Regulation of fibronectin biosynthesis by glucocorticoids in human fibrosarcoma cells and normal fibroblasts

Local Glucocorticoid Administration Impairs Embryonic Wound Healing

Understanding the complex processes of fetal wound healing and skin regeneration can help to improve fetal surgery. As part of the integumentary system, the skin protects the newborn organism against environmental factors and serves various functions. Glucocorticoids can enter the fetal circulatory system by either elevated maternal stress perception or through therapeutic administration and are known to affect adult skin composition and wound regeneration. In the present study, we aimed at investigating the effects of local glucocorticoid administration on the process of embryonic wound healing. We performed in-ovo bead implantation of dexamethasone beads into skin incisional wounds of avian embryos and observed the local effects of the glucocorticoid on the process of skin regeneration through histology, immunohistochemistry and in-situ hybridization, using vimentin, fibronectin, E-cadherin, Dermo-1 and phospho-Histone H3 as investigational markers. Local glucocorticoid administration decelerated the healing of the skin incisional wounds by impairing mesenchymal contraction and re-epithelialization resulting in morphological changes, such as increased epithelialization and disorganized matrix formation. The results contribute to a better understanding of scarless embryonic wound healing and how glucocorticoids might interfere with the underlying molecular processes, possibly indicating that glucocorticoid therapies in prenatal clinical practice should be carefully evaluated.

Cell mediated remodeling of stiffness matched collagen and fibrin scaffolds

Cells are known to continuously remodel their local extracellular matrix (ECM) and in a reciprocal way, they can also respond to mechanical and biochemical properties of their fibrous environment. In this study, we measured how stiffness around dermal fibroblasts (DFs) and human fibrosarcoma HT1080 cells differs with concentration of rat tail type 1 collagen (T1C) and type of ECM. Peri-cellular stiffness was probed in four directions using multi-axes optical tweezers active microrheology (AMR). First, we found that neither cell type significantly altered local stiffness landscape at different concentrations of T1C. Next, rat tail T1C, bovine skin T1C and fibrin cell-free hydrogels were polymerized at concentrations formulated to match median stiffness value. Each of these hydrogels exhibited distinct fiber architecture. Stiffness landscape and fibronectin secretion, but not nuclear/cytoplasmic YAP ratio differed with ECM type. Further, cell response to Y27632 or BB94 treatments, inhibiting cell contractility and activity of matrix metalloproteinases, respectively, was also dependent on ECM type. Given differential effect of tested ECMs on peri-cellular stiffness landscape, treatment effect and cell properties, this study underscores the need for peri-cellular and not bulk stiffness measurements in studies on cellular mechanotransduction.

Involvement of upregulation of fibronectin in the pro‑adhesive and pro‑survival effects of glucocorticoid on melanoma cells

Glucocorticoids (GCs) are important stress hormones, which are used as a concomitant medication during malignant tumor chemotherapy. Clinical and preclinical studies have linked GCs to melanoma growth and progression. However, the effects and mechanism of action of GCs on the adhesion and survival of melanoma cells are still unknown. In the present study the effect of dexamethasone (Dex), a synthetic GC, on fibronectin (FN) expression and its roles in regulating the adhesion and survival of melanoma cells were investigated. It was revealed that Dex significantly increased the levels of intracellular and secreted FN in melanoma cell lines by increasing glucocorticoid receptor‑mediated FN protein stability. Additionally, it was demonstrated that Dex (100 nM) significantly promoted the adhesion and survival of melanoma cells. Silencing FN expression abrogated the pro‑adhesive and pro‑survival effects of Dex in melanoma cells. Extracellular FN significantly enhanced melanoma cell adhesion and survival in the presence of cisplatin, whereas partially blocking extracellular FN signaling with a CD44 antibody significantly reduced FN‑enhanced adhesion and survival. This indicated that the upregulation of FN contributed to the pro‑survival effect of Dex by enhancing cell adhesion. It was also observed that activation of the PI3K/AKT signaling pathway by extracellular FN was involved in the FN‑mediated increase in melanoma cell survival. These findings increase understanding of the possible mechanisms by which GCs regulate melanoma cell adhesion and survival.

The pro-adhesive and pro-survival effects of glucocorticoid in human ovarian cancer cells

Cell adhesion to extracellular matrix (ECM) is controlled by multiple signaling molecules and intracellular pathways, and is pivotal for survival and growth of cells from most solid tumors. Our previous works demonstrated that dexamethasone (DEX) significantly enhances cell adhesion and cell resistance to chemotherapeutics by increasing the levels of integrin β1, α4, and α5 in human ovarian cancer cells. However, it is unclear whether the components of ECM or other membrane molecules are also involved in the pro-adhesive effect of DEX in ovarian cancer cells. In this study, we demonstrated that the treatment of cells with DEX did not change the expression of collagens (I, III, and IV), laminin, CD44, and its principal ligand hyaluronan (HA), but significantly increased the levels of intracellular and secreted fibronectin (FN). Inhibiting the expression of FN with FN1 siRNA or blocking CD44, another FN receptor, with CD44 blocking antibody significantly attenuated the pro-adhesion of DEX, indicating that upregulation of FN mediates the pro-adhesive effect of DEX by its interaction with CD44 besides integrin β1. Moreover, DEX significantly enhanced cell resistance to the chemotherapeutic agent paclitaxel (PTX) by activating PI-3K-Akt pathway. Finally, we found that DEX also significantly upregulated the expression of MUC1, a transmembrane glycoprotein. Inhibiting the expression of MUC1 with MUC1 siRNA significantly attenuated the DEX-induced effects of pro-adhesion, Akt-activation, and pro-survival. In conclusion, these results provide new data that upregulation of FN and MUC1 by DEX contributes to DEX-induced pro-adhesion and protects ovarian cancer cells from chemotherapy.

Dexamethasone Stiffens Trabecular Meshwork, Trabecular Meshwork Cells, and Matrix

PURPOSE

Treatment with corticosteroids can result in ocular hypertension and may lead to the development of steroid-induced glaucoma. The extent to which biomechanical changes in trabecular meshwork (TM) cells and extracellular matrix (ECM) contribute toward this dysfunction is poorly understood.

METHODS

Primary human TM (HTM) cells were cultured for either 3 days or 4 weeks in the presence or absence of dexamethasone (DEX), and cell mechanics, matrix mechanics and proteomics were determined, respectively. Adult rabbits were treated topically with either 0.1% DEX or vehicle over 3 weeks, and mechanics of the TM were determined.

RESULTS

Treatment with DEX for 3 days resulted in a 2-fold increase in HTM cell stiffness, and this correlated with activation of extracellular signal-related kinase 1/2 (ERK1/2) and overexpression of α-smooth muscle actin (αSMA). Further, the matrix deposited by HTM cells chronically treated with DEX is approximately 4-fold stiffer, more organized, and has elevated expression of matrix proteins commonly implicated in glaucoma (decorin, myocilin, fibrillin, secreted frizzle-related protein [SFRP1], matrix-gla). Also, DEX treatment resulted in a 3.5-fold increase in stiffness of the rabbit TM.

DISCUSSION

This integrated approach clearly demonstrates that DEX treatment increases TM cell stiffness concurrent with elevated αSMA expression and activation of the mitogen-activated protein kinase (MAPK) pathway, stiffens the ECM in vitro along with upregulation of Wnt antagonists and fibrotic markers embedded in a more organized matrix, and increases the stiffness of TM tissues in vivo. These results demonstrate glucocorticoid treatment can initiate the biophysical alteration associated with increased resistance to aqueous humor outflow and the resultant increase in IOP.

