Search

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy that is still fatal in many cases. T cell blasts are characterized by hyperactivation and strong proliferative and migratory capacities. The chemokine receptor CXCR4 is involved in mediating malignant T cell properties, and cortactin has been shown to control CXCR4 surface localization in T-ALL cells. We have previously shown that cortactin overexpression is correlated with organ infiltration and relapse in B-ALL. However, the role of cortactin in T cell biology and T-ALL remains elusive. Here, we analyzed the functional relevance of cortactin for T cell activation and migration and the implications for T-ALL development. We found that cortactin is upregulated in response to T cell receptor engagement and recruited to the immune synapse in normal T cells. Loss of cortactin caused reduced IL-2 production and proliferation. Cortactin-depleted T cells showed defects in immune synapse formation and migrated less due to impaired actin polymerization in response to T cell receptor and CXCR4 stimulation. Leukemic T cells expressed much higher levels of cortactin compared to normal T cells that correlated with greater migratory capacity. Xenotransplantation assays in NSG mice revealed that cortactin-depleted human leukemic T cells colonized the bone marrow significantly less and failed to infiltrate the central nervous system, suggesting that cortactin overexpression drives organ infiltration, which is a major complication of T-ALL relapse. Thus, cortactin could serve as a potential therapeutic target for T-ALL and other pathologies involving aberrant T cell responses.

Background: Arpin was discovered as an inhibitor of the Arp2/3 complex in the lamellipodial tip of fibroblasts, where it regulated migration steering. Recently, we described that arpin stabilized the epithelial barrier in an Arp2/3-dependent manner. However, expression of arpin in endothelial cells (EC) and its role in the regulation of endothelial barrier functions has not yet been described. Methods: Arpin expression in EC was analyzed by qRT-PCR, Western blot, and confocal microscopy under basal and inflammatory conditions. Arpin-depleted human umbilical vein EC (HUVEC) were generated to perform permeability assays and to analyze changes in endothelial junctions and the actin cytoskeleton by confocal microscopy. To elucidate arpin functions in vivo, we generated and characterized arpin-deficient mice. Results: Arpin mRNA and protein were expressed in EC and downregulated by pro-inflammatory cytokines. Arpin depletion in HUVEC caused junction destabilization and the formation of actomyosin stress fibers leading to increased permeability in an Arp2/3-independent manner. In contrast to the Arp2/3 inhibitor CK666, inhibitors of kinases involved in the generation of stress fibers, namely ROCK1 and ZIPK, were able to normalize the loss-of-arpin effects on actin filaments and permeability. Arpin-deficient mice were viable but showed a characteristic vascular phenotype in the lung including edema, microhemorrhage and vascular congestion that was accompanied by increased F-actin levels and vascular permeability. Conclusions: Our data show that apart from being an Arp2/3 inhibitor, arpin is also a regulator of actomyosin contractility and endothelial barrier integrity in vitro and in vivo. Therefore, this study will pave the way for future investigations on the role of arpin in vascular and inflammatory diseases.

The quality of life in patients with inflammatory bowel diseases (IBD) is strongly impaired. Alterations of intestinal epithelial homeostasis contribute to the development and establishment of IBD. Intestinal Paneth and Paneth-like cells produce and secrete luminal proteins sustaining epithelial homeostasis. Here we show that IFN-γ stimulates Paneth and Paneth-like cells degranulation that triggers the proliferation of intestinal epithelial cells (IEC) in a Wnt/β-catenin independent manner. Degranulation in Paneth and Paneth-like cells was mTORC1 and necroptosis dependent. Remarkably, lack of IFN-γ, inhibition of mTORC1, or impeding necroptosis reduces IEC proliferation cytokine-mediated. Our findings identify a new role for IFN-γ in stimulating IEC proliferation through inducing degranulation of Paneth and Paneth-like cells which is mTORC1 and necroptosis- dependent. In a mouse model of colitis, mTORC1 activation and necroptosis regulate Paneth and Paneth-like cell secretion. Furthermore, the colitogenic environment triggers PC metaplasia in the distal region of the large intestine to simulate cell proliferation.Highlights:IFN-γ stimulates proliferation,β-catenin independent.IFN-γ enhances mitochondrial activity and proliferationIFN-γ regulates PC biogenesis.mTORC1-dependent necroptosis mediates secretion in Paneth and Paneth-like cells.

