PubMed Health⌕ Search

Biomedical subjects

R Chammas

Publications and source records attributed to R Chammas.

At least 37 records · Page 2Linked to original sources
PubMed1995

The thymic nurse cell complex: an in vitro model for extracellular matrix-mediated intrathymic T cell migration.

The thymus is a primary lymphoid organ in which bone marrow-derived T cell precursors undergo a complex maturation process in the context of the thymic microenvironment, represented by non-lymphoid cells and extracellular matrix (ECM) components. The thymic epithelial cells are the major cellular component of the thymic microenvironment, and influence different aspects of thymocyte differentiation, via cell-cell interactions and secretions of soluble factors, such as thymic hormones. The thymic nurse cell (TNC) complexes are multicellular lymphoepithelial structures formed by one thymic epithelial cell harboring 2-200 thymocytes, primarily bearing the CD4/CD8 double-positive phenotype. TNCs probably create a special microenvironment for thymocyte differentiation and/or proliferation, with thymocytes being exposed to major histocompatibility complex (MHC) antigens and thymic hormones. Such differentiation parallels cell migration into and out of the complex. We showed the expression of ECM components and respective receptors by TNCs, and that interactions between the epithelial component of TNC and TNC-lymphocytes can be modulated by ECM components and respective receptors. Moreover, we demonstrated that intrinsic as well as extrinsic biological circuits can be involved in the control of such ECM-mediated thymic epithelial cell (TEC)/thymocyte interactions. For example, interferon-gamma can biphasically modulate the expression of ECM ligands and receptors by TEC, which results in corresponding modulation of their ability to interact with TNC-thymocytes. Additionally, hormones such as triiodothyronine, prolactin and growth hormone can influence the degree of these lymphocyte/epithelial cell adhesive interactions. Lastly, we recently furnished evidence for a de-adhesive mechanism within TNC apparently mediated by galectin 3 (an endogenous soluble beta-galactoside-binding lectin).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Extracellular matrix components of the mouse thymus microenvironment. IV. Modulation of thymic nurse cells by extracellular matrix ligands and receptors.

Extracellular matrix (ECM) proteins can influence cell migration and differentiation in a variety of cell systems. Within the thymus, these molecules are heterogeneously distributed, and their physiological role is poorly understood. This prompted us to carry out in vitro studies using the thymic nurse cell (TNC) model. We observed that fibronectin and laminin accelerate spontaneous in vitro release of thymocytes from TNC, whereas anti-ECM antibodies exhibited a blocking effect. Similar results were obtained with anti-ECM receptor reagents. Moreover, these antibodies abrogated in vitro reconstitution of TNC complexes and thymocyte adhesion to TNC-derived epithelial cultures. Our results indicate that lymphocyte traffic in TNC (comprising both entrance into and exit from the epithelial structure) is affected by interactions involving extracellular matrix ligands and receptors. In this respect, the dynamic analysis of thymic nurse cell complexes should be regarded as a relevant in vitro tool for functional studies of distinct adhesion molecules in intrathymic lymphocyte traffic.

Animals↗
PubMed1994

Regulation of vitronectin receptor expression by retinoic acid on human melanoma cells.

The integrin family of adhesion receptors is likely to be important for tumor cell invasion and dissemination. We have studied the effects of the differentiating agents retinoic acid on integrin expression by the human melanoma cell line MeWo. Our results show that this agent inhibits cellular proliferation, increases melanin content and induces morphological changes in MeWo cells. Functionally, these alterations are associated with an enhanced adhesion to matrix protein vitronectin and higher levels of expression of vitronectin receptor on the cell surface. This is accompanied by increased levels of alpha v integrin mRNA. Although the mechanism by which retinoic acid regulates the expression of vitronectin receptor in MeWo cells needs further examination, this system may represent a good model for understanding the role of this receptor in melanoma progression, as well the molecular basis for retinoic acid therapy in these tumors.

Blotting, Northern↗
PubMed1994

An acidic component of the heterogeneous Tc-85 protein family from the surface of Trypanosoma cruzi is a laminin binding glycoprotein.

Successful infection of mammalian host by trypomastigotes of Trypanosoma cruzi is a complex event, involving host receptors and parasite ligands. Interaction of the trypomastigote stage with laminin, a component of specialized extracellular matrices, as basement membranes, is studied in this report. Binding of 125I-laminin to trypomastigotes is specific and 2-5 x 10(3) laminin binding sites were calculated to be present on the surface of live trypomastigotes. Anti-laminin antibodies were able to inhibit the invasion of cultured cells by trypomastigotes (75-62%), suggesting that laminin may be involved in the adhesion of the parasite to host cells. By affinity chromatography, an 85-kDa glycoprotein was isolated (laminin binding glycoprotein, LBG) from trypomastigote lysates, but not from epimastigote lysates. It is suggested that at least fragment E8 (but not E1') from laminin could be involved in the reaction which is independent of the carbohydrate moieties from both ligand and receptor, as suggested by glycosidase or tunicamycin treatments. It is also shown that LBG is an acidic component of the polymorphic Tc-85 protein family, a trypomastigote-specific surface membrane glycoprotein which contains several polypeptides recognized by the monoclonal antibody H1A10, and previously related with the invasion process of the parasite.

