The phosphatase CD148 promotes airway hyperresponsiveness through SRC family kinases

Lipid Mediators Metabolic Chaos of Asthmatic Mice Reversed by Rosmarinic Acid

BACKGROUND AND OBJECTIVE

Asthma is a common chronic inflammatory disease of the airways with no known cure. Lipid mediators (LMs) are a kind of inflammatory signaling molecules which are believed to be involved in the development of asthma. Hyssopus cuspidatus Boriss. is a traditional Uyghur medicine, which is widely used in the treatment of asthma and other respiratory diseases. Extraction of Hyssopus cuspidatus Boriss. was reported to neutralize asthma symptoms. The purpose of the study was to investigate both the anti-inflammatory and immunoregulation properties of the Hyssopus cuspidatus Boriss. extract (SXCF) and its main active constituent, rosmarinic acid (RosA), in vivo. The effect of RosA, a major constituent of SXCF, was evaluated on an asthmatic model, with both anti-inflammatory and immunoregulation properties.

MATERIALS AND METHODS

Anti-inflammatory effect of SXCF and RosA was assessed using OVA-induced asthma model mice by UPLC-MS/MS method.

RESULTS

Overall, RosA played a critical role in anti-asthma treatment. In total, 90% of LMs species that were significantly regulated by SXCF were covered. On the most important LMs associated with asthma, RosA equivalent induced similar effects as SXCF did. It is believed that some constituents in SXCF could neutralize RosA excessive impacts on LMs.

Interplay between the tyrosine kinases Chk and Csk and phosphatase PTPRJ is critical for regulating platelets in mice

The Src family kinases (SFKs) Src, Lyn, and Fyn are essential for platelet activation and also involved in megakaryocyte (MK) development and platelet production. Platelet SFKs are inhibited by C-terminal Src kinase (Csk), which phosphorylates a conserved tyrosine in their C-terminal tail, and are activated by the receptor-type tyrosine phosphatase PTPRJ (CD148, DEP-1), which dephosphorylates the same residue. Deletion of Csk and PTPRJ in the MK lineage in mice results in increased SFK activity, but paradoxically hypoactive platelets resulting from negative feedback mechanisms, including upregulation of Csk homologous kinase (Chk) expression. Here, we investigate the role of Chk in platelets, functional redundancy with Csk, and the physiological consequences of ablating Chk, Csk, and PTPRJ in mice. Platelet count was normal in Chk knockout (KO) mice, reduced by 92% in Chk;Csk double KO (DKO) mice, and partially rescued in Chk;Csk;Ptprj triple KO (TKO) mice. Megakaryocyte numbers were significantly increased in both DKO and TKO mice. Phosphorylation of the inhibitory tyrosine of SFKs was almost completely abolished in DKO platelets, which was partially rescued in Src and Fyn in TKO platelets. This residual phosphorylation was abolished by Src inhibitors, revealing an unexpected mechanism in which SFKs autoinhibit their activity by phosphorylating their C-terminal tyrosine residues. We demonstrate that reduced inhibitory phosphorylation of SFKs leads to thrombocytopenia, with Csk being the dominant inhibitor in platelets and Chk having an auxiliary role. PTPRJ deletion in addition to Chk and Csk ameliorates the extent of thrombocytopenia, suggesting targeting it may have therapeutic benefits in such conditions.

The translation attenuating arginine-rich sequence in the extended signal peptide of the protein-tyrosine phosphatase PTPRJ/DEP1 is conserved in mammals

The signal peptides, present at the N-terminus of many proteins, guide the proteins into cell membranes. In some proteins, the signal peptide is with an extended N-terminal region. Previously, it was demonstrated that the N-terminally extended signal peptide of the human PTPRJ contains a cluster of arginine residues, which attenuates translation. The analysis of the mammalian orthologous sequences revealed that this sequence is highly conserved. The PTPRJ transcripts in placentals, marsupials, and monotremes encode a stretch of 10–14 arginine residues, positioned 11–12 codons downstream of the initiating AUG. The remarkable conservation of the repeated arginine residues in the PTPRJ signal peptides points to their key role. Further, the presence of an arginine cluster in the extended signal peptides of other proteins (E3 ubiquitin-protein ligase, NOTCH3) is noted and indicates a more general importance of this cis-acting mechanism of translational suppression.

