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PubMed1997

Integrins mediate adhesion to agrin and modulate agrin signaling.

Agrin, a basal lamina-associated proteoglycan, is a crucial nerve-derived organizer of postsynaptic differentiation at the skeletal neuromuscular junction. Because integrins serve as cellular receptors for many basal lamina components, we asked whether agrin interacts with integrins. Agrin-induced aggregation of acetylcholine receptors on cultured myotubes was completely blocked by antibodies to the beta1 integrin subunit and partially blocked by antibodies to the alpha(v) integrin subunit. Agrin-induced clustering was also inhibited by antisense oligonucleotides to alpha(v) and a peptide that blocks the alpha(v) binding site. Non-muscle cells that expressed alpha(v) and beta1 integrin subunits adhered to immobilized agrin, and this adhesion was blocked by anti-alpha(v) and anti-beta1 antibodies. Integrin alpha(v)-negative cells that did not adhere to agrin were rendered adherent by introduction of alpha(v). Together, these results implicate integrins, including alpha(v)beta1, as components or modulators of agrin's signal transduction pathway.

Agrin↗
PubMed2000

Characterization of Porphyromonas gingivalis-induced degradation of epithelial cell junctional complexes.

Porphyromonas gingivalis is considered among the etiological agents of human adult periodontitis. Although in vitro studies have shown that P. gingivalis has the ability to invade epithelial cell lines, its effect on the epithelial barrier junctions is not known. Immunofluorescence analysis of human gingival epithelial cells confirmed the presence of tight-junction (occludin), adherens junction (E-cadherin), and cell-extracellular matrix junction (beta1-integrin) transmembrane proteins. These transmembrane proteins are expressed in Madin-Darby canine kidney (MDCK) cells. In addition, MDCK cells polarize and therefore serve as a useful in vitro model for studies on the epithelial cell barrier. Using the MDCK cell system, we examined the effect of P. gingivalis on epithelial barrier function. Exposure of the basolateral surfaces of MDCK cells to P. gingivalis (>10(9) bacteria/ml) resulted in a decrease in transepithelial resistance. Immunofluorescence microscopy demonstrated decreases in the amounts of immunoreactive occludin, E-cadherin, and beta1-integrin at specific times which were related to a disruption of cell-cell junctions in MDCK cells exposed to basolateral P. gingivalis. Disruption of cell-cell junctions was also observed upon apical exposure to bacteria; however, the effects took longer than those seen upon basolateral exposure. Cell viability was not affected by either basolateral or apical exposure to P. gingivalis. Western blot analysis demonstrated hydrolysis of occludin, E-cadherin, and beta1-integrin in lysates derived from MDCK cells exposed to P. gingivalis. Immunoprecipitated occludin and E-cadherin molecules from MDCK cell lysates were also degraded by P. gingivalis, suggesting a bacterial protease(s) capable of cleaving these epithelial junction transmembrane proteins. Collectively, these data suggest that P. gingivalis is able to invade the deeper structures of connective tissues via a paracellular pathway by degrading epithelial cell-cell junction complexes, thus allowing the spread of the bacterium. These results also indicate the importance of a critical threshold concentration of P. gingivalis to initiate epithelial barrier destruction.

Animals↗
PubMed2004

Cynaropicrin, a sesquiterpene lactone, as a new strong regulator of CD29 and CD98 functions.

Cynaropicrin is a sesquiterpene lactone displaying immunomodulatory effects on the production of cytokine and nitric oxide from macrophages/monocytes. In this study we have examined inhibitory effect of cynaropicrin on activation of major adhesion molecules [CD29 (beta1 integrins), CD43, and CD98] on the cells assessed by U937 (promonocytic cells) homotypic aggregation. Cynaropicrin potently blocked CD29 (beta1 integrins)- and CD98-induced homotypic aggregation with IC(50) values of 3.46 and 2.98 microM, respectively, without displaying cytotoxicity. Similarly, flow cytometric analysis exhibited that cynaropicrin down-regulated strikingly surface level of CD29 and CD147, a functional regulator of CD98, but not CD43. More importantly, cynaropicrin inhibition was linked to blockade of extracellular signal-related kinase (ERK) activation and distinct from other enzyme inhibitors including rottlerin, propranolol, forskolin, and chloroquine, but not cytochalasin B. Therefore, our finding is the first demonstration that cynaropicrin may be a potent functional regulator of CD29 and CD98 via interrupting ERK activation which may be linked to cytoskeleton rearrangement, suggesting further application to CD29- and CD98-mediated diseases such as virus-induced chronic inflammation, and invasion, migration, and metastasis of leukocyte cancer cells.