Molecular signature of MT1-MMP: transactivation of the downstream universal gene network in cancer

Invasion-promoting MT1-MMP is directly linked to tumorigenesis and metastasis. Our studies led us to identify those genes, the expression of which is universally linked to MT1-MMP in multiple tumor types. Genome-wide expression profiling of MT1-MMP-overexpressing versus MT1-MMP-silenced cancer cells and a further data mining analysis of the preexisting expression database of 190 human tumors of 14 cancer types led us to identify 11 genes, the expression of which correlated firmly and universally with that of MT1-MMP (P < 0.00001). These genes included regulators of energy metabolism (NNT), trafficking and membrane fusion (SLCO2A1 and ANXA7), signaling and transcription (NR3C1, JAG1, PI3K delta, and CK2 alpha), chromatin rearrangement (SMARCA1), cell division (STK38/NDR1), apoptosis (DAPK1), and mRNA splicing (SNRPB2). Our subsequent extensive analysis of cultured cells, tumor xenografts, and cancer patient biopsies supported our data mining. Our results suggest that transcriptional reprogramming of the specific downstream genes, which themselves are associated with tumorigenesis, represents a distinctive "molecular signature" of the proteolytically active MT1-MMP. We suggest that the transactivation activity of MT1-MMP contributes to the promigratory cell phenotype, which is induced by this tumorigenic proteinase. The activated downstream gene network then begins functioning in unison with MT1-MMP to rework the signaling, transport, cell division, energy metabolism, and other critical cell functions and to commit the cell to migration, invasion, and, consequently, tumorigenesis.

Requirements for sulfate transport and the diastrophic dysplasia sulfate transporter in fibronectin matrix assembly

Diastrophic dysplasia sulfate transporter (DTDST) is a sulfate/chloride antiporter whose function is impaired in several human chondrodysplasias. We show that DTDST is upregulated by dexamethasone stimulation of HT1080 fibrosarcoma cells and is required for fibronectin (FN) extracellular matrix deposition by these cells. DTDST imports sulfate for the modification of glycosaminoglycans. We find that N-sulfation of these chains is important for FN matrix assembly and that sulfation of cell surface proteoglycans is reduced in the absence of DTDST. Of the candidate HT1080 cell surface proteoglycans, only loss of syndecan-2 compromises FN assembly, as shown by syndecan-2 small interfering RNA knockdown. DTDST is both necessary and sufficient to induce FN matrix assembly in HT1080 cells. Knockdown of DTDST ablates FN matrix, whereas its overexpression increases assembly without dexamethasone stimulation. These results identify a previously unrecognized regulatory pathway for matrix assembly via modulation of a sulfate transporter and proteoglycan sulfation. These data raise the possibility that FN assembly defects contribute to chondrodysplasias.

A novel role for the glucocorticoid receptor in the regulation of monocyte chemoattractant protein-1 mRNA stability

Monocyte chemoattractant protein-1 (MCP-1) plays an important role in attracting monocytes to sites of inflammation and is the dominant mediator of macrophage accumulation in atherosclerotic plaques. We have previously shown that glucocorticoids inhibit the secretion of MCP-1 in arterial smooth muscle cells (SMC) by markedly decreasing MCP-1 mRNA stability. We now report that the destabilization of MCP-1 mRNA is mediated by the glucocorticoid receptor (GR). The GR antagonist, RU486, blocked the effect of the glucocorticoid dexamethasone (Dex) on MCP-1 mRNA stability in SMC culture. Using a previously reported in vitro mRNA gel shift and stability assay, antibodies to the GR blocked the ability of cytoplasmic extracts from Dex-treated SMC to decay MCP-1 mRNA. Recombinant human GR (rhGR) bound in a concentration-dependent manner to in vitro transcribed MCP-1 mRNA, whereas other members of the steroid hormone receptor family did not. Binding of GR to MCP-1 mRNA was specific as it was not found to bind other mRNAs. Immunoprecipitation of GR in extracts from Dex-treated SMC followed by real-time reverse transcription-PCR demonstrated that endogenous GR was bound specifically to MCP-1 mRNA. The addition of exogenous rhGR blocked the ability of extracts from Dex-treated SMC to degrade MCP-1 mRNA, suggesting that exogenous rhGR can compete with an endogenous GR-containing degradative complex. These data suggest a novel role for the GR in binding to and facilitating mRNA degradation. These results provide novel insights into GR function and may provide a new approach to attenuate the inflammatory response mediated by MCP-1.

Fibronectin quantification without antibodies: A bioassay for the detection of the gelatin-captured macromolecule

We have developed a new cell-adhesion-bioassay (CAA) for the quantitative determination of fibronectin in biological fluids. The assay is based on two particular properties of fibronectin: it specifically binds to gelatin with high affinity and simultaneously it can anchor to different surface molecules of a cell. First fibronectin, derived from very different biological fluids, is purified in situ, within the wells of the microtiter plates applied for the assay, using solid surface bound gelatin. After capturing the macromolecule, it is quantified based on its cell adhesive properties. In contrast to ELISA the CAA does not require specific antibodies, and as the Jurkat cells used as indicator cells, seem to recognize fibronectin from different species equally; species specificity of the reagent plays smaller, perhaps negligible, role in the determination of the amount of the macromolecule. The CAA method may not replace fibronectin specific ELISA-s, but using its principle, improved applications, for example a capture EIA for determining fibronectin can easily be envisioned and CAA may serve as a viable alternative for EIA-s when specific antibodies are not available or when relative measurement of not only the soluble but cell surface associated fibronectin is necessary.

AP-1 differentially expressed proteins Krp1 and fibronectin cooperatively enhance Rho-ROCK-independent mesenchymal invasion by altering the function, localization, and activity of nondifferentially expressed proteins

The transcription factor AP-1, which is composed of Fos and Jun family proteins, plays an essential role in tumor cell invasion by altering gene expression. We report here that Krp1, the AP-1 up-regulated protein that has a role in pseudopodial elongation in v-Fos-transformed rat fibroblast cells, forms a novel interaction with the nondifferentially expressed actin binding protein Lasp-1. Krp1 and Lasp-1 colocalize with actin at the tips of pseudopodia, and this localization is maintained by continued AP-1 mediated down-regulation of fibronectin that in turn suppresses integrin and Rho-ROCK signaling and allows pseudopodial protrusion and mesenchyme-like invasion. Mutation analysis of Lasp-1 demonstrates that its SH3 domain is necessary for pseudopodial extension and invasion. The results support the concept of an AP-1-regulated multigenic invasion program in which proteins encoded by differentially expressed genes direct the function, localization, and activity of proteins that are not differentially expressed to enhance the invasiveness of cells.

Continuous requirement for pp60-Src and phospho-paxillin during fibronectin matrix assembly by transformed cells

Fibronectin (FN) matrix assembly is an integrin-mediated process that is regulated by both the extracellular environment and intracellular signaling pathways. The activity of Src-family kinases is important for initiation of FN assembly by normal fibroblasts. Here we report that in HT1080 fibrosarcoma cells, Src kinase activity is required not only for the assembly of FN matrix but also for the maintenance of FN matrix fibrils at the cell surface. Dexamethasone-induced FN fibril formation by these cells was completely blocked for at least 24 h when Src-family kinase activity was inhibited by either PP1 or SU6656. Inhibition of Src after significant matrix had already been assembled, resulted in an increased rate of loss of detergent-insoluble FN. Binding of activation-dependent integrin antibodies reveals a role for Src in maintaining integrin activity. The requirement for Src kinase activity appears to depend, in part, on phosphorylation of paxillin at tyrosine 118 (Y118). Phospho-paxillin co-localized with FN fibrils, and overexpression of GFP-paxillin but not of GFP-paxillinY118F enhanced cell-mediated assembly of FN. Our results indicate that Src maintains FN matrix at the cell surface through its effect on integrin activity and paxillin phosphorylation.

