Strengthening E-cadherin adhesion via antibody-mediated binding stabilization.

E-cadherins (Ecads) are a crucial cell-cell adhesion protein with tumor suppression properties. Ecad adhesion can be enhanced by the monoclonal antibody 66E8, which has potential applications in inhibiting cancer metastasis. However, the biophysical mechanisms underlying 66E8-mediated adhesion strengthening are unknown. Here, we use molecular dynamics simulations, site-directed mutagenesis, and single-molecule atomic force microscopy experiments to demonstrate that 66E8 strengthens Ecad binding by stabilizing the primary Ecad adhesive conformation: the strand-swap dimer. By forming electrostatic interactions with Ecad, 66E8 stabilizes the swapped ß-strand and its hydrophobic pocket and impedes Ecad conformational changes, which are necessary for rupture of the strand-swap dimer. Our findings identify fundamental mechanistic principles for strengthening of Ecad binding using monoclonal antibodies.

Strengthening E-cadherin adhesion via antibody mediated binding stabilization.

E-cadherins (Ecads) are a crucial cell-cell adhesion protein with tumor suppression properties. Ecad adhesion can be enhanced by the monoclonal antibody 66E8, which has potential applications in inhibiting cancer metastasis. However, the biophysical mechanisms underlying 66E8 mediated adhesion strengthening are unknown. Here, we use molecular dynamics simulations, site directed mutagenesis and single molecule atomic force microscopy experiments to demonstrate that 66E8 strengthens Ecad binding by stabilizing the primary Ecad adhesive conformation: the strand-swap dimer. By forming electrostatic interactions with Ecad, 66E8 stabilizes the swapped ß-strand and its hydrophobic pocket and impedes Ecad conformational changes, which are necessary for rupture of the strand-swap dimer. Our findings identify fundamental mechanistic principles for strengthening of Ecad binding using monoclonal antibodies.

Remodeling of E-cadherin subcellular localization during cell dissemination.

Given the role of E-cadherin (E-cad) in holding epithelial cells together, an inverse relationship between E-cad levels and cell invasion during the epithelial-mesenchymal transition and cancer metastasis has been well recognized. Here we report that E-cad is necessary for the invasiveness of RasV12-transformed intestinal epithelial cells in Drosophila. E-cad/ß-catenin disassembles at adherens junctions and assembles at invasive protrusions--the actin- and cortactin-rich invadopodium-like protrusions associated with the breach of the extracellular matrix (ECM)--during dissemination of RasV12-transformed intestinal epithelial cells. Loss of E-cad impairs the elongation of invasive protrusions and attenuates the ability of RasV12-transformed cells to compromise the ECM. Notably, E-cad and cortactin affect each other's localization to invasive protrusions. Given the essential roles of cortactin in cell invasion, our observations indicate that E-cad plays a role in the invasiveness of RasV12-transformed intestinal epithelial cells by controlling cortactin localization to invasive protrusions. Thus our study demonstrates that E-cad is a component of invasive protrusions and provides molecular insights into the unconventional role of E-cad in cell dissemination in vivo.

Regulation of multiple dimeric states of E-cadherin by adhesion activating antibodies revealed through Cryo-EM and X-ray crystallography.

E-cadherin adhesion is regulated at the cell surface, a process that can be replicated by activating antibodies. We use cryo-electron microscopy (EM) and X-ray crystallography to examine functional states of the cadherin adhesive dimer. This dimer is mediated by N-terminal beta strand-swapping involving Trp2, and forms via a different transient X-dimer intermediate. X-dimers are observed in cryo-EM along with monomers and strand-swap dimers, indicating that X-dimers form stable interactions. A novel EC4-mediated dimer was also observed. Activating Fab binding caused no gross structural changes in E-cadherin monomers, but can facilitate strand swapping. Moreover, activating Fab binding is incompatible with the formation of the X-dimer. Both cryo-EM and X-ray crystallography reveal a distinctive twisted strand-swap dimer conformation caused by an outward shift in the N-terminal beta strand that may represent a strengthened state. Thus, regulation of adhesion involves changes in cadherin dimer configurations.

