Novel mesenchymal and haematopoietic cell isoforms of the SHP-2 docking receptor, PZR: identification, molecular cloning and effects on cell migration

Probing the Immunoreceptor Tyrosine-Based Inhibition Motif Interaction Protein Partners with Proteomics

Phosphorylation of tyrosine is the basic mode of protein function and signal transduction in organisms. This process is regulated by protein tyrosine kinases (PTKs) and protein tyrosinases (PTPs). Immunoreceptor tyrosine-based inhibition motif (ITIM) has been considered as regulating the PTP activity through the interaction with the partner proteins in the cell signal pathway. The ITIM sequences need to be phosphorylated first to active the downstream signaling proteins. To explore potential regulatory mechanisms, the ITIM sequences of two transmembrane immunoglobulin proteins, myelin P0 protein-related protein (PZR) and programmed death 1 (PD-1), were analyzed to investigate their interaction with proteins involved in regulatory pathways. We discovered that phosphorylated ITIM sequences can selectively interact with the tyrosine phosphatase SHP2. Specifically, PZR-N-ITIM (pY) may be critical in the interaction between the ITIM and SH2 domains of SHP2, while PD1-C-ITSM (pY) may play a key role in the interaction between the ITIM and SH2 domains of SHP2. Quite a few proteins were identified containing the SH2 domain, exhibiting phosphorylation-mediated interaction with PZR-ITIM. In this study, 14 proteins with SH2 structural domains were identified by GO analysis on 339 proteins associated to the affinity pull-down of PZR-N-ITIM (pY). Through the SH2 domains, these proteins may interact with PZR-ITIM in a phosphorylation-dependent manner.

RNA-Seq Analysis Reveals Altered Expression of Cell Adhesion-Related Genes Following PZR Knockout in Lung Cancer Cells

Protein zero related (PZR) serves as a substrate and anchor protein for SHP-2, the product of the proto-oncogene PTPN11 that is frequently mutated in cancers. The expression level of PZR is elevated in various cancers, which is correlated with an unfavorable prognosis. The role of PZR in lung cancer is not fully studied. To investigate how PZR affects signaling pathways involved in LUAD development, we utilized the CRISPR technology to knock out PZR expression in SPC-A1 lung adenocarcinoma cells and then conducted RNA sequencing to profile the transcriptome. Our results showed that 226 genes exhibited differential expressions in PZR-knockout SPC-A1 cells vs wild-type cells. Many of the genes encode proteins involved in cell adhesion, migration, actin cytoskeleton organization, and regulation of cell shape. Furthermore, our experimental data showed that PZR-knockout SPC-A1 cells displayed faster attachment to tissue culture dishes and slower detachment from the dishes upon EDTA treatment. The data suggest an important role of PZR in cell-matrix interaction and may provide new insights into the signaling events that regulate cancer development.

Veneer Is a Webtool for Rapid, Standardized, and Transparent Interpretation, Annotation, and Reporting of Mammalian Cell Surface N-Glycocapture Data

Currently, no consensus exists regarding criteria required to designate a protein within a proteomic data set as a cell surface protein. Most published proteomic studies rely on varied ontology annotations or computational predictions instead of experimental evidence when attributing protein localization. Consequently, standardized approaches for analyzing and reporting cell surface proteome data sets would increase confidence in localization claims and promote data use by other researchers. Recently, we developed Veneer, a web-based bioinformatic tool that analyzes results from cell surface N-glycocapture workflows─the most popular cell surface proteomics method used to date that generates experimental evidence of subcellular location. Veneer assigns protein localization based on defined experimental and bioinformatic evidence. In this study, we updated the criteria and process for assigning protein localization and added new functionality to Veneer. Results of Veneer analysis of 587 cell surface N-glycocapture data sets from 32 published studies demonstrate the importance of applying defined criteria when analyzing cell surface proteomics data sets and exemplify how Veneer can be used to assess experimental quality and facilitate data extraction for informing future biological studies and annotating public repositories.

PZR suppresses innate immune response to RNA viral infection by inhibiting MAVS activation in interferon signaling mediated by RIG-I and MDA5

RNA viral infections seriously endanger human health. Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 2 (SHP2) suppresses innate immunity against influenza A virus, and pharmacological inhibition of SHP2 provokes hepatic innate immunity. SHP2 binds and catalyzes tyrosyl dephosphorylation of protein zero-related (PZR), but the regulatory effect of PZR on innate immune response to viral infection is unclear. In this study, the transcription and protein level of PZR in host cells were found to be decreased with RNA viral infection, and high level of PZR was uncovered to inhibit interferon (IFN) signaling mediated by RIG-I and MDA5. Through localizing in mitochondria, PZR targeted and interacted with MAVS (also known as IPS-1/VISA/Cardif), suppressing the aggregation and activation of MAVS. Specifically, Y263 residue in ITIM is critical for PZR to exert immunosuppression under RNA viral infection. Moreover, the recruited SHP2 by PZR that modified with tyrosine phosphorylation under RNA viral infection might inhibit phosphorylation activation of MAVS. In conclusion, PZR and SHP2 suppress innate immune response to RNA viral infection through inhibiting MAVS activation. This study reveals the regulatory mechanism of PZR-SHP2-MAVS signal axis on IFN signaling mediated by RIG-I and MDA5, which may provide new sight for developing antiviral drugs.

