SEARCH · PubMed Health

Results for “Integrin”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,405 records · Page 78Linked to original sources

PubMed1994

Selective increase in the binding of the alpha 1 beta 1 integrin for collagen type IV during neurite outgrowth of human neuroblastoma TR 14 cells.

Regulation of beta 1 integrins in neurite outgrowth following N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dBcAMP) treatment was investigated using the human neuroblastoma cell line TR 14. Three beta 1 integrins were identified: the alpha 1 beta 1 receptor bound collagen type I, collagen type IV and probably laminin; the alpha 2 beta 1 integrin bound collagen type I; and the alpha v beta i receptor bound fibronectin. Neurite extension was detectable as early as 30 minutes following dBcAMP treatment, was maximal after 24 hours and remained constant during treatment for 4 days. Adhesion-perturbing beta 1 subunit-specific antibodies, added together with dBcAMP, prevented the outgrowth of new neurites. During the first 24 hours of neurite outgrowth, no change was observed in the amount of beta 1 integrins nor in their topographic distribution. However, dBcAMP treatment increased the binding of alpha 1 beta 1 receptors to collagen type IV-Sepharose by a factor 2.3 +/- 0.6 (P < 0.02), while no alteration in the binding to collagen type I was detected. Moreover, neurites and growth cones were immunoreactive for collagen type IV but not for collagen type I. Consistently dBcAMP-induced neurite outgrowth was inhibited by adhesion-perturbing alpha 1 subunit-specific antibodies. Following maximal neurite outgrowth, the amount of beta 1 integrins determined by immunoprecipitation and by confocal microscopy decreased to 58.3 +/- 11.2% (P < 0.001) and to 55.4 +/- 17.5% (P < 0.001) of untreated levels, respectively, without any change in the level of beta 1 mRNA or de novo synthesized beta 1 precursor. However, pulse-chase experiments showed an increased turnover of the beta 1 subunit: the amount of beta 1 precursor that was degraded after 1 hour chase was 50.5 +/- 8.4% in cells treated for 4 days and 34.2 +/- 3.9% in untreated cells (P < 0.02); the amount of mature beta 1 after 24 hours chase was smaller in cells treated for 4 days compared to untreated cells. In conclusion, during neurite outgrowth, alpha 1 beta 1 integrins are required and acquire an enhanced binding activity for collagen type IV; but following maximal neurite outgrowth, expression of beta 1 integrins is reduced.

Antigens, CD↗

PubMed2000

alpha3beta1 and alpha6beta4 integrin receptors for laminin-5 are not essential for epidermal morphogenesis and homeostasis during skin development.

Continuous regeneration and homeostasis of the stratified epidermis requires coordinated regulation of cell proliferation, cell differentiation, and cell survival. Integrin-mediated cell adhesion to the extracellular matrix has important roles in regulating each of these processes. Integrins alpha3beta1 and alpha6beta4 are both receptors on epidermal keratinocytes for the basement membrane protein laminin-5, the major ligand for epidermal adhesion in mature skin. Ablation in mice of either alpha3beta1 or alpha6beta4, through null mutation of the gene encoding the alpha3, alpha6, or beta4 integrin subunit, results in epidermal blistering of varying severity. Our previous studies showed that, despite blistering, differentiation and stratification of the epidermis appeared essentially normal in mice that lacked either alpha3beta1 or alpha6beta4. However, these studies did not definitively address the specific developmental importance of each integrin, since they may have overlapping and/or compensatory functions. Given the individual importance of alpha3beta1 or alpha6beta4 in maintaining the dermo-epidermal junction in mature skin, we sought to determine the importance of these integrins for embryonic skin development and epidermal morphogenesis. In the current study, we analyzed skin development in mutant embryos that completely lack both integrins alpha3beta1 and alpha6beta4. Although alpha3beta1/alpha6beta4-deficient embryos displayed epidermal blistering by stage E15.5 of development, they also retained regions of extensive epidermal adhesion to the basement membrane through stage E16.5, indicating alternative adhesion mechanisms. Apoptosis was induced in detached epidermis of alpha3beta1/alpha6beta4-deficient embryos, exemplifying vividly the importance of epithelial attachment to the basement membrane for cell survival. However, apoptotic cells were completely absent from attached epidermis of alpha3beta1/alpha6beta4-deficient embryos, showing that epithelial adhesion that occurred independently of alpha3beta1 and alpha6beta4 also protected cells from apoptosis. Remarkably, in the absence of the known laminin-5 binding integrins (alpha3beta1, alpha6beta4, and alpha6beta1), keratinocytes retained the capacity to proliferate in the epidermis, and epidermal stratification and skin morphogenesis appeared normal prior to blister formation. These findings show that while alpha3beta1 and alpha6beta4 are both required for integrity of the dermo-epidermal junction, neither one is essential for epidermal morphogenesis during skin development.

