Type I interferon induces TCR-dependent and -independent antimicrobial responses in γδ intraepithelial lymphocytes

Intraepithelial lymphocytes (IEL) expressing the γδ T cell receptor (TCR) survey the intestinal epithelium to limit the invasion of microbial pathogens. The production of type I interferon (IFN) is a central component of an antiviral immune response, yet how these pro-inflammatory cytokines contribute to γδ IEL effector function remains unclear. Based on the unique activation status of IELs, and their ability to bridge innate and adaptive immunity, we investigated the extent to which type I IFN signaling modulates γδ IEL function. Using an ex vivo culture model, we find that type I IFN alone is unable to drive IFNγ production, yet low level TCR activation synergizes with type I IFN to induce IFNγ production in murine γδ IELs. Further investigation into the underlying molecular mechanisms of co-stimulation revealed that TCRγδ-mediated activation of NFAT and JNK is required for type I IFN to promote IFNγ expression in a STAT4- dependent manner. Whereas type I IFN rapidly upregulates antiviral gene expression independent of a basal TCRγδ signal, neither tonic TCR triggering nor the presence of a TCR agonist was sufficient to elicit type I IFN-induced IFNγ production in vivo . However, bypassing proximal TCR signaling events synergized with IFNAR/STAT4 activation to induce γδ IEL IFNγ production. These findings indicate that γδ IELs contribute to host defense in response to type I IFN by mounting a rapid antimicrobial response independent of TCRγδ signaling, and under permissive conditions, produce IFNγ in a TCR-dependent manner.

Salmonella engages CDC42 effector protein 1 for intracellular invasion

Human enterocytes are primary targets of infection by invasive bacterium Salmonella Typhimurium, and studies using nonintestinal epithelial cells established that S. Typhimurium activates Rho family GTPases, primarily CDC42, to modulate the actin cytoskeletal network for invasion. The host intracellular protein network that engages CDC42 and influences the pathogen's invasive capacity are relatively unclear. Here, proteomic analyses of canonical and variant CDC42 interactomes identified a poorly characterized CDC42 interacting protein, CDC42EP1, whose intracellular localization is rapidly redistributed and aggregated around the invading bacteria. CDC42EP1 associates with SEPTIN-7 and Villin, and its relocalization and bacterial engagement depend on host CDC42 and S. Typhimurium's capability of activating CDC42. Unlike CDC42, CDC42EP1 is not required for S. Typhimurium's initial cellular entry but is found to associate with Salmonella-containing vacuoles after long-term infections, indicating a contribution to the pathogen's intracellular growth and replication. These results uncover a new host regulator of enteric Salmonella infections, which may be targeted to restrict bacterial load at the primary site of infection to prevent systemic spread.

Infection and inflammation stimulate expansion of a CD74+ Paneth cell subset to regulate disease progression

Paneth cells (PCs), a specialized secretory cell type in the small intestine, are increasingly recognized as having an essential role in host responses to microbiome and environmental stresses. Whether and how commensal and pathogenic microbes modify PC composition to modulate inflammation remain unclear. Using newly developed PC-reporter mice under conventional and gnotobiotic conditions, we determined PC transcriptomic heterogeneity in response to commensal and invasive microbes at single cell level. Infection expands the pool of CD74+ PCs, whose number correlates with auto or allogeneic inflammatory disease progressions in mice. Similar correlation was found in human inflammatory disease tissues. Infection-stimulated cytokines increase production of reactive oxygen species (ROS) and expression of a PC-specific mucosal pentraxin (Mptx2) in activated PCs. A PC-specific ablation of MyD88 reduced CD74+ PC population, thus ameliorating pathogen-induced systemic disease. A similar phenotype was also observed in mice lacking Mptx2. Thus, infection stimulates expansion of a PC subset that influences disease progression.

CD4+ T Cell Responses to Toxoplasma gondii Are a Double-Edged Sword

CD4+ T cells have been found to play critical roles in the control of both acute and chronic Toxoplasma infection. Previous studies identified a protective role for the Toxoplasma CD4+ T cell-eliciting peptide AS15 (AVEIHRPVPGTAPPS) in C57BL/6J mice. Herein, we found that immunizing mice with AS15 combined with GLA-SE, a TLR-4 agonist in emulsion adjuvant, can be either helpful in protecting male and female mice at early stages against Type I and Type II Toxoplasma parasites or harmful (lethal with intestinal, hepatic, and spleen pathology associated with a storm of IL6). Introducing the universal CD4+ T cell epitope PADRE abrogates the harmful phenotype of AS15. Our findings demonstrate quantitative and qualitative features of an effective Toxoplasma-specific CD4+ T cell response that should be considered in testing next-generation vaccines against toxoplasmosis. Our results also are cautionary that individual vaccine constituents can cause severe harm depending on the company they keep.

The multifunctional nature of CD103 (αEβ7 integrin) signaling in tissue-resident lymphocytes

Intestinal tissue-resident lymphocytes are critical for maintenance of the mucosal barrier and to prevent enteric infections. The activation of these lymphocytes must be tightly regulated to prevent aberrant inflammation and epithelial damage observed in autoimmune diseases, yet also ensure that antimicrobial host defense remains uncompromised. Tissue-resident lymphocytes express CD103, or αE integrin, which dimerizes with the β7 subunit to bind to E-cadherin expressed on epithelial cells. Although the role of CD103 in homing and retention of lymphocytes to and within peripheral tissues has been well characterized, the molecular signals activated following CD103 engagement remain understudied. Here, we highlight recent studies that elucidate the functional contribution of CD103 in various lymphocyte subpopulations, either as an independent signaling molecule or in the context of TCR co-stimulation. Finally, we will discuss the gaps in our understanding of CD103 biology and the therapeutic potential of targeting CD103 on tissue-resident lymphocytes.

Human Plasmacytoid Dendritic Cells Express C-Type Lectin Receptors and Attach and Respond to Aspergillus fumigatus

Plasmacytoid dendritic cells (pDCs) have been implicated as having a role in antifungal immunity, but mechanisms of their interaction with fungi and the resulting cellular responses are not well understood. In this study, we identify the direct and indirect biological response of human pDCs to the fungal pathogen Aspergillus fumigatus and characterize the expression and regulation of antifungal receptors on the pDC surface. Results indicate pDCs do not phagocytose Aspergillus conidia, but instead bind hyphal surfaces and undergo activation and maturation via the upregulation of costimulatory and maturation markers. Measuring the expression of C-type lectin receptors dectin-1, dectin-2, dectin-3, and mannose receptor on human pDCs revealed intermediate expression of each receptor compared with monocytes. The specific dectin-1 agonist curdlan induced pDC activation and maturation in a cell-intrinsic and cell-extrinsic manner. The indirect activation of pDCs by curdlan was much stronger than direct stimulation and was mediated through cytokine production by other PBMCs. Overall, our data indicate pDCs express various C-type lectin receptors, recognize and respond to Aspergillus hyphal Ag, and serve as immune enhancers or modulators in the overarching fungal immune response.