SH2 domain-containing protein tyrosine phosphatase-2 (SHP-2) prevents cardiac remodeling after myocardial infarction through ERK/SMAD signaling pathway

In this study, we aimed to investigate the role of SH2 domain-containing protein tyrosine phosphatase-2 (SHP-2) in cardiac remodeling after myocardial infarction (MI) and explore the underlying molecular mechanism. MI model was established by ligation of the left anterior descending coronary artery. C57/BL6J mice were randomly administered with 3.0 mg/kg/day PHPS1 (PHPS1-treated group) or normal saline (model group) by intraperitoneal injection. After 4 weeks of infusion, the effects of PHPS1 on cardiac remodeling were evaluated. Echocardiography results showed that PHPS1 treatment aggravated the MI-induced deterioration of cardiac function, with worse cardiac function parameters. PHPS1 treatment significantly increased the infarcted area, as well as the fibrotic area and the expression of collagen I and collagen III. Western blots and immunofluorescence staining showed that PHPS1 treatment up-regulated the expression of p-GRK2, p-SMAD2/3 and p-ERK1/2, while U0126 reversed the effect of PHPS1. The present study indicated that PHPS1 treatment contributed to myocardial fibrosis and infarction by activating ERK/SMAD signaling pathway, suggesting that SHP-2 may be a promising treatment target for cardiac remodeling after MI.

Silencing myelin protein zero-like 1 expression suppresses cell proliferation and invasiveness of human glioma cells by inhibiting multiple cancer-associated signal pathways

Glioma is the most common primary malignant tumor of the adult central nervous system. It has high morbidity and poor survival. Myelin protein zero-like protein 1 (MPZL1) is a cell surface glycoprotein that activates numerous adhesion-dependent signaling pathways. MPZL1 plays important roles in human cancers that include metastatic process; however, it is not clear if MPZL1 plays a role in human glioma. Therefore, this study aimed to determine if silencing MPZL1 impacted the cell proliferative features of human glioma cells. First, MPZL1 expression was investigated in human glioma samples and tumor cell lines. Then the effects of small interfering RNA (siRNA)-targeting MPZL1 were analyzed on proliferation, colony formation, cell cycle progression, and invasion of human glioma cells. The results from this study demonstrated that MPZL1 was highly expressed in human glioma tissues and glioma cell lines. In addition, knockdown of MPZL1 significantly inhibited cell proliferation, colony formation, and invasiveness of glioma cells, and effectively induced cell cycle arrest at the G1 phase. Western blotting analysis indicated that silencing MPZL1 expression downregulated the expression of matrix metalloproteinase-2 (MMP-2), WNT1, caspase-3, cyclin A1, epidermal growth factor receptor (EGFR), and signal transducer and activator of transcription 3 (STAT3), and upregulated p53. The results from this study suggest that MPZL1 might be a marker for tumors and could be a potential therapeutic target for human glioma.

How Does Protein Zero Assemble Compact Myelin?

Myelin protein zero (P0), a type I transmembrane protein, is the most abundant protein in peripheral nervous system (PNS) myelin—the lipid-rich, periodic structure of membrane pairs that concentrically encloses long axonal segments. Schwann cells, the myelinating glia of the PNS, express P0 throughout their development until the formation of mature myelin. In the intramyelinic compartment, the immunoglobulin-like domain of P0 bridges apposing membranes via homophilic adhesion, forming, as revealed by electron microscopy, the electron-dense, double “intraperiod line” that is split by a narrow, electron-lucent space corresponding to the extracellular space between membrane pairs. The C-terminal tail of P0 adheres apposing membranes together in the narrow cytoplasmic compartment of compact myelin, much like myelin basic protein (MBP). In mouse models, the absence of P0, unlike that of MBP or P2, severely disturbs myelination. Therefore, P0 is the executive molecule of PNS myelin maturation. How and when P0 is trafficked and modified to enable myelin compaction, and how mutations that give rise to incurable peripheral neuropathies alter the function of P0, are currently open questions. The potential mechanisms of P0 function in myelination are discussed, providing a foundation for the understanding of mature myelin development and how it derails in peripheral neuropathies.

Combined Analysis of DNA Methylome and Transcriptome Reveal Novel Candidate Genes Related to Porcine Escherichia coli F4ab/ac-Induced Diarrhea

Enterotoxigenic Escherichia coli (ETEC) that express F4 (K88) fimbriae are the principal microorganisms responsible for bacterial diarrhea in neonatal and pre-weaning piglets. To better understand the molecular effects of ETEC F4ab/ac infection, we performed a genome-wide comparison of the changes in DNA methylation and gene expression in ETEC F4ab/ac infected porcine intestinal epithelial cells. We characterized the pattern of changes in methylation and found 3297 and 1593 differentially methylated regions in cells infected with F4ab and F4ac, respectively. Moreover, 606 and 780 differentially expressed genes (DEGs) in ETEC F4ab and F4ac infected cells were detected and these genes were highly enriched in immune/defense response related pathways. Integrative analysis identified 27 and 10 genes showing inverse correlations between promoter methylation and expression with ETEC F4ab/ac infection. Altered DNA methylation and expression of various genes suggested their roles and potential functional interactions upon ETEC F4ab/ac infection. Further functional analyses revealed that three DEGs (S100A9, SGO1, and ESPL1) in F4ab infected cells and three DEGs (MAP3K21, PAK6, and MPZL1) in F4ac infected cells are likely involved in the host cells response to ETEC infection. Our data provides further insight into the epigenetic and transcriptomic alterations of ETEC F4ab/ac infected porcine intestinal epithelial cells, and may advance the identification of biomarkers and drug targets for predicting susceptibility to and controlling ETEC F4ab/ac induced diarrhea.

