Integrins as mediators of epithelial cell-matrix interactions in the human small intestinal mucosa

Effects on rotavirus cell binding and infection of monomeric and polymeric peptides containing alpha2beta1 and alphaxbeta2 integrin ligand sequences

Integrin-using rotaviruses bind MA104 cell surface alpha2beta1 integrin via the Asp-Gly-Glu (DGE) sequence in virus spike protein VP4 and interact with alphaxbeta2 integrin during cell entry through outer capsid protein VP7. Infection is inhibited by the alpha2beta1 ligand Asp-Gly-Glu-Ala (DGEA) and the alphaxbeta2 ligand Gly-Pro-Arg-Pro (GPRP), and virus-alpha2beta1 binding is increased by alpha2beta1 activation. In this study, we analyzed the effects of monomers and polymers containing DGEA-, GPRP-, and DGEA-related peptides on rotavirus binding and infection in intestinal (Caco-2) and kidney (MA104) cells and virus binding to recombinant alpha2beta1. Blockade of rotavirus-cell binding and infection by peptides and anti-alpha2 antibody showed that Caco-2 cell entry is dependent on virus binding to alpha2beta1 and interaction with alphaxbeta2. At up to 0.5 mM, monomeric DGEA and DGAA inhibited binding to alpha2beta1 and infection. At higher concentrations, DGEA and DGAA showed a reduced ability to inhibit virus-cell binding and infection that depended on virus binding to alpha2beta1 but occurred without alteration in cell surface expression of alpha2, beta2, or alphavbeta3 integrin. This loss of DGEA activity was abolished by genistein treatment and so was dependent on tyrosine kinase signaling. It is proposed that this signaling activated existing cell surface alpha2beta1 to increase virus-cell attachment and entry. Polymeric peptides containing DGEA and GPRP or GPRP only were inhibitory to SA11 infection at approximately 10-fold lower concentrations than peptide monomers. As polymerization can improve peptide inhibition of virus-receptor interactions, this approach could be useful in the development of inhibitors of receptor recognition by other viruses.

The role of very late antigen-1 in immune-mediated inflammation

The alpha1beta1 integrin, also known as "very late antigen" (VLA)-1, is normally expressed on mesenchymal cells, some epithelial cells, activated T cells, and macrophages, and interacts, via the I-domain of the extracellular domain of the alpha1 subunit, with collagen molecules in the extracellular matrix (ECM). By "outside-in" transmembranal signaling to the interior of the cell, it mediates adhesion, migration, proliferation, remodeling of the ECM, and cytokine secretion by endothelial cells, mesangial cells, fibroblasts, and immunocytes. Importantly, its expressions and functions are enhanced by inflammatory cytokines including interferon (IFN)gamma and tumor necrosis factor (TNF)alpha, thus augmenting angiogenesis and fibrosis linked, in particular, to inflammation. Moreover, within the immune system, VLA-1 marks effector memory CD4+ and CD8+ T cells that are retained in extralymphatic tissues by interactions of the integrin with collagen and produce high levels of IFNgamma. Thus, immune-mediated inflammation in vivo is inhibited by blockade of the VLA-1-collagen interaction in experimental animal models of arthritis, colitis, nephritis, and graft versus host disease (GVHD), suggesting that inhibiting the interaction of the alpha1 I-domain with its ligands or modulating "outside-in" signaling by VLA-1 would be a useful approach in the human diseases simulated by these experimental models.

The maturity of intestinal neomucosa: integrin expression and ultrastructural aspects

BACKGROUND/PURPOSE

The maturity of neomucosa growing on a serosal surface for the treatment of short bowel syndrome still is questionable. The aim of this study was to evaluate the intestinal neomucosa to assess its histologic maturity.

METHODS

A 6-cm-long isolated ileal segment (IS) was prepared in 8 Wistar albino-type rats. The IS was divided from the antimesenteric side, and 2 intestinal tubes were established, which shared a common wall and a common pedicle. After ileal biopsy sampling for the control group (CG), the IS was fashioned into a mucous fistula. Eight weeks later, all the rats were killed, and the ISs were investigated for neomucosal growth. Sections were prepared with periodic acid shift (PAS) and H & E staining for light microscopy. They also were evaluated by transmission electron microscopy. The microscopic morphology of the 2 groups was evaluated. Immunohistochemical staining was performed to show the expression of the tissue beta1, alpha3 and alpha2beta1 integrin subunits of both the neomucosa (NS) and control group (CG) segments.

RESULTS

Sections of the NS showed a well-arranged columnar epithelial cell layer with goblet cells that were generally located superficially and with a complete basement membrane. Under the electron microscope, the sections from the NS group showed an epithelial cell layer with proper microvilli of the same height, although they were shorter than those of the CG, and tight intercellular junctions between the epithelial cells. Significant differences between the NS and CG groups were found in the measurements of villus width at base, microvillus surface, and microvillus height. The lamina propria consisted of rich collagen fibers and active fibroblasts in the NS group. In the immunohistochemical staining, although beta1 integrine showed a dense distribution (+++) in the lamina propria, particularly localizing at the depth of the tunica mucosa layer, alpha3 integrin was observed to have a less dense immunoreactivity (++) in both groups. The expression of alpha2beta1 integrin showed slight and dispersed (+) staining.