Adenosine metabolized from extracellular ATP promotes type 2 immunity through triggering A2BAR signaling in intestinal epithelial cells

Intestinal nematode parasites can cross the epithelial barrier, causing tissue damage and release of danger-associated molecular patterns (DAMPs) that may promote host protective type 2 immunity. We investigate whether adenosine binding to the A2B adenosine receptor (A2BAR) on intestinal epithelial cells (IECs) plays an important role. Specific blockade of IEC A2BAR inhibits the host protective memory response to the enteric helminth, Heligmosomoides polygyrus bakeri (Hpb), including disruption of granuloma development at the host-parasite interface. Memory T cell development is blocked during the primary response, and transcriptional analyses reveal profound impairment of IEC activation. Extracellular ATP is visualized 24 h after inoculation and is shown in CD39-deficient mice to be critical for the adenosine production mediating the initiation of type 2 immunity. Our studies indicate a potent adenosine-mediated IEC pathway that, along with the tuft cell circuit, is critical for the activation of type 2 immunity.

Intravital Microscopy to Visualize Murine Small Intestinal Intraepithelial Lymphocyte Migration

Intraepithelial lymphocytes (IELs) are critical sentinels involved in host defense and maintenance of the intestinal mucosal barrier. IELs expressing the γδ T-cell receptor provide continuous surveillance of the villous epithelium by migrating along the basement membrane and into the lateral intercellular space between adjacent enterocytes. Intravital imaging has furthered our understanding of the molecular mechanisms by which IELs navigate the epithelial compartment and interact with neighboring enterocytes at steady state and in response to infectious or inflammatory stimuli. Further, evaluating IEL migratory behavior can provide additional insight into the nature and extent of cellular interactions within the intestinal mucosa. Three protocols describe methodology to visualize small intestinal IEL motility in real time using fluorescent reporter-transgenic mice and/or fluorophore-conjugated primary antibodies and spinning-disk confocal microscopy. Using Imaris image analysis software, a fourth protocol provides a framework to analyze IEL migration and quantify lymphocyte/epithelial interactions. Together, these protocols for intravital imaging and subsequent analyses provide the basis for elucidating the spatiotemporal dynamics of mucosal immune cells and interactions with neighboring enterocytes under physiological or pathophysiological conditions. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Mouse preparation and laparotomy Support Protocol: Antibody labeling of cell surface markers Basic Protocol 2: Image acquisition by spinning-disk confocal microscopy Basic Protocol 3: 4D analysis of images.

Epithelial HNF4A shapes the intraepithelial lymphocyte compartment via direct regulation of immune signaling molecules

Hepatocyte nuclear factor 4 α (HNF4A) is a highly conserved nuclear receptor that has been associated with ulcerative colitis. In mice, HNF4A is indispensable for the maintenance of intestinal homeostasis, yet the underlying mechanisms are poorly characterized. Here, we demonstrate that the expression of HNF4A in intestinal epithelial cells (IECs) is required for the proper development and composition of the intraepithelial lymphocyte (IEL) compartment. HNF4A directly regulates expression of immune signaling molecules including butyrophilin-like (Btnl) 1, Btnl6, H2-T3, and Clec2e that control IEC-IEL crosstalk. HNF4A selectively enhances the expansion of natural IELs that are TCRγδ+ or TCRαβ+CD8αα+ to shape the composition of IEL compartment. In the small intestine, HNF4A cooperates with its paralog HNF4G, to drive expression of immune signaling molecules. Moreover, the HNF4A-BTNL regulatory axis is conserved in human IECs. Collectively, these findings underscore the importance of HNF4A as a conserved transcription factor controlling IEC-IEL crosstalk and suggest that HNF4A maintains intestinal homeostasis through regulation of the IEL compartment.

Zbtb20 identifies and controls a thymus-derived population of regulatory T cells that play a role in intestinal homeostasis

The expression of BTB-ZF transcription factors such as ThPOK in CD4⁺ T cells, Bcl6 in T follicular helper cells, and PLZF in natural killer T cells defines the fundamental nature and characteristics of these cells. Screening for lineage-defining BTB-ZF genes led to the discovery of a subset of T cells that expressed Zbtb20. About half of Zbtb20⁺ T cells expressed FoxP3, the lineage-defining transcription factor for regulatory T cells (T_regs). Zbtb20⁺ T_regs were phenotypically and genetically distinct from the larger conventional T_reg population. Zbtb20⁺ T_regs constitutively expressed mRNA for interleukin-10 and produced high levels of the cytokine upon primary activation. Zbtb20⁺ T_regs were enriched in the intestine and specifically expanded when inflammation was induced by the use of dextran sodium sulfate. Conditional deletion of Zbtb20 in T cells resulted in a loss of intestinal epithelial barrier integrity. Consequently, knockout (KO) mice were acutely sensitive to colitis and often died because of the disease. Adoptive transfer of Zbtb20⁺ T_regs protected the Zbtb20 conditional KO mice from severe colitis and death, whereas non-Zbtb20 T_regs did not. Zbtb20 was detected in CD24^hi double-positive and CD62L^lo CD4 single-positive thymocytes, suggesting that expression of the transcription factor and the phenotype of these cells were induced during thymic development. However, Zbtb20 expression was not induced in "conventional" T_regs by activation in vitro or in vivo. Thus, Zbtb20 expression identified and controlled the function of a distinct subset of T_regs that are involved in intestinal homeostasis.

