Isoform-dependent interaction of BRDG1 with Tec kinase

The Functional Properties and Physiological Roles of Signal-Transducing Adaptor Protein-2 in the Pathogenesis of Inflammatory and Immune Disorders

Adaptor molecules play a crucial role in signal transduction in immune cells. Several adaptor molecules, such as the linker for the activation of T cells (LAT) and SH2 domain-containing leukocyte protein of 76 kDa (SLP-76), are essential for T cell development and activation following T cell receptor (TCR) aggregation, suggesting that adaptor molecules are good therapeutic targets for T cell-mediated immune disorders, such as autoimmune diseases and allergies. Signal-transducing adaptor protein (STAP)-2 is a member of the STAP family of adaptor proteins. STAP-2 functions as a scaffold for various intracellular proteins, including BRK, signal transducer, and activator of transcription (STAT)3, STAT5, and myeloid differentiation primary response protein (MyD88). In T cells, STAP-2 is involved in stromal cell-derived factor (SDF)-1α-induced migration, integrin-dependent cell adhesion, and Fas-mediated apoptosis. We previously reported the critical function of STAP-2 in TCR-mediated T cell activation and T cell-mediated autoimmune diseases. Here, we review how STAP-2 affects the pathogenesis of T cell-mediated inflammation and immune diseases in order to develop novel STAP-2-targeting therapeutic strategies.

Expression of signal-transducing adaptor protein-1 attenuates experimental autoimmune hepatitis via down-regulating activation and homeostasis of invariant natural killer T cells

Objective

Signal-transducing adaptor protein (STAP) family members function as adaptor molecules and are involved in several events during immune responses. Notably however, the biological functions of STAP-1 in other cells are not known. We aimed to investigate the functions of STAP-1 in invariant natural killer T (iNKT) cells and iNKT cell-dependent hepatitis.

Methods

We employed concanavalin A (Con A)-induced hepatitis and α-galactosylceramide (α-GalCer)-induced hepatitis mouse models, both are models of iNKT cell-dependent autoimmune hepatitis, and STAP-1 overexpressing 2E10 cells to investigate the role of STAP-1 in iNKT cell activation in vivo an in vitro, respectively.

Results

After Con A- or α-GalCer-injection, hepatocyte necrotic areas and plasma alanine aminotransferase elevation were more severe in STAP-1 knockout (S1KO) mice and milder in lymphocyte-specific STAP-1 transgenic (S1Tg) mice, as compared to wild-type (WT) mice. Two events that may be related to Con A-induced and/or α-GalCer-induced hepatitis were influenced by STAP-1 manipulation. One is that iNKT cell populations in the livers and spleens were increased in S1KO mice and were decreased in S1Tg mice. The other is that Con A-induced interleukin-4 and interferon-γ production was attenuated by STAP-1 overexpression. These effects of STAP-1 were confirmed using 2E10 cells overexpressing STAP-1 that showed impairment of interleukin-4 and interferon-γ production as well as phosphorylation of Akt and mitogen-activated protein kinases in response to Con A stimulation.

Conclusions

These results conclude that STAP-1 regulates iNKT cell maintenance/activation, and is involved in the pathogenesis of autoimmune hepatitis.

Taking One Step Back in Familial Hypercholesterolemia: STAP1 Does Not Alter Plasma LDL (Low-Density Lipoprotein) Cholesterol in Mice and Humans

