomyosin filaments that generate force on the apical junctions and pull them toward the middle of the cell, effectively reducing the apical circumference. A current challenge is to determine whether these mechanisms are conserved in vertebrates and to identify the molecules responsible for linking apical junctions with the AC machinery. Utilizing the developing mouse eye as a model, we have uncovered evidence that lens placode AC may be partially dependent on apically positioned myosin-containing filaments associated with the zonula adherens. In addition we found that, among several junctional components, p120-catenin genetically interacts with Shroom3, a protein required for AC during embryonic morphogenesis. Further analysis revealed that, similar to Shroom3, p120-catenin is required for AC of lens cells. Finally, we determined that p120-catenin functions by recruiting Shroom3 to adherens junctions. Together, these data identify a novel role for p120-catenin during AC and further define the mechanisms required for vertebrate AC.

Differential role for p120-catenin in regulation of TLR4 signaling in macrophages

Activation of TLR signaling through recognition of pathogen-associated molecular patterns is essential for the innate immune response against bacterial and viral infections. We have shown that p120-catenin (p120) suppresses TLR4-mediated NF-кB signaling in LPS-challenged endothelial cells. In this article, we report that p120 differentially regulates LPS/TLR4 signaling in mouse bone marrow-derived macrophages. We observed that p120 inhibited MyD88-dependent NF-κB activation and release of TNF-α and IL-6, but enhanced TIR domain-containing adapter-inducing IFN-β-dependent IFN regulatory factor 3 activation and release of IFN-β upon LPS exposure. p120 silencing diminished LPS-induced TLR4 internalization, whereas genetic and pharmacological inhibition of RhoA GTPase rescued the decrease in endocytosis of TLR4 and TLR4-MyD88 signaling, and reversed the increase in TLR4-TIR domain-containing adapter-inducing IFN-β signaling induced by p120 depletion. Furthermore, we demonstrated that altered p120 expression in macrophages regulates the inflammatory phenotype of LPS-induced acute lung injury. These results indicate that p120 functions as a differential regulator of TLR4 signaling pathways by facilitating TLR4 endocytic trafficking in macrophages, and support a novel role for p120 in influencing the macrophages in the lung inflammatory response to endotoxin.

DIPA-family coiled-coils bind conserved isoform-specific head domain of p120-catenin family: potential roles in hydrocephalus and heterotopia

Isoform-specific expression of p120 affects cell motility and migration during development and tumor progression. The DIPA coiled-coil protein is a novel binding partner to the conserved isoform 1–specific head domain of p120 family members. Zebrafish data suggest that DIPA is mechanistically linked to p120 isoform–specific function in development.

p120-catenin (p120) modulates adherens junction (AJ) dynamics by controlling the stability of classical cadherins. Among all p120 isoforms, p120-3A and p120-1A are the most prevalent. Both stabilize cadherins, but p120-3A is preferred in epithelia, whereas p120-1A takes precedence in neurons, fibroblasts, and macrophages. During epithelial-to-mesenchymal transition, E- to N-cadherin switching coincides with p120-3A to -1A alternative splicing. These isoforms differ by a 101–amino acid “head domain” comprising the p120-1A N-terminus. Although its exact role is unknown, the head domain likely mediates developmental and cancer-associated events linked to p120-1A expression (e.g., motility, invasion, metastasis). Here we identified delta-interacting protein A (DIPA) as the first head domain–specific binding partner and candidate mediator of isoform 1A activity. DIPA colocalizes with AJs in a p120-1A- but not 3A-dependent manner. Moreover, all DIPA family members (Ccdc85a, Ccdc85b/DIPA, and Ccdc85c) interact reciprocally with p120 family members (p120, δ-catenin, p0071, and ARVCF), suggesting significant functional overlap. During zebrafish neural tube development, both knockdown and overexpression of DIPA phenocopy N-cadherin mutations, an effect bearing functional ties to a reported mouse hydrocephalus phenotype associated with Ccdc85c. These studies identify a novel, highly conserved interaction between two protein families that may participate either individually or collectively in N-cadherin–mediated development.

SRChing for the substrates of Src

By the mid 1980's, it was clear that the transforming activity of oncogenic Src was linked to the activity of its tyrosine kinase domain and attention turned to identifying substrates, the putative next level of control in the pathway to transformation. Among the first to recognize the potential of phosphotyrosine-specific antibodies, Parsons and colleagues launched a risky shotgun-based approach that led ultimately to the cDNA cloning and functional characterization of many of today's best-known Src substrates (for example, p85-Cortactin, p110-AFAP1, p130Cas, p125FAK and p120-catenin). Two decades and over 6000 citations later, the original goals of the project may be seen as secondary to the enormous impact of these protein substrates in many areas of biology. At the request of the editors, this review is not restricted to the current status of the substrates, but reflects also on the anatomy of the project itself and some of the challenges and decisions encountered along the way.

WAVE2 regulates epithelial morphology and cadherin isoform switching through regulation of Twist and Abl

Background

Epithelial morphogenesis is a dynamic process that involves coordination of signaling and actin cytoskeletal rearrangements.