Antigens, CD↗
PubMed1997

Rapamycin (sirolimus) inhibits proliferating cell nuclear antigen expression and blocks cell cycle in the G1 phase in human keratinocyte stem cells.

Because the immunosuppressant rapamycin (sirolimus) blocks T cell proliferation in G1 phase, it has been proposed as a potential treatment for psoriasis, a skin disease characterized by T cell activation and keratinocyte stem cell hyperproliferation. To determine another potentially important mechanism through which rapamycin can act as an antipsoriatic agent, we tested its direct effect on keratinocyte stem cell proliferation in vitro as well as in vivo. In vivo cell cycle quiescent (G0 phase) stem cell keratinocytes in primary culture sequentially express de novo cyclin D1 and proliferating cell nuclear antigen (PCNA), prior to S phase entry, and upregulate beta1 integrin. Rapamycin inhibited the growth of keratinocytes that were leaving quiescence as well as those already in cell cycle without affecting cell viability. Although beta1 integrin(bright) expression was not affected, the number of beta1 integrin(bright) cells entering S/G2/M was significantly lowered by rapamycin. Cells treated with rapamycin exhibited decreased PCNA expression while cyclin D1 expression, which precedes PCNA expression in the cell cycle, was not affected. We found similar effects on stem cell keratinocytes in patients with psoriasis treated systemically with rapamycin. Because PCNA is required for cell cycle progression from G1 to S phase, our data indicate that inhibition of PCNA protein synthesis may be an important regulatory element in the ability of rapamycin to exert a G1 block.

Cells, Cultured↗
PubMed2005

Sertoli-germ cell anchoring junction dynamics in the testis are regulated by an interplay of lipid and protein kinases.

When Sertoli and germ cells were co-cultured in vitro in serum-free chemically defined medium, functional anchoring junctions such as cell-cell intermediate filament-based desmosome-like junctions and cell-cell actin-based adherens junctions (e.g. ectoplasmic specialization (ES)) were formed within 1-2 days. This event was marked by the induction of several protein kinases such as phosphatidylinositol 3-kinase (PI3K), phosphorylated protein kinase B (PKB; also known as Akt), p21-activated kinase-2 (PAK-2), and their downstream effector (ERK) as well as an increase in PKB intrinsic activity. PI3K, phospho (p)-PKB, and PAK were co-localized to the site of apical ES in the seminiferous epithelium of the rat testis in immunohistochemistry studies. Furthermore, PI3K also co-localized with p-PKB to the same site in the epithelium as determined by fluorescence microscopy, consistent with their localization at the ES. These kinases were shown to associate with ES-associated proteins such as beta1-integrin, phosphorylated focal adhesion kinase, and c-Src by co-immunoprecipitation, suggesting that the integrin.laminin protein complex at the apical ES likely utilizes these protein kinases as regulatory proteins to modulate Sertoli-germ cell adherens junction dynamics via the ERK signaling pathway. To validate this hypothesis further, an in vivo model using AF-2364 (1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide) to perturb Sertoli-germ cell anchoring junction function, inducing germ cell loss from the epithelium in adult rats, was used in conjunction with specific inhibitors. Interestingly, the event of germ cell loss induced by AF-2364 in vivo was also associated with induction of PI3K, p-PKB, PAK-2, and p-ERK as well as a surge in intrinsic PKB activity. Perhaps the most important of all, pretreatment of rats with wortmannin (a PI3K inhibitor) or anti-beta1-integrin antibody via intratesticular injection indeed delayed AF-2364-induced spermatid loss from the epithelium. In summary, these results illustrate that Sertoli-germ cell anchoring junction dynamics in the testis are regulated, at least in part, via the beta1-integrin/PI3K/PKB/ERK signaling pathway.

Androstadienes↗
PubMed2006

Effect of antisense hypoxia-inducible factor 1alpha on progression, metastasis, and chemosensitivity of pancreatic cancer.

