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PubMed1999

The beta1-integrin cytosolic domain optimizes phospholipase A2-mediated arachidonic acid release required for NIH-3T3 cell spreading.

Inhibition of PLA2 activity and rescue by addition of exogenous AA was used to demonstrate that AA production is essential for integrin-mediated NIH-3T3 murine cell spreading. Both AA release and cell spreading after attachment to a FN substrate were inhibited by the PLA2 inhibitor mepacrine. AA release was essential for signaling spreading since the inhibition of spreading induced by mepacrine was overcome by exogenous AA. Cells ectopically expressing full-length chicken beta1-integrins both released AA and spread fully on a substrate of anti-chicken beta1-integrin monoclonal antibody, and inhibition of PLA2 by mepacrine suppressed both spreading and AA release. Exogenous AA also reversed this mepacrine-induced inhibition of spreading. The role of the beta1-integrin cytosolic domain in AA release was examined by comparing responses of cells expressing full-length chicken beta1-integrins versus cells expressing a deletion mutant chicken beta1-integrin with a truncated cytosolic domain. Cells expressing a truncated chicken beta1-integrin released significantly less AA and failed to spread on the anti-chicken beta1-integrin antibody substrate. Furthermore, clustering full-length receptors with soluble antibody stimulated greater AA release than clustering of receptors having truncated cytosolic domains. These data suggest the beta1-integrin cytosolic domain is required for optimal PLA2 activation to produce AA necessary for cell spreading.

3T3 Cells↗
PubMed2003

AlphaV- and beta1-integrin subunits are commonly expressed in malignant effusions from ovarian carcinoma patients.

OBJECTIVE: The objective was to study expression of alphav- and beta1-integrin subunits in effusions, primary tumors, and solid metastases of ovarian carcinoma patients, as well as to evaluate its potential association with previously studied metastasis-associated molecules and clinicopathologic parameters. METHODS: Sections from 121 malignant effusions and 30 corresponding primary and metastatic lesions were evaluated for protein expression of the alphav- and beta1-integrin subunits using immunohistochemistry (IHC). A subset of effusions was additionally studied using immunoblotting (IB) and flow cytometry (FCM). mRNA in situ hybridization (ISH) was performed in 58 effusions and 30 biopsies. RESULTS: Protein expression of alphav- and beta1-integrin subunits was detected in carcinoma cells in 116/121 (96%) and 113/121 (93%) effusions, respectively. alphav protein expression was limited to carcinoma cells. IB and FCM confirmed IHC results. mRNA for alphav- and beta1-integrin subunits was detected in carcinoma cells in 37/58 (64%) and 33/58 (57%) effusions, respectively. Both protein and mRNA expression were higher in peritoneal effusions, significantly for alphav mRNA (P = 0.042) and beta1 protein (P = 0.023). beta1 protein expression in effusions was more frequently detected in better-differentiated tumors (P = 0.006). alphav-integrin subunit expression correlated with that of the previously studied matrix metalloproteinase-9 (MMP-9) (P = 0.006) and the MMP inducer EMMPRIN (P = 0.001). Expression of beta1-integrin subunit showed an association with that of EMMPRIN (P = 0.029), basic fibroblast growth factor (P < 0.001), and the MMP inhibitor TIMP-2 (P = 0.025). In carcinoma cells of solid lesions, alphav protein was uniformly present, while beta1 expression was limited to 15/30 (50%) specimens. As in effusions, protein expression of alphav subunit was cancer-specific, while beta1 protein was detected also in stromal fibroblasts and endothelial cells. CONCLUSIONS: The alphav- and beta1-integrin subunits are frequently expressed in ovarian carcinoma cells in effusions, and the alphav-integrin subunit is a powerful diagnostic marker for carcinoma cells. The reduced expression of the beta1-integrin subunit in solid lesions may be attributed to the role of other subunits at these stages, such as the beta3 subunit as part of the alphavbeta3-vitronectin receptor. The high expression of integrin subunits with a role of binding mesothelium, invasion, and angiogenesis in carcinoma cells in both peritoneal and pleural effusions suggests that cells at both sites have metastatic potential.