Principal Findings

We analyzed the contribution of the branched actin regulator WAVE2 in the development of 3-dimensional (3D) epithelial structures. WAVE2-knockdown (WAVE2-KD) cells formed large multi-lobular acini that continued to proliferate at an abnormally late stage compared to control acini. Immunostaining of the cell-cell junctions of WAVE2-KD acini revealed weak and heterogeneous E-cadherin staining despite little change in actin filament localization to the same junctions. Analysis of cadherin expression demonstrated a decrease in E-cadherin and an increase in N-cadherin protein and mRNA abundance in total cell lysates. In addition, WAVE2-KD cells exhibited an increase in the mRNA levels of the epithelial-mesenchymal transition (EMT)-associated transcription factor Twist1. KD of Twist1 expression in WAVE2-KD cells reversed the cadherin switching and completely rescued the aberrant 3D morphological phenotype. Activity of the WAVE2 complex binding partner Abl kinase was also increased in WAVE2-KD cells, as assessed by tyrosine phosphorylation of the Abl substrate CrkL. Inhibition of Abl with STI571 rescued the multi-lobular WAVE2-KD 3D phenotype whereas overexpression of Abl kinase phenocopied the WAVE2-KD phenotype.

Conclusions

The WAVE2 complex regulates breast epithelial morphology by a complex mechanism involving repression of Twist1 expression and Abl kinase activity. These data reveal a critical role for WAVE2 complex in regulation of cellular signaling and epithelial morphogenesis.

Interaction of p190RhoGAP with C-terminal domain of p120-catenin modulates endothelial cytoskeleton and permeability

p120-catenin is a multidomain intracellular protein, which mediates a number of cellular functions, including stabilization of cell-cell transmembrane cadherin complexes as well as regulation of actin dynamics associated with barrier function, lamellipodia formation, and cell migration via modulation of the activities of small GTPAses. One mechanism involves p120 catenin interaction with Rho GTPase activating protein (p190RhoGAP), leading to p190RhoGAP recruitment to cell periphery and local inhibition of Rho activity. In this study, we have identified a stretch of 23 amino acids within the C-terminal domain of p120 catenin as the minimal sequence responsible for the recruitment of p190RhoGAP (herein referred to as CRAD; catenin-RhoGAP association domain). Expression of the p120-catenin truncated mutant lacking the CRAD in endothelial cells attenuated effects of barrier protective oxidized phospholipid, OxPAPC. This effect was accompanied by inhibition of membrane translocation of p190RhoGAP, increased Rho signaling, as well as suppressed activation of Rac1 and its cytoskeletal effectors PAK1 (p21-activated kinase 1) and cortactin. Expression of p120 catenin-truncated mutant lacking CRAD also delayed the recovery process after thrombin-induced endothelial barrier disruption. Concomitantly, RhoA activation and downstream signaling were sustained for a longer period of time, whereas Rac signaling was inhibited. These data demonstrate a critical role for p120-catenin (amino acids 820-843) domain in the p120-catenin·p190RhoGAP signaling complex assembly, membrane targeting, and stimulation of p190RhoGAP activity toward inhibition of the Rho pathway and reciprocal up-regulation of Rac signaling critical for endothelial barrier regulation.

Monoclonal antibodies to DIPA: a novel binding partner of p120-catenin isoform 1

The coiled-coil domain-containing delta-interacting protein A (DIPA) is a transcription factor implicated in developmental regulation. DIPA is the first protein discovered to selectively interact with the p120-catenin (p120) isoform 1, an alternatively spliced form of p120 expressed preferentially in mesenchymal cells. Although a small fraction of p120 can be observed in the nucleus under certain circumstances, the vast majority of it associates with classical cadherins at adherens junctions. We observed for the first time that a discrete fraction of DIPA exists at cell-cell junctions, in addition to its predominantly nuclear localization. Thus, the p120-DIPA interaction may regulate cell signaling and/or transcriptional events, as has been described previously for β-catenin and the LEF/TCF transcription factor family. To facilitate further study of DIPA and to determine the physiological relevance of its interaction with p120, we have generated and characterized a panel of five DIPA-specific monoclonal antibodies (MAbs) that function in immunoblotting, immunoprecipitation, and immunofluorescence assays.

A membrane fusion protein αSNAP is a novel regulator of epithelial apical junctions

