IL-13 induces tyrosine phosphorylation of phospholipase C gamma-1 following IRS-2 association in human monocytes: relationship with the inhibitory effect of IL-13 on ROI production

IL-4 and IL-13 Receptor Signaling From 4PS to Insulin Receptor Substrate 2: There and Back Again, a Historical View

In this historical perspective, written in honor of Dr. William E. Paul, we describe the initial discovery of one of the dominant substrates for tyrosine phosphorylation stimulated by IL-4. We further describe how this “IL-4-induced phosphorylated substrate” (4PS) was characterized as a member of the insulin receptor substrate (IRS) family of large adaptor proteins that link IL-4 and insulin receptors to activation of the phosphatidyl-inositol 3′ kinase pathway as well as other downstream signaling pathways. The relative contribution of the 4PS/IRS pathway to the early models of IL-4-induced proliferation and suppression of apoptosis are compared to our more recent understanding of the complex interplay between positive and negative regulatory pathways emanating from members of the IRS family that impact allergic responses.

Phospholipases: An Overview

Phospholipases are lipolytic enzymes that hydrolyze phospholipid substrates at specific ester bonds. Phospholipases are widespread in nature and play very diverse roles from aggression in snake venom to signal transduction, lipid mediator production, and metabolite digestion in humans. Phospholipases vary considerably in structure, function, regulation, and mode of action. Tremendous advances in understanding the structure and function of phospholipases have occurred in the last decades. This introductory chapter is aimed at providing a general framework of the current understanding of phospholipases and a discussion of their mechanisms of action and emerging biological functions.

Multimodal Recognition of Diverse Peptides by the C-Terminal SH2 Domain of Phospholipase C-γ1 Protein

SH2 domains recognize phosphotyrosine (pY)-containing peptide ligands and play key roles in the regulation of receptor tyrosine kinase pathways. Each SH2 domain has individualized specificity, encoded in the amino acids neighboring the pY, for defined targets that convey their distinct functions. The C-terminal SH2 domain (PLCC) of the phospholipase C-γ1 full-length protein (PLCγ1) typically binds peptides containing small and hydrophobic amino acids adjacent to the pY, including a peptide derived from platelet-derived growth factor receptor B (PDGFRB) and an intraprotein recognition site (Y783 of PLCγ1) involved in the regulation of the protein's lipase activity. Remarkably, PLCC also recognizes unexpected peptides containing amino acids with polar or bulky side chains that deviate from this pattern. This versatility in recognition specificity may allow PLCγ1 to participate in diverse, previously unrecognized, signaling pathways in response to binding chemically dissimilar partners. We have used structural approaches, including nuclear magnetic resonance and X-ray crystallography, to elucidate the mechanisms of noncognate peptide binding to PLCC by ligands derived from receptor tyrosine kinase ErbB2 and from the insulin receptor. The high-resolution peptide-bound structures reveal that PLCC has a relatively static backbone but contains a chemically rich protein surface comprised of a combination of hydrophobic pockets and amino acids with charged side chains. We demonstrate that this expansive and chemically diverse PLCC interface, in addition to peptide conformational plasticity, permits PLCC to recognize specific noncognate peptide ligands with multimodal specificity.

IL-17A enhances IL-13 activity by enhancing IL-13-induced signal transducer and activator of transcription 6 activation

BACKGROUND

Increased IL-17A production has been associated with more severe asthma; however, the mechanisms whereby IL-17A can contribute to IL-13-driven pathology in asthmatic patients remain unclear.

OBJECTIVE

We sought to gain mechanistic insight into how IL-17A can influence IL-13-driven responses.

METHODS

The effect of IL-17A on IL-13-induced airway hyperresponsiveness, gene expression, mucus hypersecretion, and airway inflammation was assessed by using in vivo models of IL-13-induced lung pathology and in vitro culture of murine fibroblast cell lines and primary fibroblasts and human epithelial cell lines or primary human epithelial cells exposed to IL-13, IL-17A, or both.

