Roles for epithelial integrin α3ß1 in regulation of the microenvironment during normal and pathological tissue remodeling.

Integrin receptors for the extracellular matrix activate intracellular signaling pathways that are critical for tissue development, homeostasis, and regeneration/repair, and their loss or dysregulation contributes to many developmental defects and tissue pathologies. This review will focus on tissue remodeling roles for integrin α3ß1, a receptor for laminins found in the basement membranes (BMs) that underlie epithelial cell layers. As a paradigm, we will discuss literature that supports a role for α3ß1 in promoting ability of epidermal keratinocytes to modify their tissue microenvironment during skin development, wound healing, or tumorigenesis. Preclinical and clinical studies have shown that this role depends largely on ability of α3ß1 to govern the keratinocyte's repertoire of secreted proteins, or the "secretome," including 1) matrix proteins and proteases involved in matrix remodeling and 2) paracrine-acting growth factors/cytokines that stimulate other cells with important tissue remodeling functions (e.g., endothelial cells, fibroblasts, inflammatory cells). Moreover, α3ß1 signaling controls gene expression that helps epithelial cells carry out these functions, including genes that encode secreted matrix proteins, proteases, growth factors, or cytokines. We will review what is known about α3ß1-dependent gene regulation through both transcription and posttranscriptional mRNA stability. Regarding the latter, we will discuss examples of α3ß1-dependent alternative splicing (AS) or alternative polyadenylation (APA) that prevents inclusion of cis-acting mRNA sequences that would otherwise target the transcript for degradation via nonsense-mediated decay or destabilizing AU-rich elements (AREs) in the 3'-untranslated region (3'-UTR). Finally, we will discuss prospects and anticipated challenges of exploiting α3ß1 as a clinical target for the treatment of cancer or wound healing.

The laminin-binding integrins regulate nuclear factor κB-dependent epithelial cell polarity and inflammation.

The main laminin-binding integrins α3ß1, α6ß1 and α6ß4 are co-expressed in the developing kidney collecting duct system. We previously showed that deleting the integrin α3 or α6 subunit in the ureteric bud, which gives rise to the kidney collecting system, caused either a mild or no branching morphogenesis phenotype, respectively. To determine whether these two integrin subunits cooperate in kidney collecting duct development, we deleted α3 and α6 in the developing ureteric bud. The collecting system of the double knockout phenocopied the α3 integrin conditional knockout. However, with age, the mice developed severe inflammation and fibrosis around the collecting ducts, resulting in kidney failure. Integrin α3α6-null collecting duct epithelial cells showed increased secretion of pro-inflammatory cytokines and displayed mesenchymal characteristics, causing loss of barrier function. These features resulted from increased nuclear factor kappa-B (NF-κB) activity, which regulated the Snail and Slug (also known as Snai1 and Snai2, respectively) transcription factors and their downstream targets. These data suggest that laminin-binding integrins play a key role in the maintenance of kidney tubule epithelial cell polarity and decrease pro-inflammatory cytokine secretion by regulating NF-κB-dependent signaling.

JAM-A interacts with α3ß1 integrin and tetraspanins CD151 and CD9 to regulate collective cell migration of polarized epithelial cells.

Junctional adhesion molecule (JAM)-A is a cell adhesion receptor localized at epithelial cell-cell contacts with enrichment at the tight junctions. Its role during cell-cell contact formation and epithelial barrier formation has intensively been studied. In contrast, its role during collective cell migration is largely unexplored. Here, we show that JAM-A regulates collective cell migration of polarized epithelial cells. Depletion of JAM-A in MDCK cells enhances the motility of singly migrating cells but reduces cell motility of cells embedded in a collective by impairing the dynamics of cryptic lamellipodia formation. This activity of JAM-A is observed in cells grown on laminin and collagen-I but not on fibronectin or vitronectin. Accordingly, we find that JAM-A exists in a complex with the laminin- and collagen-I-binding α3ß1 integrin. We also find that JAM-A interacts with tetraspanins CD151 and CD9, which both interact with α3ß1 integrin and regulate α3ß1 integrin activity in different contexts. Mapping experiments indicate that JAM-A associates with α3ß1 integrin and tetraspanins CD151 and CD9 through its extracellular domain. Similar to depletion of JAM-A, depletion of either α3ß1 integrin or tetraspanins CD151 and CD9 in MDCK cells slows down collective cell migration. Our findings suggest that JAM-A exists with α3ß1 integrin and tetraspanins CD151 and CD9 in a functional complex to regulate collective cell migration of polarized epithelial cells.