OBJECTIVES: The aim of the study was to observe the effect of antisense hypoxia-inducible factor 1alpha (HIF-1alpha) on progression, metastasis, and chemosensitivity of pancreatic cancer. METHODS: BxPc-3 cells transfected with antisense HIF-1alpha plasmid were exposed to 0.5% O2 for 4 hours. Expressions of HIF-1alpha, survivin, and beta1 integrin were detected by reverse transcriptase -polymerase chain reaction and Western blotting. Growth inhibition rates and apoptosis rates of BxPc-3 cells under different dosages of chemotherapy agents (5-fluorouracil, doxorubicin, and gemcitabine) were measured by MTT colorimetric assay and flow cytometry. The migration of BxPc-3 cells was assayed using transwell cell culture chambers. Subcutaneous transplantation of BxPc-3 cells in nude mice for 8 weeks was to assess progression and metastasis of pancreatic cancer. RESULTS: Expression of HIF-1alpha was obviously down-regulated, and at the same time, survivin and beta1-integrin expressions were markedly down-regulated in the experimental group (P < 0.05). Higher dosages (100, 200, and 400 mg/L of 5-fluorouracil; 0.05, 0.075, and 0.1 mg/L of doxorubicin; and 10(-9), 10(-8), and 10(-7) mol/L of gemcitabine) caused a greater increase of inhibition in the experimental group than in control (P < 0.05). The number of migrated BxPc-3 cells in the experimental group was far less than in control (P < 0.05). In vivo, the tumor size and weight in the experimental group were significantly lower than those in control (P < 0.05). CONCLUSION: Our data demonstrate that antisense HIF-1alpha inhibits expressions of survivin and beta1 integrin, enhancing apoptosis in human pancreatic cancer cells and restraining the progression and metastasis of pancreatic cancer. Therefore, HIF-1alpha may play a very important role in progression, metastasis, and chemosensitivity of human pancreatic cancer. Blocking HIF-1alpha in pancreatic cancer cells may offer an avenue for gene therapy.

Animals↗
PubMed2006

Urokinase receptors are required for alpha 5 beta 1 integrin-mediated signaling in tumor cells.

Up-regulation of urokinase receptors is common during tumor progression and thought to promote invasion and metastasis. Urokinase receptors bind urokinase and a set of beta1 integrins, but it remains unclear to what degree urokinase receptor/integrin binding is important to beta1 integrin signaling. Using site-directed mutagenesis, single amino acid mutants of the urokinase receptor were identified that fail to associate with either alpha3beta1 (D262A) or alpha5beta1 (H249A) but associate normally with urokinase. To study the effects of these mutations on beta1 integrin function, endogenous urokinase receptors were first stably silenced in tumor cell lines HT1080 and H1299, and then wild type or mutant receptors were expressed. Knockdown of urokinase receptors resulted in markedly reduced fibronectin and alpha5beta1-dependent ERK activation and metalloproteinase MMP-9 expression. Re-expression of wild type or D262A mutant receptors but not the alpha5beta1 binding-deficient H249A mutant reconstituted fibronectin responses. Because urokinase receptor.alpha5beta1 complexes bind in the fibronectin heparin-binding domain (Type III 12-14) whereas alpha5beta1 primarily binds in the RGD-containing domain (Type III 7-10), signaling pathways leading to ERK and MMP-9 responses were dissected. Binding to III 7-10 led to Src/focal adhesion kinase activation, whereas binding to III 7-14 caused Rac 1 activation. Tumor cells engaging fibronectin required both Type III 7-10- and 12-14-initiated signals to activate ERK and up-regulate MMP-9. Thus urokinase receptor binding to alpha5beta1 is required for maximal responses to fibronectin and tumor cell invasion, and this operates through an enhanced Src/Rac/ERK signaling pathway.

Cell Line, Tumor↗
PubMed2001

Integrin signaling inhibits paclitaxel-induced apoptosis in breast cancer cells.

Inherent or acquired drug resistance is one of the major problems in chemotherapy. The mechanisms by which cancer cells survive and escape the cytotoxic effects of chemotherapeutic agents are essentially unknown. In the present study, we demonstrate that in the MDA-MB-231 and MDA-MB-435 breast cancer cells, ligation of beta1 integrins by their extracellular matrix ligands inhibits significantly apoptosis induced by paclitaxel and vincristine, two microtubule-directed chemotherapeutic agents that are widely used in the therapy of breast cancer. We show that beta1 integrin signaling inhibits drug-induced apoptosis by inhibiting the release of cytochrome c from the mitochondria in response to drug treatment. Further, integrin-mediated protection from drug-induced apoptosis and inhibition of cytochrome c release are dependent on the activation of the PI 3-kinase/Akt pathway. Our results identify beta1 integrin signaling as an important survival pathway in drug-induced apoptosis in breast cancer cells and suggest that activation of this pathway may contribute to the generation of drug resistance.