CONCLUSIONS

The NS showed histologic maturity and ultimate structural similarity with the native small bowel mucosa, which provides strong indirect evidence for the proper functioning of the neomucosa.

Collagen IV regulates Caco-2 migration and ERK activation via alpha1beta1- and alpha2beta1-integrin-dependent Src kinase activation

Our previous work indicates intestinal epithelial cell ERK activation by collagen IV, a major component of the intestinal epithelial basement membrane, requires focal adhesion kinase (FAK) and suggests FAK and ERK may have important roles in regulating intestinal epithelial cell migration. We therefore sought to identify FAK downstream targets regulating intestinal epithelial cell spreading, migration, and ERK activation on collagen IV and the integrins involved. Both dominant-negative Src and Src inhibitor PP2 strongly inhibited collagen IV ERK activation in Caco-2 intestinal epithelial cells. Collagen IV stimulated Grb2 binding site FAK Y925 phosphorylation, which was inhibited by PP2 and required FAK Y397 autophosphorylation. Additionally, FAK Y925F expression blocked collagen IV ERK activation. alpha(1)beta(1)- Or alpha(2)beta(1)-integrin blockade with alpha(1)- or alpha(2)-integrin subunit antibodies indicated that either integrin can mediate adhesion, cell spreading, and FAK, Src, and ERK activation on collagen IV. Both dominant-negative Src and PP2 inhibited Caco-2 spreading on collagen IV. PP2 inhibited p130(Cas) tyrosine phosphorylation, but dominant-negative p130(Cas) did not inhibit cell spreading. PP2 inhibited Caco-2 migration on collagen IV much more strongly than the mitogen-activated protein kinase kinase inhibitor PD-98059, which completely inhibited collagen IV ERK activation. These results suggest a pathway for collagen IV ERK activation requiring Src phosphorylation of FAK Y925 not previously described for this matrix protein and suggest either alpha(1)beta(1)- or alpha(2)beta(1)-integrins can regulate Caco-2 spreading and ERK activation on collagen IV via Src. Additionally, these results suggest Src regulates Caco-2 migration on collagen IV primarily through ERK-independent pathways.

Enterophilin-1 Interacts with Focal Adhesion Kinase and Decreases β1 Integrins in Intestinal Caco-2 Cells

Intestinal cell growth and differentiation are tightly regulated by growth factors and extracellular matrix components along the crypt-villus axis. We previously described enterophilin-1 (Ent-1) as a new intestinal protein associated with growth arrest and enterocyte differentiation. Ent-1 interacted with sorting nexin 1 and decreased cell surface epidermal growth factor receptor. Because beta(1) integrins are mostly found in vivo in the proliferative crypt cells, we investigated the role of Ent-1 in the fate of beta(1) integrin subunits. In undifferentiated intestinal Caco-2 cells, overexpression of Ent-1 induces a marked decrease of alpha(5)beta(1) integrin pools, whereas alpha(2)beta(1) integrin is weakly affected. Conversely, overexpression of sorting nexin 1 has no effect on integrin levels despite its ability to interact with Ent-1. Interestingly, we identified focal adhesion kinase as a new Ent-1 partner using yeast two-hybrid screening and co-precipitation experiments. Furthermore by confocal microscopy, we observed that Ent-1 and beta(1) integrins partly co-localize on vesicular structures, suggesting a role for Ent-1 in integrin trafficking. Because focal adhesion kinase is able to bind both Ent-1 and beta(1) integrins, the kinase might act as a molecular bridge between the two proteins. Altogether, these results support a role of Ent-1 in regulating beta(1) integrin expression that could favor intestinal differentiation.

GnT-V, macrophage and cancer metastasis: a common link

GnT-V generated, beta1,6-branched polylactosamines are a common feature shared by normal granulocytes, monocytes, and a variety of malignant cells. Furthermore, activation of GnT-V in oncogenic transformation induces invasiveness and metastatic potential in mice as well as in humans. In view of the common expression of lymphocytic/monocytic trait, motility, and GnT-V by metastatic cancer cells, macrophage fusion hybrids were generated in vitro with Cloudman S91 mouse melanoma cells to test whether the parental traits are co-expressed in hybrids and how those are related to altered phenotypes in relation to metastasis. In fact, the fusion hybrids are highly metastatic in vivo, motile in vitro, and express macrophage-associated traits of increased GnT-V activity, beta1,6 branching, and polylactosamine content. A Spontaneously formed lung melanoma metastases have been identified and characterized as host x tumor hybrid containing higher DNA content than parental cells and increased GnT-V activity. The results, taken together, could reflect prior fusion of tumor-associated macrophages with cells of the primary tumor, and therefore establish a possible common link between elevated expression of GnT-V and malignant transformation, a well-known report. Moreover, the fusion hybrids with metastatic potential ranging from high to low offer a genetically matched model system, for identification and characterization of differentially expressed genes in association with metastasis, since the fusion partners are derived from the same species of mouse (DBA/2J).