Membrane-cytoskeleton interactions (MCIs) are mediated by actin-binding proteins (ABPs). Ezrin is a crucial ABP that links membranes to actin filaments during lamellipodia formation, cell polarization, and migration. We discuss the concept of MCI and the potential of ezrin as a druggable target for treating inflammatory diseases and cancers.

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy that is still fatal in many cases. T cell blasts are characterized by hyperactivation and strong proliferative and migratory capacities. The chemokine receptor CXCR4 is involved in mediating malignant T cell properties and cortactin has been shown to control CXCR4 surface localization in T-ALL cells. We have previously shown that cortactin overexpression is correlated with organ infiltration and relapse in B-ALL. However, the role of cortactin in T cell biology and T-ALL remains elusive. Here, we analyzed the functional relevance of cortactin for T cell activation and migration and the implications for T-ALL development. We found that cortactin is upregulated in response to TCR engagement and recruited to the immune synapse in normal T cells. Loss of cortactin caused reduced IL-2 production and proliferation. Cortactin-depleted T cells showed defects in immune synapse formation and migrated less due to impaired actin polymerization in response to TCR and CXCR4 stimulation. Leukemic T cells expressed much higher levels of cortactin compared to normal T cells that correlated with greater migratory capacity. Xenotransplantation assays in NSG mice revealed that cortactin-depleted human leukemic T cells colonized the bone marrow significantly less and failed to infiltrate the central nervous system suggesting that cortactin overexpression drives organ infiltration, which is a major complication of T-ALL relapse. Thus, cortactin could serve as a potential therapeutic target for T-ALL and other pathologies involving aberrant T cell responses.

Cell migration is a dynamic process that involves adhesion molecules and the deformation of the moving cell that depends on cytoskeletal remodeling and actin-modulating proteins such as myosins. In this work, we analyzed the role of the class I Myosin-1 g (Myo1g) in migratory processes of LPS + IL-4 activated B lymphocytes in vivo and in vitro. In vivo, the absence of Myo1g reduced homing of activated B lymphocytes into the inguinal lymph node. Using microchannel chambers and morphology analysis, we found that the lack of Myo1g caused adhesion and chemotaxis defects. Additionally, deficiency in Myo1g causes flaws in adopting a migratory morphology. Our results highlight the importance of Myo1g during B cell migration.

Neutrophil extravasation is a critical event during immune responses to infection or injury that ensures survival. However, given the destructive potential of neutrophil effector molecules such as proteases and reactive oxygen species, strict control of neutrophil recruitment is required to avoid tissue damage. Neutrophil extravasation is a multistep process of adhesive interactions between neutrophils and components of the venular wall, that is, endothelium, basement membrane and pericytes. A plethora of proteins have been identified as critical regulators of each step that provide for compensatory mechanisms thus ensuring that extravasation can happen even if one mechanism is defective. Here, we discuss recent discoveries of how extravasation is regulated with emphasis on neutrophil-specific mechanisms; and discuss potential implications for future research.

Cortactin is an actin-binding protein expressed in virtually all cell types. It regulates several cell functions, including adhesion and migration. Cortactin overexpression is associated with increased metastasis formation and worse outcome in different types of solid tumors, thus highlighting a critical role of cortactin in cancer progression. Mechanistically, this is due to increased invadopodia formation and matrix metalloproteinase secretion. Cortactin has been until recently considered absent in hematopoietic cells because these cells express the cortactin homolog hematopoietic cell-specific lyn substrate-1. However, many recent reports describe functional expression of cortactin in different hematopoietic cells, such as macrophages, dendritic cells, and lymphocytes. Of note, cortactin is strongly overexpressed in leukemic cell lines and primary patient-derived leukemic cells. In B-cell chronic lymphocytic leukemia, this is associated with poor prognosis and increased chemotaxis; in B-cell acute lymphoblastic leukemia, high cortactin levels correlate with treatment failure and relapse. Moreover, cortactin has been proposed as a diagnostic marker for non-Hodgkin B-cell lymphomas. This review summarizes current knowledge on cortactin expression in hematopoietic cells and discusses the functional implications for different hematological malignancies.

