Jacques Marvaldi

Cdx1 promotes differentiation in a rat intestinal epithelial cell line

BACKGROUND & AIMS Homeobox genes are involved in establishing and maintaining differentiated patterns in adult tissues. Cdx1 might carry out that function in the intestinal epithelium because its expression is specific to that tissue and increases during development. METHODS Cdx1 expression was induced in IEC-6 intestinal epithelial cells by stable transfection, and subsequent changes in cell growth, resistance to apoptosis, migration, and differentiation were monitored. RESULTS Compared with control, IEC-6/Cdx1 cells proliferated more rapidly, were more resistant to apoptosis, and migrated 3-4 times faster, as shown by an in vitro wound assay. IEC-6/Cdx1 cells in culture formed multilayers. Morphology of the top layer was similar to that of columnar epithelium, with cells showing typical features of differentiated enterocytes, including complex junctions and well-developed microvilli with glycocalix. Expression of 2 markers of enterocyte differentiation, aminopeptidase N and villin, was induced in IEC-6/Cdx1 cells. Aminopeptidase N was targeted to the basolateral membrane, and villin was localized to the cytoplasm. Actin filaments, which were mostly present in transcytoplasmic stress fibers in control cells, were redistributed to the cortex in Cdx1-transfected cells. CONCLUSIONS Cdx1 expression in IEC-6 cells induces phenotypic changes characteristic of differentiating enterocytes, suggesting an important role for Cdx1 in the transition from stem cells to proliferating/transit cells.

Integrins and E-cadherin cooperate with IGF-I to induce migration of epithelial colonic cells.

Although the detailed mechanisms of cell migration remain largely unknown, it is now clear that growth factors and cell adhesion molecules are crucial for this process. We have shown that type I insulin‐like growth factor (IGF‐I) promotes migration of human colonic tumour cells. Since morphological analysis suggested an involvement of adhesion molecules, we have now examined the role of integrins (cell‐matrix adhesion molecules) and E‐cadherin/catenins complex (cell‐cell adhesion molecules) in the IGF‐I‐induced migration. Using a monolayer wounding assay, we have determined that, except for α2β1, all of the integrins expressed in HT29‐D4 cells are involved in the induced cell migration. Immunofluorescence studies revealed that upon IGF‐I stimulation the integrins reorganized at the leading edge of migrating cells. We also demonstrate that E‐cadherin is involved in cell migration. A rapid tyrosine phosphorylation of E‐cadherin and β‐catenin was detected upon IGF‐I stimulation. Tyrosine phosphorylation was associated with reduced membranous expression of E‐cadherin and promotion of cell motility, suggesting a regulation of the E‐cadherin/catenins complex. This effect can be reversed by incubating cells with tyrosine kinase inhibitors. Taken together, our results suggest that IGF‐I promotes colonic cell migration through reorganization of integrin receptors and through modulation of E‐cadherin/catenins complex function. Int. J. Cancer 83: 497–505, 1999.

Protein kinases C-γ and -δ are involved in insulin-like growth factor I–induced migration of colonic epithelial cells

Abstract Background & Aims: The mechanisms by which epithelial cells migrate during the repair of damaged colonic mucosa are poorly understood. This study investigated the insulin-like growth factor I (IGF-I) signaling pathway leading to HT29-D4 human colonic epithelial cell line migration. Methods: IGF-stimulated cell migration was determined using a wound model in the presence or absence of kinase inhibitors. Activation of protein kinase C (PKC) was determined by immunodetection. Results: IGF-I and insulin induce cell migration without affecting cell proliferation through their cognate receptors. Des(1-3)-IGF-I, a truncated analogue of IGF-I, was more potent than IGF-I, suggesting that IGF-binding proteins secreted in the medium modulated IGF-I–induced cell migration. Inhibition of phosphatidylinositol 3-kinase, PKC, and mitogen-activated protein kinases eliminated cell restitution. Long-term exposure of cells to phorbol myristate acetate caused the depletion of PKC-δ and -γ and prevented also IGF-I–induced cell motility. IGF-I also induced activation of PKC-δ and -γ only. Conclusions: IGF-I stimulates colonic restitution through the activation of multiple signaling pathways including activation of phosphatidylinositol 3-kinase, PKC-δ and -γ, and mitogen-activated protein kinases. GASTROENTEROLOGY 1999;116:64-77

Migration properties of the human ovarian adenocarcinoma cell line IGROV1: Importance of αvβ3 integrins and vitronectin

