Regulation of integrin-type cell adhesion receptors by cytokines

Upmodulation of alpha v beta 1 integrin expression on human tumor cells by human interleukin for DA cells/leukemia inhibitory factor and oncostatin M: correlation with increased cell adhesion on fibronectin

Integrins belong to a large family of heterodimeric membrane glycoproteins which mediate cell-cell or cell-extracellular matrix interactions. These interactions could play a major role during the migration of tumor cells across the extracellular matrix and vascular endothelium and would thus appear to be requisite for the metastatic process. Pretreatment of the Foss human melanoma cell line with HILDA/LIF or OSM, two cytokines involved in acute-phase response, increased the expression of membrane alpha v beta 1 1.5-2-fold. The same phenomenon was observed on the SK-N-SH human neuroblastoma cell line. alpha v beta 1 upmodulation was concomitant with improved tumor cells attachment to the fibronectin matrix. This greater adhesion of tumor cells to fibronectin was inhibited by specific monoclonal antibodies against alpha v or beta 1 integrin subunits. Similar results were obtained after TNF-alpha treatment. Our findings demonstrate the ability of HILDA/LIF and OSM to modulate tumor cell capacity to adhere to the matrix component, suggesting a potential role for these cytokines in modulation of tumoral progression.

Integrin expression on colorectal tumor cells growing as monolayers, as multicellular tumor spheroids, or in nude mice

In this study we compared the expression of integrin alpha chains 2, 3, 4, 5, 6, v and the beta chains 1, 3, 4 in 2 colorectal carcinoma cell lines (HRT-18 and CX-2), growing in confluent and subconfluent monolayer cultures, as multicellular tumor spheroids and in nude mice, using the immunofluorescence technique (confocal microscopy) and flow cytometry. The fast-growing cell line HRT-18 expressed, in confluent and subconfluent monolayer cultures, alpha 2, 3 and beta 1 with a continuous membranous staining pattern, whereas alpha v, alpha 6, and beta 4 were expressed continuously membranous in the intermediate and apical part of the cell layer, and clustered at focal contacts at the base of the cells. In spheroids and tumors of nude mice the focal pattern of alpha v, 6 and beta 4 was changed into a diffuse one. Using flow cytometry, the expression of alpha 3 was found to be reduced in spheroids of HRT-18. The slowly-growing cell line CX-2 expressed, under the same conditions in monolayer culture, alpha 6, beta 1 and beta 4, and very weakly alpha 2, 3, 5 and v. Alpha 3 was expressed in spheroids of CX-2 only at the outer rim where the cells proliferate. In contrast, alpha 2 and 5 were expressed mainly in the quiescent, non-proliferating area. Alpha 6 was reduced in spheroids of CX-2. In the nude mouse tumor of CX-2, alpha 5 was expressed only focally and very weakly, alpha 2 was no longer detectable, but alpha v appeared to be enhanced in a focal pattern. These data indicate that integrin expression of tumor cells depends upon the culture system and that integrin expression in multicellular tumor spheroids is more similar to the in vivo situation in nude mouse tumors.

Integrin alpha 2 beta 1 is a positive regulator of collagenase (MMP-1) and collagen alpha 1(I) gene expression

A classical model for studying the effects of extracellular matrix is to culture cells inside a three-dimensional collagen gel. When surrounded by fibrillar collagen, many cell types decrease the production of type I collagen, and the expression of interstitial collagenase (matrix metalloproteinase-1; MMP-1) is simultaneously induced. To study the role of the collagen-binding integrins alpha 1 beta 1 and alpha 2 beta 1 in this process, we used three different osteogenic cell lines with distinct patterns of putative collagen receptors: HOS cells, which express only alpha 1 beta 1 integrin, MG-63 cells, which express only alpha 2 beta 1 integrin, and KHOS-240 cells, which express both. Inside collagen gels, alpha 1 (I) collagen mRNA levels were decreased in HOS and KHOS-240 cells but not in MG-63 cells. In contrast, MMP-1 expression was induced in KHOS-240 and MG-63 cells but not in HOS cells. Transfection of MG-63 cells with alpha 2 integrin cDNA in an antisense orientation reduced the expression level of alpha 2 integrin. These cell clones showed induction and reduction of mRNA levels for MMP-1, respectively. HOS cells normally lacking alpha 2 beta 1 integrin were forced to express it, and this prevented the down-regulation in the levels of alpha 1 (I) collagen mRNA when cells were grown inside collagen gels. The data indicate that the level of MMP-1 expression is regulated by the collagen receptor alpha 2 beta 1 integrin. The down-regulation of collagen alpha 1 (I) is mediated by another receptor. Integrin alpha 2 beta 1 may compete with it and thus be a positive regulator of collagen synthesis.