OBJECTIVE

STAP1, encoding for STAP1 (signal transducing adaptor family member 1), has been reported as a candidate gene associated with familial hypercholesterolemia. Unlike established familial hypercholesterolemia genes, expression of STAP1 is absent in liver but mainly observed in immune cells. In this study, we set out to validate STAP1 as a familial hypercholesterolemia gene. Approach and Results: A whole-body Stap1 knockout mouse model (Stap1^-/-) was generated and characterized, without showing changes in plasma lipid levels compared with controls. In follow-up studies, bone marrow from Stap1^-/- mice was transplanted to Ldlr^-/- mice, which did not show significant changes in plasma lipid levels or atherosclerotic lesions. To functionally assess whether STAP1 expression in B cells can affect hepatic function, HepG2 cells were cocultured with peripheral blood mononuclear cells isolated from heterozygotes carriers of STAP1 variants and controls. The peripheral blood mononuclear cells from STAP1 variant carriers and controls showed similar LDLR mRNA and protein levels. Also, LDL (low-density lipoprotein) uptake by HepG2 cells did not differ upon coculturing with peripheral blood mononuclear cells isolated from either STAP1 variant carriers or controls. In addition, plasma lipid profiles of 39 carriers and 71 family controls showed no differences in plasma LDL cholesterol, HDL (high-density lipoprotein) cholesterol, triglycerides, and lipoprotein(a) levels. Similarly, B-cell populations did not differ in a group of 10 STAP1 variant carriers and 10 age- and sex-matched controls. Furthermore, recent data from the UK Biobank do not show association between STAP1 rare gene variants and LDL cholesterol.

CONCLUSIONS

Our combined studies in mouse models and carriers of STAP1 variants indicate that STAP1 is not a familial hypercholesterolemia gene.

Genes Potentially Associated with Familial Hypercholesterolemia

This review addresses the contribution of some genes to the phenotype of familial hypercholesterolemia. At present, it is known that the pathogenesis of this disease involves not only a pathological variant of low-density lipoprotein receptor and its ligands (apolipoprotein B, proprotein convertase subtilisin/kexin type 9 or low-density lipoprotein receptor adaptor protein 1), but also lipids, including sphingolipids, fatty acids, and sterols. The genetic cause of familial hypercholesterolemia is unknown in 20%–40% of the cases. The genes STAP1 (signal transducing adaptor family member 1), CYP7A1 (cytochrome P450 family 7 subfamily A member 1), LIPA (lipase A, lysosomal acid type), ABCG5 (ATP binding cassette subfamily G member 5), ABCG8 (ATP binding cassette subfamily G member 8), and PNPLA5 (patatin like phospholipase domain containing 5), which can cause aberrations of lipid metabolism, are being evaluated as new targets for the diagnosis and personalized management of familial hypercholesterolemia.

High STAP1 expression in DUX4-rearranged cases is not suitable as therapeutic target in pediatric B-cell precursor acute lymphoblastic leukemia

Approximately 25% of the pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cases are genetically unclassified. More thorough elucidation of the pathobiology of these genetically unclassified (‘B-other’) cases may identify novel treatment options. We analyzed gene expression profiles of 572 pediatric BCP-ALL cases, representing all major ALL subtypes. High expression of STAP1, an adaptor protein downstream of the B-cell receptor (BCR), was identified in BCR-ABL1-like and non-BCR-ABL1-like B-other cases. Limma analysis revealed an association between high expression of STAP1 and BCR signaling genes. However, STAP1 expression and pre-BCR signaling were not causally related: cytoplasmic Igμ levels were not abnormal in cases with high levels of STAP1 and stimulation of pre-BCR signaling did not induce STAP1 expression. To elucidate the role of STAP1 in BCP-ALL survival, expression was silenced in two human BCP-ALL cell lines. Knockdown of STAP1 did not reduce the proliferation rate or viability of these cells, suggesting that STAP1 is not a likely candidate for precision medicines. Moreover, high expression of STAP1 was not predictive for an unfavorable prognosis of BCR-ABL1-like and non-BCR-ABL1-like B-other cases. Remarkably, DUX4-rearrangements and intragenic ERG deletions, were enriched in cases harboring high expression of STAP1.

