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Results for “Integrin alpha1”

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PubMed1996

The alpha1beta1 integrin is expressed during neointima formation in rat arteries and mediates collagen matrix reorganization.

Remodeling of the extracellular matrix by activated mesenchymal cells (myofibroblasts) is a critical aspect of wound repair in all adult organs. Collagen-dependent gel contraction, a process requiring integrin function, is an established in vitro assay thought to mimic in vivo matrix remodeling. Numerous data have implicated the alpha2beta1 integrin in various cell types as the primary collagen receptor responsible for collagen gel contraction. However, evidence from the literature suggests that the major collagen binding integrin expressed on mesenchymally derived cells in situ is the alpha1beta1 integrin, not the alpha2beta1 integrin. In this report, we use a rat vascular injury model to illustrate that the alpha1beta1 integrin is the major collagen receptor expressed on vascular smooth muscle cells after injury. Using two smooth muscle cell lines, expressing either the alpha1beta1 integrin alone or both the alpha1beta1 and alpha2beta1 integrins, along with Chinese hamster ovary cells transfected with the alpha1 integrin, we demonstrate that alpha1beta1 supports not only collagen-dependent adhesion and migration, but also gel contraction. These data suggest that in vivo the alpha1beta1 integrin is a critical collagen receptor on mesenchymally derived cells potentially involved in matrix remodeling after injury.

Animals↗

PubMed2000

Overexpression of alpha1beta1 integrin directly affects rat mesangial cell behavior.

BACKGROUND: Glomerular mesangial cell (MC) proliferation, hypertrophy, and abnormal matrix remodeling characterized by increased expression of fibronectin, laminin and collagen type IV, and neoexpression of collagen I and III are the main biological features of progressive glomerulonephritis (GN). Especially, persistent pathological matrix remodeling may lead to glomerular scar formation (glomerular scarring). We reported recently that alpha1beta1 integrin, a major collagen receptor for MCs, may be a potential adhesion molecule for MC-mediated pathological collagen matrix remodeling in GN. METHODS: To address further the direct role of alpha1beta1 integrin in MC behavior, such as cell growth and matrix remodeling, alpha1beta1 integrin was overexpressed in MCs by transfecting an expression vector containing a full-length rat alpha1 integrin cDNA. Flow cytometry and immunoprecipitation analysis were applied for selection of transfectants with a stable expression of the alpha1 integrin subunit. The effect of alpha1beta1 integrin overexpression on MC biology was examined with a 3H-thymidine incorporation assay, flow cytometric analysis of cell size and DNA content, Western blot analysis of a cyclin-dependent-kinase inhibitor, p27Kip1, alpha-smooth muscle actin expression, and a collagen gel contraction assay. RESULTS: The alpha1 transfectants displayed a dramatic inhibition of 3H-thymidine incorporation as compared with the mock transfectants. Increased expression of the alpha1 subunit inversely correlated with cell cycle progression and paralleled the expression of p27Kip1 and alpha-smooth muscle actin, as well as the cell size in MCs. In addition, the alpha1-transfectants were able to enhance collagen matrix reorganization effectively. CONCLUSION: These results indicate that MC-alpha1beta1 integrin expression is a critical determinant of MC phenotypes, including cell growth, cell size, and collagen matrix remodeling ability, and thereby contributes to scar matrix remodeling (sclerosis) in GN.

Actins↗

PubMed2000

Integrin function and regulation in development.