Expression of a BTB-ZF transcription factor controls the function of an innate-like Tregs essential for intestinal homeostasis

The BTB-ZF genes are a family of 49 transcription factors that control the lineage specification and development of key effector functions of different subsets of lymphocytes. Using a single-cell BTB-ZF transcription factor expression analysis, we identified a unique subset of T regulatory cells (Tregs). These Tregs are genetically and phenotypically distinct from the larger conventional Treg population. For instance, analogous to natural killer (NKT) cells they have an activated phenotype (CD62Llo, CD44hi) and constitutively express IL-10. Interestingly, these characteristics are acquired early during T cell development. The defining transcription factor is induced during thymic development, binds the IL-10 promoter, and enables T cells to rapidly produce the cytokine. The subset of Tregs is enriched in the intestine and expands during acute colitis. The deletion of the defining transcription factor in T cells results in intestinal epithelial layer damage causing loss of the barrier function making mice highly vulnerable to severe disease and death from induced colitis. Moreover, in the absence of the transcription factor in T cells, normal intestinal macrophage responses are disrupted most likely due to decreased production of IL-10 by the Tregs. Therefore, by profiling BTB-ZF transcription factor expression, we have identified a distinct subset of T cells with potent immunosuppressive abilities that are essential for the health of the intestine. Numerous aspects of these Tregs are parallel to NKT cells, indicating an existence of “naïve” Tregs that have innate-like effector functions acquired independently from the differentiation in the periphery.

Supported by NIH/NIAID R01 AI122757-01 Careers in Immunology Fellowships – 2021

A transmissible γδ intraepithelial lymphocyte hyperproliferative phenotype is associated with the intestinal microbiota and confers protection against acute infection

Intraepithelial lymphocytes expressing the γδ T cell receptor (γδ IELs) serve as a first line of defense against luminal microbes. Although the presence of an intact microbiota is dispensable for γδ IEL development, several microbial factors contribute to the maintenance of this sentinel population. However, whether specific commensals influence population of the γδ IEL compartment under homeostatic conditions has yet to be determined. We identified a novel γδ IEL hyperproliferative phenotype that arises early in life and is characterized by expansion of multiple Vγ subsets. Horizontal transfer of this hyperproliferative phenotype to mice harboring a phenotypically normal γδ IEL compartment was prevented following antibiotic treatment, thus demonstrating that the microbiota is both necessary and sufficient for the observed increase in γδ IELs. Further, we identified two guilds of small intestinal or fecal bacteria represented by 12 amplicon sequence variants (ASV) that are strongly associated with γδ IEL expansion. Using intravital microscopy, we find that hyperproliferative γδ IELs also exhibit increased migratory behavior leading to enhanced protection against bacterial infection. These findings reveal that transfer of a specific group of commensals can regulate γδ IEL homeostasis and immune surveillance, which may provide a novel means to reinforce the epithelial barrier.

γδ Intraepithelial Lymphocytes Facilitate Pathological Epithelial Cell Shedding Via CD103-Mediated Granzyme Release

BACKGROUND & AIMS

Excessive shedding of apoptotic enterocytes into the intestinal lumen is observed in inflammatory bowel disease and is correlated with disease relapse. Based on their cytolytic capacity and surveillance behavior, we investigated whether intraepithelial lymphocytes expressing the γδ T cell receptor (γδ IELs) are actively involved in the shedding of enterocytes into the lumen.

METHODS

Intravital microscopy was performed on GFP γδ T cell reporter mice treated with intraperitoneal lipopolysaccharide (10 mg/kg) for 90 minutes to induce tumor necrosis factor-mediated apoptosis. Cell shedding in various knockout or transgenic mice in the presence or absence of blocking antibody was quantified by immunostaining for ZO-1 funnels and cleaved caspase-3 (CC3). Granzyme A and granzyme B release from ex vivo-stimulated γδ IELs was quantified by enzyme-linked immunosorbent assay. Immunostaining for γδ T cell receptor and CC3 was performed on duodenal and ileal biopsies from controls and patients with Crohn's disease.

RESULTS

Intravital microscopy of lipopolysaccharide-treated mice revealed that γδ IELs make extended contact with shedding enterocytes. These prolonged interactions require CD103 engagement by E-cadherin, and CD103 knockout or blockade significantly reduced lipopolysaccharide-induced shedding. Furthermore, we found that granzymes A and B, but not perforin, are required for cell shedding. These extracellular granzymes are released by γδ IELs both constitutively and after CD103/E-cadherin ligation. Moreover, we found that the frequency of γδ IEL localization to CC3-positive enterocytes is increased in Crohn's disease biopsies compared with healthy controls.

CONCLUSIONS

Our results uncover a previously unrecognized role for γδ IELs in facilitating tumor necrosis factor-mediated shedding of apoptotic enterocytes via CD103-mediated extracellular granzyme release.

A transmissible γδ intraepithelial lymphocyte hyperproliferative phenotype is associated with the intestinal microbiota

Intraepithelial lymphocytes (IEL) expressing the γδ T cell receptor provide a first line of defense at the intestinal barrier, yet how the intestinal microbiota influences this sentinel population remains unclear. Since commensal-induced tonic type I interferon (IFN) signaling promotes lamina propria lymphocyte homeostasis, we hypothesized that IFNα/β receptor (IFNAR) signaling may contribute to maintenance of the γδ IEL compartment. Morphometric analysis revealed a 2-fold increase in the number of GFP+ γδ IELs in IFNAR KO mice compared to WT housed in a standard barrier facility (SBF). γδ IEL proliferation was enhanced 50% in SBF IFNAR KO mice relative to SBF WT. This increase in γδ IEL number was not observed in IFNAR KO mice rederived into a cleaner, enhanced barrier facility (EBF) indicating that the γδ IEL hyperproliferative (γδHYP) phenotype occurs independently of IFNAR signaling. The transfer of dirty bedding from SBF IFNAR KO mice to EBF IFNAR KO breeding cages was sufficient to induce the γδHYP phenotype in both the breeders and their offspring, and antibiotic treatment prevented this transmission. SBF WT and IFNAR KO mice were crossed to generate F2 littermates, which all exhibited the γδHYP phenotype regardless of genotype. Evidence of horizontal and vertical transmission of the γδHYP phenotype led us to analyze the fecal microbiota. Greater microbial diversity was observed in mice with the γδHYP phenotype relative to those that did not (Shannon Index, p<0.01). Moreover, 6 amplicon sequence variants (ASV) were strongly associated with the γδHYP phenotype (P=1.075e-05). Thus, we have serendipitously discovered a specific microbiota that is both necessary and sufficient to promote the expansion of the γδ IEL compartment.