Molecular mechanism for strengthening E-cadherin adhesion using a monoclonal antibody.

E-cadherin (Ecad) is an essential cell-cell adhesion protein with tumor suppression properties. The adhesive state of Ecad can be modified by the monoclonal antibody 19A11, which has potential applications in reducing cancer metastasis. Using X-ray crystallography, we determine the structure of 19A11 Fab bound to Ecad and show that the antibody binds to the first extracellular domain of Ecad near its primary adhesive motif: the strand-swap dimer interface. Molecular dynamics simulations and single-molecule atomic force microscopy demonstrate that 19A11 interacts with Ecad in two distinct modes: one that strengthens the strand-swap dimer and one that does not alter adhesion. We show that adhesion is strengthened by the formation of a salt bridge between 19A11 and Ecad, which in turn stabilizes the swapped ß-strand and its complementary binding pocket. Our results identify mechanistic principles for engineering antibodies to enhance Ecad adhesion.

Reconstitution of the full transmembrane cadherin-catenin complex.

The dynamic regulation of epithelial adherens junctions relies on all components of the E-cadherin-catenin complex. Previously, the complexes have been partially reconstituted and composed only of α-catenin, ß-catenin, and the E-cadherin cytoplasmic domain. However, p120-catenin and the full-length E-cadherin including the extracellular, transmembrane, and intra-cellular domains are vital to the understanding of the relationship between extracellular adhesion and intracellular signaling. Here, we reconstitute the complete and full-length cadherin-catenin complex, including full-length E-cadherin, α-catenin, ß-catenin, and p120-catenin, into nanodiscs. We are able to observe the cadherin in nanodiscs by cryo-EM. We also reconstitute α-catenin, ß-catenin, and p120-catenin with the E-cadherin cytoplasmic tail alone in order to analyze the affinities of their binding interactions. We find that p120-catenin does not associate strongly with α- or ß-catenin and binds much more transiently to the cadherin cytoplasmic tail than does ß-catenin. Overall, this work creates many new possibilities for biochemical studies understanding transmembrane signaling of cadherins and the role of p120-catenin in adhesion activation.

E-cadherin activating antibodies limit barrier dysfunction and inflammation in mouse inflammatory bowel disease.

Deficits in gastrointestinal (GI) paracellular permeability has been implicated in etiology of Inflammatory Bowel Disease (IBD), and E-cadherin, a key component of the epithelial junctional complex, has been implicated in both barrier function and IBD. We have previously described antibodies against E-cadherin that activate cell adhesion, and in this study, we show that they increase transepithelial electrical resistance in epithelial cell monolayers in vitro. We therefore tested the hypothesis that adhesion activating E-cadherin mAbs will enhance epithelial barrier function in vivo and limit progression of inflammation in IBD. Activating mAbs to mouse E-cadherin were tested in different mouse models of IBD including the IL10-/- and adoptive T cell transfer models of colitis. Previously established histological and biomarker measures of inflammation were evaluated to monitor disease progression. Mouse E-cadherin activating mAb treatment reduced total colitis score, individual histological measures of inflammation, and other hallmarks of inflammation compared to control treatment. Activating mAbs also reduced the fecal accumulation lipocalin2 and albumin content, consistent with enhanced barrier function. Therefore, E-cadherin activation could be a potential strategy for limiting inflammation in UC.

Enhanced endothelial barrier function by monoclonal antibody activation of vascular endothelial cadherin.