RESULTS

Compared with mice given intratracheal IL-13 alone, those exposed to IL-13 and IL-17A had augmented airway hyperresponsiveness, mucus production, airway inflammation, and IL-13-induced gene expression. In vitro, IL-17A enhanced IL-13-induced gene expression in asthma-relevant murine and human cells. In contrast to the exacerbating influence of IL-17A on IL-13-induced responses, coexposure to IL-13 inhibited IL-17A-driven antimicrobial gene expression in vivo and in vitro. Mechanistically, in both primary human and murine cells, the IL-17A-driven increase in IL-13-induced gene expression was associated with enhanced IL-13-driven signal transducer and activator of transcription 6 activation.

CONCLUSIONS

Our data suggest that IL-17A contributes to asthma pathophysiology by increasing the capacity of IL-13 to activate intracellular signaling pathways, such as signal transducer and activator of transcription 6. These data represent the first mechanistic explanation of how IL-17A can directly contribute to the pathogenesis of IL-13-driven pathology.

Phosphoinositide-specific phospholipase C in health and disease

Phospholipases are widely occurring and can be found in several different organisms, including bacteria, yeast, plants, animals, and viruses. Phospholipase C (PLC) is a class of phospholipases that cleaves phospholipids on the diacylglycerol (DAG) side of the phosphodiester bond producing DAGs and phosphomonoesters. Among PLCs, phosphoinositide-specific PLC (PI-PLC) constitutes an important step in the inositide signaling pathways. The structures of PI-PLC isozymes show conserved domains as well as regulatory specific domains. This is important, as most PI-PLCs share a common mechanism, but each of them has a peculiar role and can have a specific cell distribution that is linked to a specific function. More importantly, the regulation of PLC isozymes is fundamental in health and disease, as there are several PLC-dependent molecular mechanisms that are associated with the activation or inhibition of important physiopathological processes. Moreover, PI-PLC alternative splicing variants can play important roles in complex signaling networks, not only in cancer but also in other diseases. That is why PI-PLC isozymes are now considered as important molecules that are essential for better understanding the molecular mechanisms underlying both physiology and pathogenesis, and are also potential molecular targets useful for the development of innovative therapeutic strategies.

SRC Homology 2 Domain Binding Sites in Insulin, IGF-1 and FGF receptor mediated signaling networks reveal an extensive potential interactome

Specific peptide ligand recognition by modular interaction domains is essential for the fidelity of information flow through the signal transduction networks that control cell behavior in response to extrinsic and intrinsic stimuli. Src homology 2 (SH2) domains recognize distinct phosphotyrosine peptide motifs, but the specific sites that are phosphorylated and the complement of available SH2 domains varies considerably in individual cell types. Such differences are the basis for a wide range of available protein interaction microstates from which signaling can evolve in highly divergent ways. This underlying complexity suggests the need to broadly map the signaling potential of systems as a prerequisite for understanding signaling in specific cell types as well as various pathologies that involve signal transduction such as cancer, developmental defects and metabolic disorders. This report describes interactions between SH2 domains and potential binding partners that comprise initial signaling downstream of activated fibroblast growth factor (FGF), insulin (Ins), and insulin-like growth factor-1 (IGF-1) receptors. A panel of 50 SH2 domains screened against a set of 192 phosphotyrosine peptides defines an extensive potential interactome while demonstrating the selectivity of individual SH2 domains. The interactions described confirm virtually all previously reported associations while describing a large set of potential novel interactions that imply additional complexity in the signaling networks initiated from activated receptors. This study of pTyr ligand binding by SH2 domains provides valuable insight into the selectivity that underpins complex signaling networks that are assembled using modular protein interaction domains.

[Roles of PPAR and p21WAF1/CIP1 in monocyte/macrophage differentiation: are circulating monocytes able to proliferate?]

Macrophages are involved in the immune and the inflammatory response. The deregulation of their physiological properties is associated with several pathologies such as atherosclerosis and some cancers. Cytokines action on this blood lineage modulates p21WAF1/CIP1 expression. It appears that this protein may play a role in the inflammation regulation through PPAR (peroxysome proliferator-activated receptors) transcription factors, strongly linked to lipid metabolism. It could also be involved in the control of the proliferation of monocytes/macrophages, even if these cells are classically described as devoided of any proliferative capacity.