Integrins are a large family of membrane receptors, consisting of alpha and beta subunits, that play a pivotal role in the interaction of cells with the extracellular matrix. Such interaction regulates the organization of cells in organs and tissues during development as well as cell differentiation and proliferation. We have shown that unfertilized oocytes express integrins that might be important during fertilization. We also analyzed nervous system and muscle tissue development showing that integrin expression is precisely regulated during organization of these tissues. The results indicate that two distinct integrin alpha subunits mediate the outgrowth of processes in nerve and glial cells. Alpha1 integrin, a laminin receptor, is up-regulated by nerve growth factor and other differentiation stimuli and is involved in neurite extension by nerve cells. In contrast, process extension by glial cells is likely to involve the alphaV integrin. Moreover, the latter integrin subunit is also transiently expressed in muscle of the embryo body where it localizes predominantly at developing myotendinous junctions. After birth this integrin disappears and is substituted by the alpha7 subunit. At the same time, important changes also occur in the expression of the associated beta subunit. In fact, the beta1A isoform which is expressed in fetal muscles, is substituted by beta1D. These isoforms are generated by alternative splicing and differ in only a few amino acid residues at the COOH terminus of the protein. This region of the molecule is exposed at the cytoplasmic face of the plasma membrane and is connected to the actin filaments. Our results show that beta1D, which is expressed only in striated muscle tissues, binds to both cytoskeletal and extracellular matrix proteins with an affinity higher than beta1A. Thus, beta1D provides a stronger link between the cytoskeleton and extracellular matrix necessary to support mechanical tension during muscle contraction. These results indicate that cells can regulate their interactions with the extracellular matrix by changing their expression of alpha integrin subunits and thus ligand specificity, or by more subtle changes involving alternative usage of different cytoplasmic domains. The important role of both alpha and beta integrin subunit cytoplasmic domains during development is further illustrated by the analysis of targeted mutations which we have generated by homologous recombination in mice.

Alternative Splicing↗

PubMed1999

Steady-state mRNA levels of interleukin-1, integrins, cJun, and cFos in hairless mouse skin during short-term chronic UV exposure and the effect of topical tretinoin.

We have proposed that UV activation of cytokine and integrin signaling pathways may initiate the photoaging process and that one of the effects of tretinoin treatment may be to alter the cytokine and integrin patterns. In previous results, steady-state mRNA levels of interleukin-1alpha, tumor necrosis factor alpha, transforming growth factor beta, collagenase, stromelysin, collagen, and integrins (alpha1 and alpha2) were increased in the skin of hairless mice that were either UV treated or concurrently treated with UV followed by topical tretinoin for 5 weeks. The aim of this study was to focus on the expression of alpha1, alpha2 and alpha5 integrins, IL-1alpha, IL-1beta, cJun, and cFos at an earlier time point (3 weeks). Animals were UV irradiated thrice weekly for 3 weeks and were treated topically with either 0.05% tretinoin or the vehicle immediately after each exposure. Total RNA was prepared and used in RT-PCR with radiolabeled dCTP and specific primers. UV slightly increased steady-state mRNA levels for alpha1, alpha2 and alpha5 integrins whereas UV + tretinoin increased their expression (3-, 2- and 7-fold respectively). Steady-state mRNA levels for IL-1alpha, IL-1beta and cJun were increased with UV (3-, 12- and 6-fold respectively) and with UV + tretinoin (6-, 7- and 9-fold respectively). In contrast, cFos expression was unchanged. In situ staining for IL-1alpha mRNA was slightly more abundant in mice treated for 3 weeks with UV and UV + tretinoin than in controls whereas 5 weeks of UV + tretinoin treatment gave strongly positive staining. Results are consistent with cytokines and integrins mediating the effects of UV on the skin, with modulation of these effects by tretinoin.

Administration, Topical↗

PubMed2002

Endothelin-1 is a potent stimulator of alpha1beta1 integrin-mediated collagen matrix remodeling by rat mesangial cells.

Endothelin-1 (ET) is known to stimulate mesangial cell (MC) proliferation, extracellular matrix (ECM) synthesis, and thereby contribute to the progression of glomerulonephritis (GN). To clarify the molecular and cellular mechanisms of how ET is involved in the development of glomerular sclerosis, we investigated the influence of ET on the MC-alpha1beta1 integrin-mediated collagen matrix reorganization using a collagen gel contraction assay. ET enhanced MC-alpha1beta1 integrin-mediated gel contraction in a dose-dependent manner. Addition of the endothelin A (ETA) receptor antagonist, BQ123, into collagen gels abolished ET-induced gel contraction by MC. Cell behavior involved in ET-induced gel contraction was investigated in combination with function-blocking anti-alpha1-integrin antibody. Migration and adhesion assays revealed that ET stimulated alpha1beta1 integrin-mediated MC migration but did not influence cell adhesion to type I collagen (collagen I). Integrin-function blocking studies using anti-alpha1 integrin antibody indicated that MC-alpha1beta1 integrin is required not only for collagen-dependent migration, but also for gel contraction. Zymography showed that ET increased MC matrix metalloproteinase-2 (MMP-2) activity in a dose-dependent manner during MC-induced gel contraction process. Finally, flow cytometry analysis indicated that ET did not affect the cell surface expression of the MC-alpha1beta1 integrin within the collagen gel. These data suggested that ET promotes collagen matrix reorganization through the enhancement of MC-alpha1beta1 integrin-dependent migration and MMP-2 activity. We therefore conclude that ET is a potential molecule inducing pathological collagen matrix remodeling observed in progressive GN.