Animals↗
PubMed1994

Laminin and tenascin assembly and expression regulate HC11 mouse mammary cell differentiation.

HC11 is a normal mouse mammary epithelial cell line that requires certain growth factors, such as EGF or bFGF, to respond optimally to lactogenic hormones and produce the differentiation marker beta-casein. Growth in insulin (Ins) or PDGF does not produce cells competent to respond to lactogenic hormones. Here we show that competency for differentiation is due at least in part to the modulation of extracellular matrix components. In particular we have studied laminin and tenascin. EGF alters endogenous laminin assembly. In addition, promotion of competency can be partially mimicked by plating HC11 cells on the E8 laminin fragment, which is able to induce lactogenic responsiveness in cells grown in the absence of EGF or bFGF. The production and assembly of tenascin is also dependent upon the growth conditions of the HC11 cells. EGF- or bFGF-grown competent cells produce tenascin but do not assemble it at the extracellular matrix as efficiently as Ins- or PDGF-grown, non-competent cells. This alteration apparently leads to a change in the cellular microenvironment that supports beta-casein production. In addition, when competent cells are plated on dishes coated with tenascin, lactogenic hormone induction of beta-casein is inhibited. The data suggest that tenascin assembly and beta-casein production are opposing features of a coordinated differentiation program of HC11 cells.

Animals↗
PubMed1994

Carbohydrate-binding proteins in cell-matrix interactions.

1. Carbohydrate-dependent interactions have been more extensively studied during the last decade. Although the roles of carbohydrates in cellular functions are still poorly understood, the finding of carbohydrate-binding proteins in animal cells opened a great number of perspectives. 2. Animal lectins are associated with tumor progression, playing a key role in neoplastic cell interactions with endothelial cells and extracellular matrix glycoproteins such as laminin. 3. Here, we review the role of animal lectins in the migrating phenotype of neoplastic cells and normal cells such as T-lymphocytes.

Animals↗
PubMed1994

Adhesion to laminin is down-regulated upon retinoic acid-induced F9 cell differentiation: a role for alpha 6/beta 1 integrin.

F9 mouse teratocarcinoma cells have a high capacity to adhere to laminin and we identified alpha 6/beta 1 integrin as the principal laminin-binding protein present in these cells. F9 cells differentiated into parietal endoderm when monolayer cultures were treated with retinoic acid and dibutyryl cyclic AMP. In this process a decreased adherence to laminin was observed due to a lower expression of alpha 6/beta 1 integrin on the cell surface.

Animals↗
PubMed1994

Trypanosoma cruzi binds to laminin in a carbohydrate-independent way.

The binding of 125I-laminin to trypomastigotes is specific and 2-5 x 10(3) laminin-binding sites were calculated to be present on the surface of a live trypomastigote. Anti-laminin antibodies were able to inhibit the invasion of cultured cells by trypomastigotes (62-75%), suggesting that laminin may be involved in the adhesion of the parasite to host cells. By affinity chromatography, an 85-kDa glycoprotein was isolated (laminin-binding glycoprotein, LBG) from trypomastigote lysates, but not from epimastigote lysates. It is suggested that at least fragment E8 (but not E1') from laminin could be involved in the reaction which is independent of the carbohydrate moieties from both ligand and receptor. It is also shown that LBG is a member of the Tc-85 family, previously shown to be related to the invasion process of the parasite.

Animals↗
PubMed1994

Functional hypotheses for aberrant glycosylation in tumor cells.

Aberrant glycosylation is a common feature of neoplastic cells. Although described for many years, the role of aberrant patterns of glycosylation is not fully understood. Our group has been focusing on the role of glycosylation in cell:matrix interactions, such as adhesion, spreading and migration on defined substrata (e.g., laminin and fibronectin). Animal lectins, such as galaptins, also seem to be involved in these processes.

Animals↗
PubMed1993

Functionally distinct roles for glycosylation of alpha and beta integrin chains in cell-matrix interactions.

Laminin interaction with gp120/140, a B16-F10 laminin-binding protein immunologically related to alpha 6 beta 1 integrin, has been shown to be dependent on oligosaccharides from both ligand and receptor. Lectin analysis of gp120/140 led to the conclusion that this integrin is a sialoglycoprotein bearing mainly complex antennary structures. By means of exoglycosidase treatment, it was possible to identify alpha-galactosyl residues on the integrin alpha chain as the laminin-binding determinants. These residues are involved in cell adhesion to laminin. On the other hand, beta-chain complex antennary structures, whose synthesis could be inhibited by swainsonine, were associated with cell spreading rather than cell adhesion. Thus, it was possible to modulate integrin-mediated cell adhesion and spreading through changes in the glycosylation state of integrin alpha and beta chains.