Small Molecule Inhibitors Targeting Tec Kinase Block Unconventional Secretion of Fibroblast Growth Factor 2

Fibroblast growth factor 2 (FGF2) is a potent mitogen promoting both tumor cell survival and tumor-induced angiogenesis. It is secreted by an unconventional secretory mechanism that is based upon direct translocation across the plasma membrane. Key steps of this process are (i) phosphoinositide-dependent membrane recruitment, (ii) FGF2 oligomerization and membrane pore formation, and (iii) extracellular trapping mediated by membrane-proximal heparan sulfate proteoglycans. Efficient secretion of FGF2 is supported by Tec kinase that stimulates membrane pore formation based upon tyrosine phosphorylation of FGF2. Here, we report the biochemical characterization of the direct interaction between FGF2 and Tec kinase as well as the identification of small molecules that inhibit (i) the interaction of FGF2 with Tec, (ii) tyrosine phosphorylation of FGF2 mediated by Tec in vitro and in a cellular context, and (iii) unconventional secretion of FGF2 from cells. We further demonstrate the specificity of these inhibitors for FGF2 because tyrosine phosphorylation of a different substrate of Tec is unaffected in their presence. Building on previous evidence using RNA interference, the identified compounds corroborate the role of Tec kinase in unconventional secretion of FGF2. In addition, they are valuable lead compounds with great potential for drug development aiming at the inhibition of FGF2-dependent tumor growth and metastasis.

Mucosal plasma cell barrier disruption during intestine transplant rejection

BACKGROUND

Intestinal allograft mucosa undergoes repopulation with host immunocytes. However, critical changes within key immunocyte subsets are not known.

METHODS

To explain acute cellular rejection after intestine transplantation (ITx) on the basis of altered mucosal immunocytes, rejecting and rejection-free ITx allografts (n=17) were compared with genome-wide expression arrays. Cells identified by cell/lineage-specific genes were evaluated by immunohistochemistry. The corresponding phenotype and donor-specific alloreactivity were characterized in peripheral blood. Time-dependent changes in candidate cell(s) were evaluated in biopsies from an independent cohort of 12 children with ITx.

RESULTS

Among 107 differentially expressed genes, three B-cell lineage-specific genes, CCR10, STAP1, and IGLL1, were down-regulated during ITx rejection and were selected for and achieved technical quantitative reverse transcription polymerase chain reaction replication. Down-regulation of the immunoglobulin (Ig)A+ plasma cell-specific CCR10 gene correlated with decreased mature mucosal CD138+ plasma cell numbers in corresponding biopsy specimens (r=0.761, P=0.006) and inversely correlated with enhanced alloreactivity of CD154+ T-cytotoxic memory cells (r=-0.56, P=0.031), which predict acute cellular rejection with high sensitivity. An independent cohort of serial biopsy specimens from 12 ITx recipients (1) confirmed relative CD138+ plasma cell depletion during rejection (P=0.042) and (2) showed increased IgG+-to-IgA+ cell ratios within 4 hr of reperfusion in rejection-prone allografts (P=0.037) and during ITx rejection (P=0.025), compared with rejection-free allografts. No differences existed late after ITx. Increased peripheral IgG+ CD27+ CD19+ memory B cells (P=0.004) were seen during ITx rejection in archived peripheral blood lymphocyte from test and replication cohorts.

CONCLUSIONS

Protracted depletion of the mucosal CD138+ plasma cell barrier and early mucosal infiltration with memory IgG+ cells characterize the rejection-prone intestine allograft. Mucosal IgA+ plasma cell barrier reconstitution may augur resolution of ITx rejection.

Matchmaking the B-cell signature of tolerance to regulatory B cells

Confirmation of clinical tolerance requires the cessation of immunosuppressive drugs, which evoke immune reactivation and allograft rejection in all but the rare individuals who successfully transition into a state of operational transplantation tolerance. Therefore, the safe conduct of trials in transplantation tolerance requires two conditions: a sensitive and reliable means to identify individuals still being maintained on immunosuppression who are most likely to exhibit tolerance after immunosuppression is withdrawn and a noninvasive means that assesses the quality or robustness of the tolerant (TOL) state. Two recent studies attempting to identify a gene signature in peripheral blood of spontaneously TOL kidney transplant recipients made the unexpected observation that TOL, but not immune-suppressed transplant recipients, exhibited enriched B cells and B-cell transcripts in their blood. In concert with the emerging appreciation of a specialized subset of regulatory B cells (Bregs) that possess immune-modulatory function, these observations raise the possibility that Bregs play a critical role in the maintenance of tolerance to renal allografts in transplant patients. This review summarizes these recent findings and speculates on the relationship of Bregs to the maintenance of transplantation tolerance.