Excessive vascular permeability occurs in inflammatory disease processes. Vascular endothelial cadherin (VE-cadherin) is an adhesion protein that controls vascular permeability. We identified monoclonal antibodies (mAbs) to human VE-cadherin that activate cell adhesion and inhibit the increased permeability of endothelial cell monolayers induced by thrombin receptor activator peptide-6 (TRAP-6). Two mAbs, 8A12c and 3A5a, reduce permeability, whereas an inhibitory mAb, 2E11d, enhances permeability. Activating mAbs also reduce permeability induced by tumor necrosis factor-α (TNF-α) and vascular endothelial cell growth factor (VEGF). The activating mAbs also stabilize the organization of the adherens junctions that are disrupted by TRAP-6, VEGF, or TNF-α. The activating mAbs act directly on the adhesive function of VE-cadherin because they did not block the accumulation of actin filaments stimulated by TRAP-6 and enhance physical cell-cell adhesion of VE-cadherin-expressing tissue culture cells. Therefore, VE-cadherin function can be regulated at the cell surface to control endothelial permeability.NEW & NOTEWORTHY Excessive vascular permeability is a serious complication of many inflammatory disease conditions. We have developed monoclonal antibodies that inhibit increases in endothelial monolayer permeability induced by several signaling factors by activating VE-cadherin mediated adhesion and stabilizing cell junctions. These antibodies and/or the mechanisms they reveal may lead to important therapeutics to treat vascular leakiness and inflammation.

p120-catenin phosphorylation status alters E-cadherin mediated cell adhesion and ability of tumor cells to metastasize.

p120-catenin is considered to be a tumor suppressor because it stabilizes E-cadherin levels at the cell surface. p120-catenin phosphorylation is increased in several types of cancer, but the role of phosphorylation in cancer is unknown. The phosphorylation state of p120-catenin is important in controlling E-cadherin homophilic binding strength which maintains epithelial junctions. Because decreased cell-cell adhesion is associated with increased cancer metastasis we hypothesize that p120-catenin phosphorylation at specific Serine and Threonine residues alters the E-cadherin binding strength between tumor cells and thereby affect the ability of tumor cells to leave the primary tumor and metastasize to distant sites. In this study we show that expression of the p120-catenin phosphorylation dead mutant, by converting six Serine and Threonine sites to Alanine, leads to enhanced E-cadherin adhesive binding strength in tumor cells. We observed a decrease in the ability of tumor cells expressing the p120-catenin phosphorylation mutant to migrate and invade using in-vitro models of cancer progression. Further, tumor cells expressing the phosphorylation mutant form of p120-catenin demonstrated a decrease in ability to metastasize to the lungs using an in-vivo orthotopic mammary fat pad injection model of breast cancer development and metastasis. This suggests that regulation of p120-catenin phosphorylation at the cell surface is important in mediating cell-adhesion, thereby impacting cancer progression and metastasis.

The functional activity of E-cadherin controls tumor cell metastasis at multiple steps.

E-cadherin is a tumor suppressor protein, and the loss of its expression in association with the epithelial mesenchymal transition (EMT) occurs frequently during tumor metastasis. However, many metastases continue to express E-cadherin, and a full EMT is not always necessary for metastasis; also, positive roles for E-cadherin expression in metastasis have been reported. We hypothesize instead that changes in the functional activity of E-cadherin expressed on tumor cells in response to environmental factors is an important determinant of the ability of the tumor cells to metastasize. We find that E-cadherin expression persists in metastatic lung nodules and circulating tumor cells (CTCs) in two mouse models of mammary cancer: genetically modified MMTV-PyMT mice and orthotopically grafted 4T1 tumor cells. Importantly, monoclonal antibodies that bind to and activate E-cadherin at the cell surface reduce lung metastasis from endogenous genetically driven tumors and from tumor cell grafts. E-cadherin activation inhibits metastasis at multiple stages, including the accumulation of CTCs from the primary tumor and the extravasation of tumor cells from the vasculature. These activating mAbs increase cell adhesion and reduce cell invasion and migration in both cell culture and three-dimensional spheroids grown from primary tumors. Moreover, activating mAbs increased the frequency of apoptotic cells without affecting proliferation. Although the growth of the primary tumors was unaffected by activating mAbs, CTCs and tumor cells in metastatic nodules exhibited increased apoptosis. Thus, the functional state of E-cadherin is an important determinant of metastatic potential beyond whether the gene is expressed.

Molecular Characterization of Familial Hypercholesterolemia in a North American Cohort.