Extracellular regulation of airway smooth muscle contraction

The molecular mechanisms governing the contraction of airway smooth muscle have always been at the forefront of asthma research. New extracellular molecules affecting the contraction of airway smooth muscle are steadily being discovered. Although interesting, this is disconcerting for researchers trying to find a mend for the significant part of asthma symptoms caused by contraction. Additional efforts are being deployed to understand the intracellular signaling pathways leading to contraction. The goal being to find common pathways that are essential to convey the contractile signal emanating from any single or combination of extracellular molecules. Not only these pathways exist and their details are being slowly unveiled, but some carry the signal inside-out to interact back with extracellular molecules. These latter represent targets with promising therapeutic potential, not only because they are molecules downstream of pathways essential for contraction but also because their extracellular location makes them readily accessible by inhaled drugs.

The Gp1ba-Cre transgenic mouse: a new model to delineate platelet and leukocyte functions

Conditional knockout (KO) mouse models are invaluable for elucidating the physiological roles of platelets. The Platelet factor 4-Cre recombinase (Pf4-Cre) transgenic mouse is the current model of choice for generating megakaryocyte/platelet-specific KO mice. Platelets and leukocytes work closely together in a wide range of disease settings, yet the specific contribution of platelets to these processes remains unclear. This is partially a result of the Pf4-Cre transgene being expressed in a variety of leukocyte populations. To overcome this issue, we developed a Gp1ba-Cre transgenic mouse strain in which Cre expression is driven by the endogenous Gp1ba locus. By crossing Gp1ba-Cre and Pf4-Cre mice to the mT/mG dual-fluorescence reporter mouse and performing a head-to-head comparison, we demonstrate more stringent megakaryocyte lineage-specific expression of the Gp1ba-Cre transgene. Broader tissue expression was observed with the Pf4-Cre transgene, leading to recombination in many hematopoietic lineages, including monocytes, macrophages, granulocytes, and dendritic and B and T cells. Direct comparison of phenotypes of Csk, Shp1, or CD148 conditional KO mice generated using either the Gp1ba-Cre or Pf4-Cre strains revealed similar platelet phenotypes. However, additional inflammatory and immunological anomalies were observed in Pf4-Cre-generated KO mice as a result of nonspecific deletion in other hematopoietic lineages. By excluding leukocyte contributions to phenotypes, the Gp1ba-Cre mouse will advance our understanding of the role of platelets in inflammation and other pathophysiological processes in which platelet-leukocyte interactions are involved.

Targeting Receptor-Type Protein Tyrosine Phosphatases with Biotherapeutics: Is Outside-in Better than Inside-Out?

Protein tyrosine phosphatases (PTPs), of the receptor and non-receptor classes, are key signaling molecules that play critical roles in cellular regulation underlying diverse physiological events. Aberrant signaling as a result of genetic mutation or altered expression levels has been associated with several diseases and treatment via pharmacological intervention at the level of PTPs has been widely explored; however, the challenges associated with development of small molecule phosphatase inhibitors targeting the intracellular phosphatase domain (the “inside-out” approach) have been well documented and as yet there are no clinically approved drugs targeting these enzymes. The alternative approach of targeting receptor PTPs with biotherapeutic agents (such as monoclonal antibodies or engineered fusion proteins; the “outside-in” approach) that interact with the extracellular ectodomain offers many advantages, and there have been a number of exciting recent developments in this field. Here we provide a brief overview of the receptor PTP family and an update on the emerging area of receptor PTP-targeted biotherapeutics for CD148, vascular endothelial-protein tyrosine phosphatase (VE-PTP), receptor-type PTPs σ, γ, ζ (RPTPσ, RPTPγ, RPTPζ) and CD45, and discussion of future potential in this area.