Animals↗

PubMed2001

Bromodeoxyuridine induces integrin expression at transcriptional (alpha2 subunit) and post-transcriptional (beta1 subunit) levels, and alters the adhesive properties of two human lung tumour cell lines.

Integrins are a family of transmembrane glycoproteins that participate in a wide range of cellular events including proliferation, apoptosis and differentiation. Little is known about the mechanisms that control integrin subunit expression in epithelial cells, especially during lung cell differentiation. We have examined the effect of the differentiation-modulating agent, 5-bromo-2'-deoxyuridine (BrdU), on integrin expression in 2 human lung carcinoma cell lines, DLKP and A549. Treatment of both DLKP and A549 with 10 microM BrdU for 7 days resulted in increased expression of alpha2 and beta1 integrin subunit protein expression. Northern blot and RT-PCR analyses revealed progressively increasing levels of the alpha2 mRNA transcripts following BrdU treatment up to 21 days in both cell lines. However, no increase in beta1 integrin mRNA levels was observed in either cell, suggesting post-transcriptional regulation by BrdU. Treatment of HL-60, a leukaemic cell line, with BrdU up to 21 days resulted in no change in alpha2 or beta1 integrin subunit levels at either protein or mRNA levels suggesting that the change seen in the lung cell lines may be epithelial cell lineage-specific. BrdU has also been found to alter the adhesive properties of A549 and DLKP cells. Treated cells were found to adhere significantly faster to collagen type IV and laminin compared to untreated cells. The results presented here suggest that DLKP (and A549) may be useful cellular models to investigate the role of the alpha2beta1 integrin in lung epithelial cell differentiation.

Antigens, CD↗

PubMed2000

Maturation-dependent expression and function of the CD49d integrin on monocyte-derived human dendritic cells.

Dendritic cells (DC) are highly specialized APC that are critical for the initiation of T cell-dependent immune responses. DC exert a sentinel function while immature and, after activation by inflammatory stimuli or infectious agents, mature and migrate into lymphoid organs to prime T cells. We have analyzed integrin expression on monocyte-derived DC (MDDC) and found that expression of CD49d integrins (CD49d/CD29 and CD49d/beta7) was induced/up-regulated during TNF-alpha- or LPS-initiated MDDC maturation, reflecting the induction/up-regulation of CD49d and beta7 mRNA. CD49d mRNA steady-state level increased more than 10 times during maturation, with the highest levels observed 24 h after TNF-alpha treatment. CD49d integrin expression conferred mature MDDC with an elevated capacity to adhere to the CS-1 fragment of fibronectin, and also mediated transendothelial migration of mature MDDC. Up-regulation of CD49d integrin expression closely paralleled that of the mature DC marker CD83. CD49d integrin expression was dependent on cell maturation, as its induction was abrogated by N:-acetylcysteine, which inhibits NF-kappaB activation and the functional and phenotypic maturation of MDDC. Moreover, CD49d integrin up-regulation and MDDC maturation were prevented by SB203580, a specific inhibitor of p38 mitogen-activated protein kinase, but were almost unaffected by the mitogen-activated protein/extracellular signal-related kinase kinase 1/2 inhibitor PD98059. Our results support the existence of a link between functional and phenotypic maturation of MDDC and CD49d integrin expression, thus establishing CD49d as a maturation marker for MDDC. The differential expression of CD49d on immature and mature MDDC might contribute to their distinct motility capabilities and mediate mature DC migration into lymphoid organs.