Tight junctions (TJs) and adherens junctions (AJs) are key determinants of the structure and permeability of epithelial barriers. Although exocytic delivery to the cell surface is crucial for junctional assembly, little is known about the mechanisms controlling TJ and AJ exocytosis. This study was aimed at investigating whether a key mediator of exocytosis, soluble N-ethylmaleimide sensitive factor (NSF) attachment protein alpha (αSNAP), regulates epithelial junctions. αSNAP was enriched at apical junctions in SK-CO15 and T84 colonic epithelial cells and in normal human intestinal mucosa. siRNA-mediated knockdown of αSNAP inhibited AJ/TJ assembly and establishment of the paracellular barrier in SK-CO15 cells, which was accompanied by a significant down-regulation of p120-catenin and E-cadherin expression. A selective depletion of p120 catenin effectively disrupted AJ and TJ structure and compromised the epithelial barrier. However, overexpression of p120 catenin did not rescue the defects of junctional structure and permeability caused by αSNAP knockdown thereby suggesting the involvement of additional mechanisms. Such mechanisms did not depend on NSF functions or induction of cell death, but were associated with disruption of the Golgi complex and down-regulation of a Golgi-associated guanidine nucleotide exchange factor, GBF1. These findings suggest novel roles for αSNAP in promoting the formation of epithelial AJs and TJs by controlling Golgi-dependent expression and trafficking of junctional proteins.

p120-catenin is essential for terminal end bud function and mammary morphogenesis

Although p120-catenin (p120) is crucial for E-cadherin function, ablation experiments in epithelial tissues from different organ systems reveal markedly different effects. Here, we examine for the first time the consequences of p120 knockout during mouse mammary gland development. An MMTV-Cre driver was used to target knockout to the epithelium at the onset of puberty. p120 ablation was detected in approximately one-quarter of the nascent epithelium at the forth week post-partum. However, p120 null cells were essentially nonadherent, excluded from the process of terminal end bud (TEB) morphogenesis and lost altogether by week six. This elimination process caused a delay in TEB outgrowth, after which the gland developed normally from cells that had retained p120. Mechanistic studies in vitro indicate that TEB dysfunction is likely to stem from striking E-cadherin loss, failure of cell-cell adhesion and near total exclusion from the collective migration process. Our findings reveal an essential role for p120 in mammary morphogenesis.

Regulation of cochlear convergent extension by the vertebrate planar cell polarity pathway is dependent on p120-catenin

The vertebrate planar cell polarity (PCP) pathway consists of conserved PCP and ciliary genes. During development, the PCP pathway regulates convergent extension (CE) and uniform orientation of sensory hair cells in the cochlea. It is not clear how these diverse morphogenetic processes are regulated by a common set of PCP genes. Here, we show that cellular contacts and geometry change drastically and that the dynamic expression of N-cadherin and E-cadherin demarcates sharp boundaries during cochlear extension. The conditional knockout of a component of the adherens junctions, p120-catenin, leads to the reduction of E-cadherin and N-cadherin and to characteristic cochlear CE defects but not misorientation of hair cells. The specific CE defects in p120-catenin mutants are in contrast to associated CE and hair cell misorientation defects observed in common PCP gene mutants. Moreover, the loss-of-function of a conserved PCP gene, Vangl2, alters the dynamic distribution of N-cadherin and E-cadherin in the cochlea and causes similar abnormalities in cellular morphology to those found in p120-catenin mutants. Conversely, we found that Pcdh15 interacts genetically with PCP genes to regulate the formation of polar hair bundles, but not CE defects in the cochlea. Together, these results indicate that the vertebrate PCP pathway regulates CE and hair cell polarity independently and that a p120-catenin-dependent mechanism regulates CE of the cochlea.

Association of Rho-associated protein kinase 1 with E-cadherin complexes is mediated by p120-catenin

The dynamic functional linkage of cadherins with the underlying actin cytoskeleton is tightly regulated to achieve proper cell-cell adhesion. p120-catenin (p120) regulates both cadherin stability and actin dynamics, but the relationship between these two functions remains unclear. Using a novel proteomic approach called reversible cross-link immunoprecipitation, or ReCLIP, we previously identified a physical interaction between p120 and Rho-associated protein kinase 1 (ROCK1), a major effector of RhoA. In this paper, we show that a discrete fraction of cellular ROCK1 coimmunoprecipitates with p120 and precisely colocalizes to adherens junctions (AJs). Manipulation of AJs using a calcium-switch assay and cadherin-blocking antibodies indicates direct recruitment of ROCK1 to newly forming junctions. Importantly, we find that p120 links ROCK1 to the cadherin complex, as ROCK1 coimmunoprecipitates with wild-type but not p120-uncoupled E-cadherin. Moreover, depletion of ROCK1 using short-hairpin RNA results in dramatic mislocalization of the cadherin complex and junctional actin. These data are consistent with a model in which p120 dynamically regulates Rho-GTPase activity at the cadherin complex through transient interaction with several of its up- and downstream effectors, including ROCK1.

Epithelial organization: new perspective on α-catenin from an ancient source

Cadherins and catenins evidently partnered at the dawn of the animal kingdom to enable the first polarized epithelium, and perhaps animal evolution itself. New evidence from a primitive slime mold, however, suggests that α- and β-catenins may have engaged this function independently, long before cadherins arrived on the scene.