Animals↗

PubMed2002

Alterations in fibroblast alpha1beta1 integrin collagen receptor expression in keloids and hypertrophic scars.

Keloids and hypertrophic scars are significant symptomatic clinical problems characterized by excess collagen. Although extensive research has focused on fibroblasts and collagen turnover in these aberrant scars, little work has been done on the expression of integrins (cell membrane structures that link cells to extracellular matrix) within these lesions. Integrin-mediated regulation of collagen synthesis has previously been observed in explanted fibroblasts from normal and fibrotic dermis, and integrin alpha1 knockout mice maintain increased collagen synthesis consistent with a role for alpha1beta1 in providing negative feedback on collagen synthesis. These findings suggested the need to evaluate integrin roles in keloids and hypertrophic scars. In this study we examined integrin expression in keloids (n = 11), hypertrophic scars (n = 5), radiation ulcers (n = 2), and normal skin specimens (n = 8). We used a novel approach to analysis by isolating dermal fibroblasts directly from tissue (without explant culture) and determining surface integrin expression by flow cytometry. We found that keloids and hypertrophic scars have marked alterations in fibroblast integrin expression and contain several distinct populations of fibroblasts. One of these populations expresses high levels of alpha1 integrin, and the proportion of these cells is higher in keloids (63% +/- 3.6% SEM) and hypertrophic scars (45% +/- 2.7% SEM) than in normal skin tissues (28% +/- 4.7% SEM). The different populations of fibroblasts defined by integrin expression merge, however, when the cells are serially cultured, suggesting that there may be aspects of the dermal microenvironment that maintain the integrin phenotypic heterogeneity in dermal fibroblasts.

Adult↗

PubMed2002

Integrins and extracellular matrix proteins in the human childhood and adolescent growth plate.

Interaction of chondrocytes with the surrounding matrix significantly influences differentiation and growth. These processes involve cell surface proteins, particularly integrins. The aim of this study was to compare the expression of integrins (alpha1, alpha2, alpha3, alpha5, alpha6, alphav, beta1, beta3, and beta5 subunits) together with matching binding proteins in human childhood and adolescent growth plate cartilage using immunohistochemistry. Integrin beta1 was detected in all chondrocytes of the growth plate cartilage, beta3 only in osteoclasts of the opening zone, and beta5 in hypertrophic chondrocytes and osteoblasts. Integrin alpha1, alpha2, and alpha5 subunits were expressed by chondrocytes in the proliferative and hypertrophic zone as well as in osteoblasts and osteoclasts. Integrin av and alpha6 subunits were present in chondrocytes of all zones, alpha3 only in osteoclasts. Collagen type II and fibronectin were seen throughout the growth plate, collagen type X in the hypertrophic zone, collagen type I in the ossifying trabecules. Laminin was expressed by chondrocytes in the resting zone and more weakly in the proliferative zone, collagen VI was present in the pericellular and interterritorial matrix in all zones of the growth plate. These results differ from previous reports on the distribution of integrins in the fetal growth plate. However, there was no difference in integrin expression in children before and during puberty. Our results indicate that integrin expression is not influenced by endocrine factors during sexual maturation and suggest that the process of skeletal maturation is not regulated via altered integrin expression.

Adolescent↗

PubMed1998

Differential expression of laminin receptors in human hepatocellular carcinoma.