P0-Related Protein Accelerates Human Mesenchymal Stromal Cell Migration by Modulating VLA-5 Interactions with Fibronectin

P₀-related protein (PZR), a Noonan and LEOPARD syndrome target, is a member of the transmembrane Immunoglobulin superfamily. Its cytoplasmic tail contains two immune-receptor tyrosine-based inhibitory motifs (ITIMs), implicated in adhesion-dependent signaling and regulating cell adhesion and motility. PZR promotes cell migration on the extracellular matrix (ECM) molecule, fibronectin, by interacting with SHP-2 (Src homology-2 domain-containing protein tyrosine phosphatase-2), a molecule essential for skeletal development and often mutated in Noonan and LEOPARD syndrome patients sharing overlapping musculoskeletal abnormalities and cardiac defects. To further explore the role of PZR, we assessed the expression of PZR and its ITIM-less isoform, PZRb, in human bone marrow mesenchymal stromal cells (hBM MSC), and its ability to facilitate adhesion to and spreading and migration on various ECM molecules. Furthermore, using siRNA knockdown, confocal microscopy, and immunoprecipitation assays, we assessed PZR and PZRb interactions with β1 integrins. PZR was the predominant isoform in hBM MSC. Migrating hBM MSCs interacted most effectively with fibronectin and required the association of PZR, but not PZRb, with the integrin, VLA-5(α5β1), leading to modulation of focal adhesion kinase phosphorylation and vinculin levels. This raises the possibility that dysregulation of PZR function may modify hBM MSC migratory behavior, potentially contributing to skeletal abnormalities.

Long Non-Coding RNA SPRY4-IT1 Reverses Cisplatin Resistance by Downregulating MPZL-1 via Suppressing EMT in NSCLC

Purpose

Long non-coding RNA (lncRNA) SPRY4 intronic transcript 1 (SPRY4-IT1) is reported to play important roles in the occurrence and development of many tumors. However, the possible role of SPRY4-IT1 in cisplatin (DDP) resistance of non-small-cell lung cancer (NSCLC) remains unclear. The aim of this study is to investigate the functions and molecular mechanisms underlying SPRY4-IT1 of cisplatin resistance in NSCLC.

Methods

Expression of SPRY4-IT1 was analyzed in A549 and cisplatin-resistant A549/DDP cell lines by quantitative real-time polymerase chain reaction (RT-qPCR). Overexpression techniques were applied to investigate the biological functions of SPRY4-IT1 in cisplatin-resistant A549/DDP cells. The effects of SPRY4-IT1 on proliferation and apoptosis were evaluated using cell counting kit-8 (CCK8) assays, colony formation assay and flow-cytometric analysis. The expressions of epithelial–mesenchymal transition (EMT)-associated proteins, including E-cadherin and Vimentin, were detected by Western blot. Microarray analysis was performed to identify the putative targets of SPRY4-IT1, which were further verified by Western blotting and RT-qPCR. A549/DDP cells transfected with pCDNA-SPRY4-IT1 were injected into nude mice in order to verify the effect of SPRY4-IT1 on cisplatin resistance in vivo.

Results

The present study demonstrated that SPRY4-IT1 expression was decreased in A549/DDP cells compared with parental A549 cells. Upregulation of SPRY4-IT1 suppressed cell proliferation and caused apoptosis of A549/DDP cells both in vitro and in vivo. MPZL-1 was negatively regulated by SPRY4-IT1. Furthermore, upregulation of SPRY4-IT1 and downregulation of MPZL-1 could suppress epithelial–mesenchymal transition (EMT), which was characterized by increased E-cadherin expression and decreased Vimentin expression.

Conclusion

Upregulation of SPRY4-IT1 reversed the cisplatin-resistant phenotype of NSCLC partially by downregulating MPZL-1 via inhibiting EMT process.

MPZL1 is highly expressed in advanced gallbladder carcinoma and promotes the aggressive behavior of human gallbladder carcinoma GBC‑SD cells

Myelin protein 0‑like 1 (MPZL1) has been reported to have a role in hepatocellular carcinoma. However, to the best of our knowledge, there have been no studies on the function and molecular mechanism of MPZL1 gene in gallbladder carcinoma. The present study confirmed that MPZL1 was upregulated in four gallbladder carcinoma tissues according to the mRNA microarray analysis. The results of the immunohistochemical analysis of tissues from 82 patients with gallbladder carcinoma demonstrated that patients with advanced tumor stages (both T and N stage) had higher positive expression of MPZL1. Moreover, a total of 20 cases of gallbladder carcinoma and matched paired paracarcinoma tissues along with 20 samples of healthy gallbladder tissue from patients with cholecystitis were analyzed using reverse transcription‑quantitative PCR and western blotting. The results demonstrated that the expression of MPZL1 in gallbladder carcinoma tissues was significantly higher than that of paired paracarcinoma tissues and randomly matched normal gallbladder epithelial tissues. According to the Tumor‑Node‑Metastasis classification, the expression level of MPZL1 protein in stage IV gallbladder carcinoma was significantly higher than that in stage III gallbladder carcinoma. The enhanced expression of MPZL1 gene appeared to improve the migration ability of GBC‑SD cells. Conversely, GBC‑SD cells that transfected with MPZL1 siRNA exhibited decreased migration ability. The results of proliferation experiments showed that the knockdown of MPZL1 siRNA caused impairments in GBC‑SD cell proliferation. On the contrary, the overexpression of MPZL1 increased the proliferation ability of GBC‑SD cells. The results of flow cytometry analyses indicated that the upregulation of MPZL1 had an anti‑apoptotic effect on GBC‑SD cells. In conclusion, the present study showed that the expression and protein levels of MPZL1 were significantly higher in gallbladder carcinoma tissues, especially in patients diagnosed with advanced tumor stages. Overexpression of MPZL1 may have promoted the invasion, metastasis, proliferation and survival of GBC‑SD cells.