Adult↗
PubMed2004

Regulation of trophoblast beta1-integrin expression by contact with endothelial cells.

BACKGROUND: In human and non-human primates, migratory trophoblasts penetrate the uterine epithelium, invade uterine matrix, and enter the uterine vasculature. Invasive trophoblasts show increased expression of beta1 integrin. Since trophoblast migration within the uterine vasculature involves trophoblast attachment to endothelial cells lining the vessel walls, this raises the possibility that cell-cell contact and/or factors released by endothelial cells could regulate trophoblast integrin expression. To test this, we used an in vitro system consisting of early gestation macaque trophoblasts co-cultured on top of uterine microvascular endothelial cells. RESULTS: When cultured alone, trophoblasts expressed low levels of beta1 integrin as determined by quantitative immunofluorescence microscopy. When trophoblasts were cultured on top of endothelial cells for 24 h, the expression of trophoblast beta1 integrin was significantly increased as determined by image analysis. beta1 Integrin expression was not increased when trophoblasts were cultured with endothelial cell-conditioned medium, suggesting that upregulation requires direct contact between trophoblasts and endothelial cells. To identify endothelial cell surface molecules responsible for induction of trophoblast integrin expression, trophoblasts were cultured in dishes coated with recombinant platelet endothelial cell adhesion molecule-1 (PECAM-1), intercellular adhesion molecule-1 (ICAM-1), or alphaVbeta3 integrin. Trophoblast beta1 integrin expression (assessed by immunofluorescence microscopy and Western blotting) was increased when PECAM-1 or alphaVbeta3 integrin, but not ICAM-1, was used as substrate. CONCLUSIONS: Direct contact between trophoblasts and endothelial cells increases the expression of trophoblast beta1 integrin.

Journal Article↗
PubMedDate not supplied

Prognostic value of beta1-integrin (=CD29) in serous adenocarcinomas of the ovary.

BACKGROUND: Integrins are heterodimeric transmembranous proteins, comprised of two transmembrane subunits, called alpha and beta. They bind to various structures of the extra cellular matrix (ECM) and are responsible for cell-cell interactions. The aim of the current study was to evaluate the prognostic value of beta1-integrin in patients suffering from malignant serous surface epithelial-stromal tumors of the ovary. MATERIALS AND METHODS: With immunohistochemical methods we investigated 76 formalin-fixed, paraffin-embedded tissue samples. FIGO stages I, II, III and IV were present in 18, 10, 41 and 7 cases, respectively. RESULTS: 12 sections (15.8%) stained positive for beta1-integrin (=CD29), 64 sections (84.2%) showed no expression of beta1-integrin. The product limit method by Kaplan and Meier showed no statistical significance of beta1-integrin expression on overall survival, (p = 0.1005, log-rank test). Also the univariate Cox regression analysis showed no statistical significance of beta1-integrin expression on overall survival (p=0.1066), whereas in the multivariate analysis, adjusted for grading, FIGO stage and residual tumor, the expression of beta1-integrin turned out to be significantly correlated with reduced overall survival (p=0.0208). CONCLUSION: Our results using multivariate Cox regression analysis indicated a shorter overall survival for patients with positive staining for beta1-integrin in malignant serous surface epithelial-stromal tumors of the ovary. This pilot study warrants further investigation of the role of beta1-integrin in ovarian cancer.

Biomarkers, Tumor↗
PubMed1998

Merlin, the neurofibromatosis type 2 gene product, and beta1 integrin associate in isolated and differentiating Schwann cells.