Inflammatory bowel diseases (IBD) including Crohn's disease (CD) and ulcerative colitis (UC) are complex inflammatory disorders of the digestive tract. Dysfunctional intestinal epithelial barrier, uncontrolled neutrophil recruitment into the colon, and oxidative stress are major features of IBD. IBD cannot be cured, but symptoms can be alleviated with anti-inflammatory drugs, which often show adverse effects. Thus, safer alternative treatment options are needed. Given the known anti-inflammatory properties of Annickia polycarpa extract (APE), we hypothesized that APE improves the outcome of the inflammatory response during colitis. We assessed APE effects on colon histology, epithelial barrier function and neutrophil recruitment during DSS-induced colitis in mice treated with APE. APE treatment significantly reduced the disease activity index and prevented DSS-induced colon damage as evidenced by reduced colon shortening, ulcerations, crypt dysplasia, edema formation, and leukocyte infiltration. Expression of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β were significantly diminished in APE-treated mice. Importantly, APE administration reduced neutrophil infiltration into the lamina propria leading to reduced oxidative stress, tight junction disruption and epithelial permeability in the colon. Thus, we propose APE as additional treatment strategy to attenuate colitis symptoms and enhance life quality of individuals with IBD.

Sepsis remains an important health problem worldwide due to inefficient treatments often resulting in multi-organ failure. Neutrophil recruitment is critical during sepsis. While neutrophils are required to combat invading bacteria, excessive neutrophil recruitment contributes to tissue damage due to their arsenal of molecular weapons that do not distinguish between host and pathogen. Thus, neutrophil recruitment needs to be fine-tuned to ensure bacterial killing, while avoiding neutrophil-inflicted tissue damage. We recently showed that the actin-binding protein HS1 promotes neutrophil extravasation; and hypothesized that HS1 is also a critical regulator of sepsis progression. We evaluated the role of HS1 in a model of lethal sepsis induced by cecal-ligation and puncture. We found that septic HS1-deficient mice had a better survival rate compared to WT mice due to absence of lung damage. Lungs of septic HS1-deficient mice showed less inflammation, fibrosis, and vascular congestion. Importantly, systemic CLP-induced neutrophil recruitment was attenuated in the lungs, the peritoneum and the cremaster in the absence of HS1. Lungs of HS1-deficient mice produced significantly more interleukin-10. Compared to WT neutrophils, those HS1-deficient neutrophils that reached the lungs had increased surface levels of Gr-1, ICAM-1, and L-selectin. Interestingly, HS1-deficient neutrophils had similar F-actin content and phagocytic activity, but they failed to polymerize actin and deform in response to CXCL-1 likely explaining the reduced systemic neutrophil recruitment in HS1-deficient mice. Our data show that HS1 deficiency protects against sepsis by attenuating neutrophil recruitment to amounts sufficient to combat bacterial infection, but insufficient to induce tissue damage.

Severe coronavirus disease 2019 (COVID-19) is characterized by lung injury, cytokine storm, and increased neutrophil-to-lymphocyte ratio (NLR). Current therapies focus on reducing viral replication and inflammatory responses, but no specific treatment exists to prevent the development of severe COVID-19 in infected individuals. Angiotensin-converting enzyme-2 (ACE2) is the receptor for SARS-CoV-2, the virus causing COVID-19, but it is also critical for maintaining the correct functionality of lung epithelium and endothelium. Coronaviruses induce activation of a disintegrin and metalloprotease 17 (ADAM17) and shedding of ACE2 from the cell surface resulting in exacerbated inflammatory responses. Thus, we hypothesized that ADAM17 inhibition ameliorates COVID-19-related lung inflammation. We employed a preclinical mouse model using intratracheal instillation of a combination of polyinosinic:polycytidylic acid (poly(I:C)) and the receptor-binding domain of the SARS-CoV-2 spike protein (RBD-S) to mimic lung damage associated with COVID-19. Histologic analysis of inflamed mice confirmed the expected signs of lung injury including edema, fibrosis, vascular congestion, and leukocyte infiltration. Moreover, inflamed mice also showed an increased NLR as observed in critically ill COVID-19 patients. Administration of the ADAM17/MMP inhibitors apratastat and TMI-1 significantly improved lung histology and prevented leukocyte infiltration. Reduced leukocyte recruitment could be explained by reduced production of proinflammatory cytokines and lower levels of the endothelial adhesion molecules ICAM-1 and VCAM-1. Additionally, the NLR was significantly reduced by ADAM17/MMP inhibition. Thus, we propose inhibition of ADAM17/MMP as a novel promising treatment strategy in SARS-CoV-2-infected individuals to prevent the progression toward severe COVID-19.