BACKGROUND: Familial hypercholesterolemia (FH) confers a very high risk of premature cardiovascular disease and is commonly caused by mutations in low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), or proprotein convertase subtilisin/kexin type 9 (PCSK9) and very rarely in LDLR adaptor protein 1 (LDLRAP1) genes. OBJECTIVE: To determine the prevalence of pathogenic mutations in the LDLR, APOB, and PCSK9 in a cohort of subjects who met Simon Broome criteria for FH and compare the clinical characteristics of mutation-positive and mutation-negative subjects. METHODS: Ninety-three men and 107 women aged 19 to 80 years from lipid clinics in the United States and Canada participated. Demographic and historical data were collected, physical examination performed, and serum lipids/lipoproteins analyzed. Targeted sequencing analyses of LDLR and PCSK9 coding regions and exon 26 of APOB were performed followed by detection of LDLR deletions and duplications. RESULTS: Disease-causing LDLR and APOB variants were identified in 114 and 6 subjects, respectively. Of the 58 LDLR variants, 8 were novel mutations. Compared with mutation-positive subjects, mutation-negative subjects were older (mean 49 years vs 57 years, respectively) and had a higher proportion of African Americans (1% vs 12.5%), higher prevalence of hypertension (21% vs 46%), and higher serum triglycerides (median 86 mg/dL vs 122 mg/dL) levels. CONCLUSIONS: LDLR mutations were the most common cause of heterozygous FH in this North American cohort. A strikingly high proportion of FH subjects (40%) lacked mutations in known culprit genes. Identification of underlying genetic and environmental factors in mutation-negative patients is important to further our understanding of the metabolic basis of FH and other forms of severe hypercholesterolemia.

Cell contact and Nf2/Merlin-dependent regulation of TEAD palmitoylation and activity.

The Hippo pathway is involved in regulating contact inhibition of proliferation and organ size control and responds to various physical and biochemical stimuli. It is a kinase cascade that negatively regulates the activity of cotranscription factors YAP and TAZ, which interact with DNA binding transcription factors including TEAD and activate the expression of target genes. In this study, we show that the palmitoylation of TEAD, which controls the activity and stability of TEAD proteins, is actively regulated by cell density independent of Lats, the key kinase of the Hippo pathway. The expression of fatty acid synthase and acetyl-CoA carboxylase involved in de novo biosynthesis of palmitate is reduced by cell density in an Nf2/Merlin-dependent manner. Depalmitoylation of TEAD is mediated by depalmitoylases including APT2 and ABHD17A. Palmitoylation-deficient TEAD4 mutant is unstable and degraded by proteasome through the activity of the E3 ubiquitin ligase CHIP. These findings show that TEAD activity is tightly controlled through the regulation of palmitoylation and stability via the orchestration of FASN, depalmitoylases, and E3 ubiquitin ligase in response to cell contact.

Single and multiple ascending-dose study of glucagon-receptor antagonist RN909 in type 2 diabetes: a phase 1, randomized, double-blind, placebo-controlled trial.

PURPOSE: This first-in-human study assessed safety, immunogenicity, pharmacokinetics, and pharmacodynamics of RN909, a monoclonal antibody antagonist of the glucagon receptor, in type 2 diabetes (T2DM) subjects. METHODS: This study enrolled 84 T2DM subjects receiving stable metformin regimens. Forty-four subjects were randomized to receive single escalating doses of RN909 (0.3 to 6 mg/kg subcutaneously (SC), or 1 mg/kg intravenously (IV)), or placebo; 40 subjects were randomized to receive multiple escalating doses (50 to 150 mg SC) or placebo every 4 weeks for 12 weeks. RESULTS: RN909 was well tolerated; treatment-related elevated liver function tests (LFTs) were observed in 4/33 (12.1%) and 5/32 (15.6%) subjects treated with single and multiple doses, respectively, versus 1/10 (10%) and 0 in the respective placebo groups. RN909 dose-normalized AUCinf increased more than dose-proportionally following single SC doses, and after multiple doses, accumulation ratios ranged from 1.3 to 3.4. The incidence of antidrug antibodies (ADA) was 33% after single doses and 50% after multiple doses. RN909 produced dose-dependent, durable fasting plasma glucose (FPG)-lowering at day 29 (mean change -20.6 to -97.5 mg/dL) and day 85 (mean change; -27.2 to -43.5 mg/dL) after single and multiple doses, respectively. HbA1c also was reduced after single (mean change -0.30% to -1.44%), and multiple doses (-0.83% to -1.56%). CONCLUSION: RN909 was well tolerated after single and multiple doses in T2DM subjects, with diarrhea and elevated LFTs the most frequent adverse events. The appearance of ADA did not affect pharmacokinetics or efficacy. Robust lowering of FPG and HbA1c was observed.