The evolutionary history of the catenin gene family during metazoan evolution

BACKGROUND

Catenin is a gene family composed of three subfamilies; p120, beta and alpha. Beta and p120 are homologous subfamilies based on sequence and structural comparisons, and are members of the armadillo repeat protein superfamily. Alpha does not appear to be homologous to either beta or p120 based on the lack of sequence and structural similarity, and the alpha subfamily belongs to the vinculin superfamily. Catenins link the transmembrane protein cadherin to the cytoskeleton and thus function in cell-cell adhesion. To date, only the beta subfamily has been evolutionarily analyzed and experimentally studied for its functions in signaling pathways, development and human diseases such as cancer. We present a detailed evolutionary study of the whole catenin family to provide a better understanding of how this family has evolved in metazoans, and by extension, the evolution of cell-cell adhesion.

RESULTS

All three catenin subfamilies have been detected in metazoans used in the present study by searching public databases and applying species-specific BLAST searches. Two monophyletic clades are formed between beta and p120 subfamilies using Bayesian phylogenetic inference. Phylogenetic analyses also reveal an array of duplication events throughout metazoan history. Furthermore, numerous annotation issues for the catenin family have been detected by our computational analyses.

CONCLUSIONS

Delta2/ARVCF catenin in the p120 subfamily, beta catenin in the beta subfamily, and alpha2 catenin in the alpha subfamily are present in all metazoans analyzed. This implies that the last common ancestor of metazoans had these three catenin subfamilies. However, not all members within each subfamily were detected in all metazoan species. Each subfamily has undergone duplications at different levels (species-specific, subphylum-specific or phylum-specific) and to different extents (in the case of the number of homologs). Extensive annotation problems have been resolved in each of the three catenin subfamilies. This resolution provides a more coherent description of catenin evolution.

Adenoma formation following limited ablation of p120-catenin in the mouse intestine

p120 loss destabilizes E-cadherin and could therefore result in tumor and/or metastasis-promoting activities similar to those caused by E-cadherin downregulation. Previously, we reported that p120 is essential in the intestine for barrier function, epithelial homeostasis and survival. Conditional p120 ablation in the mouse intestine induced severe inflammatory bowel disease, but long-term cancer-related studies were impossible because none of the animals survived longer than 21 days. Here, we used a tamoxifen-inducible mouse model (Vil-Cre-ER^T2;p120^fl/fl) to limit the extent of p120 ablation and thereby enable long-term studies. Reducing p120 KO to ∼10% of the intestinal epithelium produced long-lived animals outwardly indistinguishable from controls. Effects of prolonged p120 absence were then evaluated at intervals spanning 2 to 18 months. At all time points, immunostaining revealed microdomains of p120-null epithelium interspersed with normal epithelium. Thus, stochastic p120 ablation is compatible with crypt progenitor cell function and permitted lifelong renewal of the p120-null cells. Consistent with previous observations, a barrier defect and frequent infiltration of neutrophils was observed, suggesting that focal p120 loss generates a microenvironment disposed to chronic inflammation. We report that 45% of these animals developed tumors within 18 months of tamoxifen induction. Interestingly, β-catenin was upregulated in the majority, but none of the tumors were p120 null. Although further work is required to directly establish mechanism, we conclude that limited p120 ablation can promote tumorigenesis by an indirect non-cell autonomous mechanism. Given that byproducts of inflammation are known to be highly mutagenic, we suggest that tumorigenesis in this model is ultimately driven by the lifelong inability to heal chronic wounds and the substantially increased rates of stochastic gene mutation in tissue microenvironments subjected to chronic inflammation. Indeed, although technical issues precluded direct identification of mutations, β-catenin upregulation in human colon cancer almost invariably reflects mutations in APC and/or β-catenin.

Deletion of p120-catenin results in a tumor microenvironment with inflammation and cancer that establishes it as a tumor suppressor gene

p120-catenin (p120ctn) interacts with E-cadherin, but to our knowledge, no formal proof that p120ctn functions as a bona fide tumor suppressor gene has emerged to date. We report herein that p120ctn loss leads to tumor development in mice. We have generated a conditional knockout model of p120ctn whereby mice develop preneoplastic and neoplastic lesions in the oral cavity, esophagus, and squamous forestomach. Tumor-derived cells secrete granulocyte macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF), monocyte chemotactic protein-1 (MCP-1), and tumor necrosis factor-α (TNFα). The tumors contain significant desmoplasia and immune cell infiltration. Immature myeloid cells comprise a significant percentage of the immune cells present and likely participate in fostering a favorable tumor microenvironment, including the activation of fibroblasts.

Alterations in the proteome of the NHERF2 knockout mouse jejunal brush border membrane vesicles