Antineoplastic Agents, Phytogenic↗
PubMed2001

NG2/HMPG modulation of human articular chondrocyte adhesion to type VI collagen is lost in osteoarthritis.

NG2/human melanoma proteoglycan (HMPG) is a chondroitin sulphate proteoglycan (CSPG), expressed by chondrocytes in fetal and in normal and osteoarthritic (OA) adult articular cartilage. NG2/HMPG is a receptor for extracellular matrix proteins, including type VI collagen, and regulates beta1 integrin binding to fibronectin. This study was undertaken to identify whether NG2/HMPG had similar activities in human articular chondrocytes (HACs). Normal and OA adult HAC adhesion to fibronectin, type II or type VI collagen was assessed using a methylene blue assay. The requirement for integrins, NG2/HMPG, and integrin-associated signalling molecules was investigated using anti-beta1 integrin and anti-HMPG antibodies and pharmacological inhibitors of signalling molecules. The adhesion of normal and OA HACs to fibronectin, type II and type VI collagen was beta1 integrin-dependent. Normal HAC adhesion to type VI collagen was stimulated by anti-HMPG antibodies. This effect was inhibited by pertussis toxin. Anti-HMPG antibodies had no effect on OA chondrocyte adhesion to type VI collagen, or on normal and OA cell adhesion to fibronectin and type II collagen. The results show that NG2/HMPG modulates integrin-mediated interactions of normal HACs with type VI collagen. Loss of this activity may be of importance in the progression of osteoarthritis.

Antigens↗
PubMed1999

1,25-Dihydroxyvitamin D3 suppresses the expression of the VCAM-1 receptor, VLA-4 in human leukemic HL-60 cells.

Very late antigen-4 (VLA-4) is the complex with alpha4 and beta1 integrins, which is the receptors to fibronectin and VCAM-1. We evaluate the effect of 1,25(OH)2D3 on the expression of VLA-4 in human leukemic HL-60, U937 cells and human melanoma A375 cells. Flow cytometric analysis demonstrate that the expression of alpha4 integrin is negatively regulated in the cell lines we studied. The expression of beta1 integrin is also decreased in HL-60 and U937 cells. The mRNA expression of alpha4 integrin is significantly decreased by the treatment with 1,25(OH)2D3, whereas 1,25(OH)2D3 does not alter the expression of beta1 mRNA. The adhesion assay demonstrate that the number of adherent cells treated with 1, 25(OH)2D3 is significantly lower than that untreated on VCAM-1-coated wells. Because VCAM-1 is highly expressed in the endothelial cells, it is possible that 1,25(OH)2D3 prevents the attachment of the cells from the endothelial cells in vivo.

Antigens, CD↗
PubMed1998

Evidence for a role of collagen synthesis in arterial smooth muscle cell migration.

Migration of smooth muscle cells (SMCs) and collagen synthesis by SMCs are central to the pathophysiology of vascular disease. Both processes can be induced shortly after vascular injury; however, a functional relationship between them has not been established. In this study, we determined if collagen synthesis was required for SMC migration, using ethyl-3,4-dihydroxybenzoate (EDHB), an inhibitor of prolyl-4-hydroxylase, and 3,4-DL-dehydroproline (DHP), a proline analogue, which we demonstrate inhibit collagen elaboration by porcine arterial SMCs. SMCs exposed to EDHB or DHP attached normally to collagen- and vitronectin-coated substrates; however, spreading on collagen but not vitronectin was inhibited. SMC migration speed, quantified by digital time-lapse video microscopy, was significantly and reversibly reduced by EDHB and DHP. Flow cytometry revealed that expression of beta1 integrins, through which SMCs interact with collagen, was unaffected by EDHB or DHP. However, both inhibitors prevented normal clustering of beta1 integrins on the surface of SMCs, consistent with a lack of appropriate matrix ligands for integrin engagement. Moreover, there was impaired recruitment of vinculin into focal adhesion complexes of spreading SMCs and disassembly of the smooth muscle alpha-actin-containing cytoskeleton. These findings suggest that de novo collagen synthesis plays a role in SMC migration and implicates a mechanism whereby newly synthesized collagen may be necessary to maintain the transcellular traction system required for effective locomotion.