E-cadherin in contact inhibition and cancer.

E-cadherin is a key component of the adherens junctions that are integral in cell adhesion and maintaining epithelial phenotype of cells. Homophilic E-cadherin binding between cells is important in mediating contact inhibition of proliferation when cells reach confluence. Loss of E-cadherin expression results in loss of contact inhibition and is associated with increased cell motility and advanced stages of cancer. In this review we discuss the role of E-cadherin and its downstream signaling in regulation of contact inhibition and the development and progression of cancer.

Effects of 12 weeks of treatment with intravenously administered bococizumab, a humanized monoclonal antibody blocking proprotein convertase subtilisin/kexin type 9, in hypercholesterolemic subjects on high-dose statin.

AIMS: Two multiple-dose phase II studies were conducted in subjects with primary hypercholesterolemia to evaluate the LDL-C lowering efficacy, safety, and tolerability of bococizumab, a proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor. METHODS: The results from the two phase II, double-blinded, randomized, placebo-controlled, multicenter studies conducted in the USA and Canada were combined. In Study 1, 90 subjects with LDL-C ≥100 mg/dL received intravenous (IV) placebo or bococizumab 0.25, 1, 3, or 6 mg/kg. In Study 2, 45 subjects with LDL-C ≥80 mg/dL received IV placebo or bococizumab 1 or 3 mg/kg. Subjects were treated every 4 weeks for 12 weeks. Dosing was interrupted if LDL-C dipped to ≤25 mg/dL and resumed if LDL-C returned to ≥40 mg/dL. The primary endpoint was percent LDL-C reduction from baseline at Week 12. RESULTS: At Week 12, the reductions from baseline in LDL-C vs placebo in the bococizumab 0.25, 1, 3, and 6 mg/kg groups were 9.3%, 10.2%, 41.6%, and 52.0%, respectively (P < .001 vs placebo for all). LDL-C reductions were greater (69.9%) in subjects who received all three doses of bococizumab 6 mg/kg (P < .001 vs placebo). Pharmacogenomic analysis revealed that 15% of hyperlipidemic subjects carried polymorphisms associated with familial hypercholesterolemia, with maximal LDL-C reductions being similar between carriers and noncarriers. Adverse events were mild, unrelated to bococizumab, and resolved by Week 12. CONCLUSIONS: These studies demonstrated that bococizumab safely and effectively lowered LDL-C in hypercholesterolemic subjects on high doses of statin.

The effects of single- and multiple-dose administration of bococizumab (RN316/PF-04950615), a humanized IgG2Δa monoclonal antibody binding proprotein convertase subtilisin/kexin type 9, in hypercholesterolemic subjects treated with and without atorvastatin: Results from four phase I studies.