Vitronectin's basic domain is a syndecan ligand which functions in trans to regulate vitronectin turnover

During the process of tissue remodeling, vitronectin (Vn) is deposited in the extracellular matrix where it plays a key role in the regulation of pericellular proteolysis and cell motility. In previous studies we have shown that extracellular levels of vitronectin are controlled by receptor-mediated endocytosis and that this process is dependent upon vitronectin binding to sulfated proteoglycans. We have now identified vitronectin's 12 amino acid "basic domain" which is contained within the larger 40 amino acid heparin binding domain, as a syndecan binding site. Recombinant vitronectins representing wild type vitronectin (rVn) and vitronectin with the basic domain deleted (rVnDelta347-358) were prepared in a baculoviral expression system. The rVn as well as a glutathione S-transferase (GST) fusion protein, consisting of vitronectin's 40 amino acid heparin binding domain (GST-VnHBD), exhibited dose dependent binding to HT-1080 cell surfaces, which was attenuated following deletion of the basic domain. In addition, GST-VnHBD supported both HT-1080 and dermal fibroblast cell adhesion, which was also dependent upon the basic domain. Similarly, ARH-77 cells transfected with syndecans -1, -2, or -4, but not Glypican-1, adhered to GST-VnHBD coated wells, while adhesion of these same cells was lost following deletion of the basic domain. HT-1080 cells were unable to degrade rVnDelta347-358. Degradation of rVnDelta347-358 was completely recovered in the presence of GST-VnHBD but not in the presence of GST-VnHBDDelta347-358. These results indicate that turnover of soluble vitronectin requires ligation of vitronectin's basic domain and that this binding event can work in trans to regulate vitronectin degradation.

Characterization of a fasciclin I-like protein with cell attachment activity from sea urchin (Strongylocentrotus intermedius) ovaries

Fasciclin I, a neuronal cell adhesion molecule, was first identified in the grasshopper. To date, various fasciclin I-like proteins have been identified but their biological functions have not been well characterized. Here, we have purified a fasciclin I-like protein with a molecular weight of 33kDa from sea urchin (Strongylocentrotus intermedius) ovaries using hydrophobic chromatography and gel filtration. The protein was not N-glycosylated. Partial amino acid sequences of cyanogen bromide (CNBr)-cleaved fragments were highly conserved to other sea urchin fasciclin I-like proteins identified previously. The circular dichroism (CD) spectrum analysis demonstrated that the 33kDa protein contained high content of alpha-helical structure. These results suggest that the 33kDa protein is a fasciclin I-like family. Additionally, the fasciclin I-like protein promoted HT1080 human fibrosarcoma cell attachment. Further, a synthetic peptide (P1: GLREAANIAEQVDLRQVLRDVDL) of the protein corresponding to a highly conserved region of the fasciclin I-like family promoted heparin-dependent HT1080 cell attachment. Moreover, the peptide inhibited HT1080 cell attachment to the fasciclin I-like protein. These results suggest that the 33kDa protein from sea urchin ovaries isolated here is a member of the fasciclin I family and that the N-terminal region of the protein is important for cell attachment activity. The protein has a potential to be involved in biological functions in sea urchin as a cell adhesive molecule.

Androgen regulation of the human FERM domain encoding gene EHM2 in a cell model of steroid-induced differentiation

We have developed a cell model to investigate steroid control of differentiation using a subline of HT1080 cells (HT-AR1) that have been engineered to express the human androgen receptor. Dihydrotestosterone (DHT) treatment of HT-AR1 cells induced growth arrest and cytoskeletal reorganization that was associated with the expression of fibronectin and the neuroendocrine markers chromogranin A and neuron-specific enolase. Expression profiling analysis identified the human FERM domain-encoding gene EHM2 as uniquely induced in HT-AR1 cells as compared to 16 other FERM domain containing genes. Since FERM domain proteins control cytoskeletal functions in differentiating cells, and the human EHM2 gene has not been characterized, we investigated EHM2 steroid-regulation, genomic organization, and sequence conservation. We found that DHT, but not dexamethasone, induced the expression of a 3.8 kb transcript in HT-AR1 cells encoding a 504 amino acid protein, and moreover, that human brain tissue contains a 5.8 kb transcript encoding a 913 amino acid isoform. Construction of an unrooted phylogenetic tree using 98 FERM domain proteins revealed that the human EHM2 gene is a member of a distinct subfamily consisting of nine members, all of which contain a highly conserved 325 amino acid FERM domain.

Androgen control of cell proliferation and cytoskeletal reorganization in human fibrosarcoma cells: role of RhoB signaling

We recently generated an HT-1080-derived cell line called HT-AR1 that responds to dihydrotestosterone (DHT) treatment by undergoing cell growth arrest in association with cytoskeletal reorganization and induction of neuroendocrine-like cell differentiation. In this report, we show that DHT induces a dose-dependent increase in G0/G1 growth-arrested cells using physiological levels of hormone. The arrested cells increase in cell size and contain a dramatic redistribution of desmoplakin, keratin 5, and chromogranin A proteins. DHT-induced cytoskeletal changes were also apparent from time lapse video microscopy that showed that androgen treatment resulted in the rapid appearance of neuronal-like membrane extensions. Expression profiling analysis using RNA isolated from DHT-treated HT-AR1 cells revealed that androgen receptor activation leads to the coordinate expression of numerous cell signaling genes including RhoB, PTGF-beta, caveolin-2, Egr-1, myosin 1B, and EHM2. Because RhoB has been shown to have a role in tumor suppression and neuronal differentiation in other cell types, we investigated RhoB signaling functions in the HT-AR1 steroid response. We found that steroid induction of RhoB was DHT-specific and that newly synthesized RhoB protein was post-translationally modified and localized to endocytic vesicles. Moreover, treatment with a farnesyl transferase inhibitor reduced DHT-dependent growth arrest, suggesting that prenylated RhoB might function to inhibit HT-AR1 cell proliferation. This was directly shown by transfecting HT-AR1 cells with RhoB coding sequences containing activating or dominant negative mutations.

Localization of urokinase type plasminogen activator to focal adhesions requires ligation of vitronectin integrin receptors

Previous studies have shown that the adhesion protein, vitronectin, directs the localization of urokinase-type plasminogen activator (uPA) to areas of cell-substrate adhesion, where uPA is thought to regulate cell migration as well as pericellular proteolysis. In the present study, HT-1080 cell lines expressing either wild-type vitronectin or vitronectin containing a single amino-acid substitution in the integrin binding domain were used to assess whether ligation of the alphavbeta5 integrin was required for uPA localization to focal adhesions. The synthesis of wild-type vitronectin by HT-1080 cells adherent to either collagen or fibronectin resulted in the redistribution of both the alphavbeta5 integrin as well as uPA to focal adhesion structures. In contrast, cells synthesizing mutant vitronectin, containing the amino-acid substitution in the integrin binding domain, were unable to direct the redistribution of either alphavbeta5 or uPA to focal adhesions. Recombinant forms of wild-type and mutant vitronectin were prepared in a baculovirus system and compared for their ability to direct the redistribution of vitronectin integrin receptors as well as uPA on human skin fibroblasts. In the absence of vitronectin, fibroblast cells adherent to fibronectin assemble focal adhesions which contain the beta1 integrin but do not contain uPA. Addition of recombinant wild-type, but not mutant, vitronectin to fibroblasts adherent to fibronectin resulted in the redistribution of alphavbeta3, alphavbeta5, and uPA into focal adhesions. However, when cells were plated directly onto antibodies directed against either the alphavbeta3 or alphavbeta5 integrins, uPA was not localized on the cell surface. These data indicate that ligation of vitronectin integrin receptors is necessary but not sufficient for the localization of uPA to areas of cell matrix adhesion, and suggest that vitronectin may promote cell migration by recruiting vitronectin integrin receptors and components of the plasminogen activator system to areas of cell matrix contact.

