Cigarette smoke particle-phase extract induces HO-1 expression in human tracheal smooth muscle cells: role of the c-Src/NADPH oxidase/MAPK/Nrf2 signaling pathway

Heme oxygenase-1 (HO-1) is known as an oxidative stress protein that is up-regulated by various stimuli. HO-1 has been shown to protect cells against oxidative damage. Cigarette smoke is a potential inflammatory mediator that causes chronic obstructive pulmonary disease and asthma. In this study, we report that cigarette smoke particle-phase extract (CSPE) is an inducer of HO-1 expression mediated through various signaling pathways in human tracheal smooth muscle cells (HTSMCs). CSPE-induced HO-1 protein, mRNA expression, and promoter activity were attenuated by pretreatment with a ROS scavenger (N-acetyl-l-cysteine) and inhibitors of c-Src (PP1), NADPH oxidase [diphenylene iodonium chloride (DPI) and apocynin (APO)], MEK1/2 (U0126), p38 MAPK (SB202190), and JNK1/2 (SP600125) or transfection with siRNAs for Src, p47(phox), NOX2, p42, p38, JNK2, or NF-E2-related factor 2 (Nrf2). CSPE-stimulated translocation of p47(phox) and Nrf2, ROS production, and NADPH oxidase activity was attenuated by transfection with siRNAs for Src, p47(phox), and NOX2 or pretreatment with PP1, DPI, or APO. Furthermore, CSPE-induced NOX2, c-Src, and p47(phox) complex formation was revealed by immunoprecipitation using an anti-NOX2, anti-p47(phox), or anti-c-Src Ab followed by Western blot against anti-NOX2, anti-p47(phox), or anti-c-Src Abs. These results demonstrate that CSPE-induced ROS generation is mediated through a c-Src/NADPH oxidase/MAPK pathway and in turn initiates the activation of Nrf2 and ultimately induces HO-1 expression in HTSMCs.

LYN is a mediator of epithelial-mesenchymal transition and a target of dasatinib in breast cancer

Epithelial-mesenchymal transition (EMT), a switch of polarized epithelial cells to a migratory, fibroblastoid phenotype, is considered a key process driving tumor cell invasiveness and metastasis. Using breast cancer cell lines as a model system, we sought to discover gene expression signatures of EMT with clinical and mechanistic relevance. A supervised comparison of epithelial and mesenchymal breast cancer lines defined a 200-gene EMT signature that was prognostic across multiple breast cancer cohorts. The immunostaining of LYN, a top-ranked EMT signature gene and Src-family tyrosine kinase, was associated with significantly shorter overall survival (P = 0.02) and correlated with the basal-like ("triple-negative") phenotype. In mesenchymal breast cancer lines, RNAi-mediated knockdown of LYN inhibited cell migration and invasion, but not proliferation. Dasatinib, a dual-specificity tyrosine kinase inhibitor, also blocked invasion (but not proliferation) at nanomolar concentrations that inhibit LYN kinase activity, suggesting that LYN is a likely target and that invasion is a relevant end point for dasatinib therapy. Our findings define a prognostically relevant EMT signature in breast cancer and identify LYN as a mediator of invasion and a possible new therapeutic target (and theranostic marker for dasatinib response), with particular relevance to clinically aggressive basal-like breast cancer.

Genome-wide association study in Asian populations identifies variants in ETS1 and WDFY4 associated with systemic lupus erythematosus

Systemic lupus erythematosus is a complex and potentially fatal autoimmune disease, characterized by autoantibody production and multi-organ damage. By a genome-wide association study (320 patients and 1,500 controls) and subsequent replication altogether involving a total of 3,300 Asian SLE patients from Hong Kong, Mainland China, and Thailand, as well as 4,200 ethnically and geographically matched controls, genetic variants in ETS1 and WDFY4 were found to be associated with SLE (ETS1: rs1128334, P = 2.33×10⁻¹¹, OR = 1.29; WDFY4: rs7097397, P = 8.15×10⁻¹², OR = 1.30). ETS1 encodes for a transcription factor known to be involved in a wide range of immune functions, including Th17 cell development and terminal differentiation of B lymphocytes. SNP rs1128334 is located in the 3′-UTR of ETS1, and allelic expression analysis from peripheral blood mononuclear cells showed significantly lower expression level from the risk allele. WDFY4 is a conserved protein with unknown function, but is predominantly expressed in primary and secondary immune tissues, and rs7097397 in WDFY4 changes an arginine residue to glutamine (R1816Q) in this protein. Our study also confirmed association of the HLA locus, STAT4, TNFSF4, BLK, BANK1, IRF5, and TNFAIP3 with SLE in Asians. These new genetic findings may help us to gain a better understanding of the disease and the functions of the genes involved.