Interleukin-13 neutralization modulates interleukin-13 induced suppression of reactive oxygen species production in peritoneal macrophages in a murine T-cell lymphoma

IL-13 is a Th2 cytokine that regulates the effector functions and alters the phenotype and function of normal macrophages switching to alternatively activated or type II polarized macrophages. The type II polarized macrophages differ from normal macrophages greatly in terms of receptor expression, NO and other cytokine production. It produces chemokines that preferentially attract Th2 cells, which increases the local concentration of Th2 cytokines including IL-13. As a result, normal macrophage population gets polarized as type II macrophages at the site of the tumor-microenvironment. In the present investigation, we have determined the IL-13 serum level in DL-bearing host and the effect of IL-13 on peritoneal macrophages harvested from normal healthy, control DL-bearing, and treated DL-bearing mice with respect to reactive oxygen intermediate production. It has been observed that IL-13 significantly inhibits the ROI generation in all macrophage types while by neutralizing with invivo administration of IL-13R*2 and/or potentiation with Th1 cytokine, the production of reactive oxygen intermediate increases, which indicates that IL-13R*2 and/or potentiation with Th1 cytokine could restore the cytotoxic ability of macrophage in a murine T-cell lymphoma.

Effects of Anaplasma phagocytophila on NADPH oxidase components in human neutrophils and HL-60 cells

The human granulocytic ehrlichiosis agent, Anaplasma phagocytophila, resides and multiplies exclusively in cytoplasmic vacuoles of granulocytes. A. phagocytophila rapidly inhibits the superoxide anion (O(2)(-)) generation by human neutrophils in response to various stimuli. To determine the inhibitory mechanism, the influence of A. phagocytophila on protein levels and localization of components of the NADPH oxidase were examined. A. phagocytophila decreased levels of p22(phox), but not gp91(phox), p47(phox), p67(phox), or P40(phox) reactive with each component-specific antibody in human peripheral blood neutrophils and HL-60 cells. Double immunofluorescence labeling revealed that p47(phox), p67(phox), Rac2, and p22(phox) did not colocalize with A. phagocytophila inclusions in neutrophils or HL-60 cells, and p22(phox) levels were also reduced. A. phagocytophila did not prevent either membrane translocation of cytoplasmic p47(phox) and p67(phox) or phosphorylation of p47(phox) upon stimulation by phorbol myristate acetate. The inhibitory signals for O(2)(-) generation was independent of several signals required for A. phagocytophila internalization. These results suggest that rapid alteration in p22(phox) induced by binding of A. phagocytophila to neutrophils is involved in the inhibition of O(2)(-) generation. Absence of colocalization of NADPH oxidase components with the inclusion further protects A. phagocytophila from oxidative damage.

Identification of insulin receptor substrate 1 (IRS-1) and IRS-2 as signaling intermediates in the alpha6beta4 integrin-dependent activation of phosphoinositide 3-OH kinase and promotion of invasion

Expression of the alpha6beta4 integrin increases the invasive potential of carcinoma cells by a mechanism that involves activation of phosphoinositide 3-OH kinase (PI3K). In the present study, we investigated the signaling pathway by which the alpha6beta4 integrin activates PI3K. Neither the alpha6 nor the beta4 cytoplasmic domain contains the consensus binding motif for PI3K, pYMXM, indicating that additional proteins are likely to be involved in the activation of this lipid kinase by the alpha6beta4 integrin. We identified insulin receptor substrate 1 (IRS-1) and IRS-2 as signaling intermediates in the activation of PI3K by the alpha6beta4 integrin. IRS-1 and IRS-2 are cytoplasmic adapter proteins that do not contain intrinsic kinase activity but rather function by recruiting proteins to surface receptors, where they organize signaling complexes. Ligation of the alpha6beta4 receptor promotes tyrosine phosphorylation of IRS-1 and IRS-2 and increases their association with PI3K, as determined by coimmunoprecipitation. Moreover, we identified a tyrosine residue in the cytoplasmic domain of the beta4 subunit, Y1494, that is required for alpha6beta4-dependent phosphorylation of IRS-2 and activation of PI3K in response to receptor ligation. Most importantly, Y1494 is essential for the ability of the alpha6beta4 integrin to promote carcinoma invasion. Taken together, these results imply a key role for the IRS proteins in the alpha6beta4-dependent promotion of carcinoma invasion.