AIMS: Three single-dose and one multiple-dose phase I studies were conducted in subjects with primary hypercholesterolemia to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of bococizumab, a proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor. METHODS: The dosing schedules for hypercholesterolemic subjects randomized in the four phase I studies were (1) ascending, single, intravenous (IV) bococizumab (0.3, 1, 3, 6, 12, or 18 mg/kg), or placebo (N = 48; baseline low-density lipoprotein cholesterol [LDL-C] ≥130 mg/dL); (2) single, IV bococizumab (0.5 or 4 mg/kg; no placebo) added to ongoing atorvastatin 40 mg/day (N = 24); (3) single, fixed, subcutaneous (SC) bococizumab (100 or 200 mg), or IV bococizumab (200 mg; no placebo; N = 49; baseline LDL-C ≥130 mg/dL); and (4) weekly IV bococizumab (0.25, 0.5, 1, or 1.5 mg/kg) or placebo for 4 weeks (N = 67; baseline LDL-C ≥130 mg/dL). RESULTS: Bococizumab pharmacokinetics were well characterized following single IV or SC doses and following multiple IV doses. Exposure to single-dose bococizumab increased slightly greater than dose-proportionally and clearance decreased with increasing dose. In the single-dose studies, maximal mean percent reductions from baseline in LDL-C ranged from 43% (0.3 mg/kg) to 84% (18 mg/kg) in bococizumab-treated subjects, compared with 2% for placebo. For the multiple-dose study, maximal reductions in LDL-C ranged from 55% (0.25 mg/kg) to 66% (1 mg/kg) in bococizumab-treated subjects, compared with 9% for placebo. In all studies, adverse events were infrequent, transient, and not dose-related. CONCLUSIONS: Bococizumab was generally safe and well tolerated. Bococizumab lowered LDL-C levels substantially in all four studies.

Effects of Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Inhibition with Bococizumab on Lipoprotein Particles in Hypercholesterolemic Subjects.

PURPOSE: Monoclonal antibody inhibitors of proprotein convertase subtilisin/kexin type 9 (PCSK9) elicit significant reductions in serum LDL-C levels. However, little is known about their effects on lipoprotein particles. The purpose of this analysis was to evaluate the effect of PCSK9 inhibition with bococizumab (RN316/PF-04950615), a humanized monoclonal antibody to PCSK9, on LDL, VLDL, and HDL particle concentration and size in hypercholesterolemic subjects. METHODS: Data from 3 double-blind, placebo-controlled, randomized studies were analyzed. In study 1, a total of 67 hypercholesterolemic subjects received IV placebo or bococizumab 0.25, 0.5, 1, or 1.5 mg/kg weekly for 4 weeks. In studies 2 and 3, a total of 135 hypercholesterolemic subjects taking statins received IV placebo or bococizumab 0.25, 1, 3, or 6 mg/kg monthly for 12 weeks. Lipoprotein particle concentration and size were measured by using nuclear magnetic resonance spectroscopy. FINDINGS: Overall, the majority of subjects were men (51.9%) aged >50 years of age and of white ethnic origin. In total, 189 subjects with both baseline and 2-week posttreatment data were included in the analysis. After PCSK9 inhibition with bococizumab 0.5, 1, 1.5, 3, and 6 mg/kg, concentrations of total LDL, total small LDL, and small VLDL particles decreased significantly versus baseline and placebo (P < 0.05), whereas concentrations of HDL particles increased (P < 0.05). The size of the LDL, VLDL, and HDL particles increased after PCSK9 inhibition. Reductions in LDL-C and total LDL particle concentrations were highly correlated. IMPLICATIONS: The effect of inhibiting PCSK9 with bococizumab on lipoprotein particle concentration and size are consistent with the general mechanism of PCSK9 inhibitors in blocking PCSK9-mediated downregulation of LDL receptors. PCSK9 inhibition has the potential to provide a clinical benefit through the modulation of atherogenic lipoprotein particles in addition to LDL-C lowering, and this effect will likely be assessed in future analyses of data from cardiovascular outcomes trials of PCSK9 monoclonal antibodies that are currently being conducted. ClinicalTrials.gov identifiers: NCT01243151, NCT01342211, and NCT01350141.

A Mechanism-Based Pharmacokinetic/Pharmacodynamic Model for Bococizumab, a Humanized Monoclonal Antibody Against Proprotein Convertase Subtilisin/Kexin Type 9, and Its Application in Early Clinical Development.