Regulation of fibronectin matrix assembly by activated Ras in transformed cells

Fibronectin extracellular matrix plays a critical role in the microenvironment of cells. Loss of this matrix frequently accompanies oncogenic transformation, allowing changes in cell growth, morphology, and tissue organization. The HT1080 human fibrosarcoma cell line is deficient in formation of fibronectin matrix fibrils but assembly can be induced by the glucocorticoid dexamethasone. Here we show that fibronectin assembly can also be restored by stimulation of alpha5beta1 integrin with activating antibody or with Mn2+ suggesting that integrin activity is reduced in these cells. While dexamethasone promoted actin stress fiber formation, actin filaments remained cortical following Mn2+ treatment showing that the dexamethasone effect is not due solely to cytoskeletal changes. HT1080 cells have one activated allele of N-ras and PD98059 inhibition of signaling from Ras through ERK increased fibronectin matrix accumulation. Conversely, the p38 MAP kinase inhibitor SB203580 blocked induction of matrix and increased ERK phosphorylation. Thus, two MAP kinase pathways contribute to the control of integrin-mediated fibronectin assembly. ERK activity and fibronectin assembly were linked in three different ras-transformed cell lines but not in SV40- or RSV-transformed cells indicating that oncogenic Ras uses a distinct mechanism to down-regulate cell-fibronectin interactions.

Intercellular adhesion can be visualized using fluorescently labeled fibrosarcoma HT1080 cells cocultured with hematopoietic cell lines or CD34(+) enriched human mobilized peripheral blood cells

BACKGROUND

Intercellular contacts between adjacent cells migrating over each other are important in many cellular processes. However, it has been difficult to visualize and identify dynamic intercellular adhesions between migrating cells in situ.

METHODS

Two fluorescent membrane dyes, PKH2 and PKH26 for staining HT1080 and hematopoietic cells and cell lines, and an automated fluorescence microscopy system were used to monitor intercellular adhesion.

RESULTS

Cellular extensions connecting two or more adjacent cells were visualized, showing the intercellular adhesion between migrating cells for minutes and up to hours. After cells adhered to each other, followed by cell migration in different directions, cellular extensions were dragged from the pivotal contact points in different focal planes. CD34(+)-enriched mobilized peripheral blood cells and six hematopoietic cell lines showed intercellular connections in cocultures with HT1080. However, the frequency of intercellular connections was variable in different cocultures. A cell density of about 3.1 x 10(4) cells/cm(2) for both cell lines in cocultures provided an adequate number of cells in each field of view, showing up to four intercellular connections per 100 total cells plated.

DISCUSSION

The tools derived from this study will open new areas of investigation for understanding the mechanism of the intercellular adhesion process.

Cloning, expression and characterization of a novel human Ras-related protein that is regulated by glucocorticoid hormone

Ras proteins are a family of guanine nucleotide (GDP and GTP)-binding proteins that play central roles in essential signal transduction pathways. We have isolated in a yeast two-hybrid screen a human cDNA encoding a new protein that is highly homologous (98% identical at the protein level) to mouse DexRas1, a member of the Ras superfamily. The human DexRas1 is expressed in a variety of tissues including heart, brain, placenta, lung, liver, skeletal muscle, kidney and pancreas, with the strongest expression in the heart. Using human fibrosarcoma HT-1080 cells as a model system, we show that the expression of human DexRas1 is stimulated by dexamethasone, suggesting a role of human DexRas1 in dexamethasone-induced alterations in cell morphology, growth and cell-extracellular matrix interactions.

Human fibulin-1D: molecular cloning, expression and similarity with S1-5 protein, a new member of the fibulin gene family

Fibulin-1 is an extracellular matrix (ECM) component of basement membranes and connective tissue elastic fibers, and a blood protein. Multiple forms of fibulin-1 that differ in their C-terminal regions are produced through the process of alternative splicing of their precursor RNA. Two transcripts of 2.4 and 2.7 kb are the predominant fibulin-1 mRNAs expressed in human tissues and cultured cells. While the 2.4 kb transcript had been shown to encode fibulin-1C, the 2.7 kb transcript did not correspond to any of the previously identified human fibulin-1 variants. Herein, we report on the isolation and sequencing of cDNA corresponding to the 2.7 kb fibulin-1 transcript which encodes a novel, alternatively spliced form of human fibulin-1 that we term the D form. The deduced amino acid sequence of the D form is identical in its first 566 residues to the three known fibulin-1 variants (fibulin-1A-C); however, it has a unique 137 amino acid-C-terminal segment encoded by the alternatively spliced portion of its transcript. RNA hybridization analysis showed that the fibulin-1D transcript is coordinately expressed with that of fibulin-1C both in tissues and in cultured cells. Using antibodies specific to the unique C-terminal segment of fibulin-1D and -1C, both proteins were found to be expressed in human placenta. Recombinant fibulin-1D generated in transfected mammalian cells displayed similar ligand-binding properties as placenta-derived fibulin-1 and recombinant fibulin-1C, and it was capable of incorporating into cultured cell ECM in the absence of other fibulin-1 forms. A comparative sequence analysis revealed that the unique C-terminal region of fibulin-1D is similar to the C-terminal regions of fibulin-1C and fibulin-2. Furthermore, the C-terminal regions of fibulin-1C, -1D and -2 are similar to the C-terminal region of a recently described protein termed S1-5. In addition to this C-terminal similarity, S1-5 also contains repeated EGF-like modules and a conserved N-terminal element, thereby leading to the conclusion that S1-5 is a third member of the fibulin gene family.

Fibronectin synthesis in tubular epithelial cells: up-regulation of the EDA splice variant by transforming growth factor beta

The influence of transforming growth factor beta 1 (TGF-beta 1) and of dexamethasone on fibronectin (FN) synthesis of human renal tubular epithelial cells in culture (TEC) was studied. Cocultivation with TGF-beta 1 increased the steady state level of FN RNA within 24 to 48 hours. By PCR and Northern blotting it was found that the EDA splice variant of FN was preferentially up-regulated. To quantitate FN protein synthesis, cells were cultivated in the presence of [35S]-methionine and FN was isolated from the cell supernatants, and the cell lysates by adsorption to gelatin-sepharose. In TGF-beta 1 treated cells, a small increase of FN in the cell supernatants was seen (1.7-fold), and a more prominent increase in the cell lysates (4.5-fold). The FN content of the extracellular matrix was also increased in TGF-beta 1 treated cells. Most of the de novo synthesized FN was identified as the EDA-variant of FN. As a further stimulus, dexamethasone was used. Again, an increase of FN-specific mRNA was seen as well as an increased FN protein synthesis. The ratio between FN and EDA-FN, however, was not altered when compared to untreated cells. Thus, an increase in EDA-FN synthesis is obviously stimulus dependent.