Cell migration of ovarian tumoral cells is essential for cell dissemination and for invasion of the submesothelial extracellular matrix (ECM). We have conducted a study of the migratory properties of an ovarian adenocarcinoma cell line (IGROV1) by using 2 distinct methods for the evaluation of cell migration. We found that in a short‐term transfilter migration assay, IGROV1 cells migrated toward vitronectin, fibronectin, type IV collagen and laminin in an integrin‐dependent manner. When migration was evaluated in a wound healing assay, the restitution of the wounded area was stimulated solely by added, exogenous vitronectin and was almost totally dependent on αvβ3 integrin function. Moreover, we demonstrated that αvβ3 was localized in focal contacts restricted to the leading edge of migrating cells, whereas vitronectin notably localized with actin stress fibers and cortical actin. On the other hand, several kinase inhibitors were found to impede migration of IGROV1 induced by vitronectin. It thus appears that αvβ3–vitronectin interactions lead to the activation of multiple signaling pathway including activation of protein kinase C, phosphatidyl‐inositol‐3‐phosphate kinase and protein tyrosine kinase. The “αvβ3–vitronectin system” is therefore essential to the migration of human ovarian carcinoma cells.Int. J. Cancer 80:285–294, 1999.

Role of Endoproteolytic Processing in the Adhesive and Signaling Functions of αvβ5 Integrin

Some integrin α subunits undergo a post-translational cleavage in their extracellular domain. However, the role of this cleavage in integrin function is unclear. Enzymes involved in this maturation belong to the subtilisin-like endoprotease family (convertases). To understand the role of the α subunit cleavage in integrin function, we have designed stable transfectants (PDX39P cells) expressing α1-PDX, a convertase inhibitor. Immunoprecipitation of cell surface proteins from PDX39P showed that α3, α6 and αvintegrins lack endoproteolytic cleavage. We have compared adhesion between PDX39P cells and mock-transfected cells on different extracellular matrix proteins. No difference in adhesion could be observed on laminin-1 and type I collagen, while attachment of PDX39P cells to vitronectin (ligand of the αvβ5integrin) was dramatically reduced. The reduced adhesion of PDX39P cells was not due to changes in integrin affinity as determined by solid-phase receptor assay in a cell-free environment. Intracellular signaling pathways activated by αv integrin ligation were also affected in PDX39P cells. It thus seems that the absence of endoproteolytic cleavage of αv integrins has important consequences on signal transduction pathways leading to alterations in integrin function such as cell adhesion.

The vasoactive intestinal peptide (VIP) receptor: recent data and hypothesis

Vasoactive intestinal peptide (VIP) is a neuropeptide with a broad range of biological activities in various tissues. After interaction with its membrane receptor, VIP generally induces a very large increase in the intracellular cyclic AMP level. Receptors for VIP have been described in numerous tissues and cell lines. The first results on VIP receptor structure have been obtained by covalent cross-linking using bifunctional reagents. The molecular mass of the different components characterized in this way differs greatly according to the species and the tissue used. This heterogeneity may reflect either a difference in the length of the cross-linked polypeptide backbone or differently glycosylated forms of the same polypeptide. The VIP binding site of intact human adenocarcinoma cells (HT29 cells) is an Mr 64,000 glycoprotein with 20kDa of N-linked oligosaccharide side chains containing sialic acid. The structure of the VIP binding site from HT29 cell is compared, first to the structure of the VIP receptor from other tissues, particularly that from rat liver, and second to the structure of the hepatic glucagon binding site. Recently, solubilization of the VIP receptor in an active form has provided a new way of studying this receptor. The HT29 cell line is an appropriate model to study the dynamics of the VIP receptor. After binding to its receptor, VIP is rapidly internalized, probably by receptor-mediated endocytosis. This internalization leads to a decrease in the cell surface receptor number and simultaneously to a homologous desensitization of adenylate cyclase. VIP is then degraded in the lysosomes, while most of the receptors are recycled back to the cell surface. The presence of an intracellular pool of unoccupied VIP receptors has been demonstrated after inactivation of the cell surface receptors by chymotrypsin. The kinetics of the receptor reappearance at the cell surface, after inactivation by chymotrypsin or after receptor-mediated endocytosis, indicate 2 possible intracellular pathways for occupied and unoccupied VIP receptors.

Lebectin, a Macrovipera lebetina venom‐derived C‐type lectin, inhibits angiogenesis both in vitro and in vivo

Integrins play an essential role in endothelial cell motility processes during angiogenesis and thus present interesting targets for the development of new anti‐angiogenic agents. Snake venoms naturally contain a variety of proteins that can affect integrin–ligand interactions. Recently, the C‐type lectin proteins (CLPs) have been characterized as efficient modulators of integrin functions. In this study, we investigated the anti‐angiogenic activity of lebectin, a newly discovered CLP from Macrovipera lebetina venom. Human brain microvascular endothelial cells (HBMEC), used as an in vitro model, express αvβ3, αvβ5, and α5β1 integrins, as well as the α2, α3, α6, and β4 subunits. Our data show that lebectin acts as a very potent inhibitor (IC50 ≈ 0.5 nM) of HBMEC adhesion and migration on fibronectin by blocking the adhesive functions of both the α5β1 and αV integrins. In addition, lebectin strongly inhibits both HBMEC in vitro tubulogenesis on Matrigel™ (IC50 = 0.4 nM) and proliferation. Finally, using both a chicken CAM assay and a Matrigel™ Plug assay in nude mice, our results show that lebectin displays potent anti‐angiogenic activity in vivo. Lebectin thus represents a new C‐type lectin with anti‐angiogenic properties with great potential for the treatment of angiogenesis‐related diseases. J. Cell. Physiol. 211: 307–315, 2007.