To identify additional potential functions for the multi-PDZ domain containing protein Na+/H+ exchanger regulatory factor 2 (NHERF2), which is present in the apical domain of intestinal epithelial cells, proteomic studies of mouse jejunal villus epithelial cell brush border membrane vesicles compared wild-type to homozygous NHERF2 knockout FVB mice by a two-dimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS)-iTRAQ approach. Jejunal architecture appeared normal in NHERF2 null in terms of villus length and crypt depth, Paneth cell number, and microvillus structure by electron microscopy. There was also no change in proliferative activity based on BrdU labeling. Four brush border membrane vesicles (BBMV) preparations from wild-type mouse jejunum were compared with four preparations from NHERF2 knockout mice. LC-MS/MS identified 450 proteins in both matched wild-type and NHERF2 null BBMV; 13 proteins were changed in two or more separate BBMV preparations (9 increased and 4 decreased in NHERF2 null mice), while an additional 92 proteins were changed in a single BBMV preparation (68 increased and 24 decreased in NHERF2 null mice). These proteins were categorized as 1) transport proteins (one increased and two decreased in NHERF2 null); 2) signaling molecules (2 increased in NHERF2 null); 3) cytoskeleton/junctional proteins (4 upregulated and 1 downregulated in NHERF2 null); and 4) metabolic proteins/intrinsic BB proteins) (2 upregulated and 1 downregulated in NHERF2 null). Immunoblotting of BBMV was used to validate or extend the findings, demonstrating increase in BBMV of NHERF2 null of MCT1, coronin 3, and ezrin. The proteome of the NHERF2 null mouse small intestinal BB demonstrates up- and downregulation of multiple transport proteins, signaling molecules, cytoskeletal proteins, tight junctional and adherens junction proteins, and proteins involved in metabolism, suggesting involvement of NHERF2 in multiple apical regulatory processes and interactions with luminal contents.

Innate immune function of the adherens junction protein p120-catenin in endothelial response to endotoxin

Sepsis-induced acute lung injury is a common clinical disorder in critically ill patients that is associated with high mortality. In this study, we investigated the role of p120-catenin (p120), a constituent of endothelial adherens junctions, in regulating the innate immune function of lungs. In mice in which acute lung injury was induced by i.p. administration of LPS, we observed a rapid decrease in the expression of p120 in lungs. The p120 protein expression was correlated inversely with severity of inflammation. Suppression of p120 expression in lung endothelial cells in mice using small interfering RNA resulted in high sensitivity to endotoxin and greatly increased the mortality compared with controls. Knockdown of p120 also increased the expression of ICAM-1, neutrophil recruitment, production of cytokines TNF-α and IL-6, pulmonary transvascular protein permeability, and lung water content in response to LPS. We demonstrated that endothelial p120 modulates lung innate immune function by interfering with the association of TLR4 with its adaptor MyD88 to block TLR4 signaling and NF-κB activation in endothelial cells. In conclusion, these studies have uncovered a novel innate immune function of endothelial p120 in downregulating the lung inflammatory response to endotoxin through the suppression of TLR4 signaling.

ReCLIP (reversible cross-link immuno-precipitation): an efficient method for interrogation of labile protein complexes

The difficulty of maintaining intact protein complexes while minimizing non-specific background remains a significant limitation in proteomic studies. Labile interactions, such as the interaction between p120-catenin and the E-cadherin complex, are particularly challenging. Using the cadherin complex as a model-system, we have developed a procedure for efficient recovery of otherwise labile protein-protein interactions. We have named the procedure “ReCLIP” (Reversible Cross-Link Immuno-Precipitation) to reflect the primary elements of the method. Using cell-permeable, thiol-cleavable crosslinkers, normally labile interactions (i.e. p120 and E-cadherin) are stabilized in situ prior to isolation. After immunoprecipitation, crosslinked binding partners are selectively released and all other components of the procedure (i.e. beads, antibody, and p120 itself) are discarded. The end result is extremely efficient recovery with exceptionally low background. ReCLIP therefore appears to provide an excellent alternative to currently available affinity-purification approaches, particularly for studies of labile complexes.

p120-catenin is a binding partner and substrate for Group B Pak kinases

Pak5 is a member of the Group B p21-activated kinases, which are effectors of the Rho family GTPases Cdc42 and Rac. Pak5 has been shown to promote cytoskeletal reorganization, inducing filopodia formation and neurite outgrowth in neuroblastoma cells. In this study, we used affinity chromatography followed by SDS-PAGE and mass spectrometry to identify potential downstream effectors of Pak5. Using this approach, we isolated p120-catenin (p120), a known regulator of cytoskeletal reorganization and Rho GTPases. Using co-immunoprecipitation assays we found that p120 preferentially interacts with Pak5 among the Group B Paks. Results from immunofluorescence studies revealed that Pak5 and p120 co-localize in cells. Both Pak5 and constitutively active Pak4, the founding member of the Group B Paks, directly phosphorylate p120 in vitro. The phosphorylation was shown by Western blot and immunofluorescence to take place specifically on serine 288. This study is the first report of an upstream serine/threonine kinase that phosphorylates p120.