Neurofibromatosis type 2, a disease characterized by the formation of multiple nervous system tumors, especially schwannomas, is caused by mutation in the gene-encoding merlin/schwannomin. The molecular mechanism by which merlin functions as a tumor suppressor is unknown, but is hypothesized to involve plasma membrane and cytoskeleton interaction. Several merlin antibodies were used to study merlin expression, localization, and protein association in primary cultures of rat sensory neurons, Schwann cells (SCs), and SCs grown with neurons (SC/N cultures) before and during differentiation into myelinating cells. Western blot analysis revealed that neurons predominantly expressed a 68-kD protein, but SCs expressed two additional 88- and 120-kD related proteins. Extensive immunological characterization demonstrated that the 88-kD protein shared three domains with the 68-kD merlin protein. Western blot analysis of soluble and insoluble culture fractions demonstrated that the majority of merlin and related proteins were soluble in isolated SCs and undifferentiated SC/N cultures, but became insoluble in myelinating SC/N cultures. Double immunofluorescence staining suggested that merlin translocated from the perinuclear cytoplasm in undifferentiated SCs to the subplasmalemma in differentiating SCs and partially colocalized with beta1 integrin. Finally, beta1 integrin antibody coimmunoprecipitated 68-kD merlin from isolated SC and undifferentiated SC/N cultures, but predominantly the 88-kD protein from differentiating SC/N cultures. Together, these results provide evidence that merlin interacts with beta1 integrin and that merlin localization changes from a cytosolic to cytoskeletal compartment during SC differentiation.

Animals↗
PubMed2005

CD26 regulates p38 mitogen-activated protein kinase-dependent phosphorylation of integrin beta1, adhesion to extracellular matrix, and tumorigenicity of T-anaplastic large cell lymphoma Karpas 299.

CD26 is an antigen with key role in T-cell biology and is expressed on selected subsets of aggressive T-cell malignancies. To elucidate the role of CD26 in tumor behavior, we examine the effect of CD26 depletion by small interfering RNA transfection of T-anaplastic large cell lymphoma Karpas 299. We show that the resultant CD26-depleted clones lose the ability to adhere to fibronectin and collagen I. Because anti-integrin beta1 blocking antibodies also prevent binding of Karpas 299 to fibronectin and collagen I, we then evaluate the CD26-integrin beta1 association. CD26 depletion does not decrease integrin beta1 expression but leads to dephosphorylation of both integrin beta1 and p38 mitogen-activated protein kinase (MAPK). Moreover, our data showing that the p38MAPK inhibitor SB203580 dephosphorylates integrin beta1 and that binding of the anti-CD26 antibody 202.36 dephosphorylates both p38MAPK and integrin beta1 on Karpas 299, leading to loss of cell adhesion to the extracellular matrix, indicate that CD26 mediates cell adhesion through p38MAPK-dependent phosphorylation of integrin beta1. Finally, in vivo experiments show that depletion of CD26 is associated with loss of tumorigenicity and greater survival. Our findings hence suggest that CD26 plays an important role in tumor development and may be a novel therapeutic target for selected neoplasms.

Animals↗
PubMed2006

Beta1 integrin mediates internalization of mammalian reovirus.

Reovirus infection is initiated by interactions between the attachment protein sigma1 and cell surface carbohydrate and junctional adhesion molecule A (JAM-A). Expression of a JAM-A mutant lacking a cytoplasmic tail in nonpermissive cells conferred full susceptibility to reovirus infection, suggesting that cell surface molecules other than JAM-A mediate viral internalization following attachment. The presence of integrin-binding sequences in reovirus outer capsid protein lambda2, which serves as the structural base for sigma1, suggests that integrins mediate reovirus endocytosis. A beta1 integrin-specific antibody, but not antibodies specific for other integrin subunits, inhibited reovirus infection of HeLa cells. Expression of a beta1 integrin cDNA, along with a cDNA encoding JAM-A, in nonpermissive chicken embryo fibroblasts conferred susceptibility to reovirus infection. Infectivity of reovirus was significantly reduced in beta1-deficient mouse embryonic stem cells in comparison to isogenic cells expressing beta1. However, reovirus bound equivalently to cells that differed in levels of beta1 expression, suggesting that beta1 integrins are involved in a postattachment entry step. Concordantly, uptake of reovirus virions into beta1-deficient cells was substantially diminished in comparison to viral uptake into beta1-expressing cells. These data provide evidence that beta1 integrin facilitates reovirus internalization and suggest that viral entry occurs by interactions of reovirus virions with independent attachment and entry receptors on the cell surface.