Regulation of mesenchymal extracellular matrix protein synthesis by transforming growth factor-beta and glucocorticoids in tumor stroma

We have here studied the composition and regulation of stromal extracellular matrix components in an experimental tumor model. Nude mice were inoculated with WCCS-1 cells, a human Wilms' tumor cell line. In the formed tumors the stroma was found to contain mesenchymal extracellular matrix proteins such as tenascin-C, fibulins-1 and 2 and fibronectin, but no nidogen. Nidogen was confined to basement membranes of tumor blood vessels. Since glucocorticoids have been shown to downregulate tenascin-C expression in vitro, we tested whether dexamethasone can influence biosynthesis of extracellular matrix components during tumor formation in vivo. A downregulation of tenascin-C mRNA and an upregulation of fibronectin mRNA expression by dexamethasone was noted. Transforming growth factor-beta 1 mRNA levels were unaffected by the dexamethasone treatment. Glucocorticoids can thus downregulate tenascin-C synthesis although local stimulatory growth factors are present. The competition between a negative and a positive extrinsic factor on synthesis of stromal extracellular matrix components was studied in a fibroblast/preadipocyte cell line. Transforming growth factor-beta 1 stimulated tenascin-C synthesis but did not affect fibronectin or fibulin-2 synthesis. Dexamethasone at high concentrations could completely suppress the effect of transforming growth factor-beta 1 on tenascin-C mRNA expression. Transforming growth factor-beta 1 could in turn overcome the downregulation of tenascin-C mRNA expression caused by a lower concentration of dexamethasone. We therefore suggest that the limited expression of tenascin-C in part is due to a continuous suppression by physiological levels of glucocorticoids, which can be overcome by local stimulatory growth factors when present in sufficient amounts.

A nuclear post-transcriptional mechanism mediates the induction of fibronectin by glucocorticoids

Treatment of the human fibrosarcoma cell line HT-1080 with glucocorticoids results in the induction of fibronectin (FN) protein and mRNA synthesis. We tested the contribution of transcriptional and post-transcriptional mechanisms in the regulation of FN by the synthetic glucocorticoid dexamethasone (DEX). Using nuclear run-on experiments, we found that the DEX-dependent induction of FN occurs primarily at the post-transcriptional level. The half-life of total FN mRNA was not affected by hormone treatment indicating that the induction of FN gene expression is not due to stabilization of the mature message. Interestingly, the induction by DEX was present at the level of nuclear FN RNA. We found that polyadenylation and alternative splicing of the ED-B domain of the FN transcript were not affected by glucocorticoid treatment. However, DEX was found to increase the steady-state level of unspliced FN transcript. Our data indicate that DEX exerts its effect on FN expression predominantly at the post-transcriptional level by a mechanism that, unlike most examples of post-transcriptional regulation by glucocorticoids, acts in the nucleus. Furthermore, they suggest that glucocorticoids activate a mechanism to stabilize the unspliced FN RNA. In an attempt to localize the FN RNA sequences mediating the DEX-dependent induction, we performed transfection analyses of FN minigene constructs. We suggest that the DEX-dependent regulatory elements are located in the introns since no such elements were found in the 8 kb FN mRNA.

In vivo prevention of corticosteroid-induced skin atrophy by tretinoin in the hairless mouse is accompanied by modulation of collagen, glycosaminoglycans, and fibronectin

In an earlier study we showed that tretinoin could prevent corticosteroid-induced skin atrophy in hairless mice. In this study, we examined the histochemical, biochemical, and immunochemical changes that accompanied the atrophy and its prevention. Mice were treated dorsally for 3 weeks in the morning and afternoon (AM:PM) as follows: 1) vehicle:vehicle, 2) steroid:vehicle, 3) steroid:tretinoin. Tretinoin concentration was 0.05% in an ethanol:propylene glycol vehicle. The steroid was clobetasol propionate (0.05%). The normally sparse dermal glycosaminoglycans were further reduced by steroid:vehicle treatment and increased to greater than vehicle:vehicle amounts by steroid:retinoid. Mast cells were similarly affected. Biochemical quantification of glycosaminoglycans confirmed the histochemical findings. Collagen, non-collagenous protein, and total protein content were reduced by the steroid. The latter two were returned to more normal levels by tretinoin whereas with collagen there was only a trend toward normal levels. Fibronectin, which was increased by the steroid:vehicle treatment, was reduced to more normal levels by steroid:tretinoin. We conclude that tretinoin has the ability to prevent the major steroid-induced biomechanical changes in hairless mouse dermal connective tissue that contribute to atrophy.

Downregulation of tenascin expression by glucocorticoids in bone marrow stromal cells and in fibroblasts

Tenascin, a predominantly mesenchymal extracellular matrix (ECM) glycoprotein has a rather restricted tissue distribution, but until now factors that inhibit its expression have not been identified. Glucocorticoids are known to be beneficial for establishment of myelopoiesis in long-term bone marrow cultures. Tenascin was found to be expressed in the bone marrow, and glucocorticoids were found to affect bone marrow tenascin expression. Both tenascin mRNAs and the mRNA of another ECM protein, laminin B1 chain, were drastically downregulated by glucocorticoids during initiation of bone marrow cultures. However, in already established long-term cultures glucocorticoids did not affect laminin B1 chain mRNA levels although tenascin mRNAs continued to be downregulated. Studies with a stromal cell line (MC3T3-G2/PA6) and fibroblasts (3T3) suggested that glucocorticoids act directly on the stromal cells that produce tenascin. In 3T3 cells this downregulation occurred within 12 h of glucocorticoid-treatment, suggesting that glucocorticoids acted through cis regulatory elements of the tenascin gene. We suggest that glucocorticoids in part regulate hematopoiesis by modifying the ECM. Furthermore, downregulation of tenascin expression by glucocorticoids may in part explain the restricted tissue distribution of tenascin in other tissues.

Major influence of cell differentiation status on characteristics of proteoglycans synthesized by cultured rabbit renal proximal tubule cells: role of insulin and dexamethasone

To analyze the influence of epithelial cell differentiation and the effects of hormones on the characteristics of cell-associated and secreted proteoglycans (PGs), we studied their distribution, synthesis, and biochemical features in a model of renal proximal tubule cells in primary culture in which cell differentiation could be controlled by medium composition. In cells cultured in serum-free, hormonally defined medium supplemented with insulin and dexamethasone that exhibited a high degree of morphological and functional proximal differentiation (Ronco et al., 1990), cell-associated PGs were similar to those extracted in vivo by their size estimated by Sepharose CL-6B chromatography (Kav = 0.27, vs. 0.26), composition (heparan-sulfate), and localization in a continuous basal layer of extra-cellular matrix (ECM). In contrast, major quantitative and qualitative anomalies of cell-associated PGs were observed in poorly differentiated cells grown in 1% fetal calf serum-supplemented medium (FCS). PGs alterations included: (1) reduced and irregular expression of PGs at the cell basal pole, (2) a 2.8-fold decrease in [35S]-sulfate incorporation into cell-associated PGs, (3) a 3.1-fold increase in trypsin-releasable PGs, and (4) the emergence of a high MW PG composed exclusively of chondroitin-sulfate (CS) (Kav = 0.09 on Sepharose CL-6B) as well as of putative free CS-glycosaminoglycan (GAG) chains (Kav = 0.49 on Sepharose CL-6B). The same alterations were identified in the basal defined medium devoid of hormones but were partially or totally abolished by addition of insulin and dexamethasone, respectively. At variance with cell-associated PGs, production and biochemical features of secreted PGs were not influenced by cell differentiation status and medium composition.