Expression and functional significance of an activation-dependent epitope of the beta 1 integrins in chronic inflammatory diseases

The avidity of VLA integrins for their ligands can be increased by their transition to an active conformational state. This conformational change can be detected with a novel monoclonal antibody (mAb), termed 15/7, that recognizes an activation-dependent conformational epitope on the common beta 1 polypeptide of different VLA alpha beta 1 integrins. In an attempt to understand the possible role of the active conformational state of beta 1 integrins in vivo, we first investigated the expression of 15/7 epitope on T lymphocytes from patients with chronic inflammatory joint diseases. An enhanced expression of the 15/7 epitope was found in the synovial fluid (SF) T lymphocytes from these patients as compared to their peripheral blood (PB) T cells. The effect of different cytokines on the appearance of the 15/7 activation epitope in PB T lymphocytes was subsequently analyzed; interferon-gamma, interleukin-2 and, to a lower extent, tumor necrosis factor-alpha were able to induce an increased expression of the 15/7 epitope. This enhanced 15/7 expression correlated with a higher binding ability to fibronectin of cytokine-activated T cells. The presence of this activation epitope was detected in a small proportion of T lymphocytes scattered within inflammatory foci of synovial membrane from rheumatoid arthritis and thyroid glands from Hashimoto's chronic thyroiditis. We then analyzed the possible role of 15/7 epitope expression on cell adhesion in vitro. Immunofluorescence studies showed that the 15/7 epitope displayed a spot-like distribution, selectively decorating adhesive contacts of U-937 myelomonocytic cells attached to the 80 kDa proteolytic fragment of fibronectin (FN80). Furthermore, the anti-beta 1 15/7 mAb was able to induce both T lymphocyte, Jurkat and U-937 cellular binding and spreading on FN80. Altogether these results indicate that an activated conformation of beta 1 integrins is detected in vivo in lymphocyte infiltrates from chronic inflammatory conditions. The active conformations of beta 1 integrins are regulated by physiologic mediators such as cytokines, play an important role in cellular attachment and spreading, and appear to be involved in the development of inflammatory processes.

Signal transduction pathways in oligodendrocytes: role of tumor necrosis factor-alpha

We have used a combination of electrophysiological and biochemical approaches to investigate the effects and the mechanisms of action of tumor necrosis factor-alpha (TNF-alpha) on cultured oligodendrocytes (OLGs). Our studies have led to the following conclusions: (1) prolonged exposure of mature ovine OLGs to TNF-alpha leads to inhibition of process extension, membrane depolarization and a decrease in the amplitudes of both inwardly rectifying and outward K+ currents; (2) brief exposure of OLGs to TNF-alpha does not elicit membrane depolarization or consistent changes in cytosolic Ca2+ levels; (3) incubation of OLGs with TNF-alpha for 1 hr results in inhibition of phosphorylation of myelin basic protein and 2',3'-cyclic nucleotide phosphohydrolase. Ceramides, which have been shown to be effectors of TNF-alpha, are ineffective in inhibiting phosphorylation, whereas sphingomyelinase mimics TNF-alpha in this action. These observations suggest that other products of sphingomyelin hydrolysis may be the mediator(s) of TNF-alpha effect on protein phosphorylation. We have thus demonstrated that TNF-alpha can perturb the functions of OLGs via modulation of ion channels and of protein phosphorylation without necessarily inducing cell death. It is conceivable that modulation of ion channels and protein phosphorylation constitutes effective mechanisms for the participation of cytokines in signal transduction during myelination, demyelination and remyelination.

Pre-eclampsia is associated with an excess of proliferative immature intermediate trophoblast

Pre-eclampsia/toxemia (PET) is an idiopathic hypertensive disorder of pregnancy elicited in susceptible mothers by exposure to placental trophoblast. Three facts regarding the placenta in PET are known: an association with large placentas (excessive trophoblast), a tendency for superficial implantation, and inappropriate trophoblastic immaturity, as assessed by ultrastructural and biochemical criteria. A unitary hypothesis is that PET is related to a maturation defect leading to excessive accumulation of inappropriately immature intermediate trophoblast in the placental implantation site. We studied the implantation site of PET and control placentas from three gestational age groups (25 to 30, 30 to 35, and 36 to 40 weeks old [five per group]) by morphometry and immunohistochemistry using antibodies to three phenotypic markers (cytokeratin, human placental lactogen (HPL), and beta 2-microglobulin) and two markers of cell dynamics (proliferating cell nuclear antigen [PCNA] and bcl-2]). Implantation sites in the PET group had increased amounts of intermediate trophoblast (cell number and longitudinal extent) with an increased proliferative index (percentage of PCNA positive) and evidence of phenotypic immaturity (HPL negative). Intermediate trophoblast from both groups was uniformly bcl-2 negative and beta 2-microglobulin positive. Based on these data and the findings of other investigators, we propose that the diagnostic term "atypical implantation site" be added to acute atherosis, villous infarction, and increased syncytial knotting as a characteristic of placentas from pre-eclamptic pregnancies.

