TNF-alpha and IL-4 synergistically increase vascular cell adhesion molecule-1 expression in cultured vascular smooth muscle cells.

Vascular cell adhesion molecule-1 (VCAM-1) is expressed on the endothelium and vascular smooth muscle in atherosclerosis, where it is thought to recruit alpha4 integrin-positive leukocytes, which play a role in disease progression. In this study, we show an increase of VCAM-1 expression on vascular smooth muscle cells (VSMC) results in increased adhesion of alpha4 integrin-positive lymphocytes. Additionally, we examine the regulation of VCAM-1 expression by cytokines in cultured VSMC. Previously in endothelial cells, we have demonstrated that TNF-alpha increases transcription of the VCAM-1 gene, whereas IL-4 acts to increase VCAM-1 mRNA stability. The combination of a cytokine that increases transcription with a cytokine that stabilizes mRNA results in a synergistic increase in VCAM-1 expression. In this study, we show that the combination of TNF-alpha with IL-4 also resulted in a synergistic increase in VCAM-1 expression on VSMC; however, the mechanism of cytokine activation differed. In contrast to endothelial cells, IL-4 stimulated VCAM-1 gene transcription in the VSMC, but there was little effect of TNF-alpha alone. Additionally, the synergy between TNF-alpha and IL-4 appears to result, at least in part, from a cooperative transcriptional mechanism.

Control of vascular cell adhesion molecule-1 gene promoter activity during neural differentiation.

Here we demonstrate that vascular cell adhesion molecule-1 (VCAM-1) is expressed in the developing central nervous system on neuroepithelial cells, which are the precursors of neurons and glia. As these cells differentiate, VCAM-1 is restricted to a subset of the glial population. An understanding of mechanisms responsible for this restricted pattern could provide insights into how lineage-specific gene expression is maintained during neural differentiation. As a model of neural differentiation, we turned to the P19 embryonic carcinoma cell line, which in response to retinoic acid will differentiate along a neural pathway. We show that VCAM-1 expression on the differentiating P19 cells resembles that in the central nervous system. Transfection of VCAM-1 gene promoter constructs into P19 cells revealed that the VCAM-1 gene is controlled sequentially by negative and positive elements during differentiation. We present evidence that early during differentiation, POU proteins block VCAM-1 gene activity; however, later in differentiation coincident with the appearance of VCAM-1 the pattern of POU proteins changes and the VCAM-1 gene promoter is activated. This activation is mediated through the NF kappa B/rel complex p50/p65, which forms during P19 cell differentiation.

Vascular cell adhesion molecule 1: contrasting transcriptional control mechanisms in muscle and endothelium.

Interaction between vascular cell adhesion molecule 1 (VCAM-1), which appears on the surface of endothelial cells in response to inflammation, and its integrin counter receptor, alpha 4 beta 1, on immune cells is responsible for targeting these immune cells to cytokine-stimulated endothelium. In addition to its role in the immune system, VCAM-1 is also expressed in a developmentally specific pattern on differentiating skeletal muscle, where it mediates cell-cell interactions important for myogenesis through interaction with alpha 4 beta 1. In contrast to endothelium, there is high basal expression of VCAM-1 in skeletal muscle cells and the expression is not cytokine-responsive. Here, we examine the molecular basis for these contrasting patterns of expression in muscle and endothelium, using VCAM-1 promoter constructs in a series of transfection assays. In endothelial cells, octamer binding sites act as silencers that prevent VCAM-1 expression in unstimulated cells. Tumor necrosis factor alpha overcomes the negative effects of these octamers and activates the promoter through two adjacent NF-kappa B binding sites. In muscle cells, a position-specific enhancer located between bp -21 and -5 overrides the effect of other promoter elements, resulting in constitutive VCAM-1 expression. A nuclear protein binds the position-specific enhancer in muscle but not endothelial cells; thus the pattern of expression of this protein could control enhancer activity.

Characterization of the promoter for vascular cell adhesion molecule-1 (VCAM-1).