Glucocorticoids promote development of the osteoblast phenotype by selectively modulating expression of cell growth and differentiation associated genes

To understand the mechanisms by which glucocorticoids promote differentiation of fetal rat calvaria derived osteoblasts to produce bone-like mineralized nodules in vitro, a panel of osteoblast growth and differentiation related genes that characterize development of the osteoblast phenotype has been quantitated in glucocorticoid-treated cultures. We compared the mRNA levels of osteoblast expressed genes in control cultures of subcultivated cells where nodule formation is diminished, to cells continuously (35 days) exposed to 10(-7) M dexamethasone, a synthetic glucocorticoid, which promotes nodule formation to levels usually the extent observed in primary cultures. Tritiated thymidine labelling revealed a selective inhibition of internodule cell proliferation and promotion of proliferation and differentiation of cells forming bone nodules. Fibronectin, osteopontin, and c-fos expression were increased in the nodule forming period. Alkaline phosphatase and type I collagen expression were initially inhibited in proliferating cells, then increased after nodule formation to support further growth and mineralization of the nodule. Expression of osteocalcin was 1,000-fold elevated in glucocorticoid-differentiated cultures in relation to nodule formation. Collagenase gene expression was also greater than controls (fivefold) with the highest levels observed in mature cultures (day 35). At this time, a rise in collagen and TGF beta was also observed suggesting turnover of the matrix. Short term (48 h) effects of glucocorticoid on histone H4 (reflecting cell proliferation), alkaline phosphatase, osteopontin, and osteocalcin mRNA levels reveal both up or down regulation as a function of the developmental stage of the osteoblast phenotype. A comparison of transcriptional levels of these genes by nuclear run-on assays to mRNA levels indicates that glucocorticoids exert both transcriptional and post-transcriptional effects. Further, the presence of glucocorticoids enhances the vitamin D3 effect on gene expression. Those genes which are upregulated by 1,25(OH)2D3 are transcribed at an increased rate by dexamethasone, while those genes which are inhibited by vitamin D3 remain inhibited in the presence of dexamethasone and D3. We propose that the glucocorticoids promote changes in gene expression involved in cell-cell and cell-extracellular matrix signaling mechanisms that support the growth and differentiation of cells capable of osteoblast phenotype development and bone tissue-like organization, while inhibiting the growth of cells that cannot progress to the mature osteoblast phenotype in fetal rat calvarial cultures.

Changes in cell attachment by RSV transformation in rat liver epithelial cells

BRL, a non-malignant rat liver epithelial-like cell line, possessed the ability to adhere through fibronectin to a solid substrate. Oncogenical transformation of these BRL cells with RSV induced a significant decrease in the fibronectin molecules in the extracellular matrix and reduction in its ability to adhere to fibronectin. The alpha 5 and beta 1 subunits of integrin (fibronectin receptor) were quantitatively diminished during RSV transformation in BRL cells. These results suggest that adhesive reduction of BRL cells to a substrate by RSV transformation may be caused by a decrease in cell surface fibronectin and fibronectin receptor molecules.

Keloid fibroblasts exhibit an altered response to TGF-beta

Treatment with transforming growth factor beta 1 (TGF-beta 1) results in stimulation of total protein synthesis in normal dermal fibroblasts but not in keloid fibroblasts, suggesting that the TGF-beta regulatory program is altered in keloid fibroblasts. However, both keloid and normal fibroblasts treated with TGF-beta 1 exhibit accelerated fibronectin biosynthesis, indicating that keloid cells can respond to TGF-beta 1. In the absence of serum, the TGF-beta 1-induced increase in fibronectin biosynthesis occurs more rapidly in keloid fibroblasts, also suggesting modification of this regulatory pathway. The TGF-beta 1-mediated increase in keloid fibronectin production is independent of the steroid regulatory pathway for fibronectin, which accelerates synthesis by means of a post-transcriptional mechanism. Thus, TGF-beta 1 stimulation of fibronectin production in keloid cells is likely to involve a transcriptional mechanism and keloid overproduction of extracellular matrix components may be due to an inherent modification of the TGF-beta regulatory program.

Fibronectin gene transcription is enhanced in abnormal wound healing

Abnormal wound healing in susceptible individuals can result in the formation of keloids that have an elevated content of extracellular matrix material compared to normal scars. Keloid-derived fibroblasts exhibit as much as a four-fold increase in the rate of fibronectin biosynthesis compared to fibroblasts from normal dermis and normal scars. Altered biosynthesis is due to an increase in the steady-state level of fibronectin mRNA, and in this investigation we have identified the level of fibronectin gene expression that is responsible for this increase. The rate of fibronectin gene transcription was found to be increased as much as threefold in keloid fibroblasts when compared to normal fibroblasts. Other possible changes that could account for the elevated level of fibronectin mRNA in keloids, such as increased copy number of the fibronectin gene or decreased turnover of fibronectin mRNA were also examined. The possibility of altered gene dosage was eliminated because chromosome content, G-banding patterns, and fibronectin gene content of keloid fibroblasts were all found to be normal. Analysis of fibronectin mRNA degradation revealed a half-life of approximately 13 h, and the residual fibronectin mRNA was observed to remain full length during this time period in both keloid and normal fibroblasts. Thus, altered degradation of fibronectin mRNA is unlikely to contribute to overproduction of fibronectin in keloids. Increased translational competence of fibronectin mRNA in keloids was also eliminated as a contributing factor because fibronectin mRNA remaining after one half-life were equally available for translation in both cell types. Although stimulation of transcription may not entirely account for the increase in fibronectin biosynthesis in keloids, this mechanism is best able to account for the majority of the change.

Fibronectin gene expression in proliferating, quiescent, and SV40-infected mouse kidney cells

To study alterations in cellular gene expression in mouse kidney cell cultures infected with simian virus 40 (SV40) or polyomavirus, we performed a differential screening of a mouse kidney cDNA library with probes prepared from mRNAs of virus-infected and mock-infected cells. We isolated and characterized cDNA recombinant pKT13 which detected increased mRNA levels in infected cells. Sequence analysis of pKT13 revealed close to 100% homology with the 3'-end of mouse fibronectin (FN) mRNA. Since primary cultures of baby mouse kidney cells have been extensively characterized in our laboratories, we studied FN gene expression at different stages of uninfected and virus-infected cultures. High levels of FN and of its mRNA were found in the kidneys of suckling mice, while in primary cultures of proliferating epithelial kidney cells the expression of FN was very low until the cultures became confluent. Thereafter FN increased and reached high levels in cells which were irreversibly arrested in phase Go and which had apparently exhausted their finite division potential. Infection of confluent cultures with polyomavirus or SV40 resulted in a further stimulation of FN gene expression. However, during abortive infection with SV40, FN mRNA and FN levels decreased with emergence of transformed cells and were low in an established SV40-transformed mouse kidney cell line. These changes in FN gene expression suggest that high levels of FN might be indicative in vivo for terminal differentiation and in vitro for cellular senescence.

Uterine fibronectin mRNA content and localization are modulated during implantation

Fibronectin mRNA and protein content were examined during embryonic implantation in the rat uterus. Content of total fibronectin mRNA at day 6 of pregnancy increased relative to the non-pregnant uterus. In contrast, fibronectin protein content of the subepithelial stroma was relatively decreased except in the region directly surrounding the lumen, and this fibronectin immunoreactivity was sensitive to hyaluronidase treatment. These changes are likely to reflect the degradation and subsequent remodeling of the previously stable uterine extracellular matrix in preparation for embryonic implantation. A+, B-, V + fibronectin mRNAs were present in both the non-pregnant and day 6 pregnant uterus with increased content of A+ and V+ fibronectin mRNAs in the latter. A + fibronectin mRNA was distributed throughout the endometrial stroma of the non-pregnant uterus and content of the subepithelial stroma increased by day 4 of pregnancy, coincident with progesterone action on the endometrium. On day 6 of pregnancy, fibronectin mRNAs encoding the V95 and A regions were preferentially localized to the mesometrial zone of the subepithelial stroma. Accumulation of these mRNA splicing variants at the mesometrial zone was dependent upon decidualization, but the embryo was not required. Thus, there are two major changes in uterine fibronectin gene expression as a result of pregnancy: increased fibronectin mRNA content and mesometrial localization. These changes suggest a key function for fibronectin in implantation and imply the operation of a regulatory program of fibronectin gene expression which depends on hormonal sensitization and a nidatory stimulus.