Modulation of P-glycoprotein function by sphingosine kinase-1 in brain endothelial cells

P‐glycoprotein (P‐gp), an ABC‐transporter highly expressed in brain capillaries, protects the brain by extruding xenobiotics. However, its overexpression has also been associated with the multidrug resistance phenotype in tumors. Here, we have investigated the regulation of P‐gp transport activity by sphingosine kinase 1 (SphK‐1) in brain endothelial cells. We first demonstrated that SphK‐1 is overexpressed in endothelial cells (EC) isolated from rat brain tumors compared with EC from normal brain. We also provide evidence that the overexpression of SphK‐1 in the cerebral EC line RBE4 leads to the up‐regulation of P‐gp, both at the gene and protein levels, and that this modulation depends on the catalytic activity of SphK‐1. Moreover, we determined the effect of sphingosine‐1‐phosphate (S1P), the product of SphK‐1, on P‐gp function. S1P strongly stimulates P‐gp transport activity, without modulating its expression. Finally, we found that the S1P‐mediated stimulation of P‐gp activity is mediated by S1P‐1 and S1P‐3 receptors at the RBE4 cell surface. Altogether, these results indicate that SphK‐1 and its product S1P are involved in the control of P‐gp activity in RBE4 cells. Since SphK‐1 is overexpressed in EC from brain tumors, these data also suggest that this kinase and its product could contribute to the acquisition and the maintenance of the multidrug resistance phenotype in brain tumor‐derived endothelial cells.

Lebecetin, a potent antiplatelet C-type lectin from Macrovipera lebetina venom.

A novel C-type lectin protein (CLP), lebecetin, was purified to homogeneity from the venom of Macrovipera lebetina by gel filtration on a Sephadex G75 column and ion exchange chromatography on Mono S column. Lebecetin is a basic protein with a pHi=9.9 and migrates in SDS-PAGE as a single band or two distinct bands under nonreducing and reducing conditions, respectively. These results are further confirmed by MALDI-TOF mass spectrometry that indicates a molecular mass of 29779 Da for native lebecetin and molecular masses of 15015 and 16296 Da for alpha and beta subunits, respectively. The N-terminal amino acid sequences of lebecetin subunits show a high degree of similarity with those of C-type lectin-like proteins. In addition, functional studies showed that lebecetin has a potent inhibitory effect on platelet aggregation induced by thrombin in a concentration-dependent manner. In contrast, no inhibitory effect is observed when platelets are exposed to thromboxane A2 (TxA2) mimetic (U46619) or arachidonic acid. Moreover, there was no effect either on blood coagulation or A, B and O washed human erythrocytes agglutination. Furthermore, flow cytometric analysis revealed that fluoro-isothiocyanate (FITC)-labelled lebecetin bound to human formalin fixed platelets in a saturable and concentration manner and this binding was specifically prevented by anti-glycoprotein Ib (GPIb) mAb. These observations suggest that lebecetin is a C-type lectin-like protein that selectively binds to platelet GPIb.

Inhibition of Proprotein Convertases Enhances Cell Migration and Metastases Development of Human Colon Carcinoma Cells in a Rat Model

Although proprotein convertases are involved in tumor development, nothing is known about their role in metastatic dissemination. To investigate the involvement of convertase inhibition, we used human colon carcinoma cells overexpressing alpha1-antitrypsin Portland (alpha1-PDX, PDX39P cells), a potent convertase inhibitor. We previously reported that these cells bear uncleaved integrin alpha subunits and display an altered attachment to vitronectin that is correlated with defects in the intracellular signaling pathways activated by alphavbeta5 integrin ligation. In this study, we demonstrate that the inhibition of proprotein convertase activity either by overexpression of alpha1-PDX or with the synthetic inhibitor decanoyl-Arg-Val-Lys-Arg-chloromethylketone (dec-RVKR-cmk) led to a significant increase in cell migration supported by the alphavbeta5 integrin. A collagen gel invasion assay showed that PDX39P cells also displayed an invasive ability, contrary to control cells. Moreover, when injected to immunosuppressed newborn rats, PDX39P cells were highly invasive, as they induce 10 times more metastases than mock-transfected cells. In addition, the aggressiveness of PDX39P cells can be greatly reduced by a function-blocking monoclonal antibody (mAb) against the alphav subunit. It thus seems that inhibition of proprotein convertases enhances the in vivo invasiveness of colon tumor cells likely due to an increase in cell migration mediated by alphav integrins.