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

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.

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.

MPZL1 suppresses the cancer stem-like properties of lung cancer through β-catenin/TCF4 signaling

This study was designed to explore the influence of myelin protein zero-like protein 1 (MPZL1) on the stem-like properties of cancer cells and the underlying mechanism in lung adenocarcinoma. Real-time quantitative polymerase chain reaction (RT-qPCR) was utilized to evaluate mRNA expression level. CCK8, wound healing, and transwell assays were applied to assess cell proliferation, migration, and invasion. Tumorsphere-formation assay was utilized to assess cancer stem cell-like properties. LF3 was used to block the β-catenin/Transcription factor 4 (TCF-4) signaling. Xenograft nude mouse model was conducted; tumor weight and volume were recorded. Western blot assay was utilized to detect the expression levels of CD44, CD133, β-catenin, TCF-4, and MPZL1. Following MPZL1 knockdown, the mRNA expression levels of MPZL1, β-catenin, and TCF-4 were inhibited, while the mRNA expression levels of the above genes were increased after the MPZL1 overexpression. MPZL1 knockdown suppressed cell proliferation, migration, and invasion, reduced the tumorsphere-formation capacity, and restrained the expression levels of CD44 and CD133. However, MPZL1 overexpression promoted the cell proliferation, migration, and invasion, enhanced the tumorsphere-formation capacity, and increased the expression levels of CD44 and CD133. Interestingly, LF3 treatment partially revised the effect of MPZL1 overexpression. These findings were further corroborated by in vivo experiments. We concluded that MPZL1 could suppress the lung adenocarcinoma cells' proliferation, migration, invasion, and lung cancer stem cells characteristics. The underlying mechanism is involved in the activation of β-catenin/TCF-4 signaling.

MPZL1 upregulation promotes tumor metastasis and correlates with unfavorable prognosis in non-small cell lung cancer

Non-small cell lung cancer (NSCLC), accounting for 85% of all lung cancer, is one of the leading causes of cancer-related death worldwide. Previously, we demonstrated that MPZL1 gene amplification promotes liver cancer metastasis through activating Src/Cortactin pathway. However, the clinical relevance and biological roles of the MPZL1 gene in lung cancer are still unknown. Here, we found that MPZL1 expression upregulates in human NSCLC, which is partly due to the copy number amplification of this gene. Next, we observed that high MPZL1 expression correlates with unfavorable prognosis of NSCLC patients. We further demonstrated that ectopic MPZL1 overexpression promotes in vitro migratory but not proliferation and colony formation abilities of both H1299 and H460 cells. Consistently, we found that MPZL1 knockdown impairs the migratory abilities of A549 and H1775 cells. Moreover, we found that MPZL1 knockdown inhibits in vivo metastatic but not tumor growth abilities of the A549 cells. Additionally, a total of 297 differentially expressed genes (DEGs) were identified by RNA sequencing in A549 cells upon MPZL1 knockdown. By integrative analysis of DEGs regulated by MPZL1 in A549 cells and human NSCLC tissues, we revealed that COL11A1 is the potential effector gene that positively regulated by MPZL1 and correlates with poor prognosis of NSCLC patients. In conclusion, our work indicates that one of the mechanisms by which MPZL1 promotes NSCLC metastasis is through upregulating the COL11A1, and MPZL1 can be used as a biomarker to predict the prognosis of NSCLC patients.

Time-resolved phosphoproteomics reveals scaffolding and catalysis-responsive patterns of SHP2-dependent signaling

SHP2 is a protein tyrosine phosphatase that normally potentiates intracellular signaling by growth factors, antigen receptors, and some cytokines, yet is frequently mutated in human cancer. Here, we examine the role of SHP2 in the responses of breast cancer cells to EGF by monitoring phosphoproteome dynamics when SHP2 is allosterically inhibited by SHP099. The dynamics of phosphotyrosine abundance at more than 400 tyrosine residues reveal six distinct response signatures following SHP099 treatment and washout. Remarkably, in addition to newly identified substrate sites on proteins such as occludin, ARHGAP35, and PLCγ2, another class of sites shows reduced phosphotyrosine abundance upon SHP2 inhibition. Sites of decreased phospho-abundance are enriched on proteins with two nearby phosphotyrosine residues, which can be directly protected from dephosphorylation by the paired SH2 domains of SHP2 itself. These findings highlight the distinct roles of the scaffolding and catalytic activities of SHP2 in effecting a transmembrane signaling response.