Specific expression of a BTB-ZF transcription factor defines innate-like regulatory T cells that are essential for intestinal homeostasis

Regulatory T cells (Tregs) play a pivotal role in regulating immune responses and are a significant source of the anti-inflammatory cytokine IL-10 in the intestine. Defects in Tregs function lead to the development of systemic and intestinal inflammation. Using a single-cell BTB-ZF transcription factor expression analysis, we identified a distinct subset of Tregs. These cells have an activated phenotype (CD62Llo, CD44hi) and constitutively express the Il10. Moreover, these Tregs accumulate in the intestine and expand in number following DSS induced colitis. The targeted deletion of the defining transcription factor impaired these cells' ability to secrete IL-10, leading to significant disruptions in mucosal architecture and the development of intestinal inflammation following treatment with dextran sodium sulfate (DSS). Thus, the conditional knockout (cKO) mice developed much more severe symptoms leading to the death of 60% of them. In contrast, all wild type mice fully recovered. Notably, adoptive transfer of this Treg subset was sufficient to prevent the death of cKO mice. In comparison, the transfer of cKO Tregs was not able to rescue the mice. Collectively, our data show that we have identified a distinct subset of Tregs and determined a specific member of the BTB-ZF family that controls their function. This rare population of T cells has potent immunosuppressive abilities and, we propose, rather than acutely producing IL-10 in response to activation, these cells maintain intestinal homeostasis through continuous secretion of IL-10. Our findings imply that analogous to NKT cells, some thymic-derived Tregs have innate-like effector functions that are not dependent upon differentiation in the periphery.

Type I interferon enhances γδ intraepithelial lymphocyte migratory behavior via CD47 upregulation

γδ intraepithelial lymphocytes (IEL) migrate along the basement membrane and into the lateral intracellular space (LIS) between adjacent intestinal epithelial cells (IEC) and is critical to limit microbial translocation across the barrier. Although activated γδ IELs produce interferon (IFN)-α, whether IFNα directly influences γδ IEL migratory behavior remains unknown. To test this, intravital microscopy was performed on GFP γδ T cell reporter mice treated with PBS or IFNα (1 μg, i.v., 3h). We found that γδ IEL track speed was increased 30% and migration into the LIS was enhanced by 75% in IFNα-treated mice compared to controls. To identify candidate genes involved in regulating γδ IEL motility, we performed RNAseq on γδ IELs isolated from control and IFNα-treated mice. As expected, IFNα induced IFN-stimulated gene expression including CD47 (3.5-fold increase), a transmembrane protein involved in neutrophil transepithelial migration. Stimulation of ex vivo cultured γδ IELs with IFNα resulted in a 3-fold increase in CD47 expression compared to unstimulated controls. Next, to investigate whether IFNα enhances γδ IEL motility in vitro, GFP γδ IELs were co-cultured with enteroids expressing membrane tdTomato and treated with 10ng/ml IFNα for 3h. IFNα increased γδ IEL speed (4.5±0.2 vs 3.4±0.2 μm/min; p<0.05) and displacement (47±3.0 μm vs 34±3.1, p<0.05) relative to untreated controls. Addition of anti-CD47 blocking antibody (MIAP301) abrogated the IFNα-mediated increase in γδ IEL migratory behavior. Taken together, these data demonstrate that IFNα enhances γδ IEL motility via a CD47-mediated mechanism, and suggests that CD47 may represent a conserved mechanism of leukocyte migration within the epithelial barrier.

γδ T cell migration: Separating trafficking from surveillance behaviors at barrier surfaces

γδ T cells are found in highest numbers at barrier surfaces throughout the body, including the skin, intestine, lung, gingiva, and uterus. Under homeostatic conditions, γδ T cells provide immune surveillance of the epidermis, intestinal, and oral mucosa, whereas the presence of pathogenic microorganisms in the dermis or lungs elicits a robust γδ17 response to clear the infection. Although T cell migration is most frequently defined in the context of trafficking, analysis of specific migratory behaviors of lymphocytes within the tissue microenvironment can provide valuable insight into their function. Intravital imaging and computational analyses have been used to define "search" behavior associated with conventional αβ T cells; however, based on the known role of γδ T cells as immune sentinels at barrier surfaces and their TCR-independent functions, we put forth the need to classify distinct migratory patterns that reflect the surveillance capacity of these unconventional lymphocytes. This review will focus on how γδ T cells traffic to various barrier surfaces and how recent investigation into their migratory behavior has provided unique insight into the contribution of γδ T cells to barrier immunity.

Inflammation-induced Occludin Downregulation Limits Epithelial Apoptosis by Suppressing Caspase-3 Expression

BACKGROUND & AIMS

Epithelial tight junctions are compromised in gastrointestinal disease. Processes that contribute to the resulting barrier loss include endocytic occludin removal from the tight junction and reduced occludin expression. Nevertheless, the relatively-normal basal phenotype of occludin knockout (KO) mice has been taken as evidence that occludin does not contribute to gastrointestinal barrier function. We asked whether stress could unmask occludin functions within intestinal epithelia.

METHODS

Wildtype (WT), universal and intestinal epithelial-specific occludin KO, and villin-EGFP-occludin transgenic mice as well as WT and occludin knockdown (KD) Caco-2_BBe cell monolayers were challenged with DSS, TNBS, staurosporine, 5-FU, or TNF. Occludin and caspase-3 expression were assessed in patient biopsies.

RESULTS

Intestinal epithelial occludin loss limited severity of DSS- and TNBS-induced colitis due to epithelial resistance to apoptosis; activation of both intrinsic and extrinsic apoptotic pathways was blocked in occludin KO epithelia. Promoter analysis revealed that occludin enhances CASP3 transcription and, conversely, that occludin downregulation reduces caspase-3 expression. Analysis of biopsies from Crohn's disease and ulcerative colitis patients and normal controls demonstrated that disease-associated occludin downregulation was accompanied by and correlated with reduced caspase-3 expression. In vitro, cytokine-induced occludin downregulation resulted in reduced caspase-3 expression and resistance to intrinsic and extrinsic pathway apoptosis, demonstrating an overall protective effect of inflammation-induced occludin loss.

CONCLUSIONS

The tight junction protein occludin regulates apoptosis by enhancing caspase-3 transcription. These data suggest that reduced epithelial caspase-3 expression downstream of occludin downregulation is a previously-unappreciated anti-apoptotic process that contributes to mucosal homeostasis in inflammatory conditions.