Maintenance of murine platelet homeostasis by the kinase Csk and phosphatase CD148

Src family kinases (SFKs) coordinate the initiating and propagating activation signals in platelets, but it remains unclear how they are regulated. Here, we show that ablation of C-terminal Src kinase (Csk) and receptor-like protein tyrosine-phosphatase CD148 in mice results in a dramatic increase in platelet SFK activity, demonstrating that these proteins are essential regulators of platelet reactivity. Paradoxically, Csk/CD148-deficient mice exhibit reduced in vivo and ex vivo thrombus formation and increased bleeding following injury rather than a prothrombotic phenotype. This is a consequence of multiple negative feedback mechanisms, including downregulation of the immunoreceptor tyrosine-based activation motif (ITAM)- and hemi-ITAM-containing receptors glycoprotein VI (GPVI)-Fc receptor (FcR) γ-chain and CLEC-2, respectively and upregulation of the immunoreceptor tyrosine-based inhibition motif (ITIM)-containing receptor G6b-B and its interaction with the tyrosine phosphatases Shp1 and Shp2. Results from an analog-sensitive Csk mouse model demonstrate the unconventional role of SFKs in activating ITIM signaling. This study establishes Csk and CD148 as critical molecular switches controlling the thrombotic and hemostatic capacity of platelets and reveals cell-intrinsic mechanisms that prevent pathological thrombosis from occurring.

Transforming growth factor-β enhances Rho-kinase activity and contraction in airway smooth muscle via the nucleotide exchange factor ARHGEF1

Key points

Transforming growth‐factor‐β (TGF‐β) and RhoA/Rho‐kinase are independently implicated in the airway hyper‐responsiveness associated with asthma, but how these proteins interact is not fully understood.

We examined the effects of pre‐treatment with TGF‐β on expression and activity of RhoA, Rho‐kinase and ARHGEF1, an activator of RhoA, as well as on bradykinin‐induced contraction, in airway smooth muscle.

TGF‐β enhanced bradykinin‐induced RhoA translocation, Rho‐kinase‐dependent phosphorylation and contraction, but partially suppressed bradykinin‐induced RhoA activity (RhoA‐GTP content).

TGF‐β enhanced the expression of ARHGEF1, while a small interfering RNA against ARHGEF1 and a RhoGEF inhibitor prevented the effects of TGF‐β on RhoA and Rho‐kinase activity and contraction, respectively.

ARHGEF1 expression was also enhanced in airway smooth muscle from asthmatic patients and ovalbumin‐sensitized mice.

ARHGEF1 is a key TGF‐β target gene, an important regulator of Rho‐kinase activity and therefore a potential therapeutic target for the treatment of asthmatic airway hyper‐responsiveness.

Abstract

Transforming growth factor‐β (TGF‐β), RhoA/Rho‐kinase and Src‐family kinases (SrcFK) have independently been implicated in airway hyper‐responsiveness, but how they interact to regulate airway smooth muscle contractility is not fully understood. We found that TGF‐β pre‐treatment enhanced acute contractile responses to bradykinin (BK) in isolated rat bronchioles, and inhibitors of RhoGEFs (Y16) and Rho‐kinase (Y27632), but not the SrcFK inhibitor PP2, prevented this enhancement. In cultured human airway smooth muscle cells (hASMCs), TGF‐β pre‐treatment enhanced the protein expression of the Rho guanine nucleotide exchange factor ARHGEF1, MLC₂₀, MYPT‐1 and the actin‐severing protein cofilin, but not of RhoA, ROCK2 or c‐Src. In hASMCs, acute treatment with BK triggered subcellular translocation of ARHGEF1 and RhoA and enhanced auto‐phosphorylation of SrcFK and phosphorylation of MYPT1 and MLC₂₀, but induced de‐phosphorylation of cofilin. TGF‐β pre‐treatment amplified the effects of BK on RhoA translocation and MYPT1/MLC₂₀ phosphorylation, but suppressed the effects of BK on RhoA‐GTP content, SrcFK auto‐phosphorylation and cofilin de‐phosphorylation. In hASMCs, an ARHGEF1 small interfering RNA suppressed the effects of BK and TGF‐β on RhoA‐GTP content, RhoA translocation and MYPT1 and MLC₂₀ phosphorylation, but minimally influenced the effects of TGF‐β on cofilin expression and phosphorylation. ARHGEF1 expression was also enhanced in ASMCs of asthmatic patients and in lungs of ovalbumin‐sensitized mice. Our data indicate that TGF‐β enhances BK‐induced contraction, RhoA translocation and Rho‐kinase activity in airway smooth muscle largely via ARHGEF1, but independently of SrcFK and total RhoA‐GTP content. A role for smooth muscle ARHGEF1 in asthmatic airway hyper‐responsiveness is worthy of further investigation.