Acetylcysteine↗

PubMed1999

Embryonic neurons adapt to the inhibitory proteoglycan aggrecan by increasing integrin expression.

The primary mediators of cell migration during development, wound healing and metastasis, are receptors of the integrin family. In the developing and regenerating nervous system, chondroitin sulfate proteoglycans (CSPGs) inhibit the integrin-dependent migration of neuronal growth cones. Here we report that embryonic sensory neurons cultured on the growth-promoting molecule laminin in combination with the inhibitory CSPG aggrecan rapidly adapt to inhibition. Adaptation is associated with a two- to threefold increase in the levels of RNA and surface protein for two laminin receptors, integrin alpha6beta1 and alpha3beta1, indicating that integrin expression is regulated by aggrecan. Increased integrin expression is associated both with increases in neuronal cell adhesion/outgrowth and with decreases in the ability of aggrecan to inhibit cell adhesion. Directly increasing integrin expression by adenoviral infection is sufficient to eliminate the inhibitory effects of aggrecan, indicating that upregulation of integrin receptors may promote neuronal regeneration in the presence of inhibitory matrix components.

Aggrecans↗

PubMed1994

Role of alpha 4-integrins in lymphocyte homing to mucosal tissues in vivo.

Lymphocyte recirculation through different organs is thought to be regulated by adhesion molecules ("homing receptors") recognizing tissue-specific vascular addressins on endothelium. Here we show that the alpha 4/beta 7-integrin has a key role in the migration of mouse lymphocytes to mucosal sites. Homing to Peyer's patches but not to peripheral lymph nodes is inhibited by Fab fragments of mAb PS/2 against the alpha 4-integrin chain, by mAb DATK32 recognizing a combinatorial epitope on the alpha 4/beta 7-integrin, and by mAb FIB30 against the beta 7-chain. The Abs significantly reduce homing of lymphocytes to the intestine, as well. The migration of immunoblasts to gut and gut-associated lymphoid tissue also involves the alpha 4/beta 7-integrin heterodimer. Another anti-alpha 4 Ab, R1-2, which blocks lymphocyte binding to Peyer's patches in the Stamper-Woodruff frozen section assay and lymphocyte adhesion to VCAM-1 and fibronectin, has only minor effects on lymphocyte traffic in vivo. Anti-VCAM-1 Ab as well as the fibronectin peptide CS-1 are without influence on the migration to Peyer's patches or intestine, in contrast to Ab against the mucosal addressin MAdCAM-1. Thus, homing to gut-associated sites is regulated by the alpha 4/beta 7-integrin heterodimer interacting with the vascular addressin, MAdCAM-1, and not with fibronectin or VCAM-1 as counterstructures. Inhibition of homing to Peyer's patches and intestine by the anti-integrin Abs studied was only partial. L-selectin also participates in the homing of small lymphocytes to mucosal sites, especially Peyer's patches, but does not contribute substantially to the localization of blasts into the intestinal wall. The results support a major, but not exclusive role of the alpha 4/beta 7-integrin in lymphocyte traffic to mucosal sites.

Animals↗

PubMed1996

Specific regulation of VLA-4 and alpha 4 beta 7 integrin expression on human activated T lymphocytes.