Amino Acid Sequence↗
PubMed2001

Beta1 integrin activation on human neutrophils promotes beta2 integrin-mediated adhesion to fibronectin.

Although the importance of beta1 integrin-mediated binding to adhesion molecules and extracellular matrix (ECM) molecules is well established for most types of leukocytes, the expression patterns and functional importance of beta1 integrins on neutrophils have remained controversial. Using flow cytometry, we found that human neutrophils express the alpha4, alpha5, alpha9 and beta1 integrin subunits. To examine whether the integrins VLA-4 (alpha4/beta1) and VLA-5 (alpha5/beta1) have a functional role on neutrophils, we studied adhesion to their ligand fibronectin. Treatment of neutrophils with antibody 8A2, which specifically binds and activates beta1 integrins, resulted in increased binding to fibronectin. However, addition of blocking mAb revealed that 8A2-induced adhesion did not depend on beta1 integrins, but on the beta2 integrin CD11b/CD18. Similarly, activation of beta1 integrins by 8A2 resulted in CD11b-dependent binding of neutrophils to fibrinogen. 8A2 treatment increased expression of an activation epitope of CD11b/CD18, which depended on phosphoinositide 3-OH kinase activity and an adequate concentration of intracellular free Ca2+. These data suggest that engagement of beta1 integrins on neutrophils results in a cross-talk signal that leads to activation of the beta2 integrin CD11b/CD18, followed by CD11b-mediated adhesion. As transmigrated neutrophils are surrounded by both beta1 and beta2 ligands in the ECM, this integrin cross-talk could play a role in modifying migration and cellular activation in inflamed tissues.

Androstadienes↗
PubMed2001

Beta1 integrins show specific association with CD98 protein in low density membranes.

BACKGROUND: The CD98 (4F2, FRP-1) is a widely expressed cell surface protein heterodimer composed of a glycosylated heavy chain and a non-glycosylated light chain. Originally described as a T cell activation antigen, it was later shown to function in amino acid transport, cell fusion and homotypic cell aggregation. Several lines of evidence suggest its functional interaction with integrins but the biochemical basis for this interaction has been unclear. RESULTS: We demonstrate that CD98 constitutively and specifically associates with beta1 integrins (alpha2beta1,alpha3beta1, alpha5beta1 and alpha6beta1), but minimally with alpha4beta1. Integrin-CD98 association was established by reciprocal immunoprecipitation experiments, and confirmed by CD98-induced clustering of alpha3beta1 but not alpha4beta1 on the surface of rhabdomyosarcoma cells. Integrin-CD98 association is independent of the alpha subunit cytoplasmic tail, is maintained in alpha3beta1 ligand-interaction deficient mutants, and is not inhibited by EDTA. Within the CD98 heavy chain, a C109S mutation (but not a C330S mutation) caused a loss of beta1 integrin association. The same C109S mutation also caused a loss of CD98 light chain association. Importantly, CD98 associated selectively with beta1 integrins present in low density "light membrane" fractions on a sucrose gradient. CD98 was not present in dense fractions that contained the majority of beta1 integrins. Notably, the C109S mutant of CD98, that did not associate with beta1 integrins, showed also a reduced localization into light membrane fractions. CONCLUSIONS: We demonstrate that CD98 association with beta1 integrins is specific, occurs in the context of low density membranes, and may require the CD98 light chain.

3T3 Cells↗
PubMed2004

Integrin beta1 mediates hepatocellular carcinoma cells chemotaxis to laminin.