Transforming growth‐factor‐β (TGF‐β) and RhoA/Rho‐kinase are independently implicated in the airway hyper‐responsiveness associated with asthma, but how these proteins interact is not fully understood.

We examined the effects of pre‐treatment with TGF‐β on expression and activity of RhoA, Rho‐kinase and ARHGEF1, an activator of RhoA, as well as on bradykinin‐induced contraction, in airway smooth muscle.

TGF‐β enhanced bradykinin‐induced RhoA translocation, Rho‐kinase‐dependent phosphorylation and contraction, but partially suppressed bradykinin‐induced RhoA activity (RhoA‐GTP content).

TGF‐β enhanced the expression of ARHGEF1, while a small interfering RNA against ARHGEF1 and a RhoGEF inhibitor prevented the effects of TGF‐β on RhoA and Rho‐kinase activity and contraction, respectively.

ARHGEF1 expression was also enhanced in airway smooth muscle from asthmatic patients and ovalbumin‐sensitized mice.

ARHGEF1 is a key TGF‐β target gene, an important regulator of Rho‐kinase activity and therefore a potential therapeutic target for the treatment of asthmatic airway hyper‐responsiveness.

Intelectin contributes to allergen-induced IL-25, IL-33, and TSLP expression and type 2 response in asthma and atopic dermatitis

The epithelial and epidermal innate cytokines IL-25, IL-33, and thymic stromal lymphopoietin (TSLP) have pivotal roles in the initiation of allergic inflammation in asthma and atopic dermatitis (AD). However, the mechanism by which the expression of these innate cytokines is regulated remains unclear. Intelectin (ITLN) is expressed in airway epithelial cells and promotes allergic airway inflammation. We hypothesized that ITLN is required for allergen-induced IL-25, IL-33, and TSLP expression. In two asthma models, Itln knockdown reduced allergen-induced increases in Il-25, Il-33, and Tslp and development of type 2 response, eosinophilic inflammation, mucus overproduction, and airway hyperresponsiveness. Itln knockdown also inhibited house dust mite (HDM)-induced early upregulation of Il-25, Il-33, and Tslp in a model solely inducing airway sensitization. Using human airway epithelial cells, we demonstrated that HDM-induced increases in ITLN led to phosphorylation of epidermal growth factor receptor and extracellular-signal regulated kinase, which were required for induction of IL-25, IL-33, and TSLP expression. In two AD models, Itln knockdown suppressed expression of Il-33, Tslp, and Th2 cytokines and eosinophilic inflammation. In humans, ITLN1 expression was significantly increased in asthmatic airways and in lesional skin of AD. We conclude that ITLN contributes to allergen-induced Il-25, Il-33, and Tslp expression in asthma and AD.

Tumor Suppressor PTPRJ Is a Target of miR-155 in Colorectal Cancer

PTPRJ is known for its antiproliferative role. Loss of heterozygosity (LOH) of PTPRJ has frequently been observed in various human cancers including colorectal cancer (CRC), lung cancer, and breast cancer. However, the function and mechanism of PTPRJ in CRC are not well understood. At the present study, we show that ectopic expression of PTPRJ inhibits cell growth, migration, and invasiveness in CRC cell line HCT116. Moreover, PTPRJ inhibits the tumorigenecity of HCT116 in a xenograft tumor model. MiR-155, the well-known oncomiR in CRC, is identified as an upstream factor of PTPRJ. MiR-155 directly binds to the 3' untranslated region of PTPRJ mRNA and suppresses the mRNA and protein levels of PTPRJ. Furthermore, the growth-promoting and AKT signaling activation effect of miR-155 was abrogated by PTPRJ overexpression, and vice versa. Our study reveals the crucial role of miR-155/PTPRJ/AKT axis in proliferation and migration of CRC cells and suggests a therapeutic potential of PTPRJ. J. Cell. Biochem. 118: 3391-3400, 2017. © 2017 Wiley Periodicals, Inc.