Actins↗
PubMed1999

Endothelial cells undergoing apoptosis become proadhesive for nonactivated platelets.

Under normal conditions, platelets do not adhere to endothelium. However, when platelets or endothelial cells are stimulated by thrombin or cytokines, respectively, platelets bind avidly to endothelium. Because there is accumulating evidence that endothelial cells may become apoptotic under certain proinflammatory or prothrombotic conditions, we investigated whether endothelial cells undergoing apoptosis may become proadhesive for nonactivated platelets. Human umbilical vein endothelial cells (HUVEC) were induced to undergo apoptosis by staurosporine, a nonspecific protein kinase inhibitor, or by culture in suspension with serum-deprivation. After treatment of HUVEC or platelets with different receptor antagonists, nonactivated, washed human platelets were allowed to adhere to HUVEC for 20 minutes. To exclude matrix involvement, platelet binding was measured in suspension by using flow cytometry. Independent of the method of apoptosis induction, there was a marked increase in platelet binding to apoptotic HUVEC. Although HUVEC exhibited maximal adhesiveness for platelets after 2 to 4 hours, complete DNA fragmentation of HUVEC occurred only several hours later. Adhesion assays after blockade of different platelet receptors showed only involvement of beta1-integrins. Platelet binding to apoptotic HUVEC was inhibited by more than 70% when platelets were treated with blocking anti-beta1 antibodies. Treatment of apoptotic HUVEC with blocking antibodies to different potential platelet receptors, including known ligands for beta1-integrins, did not affect platelet binding. As assessed by determination of beta-thromboglobulin and platelet factor 4 in the supernatants, platelets bound to apoptotic HUVEC became slightly activated. However, significant expression of platelet P-selectin (CD62P) was not found. These data provide further evidence that endothelial cells undergoing apoptosis may contribute to thrombotic events.

Apoptosis↗
PubMed2003

Important role for fibronectin-EIIIA during renal tubular repair and cellular recovery in uranyl acetate-induced acute renal failure of rats.

The present study was designed to identify the source and kinetics of an alternatively spliced "embryonic" cellular fibronectin EIIIA (cFn-EIIIA) in relation to regenerating renal tubules in uranyl acetate (UA)-induced acute renal failure (ARF) in rats. Damage of the proximal tubules was found as early as day 2 after induction of ARF, peaked at day 5, and was almost substituted by epithelial relining by day 7. Immunohistochemistry showed de novo deposition of cFn-EIIIA in peritubular regions as early as day 2, then on the tubular basement membrane (TBM) after day 4. beta1 Integrin, the receptor for Fn, was mainly found at the basal side of tubules in the normal control and increased in the interstitium after induction of ARF, but the staining pattern gradually returned to the control after day 7. Immunoelectron microscopy revealed that cFn-EIIIA was produced initially by the peritubular endothelium and later by fibroblastic cells and was deposited to the TBM, on which regenerating tubules proliferated, probably with cFn-EIIIA production. beta1 Integrin was expressed in cFn-EIIIA-producing cells, especially in regenerating tubular cells, suggesting that cFn-EIIIA signal transduction affects regenerating tubules. Transforming growth factor (TGF)-beta1 was found in some damaged proximal tubules and interstitial cells after induction of ARF and later in the regenerating tubules. CFn-EIIIA and beta1 integrin mRNA levels were upregulated as early as day 2. TGF-beta1 mRNA level significantly increased after day 3, suggesting a modulatory role for TGF-beta1 on cFn-EIIIA production, but not by day 2. Our data suggest that cFn-EIIIA production by the endothelium during the very early response to tubular injury and by fibroblastic cells and regenerating tubules may play an important role in the cellular recovery of UA-induced ARF in rats.

Acute Disease↗
PubMed1999

Differential responsiveness to autocrine and exogenous transforming growth factor (TGF) beta1 in cells with nonfunctional TGF-beta receptor type III.