Endocervical trophoblast for interrogating the fetal genome and assessing pregnancy health at five weeks

Prenatal testing for fetal genetic traits and risk of obstetrical complications is essential for maternal-fetal healthcare. The migration of extravillous trophoblast (EVT) cells from the placenta into the reproductive tract and accumulation in the cervix offers an exciting avenue for prenatal testing and monitoring placental function. These cells are obtained with a cervical cytobrush, a routine relatively safe clinical procedure during pregnancy, according to published studies and our own observations. Trophoblast retrieval and isolation from the cervix (TRIC) obtains hundreds of fetal cells with >90% purity as early as five weeks of gestation. TRIC can provide DNA for fetal genotyping by targeted next-generation sequencing with single-nucleotide resolution. Previously, we found that known protein biomarkers are dysregulated in EVT cells obtained by TRIC in the first trimester from women who miscarry or later develop intrauterine growth restriction or preeclampsia. We have now optimized methods to stabilize RNA during TRIC for subsequent isolation and analysis of trophoblast gene expression. Here, we report transcriptomics analysis demonstrating that the expression profile of TRIC-isolated trophoblast cells was distinct from that of maternal cervical cells and included genes associated with the EVT phenotype and invasion. Because EVT cells are responsible for remodeling the maternal arteries and their failure is associated with pregnancy disorders, their molecular profiles could reflect maternal risk, as well as mechanisms underlying these disorders. The use of TRIC to analyze EVT genomes, transcriptomes and proteomes during ongoing pregnancies could provide new tools for anticipating and managing both fetal genetic and maternal obstetric disorders.

PZR promotes metastasis of colorectal cancer through increasing FAK and Src phosphorylation

Metastasis is the main cause of death in patients with colorectal cancer (CRC), but the molecular mechanism is not yet fully understood. Previous studies have shown that P zero-related protein (PZR), a member of the immunoglobulin family, can promote fibronectin-dependent migration of mouse embryonic fibroblasts as well as invasion and metastasis of hepatic carcinoma cells. However, the role of PZR in CRC remains unclear. In this study, we determined the ectopic expression of PZR in CRC tissues, and results showed that PZR expression was increased not only in tumors with higher pathological stage, but also in tumors with distant metastasis. Through PZR-knockdown and overexpression in CRC cell lines, we found that the expression of PZR had significant effect on the invasion and migration of CRC cells as well as the phosphorylation of pro-metastasis proteins including focal adhesion kinase (FAK) and Src. Taken together, this study indicates that PZR may promote the invasion and migration of CRC cells through increasing the phosphorylation of FAK and Src, which provides a new theoretical basis and a possible marker for the diagnosis or prognosis of CRC metastasis.

Structural and biochemical studies of the extracellular domain of Myelin protein zero-like protein 1

Myelin protein zero-like protein 1 (MPZL1) is a member of the immunoglobulin superfamily, and is also a receptor of concanavalin A (ConA). MPZL1 is upregulated in hepatocellular carcinoma (HCC) and accelerates migration of HCC cells. However, function of MPZL1 as a receptor of ConA and its role in HCC development are largely unknown. To elucidate the functional basis, we have determined the crystal structure of the extracellular domain of MPZL1 at 2.7 Å resolution. Overall, it folds like a typical immunoglobulin variable-like domain that is much like MPZ. Unexpectedly, we found Asn50 is a unique glycosylation site and the glycosylation mediates its interaction with ConA. Furthermore, we also found that MPZL1 exists as a homodimer in the crystal, in which hydrogen bonds between Ser86 and Val145 play an important role. Our results demonstrate that glycosylation of Asn50 is essential for its function as a receptor of ConA. We propose that dimerization of MPZL1 participates in control of its signal transmission in cell adhesion.

An endogenous retroviral envelope syncytin and its cognate receptor identified in the viviparous placental Mabuya lizard

Syncytins are envelope genes from endogenous retroviruses that have been captured during evolution for a function in placentation. They have been found in all placental mammals in which they have been searched, including marsupials. Placental structures are not restricted to mammals but also emerged in some other vertebrates, most frequently in lizards, such as the viviparous Mabuya Scincidae. Here, we performed high-throughput RNA sequencing of a Mabuya placenta transcriptome and screened for the presence of retroviral env genes with a full-length ORF. We identified one such gene, which we named "syncytin-Mab1," that has all the characteristics expected for a syncytin gene. It encodes a membrane-bound envelope protein with fusogenic activity ex vivo, is expressed at the placental level as revealed by in situ hybridization and immunohistochemistry, and is conserved in all Mabuya species tested, spanning over 25 My of evolution. Its cognate receptor, required for its fusogenic activity, was searched for by a screening assay using the GeneBridge4 human/Chinese hamster radiation hybrid panel and found to be the MPZL1 gene, previously identified in mammals as a signal-transducing transmembrane protein involved in cell migration. Together, these results show that syncytin capture is not restricted to placental mammals, but can also take place in the rare nonmammalian vertebrates in which a viviparous placentotrophic mode of reproduction emerged. It suggests that similar molecular tools have been used for the convergent evolution of placentation in independently evolved and highly distant vertebrates.