BACKGROUND: Laminin receptors are involved in cell-extracellular matrix interactions in malignant cells that show invasion and metastasis. Hepatocellular carcinoma frequently shows early invasion into blood vessels, and intrahepatic and extrahepatic metastases. However, the role of laminin receptors in hepatocellular carcinoma is unknown. AIMS: To examine the expression of mRNA for laminin receptors and their isoforms in hepatocellular carcinoma. METHODS: The expression of several laminin receptors, including alpha1 integrin, alpha6 integrin and its isoforms alpha6A and alpha6B, beta1 integrin and its isoforms beta1A and beta1B, and 32kD/67kDa laminin binding protein was examined in human hepatocellular carcinomas and non-cancerous liver tissues using the reverse transcription polymerase chain reaction. RESULTS: Alpha6 Integrin, beta1 integrin, and laminin binding protein showed notably increased expression in hepatocellular carcinoma, compared with non-cancerous liver tissue, although the alpha1 integrin did not show a significant change. Furthermore, beta1B integrin, a splicing variant of beta1 integrin, was overexpressed in hepatocellular carcinoma while the beta1A integrin isoform did not show significant changes between hepatocellular carcinoma and surrounding non-cancerous liver tissue. CONCLUSIONS: The differential upregulation of laminin receptors and their splicing isoforms was shown in hepatocellular carcinoma, suggesting that certain laminin receptors and their isoforms may be involved in the development and progression of hepatocellular carcinoma.

Aged↗

PubMed2001

Laminin deposition to type IV collagen enhances haptotaxis, chemokinesis, and adhesion of hepatoma cells through beta1-integrins.

BACKGROUND/AIMS: In hepatocellular carcinoma, laminin deposition to type IV collagen along the sinusoids is observed with the development of arterial network, coinciding with intrahepatic metastasis. We investigated the influence of laminin deposition to type IV collagen on hepatoma cell adhesion, motility and secretion of matrix metalloproteinases (MMPs), which are indispensable behaviors for tumor metastasis. METHODS: Hepatoma cell lines (KYN-1, -2 and -3) were used. The expression of integrin subunit mRNAs in hepatoma cells was confirmed by RT-PCR. The influence of laminin addition to type IV collagen on the adhesion, chemokinesis, and migration of KYN-1, -2 and -3 was evaluated by the haptotactic migration, phagokinetic track motility, and cell adhesion assays. The effects of integrin subunits on these activities were evaluated using the function-blocking antibodies for integrins. Phosphorylation of MEK1/2 and secretion of MMPs were investigated by Western blotting and gelatin zymography. RESULTS: Integrin alpha1, alpha2, alpha3, alpha6 and beta1 subunit mRNAs were detected. The combination of type IV collagen and laminin enhanced the migration, chemokinesis, and adhesion of hepatoma cells compared to that of type IV collagen when used alone. The enhanced activity was significantly suppressed by function-blocking antibodies for integrin alpha1, alpha2, alpha3, alpha6 and beta1 subunits. Hepatoma cells cultured on the combination of type IV collagen and laminin showed phosphorylation of MEK1/2 and increased secretion of MMPs. CONCLUSIONS: The addition of laminin to type IV collagen enhances hepatoma cell adhesion and motility through beta1-integrins.

Carcinoma, Hepatocellular↗

PubMed2000

Immunohistochemical analysis of cell-matrix adhesion molecules and their ligands in the portal tracts of primary biliary cirrhosis.

Intraepithelial migration of lymphoid cells (epitheliotropism) through the basement membrane of the bile duct is a key event in the development of chronic non-suppurative destructive cholangitis (CNSDC) and eventual immune-mediated bile duct loss in primary biliary cirrhosis (PBC). Cell-to-cell and cell-to-extracellular matrix proteins may play an important role in the development of CNSDC. To address the events of epitheliotropism in CNSDC, the expression of cell-matrix adhesion molecules such as integrins alpha1, alpha3, alpha4, alpha5, and alpha6 and the distribution of fibronectin, laminin, and collagen type IV were studied immunohistochemically, with emphasis on both infiltrating lymphocytes and the bile ducts, in frozen sections from 15 PBC cases and 34 controls (chronic viral hepatitis, extrahepatic biliary obstruction, and normal liver). In PBC and chronic viral hepatitis, most of the infiltrating lymphoid cells expressed integrin alpha4, while such expression was less common in extrahepatic biliary obstruction and normal liver. A biliary basement membrane-like structure was delineated by immunostaining of collagen type IV and laminin in PBC and controls. On the basement membrane of CNSDC, fibronectin, a ligand of integrin alpha4, was strongly and frequently expressed in PBC, while such expression on the biliary basement membrane was rare in other controls. These results suggest that increased fibronectin expression on the biliary basement membrane and integrin alpha4-fibronectin interaction facilitate adhesion and the penetration of infiltrating alpha4-expressing lymphocytes into the biliary epithelial layer in PBC.