Integrins and reproduction

The integrins are a large family of cell adhesion receptors, involved in cell-cell and cell-matrix interactions. At present, 20 different integrin heterodimers are known. They not only anchor cells to their proper locations, but also activately mediate the passage of information into the cell. They are involved in such diverse processes as immune response, lymphocyte homing, platelet aggregation, metastatic spread of certain malignancies, healing process of tissue injuries and, embryologic development. The role of integrins in reproduction had been only recently suggested. Several reasons make these molecules very attractive, due to their constant involvement from egg to birth. A normal expression of integrins can disrupt every reproductive stage. Most likely diagnostic tools and therapeutic propositions will emerge from the knowledge of these receptors. Integrins are a family of membrane glycoproteines that mediate cell-substratum or cell-cell adhesion. In respect of one fundamental principle of cellular biology consisting of 'what a cell touches has a major role in determining what a cell does', adhesion has a main part in many cell functions. Adhesion not only anchors cells to their proper locations, but also activately mediates the passage of information into the cell. Cellular adhesion is implicated in the immune response, lymphocyte homing, platelet aggregation, metastatic spread of certain malignancies, embryologic development and wound healing. The role of integrins in reproduction appears interesting. The aim of this review is to introduce these molecules, to outline their roles in cellular function and to consider their involvement in reproduction before foreseeing their potential implications for therapy.

The dynamics of beta 1 integrin expression during peripheral nerve regeneration

The aim of the present study was to examine the expression of beta 1 integrin subunit after peripheral nerve transection. After sciatic nerve transection two experimental procedures were used; changes in the freely regenerating rat sciatic nerve were compared to a situation in which spontaneous regeneration was prevented by suturing both ends of the nerve to the muscle next to the point of transection. Specimens for morphological analysis were collected 6 h, 1, 3, 5, 7 days and 2, 4, 6 and 8 weeks after the axotomy. Sections from the proximal (two zones) and distal (three zones) stumps next to the point of transection were stained with antibodies against beta 1 integrin subunit, macrophages, collagen types I and III, and S-100 protein. The control nerves showed beta 1 integrin-stained cells in the perineurium and vasa nervorum but the endoneurium was negative. Positively stained endoneurial fibroblast-like cells could be seen in the proximal part of the nerve already at 24 h after transection. The number of these positively stained cells increased steadily; they were most numerous 4 weeks after transection in the distal zone 2. Subsequently, the number of positively stained endoneural cells declined sharply and 8 weeks after transection no positively stained cells could be found. The morphological appearance and the immunohistochemical properties of the cells suggest that the majority of beta 1 integrin-positive cells are endoneurial fibroblast-like cells. Thus, the process appeared to be dynamic, starting from the proximal part and continuing to the distal parts, and was similar in both experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Integrin expression by human epidermal keratinocytes can be modulated by interferon-gamma, transforming growth factor-beta, tumor necrosis factor-alpha, and culture on a dermal equivalent

Receptors of the integrin family are largely confined to the basal layer of keratinocytes, both in human epidermis and in stratified cultures of human keratinocytes. However, suprabasal integrin expression is observed during epidermal wound healing and in psoriatic lesions. We have investigated potential stimuli of suprabasal expression. Addition of transforming growth factor-beta (TGF-beta), interferon-gamma (IFN-gamma), or tumor necrosis factor-alpha (TNF-alpha) to keratinocytes cultured with a 3T3 feeder layer did not induce suprabasal expression. The cytokines caused small changes in the levels of alpha 2 beta 1 or alpha 3 beta 1 on the surface of basal keratinocytes but had no significant effect on the proportion of cells adhering to fibronectin, type IV collagen, and laminin, and did not cause changes in the mobility of integrin subunits on polyacrylamide gels. Injection of TNF-alpha or IFN-gamma intradermally into healthy human volunteers induced an inflammatory response but did not induce suprabasal integrin expression. However, we did observe transient suprabasal integrin expression when keratinocytes were grown on a dermal equivalent consisting of fibroblasts in a collagen gel. One week after raising the cultures to the air-liquid interface, beta 1 integrins were found in all the viable cell layers, with suprabasal cells co-expressing integrins and involucrin; 1 week later integrins were confined to the basal layer. Addition of TGF-beta, IFN-gamma, or TNF-alpha to the dermal equivalents neither induced nor inhibited suprabasal integrin expression. We conclude that suprabasal integrin expression is not induced by the inflammatory cytokines tested, and instead may reflect the proliferation/differentiation status of the epidermis.