Modulation of VEGF receptor 2 signaling by protein phosphatases

Phosphorylation of serines, threonines, and tyrosines is a central event in signal transduction cascades in eukaryotic cells. The phosphorylation state of any particular protein reflects a balance of activity between kinases and phosphatases. Kinase biology has been exhaustively studied and is reasonably well understood, however, much less is known about phosphatases. A large body of evidence now shows that protein phosphatases do not behave as indiscriminate signal terminators, but can function both as negative or positive regulators of specific signaling pathways. Genetic models have also shown that different protein phosphatases play precise biological roles in health and disease. Finally, genome sequencing has unveiled the existence of many protein phosphatases and associated regulatory subunits comparable in number to kinases. A wide variety of roles for protein phosphatase roles have been recently described in the context of cancer, diabetes, hereditary disorders and other diseases. In particular, there have been several recent advances in our understanding of phosphatases involved in regulation of vascular endothelial growth factor receptor 2 (VEGFR2) signaling. The receptor is the principal signaling molecule mediating a wide spectrum of VEGF signal and, thus, is of paramount significance in a wide variety of diseases ranging from cancer to cardiovascular to ophthalmic. This review focuses on the current knowledge about protein phosphatases' regulation of VEGFR2 signaling and how these enzymes can modulate its biological effects.

Chemerin-induced arterial contraction is Gi- and calcium-dependent

Chemerin is an adipokine associated with increased blood pressure, and may link obesity with hypertension. We tested the hypothesis that chemerin-induced contraction of the vasculature occurs via calcium flux in smooth muscle cells. Isometric contraction of rat aortic rings was performed in parallel with calcium kinetics of rat aortic smooth muscle cells to assess the possible signaling pathway. Chemerin-9 (nonapeptide of the chemerin S¹⁵⁷ isoform) caused a concentration-dependent contraction of isolated aorta (EC₅₀ 100nM) and elicited a concentration-dependent intracellular calcium response (EC₅₀ 10nM). Pertussis toxin (G_i inhibitor), verapamil (L-type Ca²⁺ channel inhibitor), PP1 (Src inhibitor), and Y27632 (Rho kinase inhibitor) reduced both calcium influx and isometric contraction to chemerin-9 but PD098059 (Erk MAPK inhibitor) and U73122 (PLC inhibitor) had little to no effect on either measure of chemerin signaling. Although our primary aim was to examine chemerin signaling, we also highlight differences in the mechanisms of chemerin-9 and recombinant chemerin S¹⁵⁷. These data support a chemerin-induced contractile mechanism in vascular smooth muscle that functions through G_i proteins to activate L-type Ca²⁺ channels, Src, and Rho kinase. There is mounting evidence linking chemerin to hypertension and this mechanism brings us closer to targeting chemerin as a form of therapy.

Positive Regulation of Lyn Kinase by CD148 Is Required for B Cell Receptor Signaling in B1 but Not B2 B Cells

B1 and B2 B cells differ in their ability to respond to T-cell-independent (TI) antigens. Here we report that the Src-family kinase (SFK) regulator CD148 has a unique and critical role in the initiation of B1 but not B2 cell antigen receptor signaling. CD148 loss-of-function mice were found to have defective B1 B-cell-mediated antibody responses against the T-cell-independent antigens NP-ficoll and Pneumovax 23 and had impaired selection of the B1 B cell receptor (BCR) repertoire. These deficiencies were associated with a decreased ability of B1 B cells to induce BCR signaling downstream of the SFK Lyn. Notably, Lyn appeared to be selectively regulated by CD148 and loss of this SFK resulted in opposite signaling phenotypes in B1 and B2 B cells. These findings reveal that the function and regulation of Lyn during B1 cell BCR signaling is distinct from other B cell subsets.