The two major intestinal epithelial cell lineages are columnar fluid-absorbing cells and mucin-producing goblet cells. High levels of transforming growth factor (TGF) beta1 are found surrounding postmitotic cells in the colonic crypt, suggesting that TGF-beta1 mediates the maturation and growth inhibition of both epithelial cell types. However, we now show that the injection of recombinant TGF-beta1 into mice leads to an enrichment of goblet cells, indicating that these normal epithelial cells are resistant to TGF-beta1. In support of this interpretation, each of two independently isolated cell lines modeling normal colon goblet cells was also growth resistant to exogenous TGF-beta1 but made levels of TGF-beta receptor (TbetaR) I, TbetaRII, and TbetaIII mRNA and protein equal to those made by two TGF-beta1-sensitive cell lines. No mutations were found in the alk5 or alk2 forms of TbetaRI or in TbetaRII; these receptors were found on the cell surface, although they could not bind 125I-labeled TGF-beta1. TbetaRIII binds TGF-beta1, concentrates it, and presents it to TbetaRII. The major TbetaRIII form, betaglycan, did not undergo normal posttranslational modification in either of the goblet cell lines and could not bind 125I-labeled TGF-beta1; thus, it was nonfunctional. TGF-beta resistance was overcome by raising TGF-beta1 levels 100-fold, at which point TbetaRII could bind TGF-beta1. Signaling initiated by these higher TGF-beta1 levels was blocked by the expression of dominant negative TbetaRII, demonstrating that TbetaRII and TbetaRI were functional. Cells resistant to exogenous TGF-beta1 maintained functional cell surface TbetaRI and TbetaRII to mediate responses to autocrine TGF-beta1, which controlled the maturation of the adhesion protein integrin beta1. Expression of dominant negative TbetaRII in goblet cells greatly inhibited the conversion of the beta1 integrin from its precursor to its mature form. Thus, in normal intestinal epithelial goblet cells, TbetaRI and TbetaRII can respond to autocrine but not exogenous TGF-beta without the participation of TbetaRIII. Absorptive epithelial cells are growth inhibited by TGF-beta1 both in vivo and in vitro; therefore, the loss of functional TbetaRIIIs on goblet cells allows differential regulation of the two major intestinal epithelial cell types.

Activin Receptors, Type I↗
PubMed1998

Antagonistic regulation of cell migration by epidermal growth factor and glucocorticoid in human gastric carcinoma cells.

Epidermal growth factor (EGF) induced the disruption and scattering of colonies of TMK-1, a cell line derived from a human gastric carcinoma. A stimulatory action of EGF on cell migration was also observed as determined by a wound assay. However, these actions of EGF were inhibited if the cells were pretreated with dexamethasone, a synthetic glucocorticoid. Dexamethasone increased cell adhesion to collagen type IV and laminin, but not to poly-L-lysine and fibronectin. In contrast, EGF did not affect cell adhesion to these extracellular matrices whether dexamethasone was present or not. Dexamethasone enhanced the protein levels of both alpha1 and beta1 integrin subunits, and that of the alpha1 beta1 heterodimer. Further, flow cytometric analysis revealed that dexamethasone increased the expression of beta1 and alpha1 integrin subunits at the cell surface, whereas EGF increased expression of beta1 and alpha2 subunits at the cell surface. Antibodies against alpha1 and beta1 integrin subunits inhibited the increased cell adhesion seen in the presence of dexamethasone. An immunofluorescence study indicated that dexamethasone increased the formation of focal adhesions along the entire edges of cell colonies. In contrast, EGF led to the formation of focal adhesions preferentially at the cell front, and this EGF-induced preferential formation was not observed if the cells were pretreated with dexamethasone. These results suggest that glucocorticoid increased cell adhesion to the extracellular matrix via alpha1 beta1 integrin, and thereby antagonized EGF-induced cell migration.

Cadherins↗
PubMed2004

Recombinant Escherichia coli as a gene delivery vector into airway epithelial cells.

To transfer genes into airway epithelial cells, we have generated auxotrophic dap Escherichia coli BM2710 mutant that expresses the invasin of Yersinia pseudotuberculosis and the listeriolysin of Listeria monocytogenes. E. coli BM2710 harboring a plasmid carrying the gfp gene was incubated with immortalized normal or cystic fibrosis (CF) airway epithelial cells or with primary bronchial epithelial cells grown as an explant-outgrowth cell culture model. Approximately 2% of immortalized cells expressed GFP. Few primary cells were transfected that were always poorly differentiated and located at the edge of the outgrowth. This was consistent with the expression of beta1-integrins only on these cells and with the required interaction for cell entry of E. coli expressing the invasin with beta1-integrins. The subsequent intracellular trafficking of E. coli BM2710 studied by confocal and electronic microscopy showed that the E. coli-containing phagosomes rapidly matured into phagolysosomes. This is the first demonstration that recombinant bacteria are able to transfer genes into primary airway epithelial cells, provided that they are able to invade the cells.