Antigens, CD↗

PubMed2002

Network of cytokines, integrins and hormones in human trophoblast cells.

Trophoblast cells of the developing embryo are unique not only for transporting oxygen and nutrients from the mother to the fetus but also for their array of other functions throughout the pregnancy beginning from the attachment of the blastocyst to the endometrium during the process of implantation, its well regulated invasion in the uterine tissue, proliferation, differentiation and immuno-endocrine functions which subsequently maintain the pregnancy. Using human trophoblast cells in culture, we have tried to understand the molecular mechanisms which regulate such a variety of functions for trophoblast cells. Our RT-PCR studies show that trophoblast cells express the laminin and collagen receptors: integrins alpha1 and alpha2, which are both stimulated by IL-1 and IL-6. These two cytokines, also synthesised by the trophoblast cells themselves, act in an autocrine/paracrine manner to induce their own expression. In addition, IL-1 expression seems to be modulated by a large variety of cytokines and growth factors usually present in the uterine milieu whereas IL-6 expression appears to be significantly stimulated by growth factors like EGF and bFGF only. Hormones like estrogen, progesterone and hCG exhibit a general negative modulation in the expression of IL-1 and IL-6. Since, both IL-1 and IL-6 are known to be involved in the proliferation, invasion and differentiation of trophoblast cells, they might be the key factors involved in trophoblast functions.

Antigens, CD↗

PubMed2002

TNFalpha-induced apoptosis and integrin switching in human extravillous trophoblast cell line.

Differentiation of extravillous trophoblast cells (EVT) to an invasive phenotype plays an essential role in establishing and maintaining feto-placental organization during human pregnancy. A switch in integrin expression occurs during this differentiation and is accompanied by changes in the extracellular matrix (ECM). Alteration of EVT behavior is also modulated by cytokines. To investigate the molecular interactions involved in the EVT differentiation, we examined the effects of cytokines and ECM on the human EVT cell line, TCL1 cells. We found that tumor necrosis factor alpha (TNFalpha) induced apoptosis in TCL1 cells but not in JEG3 cells derived from choriocarcinoma while the addition of interleukin-1beta, leukemia inhibitory factor, or transforming growth factor had no effect on TCL1 cells. This apoptosis was suppressed when TCL1 cells were seeded on fibronectin (Fn), collagen type I (C1), collagen type IV (C4), or laminin (Ln). Wortmannin, a specific PI3 kinase inhibitor, inhibited this suppression. Spreading assays and adhesion blocking assays indicated that TCL1 cells express integrin-alpha5 and -alpha6 and beta1 and beta4 subunits. Adhesion on Fn is mediated by alpha5beta1, and adhesion on C1, C4, or Ln is mediated by alpha6beta1 integrins. TNFalpha suppressed alpha6 integrin expression and enhanced alpha1 integrin expression in a dose-dependent manner. In addition, aggregation of beta1 subunits on C4 was detected after addition of TNFalpha. Taken together, these results suggest that TNFalpha and ECM, through activation of PI3 kinase mediated by beta1 integrin signaling, might collaboratively regulate differentiation of trophoblast cells through integrin signaling in establishing and maintaining successful pregnancy.

Apoptosis↗

PubMed1999

Different cation binding to the I domains of alpha1 and alpha2 integrins: implication of the binding site structure.

In the present work, we studied the interactions of recombinant alpha1 and alpha2 integrin I domains with cations Tb(3+), Mn(2+), Mg(2+) and Ca(2+). We observed that alpha1 and alpha2 I domains bind these cations with significantly different characteristics. The binding of Mg(2+) by the alpha1 I domain was accompanied by significant changes of tryptophan fluorescence which could be interpreted as a conformational change. Comparison of the alpha1 integrin I domain structure obtained by comparative modeling with a known structure of the alpha2 integrin I domain shows distinct differences in the metal ion binding sites which could explain the differences in cation binding.

