Minimally modified low-density lipoprotein induces monocyte adhesion to endothelial connecting segment-1 by activating beta1 integrin. (17/6624)

We have shown previously that treatment of human aortic endothelial cells (HAECs) with minimally modified low-density lipoprotein (MM-LDL) induces monocyte but not neutrophil binding. This monocyte binding was not mediated by endothelial E-selectin, P-selectin, vascular cell adhesion molecule-I, or intercellular adhesion molecule-I, suggesting an alternative monocyte-specific adhesion molecule. We now show that moncytic alpha4beta1 integrins mediate binding to MM-LDL-treated endothelial cells. We present data suggesting that the expression of the connecting segment-1 (CS-1) domain of fibronectin (FN) is induced on the apical surface of HAEC by MM-LDL and is the endothelial alpha4beta1 ligand in MM-LDL-treated cells. Although the levels of CS-1 mRNA and protein were not increased, we show that MM-LDL treatment causes deposition of FN on the apical surface by activation of beta1integrins, particularly those associated with alpha5 integrins. Activation of beta1 by antibody 8A2 also induced CS-1-mediated monocyte binding. Confocal microscopy demonstrated the activated beta1 and CS-1colocalize in concentrated filamentous patches on the apical surface of HAEC. Both anti-CS-1 and an antibody to activated beta1 showed increased staining on the luminal endothelium of human coronary lesions with active monocyte entry. These results suggest the importance of these integrin ligand interactions in human atherosclerosis.  (+info)

Crystal structure of a heparin- and integrin-binding segment of human fibronectin. (18/6624)

The crystal structure of human fibronectin (FN) type III repeats 12-14 reveals the primary heparin-binding site, a clump of positively charged residues in FN13, and a putative minor site approximately 60 A away in FN14. The IDAPS motif implicated in integrin alpha4beta1 binding is at the FN13-14 junction, rendering the critical Asp184 inaccessible to integrin. Asp184 clamps the BC loop of FN14, whose sequence (PRARI) is reminiscent of the synergy sequence (PHSRN) of FN9. Mutagenesis studies prompted by this observation reveal that both arginines of the PRARI sequence are important for alpha4beta1 binding to FN12-14. The PRARI motif may represent a new class of integrin-binding sites. The spatial organization of the binding sites suggests that heparin and integrin may bind in concert.  (+info)

Stretch-induced overproduction of fibronectin in mesangial cells is mediated by the activation of mitogen-activated protein kinase. (19/6624)

An excessive production of extracellular matrix (ECM) proteins in glomerular mesangial cells is considered to be responsible for the development of mesangial expansion seen in diabetic nephropathy. Mechanical stretch due to glomerular hypertension has been proposed as one of the factors leading to an increase in the production of ECM proteins in mesangial cells, but the precise mechanism of stretch-induced overproduction of ECM proteins has not been elucidated. Herein, we provide the evidence that mitogen-activated protein kinase (MAPK) may play a key role in the overproduction of fibronectin (FN) in mesangial cells exposed to mechanical stretch. MAPK, also termed extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK), was activated by mechanical stretch in time- and intensity-dependent manners. Stretch-induced activation of ERK was inhibited by herbimycin A, a tyrosine kinase inhibitor, but not by GF109203X or calphostin C, the inhibitors of protein kinase C. Mechanical stretch also enhanced DNA-binding activity of AP-1, and this enhancement was inhibited by PD98059, an inhibitor of MAPK or ERK kinase (MEK). Furthermore, mechanical stretch stimulated the expression of FN mRNA followed by a significant increase in its protein accumulation. PD98059 could prevent stretch-induced increase in the expression of FN mRNA and protein. These results indicate that the activation of ERK may mediate the overproduction of ECM proteins in mesangial cells exposed to mechanical stretch, an in vitro model for glomerular hypertension seen in diabetes.  (+info)

Fatty acids modulate the composition of extracellular matrix in cultured human arterial smooth muscle cells by altering the expression of genes for proteoglycan core proteins. (20/6624)

In diabetes-associated microangiopathies and atherosclerosis, there are alterations of the extracellular matrix (ECM) in the intima of small and large arteries. High levels of circulating nonesterified fatty acids (NEFAs) are present in insulin resistance and type 2 diabetes. High concentrations of NEFAs might alter the basement membrane composition of endothelial cells. In arteries, smooth muscle cells (SMCs) are the major producers of proteoglycans and glycoproteins in the intima, and this is the site of lipoprotein deposition and modification, key events in atherogenesis. We found that exposure of human arterial SMCs to 100-300 micromol/albumin-bound linoleic acid lowered their proliferation rate and altered cell morphology. SMCs expressed 2-10 times more mRNA for the core proteins of the proteoglycans versican, decorin, and syndecan 4 compared with control cells. There was no change in expression of fibronectin and perlecan. The decorin glycosaminoglycan chains increased in size after exposure to linoleic acid. The ECM produced by cells grown in the presence of linoleic acid bound 125I-labeled LDL more tightly than that of control cells. Darglitazone, a peroxisome proliferator-activated receptor (PPAR)-gamma ligand, neutralized the NEFA-mediated induction of the decorin gene. This suggests that some of the NEFA effects are mediated by PPAR-gamma. These actions of NEFAs, if present in vivo, could contribute to changes of the matrix of the arterial intima associated with micro- and macroangiopathies.  (+info)

Regulation of fibronectin EDA exon alternative splicing: possible role of RNA secondary structure for enhancer display. (21/6624)