BACKGROUND: Chemotaxis is an important step during the invasion of carcinoma cells. And integrins are most important receptors mediating interaction between cells and extracellular matrix (ECM). This study was designed to study integrin beta1 mediating chemotaxis of hepatocellular carcinoma (HCC) cells to laminin(LN). METHODS: A micropipette technique was adopted to investigate the effect of blockade of integrin beta1 on pseudopod protrusion of HCC cells in response to LN stimulation. Chemotactic pseudopod protrusion of a HCC cell was evaluated using a dual-pipette set-up, in which two pipettes filled with LN solution were positioned in close contact with the same cell, and pseudopod protrusion into each pipette was viewed dynamically and recorded with a tape recorder. The lengths of pseudopods were measured and plotted against time to obtain a pseudopod growth curve. The integrin beta1 subunit on the surfaces of HCC cells were analyzed by flow cytometry. RESULTS: In dual pipette chemotaxis experiment, when the two pipettes were filled with LN(50 microg/ml, 200 microg/ml), pseudopods extended from the HCC cell into each of the pipettes nearly symmetrically, ie, with nearly identical maximum pseudopod length and similar pseudopod growth curves. Upon addition of anti-CD29 (20 microg/ml) to one of the pipettes, pseudopod protrusion was blocked nearly completely while protrusion into the opposite pipette became more evidently, with a larger maximum length. Expression of integrin beta1 was up to 95.78% to cells chosen in the experiment. CONCLUSION: Integrin beta1 subunit was an important constituent receptor subunit for mediating chemotactic pseudopod protrusion of HCC cell to LN.

Carcinoma, Hepatocellular↗
PubMed2004

High expression of integrin beta1 and p53 is a greater poor prognostic factor than clinical stage in small-cell lung cancer.

The purpose of this study was to investigate the possible association between expression of integrin beta1 and p53 and survival in patients with small-cell lung cancer (SCLC). One hundred four patients with SCLC who had received an initial course of a full-dose of combination chemotherapy between February 1989 and July 1999 were entered in the study. Transbronchial biopsy specimens of tumors obtained before chemotherapy were subjected to immunostaining for integrin beta1 and p53. Twenty-eight and 58 patients could not be evaluated for integrin beta1 and p53 immunostaining, respectively, because the tissue samples had been crushed during the biopsy. Fifty-four patients had tumors with less than or equal to 25% integrin beta1-positive cells and 22 patients had tumors with more than 25% integrin beta1-positive cells, whereas 19 and 27 patients had tumors with less than or equal to 50% and more than 50% p53-positive cells, respectively. By comparison, the overall survival of patients with high expression of integrin beta1 and p53 were significantly worse than those of individuals whose tumors had low expression (log-rank test, p = 0.046 and p = 0.0067, respectively). Moreover, the overall survival of patients with high expression of either integrin beta1 or p53 (n = 42) was significantly worse than that of other patients without high expression of integrin beta1 and p53 (n = 38; log-rank test, p = 0.0003; Wilcoxon test, p = 0.0026). The association between survival and prognostic factors, including gender, age, performance status, clinical stage, and integrin beta1/p53 expression was examined by the Cox proportional hazards model; only integrin beta1/p53 expression was found to be a significant independent factor (hazard ratio = 0.394, p = 0.0005). In conclusion, the high expression of integrin beta1 and p53 in tumor cells is a greater poor prognostic factor than clinical stage in patients with SCLC.

Aged↗
PubMed1996

Perturbation of the developing Xenopus retinotectal projection following injections of antibodies against beta1 integrin receptors and N-cadherin.