IL-13 stimulates vascular endothelial cell growth factor and protects against hyperoxic acute lung injury

Hyperoxia is an important cause of acute lung injury. To determine whether IL-13 is protective in hyperoxia, we compared the survival in 100% O(2) of transgenic mice that overexpress IL-13 in the lung and of nontransgenic littermate controls. IL-13 enhanced survival in 100% O(2). One hundred percent of nontransgenic mice died in 4-5 days, whereas 100% of IL-13-overexpressing mice lived for more than 7 days, and many lived 10-14 days. IL-13 also stimulated VEGF accumulation in mice breathing room air, and it interacted with 100% (2) to increase VEGF accumulation further. The 164-amino acid isoform was the major VEGF moiety in bronchoalveolar lavage from transgenic mice in room air, whereas the 120- and 188-amino acid isoforms accumulated in these mice during hyperoxia. In addition, antibody neutralization of VEGF decreased the survival of IL-13-overexpressing mice in 100% (2). These studies demonstrate that IL-13 has protective effects in hyperoxic acute lung injury. They also demonstrate that IL-13, alone and in combination with 100% (2), stimulates pulmonary VEGF accumulation, that this stimulation is isoform-specific, and that the protective effects of IL-13 are mediated, in part, by VEGF.

Increased cyclooxygenase-2 and 5-lipoxygenase activating protein expression in peritoneal macrophages during ovalbumin immunization of mice and cytosolic phospholipase A(2) activation after antigen challenge

The present study investigates phenotypic and functional differentiation of peritoneal macrophages during ovalbumin-induced subcutaneous immunization of mice. For the first time we show that, in mouse peritoneal macrophages, ovalbumin immunization induces an increase in cyclooxygenase-2 (COX-2) and 5-lipoxygenase activating protein (FLAP) expression whereas it inhibits cytosolic phospholipase A(2) (cPLA2) expression. The study of arachidonic acid (AA) metabolism in peritoneal macrophages from control (cPM) and ovalbumin-immunized (iPM) mice shows that the reduced cPLA2 expression is correlated to a reduced basal AA metabolism, but is not a limiting factor for the opsonized zymosan-, PMA-, or A23187-triggered AA metabolism. We also show that in vitro ovalbumin challenge induces, only in iPM, cPLA2 activation through phosphorylation of serine residues, via a mechanism involving MAP kinases, and through increased intracellular calcium concentrations, leading to eicosanoid production. In parallel, we report that, in peritoneal macrophages, ovalbumin immunization induces the expression of CD23, the low affinity receptor for IgEs known for its involvement in allergic diseases. Thus, the modified expression of the enzymes involved in AA metabolism and the difference of response of cPM and iPM toward the antigen are important elements to understand the underlying mechanisms of ovalbumin-induced allergic responses.

IL-13 induces serine phosphorylation of cPLA2 in mouse peritoneal macrophages leading to arachidonic acid and PGE2 production and blocks the zymosan-induced serine phosphorylation of cPLA2 and eicosanoid production

In a recent investigation, we demonstrated that long-term treatment of macrophages with IL-13 enhances cPLA2 expression and modulates zymosan-stimulated AA mobilization. In the present study, we examine the ability of IL-13 to modify the cPLA2 activity and the AA mobilization of macrophages after a short-period of treatment. We demonstrate that in resting macrophages, IL-13 induces, through a MAP kinase-dependent process, (1) an increase of free AA release within 15 min, followed by increased PGE2 production and (2) a time-dependent serine phosphorylation of cPLA2. Conversely, in macrophages stimulated by zymosan, IL-13 added 30 min before zymosan inhibited the AA release and the serine phosphorylation of cPLA2 induced by the phagocytic agonist. In conclusion, these findings show for the first time that a Th2-type cytokine can upregulate cPLA2 activity and downregulate zymosan-induced AA metabolism. Thus, establishment of the connection between these two events may help to understand the complex regulatory role of IL-13 on the macrophage AA metabolism.