Intravital Imaging of Intraepithelial Lymphocytes in Murine Small Intestine

Intraepithelial lymphocytes expressing γδ T cell receptor (γδ IEL) play a key role in immune surveillance of the intestinal epithelium. Due in part to the lack of a definitive ligand for the γδ T cell receptor, our understanding of the regulation of γδ IEL activation and their function in vivo remains limited. This necessitates the development of alternative strategies to interrogate signaling pathways involved in regulating γδ IEL function and the responsiveness of these cells to the local microenvironment. Although γδ IELs are widely understood to limit pathogen translocation, the use of intravital imaging has been critical to understanding the spatiotemporal dynamics of IEL/epithelial interactions at steady-state and in response to invasive pathogens. Herein, we present a protocol for visualizing IEL migratory behavior in the small intestinal mucosa of a GFP γδ T cell reporter mouse using inverted spinning disk confocal laser microscopy. Although the maximum imaging depth of this approach is limited relative to the use of two-photon laser-scanning microscopy, spinning disk confocal laser microscopy provides the advantage of high speed image acquisition with reduced photobleaching and photodamage. Using 4D image analysis software, T cell surveillance behavior and their interactions with neighboring cells can be analyzed following experimental manipulation to provide additional insight into IEL activation and function within the intestinal mucosa.

Graft-versus-host disease propagation depends on increased intestinal epithelial tight junction permeability

Graft-versus-host disease (GVHD) is a complication of hematopoietic stem cell transplantation (HSCT) that affects multiple organs. GVHD-associated intestinal damage can be separated into two distinct phases, initiation and propagation, which correspond to conditioning-induced damage and effector T cell activation and infiltration, respectively. Substantial evidence indicates that intestinal damage induced by pretransplant conditioning is a key driver of GVHD initiation. Here, we aimed to determine the impact of dysregulated intestinal permeability on the subsequent GVHD propagation phase. The initiation phase of GVHD was unchanged in mice lacking long MLCK (MLCK210), an established regulator of epithelial tight junction permeability. However, MLCK210-deficient mice were protected from sustained barrier loss and exhibited limited GVHD propagation, as indicated by reduced histopathology, fewer CD8+ effector T cells in the gut, and improved overall survival. Consistent with these findings, intestinal epithelial MLCK210 expression and enzymatic activity were similarly increased in human and mouse GVHD biopsies. Intestinal epithelial barrier loss mediated by MLCK210 is therefore a key driver of the GVHD propagation. These data suggest that inhibition of MLCK210-dependent barrier regulation may be an effective approach to limiting GVHD progression.

Epithelial IL-15 Is a Critical Regulator of γδ Intraepithelial Lymphocyte Motility within the Intestinal Mucosa

Intraepithelial lymphocytes (IELs) expressing the γδ TCR (γδ IELs) provide continuous surveillance of the intestinal epithelium. However, the mechanisms regulating the basal motility of these cells within the epithelial compartment have not been well defined. We investigated whether IL-15 contributes to γδ IEL localization and migratory behavior in addition to its role in IEL differentiation and survival. Using advanced live cell imaging techniques in mice, we find that compartmentalized overexpression of IL-15 in the lamina propria shifts the distribution of γδ T cells from the epithelial compartment to the lamina propria. This mislocalization could be rescued by epithelial IL-15 overexpression, indicating that epithelial IL-15 is essential for γδ IEL migration into the epithelium. Furthermore, in vitro analyses demonstrated that exogenous IL-15 stimulates γδ IEL migration into cultured epithelial monolayers, and inhibition of IL-2Rβ significantly attenuates the basal motility of these cells. Intravital microscopy showed that impaired IL-2Rβ signaling induced γδ IEL idling within the lateral intercellular space, which resulted in increased early pathogen invasion. Similarly, the redistribution of γδ T cells to the lamina propria due to local IL-15 overproduction also enhanced bacterial translocation. These findings thus reveal a novel role for IL-15 in mediating γδ T cell localization within the intestinal mucosa and regulating γδ IEL motility and patrolling behavior as a critical component of host defense.

Policing the intestinal epithelial barrier: Innate immune functions of intraepithelial lymphocytes

PURPOSE OF REVIEW

This review will explore the contribution of IELs to mucosal innate immunity and highlight the similarities in IEL functional responses to bacteria, viruses and protozoan parasite invasion.

RECENT FINDINGS

IELs rapidly respond to microbial invasion by activating host defense responses, including the production of mucus and antimicrobial peptides to prevent microbes from reaching the epithelial surface. During active infection, IELs promote epithelial cytolysis, cytokine and chemokine production to limit pathogen invasion, replication and dissemination. Commensal-induced priming of IEL effector function or continuous surveillance of the epithelium may be important contributing factors to the rapidity of response.

SUMMARY

Impaired microbial recognition, dysregulated innate immune signaling or microbial dysbiosis may limit the protective function of IELs and increase susceptibility to disease. Further understanding of the mechanisms regulating IEL surveillance and sentinel function may provide insight into the development of more effective targeted therapies designed to reinforce the mucosal barrier.

Marked differences in tight junction composition and macromolecular permeability among different intestinal cell types

BACKGROUND

Mammalian small intestinal tight junctions (TJ) link epithelial cells to one another and function as a permselective barrier, strictly modulating the passage of ions and macromolecules through the pore and leak pathways, respectively, thereby preventing the absorption of harmful compounds and microbes while allowing regulated transport of nutrients and electrolytes. Small intestinal epithelial permeability is ascribed primarily to the properties of TJs between adjoining enterocytes (ENTs), because there is almost no information on TJ composition and the paracellular permeability of nonenterocyte cell types that constitute a small but significant fraction of the intestinal epithelia.

RESULTS

Here we directed murine intestinal crypts to form specialized organoids highly enriched in intestinal stem cells (ISCs), absorptive ENTs, secretory goblet cells, or Paneth cells. The morphological and morphometric characteristics of these cells in organoids were similar to those in vivo. The expression of certain TJ proteins varied with cell type: occludin and tricellulin levels were high in both ISCs and Paneth cells, while claudin-1, -2, and -7 expression was greatest in Paneth cells, ISCs, and ENTs, respectively. In contrast, the distribution of claudin-15, zonula occludens 1 (ZO-1), and E-cadherin was relatively homogeneous. E-cadherin and claudin-7 marked mainly the basolateral membrane, while claudin-2, ZO-1, and occludin resided in the apical membrane. Remarkably, organoids enriched in ENTs or goblet cells were over threefold more permeable to 4 and 10 kDa dextran compared to those containing stem and Paneth cells. The TJ-regulator larazotide prevented the approximately tenfold increases in dextran flux induced by the TJ-disrupter AT1002 into organoids of different cell types, indicating that this ZO toxin nonselectively increases permeability. Forced dedifferentiation of mature ENTs results in the reacquisition of ISC-like characteristics in TJ composition and dextran permeability, suggesting that the post-differentiation properties of TJs are not hardwired.