Xenopus Kazrin interacts with ARVCF-catenin, spectrin and p190B RhoGAP, and modulates RhoA activity and epithelial integrity

In common with other p120-catenin subfamily members, Xenopus ARVCF (xARVCF) binds cadherin cytoplasmic domains to enhance cadherin metabolic stability or, when dissociated, modulates Rho-family GTPases. We report here that xARVCF binds and is stabilized by Xenopus KazrinA (xKazrinA), a widely expressed conserved protein that bears little homology to established protein families, and which is known to influence keratinocyte proliferation and differentiation and cytoskeletal activity. Although we found that xKazrinA binds directly to xARVCF, we did not resolve xKazrinA within a larger ternary complex with cadherin, nor did it co-precipitate with core desmosomal components. Instead, screening revealed that xKazrinA binds spectrin, suggesting a potential means by which xKazrinA localizes to cell-cell borders. This was supported by the resolution of a ternary biochemical complex of xARVCF-xKazrinA-xβ2-spectrin and, in vivo, by the finding that ectodermal shedding followed depletion of xKazrin in Xenopus embryos, a phenotype partially rescued with exogenous xARVCF. Cell shedding appeared to be the consequence of RhoA activation, and thereby altered actin organization and cadherin function. Indeed, we also revealed that xKazrinA binds p190B RhoGAP, which was likewise capable of rescuing Kazrin depletion. Finally, xKazrinA was found to associate with δ-catenins and p0071-catenins but not with p120-catenin, suggesting that Kazrin interacts selectively with additional members of the p120-catenin subfamily. Taken together, our study supports the essential role of Kazrin in development, and reveals the biochemical and functional association of KazrinA with ARVCF-catenin, spectrin and p190B RhoGAP.

Integrated biochemical and mechanical signals regulate multifaceted human embryonic stem cell functions

Nonmuscle myosin IIA and p120-catenin control E-cadherin–mediated cell–cell adhesions essential for hESC pluripotency and long-term survival.

Human embryonic stem cells (ESCs [hESCs]) proliferate as colonies wherein individual cells are strongly adhered to one another. This architecture is linked to hESC self-renewal, pluripotency, and survival and depends on epithelial cadherin (E-cadherin), NMMIIA (nonmuscle myosin IIA), and p120-catenin. E-cadherin and p120-catenin work within a positive feedback loop that promotes localized accumulation of E-cadherin at intercellular junctions. NMMIIA stabilizes p120-catenin protein and controls E-cadherin–mediated intercellular adhesion. Perturbations of this signaling network disrupt colony formation, destabilize the transcriptional regulatory circuitry for pluripotency, and impair long-term survival of hESCs. Furthermore, depletion of E-cadherin markedly reduces the efficiency of reprogramming of human somatic cells to an ESC-like state. The feedback regulation and mechanical–biochemical integration provide mechanistic insights for the regulation of intercellular adhesion and cellular architecture in hESCs during long-term self-renewal. Our findings also contribute to the understanding of microenvironmental regulation of hESC identity and somatic reprogramming.

p120 regulates endothelial permeability independently of its NH2 terminus and Rho binding

The association of p120-catenin (p120) with the juxtamembrane domain (JMD) of vascular endothelial (VE)-cadherin is required to maintain VE-cadherin levels and transendothelial resistance (TEER) of endothelial cell monolayers. To distinguish whether decreased TEER was due to a loss of p120 and not to the decrease in VE-cadherin, we established a system in which p120 was depleted by short hairpin RNA delivered by lentivirus and VE-cadherin was restored via expression of VE-cadherin fused to green fluorescent protein (GFP). Loss of p120 resulted in decreased TEER, which was associated with decreased expression of VE-cadherin, β-catenin, plakoglobin, and α-catenin. Decreased TEER was rescued by restoration of p120 but not by the expression of VE-cadherin-GFP, despite localization of VE-cadherin-GFP at cell-cell borders. Expression of VE-cadherin-GFP restored levels of β-catenin and α-catenin but not plakoglobin, indicating that p120 may be important for recruitment of plakoglobin to the VE-cadherin complex. To evaluate the role of p120 interaction with Rho GTPase in regulating endothelial permeability, we expressed a recombinant form of p120, lacking the NH(2) terminus and containing alanine substitutions, that eliminates binding of Rho to p120. Expression of this isoform restored expression of the adherens junction complex and rescued permeability as measured by TEER. These results demonstrate that p120 is required for maintaining VE-cadherin expression and TEER independently of its NH(2) terminus and its role in regulating Rho.

Targeted p120-catenin ablation disrupts dental enamel development

Dental enamel development occurs in stages. The ameloblast cell layer is adjacent to, and is responsible for, enamel formation. When rodent pre-ameloblasts become tall columnar secretory-stage ameloblasts, they secrete enamel matrix proteins, and the ameloblasts start moving in rows that slide by one another. This movement is necessary to form the characteristic decussating enamel prism pattern. Thus, a dynamic system of intercellular interactions is required for proper enamel development. Cadherins are components of the adherens junction (AJ), and they span the cell membrane to mediate attachment to adjacent cells. p120 stabilizes cadherins by preventing their internalization and degradation. So, we asked if p120-mediated cadherin stability is important for dental enamel formation. Targeted p120 ablation in the mouse enamel organ had a striking effect. Secretory stage ameloblasts detached from surrounding tissues, lost polarity, flattened, and ameloblast E- and N-cadherin expression became undetectable by immunostaining. The enamel itself was poorly mineralized and appeared to be composed of a thin layer of merged spheres that abraded from the tooth. Significantly, p120 mosaic mouse teeth were capable of forming normal enamel demonstrating that the enamel defects were not a secondary effect of p120 ablation. Surprisingly, blood-filled sinusoids developed in random locations around the developing teeth. This has not been observed in other p120-ablated tissues and may be due to altered p120-mediated cell signaling. These data reveal a critical role for p120 in tooth and dental enamel development and are consistent with p120 directing the attachment and detachment of the secretory stage ameloblasts as they move in rows.