Basement membrane defects in CD151-associated glomerular disease.

BACKGROUND: CD151 is a cell-surface molecule of the tetraspanin family. Its lateral interaction with laminin-binding integrin ɑ3ß1 is important for podocyte adhesion to the glomerular basement membrane (GBM). Deletion of Cd151 in mice induces glomerular dysfunction, with proteinuria and associated focal glomerulosclerosis, disorganisation of GBM and tubular cystic dilation. Despite this, CD151 is not routinely screened for in patients with nephrotic-range proteinuria. We aimed to better understand the relevance of CD151 in human kidney disease. METHODS: Next-generation sequencing (NGS) was used to detect the variant in CD151. Electron and light microscopy were used to visualise the filtration barrier in the patient kidney biopsy, and immunoreactivity of patient red blood cells to anti-CD151/MER2 antibodies was performed. Further validation of the CD151 variant as disease-causing was performed in zebrafish using CRISPR-Cas9. RESULTS: We report a young child with nail dystrophy and persistent urinary tract infections who was incidentally found to have nephrotic-range proteinuria. Through targeted NGS, a novel, homozygous truncating variant was identified in CD151, a gene rarely reported in patients with nephrotic syndrome. Electron microscopy imaging of patient kidney tissue showed thickening of GBM and podocyte effacement. Immunofluorescence of patient kidney tissue demonstrated that CD151 was significantly reduced, and we did not detect immunoreactivity to CD151/MER2 on patient red blood cells. CRISPR-Cas9 depletion of cd151 in zebrafish caused proteinuria, which was rescued by injection of wild-type CD151 mRNA, but not CD151 mRNA containing the variant sequence. CONCLUSIONS: Our results indicate that a novel variant in CD151 is associated with nephrotic-range proteinuria and microscopic haematuria and provides further evidence for a role of CD151 in glomerular disease. Our work highlights a functional testing pipeline for future analysis of patient genetic variants. A higher resolution version of the Graphical abstract is available as Supplementary information.

Tetraspanin CD151 and integrin α3ß1 contribute to the stabilization of integrin α6ß4-containing cell-matrix adhesions.

Tetraspanin CD151 has been suggested to regulate cell adhesion through its association with laminin-binding integrins α3ß1 and α6ß4; however, its precise function in keratinocyte adhesion remains elusive. In this study, we investigated the role of CD151 in the formation and maintenance of laminin-associated adhesions. We show that CD151, through binding to integrin α3ß1, plays a critical role in the stabilization of an adhesion structure with a distinct molecular composition of hemidesmosomes with tetraspanin features. These hybrid cell-matrix adhesions, which are formed early during cell adhesion and spreading and at later stages of cell spreading, are present in the central region of the cells. They contain the CD151-α3ß1/α6ß4 integrin complexes and the cytoskeletal linker protein plectin, but are not anchored to the keratin filaments. In contrast, hemidesmosomes, keratin filament-associated adhesions that contain integrin α6ß4, plectin, BP180 (encoded by COL17A1) and BP230 (encoded by DST), do not require CD151 for their formation or maintenance. These findings provide new insights into the dynamic and complex regulation of adhesion structures in keratinocytes and the pathogenic mechanisms underlying skin blistering diseases caused by mutations in the gene for CD151.

How Cancer Cells Invade Bladder Epithelium and Form Tumors: The Mouse Bladder Tumor Model as a Model of Tumor Recurrence in Patients.