Epithelial cells lining the intestinal mucosa create a physical barrier that separates the luminal content from the interstitium. Epithelial barrier impairment has been associated with the development of various pathologies such as inflammatory bowel diseases (IBD). In the inflamed mucosa, superficial erosions or micro-erosions that corrupt epithelial monolayers correspond to sites of high permeability. Several mechanisms have been implicated in the formation of micro-erosions including cell shedding and apoptosis. These micro-erosions often represent microscopic epithelial gaps randomly distributed in the colon. Visualization and quantification of those epithelial gaps has emerged as an important tool to investigate intestinal epithelial barrier function. Here, we describe a new method to visualize the specific location of where transcellular and paracellular permeability is enhanced in the inflamed colonic mucosa. In this assay, we apply a 10 kDa fluorescent dye conjugated to a lysine fixable dextran to visualize high permeability regions (HPR) in the colonic mucosa. Additional use of cell death markers revealed that HPR encompass apoptotic foci where epithelial extrusion/shedding occurs. The protocol described here provides a simple but effective approach to visualize and quantify micro-erosions in the intestine, which is a very useful tool in disease models, in which the intestinal epithelial barrier is compromised.

Acute and chronic colitis affect a huge proportion of the population world-wide. The etiology of colitis cases can be manifold, and diet can significantly affect onset and outcome of colitis. While many forms of acute colitis are easily treatable, chronic forms of colitis such as ulcerative colitis and Crohn's disease (summarized as inflammatory bowel diseases) are multifactorial with poorly understood pathogenesis. Inflammatory bowel diseases are characterized by exacerbated immune responses causing epithelial dysfunction and bacterial translocation. There is no cure and therapies aim at reducing inflammation and restoring intestinal barrier function. Unfortunately, most drugs can have severe side effects. Changes in diet and inclusion of nutritional supplements have been extensively studied in cell culture and animal models, and some supplements have shown promising results in clinical studies. Most of these nutritional supplements including vitamins, fatty acids and phytochemicals reduce oxidative stress and inflammation and have shown beneficial effects during experimental colitis in rodents induced by dextran sulphate sodium or 2,4,6-trinitrobenzene sulfonic acid, which remain the gold standard in pre-clinical colitis research. Here, we summarize the mechanisms through which such nutritional supplements contribute to epithelial barrier stabilization.

Chemokines play crucial roles in combating microbial infection and initiating tissue repair by recruiting neutrophils in a timely and coordinated manner. In humans, no less than seven chemokines (CXCL1, CXCL2, CXCL3, CXCL5, CXCL6, CXCL7, and CXCL8) and two receptors (CXCR1 and CXCR2) mediate neutrophil functions but in a context dependent manner. Neutrophil-activating chemokines reversibly exist as monomers and dimers, and their receptor binding triggers conformational changes that are coupled to G-protein and β-arrestin signaling pathways. G-protein signaling activates a variety of effectors including Ca2+ channels and phospholipase C. β-arrestin serves as a multifunctional adaptor and is coupled to several signaling hubs including MAP kinase and tyrosine kinase pathways. Both G-protein and β-arrestin signaling pathways play important non-overlapping roles in neutrophil trafficking and activation. Functional studies have established many similarities but distinct differences for a given chemokine and between chemokines at the level of monomer vs. dimer, CXCR1 vs. CXCR2 activation, and G-protein vs. β-arrestin pathways. We propose that two forms of the ligand binding two receptors and activating two signaling pathways enables fine-tuned neutrophil function compared to a single form, a single receptor, or a single pathway. We summarize the current knowledge on the molecular mechanisms by which chemokine monomers/dimers activate CXCR1/CXCR2 and how these interactions trigger G-protein/β-arrestin-coupled signaling pathways. We also discuss current challenges and knowledge gaps, and likely advances in the near future that will lead to a better understanding of the relationship between the chemokine-CXCR1/CXCR2-G-protein/β-arrestin axis and neutrophil function.