Vascular cell adhesion molecule-1 (VCAM-1) was first identified as a protein that appears on the surface of endothelial cells after exposure to inflammatory cytokines. Through interaction with its integrin counter receptor VLA-4, VCAM-1 mediates cell-cell interactions important for immune function. We have cloned and begun characterization of the promoter for the VCAM-1 gene. In a series of transfection assays into human umbilical vein endothelial cells (HUVECs), we find that silencers between positions -1.641 kilobases and -288 base pairs restrict promoter activity, and that treatment with tumor necrosis factor-alpha overcomes this inhibition and activates the promoter through two NF kappa B sites located at positions -77 and -63 base pairs of the VCAM-1 gene. This responsiveness appears cell-specific since constructs containing the VCAM-1 NF kappa B sites are not responsive to tumor necrosis factor alpha in the T-cell line Jurkat. The two VCAM-1 NF kappa B sites, which differ slightly in their sequence, form distinct complexes in gel retardation assays, suggesting that they interact with different NF kappa B-site binding proteins. The distribution of these proteins could then control activity of the NF kappa B sites. We conclude that the pattern of VCAM-1 expression in HUVECs is controlled by a combination of these silencers and NF kappa B sites.

Identification of a protein that interacts with the nuclear factor-1 (NF-1) binding site in cells that do not express NF-1: comparison to NF-1, cellular distribution, and effect on transcription.

We examined expression of nuclear factor-1 (NF-1) in different cell lines. Expression was low or undetectable in T and B lymphocyte cell lines, whereas fibroblasts and other adherent cell lines generally had a relatively high level of NF-1 mRNA. In cell lines that did not express NF-1, gel retardation assays, nevertheless, indicated complexes between a protein or proteins and the NF-1 site. These complexes were less abundant than those formed with NF-1, they migrated more slowly, and they appeared as single species instead of the multiple species observed with NF-1. NF-1 site-binding proteins were compared in the fibrosarcoma cell line HT-1080 (expressed the highest level of NF-1 in our study) and the B cell line Raji (does not express NF-1). UV-crosslinking studies indicated that the NF-1 site-binding proteins in both cell lines were similar in size. Proteolytic clipping band shift assays suggested that the Raji protein and NF-1 share structural similarity in their DNA binding domains, but are distinct proteins. The NF-1 site mediated transcriptional stimulation in cell lines where NF-1 is expressed; however, this element did not affect transcription in cell lines that do not express NF-1, suggesting that the NF-1 site-binding protein in these cells is functionally distinct from NF-1.

The alpha 5 beta 1 fibronectin receptor. Characterization of the alpha 5 gene promoter.

A genomic clone containing the gene for the alpha 5 subunit of the human alpha 5 beta 1 integrin complex was isolated by screening a human genomic library with the previously described alpha 5 cDNA (Argraves, W. S., Suzuki, S., Arai, H., Thompson, K., Pierschbacher, M. D., and Ruoslahti, E. (1987) J. Cell Biol 105, 1183-1190). The alpha 5 gene 5'-flanking region lacks both TATA and CCAAT boxes, and it is located in a CpG island. This region was an active promoter in transfection assays using the HT-1080 cell line (fibrosarcoma), which expresses alpha 5, but was inactive in the Raji cell line (B cell), which does not express alpha 5. These results indicate that the alpha 5 gene 5'-flanking region acts as a promoter that exhibits the expected cell-type specificity. Deletion of alpha 5 promoter sequences from position -657 to -178 caused transcription stimulation, suggesting that a silencer is located between these sites. Successive 5' deletions from position -178 decreased promoter activity until activity was essentially eliminated on deletion to position -27. Isolation of a functional promoter for the alpha 5 gene is a first step in understanding how expression of this gene is controlled at the molecular level.

Characterization of three different elements in the 5'-flanking region of the fibronectin gene which mediate a transcriptional response to cAMP.