Dynamic changes in the functional characteristics of the interstitial fibroblast during lung repair

To evaluate the mechanisms involved in the regulation of fibroblast function during the repair of fibrotic lung injury, we isolated lung fibroblasts from adult male Fischer-344 rats before the induction of severe unilateral paraquat lung injury, as well as 1 and 14 days later. Fibroblasts were utilized at an early generation time to avoid senescence. In general, fibroblasts of injured lungs displayed significant increases in proliferative and matrix synthesis properties, with more pronounced increases detected early after the induction of injury. This was true of DNA synthesis, which increased by 3- and 1.4-fold on days 1 and 14, respectively; tyrosine kinase activity, which increased by 4- and 3.5-fold; fibronectin synthesis, 14- and 8-fold, respectively; and glycosaminoglycans synthesis, 4.4- and 3-fold, respectively. The increase in function of fibroblasts isolated from the immediate influence of extrinsic growth factors suggests that fibroblast function during repair may be under intrinsic as well as extrinsic control. In the early phases of repair, intrinsic changes may be more dominant and may result in autoregulation of fibroblast function. In the later phases of repair, despite some reduction in intrinsic fibroblast activation, exposure to extrinsic growth factors may result in maintaining the state of activation and in sustaining the repair process.

Biological effects of glucocorticoid hormones on two rat colon adenocarcinoma cell lines

Glucocorticoid hormones are thought to play a role in carcinogenesis as they regulate cell differentiation and proliferation. We have investigated the effect of dexamethasone on two cell lines derived from a colon carcinoma, which differ by their tumorigenicity. Dexamethasone was found to inhibit growth of both the progressive (PROb) and the regressive clone (REGb). Upon glucocorticoid treatment, PROb cells were found to secrete an additional Mr approximately 40,000 protein. The synthesis and the release in the culture medium of this protein is stimulated specifically by glucocorticoid agonists, and not by other steroid hormones. The anti-glucocorticoid RU 38486 is inefficient and suppresses the induction of this protein by dexamethasone. Induction is sensitive to actinomycin D, suggesting that regulation may be related to an alteration of the rate of mRNA synthesis. The cellular effect of glucocorticoid hormones being mediated through a specific soluble receptor, we have characterized this protein. The PROb cells contained more specific glucocorticoid-binding sites (approximately 170,000 sites per cell) than the regressive ones (REGb cells; approximately 100,000 sites per cell). In both clones, the receptor was associated with the Mr approximately 90,000 heat shock protein to yield large complexes (Stokes radius Rs approximately 7.5 nm), which were dissociated to the same extent upon heat- and salt-treatment. The steroid- and DNA-binding unit of the receptor, characterized under denaturing conditions using an anti-receptor monoclonal antibody, was found to be more degraded in the PROb cell line.

G1/S control of anchorage-independent growth in the fibroblast cell cycle

We have developed methodology to identify the block to anchorage-independent growth and position it within the fibroblast cell cycle. Results with NRK fibroblasts show that mitogen stimulation of the G0/G1 transition and G1-associated increases in cell size are minimally affected by loss of cell anchorage. In contrast, the induction of G1/S cell cycle genes and DNA synthesis is markedly inhibited when anchorage is blocked. Moreover, we demonstrate that the anchorage-dependent transition maps to late G1 and shortly before activation of the G1/S p34cdc2-like kinase. The G1/S block was also detectable in NIH-3T3 cells. Our results: (a) distinguish control of cell cycle progression by growth factors and anchorage; (b) indicate that anchorage mediates G1/S control in fibroblasts; and (c) identify a physiologic circumstance in which the phenotype of mammalian cell cycle arrest would closely resemble Saccharomyces cerevisiae START. The close correlation between anchorage independence in vitro and tumorigenicity in vivo emphasizes the key regulatory role for G1/S control in mammalian cells.

c-fos oncogene expression in dexamethasone stimulated osteogenic cells in chick embryo periosteal cultures

Although the complex effects of glucocorticoids on bone cells have been studied extensively in vitro, little is known about the molecular mechanisms of glucocorticoid responses in osteogenic cells. As c-fos and its protein product are believed to play a key role in intracellular signal transduction, and since their role in regulation of bone formation is well-recognized, we studied the effect of the glucocorticoid analogue dexamethasone (DEX) on the expression of c-fos oncogene in the chick periosteal osteogenesis (CPO) model. C-fos mRNA expression was determined by in situ hybridization at various time points after 10(-7) M DEX treatment. Prior to DEX treatment, the cultures had been synchronized with 2 mM thymidine. The mean area of positively hybridized cells in experimental (DEX-treated) and control (DEX-free) cultures was quantitated by computer assisted morphometry. In DEX-treated cultures c-fos mRNA could be detected transiently and mainly in the osteogenic layer at 30, 45 and 60 min after treatment whereas no c-fos expression could be detected above background level in the control groups. Differences between experimental and control groups were significant (P less than 0.01) as determined by a general linear model (GLM) analysis of variance. These data indicate that in the CPO culture system, DEX (10(-7) M) induces c-fos expression. The findings are compatible with the hypothesis which states that glucocorticoid-induced phenotypic changes in osteogenic cells may be mediated by c-fos.

Dexamethasone modulates alpha 2-macroglobulin and apolipoprotein E gene expression in cultured rat liver fat-storing (Ito) cells

Fat-storing (Ito) cells are perisinusoidal liver cells thought to play a central role in vitamin A metabolism and fibrongenesis. Glucocorticoids have been shown to be beneficial in the treatment of certain types of liver diseases by delaying the development of cirrhosis. To study the regulatory effects of dexamethasone on Ito cell gene expression, Ito cells were isolated from normal rat liver and primary cultures were established. The effect of dexamethasone on the synthesis of alpha 2-macroglobulin, apolipoprotein E, fibronectin and actin was examined. Protein synthesis was studied both at the protein level and at the RNA level by means of biosynthetic labeling, immunoprecipitation followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by Northern blot analysis of total RNA. After exposure to dexamethasone for 20 hr, alpha 2-macroglobulin protein synthesis was increased threefold, whereas apolipoprotein E expression was decreased 80%. Biosynthesis of fibronectin remained unaffected by hormone treatment. The dexamethasone effect became detectable 5 hr after beginning the exposure. Deinduction kinetic experiments showed that the glucocorticoid effect was detectable more than 12 hr after the replacement of the dexamethasone-containing culture medium by medium without the hormone. Corresponding to the data obtained at the protein level, dexamethasone increased the steady-state levels of alpha 2-macroglobulin-specific messenger RNA and reduced apolipoprotein E-specific transcripts, whereas fibronectin and actin messenger mRNA remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

New aspects of the mechanism of corticosteroid-induced dermal atrophy

Glucocorticoids are effective for the treatment of various inflammatory skin diseases, but their long-term use may lead to serious side-effects such as osteoporosis and skin atrophy. The incidence of skin atrophy following application of potent corticosteroids is especially high among children and the elderly. During recent years the effects of glucocorticoids on connective tissue have been elucidated, and it is evident that skin atrophy is mostly due to a decrease in collagen synthesis. Since collagen is the most abundant protein in the skin, the inhibition of its synthesis leads to atrophy. This review discusses the molecular mechanisms of glucocorticosteroid-induced skin atrophy and therapeutic possibilities.