MPZL1 forms a signalling complex with GRB2 adaptor and PTPN11 phosphatase in HER2-positive breast cancer cells

HER2/ErbB2 is overexpressed in a significant fraction of breast tumours and is associated with a poor prognosis. The adaptor protein GRB2 interacts directly with activated HER2 and is sufficient to transmit oncogenic signals. However, the consequence of HER2 activation on global GRB2 signalling networks is poorly characterized. We performed GRB2 affinity purification combined with mass spectrometry analysis of associated proteins in a HER2+ breast cancer model to delineate GRB2-nucleated protein interaction networks. We report the identification of the transmembrane protein MPZL1 as a new GRB2-associated protein. Our data show that the PTPN11 tyrosine phosphatase acts as a scaffold to bridge the association between GRB2 and MPZL1 in a phosphotyrosine-dependent manner. We further demonstrate that the formation of this MPZL1-PTPN11-GRB2 complex is triggered by cell attachment to fibronectin. Thus, our data support the importance of this new signalling complex in the control of cell adhesion of HER2+ breast cancer cells, a key feature of the metastatic process.

Low-dose dasatinib rescues cardiac function in Noonan syndrome

Noonan syndrome (NS) is a common autosomal dominant disorder that presents with short stature, craniofacial dysmorphism, and cardiac abnormalities. Activating mutations in the PTPN11 gene encoding for the Src homology 2 (SH2) domain-containing protein tyrosine phosphatase-2 (SHP2) causes approximately 50% of NS cases. In contrast, NS with multiple lentigines (NSML) is caused by mutations that inactivate SHP2, but it exhibits some overlapping abnormalities with NS. Protein zero-related (PZR) is a SHP2-binding protein that is hyper-tyrosyl phosphorylated in the hearts of mice from NS and NSML, suggesting that PZR and the tyrosine kinase that catalyzes its phosphorylation represent common targets for these diseases. We show that the tyrosine kinase inhibitor, dasatinib, at doses orders of magnitude lower than that used for its anticancer activities inhibited PZR tyrosyl phosphorylation in the hearts of NS mice. Low-dose dasatinib treatment of NS mice markedly improved cardiomyocyte contractility and functionality. Remarkably, a low dose of dasatinib reversed the expression levels of molecular markers of cardiomyopathy and reduced cardiac fibrosis in NS and NSML mice. These results suggest that PZR/SHP2 signaling is a common target of both NS and NSML and that low-dose dasatinib may represent a unifying therapy for the treatment of PTPN11-related cardiomyopathies.

Kinome-wide screening of HER2+ breast cancer cells for molecules that mediate cell proliferation or sensitize cells to trastuzumab therapy

Understanding the signaling differences that distinguish human HER2-amplified (HER2-positive (HER2+)) breast cancers from other breast cancer subtypes may help to identify protein drug targets for the specific treatment of HER2+ breast cancers. We performed two kinome-wide small interfering RNA (siRNA) screens on five HER2+ breast cancer cell lines, seven breast cancer cell lines in which HER2 was not amplified and two normal breast cell lines. To pinpoint the main kinases driving HER2 signaling, we performed a comprehensive siRNA screen that identified loss of the HER2/HER3 heterodimer as having the most prominent inhibitory effect on the growth of HER2+ breast cancer cells. In a second siRNA screen focused on identifying genes that could sensitize HER2+ cells to trastuzumab treatment, we found that loss of signaling members downstream of phosphatidylinositol 3 kinase (PI3K) potentiated the growth inhibitory effects of trastuzumab. Loss of HER2 and HER3, as well as proteins involved in mitogenic and environmental stress pathways inhibited the proliferation of HER2+ cells only in the absence of trastuzumab, suggesting that these pathways are inhibited by trastuzumab treatment. Loss of essential G2/M cell cycle mediators or proteins involved in vesicle organization exerted inhibitory effects on HER2+ cell growth that were unaffected by trastuzumab. Furthermore, the use of a sensitization index (SI) identified targeting the PI3K pathway to sensitize to trastuzumab treatment. Antagonism using the SI identified MYO3A, MYO3B and MPZL1 as antagonizers to trastuzumab treatment among HER2+ cell lines. Our results suggest that the dimerization partners of HER2 are important for determining the activation of downstream proliferation pathways. Understanding the complex layers of signaling triggered downstream of HER2 homodimers and heterodimers will facilitate the selection of better targets for combination therapies intended to treat HER2+ breast cancers.

PZR coordinates Shp2 Noonan and LEOPARD syndrome signaling in zebrafish and mice

Noonan syndrome (NS) is an autosomal dominant disorder caused by activating mutations in the PTPN11 gene encoding Shp2, which manifests in congenital heart disease, short stature, and facial dysmorphia. The complexity of Shp2 signaling is exemplified by the observation that LEOPARD syndrome (LS) patients possess inactivating PTPN11 mutations yet exhibit similar symptoms to NS. Here, we identify "protein zero-related" (PZR), a transmembrane glycoprotein that interfaces with the extracellular matrix to promote cell migration, as a major hyper-tyrosyl-phosphorylated protein in mouse and zebrafish models of NS and LS. PZR hyper-tyrosyl phosphorylation is facilitated in a phosphatase-independent manner by enhanced Src recruitment to NS and LS Shp2. In zebrafish, PZR overexpression recapitulated NS and LS phenotypes. PZR was required for zebrafish gastrulation in a manner dependent upon PZR tyrosyl phosphorylation. Hence, we identify PZR as an NS and LS target. Enhanced PZR-mediated membrane recruitment of Shp2 serves as a common mechanism to direct overlapping pathophysiological characteristics of these PTPN11 mutations.