A cAMP regulatory element (CRE) at nucleotide position -170 of the fibronectin gene was characterized previously (Dean, D. C., Blakeley, M. S., Newby, R. F., Ghazal, P., Hennighausen, L., and Bourgeois, S. (1989) Mol. Cell. Biol. 9, 1498-1506). Here we identify two additional low affinity CREs at nucleotide positions -260 and -415 which differ in sequence by 1 base pair. Interestingly, these CREs did not compete for binding of nuclear proteins in gel retardation assays and partial tryptic digestion of protein-DNA complexes produced a different pattern with each CRE, indicating that they bind different proteins. CRE (-170) competed for binding of proteins to both CREs, suggesting that it may represent a composite of the two elements. CRE (-415) competed effectively for binding of nuclear proteins to the somatostatin gene CRE, suggesting that, like the somatostatin CRE, it binds the nuclear protein CREB. On the other hand, CRE (-260) appears to bind the nuclear protein PEA-2, which also binds a site in the polyoma virus enhancer. In summary, disruption of dyad symmetry in the 3' region of the CRE, as occurs with CRE (-260) and CRE (-415), results in a lower affinity site and may also change the specificity for different nuclear proteins.

Serum stimulation of fibronectin gene expression appears to result from rapid serum-induced binding of nuclear proteins to a cAMP response element.

Fibronectin (FN) mRNA levels increased when quiescent cells (serum starved) were stimulated to undergo the G0/G1 transition by the addition of 20% given fetal calf serum to the media. The 5'-flanking region of the FN gene (position +69 to -510 base pairs (bp] was fused to the coding region of the chloramphenicol acetyltransferase (CAT), and the fusion gene was used in transfection assays. Expression of FNCAT increased on serum treatment indicating that the region of the FN gene between positions +69 and -510 bp mediated serum responsiveness. Deletion of FN gene 5'-flanking sequences from position -510 to -122 bp eliminated serum responsiveness suggesting that an element between these positions was mediating the effect. Sequences between positions -122 and -510 bp of the FN gene were able to confer serum responsiveness on a herpes virus thymidine kinase promoter-CAT fusion gene (TKCAT) when the FN gene sequences were cloned upstream of TKCAT. The ability to confer serum responsiveness on TKCAT was retained with a smaller 100-bp sequence (position -122 to -222 bp). Both a cAMP response element (position -170 bp) and a nuclear factor-1 binding site (position -155 bp) have been identified within this sequence (Dean, D. C., Blakeley, M. S., Newby, R. F., Ghazal, P., Hennighausen, L., and Bourgeois, S. (1989) Mol. Cell. Biol. 9, 1498-1506). The cAMP response element was serum-responsive when cloned upstream of TKCAT or a minimal FN promoter (deleted to position -56 bp) while the nuclear factor-1 binding site was unresponsive. Therefore, the cAMP regulatory element (CRE) is the serum-responsive element between position -122 and -222 bp. Serum-induced binding of proteins to the CRE was detected in gel retardation assays with extracts from cell lines where FN expression was serum-responsive. However, no serum-induced binding was detected with extracts from the JEG-3 cell line where FN expression was not serum-responsive. Serum-induced binding occurred rapidly, within 15 min, and did not require protein synthesis. The decay of serum-induced binding was relatively slow as increased binding was still detectable 24 h after removal of serum. The CRE also mediates transcriptional stimulation by cAMP, but unlike serum stimulation increased CRE binding activity was not detectable in extracts from cAMP-treated cells (Dean, D. C., Blakeley, M. S., Newby, R. F., Ghazal, P., Hennighausen, L., and Bourgeois, S. (1989) Mol. Cell. Biol. 9, 1498-1506).(ABSTRACT TRUNCATED AT 400 WORDS)

Transforming growth factor beta stimulates the expression of fibronectin and of both subunits of the human fibronectin receptor by cultured human lung fibroblasts.