In this study, we first conducted a genome-wide association study in a Hong Kong Chinese population, followed by replication in three other cohorts from Mainland China and a cohort from Thailand, which totaled 3,300 Asian patients and 4,200 ethnically and geographically matched controls. We identified novel variants in ETS1 and WDFY4 associated with SLE with genome-wide significance and confirmed the association of HLA locus, STAT4, BLK, IRF5, BANK1, TNFSF, and IRF5 with the disease. ETS1 encodes a critical transcription factor involved in Th17 and B cell development. Allelic expression study showed a significantly lower expression of ETS1 from the risk allele, which provided functional support to the genetic findings. WDFY4 is a huge protein with unknown function but is predominantly expressed in primary and secondary immune tissues, and a nonsynonymous SNP in this gene was found to be highly associated with SLE susceptibility. Our findings shed new light on the function of these genes as well as the mechanism of this devastating disease.

[Neuronal isoforms of Src, Fyn and Lck tyrosine kinases: A specific role for p56lckN in neuron protection]

The two main tyrosine kinases (TK) in the brain are p60Src and p59Fyn, expressed as specific isoforms (p60SrcNI, p60SrcNI+NII and p59fynB). They play a pivotal role in some major processes such as neuronal growth and myelinisation. Another member of this TK family was then reported in brain, the p56lck. Its name Lck (lymphocyte cell kinase) indicates its cellular specificity observed initially, so its presence in the brain was intriguing. But no further studies were performed to understand its role in brain until recent clinical studies on Alzheimer patients' brains. One study reveals a decreased p56lck level in the brains of these patients while another study shows an association between one peculiar SNP (single nucleotide polymorphism) of the lck gene and some cases of the disease. These new data prompt us to reinvestigate the original biochemical data and to confront them with the present knowledge. This analysis suggests some hypothesis concerning both the Lck protein expressed in the brain (rather an isoform than the lymphocyte protein itself) and its role (to maintain the neuronal survival presumably by protecting them from inflammation, the main pathway that leads to neuron degeneracy).

[Effect of dendritic cells pulsed with Talpha146-162 on autoimmune myasthenia graves and the role of B cells activation]

OBJECTIVE

To explore the therapeutic effect of Talpha146-162-iMDCs on C57BL/6 mice with EAMG and the role of changes in B cell activation regulated by Cbl.

METHODS

Thirty four adult male C57BL/6 mice were randomly divided into EAMG group (A group), EAMG group with interventions (B group) and control group (C group). T-AChR antigens were injected to the mice in A and B groups to induce EAMG. Meanwhile, dendritic cells from immature bone marrows were cultured and pulsed with Talpha146-162, and injected to the mice in the intervention group. The mRNA expression of Cbl was detected by RT-PCR 90 days after the termination of experiment. The expression and phosphorylation of Syk and Lyn proteins were measured by Western blot.

RESULTS

More mice (9/12, 75%) in A group developed EAMG than in B group (3/12, 25%, P<0.05). Mice in A group also suffered more serious illness in terms of clinical scores than mice in B group (1.69+/-1.12 vs 0.35+/-0.67, P<0.01). No EAMG occurred in mice in C group. Mice in B group had lower mRNA expressions of Cbl in the spleens and lymphonodes than mice in A groups, but both had higher expressions than mice in C group (P<0.05). Mice in B group had higher mRNA expression of Cbl than mice in A group (P<0.05).

CONCLUSION

Talpha146-162-iMDCs prevent EAMG, possibly through negative regulation of Cbl on BCR signaling.