Modulation of VLA integrins was studied in several human T cell clones upon specific and nonspecific cellular activation. Human activated T lymphocytes down-regulated both alpha 4 beta 1 and alpha 4 beta 7 integrins upon specific recognition of alloantigens (cytotoxic T cells) or in the presence of Staphylococcus enterotoxin B (superantigen recognizing noncytotoxic T cells). In contrast, the expression of other membrane integrins, such as VLA-1 and VLA-5 integrins, was not modified. Down-regulation of alpha 4 beta 1 and alpha 4 beta 7 integrins was observed as early as 3 h after stimulation, lasted later than 72 h and was partially inhibited by cytochalasin D. Interestingly, neither target cells nor NK cells modulated CD49d expression after interaction with T cells of K562, respectively, suggesting that CD49d expression was linked to specific T cell activation. The down-regulation of the CD49d chain in T cell clones stimulated with immobilized anti-CD3 mAbs confirmed the role of TCR-mediated activation in CD49d regulation. However, the CD3-independent cellular aggregation induced by soluble anti-CD43 mAb was also able to strongly down-regulate alpha 4 beta 1 and alpha 4 beta 7. The present work shows the first evidence that CD49d subunit-bearing integrin expression is distinctly regulated from other integrins after Ag or superantigen recognition by human activated T cells. CD49d modulation may be relevant for the traffic and tissue localization of locally activated T cells during immune responses.

Antigen-Presenting Cells↗

PubMed1997

Blocking of alpha 1 beta 1 integrin strongly improves survival of hepatocytes in allogeneic transplantation.

The survival rate of hepatocytes after allogeneic hepatocyte transplatation (HTX) is low, possibly because of formation of intravascular hepatocyte aggregates. The aim of this study was to determine the role of integrins in intravascular aggregation and intraparenchymal survival of transplanted hepatocytes in a fully allogeneic rat model. First, the expression profile of various integrins was determined on both isolated hepatocytes in vitro and on hepatocyte aggregates in recipient livers after intraportal transplantation of allogeneic hepatocytes. Next, the role of these integrins in hepatocyte aggregation was determined in an in vitro attachment assay on liver sections with function-blocking anti-integrin monoclonal antibodies (mAb). The results showed that anti-alpha 1 beta 1 integrin mAb significantly block hepatocyte attachment to vessel walls and liver parenchyma in vitro. Subsequently, the effect of preincubation of hepatocytes with anti-integrin mAb on their intravascular aggregation and on intraparenchymal survival was studied in an allogeneic HTX model. Preincubation with anti-leukocyte function-associated antigen-1 alpha or anti-beta 2 mAb significantly intravascular hepatocyte aggregation, and anti-leukocyte function-associated antigen-1 alpha mAb enhanced intraparenchymal survival. Preincubation with anti-alpha 1 or anti-beta 1 mAb did not inhibit aggregation but significantly improved survival from 2% to up to 45% at Day 2 after transplantation (p < 0.001). In conclusion, our results suggest that the blocking of alpha 1 beta 1 integrin significantly improves survival of allotransplanted hepatocytes.

Animals↗

PubMed1996

Differential effects of the integrins alpha9beta1, alphavbeta3, and alphavbeta6 on cell proliferative responses to tenascin. Roles of the beta subunit extracellular and cytoplasmic domains.

Members of the integrin family manifest considerable overlap in ligand specificity, and many cells have the capacity to express multiple integrin receptors for the same ligand. For example, at least 5 different integrins recognize tenascin as a ligand, and 4 of these bind to the same region of the protein, the third fibronectin type III repeat (TNfn3). We utilized colon carcinoma cells (SW480) that do not normally attach to TNfn3 to examine the possibility that ligation of different integrin receptors for this ligand would induce different effects on cell behavior and intracellular signaling. Heterologous expression of the tenascin receptors alphavbeta3 and alpha9beta1 produced comparable effects on cell adhesion and spreading on TNfn3, but alphavbeta3-transfectants proliferated considerably better on each concentration examined. alphavbeta6-transfectants attached (although less avidly), but completely failed to spread or proliferate. Expression of a chimeric beta subunit composed of the beta3 extracellular domain fused to the beta6 transmembrane and cytoplasmic domains resulted in adhesion and spreading similar to that seen with beta3-transfectants, but considerably less proliferation. When the same cell lines were plated on fibronectin, alphavbeta6-transfectants spread and proliferated as well as cells transfected with the chimeric beta3/beta6 subunit, but, again, neither cell line proliferated as well as cells expressing alphavbeta3. Cell proliferation was always associated with spreading and with phosphorylation of the focal adhesion kinase, paxillin, and the mitogen-activated kinase, Erk2, but cell attachment in the absence of spreading or proliferation was not associated with phosphorylation of any of these proteins. These data suggest that different integrin receptors for a single ligand can produce markedly different effects on cell proliferation, and that both the extracellular and cytoplasmic domains of integrin beta subunits contribute to these differences.