Amino Acid Sequence↗

PubMed1996

Synaptic integrins in developing, adult, and mutant muscle: selective association of alpha1, alpha7A, and alpha7B integrins with the neuromuscular junction.

Differentiation of both pre- and postsynaptic structures at the skeletal neuromuscular junction is organized by the basal lamina that occupies the synaptic cleft. As beta1 integrins are a major class of receptors for basal lamina components, we stained muscles with antibodies to the 10 integrin alpha subunits known to form dimers with beta1, to determine if any of these molecules were concentrated at synaptic sites on muscle fibers. In both developing and adult muscle, the integrin alpha1 chain was selectively associated with presynaptic cells (Schwann cells and/or nerve terminals), while alpha7 was present on both synaptic and extrasynaptic portions of the muscle fiber surface. Thus alpha1 and alpha7 integrins are present in synaptic membranes. Expression of the alpha7 chain was analyzed further by staining with antibodies specific for three alternatively spliced products of the alpha7 gene (A, B, and C), all of which were expressed in muscle. The alpha7A and alpha7B isoforms were confined to synaptic sites in adult muscle, while alpha7C was present both synaptically and extrasynaptically. In developing muscle, alpha7A appeared postnatally and specifically at the synapse; alpha7B was present throughout the muscle fiber perinatally, becoming confined to the synapse in the second postnatal week; and alpha7C was present extrasynaptically both perinatally and in adulthood. Thus, two of the alpha7 integrins are synapse-specific, and all three show distinct spatiotemporal patterns of expression within a single cell type. Finally, we asked whether perturbation of laminin expression affected the distribution of the alpha7 integrins. In normal mice, laminin beta2 is concentrated in synaptic basal lamina. In beta2-null mutant mice, alpha7A was still present at synaptic sites, but alpha7B was absent. This result provides genetic evidence that basal lamina composition is a determinant of integrin distribution.

Amino Acid Sequence↗

PubMed2000

Role of the alpha1 and alpha2 integrin cytoplasmic domains in cell morphology, motility and responsiveness to stimulation by the protein kinase C pathway.

The alpha1beta1 and alpha2beta1 integrins, extracellular matrix receptors for collagens and/or laminins, have similarities in structure and ligand binding. Recent studies suggest that the two receptors mediate distinct post-ligand binding events and are not simply redundant receptors. To discern the mechanisms by which the two receptors differ, we focused on the roles of the cytoplasmic domains of the alpha subunits. We expressed either full-length alpha1 integrin subunit cDNA (X1C1), full-length alpha2 integrin subunit cDNA (X2C2), chimeric cDNA composed of the extracellular and transmembrane domains of alpha2 subunit and the cytoplasmic domain of alpha1 (X2C1), chimeric cDNA composed of the extracellular and transmembrane domains of alpha1 subunit and the cytoplasmic domain of alpha2 (X1C2), alpha1 cDNA truncated after the GFFKR sequence (X1C0) or alpha2 cDNA truncated after the GFFKR sequence (X2C0) in K562 cells. Although the cytoplasmic domains of the alpha1 and alpha2 subunits were not required for adhesion, the extent of adhesion at low substrate density was enhanced by the presence of either the alpha1 or alpha2 cytoplasmic tail. Spreading was also influenced by the presence of an alpha subunit cytoplasmic tail. Activation of the protein kinase C pathway with phorbol dibutyrate-stimulated motility that was dependent upon the presence of the alpha2 cytoplasmic tail. Both the phosphatidylinosotide-3-OH kinase and the mitogen-activated protein kinase pathways were required for phorbol-activated, alpha2-cytoplasmic tail-dependent migration.

Antigens, CD↗

PubMed2000

Parenteral administration of an activating monoclonal antibody to the alpha1beta1 integrin in dogs.