Cancer is a major cause of death in children worldwide, with B-lineage cell acute lymphoblastic leukemia (B-ALL) being the most frequent childhood malignancy. Relapse, treatment failure and organ infiltration worsen the prognosis, warranting a better understanding of the implicated mechanisms. Cortactin is an actin-binding protein involved in cell adhesion and migration that is overexpressed in many solid tumors and in adult B-cell chronic lymphocytic leukemia. Here, we investigated cortactin expression and potential impact on infiltration and disease prognosis in childhood B-ALL. B-ALL cell lines and precursor cells from bone marrow (BM) and cerebrospinal fluid (CSF) of B-ALL patients indeed overexpressed cortactin. In CXCL12-induced transendothelial migration assays, transmigrated B-ALL cells had highest cortactin expression. In xenotransplantation models, only cortactinhigh-leukemic cells infiltrated lungs, brain, and testis; and they colonized more easily hypoxic BM organoids. Importantly, cortactin-depleted B-ALL cells were significantly less efficient in transendothelial migration, organ infiltration and BM colonization. Clinical data highlighted a significant correlation between high cortactin levels and BM relapse in drug-resistant high-risk B-ALL patients. Our results emphasize the importance of cortactin in B-ALL organ infiltration and BM relapse and its potential as diagnostic tool to identify high-risk patients and optimize their treatments.

International audience; The intestinal epithelial barrier (IEB) depends on stable interepithelial protein complexes such as tight junctions (TJ), adherens junctions (AJ), and the actin cytoskeleton. During inflammation, the IEB is compromised due to TJ protein internalization and actin remodeling. An important actin regulator is the actin-related protein 2/3 (Arp2/3) complex, which induces actin branching. Activation of Arp2/3 by nucleation-promoting factors is required for the formation of epithelial monolayers, but little is known about the relevance of Arp2/3 inhibition and endogenous Arp2/3 inhibitory proteins for IEB regulation. We found that the recently identified Arp2/3 inhibitory protein arpin was strongly expressed in intestinal epithelial cells. Arpin expression decreased in response to tumor necrosis factor (TNF)α and interferon (IFN)γ treatment, whereas the expression of gadkin and protein interacting with protein C-kinase α-subunit 1 (PICK1), other Arp2/3 inhibitors, remained unchanged. Of note, arpin coprecipitated with the TJ proteins occludin and claudin-1 and the AJ protein E-cadherin. Arpin depletion altered the architecture of both AJ and TJ, increased actin filament content and actomyosin contractility, and significantly increased epithelial permeability, demonstrating that arpin is indeed required for maintaining IEB integrity. During experimental colitis in mice, arpin expression was also decreased. Analyzing colon tissues from ulcerative colitis patients by Western blot, we found different arpin levels with overall no significant changes. However, in acutely inflamed areas, arpin was significantly reduced compared to non-inflamed areas. Importantly, patients receiving mesalazine had significantly higher arpin levels than untreated patients. As arpin depletion (theoretically meaning more active Arp2/3) increased permeability, we wanted to know whether Arp2/3 inhibition would show the opposite. Indeed, the specific Arp2/3 inhibitor CK666 ameliorated TNFα/IFNγ-induced permeability in established Caco-2 monolayers by preventing TJ disruption. CK666 treatment also attenuated colitis development, colon tissue damage, TJ disruption, and permeability in dextran sulphate sodium (DSS)-treated mice. Our results demonstrate that loss of arpin triggers IEB dysfunction during inflammation and that low arpin levels can be considered a novel hallmark of acute inflammation.

Severe coronavirus disease 2019 (Covid-19) is characterized by lung injury, cytokine storm and increased neutrophil-to-lymphocyte ratio (NLR). Current therapies focus on reducing viral replication and inflammatory responses, but no specific treatment exists to prevent the development of severe Covid-19 in infected individuals. Angiotensin-converting enzyme-2 ACE-2) is the receptor for SARS-CoV-2, the virus causing Covid-19, but it is also critical for maintaining the correct functionality of lung epithelium and endothelium. Coronaviruses induce activation of a disintegrin and metalloprotease 17 (ADAM17) and shedding of ACE-2 from the cell surface resulting in exacerbated inflammatory responses. Thus, we hypothesized that ADAM17 inhibition ameliorates Covid-19-related lung inflammation. We employed a pre-clinical mouse model using intra-tracheal instillation of a combination of polyinosinic:polycytidylic acid (poly-I:C) and the receptor-binding domain of the SARS-CoV-2 spike protein (RBD-S) to mimic lung damage associated with Covid-19. Histological analysis of inflamed mice confirmed the expected signs of lung injury including edema, fibrosis, vascular congestion and leukocyte infiltration. Moreover, inflamed mice also showed an increased NLR as observed in critically ill Covid-19 patients. Administration of the ADAM17 inhibitors apratastat and TMI-1 significantly improved lung histology and prevented leukocyte infiltration. Reduced leukocyte recruitment could be explained by reduced production of pro-inflammatory cytokines and lower levels of the endothelial adhesion molecules ICAM-1 and VCAM-1. Additionally, the NLR was significantly reduced by ADAM17 inhibition. Thus, we propose inhibition of ADAM17 as a novel promising treatment strategy in SARS-CoV-2-infected individuals to prevent the progression towards severe Covid-19.