Antigens, CD↗

PubMed1998

Modulation of laminin integrin receptors in the postnatal and adult rat lung.

Recent studies have shown that type II pneumocytes, at birth and day 3 postnatally, have a diffuse distribution and localize at alveolar 'corners' between 3 and 7 days. Since alpha 3 beta 1 and alpha 6 beta 1 are laminin-binding receptors that are well expressed by rat type II alveolar epithelial cells, we postulated that they may play a role in the localization of the cells in the alveolus. To begin the evaluation of this hypothesis, we studied the temporal and spatial expression of the alpha 3, alpha 6, and beta 1 integrin subunit protein and mRNA in whole rat lungs during postnatal development by immunofluorescence, confocal microscopy, and Northern blot analysis. The temporal expression of proteins analyzed by immunochemistry, with integrin subunit specific antibodies, increased during the 3- to 7-day postnatal period and in adult lungs. Densitometric values of the alpha 3, alpha 6, and beta 1 mRNA expression, normalized to 28S rRNA, quadrupled from day 1 to day 3 postnatally. The mRNA expression of different integrin chains was elevated 1.5- to threefold from days 5 to 7 postnatally compared to day 1 levels. The alpha 3 and alpha 6 integrin subunit mRNA decreased to newborn levels in adult lungs, whereas the beta 1 integrin mRNA in adult lungs was expressed at approximately 50% of its level in newborn lungs. We postulate that the increases in alpha 3, alpha 6, and beta 1 integrin mRNA expression during the early neonatal period may be important for the spatial distribution of type II pneumocytes.

Aging↗

PubMed1997

Nitric oxide inhibits neutrophil beta 2 integrin function by inhibiting membrane-associated cyclic GMP synthesis.

The aim of this investigation was to identify the mechanism by which nitric oxide inhibits neutrophil beta 2 integrin dependent adherence. Isolated rat neutrophils from blood and peritoneal exudates were exposed for 2 min to nitric oxide generated by diethylamine-NO at rates between 1.6 and 138 nmol/min. Exposure to nitric oxide at rates less than 14 nmol/min had no effect on adherence. Exposure to 14 to 56 nmol nitric oxide/min inhibited beta 2 integrin dependent adherence to endothelial cells, nylon columns, and fibrinogen-coated plates, but higher concentrations had no significant effect on adherence. Adherence by beta 2 integrins could be restored by incubating cells with dithioerythritol, phorbol 12-myristate 13-acetate, or 8-bromo cyclic GMP. Elevations in cellular cyclic GMP concentration were associated with adherence, but this did not occur after cells were exposed to concentrations of nitric oxide that inhibited beta 2 integrin-dependent adherence. Elevations in cyclic GMP did occur after cells were incubated with dithioerythritol or phorbol 12-myristate 13-acetate. Concentrations of nitric oxide that inhibited beta 2 integrin-dependent adherence also inhibited catalytic activity of membrane associated guanylate cyclase and binding of atrial natriuretic peptide, but were insufficient to activate cytosolic guanylate cyclase. Nitric oxide did not inhibit neutrophil oxidative burst or degranulation, nor effect beta 2 integrin expression or adherence that did not depend on beta 2 integrins, nor cause oxidative stress identified in terms of cellular glutathione concentration or protein nitrotyrosine. The results indicate that nitric oxide inhibited beta 2 integrins in a concentration-dependent fashion by inhibiting cell-surface transduction of signals linked to the activity of membrane-bound guanylate cyclase. The inhibitory effect could be overcome by providing cells with cyclic GMP exogenously or by stimulating cytosolic guanylate cyclase.