Glucocorticoid receptors in human malignancies: a review

The present knowledge of the human glucocorticoid receptor (hGCR) in primary malignancies is reviewed. It is concluded that hGCR is present in a large number of these tissues; in all tissue specimens of lymphoid malignancies and in varying fractions of the different solid tumors. The hGCR functions as a hormone dependent, specific enhancer interacting protein in mediating the considerable effects of glucocorticoids on growth regulation, both through stimulation and inhibition of expression of the target genes, including other transcription regulation systems. The processes of receptor activation and regulation, as well as the effects of glucocorticoids, are tissue-specific. Subjects for future research are proposed: Establishment of more cell lines and animal models to extend investigation beyond the present concentration on only a few cell lines, especially CEM-C7, application of 'dynamic' assays to cells obtained from patients, in an attempt to predict development of glucocorticoid resistance, and further investigation of the relationships among GCR and growth factors and oncogenes.

A secreted Mr approximately 40,000 glycoprotein specifically induced by glucocorticoids in a rat colon carcinoma cell line

Glucocorticoid hormones are thought to play a role in carcinogenesis, as they regulate cell differentiation and proliferation. We have previously shown that dexamethasone inhibits the growth of a rat colon carcinoma cell line, and induces the secretion of an Mr approximately 40,000 protein. We now report that the synthesis and the release in the culture medium of this protein is stimulated specifically by glucocorticoid agonists, and not by other steroid hormones. The anti-glucocorticoid RU 38486 is inefficient and suppresses the induction of this protein by dexamethasone. Induction is sensitive to actinomycin D, suggesting that regulation may be exerted by altering the rate of mRNA synthesis. Characterization of culture medium from dexamethasone-treated cells revealed that the Mr approximately 40,000 protein is glycosylated, and can be further separated from other secreted proteins by high-performance anion-exchange chromatography.

Bidirectional morphological changes induced by dexamethasone in Morris hepatoma cell lines McA-RH7777 and McA-RH8994: independence of fibronectin and its receptor

Two Morris hepatoma-derived cell lines, McA-RH7777 (7777) and McA-RH8994 (8994), exhibit different alterations in morphology upon exposure to glucocorticoid. After treatment with synthetic glucocorticoid dexamethasone (DEX), 7777 cells show increased adhesiveness and more flattened shape, while DEX-treated 8994 cells show decreased adhesiveness to substratum and exhibit a marked increase of round and detached cells. Since fibronectin has been thought to play an important role in cell adhesiveness to substratum in hepatoma cell culture, we have also compared the effects of DEX on the biosynthesis of fibronectin (FN) and the functional level of FN receptor in 7777 and 8994 cells. Northern blot analysis and immunofluorescent studies showed that 7777 cells have a high basal expression level of FN synthesis and that DEX treatment induces FN expression two- to threefold with establishment of an extensive fibrillar FN network around the cells. On the other hand, 8994 cells were shown to express little FN and no apparent FN was localized on nonstimulated 8994 cells. However, DEX-treatment drastically increased FN expression in 8994 cells to the level of more than that of DEX-treated 7777 cells and induced a detectable level of cell-associated FN around DEX-treated 8994 cells, which appears to be contradictory to the decreased adhesiveness to the substratum in DEX-treated 8994 cells. Cell attachment assays using FN-coated plates demonstrated that DEX does not exhibit significant effects on the attachment of either 7777 or 8994 cells to FN-coated dishes. Our results suggest that decrease of adhesiveness to the substratum and increase of round detached cells in DEX-treated 8994 cells are independent of changes in the FN expression and the function of FN receptor.

Production of fibronectin by human tumor cells and interaction with exogenous fibronectin: comparison of cell lines obtained from colon adenocarcinomas and squamous carcinomas of the upper aerodigestive tract

Cell lines derived from 13 different human colon adenocarcinomas were examined for production of fibronectin by ELISA and for cell-surface expression of fibronectin by indirect immunofluorescence. Two squamous epithelial cell lines obtained from tumors of the upper aerodigestive tract were used as controls. None of the 13 colon carcinoma lines produced detectable amounts of fibronectin or showed detectable cell-surface staining with anti-fibronectin. The 2 squamous epithelial cell lines, in contrast, produced large amounts of fibronectin which could be detected in the culture medium and bound to the substratum. The squamous carcinoma cells also stained brightly when examined in the viable state by immunofluorescence with anti-fibronectin. In addition to being studied for fibronectin production, each cell line was also examined for the ability to interact with exogenous fibronectin in an adhesion assay. None of the colon carcinoma cells were adherent to fibronectin-coated culture dishes while the 2 squamous carcinoma cells rapidly attached and spread on this substratum. These data suggest that cell lines derived from adenocarcinomas of the colon are deficient in production of fibronectin and in their ability to interact with exogenous fibronectin. In their degree of deficiency, the colon carcinoma cells are significantly different from several different types of human tumor cell. The failure of the colon carcinoma cells to synthesize detectable amounts of fibronectin endogenously or to interact with exogenous fibronectin may explain, in part, the low degree of adhesive interaction which these cells have for their substratum. This, in turn, may influence the in vitro and in vivo properties of colon carcinoma cells.

Procedure for the purification of the fibronectin proteolytic fragments containing the ED-B oncofetal domain

Fibronectin (FN) is the blend of structurally different molecules (isoforms) whose makeup varies depending on the FN sources. Fibronectin polymorphism is caused by three sequences (called ED-A, ED-B, and IIICS) which may be included or excluded from the FN molecule depending on the alternative splicing patterns of a single primary transcript. The sequence ED-B, which is a complete type III repeat of 91 amino acids, presents some interesting peculiarities: it is the most conserved FN region and, in normal adult tissues, the ED-B-containing FN has an extremely restricted distribution while having a much greater expression in fetal and tumor tissues (Carnemolla et al., 1989, J. Cell Biol. 108, 1139-1148), suggesting that the ED-B sequence may confer to the FN molecules specific biological activities required during ontogenesis and oncogenetic processes. Here we describe a detailed procedure to purify fibronectin fragments containing the ED-B sequence. These purified fragments are useful reagents in the study of the biological function(s) of the ED-B-containing FN molecules.

Plasminogen activator inhibitor type I stabilizes vitronectin-dependent adhesions in HT-1080 cells

Polyclonal antibodies against plasminogen activator inhibitor type-I (PAI-1) caused rapid retraction and rounding of substrate-attached HT-1080 cells. The kinetics and extent of antibody-mediated cell rounding were not dependent on either urokinase or plasmin activity. Cells adherent to vitronectin-coated substrates detached within 2 h of antibody addition. Cells adherent to fibronectin were unaffected by the antibodies. Immunoblotting of substrate-attached material indicated that HT-1080 cells deposited PAI-1 into vitronectin, but not fibronectin, dependent contacts. These data suggest that the antibody-mediated cell rounding resulted from a steric disruption of vitronectin-dependent adhesions, indicating that the binding site on vitronectin for PAI-1 is near, but does not overlap, the binding site for vitronectin receptor. The accumulation of PAI-1 into vitronectin-dependent adhesion sites correlated temporally with the preferential degradation of fibronectin from the substrate. HT-1080 cells adherent to either fibronectin or vitronectin were able to activate exogenous plasminogen to plasmin. Plasmin levels were increased 200% on cells adherent to fibronectin and 100% on cells adherent to vitronectin. In the presence of a neutralizing antibody against PAI-1, vitronectin adherent cells activated plasminogen to the same extent as fibronectin adherent cells. Plasmin levels of 200% above baseline were associated with retraction of cells from the substrate. The ability of vitronectin adherent cells to activate exogenous plasmin was completely blocked in the presence of neutralizing antibodies against urokinase. These data represent the first demonstration that vitronectin-associated PAI-1 regulates urokinase in focal contact areas.