CONCLUSIONS

Differentiation of adult intestinal stem cells into mature secretory and absorptive cell types causes marked, but potentially reversible, changes in TJ composition, resulting in enhanced macromolecular permeability of the TJ leak pathway between ENTs and between goblet cells. This work advances our understanding of how cell differentiation affects the paracellular pathway of epithelia.

Sentinels at the frontline: the role of intraepithelial lymphocytes in inflammatory bowel disease

Purpose of review

Intestinal mucosal immunity is tightly regulated to ensure effective host defense against invasive microorganisms while limiting the potential for aberrant damage. In inflammatory bowel disease (IBD), an imbalance between effector and regulatory T cell populations results in an uncontrolled inflammatory response to commensal bacteria. Intraepithelial lymphocytes (IEL) are perfectly positioned within the intestinal epithelium to provide the first line of mucosal defense against luminal microbes or rapidly respond to epithelial injury. This review will highlight how IELs promote protective intestinal immunity and discuss the evidence indicating that altered IEL responses contribute to the pathogenesis of IBD.

Recent findings

Although the role of IELs in mucosal homeostasis has been largely underappreciated, many of the same factors that contribute to the dysregulation of host defense in IBD also adversely affect IELs. For example, IL-23 and the endoplasmic reticulum stress response can enhance IEL lytic activity toward enterocytes. Microbial dysbiosis or defective microbial recognition results in the loss of regulatory IELs, further amplifying these pro-inflammatory effects. Migration of T cells into or within the intraepithelial compartment has a profound effect on their differentiation or effector function demonstrating that IELs are exquisitely sensitive to changes in the local intestinal microenvironment.

Summary

Enhanced mechanistic insight into the regulation of IEL survival, differentiation and effector function may provide useful tools to modulate IEL surveillance or enhance IEL regulatory function. Elucidation of these processes may result in the development of novel therapeutics to reduce intestinal inflammation and reinforce the mucosal barrier in IBD.

Paneth Cell Specific Lysozyme Regulates Intestinal Mucosal Immune Response by Shaping Gut Microbiota Landscape

Paneth cells produce antimicrobial proteins such as lysozyme and cytokines to interact with gut microbiota and mucosal immune system respectively, maintaining delicate mucosal immune homeostasis. Abnormalities in lysozyme expression or intracellular distribution have been cataloged in patients with inflammatory bowel disease (IBD) and mouse IBD models. However, it is unclear whether these defects are simply the consequences of IBD pathogenesis or they may also contribute to disease progression. To explore the role of Paneth cell lysozyme in such a microbe-friendly environment, we derived two mouse models: Paneth cell Lyz1 knockout (Lyz1KO) and gut epithelial Lyz1 overexpression (Villin-Lyz1). Using these two models, we performed fecal 16s rRNA sequencing and found that the abundance of several mucolytic bacteria (e.g. D. formicigenerans and R. gnavus) was increased in Lyz1KO mice but decreased in Villin-Lyz1, as confirmed by species specific qPCR. In addition, we confirmed that lysozyme could inhibit the growth of D. formicigenerans and R. gnavus in vitro. Interestingly, the number of goblet and tuft cell in Lyz1KO mice was increased compared to that in wildtype littermates. In line with this, type 2 cytokines (e.g. Il25 and Il13) were elevated in Lyz1KO mice. Antibiotics cocktail treatment rescued goblet and tuft cell hyperplasia, suggesting altered gut microbiota landscape is a critical factor inducing goblet and tuft cell hyperplasia. Consistently, disruption of intestinal type 2 immunity axis by anti-CD90.2 or anti-Il13 neutralizing antibody also ameliorated goblet and tuft cell hyperplasia. Taken together, our findings suggest lysozyme modulates intestinal type 2 immune response via shaping gut microbiota landscape.

γδ Intraepithelial Lymphocyte Migration Limits Transepithelial Pathogen Invasion and Systemic Disease in Mice

BACKGROUND & AIMS

Intraepithelial lymphocytes that express the γδ T-cell receptor (γδ IELs) limit pathogen translocation across the intestinal epithelium by unknown mechanisms. We investigated whether γδ IEL migration and interaction with epithelial cells promote mucosal barrier maintenance during enteric infection.

METHODS

Salmonella typhimurium or Toxoplasma gondii were administered to knockout (KO) mice lacking either the T cell receptor δ chain (Tcrd) or CD103, or control TcrdEGFP C57BL/6 reporter mice. Intravital microscopy was used to visualize migration of green fluorescent protein (GFP)-tagged γδ T cells within the small intestinal mucosa of mice infected with DsRed-labeled S typhimurium. Mixed bone marrow chimeras were generated to assess the effects of γδ IEL migration on early pathogen invasion and chronic systemic infection.

RESULTS

Morphometric analyses of intravital video microscopy data showed that γδ IELs rapidly localized to and remained near epithelial cells in direct contact with bacteria. Within 1 hour, greater numbers of T gondii or S typhimurium were present within mucosae of mice with migration-defective occludin KO γδ T cells, compared with controls. Pathogen invasion in Tcrd KO mice was quantitatively similar to that in mice with occludin-deficient γδ T cells, whereas invasion in CD103 KO mice, which have increased migration of γδ T cells into the lateral intercellular space, was reduced by 63%. Consistent with a role of γδ T-cell migration in early host defense, systemic salmonellosis developed more rapidly and with greater severity in mice with occludin-deficient γδ IELs, relative to those with wild-type or CD103 KO γδ IELs.

CONCLUSIONS

In mice, intraepithelial migration to epithelial cells in contact with pathogens is essential to γδ IEL surveillance and immediate host defense. γδ IEL occludin is required for early surveillance that limits systemic disease.

Recipient NK cell inactivation and intestinal barrier loss are required for MHC-matched graft-versus-host disease

Previous studies have shown a correlation between pretransplant conditioning intensity, intestinal barrier loss, and graft-versus-host disease (GVHD) severity. However, because irradiation and other forms of pretransplant conditioning have pleiotropic effects, the precise role of intestinal barrier loss in GVHD pathogenesis remains unclear. We developed GVHD models that allowed us to isolate the specific contributions of distinct pretransplant variables. Intestinal damage was required for the induction of minor mismatch [major histocompatibility complex (MHC)-matched] GVHD, but was not necessary for major mismatch GVHD, demonstrating fundamental pathogenic distinctions between these forms of disease. Moreover, recipient natural killer (NK) cells prevented minor mismatch GVHD by limiting expansion and target organ infiltration of alloreactive T cells via a perforin-dependent mechanism, revealing an immunoregulatory function of MHC-matched recipient NK cells in GVHD. Minor mismatch GVHD required MyD88-mediated Toll-like receptor 4 (TLR4) signaling on donor cells, and intestinal damage could be bypassed by parenteral lipopolysaccharide (LPS) administration, indicating a critical role for the influx of bacterial components triggered by intestinal barrier loss. In all, the data demonstrate that pretransplant conditioning plays a dual role in promoting minor mismatch GVHD by both depleting recipient NK cells and inducing intestinal barrier loss.