Animals↗

PubMed1999

Redox regulation of beta2-integrin CD11b/CD18 activation.

Although the central role of beta2-integrin CD11b / CD18 in neutrophil functions is well recognized, signaling pathway that regulate integrin activation remain to be elucidated. We analyzed the contribution of oxido-reduction mechanisms in this signaling. Exogenously added H(2)O(2) induced CD11b/CD18-dependent neutrophil adhesion and expression of an integrin activation neoepitope recognized by monoclonal antibody (mAb) clone 24. H(2)O(2)-triggered beta2-integrin activation was inhibited by tyrosine kinase inhibitors and by complexing sulfhydryl groups with phenylarsine oxide (PAO). CD11b/CD18-dependent adhesion and mAb 24 antigen expression triggered by physiological agonists such as TNF-alpha were inhibited by diphenylene iodonium (DPI, an inhibitor of flavoprotein oxidoreductase), by free radical scavengers, by tyrosine kinase inhibitors and by PAO. No inhibition was observed when adhesion was induced by the integrin-activating KIM 185 mAb. Taken together, these results emphasize the importance of an oxidative S-thiolation step(s) in the tyrosine kinase-dependent signaling pathway leading to beta2-integrin activation. H(2)O(2) would directly mediate this oxidative reaction and bypass the initial agonist/receptor pathway to promote integrin-dependent adhesion. The putative oxidase(s) involved in this process is not NADPH oxidase, since adhesion of neutrophils from patients with chronic granulomatous disease was normal and inhibited by scavengers and DPI. These data shed a new light on the regulation of integrin activation required for cell migration into inflamed organs.

CD18 Antigens↗

PubMed2000

Intercellular adhesion molecule 1 and beta2 integrins in C1q-stimulated superoxide production by human neutrophils: an example of a general regulatory mechanism governing acute inflammation.

OBJECTIVE: To investigate the role of intercellular adhesion molecule 1 (ICAM-1) and beta2 integrins in the production of superoxide (O2-) by C1q-stimulated human polymorphonuclear leukocytes (PMN). METHODS: PMN were pretreated with F(ab')2 fragments of monoclonal antibodies (mAb) that blocked or did not block beta2 integrin-mediated adhesion. The cells were added to wells coated with C1q, and the production of O2- was monitored kinetically as a color change due to reduction of cytochrome c. In some experiments, C1q was co-immobilized with purified ICAM-1. RESULTS: Blocking mAb to the shared beta2 integrin subunit, CD18, completely inhibited the O2- response triggered by immobilized C1q, while blocking mAb to the alpha subunits of the beta2 integrins each partially blocked the O2- response. PMN treated with C1q were found to activate the beta2 integrins lymphocyte function-associated antigen 1 and CR3 for binding to ICAM-1. Co-immobilization of ICAM-1 with C1q cooperatively triggered O2- production by PMN. CONCLUSION: beta2 integrin binding to an ICAM provided an essential costimulatory signal for O2-production triggered by C1q in PMN. Our findings suggest a model for PMN activation in which 2 stimuli are required for O2- production: a first signal that also activates PMN beta2 integrins, followed by a second, beta2 integrin-mediated signal, which occurs physiologically upon PMN binding to ICAM-1. The requirement for this dual signal for PMN generation of O2- would serve as a regulatory mechanism to limit the production of O2- to a tissue environment where C1q, or some other stimulus, is colocalized with stromal cells bearing up-regulated ICAM-1. This mechanism may explain why all tissues can express ICAM-1 and may explain in part why inhibitors of tumor necrosis factor alpha, a major physiologic stimulus of ICAM-1 up-regulation, are potent antiinflammatory agents.

Antibodies, Blocking↗

PubMed1997

Myoblast alpha v beta3 integrin levels are controlled by transcriptional regulation of expression of the beta3 subunit and down-regulation of beta3 subunit expression is required for skeletal muscle cell differentiation.