Scaffolding protein Gab1 regulates myeloid dendritic cell migration in allergic asthma

Asthma is a common allergic disorder involving a complex interplay among multiple genetic and environmental factors. Recent studies identified genetic variants of human GAB1 as a novel asthma susceptibility factor. However, the functions of Gab1 in lung remain largely unexplored. In this study, we first observed an elevation of Gab1 level in peripheral blood mononuclear cells from asthmatic patients during acute exacerbation compared with convalescence. Mice with a selectively disrupted Gab1 in myeloid dendritic cells (mDCs) considerably attenuated allergic inflammation in experimental models of asthma. Further investigations revealed a prominent reduction in CCL19-mediated migration of Gab1-deficient mDCs to draining lymph nodes and subsequent impairment of Th2-driven adaptive activation. Mechanistically, Gab1 is an essential component of the CCL19/CCR7 chemokine axis that regulates mDC migration during asthmatic responses. Together, these findings provide the first evidence for the roles of Gab1 in lung, giving us deeper understanding of asthmatic pathogenesis.

Tyrosine Phosphatase PTPRJ/DEP-1 Is an Essential Promoter of Vascular Permeability, Angiogenesis, and Tumor Progression

The protein tyrosine phosphatase PTPRJ/DEP-1 has been implicated in negative growth regulation in endothelial cells, where its expression varies at transitions between proliferation and contact inhibition. However, in the same cells, DEP-1 has also been implicated in VEGF-dependent Src activation, permeability, and capillary formation, suggesting a positive role in regulating these functions. To resolve this dichotomy in vivo, we investigated postnatal angiogenesis and vascular permeability in a DEP-1-deficient mouse. In this study, we report that DEP-1 is required for Src activation and phosphorylation of its endothelial cell-specific substrate, VE-cadherin, after systemic injection of VEGF. Accordingly, VEGF-induced vascular leakage was abrogated in the DEP-1-deficient mice. Furthermore, capillary formation was impaired in murine aortic tissue rings or Matrigel plugs infused with VEGF. In the absence of DEP-1, angiogenesis triggered by ischemia or during tumor formation was defective, which in the latter case was associated with reduced tumor cell proliferation and increased apoptosis. Macrophage infiltration was also impaired, reflecting reduced vascular permeability in the tumors or a possible cell autonomous effect of DEP-1. Consequently, the formation of spontaneous and experimental lung metastases was strongly decreased in DEP-1-deficient mice. In clinical specimens of cancer, less vascularized tumors exhibited lower microvascular expression of DEP-1. Altogether, our results established DEP-1 as an essential driver of VEGF-dependent permeability, angiogenesis, and metastasis, suggesting a novel therapeutic route to cancer treatment. Cancer Res; 76(17); 5080-91. ©2016 AACR.

Divergent modulation of Rho-kinase and Ca(2+) influx pathways by Src family kinases and focal adhesion kinase in airway smooth muscle

Background and Purpose

The importance of tyrosine kinases in airway smooth muscle (ASM) contraction is not fully understood. The aim of this study was to investigate the role of Src‐family kinases (SrcFK) and focal adhesion kinase (FAK) in GPCR‐mediated ASM contraction and associated signalling events.

Experimental Approach

Contraction was recorded in intact or α‐toxin permeabilized rat bronchioles. Phosphorylation of SrcFK, FAK, myosin light‐chain‐20 (MLC₂₀) and myosin phosphatase targeting subunit‐1 (MYPT‐1) was evaluated in cultured human ASM cells (hASMC). [Ca²⁺]_i was evaluated in Fura‐2 loaded hASMC. Responses to carbachol (CCh) and bradykinin (BK) and the contribution of SrcFK and FAK to these responses were determined.