Amplification of MPZL1/PZR promotes tumor cell migration through Src-mediated phosphorylation of cortactin in hepatocellular carcinoma

We have previously identified 1 241 regions of somatic copy number alterations (CNAs) in hepatocellular carcinoma (HCC). In the present study, we found that a novel recurrent focal amplicon, 1q24.1-24.2, targets the MPZL1 gene in HCC. Notably, there is a positive correlation between the expression levels of MPZL1 and intrahepatic metastasis of the HCC specimens. MPZL1 can significantly enhance the migratory and metastatic potential of the HCC cells. Moreover, we found that one of the mechanisms by which MPZL1 promotes HCC cell migration is by inducing the phosphorylation and activation of the pro-metastatic protein, cortactin. Additionally, we found that Src kinase mediates the phosphorylation and activation of cortactin induced by MPZL1 overexpression. Taken together, these findings suggest that MPZL1 is a novel pro-metastatic gene targeted by a recurrent region of copy number amplification at 1q24.1-24.2 in HCC.

In vitro and in vivo properties of distinct populations of amniotic fluid mesenchymal progenitor cells

Human mesenchymal progenitor cells (MPCs) are considered to be of great promise for use in tissue repair and regenerative medicine. MPCs represent multipotent adherent cells, able to give rise to multiple mesenchymal lineages such as osteoblasts, adipocytes or chondrocytes. Recently, we identified and characterized human second trimester amniotic fluid (AF) as a novel source of MPCs. Herein, we found that early colonies of AF-MPCs consisted of two morphologically distinct adherent cell types, termed as spindle-shaped (SS) and round-shaped (RS). A detailed analysis of these two populations showed that SS-AF-MPCs expressed CD90 antigen in a higher level and exhibited a greater proliferation and differentiation potential. To characterize better the molecular identity of these two populations, we have generated a comparative proteomic map of SS-AF-MPCs and RS-AF-MPCs, identifying 25 differentially expressed proteins and 10 proteins uniquely expressed in RS-AF-MPCs. Furthermore, SS-AF-MPCs exhibited significantly higher migration ability on extracellular matrices, such as fibronectin and laminin in vitro, compared to RS-AF-MPCs and thus we further evaluated SS-AF-MPCs for potential use as therapeutic tools in vivo. Therefore, we tested whether GFP-lentiviral transduced SS-AF-MPCs retained their stem cell identity, proliferation and differentiation potential. GFP-SS-AF-MPCs were then successfully delivered into immunosuppressed mice, distributed in different tissues and survived longterm in vivo. In summary, these results demonstrated that AF-MPCs consisted of at least two different MPC populations. In addition, SS-AF-MPCs, isolated based on their colony morphology and CD90 expression, represented the only MPC population that can be expanded easily in culture and used as an efficient tool for future in vivo therapeutic applications.

Embryonic corneal Schwann cells express some Schwann cell marker mRNAs, but no mature Schwann cell marker proteins

PURPOSE

Embryonic chick nerves encircle the cornea in pericorneal tissue until embryonic day (E)9, then penetrate the anterior corneal stroma, invade the epithelium, and branch over the corneal surface through E20. Adult corneal nerves, cut during transplantation or LASIK, never fully regenerate. Schwann cells (SCs) protect nerve fibers and augment nerve repair. This study evaluates SC differentiation in embryonic chick corneas.

METHODS

Fertile chicken eggs were incubated from E0 at 38 degrees C, 45% humidity. Dissected permeabilized corneas plus pericorneal tissue were immunostained for SC marker proteins. Other corneas were paraffin embedded, sectioned, and processed by in situ hybridization for corneal-, nerve-related, and SC marker gene expression. E9 to E20 corneas, dissected from pericorneal tissue, were assessed by real-time PCR (QPCR) for mRNA expression.

RESULTS

QPCR revealed unchanging low to moderate SLIT2/ROBO and NTN/UNC5 family, BACE1, and CADM3/CADM4 expressions, but high NEO1 expression. EGR2 and POU3F1 expressions never surpassed PAX3 expression. ITGNA6/ITGNB4 expressions increased 20-fold; ITGNB1 expression was high. SC marker S100 and MBP expressions increased; MAG, GFAP, and SCMP expressions were very low. Antibodies against the MPZ, MAG, S100, and SCMP proteins immunostained along pericorneal nerves, but not along corneal nerves. In the cornea, SLIT2 and SOX10 mRNAs were expressed in anterior stroma and epithelium, whereas PAX3, S100, MBP, and MPZL1 mRNAs were expressed only in corneal epithelium.

CONCLUSIONS

Embryonic chick corneas contain SCs, as defined by SOX10 and PAX3 transcription, which remain immature, at least in part because of stromal transcriptional and epithelial translational regulation of some SC marker gene expression.

Phosphorylation and localization of protein-zero related (PZR) in cultured endothelial cells

Protein-zero related (PZR) is an immunoglobulin V (IgV)-type immunoreceptor with two immunoreceptor tyrosine-based inhibitory motifs (ITIMs). PZR interacts with Src homology 2 domain-containing tyrosine phosphatase (SHP-2) via its tyrosine-phosphorylated ITIMs, for which c-Src is a putative kinase. Towards elucidating PZR function in endothelial cells (ECs), the authors cloned PZR from bovine aortic endothelial cells (BAECs) and characterized it. Mature bovine PZR had 94.8% and 92.7% sequence identity with canine and human proteins, respectively, and the two ITIM sequences were conserved among higher vertebrates. PZR was expressed in many cell types and was localized to cell contacts and intracellular granules in BAECs and mesothelioma (REN) cells. Coimmunoprecipitation revealed that PZR, Grb-2-associated binder-1 (Gab1), and platelet endothelial cell adhesion molecule-1 (PECAM-1) were three major SHP-2-binding proteins in BAECs. H(2)O(2) enhanced PZR tyrosine phosphorylation and PZR/SHP-2 interaction in ECs in a dose-and time-dependent manner. To see if tyrosine kinases other than Src are also capable of phosphorylating PZR, the authors cotransfected HEK293 cells with PZR and one of several tyrosine kinases and found that c-Src, c-Fyn, c-Lyn, Csk, and c-Abl, but not c-Fes, phosphorylated PZR and increased PZR/SHP-2 interaction. These results suggest that PZR is a cell adhesion protein that may be involved in SHP-2-dependent signaling at interendothelial cell contacts.