Mutations at the BLK locus linked to maturity onset diabetes of the young and beta-cell dysfunction

Maturity-onset diabetes of the young (MODY) is a subtype of diabetes defined by an autosomal pattern of inheritance and a young age at onset, often before age 25. MODY is genetically heterogeneous, with 8 distinct MODY genes identified to date and more believed to exist. We resequenced 732 kb of genomic sequence at 8p23 in 6 MODY families unlinked to known MODY genes that showed evidence of linkage at that location. Of the 410 sequence differences that we identified, 5 had a frequency <1% in the general population and segregated with diabetes in 3 of the families, including the 2 showing the strongest support for linkage at this location. The 5 mutations were all placed within 100 kb corresponding to the BLK gene. One resulted in an Ala71Thr substitution; the other 4 were noncoding and determined decreased in vitro promoter activity in reporter gene experiments. We found that BLK--a nonreceptor tyrosine-kinase of the src family of proto-oncogenes--is expressed in beta-cells where it enhances insulin synthesis and secretion in response to glucose by up-regulating transcription factors Pdx1 and Nkx6.1. These actions are greatly attenuated by the Ala71Thr mutation. These findings point to BLK as a previously unrecognized modulator of beta-cell function, the deficit of which may lead to the development of diabetes.

Genetic associations of LYN with systemic lupus erythematosus

We targeted LYN, a src-tyosine kinase involved in B-cell activation, in case-control association studies using populations of European-American, African-American and Korean subjects. Our combined European-derived population, consisting of 2463 independent cases and 3131 unrelated controls, shows significant association with rs6983130 in a female-only analysis with 2254 cases and 2228 controls (P=1.1 x 10(-4), odds ratio (OR)=0.81 (95% confidence interval: 0.73-0.90)). This single nucleotide polymorphism (SNP) is located in the 5' untranslated region within the first intron near the transcription initiation site of LYN. In addition, SNPs upstream of the first exon also show weak and sporadic association in subsets of the total European-American population. Multivariate logistic regression analysis implicates rs6983130 as a protective factor for systemic lupus erythematosus (SLE) susceptibility when anti-dsDNA, anti-chromatin, anti-52 kDa Ro or anti-Sm autoantibody status were used as covariates. Subset analysis of the European-American female cases by American College of Rheumatology classification criteria shows a reduction in the risk of hematological disorder with rs6983130 compared with cases without hematological disorders (P=1.5 x 10(-3), OR=0.75 (95% CI: 0.62-0.89)). None of the 90 SNPs tested show significant association with SLE in the African American or Korean populations. These results support an association of LYN with European-derived individuals with SLE, especially within autoantibody or clinical subsets.

SRC-induced disassembly of adherens junctions requires localized phosphorylation and degradation of the rac activator tiam1

The Rac activator Tiam1 is required for adherens junction (AJ) maintenance, and its depletion results in AJ disassembly. Conversely, the oncoprotein Src potently induces AJ disassembly and epithelial-mesenchymal transition (EMT). Here, we show that Tiam1 is phosphorylated on Y384 by Src. This occurs predominantly at AJs, is required for Src-induced AJ disassembly and cell migration, and creates a docking site on Tiam1 for Grb2. We find that Tiam1 is associated with ERK. Following recruitment of the Grb2-Sos1 complex, ERK becomes activated and triggers the localized degradation of Tiam1 at AJs, likely involving calpain proteases. Furthermore, we demonstrate that, in human tumors, Y384 phosphorylation positively correlates with Src activity, and total Tiam1 levels are inversely correlated. Thus, our data implicate Tiam1 phosphorylation and consequent degradation in Src-mediated EMT and resultant cell motility and establish a paradigm for regulating local concentrations of Rho-GEFs.