We have examined the function of beta1 integrin receptors and N-cadherin in the development of the Xenopus retinotectal projection. In vivo perturbation experiments were performed by injecting antibodies directed against beta1 integrin receptors and N-cadherin into the embryonic optic pathway. The antibodies were present during the initial development of the retinal projection, when the axons of the ganglion cells are migrating through the optic tract and terminating within the optic tectum. When injected individually, the antibodies were insufficient to cause obvious pathfinding errors. However, when injected together, the antibodies caused specific abnormalities in the development of the retinotectal projection. Pathfinding errors most commonly observed included ectopically projecting axons within the optic tract region, meandering and splaying of axons in the optic tectum, and the induction of prominent ipsilateral projections. IgGs and Fab' fragments of the antibodies produced pathfinding errors; these defects were not observed in animals injected with control antibodies. These in vivo results show that beta1 integrin receptors and N-cadherin have important roles during the development of the visual projection and provide evidence that a balance between cell-cell and cell-matrix adhesion may be critical for the normal development of the vertebrate visual system.

Animals↗
PubMed2006

beta1-integrin-mediated signaling essentially contributes to cell survival after radiation-induced genotoxic injury.

Integrin-mediated adhesion to extracellular matrix proteins confers resistance to radiation- or drug-induced genotoxic injury. To analyse the underlying mechanisms specific for beta1-integrins, wild-type beta1A-integrin-expressing GD25beta1A cells were compared to GD25beta1B cells, which express signaling-incompetent beta1B variants. Cells grown on fibronectin, collagen-III, beta1-integrin-IgG or poly-l-lysine were exposed to 0-6 Gy X-rays in presence or depletion of growth factors and phosphatidylinositol-3 kinase (PI3K) inhibitors (LY294002, wortmannin). In order to test the relevance of these findings in tumor cells, human A-172 glioma cells were examined under the same conditions after siRNA-mediated silencing of beta1-integrins. We found that beta1A-integrin-mediated adhesion to fibronectin, collagen-III or beta1-IgG was essential for cell survival after radiation-induced genotoxic injury. Mediated by PI3K, pro-survival beta1A-integrin/Akt signaling was critically involved in this process. Additionally, the beta1-integrin downstream targets p130Cas and paxillin-impaired survival-regulating PI3K-dependent JNK. In A-172 glioma cells, beta1-integrin knockdown and PI3K inhibition confirmed the central role of beta1-integrins in Akt- and p130Cas/paxillin-mediated prosurvival signaling. These findings suggest beta1-integrins as critical regulators of cell survival after radiation-induced genotoxic injury. Elucidation of the molecular circuitry of prosurvival beta1-integrin-mediated signaling in tumor cells may promote the development of innovative molecular-targeted therapeutic antitumor strategies.

Animals↗
PubMed1997

Unmasking of intestinal epithelial lateral membrane beta1 integrin consequent to transepithelial neutrophil migration in vitro facilitates inv-mediated invasion by Yersinia pseudotuberculosis.

Idiopathic intestinal disease states characterized by active inflammation associated with transepithelial migration of neutrophils may, paradoxically, be associated with an increased risk of infection by enteric pathogens. Although the specific ligands with which various intestinal pathogens associate remain largely unknown, it is thought that many reside on the basolateral membrane. For example, beta1 integrin, a basolateral membrane protein, mediates the specific interaction between epithelial cells and the inv gene product (invasin) on the surface of Yersinia pseudotuberculosis. Our observations indicate that neutrophil migration across model T84 cell intestinal epithelia produced transient separation of epithelial cells at sites of neutrophil migration, resulting in microdiscontinuities that remained unsealed for several hours. We hypothesized that such sites of microdiscontinuities would yield a potential route for luminal pathogens to gain access to basolateral ligands and, thus, provide a window of risk for enteric infection. The surface biotinylation and fluorescence localization studies reported here revealed that, as in natural intestinal epithelia, beta1 integrin was strictly polarized to the basolateral membrane in confluent T84 monolayers. However, the transient microdiscontinuities resulting from neutrophil migration permitted access to beta1 integrin from the apical reservoir. Coincident with such basolateral exposure of beta1 integrin, monolayers became susceptible to invasion by Y. pseudotuberculosis. Fluorescence localization indicated that Y. pseudotuberculosis selectively associated with monolayers at sites where small discontinuities resulting from neutrophil transmigration were found. An increased risk for Y. pseudotuberculosis infection was specifically related to exposure of beta1 integrin (normally concealed by tight junctions) to the apical compartment, as Y. pseudotuberculosis cells lacking the inv gene were unable to invade following neutrophil transepithelial migration. Following closure of the microdiscontinuities associated with neutrophil migration, a small pool of beta1 integrin remained apically localized, presumably due to incomplete repolarization. However, this small apical pool of beta1 integrin was insufficient to support a detectable increased risk of Yersinia infection. Together, these observations indicate that by transiently perturbing monolayer continuity, neutrophil transepithelial migration is associated with a window of risk in which luminal pathogens can access basolateral ligands such as beta1 integrin.