Noonan syndrome-associated SHP-2/Ptpn11 mutants enhance SIRPalpha and PZR tyrosyl phosphorylation and promote adhesion-mediated ERK activation

Noonan syndrome (NS) is an autosomal dominant disorder that is associated with multiple developmental abnormalities. Activated mutations of the protein-tyrosine phosphatase, SHP-2/PTPN11, have been reported in approximately 50% of NS cases. Despite being activated, NS-associated SHP-2 mutants require plasma membrane proximity to evoke disease-associated signaling. Here we show that NS-associated SHP-2 mutants induce hypertyrosyl phosphorylation of the transmembrane glycoproteins, SIRPalpha (signal-regulatory protein alpha) and PZR (protein zero-related), resulting in their increased association with NS-associated SHP-2 mutants. NS-associated SHP-2 mutants enhanced SIRPalpha and PZR tyrosyl phosphorylation either by impairing SIRPalpha dephosphorylation or by promoting PZR tyrosyl phosphorylation. Importantly, during embryogenesis in a mouse model of NS, SIRPalpha and PZR were hypertyrosyl-phosphorylated and bound increased levels of the NS-associated SHP-2 mutant. SIRPalpha and PZR have been implicated in extracellular matrix-dependent signaling. Mouse embryonic fibroblasts derived from a mouse model of NS displayed enhanced ERK activation in response to fibronectin plating. Knockdown of SIRPalpha and PZR in these cells attenuated the enhanced activation of ERK following fibronectin plating. Thus, SIRPalpha and PZR serve as scaffolds that facilitate plasma membrane recruitment and signaling of NS-associated SHP-2 mutants.

Molecular and proteomic characterization of human mesenchymal stem cells derived from amniotic fluid: comparison to bone marrow mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) constitute a population of multipotent adherent cells able to give rise to multiple mesenchymal lineages such as osteoblasts, adipocytes, or chondrocytes. So far, the most common source of MSCs has been the bone marrow (BM); however BM-MSC harvesting and processing exhibits major drawbacks and limitations. Thus, identification and characterization of alternative sources of MSCs are of great importance. In the present study, we isolated and expanded fetal MSCs from second-trimester amniotic fluid (AF). We documented that these cells are of embryonic origin, can differentiate under appropriate conditions into cell types derived from all three germ layers, and express the pluripotency marker Oct-4, the human Nanog protein, and the stage-specific embryonic antigen-4 (SSEA-4). Furthermore, we systematically tested the immunophenotype of cultured MSCs by flow cytometry analysis using a wide variety of markers. Direct comparison of this phenotype to the one derived from cultured BM-MSCs demonstrated that cultured MSCs from both sources exhibit similar expression patterns. Using the two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) approach, we have generated for the first time the protein map of cultured AF-MSCs by identifying 261 proteins, and we compared it directly to that of cultured BM-MSCs. The functional pattern of the identified proteins from both sources was similar. However, cultured AF-MSCs displayed a number of unique proteins related to proliferation and primitive phenotype, which may confer to the distinct features of the two types. Considering the easy access to this new cell source and the yield of expanded MSCs for stem cell research, AF may provide an excellent source of MSCs both for basic research and for potential therapeutic applications.

The murine ortholog of the SHP-2 binding molecule, PZR accelerates cell migration on fibronectin and is expressed in early embryo formation

The human P zero-related protein (hPZR) has a unique function in regulating cell migration. This activity is dependent on both its cytoplasmic immunoreceptor tyrosine inhibitory motif (ITIM) and its interaction with the tyrosine protein phosphatase, src homology phosphatase-2 (SHP-2). Here, using in silico and cDNA cloning approaches, we identify the murine ITIM-containing hPZR ortholog, mPZR, together with its ITIM-less isoform, mPZRb. We demonstrate that, like hPZR, these type 1 integral murine transmembrane isoforms are derived by differential splicing from a single gene transcription unit on mouse chromosome 1, and differ only in the sequence of their cytoplasmic domains. Importantly, mPZR mimicks hPZR functionally by accelerating SHP-2-mediated cell migration on fibronectin. Interestingly, we further demonstrate that although neither mPZR nor mPZRb is expressed in murine pluripotent embryonic stem cells, they first appear at approximately day 3 of blastocyst formation in vivo and of embryoid body formation in vitro. These studies thus provide the basis for defining the function of the mPZR isoforms in vivo, particularly with respect to their roles in regulating SHP-2-dependent cell migration during development.