Bococizumab (RN316/PF-04950615), a humanized monoclonal antibody, binds to secreted proprotein convertase subtilisin/kexin type 9 (PCSK9) and prevents its downregulation of low-density lipoprotein receptor, leading to improved clearance and reduction of low-density lipoprotein cholesterol (LDL-C) in plasma. A mechanism-based drug-target binding model was developed, accounting for bococizumab, PCSK9, and LDL-C concentrations and the effects of concomitant administration of statins. This model was utilized to better understand the pharmacokinetic/pharmacodynamic (PK/PD) data obtained from 3 phase 1 and 2 phase 2a clinical studies. First, simulations performed with this model demonstrated that the conventional method of the area-under-the-curve ratio for bioavailability determination underestimated the subcutaneous bioavailability of bococizumab due to its target-mediated disposition. Second, a covariate model component for statin effects on bococizumab PK/PD was characterized, including a description of the decreased baseline LDL-C, increased baseline PCSK9, and increased LDL-C lowering with concomitant use of statins. Last, the impact of the dosing regimens with and without a dose holiday on bococizumab's LDL-C-lowering effectiveness was shown to be predictable due to the well-characterized PK-PD relationship.

Deregulation of the Hippo pathway in mouse mammary stem cells promotes mammary tumorigenesis.

The Hippo-YAP pathway mediates organ size control, contact inhibition, and tumorigenesis. It is a kinase cascade that inhibits the nuclear localization and transcriptional activities of YAP and TAZ. E-cadherin, cell junctions, polarity proteins, and the merlin/NF2 tumor suppressor activate the pathway to inhibit YAP/TAZ activity, while growth factor signaling inhibits the pathway to activate YAP/TAZ in the nucleus. We examined its role in the development of mouse mammary glands and tumor formation using gland reconstitution by transplantation of genetically modified mammary stem cells (MaSCs). Knockdown of YAP and TAZ with shRNA in MaSCs did not inhibit gland reconstitution. In contrast, knockdown of ß-catenin blocked gland reconstitution, consistent with the known role of Wnt signaling in mammary gland development. However, we find that Hippo signaling is involved in mammary tumor formation. Expression of a constitutively active form of YAP caused rapid formation of large tumors. Moreover, knockdown of YAP/TAZ slowed the development of tumors in polyoma middle T transgenic mice, a well-studied mammary tumor model involving activation of several signaling pathways. YAP accumulated in nuclei of mammary glands in ErbB2/EGFR-transgenic mice, suggesting that EGFR signaling affects YAP in vivo similar to cell culture. ErbB2/EGFR-transgenic mice develop mammary tumors in 7-8 months, but surprisingly, MaSCs from these mice did not form tumors when transplanted into host mice. Nonetheless, expression of dominant-negative Lats, which inhibits Hippo signaling, leads to tumor formation in ErbB2-transgenic mice, suggesting that Hippo signaling is involved in EGFR-induced mammary tumorigenesis.

Roles for E-cadherin cell surface regulation in cancer.

The loss of E-cadherin expression in association with the epithelial-mesenchymal transition (EMT) occurs frequently during tumor metastasis. However, metastases often retain E-cadherin expression, an EMT is not required for metastasis, and metastases can arise from clusters of tumor cells. We demonstrate that the regulation of the adhesive activity of E-cadherin present at the cell surface by an inside-out signaling mechanism is important in cancer. First, we find that the metastasis of an E-cadherin-expressing mammary cell line from the mammary gland to the lung depends on reduced E-cadherin adhesive function. An activating monoclonal antibody to E-cadherin that induces a high adhesive state significantly reduced the number of cells metastasized to the lung without affecting the growth in size of the primary tumor in the mammary gland. Second, we find that many cancer-associated germline missense mutations in the E-cadherin gene in patients with hereditary diffuse gastric cancer selectively affect the mechanism of inside-out cell surface regulation without inhibiting basic E-cadherin adhesion function. This suggests that genetic deficits in E-cadherin cell surface regulation contribute to cancer progression. Analysis of these mutations also provides insights into the molecular mechanisms underlying cadherin regulation at the cell surface.