Reversing endogenous alloreactive B cell GC responses with anti-CD154 or CTLA-4Ig

Alloantibodies mediate acute antibody-mediated rejection as well as chronic allograft rejection in clinical transplantation. To better understand the cellular dynamics driving antibody production, we focused on the activation and differentiation of alloreactive B cells in the draining lymph nodes and spleen following sensitization to allogeneic cells or hearts. We used a modified staining approach with a single MHC Class I tetramer (K(d)) bound to two different fluorochromes to discriminate between the Class I-binding and fluorochrome-streptavidin-binding B cells with a high degree of specificity and binding efficiency. By Day 7-8 postsensitization, there was a 1.5- to 3.2-fold increase in the total numbers of K(d) -binding B cells. Within this K(d) -binding B cell population, approximately half were IgD(low) , MHC Class II(high) and CD86(+), 30-45% expressed a germinal center (Fas(+) GL7(+)) phenotype and 3-12% were IRF4(hi) plasma cells. Remarkably, blockade with anti-CD40 or CTLA-4Ig, starting on Day 7 postimmunization for 1 or 4 weeks, completely dissolved established GCs and halted further development of the alloantibody response. Thus MHC Class I tetramers can specifically track the in vivo fate of endogenous, Class I-specific B cells and was used to demonstrate the ability of delayed treatment with anti-CD154 or CTLA-4Ig to halt established allo-B cell responses.

TNF transactivation of EGFR stimulates cytoprotective COX-2 expression in gastrointestinal epithelial cells

TNF and epidermal growth factor (EGF) are well-known stimuli of cyclooxygenase (COX)-2 expression, and TNF stimulates transactivation of EGF receptor (EGFR) signaling to promote survival in colon epithelial cells. We hypothesized that COX-2 induction and cell survival signaling downstream of TNF are mediated by EGFR transactivation. TNF treatment was more cytotoxic to COX-2(-/-) mouse colon epithelial (MCE) cells than wild-type (WT) young adult mouse colon (YAMC) epithelial cells or COX-1(-/-) cells. TNF also induced COX-2 protein and mRNA expression in YAMC cells, but blockade of EGFR kinase activity or expression inhibited COX-2 upregulation. TNF-induced COX-2 expression was reduced and absent in EGFR(-/-) and TNF receptor-1 (TNFR1) knockout MCE cells, respectively, but was restored upon expression of the WT receptors. Inhibition of mediators of EGFR transactivation, Src family kinases and p38 MAPK, blocked TNF-induced COX-2 protein and mRNA expression. Finally, TNF injection increased COX-2 expression in colon epithelium of WT, but not kinase-defective EGFR(wa2) and EGFR(wa5), mice. These data indicate that TNFR1-dependent transactivation of EGFR through a p38- and/or an Src-dependent mechanism stimulates COX-2 expression to promote cell survival. This highlights an EGFR-dependent cell signaling pathway and response that may be significant in colitis-associated carcinoma.

The epithelial barrier is maintained by in vivo tight junction expansion during pathologic intestinal epithelial shedding

BACKGROUND & AIMS

Tumor necrosis factor (TNF) increases intestinal epithelial cell shedding and apoptosis, potentially challenging the barrier between the gastrointestinal lumen and internal tissues. We investigated the mechanism of tight junction remodeling and barrier maintenance as well as the roles of cytoskeletal regulatory molecules during TNF-induced shedding.

METHODS

We studied wild-type and transgenic mice that express the fluorescent-tagged proteins enhanced green fluorescent protein-occludin or monomeric red fluorescent protein 1-ZO-1. After injection of high doses of TNF (7.5 μg intraperitoneally), laparotomies were performed and segments of small intestine were opened to visualize the mucosa by video confocal microscopy. Pharmacologic inhibitors and knockout mice were used to determine the roles of caspase activation, actomyosin, and microtubule remodeling and membrane trafficking in epithelial shedding.

RESULTS

Changes detected included redistribution of the tight junction proteins ZO-1 and occludin to lateral membranes of shedding cells. These proteins ultimately formed a funnel around the shedding cell that defined the site of barrier preservation. Claudins, E-cadherin, F-actin, myosin II, Rho-associated kinase (ROCK), and myosin light chain kinase (MLCK) were also recruited to lateral membranes. Caspase activity, myosin motor activity, and microtubules were required to initiate shedding, whereas completion of the process required microfilament remodeling and ROCK, MLCK, and dynamin II activities.

CONCLUSIONS

Maintenance of the epithelial barrier during TNF-induced cell shedding is a complex process that involves integration of microtubules, microfilaments, and membrane traffic to remove apoptotic cells. This process is accompanied by redistribution of apical junctional complex proteins to form intercellular barriers between lateral membranes and maintain mucosal function.

The tight junction in inflammatory disease: communication breakdown

The intestinal epithelium restricts free passage of toxic and infectious molecules from the gut lumen while allowing selective paracellular absorption across the tight junction. Inflammatory bowel disease (IBD) patients demonstrate a loss of tight junction barrier function, increased pro-inflammatory cytokine production, and immune dysregulation; however, the relationship between these events is incompletely understood. Although tight junction barrier defects are insufficient to cause experimental IBD, mucosal immune activation is altered in response to increased epithelial permeability. Thus, an evolving model suggests that barrier dysfunction may predispose or enhance disease progression and therapies targeted to specifically restore the barrier function may provide an alternative or supplement to immunology-based therapies.

The ErbB4 growth factor receptor is required for colon epithelial cell survival in the presence of TNF

BACKGROUND & AIMS

The ErbB4 receptor tyrosine kinase regulates cell growth, survival, and differentiation in several tissues, but its role in the gastrointestinal tract has not been reported. We tested the hypothesis that ErbB4 promotes intestinal cell survival and restitution following injury or inflammation.