Non-muscle-invasive bladder cancer is the most common form of bladder cancer. The main problem in managing bladder tumors is the high recurrence after the transurethral resection of bladder tumors (TURBT). Our study aimed to examine the fate of intravesically applied cancer cells as the implantation of cancer cells after TURBT is thought to be a cause of tumor recurrence. We established an orthotopic mouse bladder tumor model with MB49-GFP cancer cells and traced them during the first three days to define their location and contacts with normal urothelial cells. Data were obtained by Western blot, immunolabeling, and light and electron microscopy. We showed that within the first two hours, applied cancer cells adhered to the traumatized epithelium by cell projections containing α3ß1 integrin on their tips. Cancer cells then migrated through the epithelium and on day 3, they reached the basal lamina or even penetrated it. In established bladder tumors, E-cadherin and desmoplakin 1/2 were shown as feasible immunohistochemical markers of tumor margins based on the immunolabeling of various junctional proteins. Altogether, these results for the first time illustrate cancer cell implantation in vivo mimicking cellular events of tumor recurrence in bladder cancer patients.

A complex between phosphatidylinositol 4-kinase IIα and integrin α3ß1 is required for N-glycan sialylation in cancer cells.

Aberrant N-glycan sialylation of glycoproteins is closely associated with malignant phenotypes of cancer cells and metastatic potential, which includes cell adhesion, migration, and growth. Recently, phosphatidylinositol 4-kinase IIα (PI4KIIα), which is localized to the trans-Golgi network, was identified as a regulator of Golgi phosphoprotein 3 (GOLPH3) and of vesicle transport in the Golgi apparatus. GOLPH3 is a target of PI4KIIα and helps anchor sialyltransferases and thereby regulates sialylation of cell surface receptors. However, how PI4KIIα-mediated sialyation of cell surface proteins is regulated remains unclear. In this study, using several cell lines, CRISPR/Cas9-based gene knockout and short hairpin RNA-mediated silencing, RT-PCR, lentivirus-mediated overexpression, and immunoblotting methods, we confirmed that PI4KIIα knockdown suppresses the sialylation of N-glycans on the cell surface, in Akt phosphorylation and activation, and integrin α3-mediated cell migration of MDA-MB-231 breast cancer cells. Interestingly, both integrin α3ß1 and PI4KIIα co-localized to the trans-Golgi network, where they physically interacted with each other, and PI4KIIα specifically associated with integrin α3 but not α5. Furthermore, overexpression of both integrin α3ß1 and PI4KIIα induced hypersialylation. Conversely, integrin α3 knockout significantly inhibited the sialylation of membrane proteins, such as the epidermal growth factor receptor, as well as in total cell lysates. These findings suggest that the malignant phenotype of cancer cells is affected by a sialylation mechanism that is regulated by a complex between PI4KIIα and integrin α3ß1.

A systematic survey of conformational states in ß1 and ß4 integrins using negative-stain electron microscopy.

Structural analyses of ß2 and ß3 integrins have revealed that they generally assume a compact bent conformation in the resting state and undergo a global conformational transition involving extension during upregulation of ligand affinity, collectively called the 'switchblade model'. This hypothesis, however, has not been extensively tested for other classes of integrins. We prepared a set of recombinant integrin ectodomain fragments including αvß3, α2ß1, α3ß1, α5ß1, α6ß1 and α6ß4, and used negative-stain electron microscopy to examine their structures under various conditions. In contrast to αvß3 integrin, which exhibited a severely bent conformation in low-affinity 5 mM Ca2+ conditions, all ß1 integrin heterodimers displayed a mixed population of half-bent to fully extended conformations. Moreover, they did not undergo significant conformational change upon activation by Mn2+ Integrin α6ß4 was even more resistant to conformational regulation, showing a completely extended structure regardless of the buffer conditions. These results suggest that the mechanisms of conformational regulation of integrins are more diverse and complex than previously thought, requiring more experimental scrutiny for each integrin subfamily member.