Review article: the expanding role of biological agents in the treatment of inflammatory bowel disease - focus on selective adhesion molecule inhibition

Inflammatory bowel disease presents in various forms. Its increasing incidence indicates that modern lifestyle triggers disease in genetically susceptible individuals. We present a model for inflammatory bowel disease pathophysiology and review the new biological therapies available. These biological agents have been developed to antagonise the processes of pathogenic inflammation, such as the reduction in T-lymphocyte apoptosis, increase in T-lymphocyte proliferation and increase in T-lymphocyte trafficking into the intestinal mucosa. Inhibitors of various inflammatory cytokines, including some antagonists to tumour necrosis factor, are effective therapies for inflammatory bowel disease. However, this class is associated with the risk of rare, but serious, side-effects, such as opportunistic infections and demyelinating diseases. The administration of anti-inflammatory cytokines, including interleukin-10 and interleukin-11, may theoretically be effective in reducing inflammation, although the clinical development of some of these therapies has been terminated. The selective inhibition of the adhesion molecules involved in T-lymphocyte trafficking can be effective in reducing gut inflammation. Of the selective adhesion molecule inhibitors under investigation, natalizumab has demonstrated efficacy in inflammatory bowel disease. The future of biological therapy for inflammatory bowel disease shows promise.

Regulation of the intestinal epithelial response to cyclic strain by extracellular matrix proteins

Repetitive mechanical deformation may stimulate intestinal epithelial proliferation. Because the extracellular matrix modulates static intestinal epithelial biology, we examined whether matrix proteins influence intestinal epithelial responses to deformation. Human Caco-2BBE cells and nontransformed human enterocytes (HIPEC) were subjected to 10% average cyclic strain at 10 cycles/min on flexible membranes precoated with matrix proteins without or with plasma fibronectin or functional anti-integrin antibodies in the medium. Strain stimulated proliferation, focal adhesion kinase, extracellular signal-regulated protein kinase (ERK), p38, and Jun N-terminal kinase similarly on collagen I or IV, and more weakly on laminin, but had no effect on fibronectin. MEK blockade (PD98059) prevented strain-stimulated proliferation on collagen but did not affect proliferation on fibronectin. Adding tissue fibronectin to a collagen substrate or plasma fibronectin to the media suppressed strain s mitogenic and signal effects, but not those of epidermal growth factor. Functional antibodies to the alpha5 or alpha(v) integrin subunit blocked strain's effects on Caco-2 proliferation and ERK activation, although ligation of the alpha2 or alpha6 subunit did not. Repetitive strain also stimulated, and fibronectin inhibited, human intestinal primary epithelial cell proliferation. Repetitive deformation stimulates transformed and nontransformed human intestinal epithelial proliferation in a matrix-dependent manner. Tissue or plasma fibronectin may regulate the intestinal epithelial response to strain via integrins containing alpha5 or alpha(v).

Converging signals synergistically activate the LAMC2 promoter and lead to accumulation of the laminin gamma 2 chain in human colon carcinoma cells

The trimeric extracellular matrix molecule laminin-5 and its constituent chains (alpha 3, beta 3, gamma 2) are normally not detectable intracellularly in intestinal epithelial cells but the laminin gamma 2 chain can be detected in cancer cells at the invasive front of a subset of colon carcinomas. These cells are subjected to cytokines such as transforming growth factor beta 1 (TGF-beta 1) and hepatocyte growth factor (HGF), produced by the tumour cells or by the surrounding stromal cells. The purpose of the present work was to investigate whether TGF-beta 1 and HGF, known to stimulate the LAMC2 gene encoding the laminin gamma 2 chain, might synergize to activate the LAMC2 promoter, and to identify the promoter elements involved. We find evidence for synergy between TGF-beta and HGF with respect to laminin gamma 2 chain expression and promoter activation and demonstrate that this requires the 5' activator protein-1 (AP-1) element of the promoter and an additional upstream element which is also responsive to co-expression of the Smad3 protein from the TGF-beta signalling pathway. The transcripts encoding the other laminin-5 chains are not synergistically activated by HGF and TGF-beta. Thus the synergistic activation of the LAMC2 gene is mediated via different cis-elements and results in an overproduction of the laminin gamma 2 chain relative to the other laminin-5 constituent chains. This difference may explain why laminin gamma 2 chains accumulate in the cells at the invasive front of colon carcinomas.

A role for membrane-type serine protease (MT-SP1) in intestinal epithelial turnover

Membrane type-serine protease 1 (MT-SP1) plays potential roles in the process of invasion and metastasis of carcinomas. In the present study, we cloned a rat MT-SP1 cDNA and investigated the intestinal distribution and proteolytic properties of the enzyme. By in situ hybridization we found the prominent expression of the mRNA in the epithelial layer of the small intestinal upper villi and of the colon, where cells are loosely attached to the basement membrane. When MT-SP1 was expressed in Caco-2, a colonic carcinoma cell line, the protein was localized exclusively on the basolateral side. A secreted form of the enzyme produced in COS-1 cells digested fibronectin and laminin. These findings suggest that MT-SP1 participates in the control of intestinal epithelial turnover by regulating the cell-substratum adhesion.