Growth factors outside of the platelet-derived growth factor (PDGF) family employ reactive oxygen species/Src family kinases to activate PDGF receptor alpha and thereby promote proliferation and survival of cells

The vitreous contains a plethora of growth factors that are strongly implicated in the formation of fibroproliferative diseases such as proliferative vitreoretinopathy. Although platelet-derived growth factors (PDGFs) are present in the vitreous, vitreal growth factors outside of the PDGF family activated the PDGF alpha receptor (PDGFRalpha) and promoted disease progression in a rabbit model of proliferative vitreoretinopathy (H. Lei, G. Velez, P. Hovland, T. Hirose, D. Gilbertson, and A. Kazlauskas (2008) submitted for publication.) In this report we investigated the mechanism by which non-PDGFs activated PDGFRalpha. We found that non-PDGFs increased the cellular level of reactive oxygen species (ROS) and that this event was necessary and sufficient for phosphorylation of PDGFRalpha. We speculated that the underlying mechanism was ROS-mediated inhibition of phosphotyrosine phosphatases, which antagonize receptor auto-phosphorylation. However, this did not appear to be the case. Non-PDGFs promoted tyrosine phosphorylation of catalytically inactive PDGFRalpha, and thereby indicated that at least one additional tyrosine kinase was involved. Indeed, preventing expression or blocking the kinase activity of Src family kinases suppressed non-PDGF-dependent tyrosine phosphorylation of PDGFRalpha. Thus non-PDGFs increased the level of ROS, which activated Src family kinases and resulted in phosphorylation of PDGFRalpha. Finally, although non-PDGFs induced only modest phosphorylation of PDGFRalpha, proliferation and survival of cells in response to non-PDGFs was significantly enhanced by expression of PDGFRalpha. These studies reveal a novel mechanism for activation of PDGFRalpha that appears capable of enhancing the responsiveness of cells to growth factors outside of the PDGF family.

Src promotes delta opioid receptor (DOR) desensitization by interfering with receptor recycling

Abstract An important limitation in the clinical use of opiates is progressive loss of analgesic efficacy over time. Development of analgesic tolerance is tightly linked to receptor desensitization. In the case of delta opioid receptors (DOR), desensitization is especially swift because receptors are rapidly internalized and are poorly recycled to the membrane. In the present study, we investigated whether Src activity contributed to this sorting pattern and to functional desensitization of DORs. A first series of experiments demonstrated that agonist binding activates Src and destabilizes a constitutive complex formed by the spontaneous association of DORs with the kinase. Src contribution to DOR desensitization was then established by showing that pre-treatment with Src inhibitor PP2 (20 microM; 1 hr) or transfection of a dominant negative Src mutant preserved DOR signalling following sustained exposure to an agonist. This protection was afforded without interfering with endocytosis, but suboptimal internalization interfered with PP2 ability to preserve DOR signalling, suggesting a post-endocytic site of action for the kinase. This assumption was confirmed by demonstrating that Src inhibition by PP2 or its silencing by siRNA increased membrane recovery of internalized DORs and was further corroborated by showing that inhibition of recycling by monensin or dominant negative Rab11 (Rab11S25N) abolished the ability of Src blockers to prevent desensitization. Finally, Src inhibitors accelerated recovery of DOR-Galphal3 coupling after desensitization. Taken together, these results indicate that Src dynamically regulates DOR recycling and by doing so contributes to desensitization of these receptors.

Src activation and translocation from focal adhesions to membrane ruffles contribute to formation of new adhesion sites

Cell migration requires the coordinated turnover of focal adhesions, a process that involves FAK phosphorylation. Since Src is the major kinase implicated in FAK phosphorylation, we focus here on the role of Src activation on adhesion remodelling. In astrocytoma cells, constitutively activated Src induces both FAK phosphorylation and adhesion rearrangement. To evaluate how Src controls these processes, we used a recently described Src reporter to monitor the dynamics of Src phosphorylation. Upon Src activation, focal adhesions started to disassemble while Src appeared highly expressed at newly formed membrane ruffles. Kinetic analysis of time-lapse movies showed that loss of phospho-Src at focal adhesions was time-correlated with the appearance of membrane ruffles containing phospho-Src. Moreover, FLIP analysis revealed a dynamic equilibrium of Src between focal adhesions and membrane ruffles. We conclude that upon phosphorylation, Src is directly translocated from focal adhesions to membrane ruffles, thereby promoting formation of new adhesion complexes.