In mice, monoclonal antibody (mAb) to the alpha1 integrin abrogate gastro-intestinal damage during graft-versus-host-disease (GVHD), suggesting anti alpha1 mAb as candidates for treatment in humans as well. Our current data show that one such reagent, mAb 1B3.1, when immobilized to plastic wells via rabbit- anti murine (ram) immunoglobulin (Ig) induces a protein kinase-dependent spreading of activated human T cells. Furthermore, it significantly increases the proliferative response, and expression of interleukin-2 (IL-2) receptors (R) and CD69, of resting T cells, expressing minimal integrin on the cell surface, to sub-optimal stimulation by anti-CD3 mAb. We found, in addition, that mAb 1B3.1 a) immuno-precipitates alpha1beta1 integrins from cell-surface iodinated canine epithelial cells b) is highly reactive with canine T cells after their activation and c) inhibits adhesion of canine T cells to collagen IV. Despite the potential ability of the mAb to co-activate T cells in vitro, two dogs that received 4 injections of 0.5-0.3 mg/Kg of mAb 1B3.1 remained healthy, developing only marginal transient lymphopenia. Injection of 0.75mg/Kg in a third dog induced a more marked lymphopenia, and an additional dose of 1.0 mg/Kg 2 weeks later was followed by gastrointestinal hemorrhage. importantly, the lymphopenia was associated with a greater and more persistent decrease of CD8+ than of CD4+ T cells, leading to an increase in the CD4/CD8 ratio 24 hours after the injection. Thus, despite it's co-activating effects in vitro, administration of this mAb in vivo is feasible when appropriately dosed, and may have immuno-modulatory effects.

Animals↗

PubMed2000

The microanatomy of the distal arrector pili: possible role for alpha1beta1 and alpha5beta1 integrins in mediating cell-cell adhesion and anchorage to the extracellular matrix.

The arrector pili (AP) muscle is a small band of smooth muscle that attaches proximally to the bulge area of the pilosebaceous apparatus in the reticular dermis and extends up toward the epidermis. The distal anatomy of the AP and the anchorage mechanism allowing hair erection have not been previously described. Integrins are likely candidates mediating this attachment. Immunohistochemical techniques were used to determine the distribution of the following integrins: alpha1, alpha2, alpha3, alpha4, alpha5, alpha6 and beta1 as well as fibronectin. Frozen human scalp tissue was sectioned in traditional planes, obliquely and horizontally to visualize microanatomy in three dimensions. Histological examination revealed that the distal portions of smooth muscle fibers splay extensively between collagen bundles of the upper dermis. Integrin subunits alpha1, alpha5 and beta1 were expressed by the AP muscle. Analysis of the relative density of immunoreactivity in digitized sections revealed increased alpha5 subunit expression at the extracellular matrix (ECM)-muscle interface. These data suggest that anchorage of the AP muscle to the ECM is via alpha5beta1 integrin and alpha1beta1 integrin functions in muscle cell-cell adhesion. Extensive splaying of smooth muscle fibers may allow increased surface area contact between the ECM and smooth muscle cells expressing peripherally situated alpha5 integrin.

Aged↗

PubMed1999

Integrin alpha2beta1 mediates isoform-specific activation of p38 and upregulation of collagen gene transcription by a mechanism involving the alpha2 cytoplasmic tail.

Two collagen receptors, integrins alpha1beta1 and alpha2beta1, can regulate distinct functions in cells. Ligation of alpha1beta1, unlike alpha2beta1, has been shown to result in recruitment of Shc and activation of the Ras/ERK pathway. To identify the downstream signaling molecules activated by alpha2beta1 integrin, we have overexpressed wild-type alpha2, or chimeric alpha2 subunit with alpha1 integrin cytoplasmic domain in human osteosarcoma cells (Saos-2) lacking endogenous alpha2beta1. The chimeric alpha2/alpha1 chain formed a functional heterodimer with beta1. In contrast to alpha2/alpha1 chimera, forced expression of alpha2 integrin resulted in upregulation of alpha1 (I) collagen gene transcription in response to three-dimensional collagen, indicating that the cytoplasmic domain of alpha2 integrin was required for signaling. Furthermore, signals mediated by alpha2beta1 integrin specifically activated the p38alpha isoform, and selective p38 inhibitors blocked upregulation of collagen gene transcription. Dominant negative mutants of Cdc42, MKK3, and MKK4 prevented alpha2beta1 integrin-mediated activation of p38alpha. RhoA had also some inhibitory effect, whereas dominant negative Rac was not effective. Our findings show the isoform-specific activation of p38 by alpha2beta1 integrin ligation and identify Cdc42, MKK3, and MKK4 as possible downstream effectors. These observations reveal a novel signaling mechanism of alpha2beta1 integrin that is distinct from ones previously described for other integrins.

Collagen↗