A considerable portion of our knowledge on T and B cell biology is acquired from research using acute lymphoblastic leukemia (ALL) cell lines, which are invaluable tools used in many immunology and leukemia studies. Here, we discuss the advantages and limitations of ALL cell lines and provide guidelines on their proper usage.

The calponin homology (CH) domain is one of the most common modules in various actin-binding proteins and is characterized by an α-helical fold. The CH domain plays important regulatory roles in both cytoskeletal dynamics and signaling. The CH domain is required for stability and organization of the actin cytoskeleton, calcium mobilization and activation of downstream pathways. The CH domain has recently garnered increased attention due to its importance in the onset of different diseases, such as cancers and asthma. However, many roles of the CH domain in various protein functions and corresponding diseases are still unclear. Here, we review current knowledge about the structural features, interactome and related diseases of the CH domain.

The hematopoietic-specific protein 1 (Hem1) comprises an essential subunit of the WAVE Regulatory Complex (WRC) in immune cells. WRC has a fundamental role in Arp2/3 complex activation and the protrusion of branched actin networks in motile cells.Hem1 deficiency leads to suppression of the entire WRC in immune cells. Defective WRC function in macrophages results in loss of lamellipodia and migration defects. Moreover, phagocytosis, commonly accompanied by lamellipodium protrusion during cup formation, is altered in Hem1 null cells concerning frequency and efficacy. When analyzing cell spreading, adhesion and podosome formation, we found that Hem1 null cells are capable, in principle, of podosome formation and consequently, do not show any quantitative differences in extracellular matrix degradation. Their adhesive behavior, however, was significantly altered. Specifically, adhesion as well as de-adhesion of Hem1 null cells was strongly compromised, likely contributing to the observed reduced efficiency of phagocytosis. In line with this, phosphorylation of the prominent adhesion component paxillin was diminished. Non-hematopoietic somatic cells disrupted in expression for both Hem1 and its ubiquitous orthologue Nck-associated protein 1 (Nap1) or the essential WRC components Sra-1/PIR121 did not only confirm defective paxillin phosphorylation, but also revealed that paxillin turnover in focal adhesions is accelerated in the absence of WRC. Finally, adhesion assays using platelets lacking functional WRC as model system unmasked radically decreased αIIbβ3 integrin activation.Our results thus demonstrate that WRC-driven actin networks impact on integrin-dependent processes controlling formation and dismantling of different types of cell-substratum adhesion.One sentence summaryInterference of Hem1 function in mice and cells uncovers a hitherto unrecognized role in integrin-mediated cell adhesion that is crucial for macrophage function and connects to recently discovered immunodeficiencies in patients carrying Hem1 mutations.