The fibronectin primary transcript undergoes alternative splicing in three noncoordinated sites: the cassette-type EDA and EDB exons and the more complex IIICS region. We have shown previously that an 81-nucleotide region within the EDA exon is necessary for exon recognition and that this region contains at least two splicing-regulatory elements: a polypurinic enhancer (exonic splicing enhancer [ESE]) and a nearby silencer element (exonic splicing silencer [ESS]). Here, we have analyzed the function of both elements in different cell types. We have mapped the ESS to the nucleotide level, showing that a single base change is sufficient to abolish its function. Testing of the ESE and ESS elements in heterologous exons, individually or as part of the complete EDA regulatory region, showed that only the ESE element is active in different contexts. Functional studies coupled to secondary-structure enzymatic analysis of the EDA exon sequence variants suggest that the role of the ESS element may be exclusively to ensure the proper RNA conformation and raise the possibility that the display of the ESE element in a loop position may represent a significant feature of the exon splicing-regulatory region.  (+info)

Development of cytotrophoblast columns from explanted first-trimester human placental villi: role of fibronectin and integrin alpha5beta1. (22/6624)

Human first-trimester floating mesenchymal villi explanted onto gels of collagen I or Matrigel were observed to undergo de novo development of anchoring sites. These consisted of cytotrophoblast columns that formed by proliferation of stem villous cytotrophoblast cells, as revealed by whole-mount and thin-section microscopy and incorporation of bromodeoxyuridine into DNA. Column formation occurred exclusively at the distal tips of the villi. No column formation was observed in tissue explanted onto agarose. On Matrigel, the developing columns penetrated downwards into the matrix, whereas on collagen I, cytotrophoblast sheets spread across the surface of the gel and merged to form a shell. The developing columnar cytotrophoblast up-regulated integrins alpha1beta1 and alpha5beta1 and produced an extracellular matrix containing oncofetal fibronectin, as in vivo. Function-blocking antibodies were used to investigate the role of the integrin-fibronectin interaction in anchoring villus development on collagen I. Antibodies to fibronectin and the integrin subunits alpha5 and beta1, added at 24 h, all changed the pattern of cytotrophoblast outgrowth. Anti-fibronectin caused cell rounding within the cytotrophoblast sheet and increased the population of single cells at its periphery. Anti-integrin alpha5 caused rounding and redistribution of cells within the outgrowth. In the presence of anti-integrin beta1, cell-collagen interactions within the sheet were destabilized, often leading to the appearance of an annulus of aggregated cells at the periphery. These results show that 1) mesenchymal villi retain the potential to form anchoring sites until at least the end of the first trimester, 2) adhesion to a permissive extracellular matrix stimulates cytotrophoblast proliferation and differentiation along the extravillous lineage, 3) integrin alpha5beta1-fibronectin interactions contribute significantly to anchorage of the placenta to uterine extracellular matrix. We suggest that as the developing placenta ramifies, new sites of anchorage form whenever peripheral villi contact decidua. This process is predicted to contribute to the stability of the placental-decidual interface.  (+info)

Stage-specific excitation of cannabinoid receptor exhibits differential effects on mouse embryonic development. (23/6624)

Anandamide (N-arachidonoylethanolamine), an arachidonic acid derivative, is an endogenous ligand for both the brain-type (CB1-R) and spleen-type (CB2-R) cannabinoid receptors. We have previously demonstrated that preimplantation mouse embryos express mRNA for these receptors and that the periimplantation uterus contains the highest level of anandamide yet discovered in a mammalian tissue. We further demonstrated that 2-cell mouse embryos exposed to low levels of anandamide (7 nM) or other known cannabinoid agonists in culture exhibit markedly compromised embryonic development to blastocysts and that this effect is mediated by CB1-R. In contrast, the present study demonstrates that blastocysts exposed in culture to the same low levels of cannabinoid agonists exhibited accelerated trophoblast differentiation with respect to fibronectin-binding activity and trophoblast outgrowth. Again, these effects resulted from activation of embryonic CB1-R. There was a differential concentration-dependent effect of cannabinoids on the trophoblast, with an observed inhibition of differentiation at higher doses. These results provide evidence for the first time that cannabinoid effects are differentially executed depending on the embryonic stage and cannabinoid levels in the environment. Since uterine anandamide levels are lowest at the sites of implantation and highest at the interimplantation sites, the new findings imply that site-specific levels of anandamide and/or other endogenous ligands in the uterus may regulate implantation spatially by promoting trophoblast differentiation at the sites of blastocyst implantation.  (+info)

Isolation of Enterococcus faecalis clinical isolates that efficiently adhere to human bladder carcinoma T24 cells and inhibition of adhesion by fibronectin and trypsin treatment. (24/6624)

The adherence of Enterococcus faecalis strains to human T24 cells was examined by scanning electron microscopy. Five highly adhesive strains were identified from 30 strains isolated from the urine of patients with urinary tract infections. No efficiently adhesive strains were found among the 30 strains isolated from the feces of healthy students. The five isolated strains also adhered efficiently to human bladder epithelial cells. Analysis of restriction endonuclease-digested plasmid DNAs and chromosome DNAs showed that the five strains were different strains isolated from different patients. The adhesiveness of these strains was inhibited by treatment with fibronectin or trypsin, implying that a specific protein (adhesin) on the bacterial cell surface mediates adherence to fibronectin on the host cell surfaces, and the adhesin differs from the reported adhesins.  (+info)