Key Results

Contractile responses in intact bronchioles were inhibited by antagonists of SrcFK, FAK and Rho‐kinase, while after α‐toxin permeabilization, they were sensitive to inhibition of SrcFK and Rho‐kinase, but not FAK. CCh and BK increased phosphorylation of MYPT‐1 and MLC₂₀ and auto‐phosphorylation of SrcFK and FAK. MYPT‐1 phosphorylation was sensitive to inhibition of Rho‐kinase and SrcFK, but not FAK. Contraction induced by SR Ca²⁺ depletion and equivalent [Ca²⁺]_i responses in hASMC were sensitive to inhibition of both SrcFK and FAK, while depolarization‐induced contraction was sensitive to FAK inhibition only. SrcFK auto‐phosphorylation was partially FAK‐dependent, while FAK auto‐phosphorylation was SrcFK‐independent.

Conclusions and Implications

SrcFK mediates Ca²⁺‐sensitization in ASM, while SrcFK and FAK together and individually influence multiple Ca²⁺ influx pathways. Tyrosine phosphorylation is therefore a key upstream signalling event in ASM contraction and may be a viable target for modulating ASM tone in respiratory disease.

An HNF1α-regulated feedback circuit modulates hepatic fibrogenesis via the crosstalk between hepatocytes and hepatic stellate cells

Hepatocytes are critical for the maintenance of liver homeostasis, but its involvement in hepatic fibrogenesis remains elusive. Hepatocyte nuclear factor 1α (HNF1α) is a liver-enriched transcription factor that plays a key role in hepatocyte function. Our previous study revealed a significant inhibitory effect of HNF1α on hepatocellular carcinoma. In this study, we report that the expression of HNF1α is significantly repressed in both human and rat fibrotic liver. Knockdown of HNF1α in the liver significantly aggravates hepatic fibrogenesis in either dimethylnitrosamine (DMN) or bile duct ligation (BDL) model in rats. In contrast, forced expression of HNF1α markedly alleviates hepatic fibrosis. HNF1α regulates the transcriptional expression of SH2 domain-containing phosphatase-1 (SHP-1) via directly binding to SHP-1 promoter in hepatocytes. Inhibition of SHP-1 expression abrogates the anti-fibrotic effect of HNF1α in DMN-treated rats. Moreover, HNF1α repression in primary hepatocytes leads to the activation of NF-κB and JAK/STAT pathways and initiates an inflammatory feedback circuit consisting of HNF1α, SHP-1, STAT3, p65, miR-21 and miR-146a, which sustains the deregulation of HNF1α in hepatocytes. More interestingly, a coordinated crosstalk between hepatocytes and hepatic stellate cells (HSCs) participates in this positive feedback circuit and facilitates the progression of hepatocellular damage. Our findings demonstrate that impaired hepatocytes play an active role in hepatic fibrogenesis. Early intervention of HNF1α-regulated inflammatory feedback loop in hepatocytes may have beneficial effects in the treatment of chronic liver diseases.

CD148 tyrosine phosphatase promotes cadherin cell adhesion

CD148 is a transmembrane tyrosine phosphatase that is expressed at cell junctions. Recent studies have shown that CD148 associates with the cadherin/catenin complex and p120 catenin (p120) may serve as a substrate. However, the role of CD148 in cadherin cell-cell adhesion remains unknown. Therefore, here we addressed this issue using a series of stable cells and cell-based assays. Wild-type (WT) and catalytically inactive (CS) CD148 were introduced to A431D (lacking classical cadherins), A431D/E-cadherin WT (expressing wild-type E-cadherin), and A431D/E-cadherin 764AAA (expressing p120-uncoupled E-cadherin mutant) cells. The effects of CD148 in cadherin adhesion were assessed by Ca²⁺ switch and cell aggregation assays. Phosphorylation of E-cadherin/catenin complex and Rho family GTPase activities were also examined. Although CD148 introduction did not alter the expression levels and complex formation of E-cadherin, p120, and β-catenin, CD148 WT, but not CS, promoted cadherin contacts and strengthened cell-cell adhesion in A431D/E-cadherin WT cells. This effect was accompanied by an increase in Rac1, but not RhoA and Cdc42, activity and largely diminished by Rac1 inhibition. Further, we demonstrate that CD148 reduces the tyrosine phosphorylation of p120 and β-catenin; causes the dephosphorylation of Y529 suppressive tyrosine residue in Src, a well-known CD148 site, increasing Src activity and enhancing the phosphorylation of Y228 (a Src kinase site) in p120, in E-cadherin contacts. Consistent with these findings, CD148 dephosphorylated both p120 and β-catenin in vitro. The shRNA-mediated CD148 knockdown in A431 cells showed opposite effects. CD148 showed no effects in A431D and A431D/E-cadherin 764AAA cells. In aggregate, these findings provide the first evidence that CD148 promotes E-cadherin adhesion by regulating Rac1 activity concomitant with modulation of p120, β-catenin, and Src tyrosine phosphorylation. This effect requires E-cadherin and p120 association.