Transforming growth factor-beta regulates collagen gel contraction by increasing alpha 2 beta 1 integrin expression in osteogenic cells

The contraction of floating collagen gels is suggested to mimic the reorganization of collagenous matrix during development and tissue healing. Here, we have studied two osteogenic cell lines, namely MG-63 and HOS, and a chemically transformed subclone of HOS cells, HOS-MNNG. Transforming growth factor-beta (TGF-beta), a putative regulator of bone fracture healing, increased collagen gel contraction by MG-63 and HOS-MNNG, but not by HOS cells. Our data show that TGF-beta-induced fibronectin synthesis is not sufficient for the process. Instead, anti-beta 1 integrin antibodies could prevent the contraction. There are three different integrin heterodimers that are known to mediate the cell-collagen interaction, namely alpha 1 beta 1, alpha 2 beta 1, and alpha 3 beta 1. In MG-63 cells TGF-beta increased the expression of alpha 2 beta 1 integrin and decreased the expression of alpha 3 beta 1 integrin, whereas alpha 1 beta 1 integrin is not expressed. HOS cells had no alpha 2 beta 1 integrin, neither did TGF-beta induce its expression. However, HOS-MNNG cells expressed more alpha 2 beta 1 integrin when treated with TGF-beta. Thus, we suggest that the mechanism of the enhanced collagen gel contraction by TGF-beta is the increased expression of alpha 2 beta 1 integrin heterodimer. To further test this hypothesis, we expressed a full-length alpha 2 integrin cDNA in HOS cells and in MG-63 cells. We obtained HOS cell clones that expressed alpha 2 beta 1 heterodimer, and the ability of these cells to contract collagen gels was greatly enhanced. Furthermore, the contraction by MG-63 cells transfected with alpha 2 integrin cDNA was enhanced, and the contraction by cells transfected with antisense oriented alpha 2 integrin cDNA was decreased. Thus, both in MG-63 and HOS cells the increased alpha 2 integrin expression alone was sufficient for the enhanced contraction of collagen gels. Furthermore, the amount of alpha 2 integrin is critical for the process, and its decrease leads to diminished ability to contract gels.

Branching morphogenesis of human mammary epithelial cells in collagen gels

To study the morphogenesis of human epithelial cells in vitro we have used a three-dimensional collagen matrix and a newly developed mammary epithelial cell line, 1–7 HB2. In standard medium 1–7 HB2 cells formed compact balls/spheres inside collagen type I gels, while cocultivation with various fibroblast cell lines or growth in fibroblast-conditioned media resulted in the appearance of branching structures. At least two different soluble factors secreted by fibroblasts were found to be implicated in the branching morphogenesis. Firstly, hepatocyte growth factor/scatter factor could induce branching in a concentration-dependent manner. Moreover, a polyclonal serum against hepatocyte growth factor/scatter factor completely inhibited the branching morphogenesis induced by medium conditioned by MRC-5 fibroblast cells. In contrast, a morphogenetic activity secreted by human foreskin fibroblasts was identified that appears to be different from hepatocyte growth factor/scatter factor and from a number of other well-characterized growth factors or cytokines. This model system has been used to examine the role of integrins in mammary morphogenesis. The expression of the alpha 2 beta 1, alpha 3 beta 1 and alpha 6 beta 4 integrins was decreased when cells were plated on collagen gels. The addition of specific blocking monoclonal antibodies directed to the alpha 2- and beta 1-integrin subunits to growth media impaired cell-cell interactions and interfered with the formation of compact structures inside collagen gels, suggesting that the alpha 2 beta 1 integrin can control intercellular adhesion in mammary morphogenesis. In contrast one of the blocking monoclonal antibodies against the alpha 3-integrin subunit (P1B5) mimicked the effect of soluble ‘morphogens’. Our results suggest that the modulation of alpha 3 beta 1 activity may represent an important event in the induction of branching morphogenesis of human mammary epithelial cells.