Synthesis and Preclinical Evaluation of a 68Ga-Radiolabeled Peptide Targeting Very Late Antigen-3 for PET Imaging of Pancreatic Cancer.

Pancreatic cancer is highly malignant and has a five-year survival rate of 5% due to an early lymph node, nerve, and vascular metastasis. Integrin α3ß1 (also called very late antigen-3, VLA-3) is overexpressed in many tumors and plays a vital role in tumor formation, recurrence, and metastasis. In this study, we developed a 68Ga-radiolabeled peptide tracer targeting the α3 unit of VLA-3 and evaluated its potential application in positron emission computed tomography (PET) imaging of pancreatic cancer. NOTA-CK11 was prepared by solid-phase synthesis and successfully radiolabeled with 68Ga with greater than 99% radiochemical purity and a specific activity of 37 ± 5 MBq/nmol (n = 5). The expression level of integrin α3 in three human pancreatic cancer cells was evaluated with the order of SW1990, BXPC-3, and PANC-1 from high to low, while the expression level of integrin ß1 was relatively close. When SW1990 cells with the highest expression level of VLA-3 were stained with FITC-CK11, strong fluorescence was observed by flow cytometry and under a laser confocal microscope. However, no significant fluorescence was observed in the blocking group when treated with excessive CK11. 68Ga-NOTA-CK11 showed significant radioactivity accumulation in SW1990 cells and was blocked by CK11 successfully. Subsequent small-animal PET imaging and biodistribution studies in mice bearing SW1990 xenografts confirmed its high tumor uptake with a good tumor-to-blood ratio and tumor-to-muscle ratio (2.45 ± 0.31 and 3.65 ± 0.33, respectively) at 1 h post injection of the probe. In summary, we successfully developed a peptide-based imaging agent, 68Ga-NOTA-CK11, that showed a strong binding affinity with VLA-3 and good target specificity for SW1990 cells and xenografted pancreatic tumor, rending it a promising radiotracer for PET imaging of VLA-3 expression in pancreatic cancer.

An update on the RAPH blood group system.

CONCLUSIONS: This update of the RAPH blood group system (Hayes M. RAPH blood group system. Immunohematology 2014;30:6-10) reports no new alleles. The RAPH blood group system (International Society of Blood Transfusion system 25) consists of a single anti-gen (MER2) expressed on CD151, a member of the tetraspanin family of proteins. CD151 regulates interactions with laminin-binding integrins α3ß1, α6ß1, α6ß4, and α7ß1 and is expressed on red blood cells as well as many other tissues and cancer types. Lack of the RAPH protein is associated with nephropathy with pretibial epidermolysis bullosa and deafness.

Alterations in the immunoreactivity of laminin, type IV collagen and α3ß1 integrin in diabetic rat ovarian follicles.

AIM: In order to determine the possible effects of diabetes, we aimed to investigate the expression of extracellular matrix proteins in the theca and granulosa layers in different follicular stages. METHODS: Thirty-two adult Wistar albino male rats were divided into 4 groups as control and sampled groups. Four, eight and twelve weeks after inducing diabetes with an intraperitoneal injection of streptozotocin (40 mg/kg), the expressions of laminin, type IV collagen and α3ß1 integrin in ovarian tissues were evaluated by immunohistochemical method. RESULTS: In our study, in the first month of diabetes, a significant increase was observed in laminin, type IV collagen and α3ß1 integrin expressions in all follicle types compared to the control group in both the theca and granulosa layers. Laminin and type IV collagen immunoreactivity tended to increase in D2 and D3 groups also. Integrin expression did not change in the newly formed follicles in the D2 and D3 groups, however, it tended to change and increase in the developing follicles. CONCLUSIONS: The changes in the expression of laminin, type IV collagen and α3ß1 integrin, which are the extracellular matrix proteins in the follicle, along with diabetes, show that diabetes plays a role in the regulation of follicular development (Tab. 4, Fig. 36, Ref. 29).

The N-terminal domain of the R28 protein promotes emm28 group A Streptococcus adhesion to host cells via direct binding to three integrins.