Alterations in the proteome of the NHERF1 knockout mouse jejunal brush border membrane vesicles

Na/H exchanger regulatory factor 1 (NHERF1) is a scaffold protein made up of two PDZ domains and an ERM binding domain. It is in the brush border of multiple epithelial cells where it modulates 1) Na absorption by regulating NHE3 complexes and cytoskeletal association, 2) Cl secretion through trafficking of CFTR, and 3) Na-coupled phosphate absorption through membrane retention of NaPi2a. To further understand the role of NHERF1 in regulation of small intestinal Na absorptive cell function, with emphasis on apical membrane transport regulation, quantitative proteomic analysis was performed on brush border membrane vesicles (BBMV) prepared from wild-type (WT) and homozygous NHERF1 knockout mouse jejunal villus Na absorptive cells. Jejunal architecture appeared normal in NHERF1 null; however, there was increased proliferative activity, as indicated by increased crypt BrdU staining. LC-MS/MS analysis using iTRAQ to compare WT and NHERF1 null BBMV identified 463 proteins present in both WT and NHERF1 null BBMV of simultaneously prepared and studied samples. Seventeen proteins had an altered amount of expression between WT and NHERF1 null in two or more separate preparations, and 149 total proteins were altered in at least one BBMV preparation. The classes of the majority of proteins altered included transport proteins, signaling and trafficking proteins, and proteins involved in proliferation and cell division. Affected proteins also included tight junction and adherens junction proteins, cytoskeletal proteins, as well as metabolic and BB digestive enzymes. Changes in abundance of several proteins were confirmed by immunoblotting [increased CEACAM1, decreased ezrin (p-ezrin), NHERF3, PLCβ3, E-cadherin, p120, β-catenin]. The changes in the jejunal BBMV proteome of NHERF1 null mice are consistent with a more complex role of NHERF1 than just forming signaling complexes and anchoring proteins to the apical membrane and include at least alterations in proteins involved in transport, signaling, and proliferation.

A p120-catenin-CK1epsilon complex regulates Wnt signaling

p120-catenin is an E-cadherin-associated protein that modulates E-cadherin function and stability. We describe here that p120-catenin is required for Wnt pathway signaling. p120-catenin binds and is phosphorylated by CK1ε in response to Wnt3a. p120-catenin also associates to the Wnt co-receptor LRP5/6, an interaction mediated by E-cadherin, showing an unexpected physical link between adherens junctions and a Wnt receptor. Depletion of p120-catenin abolishes CK1ε binding to LRP5/6 and prevents CK1ε activation upon Wnt3a stimulation. Elimination of p120-catenin also inhibits early responses to Wnt, such as LRP5/6 and Dvl-2 phosphorylation and axin recruitment to the signalosome, as well as later effects, such as β-catenin stabilization. Moreover, since CK1ε is also required for E-cadherin phosphorylation, a modification that decreases the affinity for β-catenin, p120-catenin depletion prevents the increase in β-catenin transcriptional activity even in the absence of β-catenin degradation. Therefore, these results demonstrate a novel and crucial function of p120-catenin in Wnt signaling and unveil additional points of regulation by this factor of β-catenin transcriptional activity different of β-catenin stability.

p120-catenin is essential for maintenance of barrier function and intestinal homeostasis in mice

Epithelial-cadherin (E-cadherin) is a master organizer of the epithelial phenotype. Its function is regulated in part by p120-catenin (referred to herein as p120), a cytoplasmic binding partner that directly regulates cadherin stability. As it has been suggested that cadherins have a role in inflammatory bowel disease (IBD), we sought to investigate this further by assessing the effect of p120 deficiency in mouse small intestine and colon. p120 conditional KO mice were superficially normal at birth but declined rapidly and died within 21 days. Cell-cell adhesion defects and inflammation led to progressive mucosal erosion and terminal bleeding, similar to what is observed in a dominant-negative cadherin mouse model of IBD. Additionally, selective loss of adherens junctions and accumulation of atypical COX-2-expressing neutrophils in p120-null areas of the colon were observed. To elucidate the mechanism, direct effects of p120 deficiency were assessed in vitro in a polarizing colon cancer cell line. Notably, transepithelial electrical resistance was dramatically reduced, neutrophil binding was increased 30 fold, and levels of COX-2, an enzyme associated with IBD, were markedly increased in neutrophils. Our data suggest that p120 loss disrupts the neonatal intestinal barrier and amplifies neutrophil engagement and that these changes lead to catastrophic inflammation during colonization of the neonatal gut with bacteria and other luminal antigens. Thus, we conclude that p120 has an essential role in barrier function and epithelial homeostasis and survival in the intestine.

p120-Catenin is required for mouse vascular development

RATIONALE

p120-catenin (p120) is an armadillo family protein that binds to the cytoplasmic domain of classical cadherins and prevents cadherin endocytosis. The role of p120 in vascular development is unknown.