Animals↗
PubMed1993

Extracellular matrix components of the mouse thymic microenvironment. III. Thymic epithelial cells express the VLA6 complex that is involved in laminin-mediated interactions with thymocytes.

We describe herein the expression of the VLA6 complex by murine thymic epithelial cells (TEC). The immunohistochemical distribution revealed that VLA6 is found in both thymic medullary and subcapsullary areas. Moreover, studies by immunoelectron microscopy revealed a membrane labeling of the VLA6 molecule, including at desmosomal sites. By means of immunoblotting, immunoprecipitation, and affinity chromatography of extracts from a mouse TEC line, we further demonstrated that VLA6 is a laminin (LN) receptor in these cells. In keeping with this finding, we showed that TEC adhesion, spreading, and proliferation were enhanced in vitro by LN. The fact that VLA6 is also expressed by the large majority of thymocytes raised the hypothesis that it might be involved in LN-mediated TEC-thymocyte interactions. Interestingly, in vitro experiments showed that there is an increase in the TEC-thymocyte adhesion upon glucocorticoid hormone treatment, a situation in which the expression of VLA6 as well as LN is enhanced. Most importantly, this adhesion can be reversed by pre-treating TEC with an anti-alpha 6 integrin mAb. Additionally, spontaneous in vitro thymocyte release by thymic nurse cell complexes was enhanced by LN and partially blocked by anti-alpha 6 or anti-beta 1 antibodies. Our results suggest that VLA6 is involved in LN-mediated TEC-thymocyte interactions that can be relevant for thymic microenvironmental cell physiology and intrathymic T cell differentiation events.

Animals↗
PubMed1991

Effects of steroids on laminin-binding integrins in a human melanoma cell line.

The MEL-85 human melanoma cell line was used to investigate the effects of both estradiol and dexamethasone on expression of laminin (LM) receptors and cell adhesion capacity. Immunoblotting of eluates from whole-cell extracts applied to LM Sepharose indicates the presence of an LM-binding protein of 116-130 kDa that reacted with an anti-beta 1 integrin antibody, suggesting that the putative LM receptor of MEL-85 cells is a member of the integrin family. Analysis of 125I-LM binding to whole cells indicates the existence of low-affinity components which display positive co-operativity. LM-fragment-8 competes for this binding to the same extent as unlabelled LM (75%), while fragment PI is inactive and fibronectin (FN) competes by about 30% only. Binding of labelled fragment-8 exhibits a pattern similar to that of intact LM. Cell adhesion to substrates coated with LM and LM fragments closely parallels binding to cells in suspension. MEL-85 cells were estradiol-receptor-negative. Estradiol treatment did not stimulate LM receptor levels or attachment to LM. Growth rate also remained unaltered. To characterize the glucocorticoid dependence of MEL-85 cells, we first established the presence of glucocorticoid receptors and an inhibitory effect on growth rate. Dexamethasone treatment resulted in marked enhancement of adhesion to LM, without altering LM receptor number or affinity. In addition, dexamethasone changed the morphology of MEL-85 cells in conjunction with higher LM expression as evaluated by immunofluorescence.

Cell Adhesion↗
PubMed1991

Asn-linked oligosaccharide-dependent interaction between laminin and gp120/140. An alpha 6/beta 1 integrin.

Receptor-mediated recognition and adhesion to laminin, a specific glycoprotein from basement membranes, exert an important role in many biological phenomena. Studying cell surface proteins of B16-F10, a metastatic murine melanoma cell line, we identified a 120-140 kDa glycoprotein (gp120/140) that binds laminin. This glycoprotein was recognized by a polyclonal antibody raised against the human fibronectin receptor beta 1-integrin chain, as well as immunoprecipitated by an anti-alpha 6 chain (monoclonal antibody GoH3), characterizing it as an alpha 6/beta 1-integrin. Its binding to laminin was specific and displayed moderate affinity, as its apparent dissociation constant was 18 nM. To characterize the influence of carbohydrate moieties on the laminin-gp120/140 interaction, metaperiodate oxidation, metabolic inhibition of glycosylation, and enzymatic deglycosylation studies were performed. Our results indicate that gp120/140 Asn-linked oligosaccharides play a part in this interaction. Reciprocally, both metaperiodate and N-glycanase treatment of native laminin reduced its binding to gp120/140, characterizing the latter as a lectin-like molecule. These results point to glycosylation processes as a possible mechanism for variable binding specificity profiles among integrins.

Animals↗
PubMed1991

Integrins and metastases: an overview.

Metastasis, the major cause of cancer deaths, is represented by a complex, multistep cascade of events characterized by the interaction between neoplastic cells and host tissue elements (cells and extracellular matrix components). These interactions are mediated by specific receptors; among them are members of a growing family of heterodimeric cell surface glycoproteins, called integrins. The role of integrins along tumor progression key steps, as well as their value as diagnostic and prognostic markers are discussed herein. Emphasis on the nature of integrin-ligand interaction is given; in particular, concerning the role of carbohydrate moieties on the generation of diversity in integrin specificity and varying affinity states.

Animals↗