Group A Streptococcus (GAS) is a human-specific pathogen responsible for a wide range of diseases, ranging from superficial to life-threatening invasive infections, including endometritis, and autoimmune sequelae. GAS strains express a vast repertoire of virulence factors that varies depending on the strain genotype, and many adhesin proteins that enable GAS to adhere to host cells are restricted to some genotypes. GAS emm28 is the third most prevalent genotype in invasive infections in France and is associated with gyneco-obstetrical infections. emm28 strains harbor R28, a cell wall-anchored surface protein that has previously been reported to promote adhesion to cervical epithelial cells. Here, using cellular and biochemical approaches, we sought to determine whether R28 supports adhesion also to other cells and to characterize its cognate receptor. We show that through its N-terminal domain, R28Nt, R28 promotes bacterial adhesion to both endometrial-epithelial and endometrial-stromal cells. R28Nt was further subdivided into two domains, and we found that both are involved in cell binding. R28Nt and both subdomains interacted directly with the laminin-binding α3ß1, α6ß1, and α6ß4 integrins; interestingly, these bindings events did not require divalent cations. R28 is the first GAS adhesin reported to bind directly to integrins that are expressed in most epithelial cells. Finally, R28Nt also promoted binding to keratinocytes and pulmonary epithelial cells, suggesting that it may be involved in supporting the prevalence in invasive infections of the emm28 genotype.

Absence of integrin α3ß1 promotes the progression of HER2-driven breast cancer in vivo.

BACKGROUND: HER2-driven breast cancer is correlated with poor prognosis, especially during its later stages. Numerous studies have shown the importance of the integrin α3ß1 during the initiation and progression of breast cancer; however, its role in this disease is complex and often opposite during different stages and in different types of tumors. In this study, we aim to elucidate the role of integrin α3ß1 in a genetically engineered mouse model of HER2-driven mammary tumorigenesis. METHODS: To investigate the role of α3ß1 in HER2-driven tumorigenesis in vivo, we generated a HER2-driven MMTV-cNeu mouse model of mammary tumorigenesis with targeted deletion of Itga3 (Itga3 KO mice). We have further used several established triple-negative and HER2-overexpressing human mammary carcinoma cell lines and generated ITGA3-knockout cells to investigate the role of α3ß1 in vitro. Invasion of cells was assessed using Matrigel- and Matrigel/collagen I-coated Transwell assays under static or interstitial fluid flow conditions. The role of α3ß1 in initial adhesion to laminin and collagen was assessed using adhesion assays and immunofluorescence. RESULTS: Tumor onset in mice was independent of the presence of α3ß1. In contrast, the depletion of α3ß1 reduced the survival of mice and increased tumor growth and vascularization. Furthermore, Itga3 KO mice were significantly more likely to develop lung metastases and had an increased metastatic burden compared to WT mice. In vitro, the deletion of ITGA3 caused a significant increase in the cellular invasion of HER2-overexpressing SKBR3, AU565, and BT474 cells, but not of triple-negative MDA-MB-231. This invasion suppressing function of α3ß1 in HER2-driven cells depended on the composition of the extracellular matrix and the interstitial fluid flow. CONCLUSION: Downregulation of α3ß1 in a HER2-driven mouse model and in HER2-overexpressing human mammary carcinoma cells promotes progression and invasiveness of tumors. The invasion-suppressive role of α3ß1 was not observed in triple-negative mammary carcinoma cells, illustrating the tumor type-specific and complex function of α3ß1 in breast cancer.

A Kaposi's Sarcoma-Associated Herpesvirus Infection Mechanism Is Independent of Integrins α3ß1, αVß3, and αVß5.