Dystroglycan, Tks5 and Src mediated assembly of podosomes in myoblasts

Background

Dystroglycan is a ubiquitously expressed cell adhesion receptor best understood in its role as part of the dystrophin glycoprotein complex of mature skeletal muscle. Less is known of the role of dystroglycan in more fundamental aspects of cell adhesion in other cell types, nor of its role in myoblast cell adhesion.

Principal Findings

We have examined the role of dystroglycan in the early stages of myoblast adhesion and spreading and found that dystroglycan initially associates with other adhesion proteins in large puncta morphologically similar to podosomes. Using a human SH3 domain phage display library we identified Tks5, a key regulator of podosomes, as interacting with β-dystroglycan. We verified the interaction by immunoprecipitation, GST-pulldown and immunfluorescence localisation. Both proteins localise to puncta during early phases of spreading, but importantly following stimulation with phorbol ester, also localise to structures indistinguishable from podosomes. Dystroglycan overexpression inhibited podosome formation by sequestering Tks5 and Src. Mutation of dystroglycan tyrosine 890, previously identified as a Src substrate, restored podosome formation.

Conclusions

We propose therefore, that Src-dependent phosphorylation of β-dystroglycan results in the formation of a Src/dystroglycan complex that drives the SH3-mediated association between dystroglycan and Tks5 which together regulate podosome formation in myoblasts.

Structure and dynamic regulation of Src-family kinases

Src-family kinases are modular signaling proteins involved in a diverse array of cellular processes. All members of the Src family share the same domain organization, with modular SH3, SH2 and kinase domains followed by a C-terminal negative regulatory tail. X-ray crystallographic analyses of several Src family members have revealed critical roles for the SH3 and SH2 domains in the down-regulation of the kinase domain. This review focuses on biological, biophysical, and computational studies that reveal conformationally distinct active states within this unique kinase family.

Parallel phosphatidylinositol 3-kinase (PI3K)-dependent and Src-dependent pathways lead to CXCL8-mediated Rac2 activation and chemotaxis

The requirement for phosphatidylinositol 3-kinase (PI3K) in the establishment of cell polarity and motility in a number of cell types has recently come into question. In this study, we demonstrate that inhibition of PI3K by wortmannin in neutrophil-like differentiated HL60 cells expressing CXCR2 resulted in reduced cell motility but normal chemotaxis in response to a gradient of CXCL8. However, wortmannin inhibition of PI3K did impair the ability of cells to re-orient their polarity and respond quickly to a change in the direction of the CXCL8 gradient. We hypothesized that Src-regulated ELMO-Dock2-Rac2 activation mediates chemotaxis in the absence of PI3K activity. Inhibition of Src with the small molecule inhibitor, PP2, or inhibition of Dock2 by shRNA knockdown confirmed the functional role of Src and Dock2 in regulating chemotaxis when PI3K was inhibited. Moreover, neutrophils isolated from bone marrow of hck(-/-)fgr(-/-)lyn(-/-) mice exhibited much more severe inhibition of chemotaxis when PI3K was blocked with wortmannin as compared with neutrophils isolated from bone marrow of wild-type mice. Thus, PI3K and Src-ELMO-Dock2 pathways work in parallel to activate Rac2 and modulate chemotaxis in response to a CXCL8 gradient in neutrophils.

Regulation of phagocyte migration and recruitment by Src-family kinases

Src-family kinases (SFKs) regulate different granulocyte and monocyte/macrophage responses. Accumulating evidence suggests that members of this family are implicated in signal transduction pathways regulating phagocytic cell migration and recruitment into inflammatory sites. Macrophages with a genetic deficiency of SFKs display marked alterations in cytoskeleton dynamics, polarization and migration. This same phenotype is found in cells with either a lack of SFK substrates and/or interacting proteins such as Pyk2/FAK, c-Cbl and p190RhoGAP. Notably, SFKs and their downstream targets also regulate monocyte recruitment into inflammatory sites. Depending on the type of assay used, neutrophil migration in vitro may be either dependent on or independent of SFKs. Also neutrophil recruitment in in vivo models of inflammation may be regulated differently by SFKs depending on the tissue involved. In this review we will discuss possible mechanisms by which SFKs may regulate phagocytic cell migratory abilities.