Loops govern SH2 domain specificity by controlling access to binding pockets

Cellular functions require specific protein-protein interactions that are often mediated by modular domains that use binding pockets to engage particular sequence motifs in their partners. Yet, how different members of a domain family select for distinct sequence motifs is not fully understood. The human genome encodes 120 Src homology 2 (SH2) domains (in 110 proteins), which mediate protein-protein interactions by binding to proteins with diverse phosphotyrosine (pTyr)-containing sequences. The structure of the SH2 domain of BRDG1 bound to a peptide revealed a binding pocket that was blocked by a loop residue in most other SH2 domains. Analysis of 63 SH2 domain structures suggested that the SH2 domains contain three binding pockets, which exhibit selectivity for the three positions after the pTyr in a peptide, and that SH2 domain loops defined the accessibility and shape of these pockets. Despite sequence variability in the loops, we identified conserved structural features in the loops of SH2 domains responsible for controlling access to these surface pockets. We engineered new loops in an SH2 domain that altered specificity as predicted. Thus, selective blockage of binding subsites or pockets by surface loops provides a molecular basis by which the diverse modes of ligand recognition by the SH2 domain may have evolved and provides a framework for engineering SH2 domains and designing SH2-specific inhibitors.

Tissue distribution and signal transduction of Tec tyrosine kinase in rats

AIM: To detect the tissue distribution of Tec tyrosine kinase in rats, and to investigate the possible signal transduction pathways in which Tec is involved.

METHODS: The total RNA was extracted from the tissues of rat heart, liver, spleen, lung, brain, thymus gland and muscle. Northern blot was used to detect the expression of Tec RNA. Reporting gene plasmids and Tec expression vector were co-transfected into WBF-344 cells, and post-transfection cells were stimulated by hepatic growth factor (HGF). Then cells were lysed and the luciferace activity was measured.

RESULTS: Northern blot suggested that Tec tyrosine kinase was highly expressed in the tissues of rat liver and kidney. Report gene assay showed the Elk luciferase activity was increased about 2-3 folds in comparison with that of the controls, while other signaling pathways had no obviously changes.

CONCLUSION: Tec tyrosine kinase is involved in Erk/mitogen-activated protein kinase signal pathway mediated by HGF. Tec probably plays an important role in the proliferation of liver cells.

Activation of TEC and STAT3 after partial hepatectomy or hepatocytic growth factor stimulation

AIM: To study the activation of TEC and STAT3 in the hepatocyte after partial hepatectomy (PH) or hepatocytic growth factor (HGF) stimulation in the mice.

METHODS: Mice of SPF degree and WB F-344 cell (liver stem cell line) were used in this study. In vivo and in vitro experimental models of PH and HGF stimulation were established respectively. Immunoprecipitation (IP) and immunoblotting (IB) were used to observe the phosphorylation level and time of TEC and STAT3. On the other hand, electrophoretic mobility shift assay (EMSA) was used to detect the binding ability of STAT3 DNA.

RESULTS: TEC and STAT3 were both inducibly phosphorylated in one hour after PH or HGF stimulation. Ten to twenty minutes after PH, levels of TEC and STAT3 reached the peak. About 10 min after HGF stimulation, TEC phosphorylation level reached maximum value and about 30 min STAT3 phosphorylation level reached peak value. Meanwhlie, STAT3 DNA binding activity was enhanced both In vivo and in vitro experiments.

CONCLUSION: After PH or HGF-stimulation, both TEC and STAT3 are quickly phosphorylated in one hour, and they synergically affect the early proliferation of hepatocytes.