Host receptor usage by Kaposi's sarcoma-associated herpesvirus (KSHV) has been best studied using primary microvascular endothelial and fibroblast cells, although the virus infects a wide variety of cell types in culture and in natural infections. In these two infection models, KSHV adheres to the cell though heparan sulfate (HS) binding and then interacts with a complex of EphA2, xCT, and integrins α3ß1, αVß3, and αVß5 to catalyze viral entry. We dissected this receptor complex at the genetic level with CRISPR-Cas9 to precisely determine receptor usage in two epithelial cell lines. Surprisingly, we discovered an infection mechanism that requires HS and EphA2 but is independent of αV- and ß1-family integrin expression. Furthermore, infection appears to be independent of the EphA2 intracellular domain. We also demonstrated that while two other endogenous Eph receptors were dispensable for KSHV infection, transduced EphA4 and EphA5 significantly enhanced infection of cells lacking EphA2.IMPORTANCE Our data reveal an integrin-independent route of KSHV infection and suggest that multiple Eph receptors besides EphA2 can promote and regulate infection. Since integrins and Eph receptors are large protein families with diverse expression patterns across cells and tissues, we propose that KSHV may engage with several proteins from both families in different combinations to negotiate successful entry into diverse cell types.

Age-dependent increase in antibodies that inhibit Plasmodium falciparum adhesion to a subset of endothelial receptors.

BACKGROUND: Plasmodium falciparum-infected erythrocytes (IE) sequester in deep vascular beds where their adhesion is mediated by an array of endothelial surface receptors. Because parasite adhesion has been associated with disease, antibodies that block this activity may confer protective immunity. Here, levels of plasma anti-adhesion activity and surface reactivity against freshly collected IEs from malaria-infected children were measured in a Malian birth cohort and related to child age and malaria infection history. METHODS: Plasma samples from children enrolled at birth in a longitudinal cohort study of mother-infant pairs in Ouelessebougou, Mali were collected at multiple time points during follow-up visits. Anti-adhesion antibodies (i.e., inhibit IE binding to any of several endothelial receptors) and reactivity with surface IE proteins were measured using a binding inhibition assay and by flow cytometry, respectively. RESULTS: Levels of antibodies that inhibit the binding of children's IE to the receptors ICAM-1, integrin α3ß1 and laminin increased with age. The breadth of antibodies that inhibit ICAM-1 and laminin adhesion (defined as the proportion of IE isolates whose binding was reduced by ≥ 50%) also significantly increased with age. The number of malaria infections prior to plasma collection was associated with levels of plasma reactivity to IE surface proteins, but not levels of anti-adhesion activity. CONCLUSIONS: Age is associated with increased levels of antibodies that reduce adhesion of children's IE to three of the ten endothelial receptors evaluated here. These results suggest that anti-adhesion antibodies to some but not all endothelial receptors are acquired during the first few years of life.

Integrin Cross-Talk Regulates the Human Neutrophil Response to Fungal ß-Glucan in the Context of the Extracellular Matrix: A Prominent Role for VLA3 in the Antifungal Response.

Candida albicans infection produces elongated hyphae resistant to phagocytic clearance compelling alternative neutrophil effector mechanisms to destroy these physically large microbial structures. Additionally, all tissue-based neutrophilic responses to fungal infections necessitate contact with the extracellular matrix (ECM). Neutrophils undergo a rapid, ECM-dependent mechanism of homotypic aggregation and NETosis in response to C. albicans mediated by the ß2 integrin, complement receptor 3 (CR3, CD11b/CD18, αMß2). Neither homotypic aggregation nor NETosis occurs when human neutrophils are exposed either to immobilized fungal ß-glucan or to C. albicans hyphae without ECM. The current study provides a mechanistic basis to explain how matrix controls the antifungal effector functions of neutrophils under conditions that preclude phagocytosis. We show that CR3 ligation initiates a complex mechanism of integrin cross-talk resulting in differential regulation of the ß1 integrins VLA3 (α3ß1) and VLA5 (α5ß1). These ß1 integrins control distinct antifungal effector functions in response to either fungal ß-glucan or C. albicans hyphae and fibronectin, with VLA3 inducing homotypic aggregation and VLA5 regulating NETosis. These integrin-dependent effector functions are controlled temporally whereby VLA5 and CR3 induce rapid, focal NETosis early after binding fibronectin and ß-glucan. Within minutes, CR3 undergoes inside-out auto-activation that drives the downregulation of VLA5 and the upregulation of VLA3 to support neutrophil swarming and aggregation. Forcing VLA5 to remain in the activated state permits NETosis but prevents homotypic aggregation. Therefore, CR3 serves as a master regulator during the antifungal neutrophil response, controlling the affinity states of two different ß1 integrins, which in turn elicit distinct effector functions.