Transient ectopic expression as a method to detect genes conferring drug resistance

Ectopic expression provides an alternative to RNAi to conduct functional genomic screens. We have determined whether transient expression can be used to identify genes which confer drug resistance. We constructed a bigenic vector that allows high throughput cloning and which also encodes a red fluorescent protein to monitor transfection. Assay conditions were optimized to allow detection of changes in sensitivity to carboplatin or paclitaxel. Following transient expression of MDR-1 and MCJ, changes in the sensitivity of Sk-Ov-3 cells to paclitaxel were detected whereas expression of Src, Bcl-2 and Bcl-X(L) decreased the sensitivity of Sk-Ov-3 cells to carboplatin. This approach may potentially be used as an independent screen or as a method to help rank hit identified in screens utilizing methods such as RNAi.

The ups and downs of SRC regulation: tumor suppression by Cbp

Tight control of the tyrosine kinase activity of c-Src is critical for regulating its oncogenic potential. In a recent issue of Molecular Cell, Oneyama et al. (2008a) report that the membrane-bound adaptor protein Cbp (also known as PAG) can suppress c-Src-mediated cell transformation and tumorigenesis by binding and sequestering c-Src within lipid rafts. Cbp is also a raft-associated binding partner for Csk, a negative regulator of c-Src. However, the authors show that Cbp-mediated Src suppression is Csk independent. These findings suggest that Cbp is a tumor suppressor whose expression is downregulated during Src-driven cancer progression.

TLR4 signaling is coupled to SRC family kinase activation, tyrosine phosphorylation of zonula adherens proteins, and opening of the paracellular pathway in human lung microvascular endothelia

Bacterial lipopolysaccharide (LPS) is a key mediator in the vascular leak syndromes associated with Gram-negative bacterial infections. LPS opens the paracellular pathway in pulmonary vascular endothelia through protein tyrosine phosphorylation. We now have identified the protein-tyrosine kinases (PTKs) and their substrates required for LPS-induced protein tyrosine phosphorylation and opening of the paracellular pathway in human lung microvascular endothelial cells (HMVEC-Ls). LPS disrupted barrier integrity in a dose- and time-dependent manner, and prior broad spectrum PTK inhibition was protective. LPS increased tyrosine phosphorylation of zonula adherens proteins, VE-cadherin, gamma-catenin, and p120(ctn). Two SRC family PTK (SFK)-selective inhibitors, PP2 and SU6656, blocked LPS-induced increments in tyrosine phosphorylation of VE-cadherin and p120(ctn) and paracellular permeability. In HMVEC-Ls, c-SRC, YES, FYN, and LYN were expressed at both mRNA and protein levels. Selective small interfering RNA-induced knockdown of c-SRC, FYN, or YES diminished LPS-induced SRC Tyr(416) phosphorylation, tyrosine phosphorylation of VE-cadherin and p120(ctn), and barrier disruption, whereas knockdown of LYN did not. For VE-cadherin phosphorylation, knockdown of either c-SRC or FYN provided total protection, whereas YES knockdown was only partially protective. For p120(ctn) phosphorylation, knockdown of FYN, c-SRC, or YES each provided comparable but partial protection. Toll-like receptor 4 (TLR4) was expressed both on the surface and intracellular compartment of HMVEC-Ls. Prior knockdown of TLR4 blocked both LPS-induced SFK activation and barrier disruption. These data indicate that LPS recognition by TLR4 activates the SFKs, c-SRC, FYN, and YES, which, in turn, contribute to tyrosine phosphorylation of zonula adherens proteins to open the endothelial paracellular pathway.

Focal adhesion kinase/Src suppresses early chondrogenesis: central role of CCN2

Adhesive signaling plays a key role in cellular differentiation, including in chondrogenesis. Herein, we probe the contribution to early chondrogenesis of two key modulators of adhesion, namely focal adhesion kinase (FAK)/Src and CCN2 (connective tissue growth factor, CTGF). We use the micromass model of chondrogenesis to show that FAK/Src signaling, which mediates cell/matrix attachment, suppresses early chondrogenesis, including the induction of Ccn2, Agc, and Sox6. The FAK/Src inhibitor PP2 elevates Ccn2, Agc, and Sox6 expression in wild-type mesenchymal cells in micromass culture, but not in cells lacking CCN2. Our results suggest a reduction in FAK/Src signaling is a critical feature permitting chondrogenic differentiation and that CCN2 operates downstream of this loss to promote chondrogenesis.