METHODS

ErbB4 expression in human inflammatory bowel disease was determined by immunohistochemistry. Mice were subjected to dextran sulfate sodium (DSS, 3%) colitis or injected with tumor necrosis factor (TNF), and ErbB4 expression was quantified by immunohistochemistry and Western blot. Cultured young adult mouse colon (YAMC) cells were exposed to TNF, and ErbB4 messenger RNA, protein, and phosphorylation levels were measured. Cells transfected with ErbB4 small interfering RNA (siRNA), or over expressing ErbB4, were subjected to wound healing and apoptosis assays.

RESULTS

ErbB4 levels increased in Crohn's colitis and the colon epithelium of mice with DSS colitis or injected with TNF. In YAMC cells, TNF induced ErbB4 messenger RNA, protein, and phosphorylation; nuclear factor kappaB activation also stimulated ErbB4 accumulation. ErbB4 siRNA sensitized cells to TNF-stimulated apoptosis, while over expression blocked apoptosis induced by TNF plus cycloheximide. Additionally, ErbB4 siRNA decreased YAMC cell wound healing. ErbB4 knockdown attenuated, while over expression elevated, phosphorylation of Akt in response to TNF. Inhibition of the phosphatidylinositol 3-kinase/Akt signaling cascade reversed the ability of ErbB4 over expression to protect from cytokine-induced apoptosis.

CONCLUSIONS

ErbB4 expression and signaling are key elements for TNF responses in vivo and in cell culture, protecting intestinal epithelial cells from apoptosis in the inflammatory environment, possibly through Akt activation.

TNFR1 promotes tumor necrosis factor-mediated mouse colon epithelial cell survival through RAF activation of NF-kappaB

Tumor necrosis factor (TNF) is a therapeutic target in the treatment of inflammatory bowel disease; however, the exact role of TNF signaling in the colon epithelium remains unclear. We demonstrate that TNF activation of TNF receptor (R)1 stimulates both pro- and anti-apoptotic signaling pathways in the colon epithelium; however, TNFR1 protects against colon epithelial cell apoptosis following TNF exposure. To investigate anti-apoptotic signaling pathways downstream of TNFR1, we generated an intestinal epithelium-specific Raf knock-out mouse and identified Raf kinase as a key regulator of colon epithelial cell survival in response to TNF. Surprisingly, Raf promotes NF-kappaB p65 phosphorylation, independent of MEK signaling, to support cell survival. Taken together, these data demonstrate a novel pathway in which Raf promotes colon epithelial cell survival through NF-kappaB downstream of TNFR1 activation. Thus, further understanding of colon epithelial cell-specific TNFR signaling may result in the identification of new targets for inflammatory bowel disease treatment and define novel mediators of colitis-associated cancer.

Raf protects against colitis by promoting mouse colon epithelial cell survival through NF-kappaB

BACKGROUND & AIMS

Raf-1 kinase is a key regulator of a number of cellular processes, which promote the maintenance of a healthy colon epithelium. This study addresses the role of Raf in epithelial cell survival in response to dextran sulfate sodium (DSS)-induced injury and inflammation.

METHODS

Inducible intestinal epithelium-specific Raf knockout mice were generated and subjected to acute colitis followed by a short recovery period. Colon sections were analyzed by in situ oligo ligation or immunostaining for Ki67, phospho-extracellular signal regulated kinase, and nuclear factor-kappaB p65. Western blot analysis and terminal deoxynucleotidyl transferase nick-end labeling assays were performed on Raf small interfering RNA-transfected young adult mouse colon cells following DSS treatment.

RESULTS

We report that Raf protects against epithelial injury and inflammation and promotes recovery from acute DSS-induced colitis by both MAPK/ERK kinase (MEK)-dependent and -independent pathways. Furthermore, we demonstrate that Raf induces novel cell survival responses through activating nuclear factor-kappaB in a MEK-independent manner.

CONCLUSIONS

These novel findings indicate a protective role for Raf in colon epithelium following ulcerative damage through inhibiting cell apoptosis and promoting proliferation with important implications for responses such as inflammation-associated carcinogenesis.

Tumor necrosis factor inhibits ligand-stimulated EGF receptor activation through a TNF receptor 1-dependent mechanism

Tumor necrosis factor (TNF) and epidermal growth factor (EGF) are key regulators in the intricate balance maintaining intestinal homeostasis. Previous work from our laboratory shows that TNF attenuates ligand-driven EGF receptor (EGFR) phosphorylation in intestinal epithelial cells. To identify the mechanisms underlying this effect, we examined EGFR phosphorylation in cells lacking individual TNF receptors. TNF attenuated EGF-stimulated EGFR phosphorylation in wild-type and TNFR2(-/-), but not TNFR1(-/-), mouse colon epithelial (MCE) cells. Reexpression of wild-type TNFR1 in TNFR1(-/-) MCE cells rescued TNF-induced EGFR inhibition, but expression of TNFR1 deletion mutant constructs lacking the death domain (DD) of TNFR1 did not, implicating this domain in EGFR downregulation. Blockade of p38 MAPK, but not MEK, activation of ERK rescued EGF-stimulated phosphorylation in the presence of TNF, consistent with the ability of TNFR1 to stimulate p38 phosphorylation. TNF promoted p38-dependent EGFR internalization in MCE cells, suggesting that desensitization is achieved by reducing receptor accessible to ligand. Taken together, these data indicate that TNF activates TNFR1 by DD- and p38-dependent mechanisms to promote EGFR internalization, with potential impact on EGF-induced proliferation and migration key processes that promote healing in inflammatory intestinal diseases.

p38 kinase regulates epidermal growth factor receptor downregulation and cellular migration

Internalization and proteolytic degradation of epidermal growth factor (EGF) receptor (R) following ligand binding is an important mechanism for regulating EGF-stimulated signals. Using pharmacological and RNA interference inhibition of p38 mitogen-activated protein kinase, we show that p38 is required for efficient EGF-induced EGFR destruction but not internalization. In the absence of p38 activity, EGF fails to stimulate the ubiquitin ligase Cbl or ubiquitinylation of EGFR, and internalized EGFR accumulates in intracellular vesicles containing caveolin-1. These effects are accompanied by loss of EGFR phosphorylation on Y1045, a phosphorylation site required for Cbl activation. Furthermore, similar to cells treated with p38 inhibitors, intestinal epithelial cells expressing Y1045F EGFR mutants show increased proliferation but not migration in response to EGF, thus uncoupling these biological responses. Together these data position p38 as a modulator of ligand-stimulated EGFR processing and demonstrate that this processing has a profound impact on the cellular outcome of EGFR signaling.