Activated Protein C Attenuates Severe Inflammation by Targeting VLA-3high Neutrophil Subpopulation in Mice.

The host injury involved in multiorgan system failure during severe inflammation is mediated, in part, by massive infiltration and sequestration of hyperactive neutrophils in the visceral organ. A recombinant form of human activated protein C (rhAPC) has shown cytoprotective and anti-inflammatory functions in some clinical and animal studies, but the direct mechanism is not fully understood. Recently, we reported that, during endotoxemia and severe polymicrobial peritonitis, integrin VLA-3 (CD49c/CD29) is specifically upregulated on hyperinflammatory neutrophils and that targeting the VLA-3high neutrophil subpopulation improved survival in mice. In this article, we report that rhAPC binds to human neutrophils via integrin VLA-3 (CD49c/CD29) with a higher affinity compared with other Arg-Gly-Asp binding integrins. Similarly, there is preferential binding of activated protein C (PC) to Gr1highCD11bhighVLA-3high cells isolated from the bone marrow of septic mice. Furthermore, specific binding of rhAPC to human neutrophils via VLA-3 was inhibited by an antagonistic peptide (LXY2). In addition, genetically modified mutant activated PC, with a high affinity for VLA-3, shows significantly improved binding to neutrophils compared with wild-type activated PC and significantly reduced neutrophil infiltration into the lungs of septic mice. These data indicate that variants of activated PC have a stronger affinity for integrin VLA-3, which reveals novel therapeutic possibilities.

A crosstalk between muscarinic and CRF2 receptors regulates cellular adhesion properties of human colon cancer cells.

Patients with inflammatory bowel disease often suffer from chronic and relapsing intestinal inflammation that favor the development of colitis associated cancer. An alteration of the epithelial intestinal barrier function observed in IBD is supposed to be a consequence of stress. It has been proposed that corticotrophin-releasing factor receptor (CRF2), one of the two receptors of CRF, the principal neuromediator of stress, acts on cholinergic nerves to induce stress-mediated epithelial barrier dysfunction. Non-neuronal acetylcholine (Ach) and muscarinic receptors (mAchR) also contribute to alterations of epithelial cell functions. In this study, we investigated the mechanisms through which stress and Ach modulate epithelial cell adhesive properties. We show that Ach-induced activation of mAchR in HT-29 cells results in cell dissociation together with changes in cell-matrix contacts, which correlates with the acquisition of invasive potential consistent with a matrix metalloproteinase (MMP) mode of invasion. These processes result from mAchR subsequent stimulation of the cascade of src/Erk and FAK activation. Ach-induced secretion of laminin 332 leads to α3ß1 integrin activation and RhoA-dependent reorganization of the actin cytoskeleton. We show that Ach-mediated effects on cell adhesion are blocked by astressin 2b, a CRF2 antagonist, suggesting that Ach action depends partly on CRF2 signaling. This is reinforced by the fact that Ach-mediated activation of mAchR stimulates both the synthesis and the release of CRF2 ligands in HT-29 cells (effects blocked by atropine). In summary, our data provides evidence for a novel intracellular circuit involving mAchR acting on CRF2-signaling that could mediate colonic mucosal barrier dysfunction and exacerbate mucosal inflammation.

Human Adenovirus Type 37 Uses αVß1 and α3ß1 Integrins for Infection of Human Corneal Cells.