Adhesins, Bacterial↗
PubMed2000

Fibronectin-bound TNF-alpha stimulates monocyte matrix metalloproteinase-9 expression and regulates chemotaxis.

Tumor necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine implicated in the stimulation of matrix metalloproteinase (MMP) production by several cell types. Our previous studies demonstrated that TNF-alpha avidly binds fibronectin (FN) and laminin, major adhesive glycoproteins of extracellular matrix (ECM) and basement membranes. These findings suggested that TNF-alpha complexing to insoluble ECM components may serve to concentrate its activities to distinct inflamed sites. Herein, we explored the bioactivity and possible function of ECM-bound TNF-alpha by examining its effects on MMP-9 secretion by monocytes. Immunofluorescent staining indicated that LPS-activated monocytes deposited newly synthesized TNF-alpha into ECM-FN. FN-bound TNF-alpha (FN/TNF-alpha) significantly up-regulated MMP-9 expression and secretion by the human monocytic cell line MonoMac-6 and peripheral blood monocytes. Such secretion could be inhibited by antibodies that block TNF-alpha activity and binding to its receptors TNF RI (p55) and TNF RII (p75). Cheniotaxis through ECM gels in the presence of soluble or bound TNF-alpha was inhibited by a hydroxamic acid inhibitor of MMPs (GM6001). It is interesting that, although the adhesion of MonoMac-6 cells to FN/TNF-alpha required functional activated beta1 integrins, FN/TNF-alpha-induced MMP-9 secretion was independent of binding to beta1 integrins, since MMP-9 secretion was unaffected by: (1) neutralizing nAb to alpha4, alpha5, and beta1 subunits, which blocked cell adhesion; (2) a mAb that stimulated beta1 integrin-mediated adhesion; and (3) binding TNF-alpha to the 30-kDa amino-terminal fragment of FN, which lacks the major cell adhesive binding sites. Thus, in addition to their cell-adhesive roles, ECM glycoproteins, such as FN, may play a pivotal role in presenting proinflammatory cytokines to leukocytes within the actual inflamed tissue, thereby affecting their capacities to secrete ECM-degrading enzymes. These TNF-alpha-ECM interactions may serve to limit the cytokine's availability and bioactivity to target areas of inflammation.

Animals↗
PubMed2001

Cell adhesion and signaling on the fibronectin 1st type III repeat; requisite roles for cell surface proteoglycans and integrins.

BACKGROUND: The first type III repeat of fibronectin is known to be involved in fibronectin matrix assembly, and recombinant proteins from this type III repeat can inhibit cell proliferation, tumor metastasis and angiogenesis. We have analyzed the way rat aortic smooth muscle cells (RASMCs) interact with a recombinant protein encompassing a C-terminal portion of the first type III repeat of fibronectin (protein III1-C). RESULTS: Cells are able to adhere to and spread on III1-C coated on a dish. Both beta1 integrins and cell surface heparan sulfate proteoglycans serve as receptors for III1-C. For example, cell attachment to III1-C is partially inhibited by agents that block beta1 integrins or by heparin. Complete inhibition of cell attachment is seen only when integrin blocking agents are combined with heparin. Affinity chromatography revealed the binding of proteins that likely represent the integrin beta1 and alpha5 submits to a III1-C column. Cell adhesion to III1-C results in robust ERK1/2 activation that is blocked by integrin-blocking agents. In addition, cell adhesion to III1-C and ERK1/2 activation by III1-C are both inhibited by heparan sulfate but not by chondroitin sulfate. Moreover, heparitinase treatment, but not chondroitinase treatment of RASMCs results in reduced cell adhesion and ERK1/2 activation. Affinity chromatography experiments demonstrated that 35SO4-labeled cell surface heparan sulfate proteoglycans bound specifically to III1-C. CONCLUSIONS: The results suggest that the 1st type III repeat of fibronectin contains a previously unrecognized cell adhesion domain that stimulates robust ERK1/2 activation in RASMCs. Cells interact with this domain through cell surface heparan sulfate proteoglycans and integrins, and both classes of receptors are required for optimal cell adhesion and ERK1/2 activation.

Animals↗