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.

Cell-Adhesion Properties of β-Subunits in the Regulation of Cardiomyocyte Sodium Channels

Voltage-gated sodium (Nav) channels drive the rising phase of the action potential, essential for electrical signalling in nerves and muscles. The Nav channel α-subunit contains the ion-selective pore. In the cardiomyocyte, Nav1.5 is the main Nav channel α-subunit isoform, with a smaller expression of neuronal Nav channels. Four distinct regulatory β-subunits (β1–4) bind to the Nav channel α-subunits. Previous work has emphasised the β-subunits as direct Nav channel gating modulators. However, there is now increasing appreciation of additional roles played by these subunits. In this review, we focus on β-subunits as homophilic and heterophilic cell-adhesion molecules and the implications for cardiomyocyte function. Based on recent cryogenic electron microscopy (cryo-EM) data, we suggest that the β-subunits interact with Nav1.5 in a different way from their binding to other Nav channel isoforms. We believe this feature may facilitate trans-cell-adhesion between β1-associated Nav1.5 subunits on the intercalated disc and promote ephaptic conduction between cardiomyocytes.

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.

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.

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.

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.

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.

PECAM1 regulates flow-mediated Gab1 tyrosine phosphorylation and signaling

Endothelial dysfunction, characterized by impaired activation of endothelial nitric oxide (NO) synthase (eNOS) and ensued decrease of NO production, is a common mechanism of various cardiovascular pathologies, including hypertension and atherosclerosis. Laminar blood flow-mediated specific signaling cascades modulate vascular endothelial cells (ECs) structure and functions. We have previously shown that flow-stimulated Gab1 (Grb2-associated binder-1) tyrosine phosphorylation mediates eNOS activation in ECs, which in part confers laminar flow atheroprotective action. However, the molecular mechanisms whereby flow regulates Gab1 tyrosine phosphorylation and its downstream signaling events remain unclear. Here we show that platelet endothelial cell adhesion molecule-1 (PECAM1), a key molecule in an endothelial mechanosensing complex, specifically mediates Gab1 tyrosine phosphorylation and its downstream Akt and eNOS activation in ECs upon flow rather than hepatocyte growth factor (HGF) stimulation. Small interfering RNA (siRNA) targeting PECAM1 abolished flow- but not HGF-induced Gab1 tyrosine phosphorylation and Akt, eNOS activation as well as Gab1 membrane translocation. Protein-tyrosine phosphatase SHP2, which has been shown to interact with Gab1, was involved in flow signaling and HGF signaling, as SHP2 siRNA diminished the flow- and HGF-induced Gab1 tyrosine phosphorylation, membrane localization and downstream signaling. Pharmacological inhibition of PI3K decreased flow-, but not HGF-mediated Gab1 phosphorylation and membrane localization as well as eNOS activation. Finally, we observed that flow-mediated Gab1 and eNOS phosphorylation in vivo induced by voluntary wheel running was reduced in PECAM1 knockout mice. These results demonstrate a specific role of PECAM1 in flow-mediated Gab1 tyrosine phosphorylation and eNOS signaling in ECs.

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.

Quantitative phosphoproteomics reveals SLP-76 dependent regulation of PAG and Src family kinases in T cells

The SH2-domain-containing leukocyte protein of 76 kDa (SLP-76) plays a critical scaffolding role in T cell receptor (TCR) signaling. As an adaptor protein that contains multiple protein-binding domains, SLP-76 interacts with many signaling molecules and links proximal receptor stimulation to downstream effectors. The function of SLP-76 in TCR signaling has been widely studied using the Jurkat human leukaemic T cell line through protein disruption or site-directed mutagenesis. However, a wide-scale characterization of SLP-76-dependant phosphorylation events is still lacking. Quantitative profiling of over a hundred tyrosine phosphorylation sites revealed new modes of regulation of phosphorylation of PAG, PI3K, and WASP while reconfirming previously established regulation of Itk, PLCγ, and Erk phosphorylation by SLP-76. The absence of SLP-76 also perturbed the phosphorylation of Src family kinases (SFKs) Lck and Fyn, and subsequently a large number of SFK-regulated signaling molecules. Altogether our data suggests unique modes of regulation of positive and negative feedback pathways in T cells by SLP-76, reconfirming its central role in the pathway.