Adhesins, Bacterial↗
PubMed2005

Junctional adhesion molecule 1 regulates epithelial cell morphology through effects on beta1 integrins and Rap1 activity.

Epithelial tight junctions form a selectively permeable barrier to ions and small molecules. Junctional adhesion molecule 1 (JAM1/JAM-A/F11R) is a tight junction-associated transmembrane protein that has been shown to participate in the regulation of epithelial barrier function. In a recent study, we presented evidence suggesting that JAM1 homodimer formation is critical for epithelial barrier function (Mandell, K. J., McCall, I. C., and Parkos, C. A. (2004) J. Biol. Chem. 279, 16254-16262). Here we have used small interfering RNA to investigate the effect of the loss of JAM1 expression on epithelial cell function. Consistent with our previous study, knockdown of JAM1 was observed to increase paracellular permeability in epithelial monolayers. Interestingly, knockdown of JAM1 also produced dramatic changes in cell morphology, and a similar effect was observed with expression of a JAM1 mutant lacking the putative homodimer interface. Further studies revealed that JAM1 knockdown decreased cell-matrix adhesion and spreading on matrix proteins that are ligands of beta1 integrins. These changes were characterized by a decrease in beta1 integrin protein levels and loss of beta1 integrin staining at the cell surface. Immunolabeling of cells for the small GTPase Rap1, a known activator of beta1 integrins, revealed colocalization of Rap1 with JAM1 at intercellular junctions, and knockdown of JAM1 resulted in decreased Rap1 activity. Lastly, knockdown of Rap1b resulted in diminished beta1 integrin expression and altered cell morphology analogous to that observed with knockdown of JAM1. Together, these results suggest that JAM1 regulates epithelial cell morphology and beta1 integrin expression by modulating activity of the small GTPase Rap1.

Cell Adhesion↗
PubMed2003

Beta1-integrins co-localize with Na, K-ATPase, epithelial sodium channels (ENaC) and voltage activated calcium channels (VACC) in mechanoreceptor complexes of mouse limb-bud chondrocytes.

Interactions between chondrocytes and their extracellular matrix are partly mediated by beta1-integrin receptors. Recent studies have shown that beta1-integrins co-localize with a variety of cytoskeletal complexes, signaling proteins and growth factor receptors. Since mechanosensitive ion channels and integrins have been proposed to participate in skeletal mechanotransduction, in this study, we investigated the possible co-localization of beta1-integrins with two ion channels and a P-type ATPase in mouse limb-bud chondrocytes. The alpha subunits of Na, K-ATPase, the epithelial sodium channel (ENaC) and the voltage activated calcium channel (VACC) were immunostained in organoid cultures derived from limb-buds of 12-day-old mice using well-characterized antibodies. Indirect immunofluorescence revealed abundant expression of beta1-integrins and each of the selected systems in limb-bud chondrocytes. Two-fluorochrome immunostaining demonstrated that beta1-integrin, Na, K-ATPase, ENaC and VACC co-localize in chondrocytes. Co-imunoprecipitation experiments revealed co-localization and association of integrins with ENaC, VACC and Na, K-ATPase. Cellular responses and signaling cascades initiated by the influx of calcium or sodium through putative mechanosensitive channels may be regulated more effectively if such channels were organized around integrins with receptors, kinases and cytoskeletal complexes clustered about them. The close proximity of ATPase ion pumps such as Na, K-ATPase to chondrocyte mechanoreceptor complexes could facilitate rapid homeostatic responses to the ionic perturbations brought about by activation of mechanically gated cation channels and efficiently regulate the intracellular milieu of chondrocytes.