Loss of regulator of G protein signaling 5 promotes airway hyperresponsiveness in the absence of allergic inflammation

BACKGROUND

Although eosinophilic inflammation typifies allergic asthma, it is not a prerequisite for airway hyperresponsiveness (AHR), suggesting that underlying abnormalities in structural cells, such as airway smooth muscle (ASM), contribute to the asthmatic diathesis. Dysregulation of procontractile G protein-coupled receptor (GPCR) signaling in ASM could mediate enhanced contractility.

OBJECTIVE

We explored the role of a regulator of procontractile GPCR signaling, regulator of G protein signaling 5 (RGS5), in unprovoked and allergen-induced AHR.

METHODS

We evaluated GPCR-evoked Ca(2+) signaling, precision-cut lung slice (PCLS) contraction, and lung inflammation in naive and Aspergillus fumigatus-challenged wild-type and Rgs5(-/-) mice. We analyzed lung resistance and dynamic compliance in live anesthetized mice using invasive plethysmography.

RESULTS

Loss of RGS5 promoted constitutive AHR because of enhanced GPCR-induced Ca(2+) mobilization in ASM. PCLSs from naive Rgs5(-/-) mice contracted maximally at baseline independently of allergen challenge. RGS5 deficiency had little effect on the parameters of allergic inflammation, including cell counts in bronchoalveolar lavage fluid, mucin production, ASM mass, and subepithelial collagen deposition. Unexpectedly, induced IL-13 and IL-33 levels were much lower in challenged lungs from Rgs5(-/-) mice relative to those seen in wild-type mice.

CONCLUSION

Loss of RGS5 confers spontaneous AHR in mice in the absence of allergic inflammation. Because it is selectively expressed in ASM within the lung and does not promote inflammation, RGS5 might be a therapeutic target for asthma.

Population of sensory neurons essential for asthmatic hyperreactivity of inflamed airways

Asthma is a common debilitating inflammatory lung disease affecting over 200 million people worldwide. Here, we investigated neurogenic components involved in asthmatic-like attacks using the ovalbumin-sensitized murine model of the disease, and identified a specific population of neurons that are required for airway hyperreactivity. We show that ablating or genetically silencing these neurons abolished the hyperreactive broncho-constrictions, even in the presence of a fully developed lung inflammatory immune response. These neurons are found in the vagal ganglia and are characterized by the expression of the transient receptor potential vanilloid 1 (TRPV1) ion channel. However, the TRPV1 channel itself is not required for the asthmatic-like hyperreactive airway response. We also demonstrate that optogenetic stimulation of this population of TRP-expressing cells with channelrhodopsin dramatically exacerbates airway hyperreactivity of inflamed airways. Notably, these cells express the sphingosine-1-phosphate receptor 3 (S1PR3), and stimulation with a S1PR3 agonist efficiently induced broncho-constrictions, even in the absence of ovalbumin sensitization and inflammation. Our results show that the airway hyperreactivity phenotype can be physiologically dissociated from the immune component, and provide a platform for devising therapeutic approaches to asthma that target these pathways separately.

Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.