The expression of alpha v beta3 integrin was examined in human skeletal muscle cells grown in vitro. The alpha v and beta3 subunits showed different patterns of expression during myogenesis. Expression of the alphav subunit did not change significantly during the growth and differentiation of muscle cells, whereas expression of the beta3 subunit was markedly down-regulated at both the message and protein levels. Down-regulation of beta3 subunit expression did not occur when cultures were treated with 5-bromo-2'-deoxyuridine to inhibit myoblast terminal differentiation, but did occur in cultures in which fusion was selectively inhibited by growth in EGTA-containing medium. These results suggest that the regulation of integrin beta3 subunit expression is tightly coupled to the myogenic terminal differentiation program, but is not simply a consequence of membrane reorganization due to the fusion process. Several stably transfected lines of mouse C2 myoblasts were derived from cultures transfected with a cDNA encoding the complete human beta3 integrin sequence under the control of the CMV promoter. Lines which constitutively expressed high levels of the human beta3 integrin subunit did not fuse or biochemically differentiate, whereas lines expressing moderate levels of the beta3 integrin subunit showed delayed fusion and differentiation. Lines expressing very low to undetectable levels of the human beta3 integrin subunit exhibited unimpaired fusion and differentiation. Taken together these results suggest (i) that down-regulation of alpha v beta3 integrin normally occurs as part of the myogenic terminal differentiation program, (ii) that this is mediated by regulation of the expression of the beta3 subunit, and (iii) that down-regulation of expression of the beta3 integrin subunit appears essential for myoblast differentiation.

Animals↗

PubMed1998

MAP-kinase dependent induction of monocytic procoagulant activity by beta2-integrins.

beta2-Integrin adhesion molecules play crucial roles in monocyte transmigration and adherence to the inflamed extracellular matrix. While integrin engagement contributes to inflammatory cell activation, little is known about the precise signaling pathways that are important to integrin-dependent monocyte activation. We examined the role of tyrosine phosphorylation and extracellular-signal regulated kinase (ERK) activity in beta2-integrin signaling in monocytes. Cross-linking of the LFA-1 (CD11a/CD18) and MAC-1 (CD11b/CD18) integrins on the surface of THP-1 monocytic cells induced the accumulation of tyrosine phosphoproteins. As part of this signal both ERK-1 and ERK-2 are tyrosine phosphorylated. In vitro kinase assays documented an increase in ERK-2 activity following both LFA-1 and MAC-1 cross-linking. beta2-Integrin cross-linking also led to a marked increase in 4-h procoagulant activity (PCA) in THP-1 cells and purified human monocytes. Inhibition of tyrosine phosphorylation by genistein (10 microg/ml), or selective ERK inhibition with PD98059 (10 microM), was able to block the integrin-dependent induction of PCA in both THP-1 cells and human monocytes. Thus, beta2 integrin signaling in monocytic cells can flow through the tyrosine phosphorylation and activation of the ERK mitogen activated protein kinases, which is essential for the subsequent expression of tissue factor. These results suggest that the ERK proteins likely function to integrate various adhesion-dependent signals during the process of monocyte transmigration.

Blood Coagulation Factors↗

PubMed2001

Integrins alphavbeta3 and alphavbeta5 mediate VSMC migration and are elevated during neointima formation in the rat aorta.