OBJECTIVE

The purpose of this study is to examine the role of p120 in mammalian vascular development by generating a conditionally mutant mouse lacking endothelial p120 and determining the effects of the knockout on vasculogenesis, angiogenic remodeling, and the regulation of endothelial cadherin levels.

METHODS AND RESULTS

A conditional Cre/loxP gene deletion strategy was used to ablate p120 expression, using the Tie2 promoter to drive endothelial Cre recombinase expression. Mice lacking endothelial p120 died embryonically beginning at embryonic day 11.5. Major blood vessels appeared normal at embryonic day 9.5. However, both embryonic and extraembryonic vasculature of mutant animals were disorganized and displayed decreased microvascular density by embryonic day 11.5. Importantly, both vascular endothelial cadherin and N-cadherin levels were significantly reduced in vessels lacking p120. This decrease in cadherin expression was accompanied by reduced pericyte recruitment and hemorrhaging. Furthermore, p120-null cultured endothelial cells exhibited proliferation defects that could be rescued by exogenous expression of vascular endothelial cadherin.

CONCLUSIONS

These findings reveal a fundamental role for p120 in regulating endothelial cadherin levels during vascular development, as well as microvascular patterning, vessel integrity, and endothelial cell proliferation. Loss of endothelial p120 results in lethality attributable to decreased microvascular density and hemorrhages.

Microenvironmental independence associated with tumor progression

Tumor-microenvironment interactions are increasingly recognized to influence tumor progression. To understand the competitive dynamics of tumor cells in diverse microenvironments, we experimentally parameterized a hybrid discrete-continuum mathematical model with phenotypic trait data from a set of related mammary cell lines with normal, transformed, or tumorigenic properties. Surprisingly, in a resource-rich microenvironment, with few limitations on proliferation or migration, transformed (but not tumorigenic) cells were most successful and outcompeted other cell types in heterogeneous tumor simulations. Conversely, constrained microenvironments with limitations on space and/or growth factors gave a selective advantage to phenotypes derived from tumorigenic cell lines. Analysis of the relative performance of each phenotype in constrained versus unconstrained microenvironments revealed that, although all cell types grew more slowly in resource-constrained microenvironments, the most aggressive cells were least affected by microenvironmental constraints. A game theory model testing the relationship between microenvironment resource availability and competitive cellular dynamics supports the concept that microenvironmental independence is an advantageous cellular trait in resource-limited microenvironments.

An essential role for p120-catenin in Src- and Rac1-mediated anchorage-independent cell growth

p120-catenin regulates epithelial cadherin stability and has been suggested to function as a tumor suppressor. In this study, we used anchorage-independent growth (AIG), a classical in vitro tumorigenicity assay, to examine the role of p120 in a different context, namely oncogene-mediated tumorigenesis. Surprisingly, p120 ablation by short hairpin RNA completely blocked AIG induced by both Rac1 and Src. This role for p120 was traced to its activity in suppression of the RhoA-ROCK pathway, which appears to be essential for AIG. Remarkably, the AIG block associated with p120 ablation was completely reversed by inhibition of the downstream RhoA effector ROCK. Harvey-Ras (H-Ras)-induced AIG was also dependent on suppression of the ROCK cascade but was p120 independent because its action on the pathway occurred downstream of p120. The data suggest that p120 modulates oncogenic signaling pathways important for AIG. Although H-Ras bypasses p120, a unifying theme for all three oncogenes is the requirement to suppress ROCK, which may act as a gatekeeper for the transition to anchorage independence.

p120 and Kaiso regulate Helicobacter pylori-induced expression of matrix metalloproteinase-7

Helicobacter pylori is the strongest known risk factor for gastric adenocarcinoma, yet only a fraction of infected persons develop cancer. One H. pylori constituent that augments disease risk is the cytotoxin-associated gene (cag) pathogenicity island, which encodes a secretion system that translocates bacterial effector molecules into host cells. Matrix metalloproteinase (MMP)-7, a member of a family of enzymes with tumor-initiating properties, is overexpressed in premalignant and malignant gastric lesions, and H. pylori cag(+) strains selectively increase MMP-7 protein levels in gastric epithelial cells in vitro and in vivo. We now report that H. pylori-mediated mmp-7 induction is transcriptionally regulated via aberrant activation of p120-catenin (p120), a component of adherens junctions. H. pylori increases mmp-7 mRNA levels in a cag- and p120-dependent manner and induces translocation of p120 to the nucleus in vitro and in a novel ex vivo gastric gland culture system. Nuclear translocation of p120 in response to H. pylori relieves Kaiso-mediated transcriptional repression of mmp-7, which is implicated in tumorigenesis. These results indicate that selective and coordinated induction of mmp-7 expression by H. pylori cag(+) isolates may explain in part the augmentation in gastric cancer risk associated with these strains.