Two independent forms of endocytosis maintain embryonic cell surface homeostasis during early development

Eukaryotic cells have multiple forms of endocytosis which maintain cell surface homeostasis. One explanation for this apparent redundancy is to allow independent retrieval of surface membranes derived from different types of vesicles. Consistent with this hypothesis we find that sea urchin eggs have at least two types of compensatory endocytosis. One is associated with retrieving cortical vesicle membranes, and formed large endosomes by a mechanism that was inhibited by agatoxin, cadmium, staurosporine and FK506. The second type is thought to compensate for constitutive exocytosis, and formed small endosomes using a mechanism that was insensitive to the above mentioned reagents, but was inhibited by phenylarsine oxide (PAO), and by microinjection of mRNA encoding Src kinase. Both mechanisms could act concurrently, and account for all of the endocytosis occurring during early development. Inhibition of either form did not trigger compensation by the other form, and phorbol ester treatment rescued the endocytotic activity blocked by agatoxin, but not the retrieval blocked by PAO.

Association of systemic lupus erythematosus with C8orf13-BLK and ITGAM-ITGAX

BACKGROUND

Systemic lupus erythematosus (SLE) is a clinically heterogeneous disease in which the risk of disease is influenced by complex genetic and environmental contributions. Alleles of HLA-DRB1, IRF5, and STAT4 are established susceptibility genes; there is strong evidence for the existence of additional risk loci.

METHODS

We genotyped more than 500,000 single-nucleotide polymorphisms (SNPs) in DNA samples from 1311 case subjects with SLE and 1783 control subjects; all subjects were North Americans of European descent. Genotypes from 1557 additional control subjects were obtained from public data repositories. We measured the association between the SNPs and SLE after applying strict quality-control filters to reduce technical artifacts and to correct for the presence of population stratification. Replication of the top loci was performed in 793 case subjects and 857 control subjects from Sweden.

RESULTS

Genetic variation in the region upstream from the transcription initiation site of the gene encoding B lymphoid tyrosine kinase (BLK) and C8orf13 (chromosome 8p23.1) was associated with disease risk in both the U.S. and Swedish case-control series (rs13277113; odds ratio, 1.39; P=1x10(-10)) and also with altered levels of messenger RNA in B-cell lines. In addition, variants on chromosome 16p11.22, near the genes encoding integrin alpha M (ITGAM, or CD11b) and integrin alpha X (ITGAX), were associated with SLE in the combined sample (rs11574637; odds ratio, 1.33; P=3x10(-11)).

CONCLUSIONS

We identified and then confirmed through replication two new genetic loci for SLE: a promoter-region allele associated with reduced expression of BLK and increased expression of C8orf13 and variants in the ITGAM-ITGAX region.

MyD88-dependent autoimmune disease in Lyn-deficient mice

Recent evidence suggests that systemic autoimmune disease depends on signals from TLR ligands, but little is known about how TLR-dependent pathways lead to the loss of self tolerance in vivo. To address this, we have examined the role of TLR signaling in Lyn-deficient mice, which develop an autoimmune disease similar to SLE. We found that absence of the TLR signaling adaptor molecule MyD88 suppresses plasma cell differentiation of switched and unswitched B cells, and prevents the generation of antinuclear IgG antibodies and glomerulonephritis. In mixed chimeras the increased IgM and IgG antibody secretion in Lyn-deficient mice is at least partially due to B cell-independent effects of Lyn. We now show that MyD88 deficiency blocks the expansion and activation of DC in which Lyn is also normally expressed, and prevents the hypersecretion of proinflammatory cytokines IL-6 and IL-12 by Lyn-deficient DC. These findings further highlight the important role of TLR-dependent signals in both lymphocyte activation and autoimmune pathogenesis.