Neointima formation involves tissue expression of matrix proteins and growth factors. The role of alphavbeta3, but not alphavbeta5 integrin in vascular cells has been sufficiently investigated. The aim of the present study was to determine and compare the function of alphavbeta3 and alphavbeta5 integrins in rat aortic (RASMC) and human coronary vascular smooth muscle cells (HCSMC) and to characterize their expression accompanying neointima formation in vivo. RASMC and HCSMC express alphavbeta3 and alphavbeta5 integrin subunits. The alphavbeta5 integrin predominantly mediated adhesion of RASMCs to vitronectin and spreading on vitronectin via RGD-binding sequences. In contrast, the alphavbeta3 integrin did not contribute to the adhesion and spreading on fibronectin, vitronectin, gelatin or collagen I coated layers. PDGF-directed migration through gelatin coated membranes involved both alphavbeta3 and alphavbeta5 integrins. Selective blocking antibodies for alphavbeta3 and alphavbeta5 inhibited migration of RASMC and HCSMC by more than 60 % (p < 0.01). Integrin expression was studied in vivo in thoracic aorta of Sprague Dawley rats before and after balloon injury. In situ hybridization demonstrated low signals for alphav, beta3 and beta5 mRNA in uninjured aorta, which increased significantly at 14 days, localized predominantly in the neointima. Northern analysis of aorta after 14 days of injury also demonstrated an upregulation of alphav, beta3 and beta5 mRNA compared to uninjured aorta. Consistent with the increase in message levels, increased integrin protein expression was seen in the neointima after 7 and 14 days. This study provides evidence that alphavbeta3 and alphavbeta5 are elevated during neointima formation in the rat and indicates a novel role for alphavbeta5 participating in mechanisms regulating smooth muscle cell migration.

Animals↗

PubMed1999

Immunocytochemical localization of a cell adhesion molecule, integrin alpha5beta1, in nerve growth cones.

It is well-known that nerve growth cones, the growing tips of nerves, play a central role in determining the direction taken by regenerating peripheral nerves though neurotropism and contact guidance. In order to identify the molecules expressed on growth cones that are responsible for contact guidance, we investigated the possible involvement of integrins as sensors for the extracellular matrix. In cultured rat PC-12i cells and chick dorsal root ganglion cells, we found that integrin alpha5beta1 was concentrated in the filopodia and central regions of the growth cones. These integrin alpha5beta1-rich regions corresponded well with the sites where the growth cones came into contact with and adhered to the extracellular matrix. Integrin alpha5beta1 has been reported to bind with fibronectin in the extracellular matrix. When examined by triple staining and confocal laser scanning microscopy, we found that the distribution of integrin alpha5beta1 in the growth cones was very similar to that of actin filaments. Integrin alpha5beta1 was also expressed by Schwann cells. On immuno-electron microscopy, integrin alpha5beta1 was also identified in regenerating axons in vivo. These results suggest that integrin alpha5beta1 expressed on growth cones may function as a sensor for the extracellular matrix and Schwann cells, and thus mediate functionally important interactions in the development and regeneration of peripheral nerves.

Actin Cytoskeleton↗

PubMed2000

Manganese induces neurite outgrowth in PC12 cells via upregulation of alpha(v) integrins.

Previous studies have demonstrated that the divalent cation manganese (Mn) causes PC12 cells to form neurites in the absence of NGF. Since divalent cations modulate the binding affinity and specificity of integrins, and integrin function affects neurite outgrowth, we tested the hypothesis that Mn induces neurite outgrowth through an integrin-dependent signaling pathway. Our studies support this hypothesis. Function-blocking antisera specific for beta(1) integrins block the neurite-promoting activity of Mn by 90-95%. Bioassays and biochemical studies with antisera specific for the alpha(v), alpha(5), or alpha(8) integrin subunit suggest that the alpha(v)beta(1) heterodimer is one of the principal beta(1) integrins mediating the response of PC12 cells to Mn. This is corroborated by studies in which Mn failed to induce neurite outgrowth in a clone of PC12 cells that does not express alpha(v) at levels detectable by immunoprecipitation or immunocytochemistry. SDS-PAGE analysis of biotinylated surface proteins immunoprecipitated from Mn-responsive PC12 cells, as well as confocal laser microscopy of PC12 immunostained for surface alpha(v) indicate that Mn increases the surface expression of alpha(v) integrins. This increase appears to be due in part to synthesis of alpha(v) since specific inhibitors of RNA and protein synthesis block the neurite-promoting activity of Mn. These data indicate that Mn induces neurite outgrowth in PC12 cells by upregulating alpha(v) integrins, suggesting that Mn potentially represents an additional mechanism for regulating the rate and direction of neurite outgrowth during development and regeneration.

Animals↗