Transcriptional profiling of human cord blood CD133+ and cultured bone marrow mesenchymal stem cells in response to hypoxia

Umbilical cord blood (UCB) and bone marrow (BM)-derived stem and progenitor cells possess two characteristics required for successful tissue regeneration: extensive proliferative capacity and the ability to differentiate into multiple cell lineages. Within the normal BM and in pathological conditions, areas of hypoxia may have a role in maintaining stem cell fate or determining the fine equilibrium between their proliferation and differentiation. In this study, the transcriptional profiles and proliferation and differentiation potential of UCB CD133(+) cells and BM mesenchymal cells (BMMC) exposed to normoxia and hypoxia were analyzed and compared. Both progenitor cell populations responded to hypoxic stimuli by stabilizing the hypoxia inducible factor (HIF)-1alpha protein. Short exposures to hypoxia increased the clonogenic myeloid capacity of UCB CD133(+) cells and promoted a significant increase in BMMC number. The differentiation potential of UCB CD133(+) clonogenic myeloid cells was unaltered by short exposures to hypoxia. In contrast, the chondrogenic differentiation potential of BMMCs was enhanced by hypoxia, whereas adipogenesis and osteogenesis were unaltered. When their transcriptional profiles were compared, 183 genes in UCB CD133(+) cells and 45 genes in BMMC were differentially regulated by hypoxia. These genes included known hypoxia-responsive targets such as BNIP3, PGK1, ENO2, and VEGFA, and other genes not previously described to be regulated by hypoxia. Several of these genes, namely CDTSPL, CCL20, LSP1, NEDD9, TMEM45A, EDG-1, and EPHA3 were confirmed to be regulated by hypoxia using quantitative reverse transcriptase polymerase chain reaction. These results, therefore, provide a global view of the signaling and regulatory network that controls oxygen sensing in human adult stem/progenitor cells derived from hematopoietic tissues.

Regulation of interleukin-3-induced substrate phosphorylation and cell survival by SHP-2 (Src-homology protein tyrosine phosphatase 2)

The cytosolic SHP-2 (Src homology protein tyrosine phosphatase 2) has previously been implicated in IL-3 (interleukin-3) signalling [Bone, Dechert, Jirik, Schrader and Welham (1997) J. Biol. Chem. 272, 14470 -14476; Craddock and Welham (1997) J. Biol. Chem. 272, 29281-29289; Welham, Dechert, Leslie, Jirik and Schrader (1994) J. Biol. Chem. 269, 23764-23768; Qu, Nguyen, Chen and Feng (2001) Blood 97, 911-914]. To investigate the role of SHP-2 in IL-3 signalling in greater detail, we have inducibly expressed WT (wild-type) or two potentially substrate-trapping mutant forms of SHP-2, generated by mutation of Asp-425 to Ala (D425A) or Cyst-459 to Ser (C459S), in IL-3-dependent BaF/3 cells. Effects on IL-3-induced tyrosine phosphorylation, signal transduction and functional responses were examined. Expression of C459S SHP-2 protected the beta-chain of the murine IL-3R (IL-3 receptor), the adaptor protein Gab2 (Grb2-associated binder 2), and a cytosolic protein of 48 kDa from tyrosine dephosphorylation, consistent with them being bona fide substrates of SHP-2 in IL-3 signalling. The tyrosine phosphorylation of a 135 kDa transmembrane protein was also protected upon expression of C459S SHP-2. We have identified the inhibitory immunoreceptor PECAM-1 (platelet endothelial cell adhesion molecule-1)/CD31 (cluster determinant 31) as a component of this 135 kDa substrate and also show that IL-3 can induce tyrosine phosphorylation of PECAM-1. Expression of WT, C459S and D425A forms of SHP-2 had little effect on IL-3-driven proliferation or STAT5 (signal transduction and activators of transcription) phosphorylation or activation of protein kinase B. However, expression of WT SHP-2 increased ERK (extracellular-signal-regulated kinase) activation. Interestingly, expression of C459S SHP-2 decreased ERK activation at later times after IL-3 stimulation, but potentiated IL-3-induced activation of Jun N-terminal kinases. In addition, expression of C459S SHP-2 decreased cell survival in suboptimal IL-3 and upon IL-3 withdrawal. These findings indicate that SHP-2 plays an important role in mediating the anti-apoptotic effect of IL-3 and raises the possibility that PECAM-1 participates in the modulation of cytokine-induced signals.

Physical proximity and functional interplay of PECAM-1 with the Fc receptor Fc gamma RIIa on the platelet plasma membrane

We and others have recently defined that Platelet Endothelial Cell Adhesion Molecule-1 (PECAM-1/CD31) functions as a negative regulator of platelet-collagen interactions involving the glycoprotein VI/Fc receptor gamma chain (GPVI/FcR-gamma chain) signaling pathway.1,2 In this study, we hypothesized that PECAM-1 may be physically and functionally associated with Fc gamma RIIa on the platelet membrane. The functional relationship between PECAM-1 and Fc gamma RIIa was assessed by determining the effect of anti-PECAM-1 monoclonal antibody Fab fragments on Fc gamma RIIa-mediated platelet aggregation and heparin-induced thrombocytopenia (HITS)-mediated platelet aggregation. Preincubation of washed platelets with monoclonal antibody fragments of 2BD4 directed against PECAM-1 and IV.3 directed against Fc gamma RIIa completely blocked Fc gamma RIIa-mediated platelet aggregation and HITS-mediated platelet aggregation, whereas anti-CD151 antibody had no blocking effect. Coengagement of Fc gamma RIIa and PECAM-1 resulted in negative regulation of Fc gamma RIIa-mediated phospholipase C gamma 2 activation, calcium mobilization, and phosphoinositide 3-kinase-dependent signaling pathways. In addition, the physical proximity of Fc gamma RIIa and PECAM-1 was confirmed by using fluorescence resonance energy transfer and coimmunoprecipitation studies. These results indicate that PECAM-1 and Fc gamma RIIa are colocalized on the platelet membrane and PECAM-1 down-regulates Fc gamma RIIa-mediated platelet responses.