Inflammatory bowel diseases (IBD) are multifactorial disorders affecting millions of people worldwide with alarmingly increasing incidences every year. Dysfunction of the intestinal epithelial barrier is associated with IBD pathogenesis, and therapies include anti-inflammatory drugs that enhance intestinal barrier function. However, these drugs often have adverse side effects thus warranting the search for alternatives. Compatible solutes such as bacterial ectoines stabilize cell membranes and proteins. To unravel whether ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid) and homoectoine (4,5,6,7-tetrahydro-2-methyl-1H-(1,3)-diazepine-4-carboxylic acid), a synthetic derivative of ectoine, have beneficial effects during dextran sulfate sodium (DSS)-induced colitis in mice. We found that the disease activity index was significantly reduced by both ectoines. DSS-induced edema formation, epithelial permeability, leukocyte recruitment and tissue damage were reduced by ectoine and homoectoine, with the latter having stronger effects. Interestingly, the claudin switch usually observed during colitis (decreased expression of claudin-1 and increased expression of the leaky claudin-2) was completely prevented by homoectoine, whereas ectoine only reduced claudin-2 expression. Concomitantly, only homoectoine ameliorated the drop in transepithelial electrical resistance induced by IFN-γ and TNF-α in Caco-2 cells. Both ectoines inhibited loss of ZO-1 and occludin and prevented IFN-γ/TNF-α-induced increased paracellular flux of 4 kDa FITC-dextran in vitro. Moreover, both ectoines reduced expression of pro-inflammatory cytokines and oxidative stress during colitis. While both ectoine and homoectoine have protective effects on the epithelial barrier during inflammation, only homoectoine completely prevented the inflammatory claudin switch in tight junctions. Thus, homoectoine may serve as diet supplement in IBD patients to reach or extend remission.

Neutrophil extravasation is a migratory event in response to inflammation that depends on cytoskeletal dynamics regulated by myosins. Myosin-1e (Myo1e) is a long-tailed class-I myosin that has not yet been studied in the context of neutrophil-endothelial interactions and neutrophil extravasation. Intravital microscopy of TNFα-inflamed cremaster muscles in Myo1e-deficient mice revealed that Myo1e is required for efficient neutrophil extravasation. Specifically, Myo1e deficiency caused increased rolling velocity, decreased firm adhesion, aberrant crawling, and strongly reduced transmigration. Interestingly, we observed a striking discontinuous rolling behavior termed "intermittent rolling," during which Myo1e-deficient neutrophils showed alternating rolling and jumping movements. Surprisingly, chimeric mice revealed that these effects were due to Myo1e deficiency in leukocytes. Vascular permeability was not significantly altered in Myo1e KO mice. Myo1e-deficient neutrophils showed diminished arrest, spreading, uropod formation, and chemotaxis due to defective actin polymerization and integrin activation. In conclusion, Myo1e critically regulates adhesive interactions of neutrophils with the vascular endothelium and neutrophil extravasation. Myo1e may therefore be an interesting target in chronic inflammatory diseases characterized by excessive neutrophil recruitment.

Cortactin is an actin-binding protein expressed in virtually all cell types. It regulates several cell functions, including adhesion and migration. Cortactin overexpression is associated with increased metastasis formation and worse outcome in different types of solid tumors, thus highlighting a critical role of cortactin in cancer progression. Mechanistically, this is due to increased invadopodia formation and matrix metalloproteinase secretion. Cortactin has been until recently considered absent in hematopoietic cells because these cells express the cortactin homolog hematopoietic cell-specific lyn substrate-1. However, many recent reports describe functional expression of cortactin in different hematopoietic cells, such as macrophages, dendritic cells, and lymphocytes. Of note, cortactin is strongly overexpressed in leukemic cell lines and primary patient-derived leukemic cells. In B-cell chronic lymphocytic leukemia, this is associated with poor prognosis and increased chemotaxis; in B-cell acute lymphoblastic leukemia, high cortactin levels correlate with treatment failure and relapse. Moreover, cortactin has been proposed as a diagnostic marker for non-Hodgkin B-cell lymphomas. This review summarizes current knowledge on cortactin expression in hematopoietic cells and discusses the functional implications for different hematological malignancies.

The inclusion of lymphocytes in high endothelial venules and their migration to the lymph nodes are critical steps in the immune response. Cell migration is regulated by the actin cytoskeleton and myosins. Myo1e is a long-tailed class I myosin and is highly expressed in B cells, which have not been studied in the context of cell migration. By using intravital microscopy in an in vivo model and performing in vitro experiments, we studied the relevance of Myo1e for the adhesion and inclusion of activated B cells in high endothelial venules. We observed reduced expression of integrins and F-actin in the membrane protrusions of B lymphocytes, which might be explained by deficiencies in vesicular trafficking. Interestingly, the lack of Myo1e reduced the phosphorylation of focal adhesion kinase (FAK; also known as PTK2), AKT (also known as AKT1) and RAC-1, disturbing the FAK–PI3K–RAC-1 signaling pathway. Taken together, our results indicate a critical role of Myo1e in the mechanism of B-cell adhesion and migration.