Epidemic keratoconjunctivitis (EKC) is a severe, contagious ocular disease that affects 20 to 40 million individuals worldwide every year. EKC is mainly caused by six types of human adenovirus (HAdV): HAdV-8, -19, -37, -53, -54, and -56. Of these, HAdV-8, -19, and -37 use sialic acid-containing glycans as cellular receptors. αVß3, αVß5, and a few additional integrins facilitate entry and endosomal release of other HAdVs. With the exception of a few biochemical analyses indicating that HAdV-37 can interact physically with αVß5, little is known about the integrins used by EKC-causing HAdVs. Here, we investigated the overall integrin expression on human corneal cells and found expression of α2, α3, α6, αV, ß1, and ß4 subunits in human corneal in situ epithelium and/or in a human corneal epithelial (HCE) cell line but no or less accessible expression of α4, α5, ß3, or ß5. We also identified the integrins used by HAdV-37 through a series of binding and infection competition experiments and different biochemical approaches. Together, our data suggest that HAdV-37 uses αVß1 and α3ß1 integrins for infection of human corneal epithelial cells. Furthermore, to confirm the relevance of these integrins in the HAdV-37 life cycle, we developed a corneal multilayer tissue system and found that HAdV-37 infection correlated well with the patterns of αV, α3, and ß1 integrin expression. These results provide further insight into the tropism and pathogenesis of EKC-causing HAdVs and may be of importance for future development of new antiviral drugs.IMPORTANCE Keratitis is a hallmark of EKC, which is caused by six HAdV types (HAdV-8, -19, -37, -53, -54, and -56). HAdV-37 and some other HAdV types interact with integrin αVß5 in order to enter nonocular human cells. In this study, we found that αVß5 is not expressed on human corneal epithelial cells, thus proposing other host factors mediate corneal infection. Here, we first characterized integrin expression patterns on corneal tissue and corneal cells. Among the integrins identified, competition binding and infection experiments and biochemical assays pointed out αVß1 and α3ß1 to be of importance for HAdV-37 infection of corneal tissue. In the absence of a good animal model for EKC-causing HAdVs, we also developed an in vitro system with multilayer HCE cells and confirmed the relevance of the suggested integrins during HAdV-37 infection.

Hepatitis B Virus X Protein Reduces Podocyte Adhesion via Downregulation of α3ß1 Integrin.

BACKGROUND/AIMS: Hepatitis B virus (HBV)-associated glomerulonephritis (HBV-GN) is characterized by a reduced number of podocytes due to apoptosis and shedding from the basement membrane. However, the pathological mechanism of HBV-GN is unclear. We previously showed that hepatitis B virus X protein (HBx) promotes apoptosis in tubular epithelial cells. In this study, we transfected podocytes with HBx and examined the effects on adhesion and apoptosis of these cells. METHODS: Podocytes were transfected with pc-DNA3.1 (+)-HBx. One control group was not transfected and another control group was transfected with empty plasmids. Podocyte adhesion was assessed by a fluorescence assay, apoptosis was measured by flow cytometry and fluorescence microscopy, and expression of α3ß1 integrin was determined by western blotting and the reverse transcription polymerase chain reaction (RT-PCR). Activity of caspase-8 was measured by a spectrophotometric assay. RESULTS: Relative to controls, podocytes with pc-DNA3.1(+)-HBx had reduced cell adhesion, increased apoptosis, reduced expression of α3ß1 integrin, and increased caspase-8 activity. ß1 integrin blockage reduced podocyte adhesion, but increased apoptosis and caspase-8 activity. Treatment of transfected podocytes with a caspase-8 inhibitor (Z-IETD-FMK) had no effect on the HBx-mediated integrin downregulation and reduced podocyte adhesion, suggesting that α3ß1 integrin downregulaton is sufficient to alter cell adhesion. CONCLUSIONS: Our in vitro results indicate that HBx reduced podocyte adhesion and expression of α3ß1 integrin, and increased apoptosis. Moreover, HBx-mediated downregulation of α3ß1 integrin expression is sufficient to reduce podocyte adhesion. HBx-induced apoptosis of podocytes may contribute to HBV-GN.