Amino Acid Sequence↗
PubMed2002

Perturbation of beta1-integrin function in involuting mammary gland results in premature dedifferentiation of secretory epithelial cells.

To study the mechanism of beta1-integrin function in vivo, we have generated transgenic mouse expressing a dominant negative mutant of beta1-integrin under the control of mouse mammary tumor virus (MMTV) promoter (MMTV-beta1-cyto). Mammary glands from MMTV-beta1-cyto transgenic females present significant growth defects during pregnancy and lactation and impaired differentiation of secretory epithelial cells at the onset of lactation. We report herein that perturbation of beta1-integrin function in involuting mammary gland induced precocious dedifferentiation of the secretory epithelium, as shown by the premature decrease in beta-casein and whey acidic protein mRNA levels, accompanied by inactivation of STAT5, a transcription factor essential for mammary gland development and up-regulation of nuclear factor-kappaB, a negative regulator of STAT5 signaling. This is the first study demonstrating in vivo that cell-extracellular matrix interactions involving beta1-integrins play an important role in the control of milk gene transcription and in the maintenance of the mammary epithelial cell differentiated state.

Animals↗
PubMed2003

Insulin-like growth factor-1 induces adhesion and migration in human multiple myeloma cells via activation of beta1-integrin and phosphatidylinositol 3'-kinase/AKT signaling.

Insulin-like growth factor-1 (IGF-I) is a growth and survival factor in human multiple myeloma (MM) cells. Here we examine the effect of IGF-I on MM cell adhesion and migration, and define the role of beta1 integrin in these processes. IGF-I increases adhesion of MM.1S and OPM6 MM cells to fibronectin (FN) in a time- and dose-dependent manner, as a consequence of IGF-IR activation. Conversely, blocking anti-beta1 integrin monoclonal antibody, RGD peptide, and cytochalasin D inhibit IGF-I-induced cell adhesion to FN. IGF-I rapidly and transiently induces association of IGF-IR and beta1 integrin, with phosphorylation of IGF-IR, IRS-1, and p85(PI3-K). IGF-I also triggers phosphorylation of AKT and ERK significantly. Both IGF-IR and beta1 integrin colocalize to lipid rafts on the plasma membrane after IGF-I stimulation. In addition, IGF-I triggers polymerization of F-actin, induces phosphorylation of p125(FAK) and paxillin, and enhances beta1 integrin interaction with these focal adhesion proteins. Importantly, using pharmacological inhibitors of phosphatidylinositol 3'-kinase (PI3-K) (LY294002 and wortmannin) and extracellular signal-regulated kinase (PD98059), we demonstrate that IGF-I-induced MM cell adhesion to FN is achieved only when PI3-K/AKT is activated. IGF-I induces a 1.7-2.2 (MM.1S) and 2-2.5-fold (OPM6) increase in migration, whereas blocking anti-IGF-I and anti-beta1 integrin monoclonal antibodies, PI3-K inhibitors, as well as cytochalasin D abrogate IGF-I-induced MM cell transmigration. Finally, IGF-I induces adhesion of CD138+ patient MM cells. Therefore, these studies suggest a role for IGF-I in trafficking and localization of MM cells in the bone marrow microenvironment. Moreover, they define the functional association of IGF-IR and beta1 integrin in mediating MM cell homing, providing the preclinical rationale for novel treatment strategies targeting IGF-I/IGF-IR in MM.

Antibodies, Monoclonal↗