Transforming growth factors of the beta-class (TGFs-beta) stimulate extracellular matrix synthesis and have been implicated in embryogenesis, wound healing, and fibroproliferative responses to tissue injury. Because cells communicate with several extracellular matrix components via specific cell membrane receptors, we hypothesized that TGFs-beta may also regulate the expression of such receptors. We confirmed that TGF-beta 1 increases the expression of fibronectin, an adhesive glycoprotein expressed during embryogenesis and tissue remodeling. Based upon the 48-72-h period required for a maximal fibroproliferative response to dermal injections of TGF-beta 1, we exposed human fetal lung fibroblasts (IMR-90) to TGF-beta 1 for periods up to 48 h in vitro. We observed as much as 6-fold increases in fibronectin synthesis by 24 h as previously reported for fibroblastic cells (Ignotz, R. A., and Massagué, J. (1986) J. Biol. Chem. 261, 4337-4345; Ignotz, R. A., Endo, T., and Massagué, J. (1987) J. Biol. Chem. 262, 6443-6446; Raghow, R., Postlethwaithe, A. E., Keski-Oja, J., Moses, H. L., and Kang, A. H. (1987) J. Clin. Invest. 79, 1285-1288), but up to 30-fold increases by 48 h. These increases are accompanied by similar increases in fibronectin mRNA levels which are prevented by actinomycin D treatment. Using a monospecific antibody raised to the human placental fibronectin receptor complex, we found that TGF-beta 1 stimulated fibronectin receptor synthesis up to 20-40-fold and increases mRNA levels encoding both the alpha- and beta-subunits up to 3-fold, compared to control IMR-90 in serum-free medium. Actinomycin D blocks TGF-beta 1-mediated increases in receptor mRNA levels. The earliest detectable TGF-beta 1-mediated increases in fibronectin receptor complex protein synthesis and mRNA levels occur at 8 h, whereas the earliest increases in fibronectin protein synthesis and mRNA levels occur at 12 h. These results demonstrate that TGF-beta 1 stimulates fibronectin receptor synthesis, extending the diverse stimulatory activities of this polypeptide to matrix receptors. In addition, because fibronectin matrix assembly may involve the fibronectin cell adhesive receptor complex, increased receptor expression may help drive fibronectin deposition into matrix.

Expression of rat intestinal fatty acid-binding protein in Escherichia coli. Purification and comparison of ligand binding characteristics with that of Escherichia coli-derived rat liver fatty acid-binding protein.

Rat intestinal fatty acid-binding protein (I-FABP) is an abundant, 15,124-Da polypeptide found in the cytosol of small intestinal epithelial cells (enterocytes). It is homologous to rat liver fatty acid-binding protein (L-FABP), a 14,273-Da cytosolic protein which is found in enterocytes as well as hepatocytes. It is unclear why the small intestinal epithelium contains two abundant fatty acid-binding proteins. A systematic comparative analysis of the ligand binding characteristics of the two FABPs has not been reported. To undertake such a study we expressed the coding region of a full length I-FABP cDNA in Escherichia coli and purified large quantities of the protein. We also purified rat L-FABP from a similar, previously described expression system (Lowe, J. B., Strauss, A. W., and Gordon, J. I. (1984) J. Biol. Chem. 259, 12696-12704). Analysis of fatty acids associated with each of the homogeneous E. coli-derived FABPs suggested that the two proteins differed in their ligand binding specificity and capacity. All of the fatty acids associated with I-FABP were saturated while 30% of the E. coli fatty acids bound to L-FABP were unsaturated (16:1, 18:1, 18:2). We directly analyzed the ability of I- and L-FABP to bind fatty acids of different chain length and degree of saturation using a hydroxyalkoxypropyl dextran-based assay. Scatchard analysis revealed that each mole of L-FABP can bind up to 2 mol of long chain fatty acid while each mole of I-FABP can bind only 1 mole of fatty acid. L-FABP exhibited a relatively higher affinity for unsaturated fatty acids (oleate, arachidonate) than for saturated fatty acid (palmitate). By contrast, we were not able to detect a significant difference in the affinity of I-FABP for palmitate, oleate, and arachidonate. Neither protein exhibited any appreciable affinity for fatty acids whose chain length was less than C16. The observed differences in ligand affinities and capacities suggest that these proteins may have distinct roles in metabolism and/or compartmentalization of fatty acids within enterocytes.