Altered interaction of human granulation-tissue fibroblasts with fibronectin is regulated by alpha 5 beta 1 integrin

Granulation-tissue fibroblasts express an unique phenotype distinct from normal fibroblasts. Due to the importance of the cell-matrix interactions in the regulation of cell morphology and behavior, we have compared the cell adhesion apparatus, especially integrin-type receptors, in fibroblasts cultured from healthy human periodontal connective tissues and from chronic and wound granulation tissues. The spreading of granulation-tissue cells on fibronectin, but not on type I collagen or laminin, was slower when compared with the normal fibroblasts. Cell spreading on fibronectin could be inhibited by RGD-containing peptide, suggesting integrin-mediated interaction. Both cell types expressed beta 1 integrin subunit, which associated with several integrin alpha subunits, namely alpha 1, alpha 2, alpha 3, alpha 5 and alpha v. In addition to beta 1 subunit, alpha v chain formed heterodimers with beta 3 and beta 5 subunits. Thus, these cells have multiple putative fibronectin, laminin, collagen, and vitronectin receptors. Cell spreading of both cell types on fibronectin was inhibited with anti-beta 1 and anti-alpha 5 antibodies, but antibodies against other putative FN-binding integrins (alpha 3, alpha v, and alpha v beta 3) had no effects. Furthermore, granulation-tissue fibroblasts showed delayed spreading on substrates coated with anti-beta 1 or anti-alpha 5 integrin antibodies. On substrates coated with anti-alpha 3 antibody, both cell types spread equally well. By FACS analysis, the amount of beta 1 and alpha 5 integrin subunits expressed on the cell surfaces was slightly elevated in GTFs compared with HGFs. Thus, the findings in this study indicate that the weakened interaction of granulation-tissue fibroblasts with fibronectin is regulated by altered function of alpha 5 beta 1 integrin.

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.

Proinflammatory cytokines (interleukin-1 beta and tumor necrosis factor-alpha) down regulate synthesis and secretion of thrombospondin by human endothelial cells

We examined the effects of proinflammatory cytokines on the expression of two extracellular matrix proteins, e.g., thrombospondin (TSP) and fibronectin (FN) b cultured human umbilical vein endothelial cells (HUVECs). Treatment of HUVECs with human recombinant interleukin-1 beta (IL-1 beta) or human tumor necrosis factor-alpha (TNF-alpha) caused a time-and dose-dependent decline in TSP production whereas FN production was not modified. At low concentrations, IL-1 beta and TNF-alpha in combination ha a greater effect than either agent alone. Interferon-gamma (IFN-gamma) was without effect. The decline in TSP synthesis resulted in a decreased secretion of this glycoprotein into the extracellular matrix. Endothelial cell monolayers cultured on porous filters were used to study the polarity of TSP secretion. Approximately two thirds of the synthesized protein was secreted to the apical side medium and one third to the basal side medium and both types of secretion were inhibited to a similar extent by cytokine treatment. Immunoprecipitation experiments revealed no apparent degradation of secreted TSP, either in the apical or in the basal compartment. Treatment of HUVECs with lL-1 beta, either alone or in combination with TNF-alpha, had no significant effect on the steady-state TSP mRNA levels, suggesting a posttranscriptional regulation. Our results indicate that IL-1 beta decreasing TSP deposition and suggest different regulatory mechanisms for the expression of various secreted proteins by endothelial cells.

Differential effects of interleukin 1-alpha (IL-1 alpha) or tumor necrosis factor-alpha (TNF-alpha) on motility of human melanoma cell lines on fibronectin

Interleukin-1 alpha (IL-1 alpha) and tumor necrosis factor-alpha (TNF-alpha) induce a motogenic response in a number of benign and malignant cells. We examined the chemokinetic effects of these cytokines on the cell migration of four melanoma cell lines on fibronectin using modified Boyden chambers and video-time lapse analysis. Flow cytometry analysis of IL-1 receptors, TNF receptors, and shifts in beta 1 integrin expression were correlated with the effects of these cytokines on cell migration on fibronectin. The four melanoma cell lines exhibited heterogeneous expression of types I and II IL-1 receptors as well as p60 TNF receptors. Scant p80 TNF receptor expression was detected on only one cell line. Three of four melanoma cell lines demonstrated type I IL-1 receptors by Western blotting. IL-1 alpha and TNF-alpha induced heterogeneous modulation of beta 1 integrin expression in the four melanoma cell lines tested; downward shift of the alpha 2, alpha 3, alpha 4, and beta 1 integrin subunits was detected among three of the melanoma cell lines as were upward shifts of the alpha 4, alpha 5, and alpha 6 integrin subunits among three of the melanoma cell lines. IL-1 alpha and TNF-alpha induced enhanced migration on fibronectin in one of the melanoma cell lines and were related to an upward shift in the alpha 4 and alpha 5 integrin subunit expression. Taken together, the findings indicate that expression of a particular receptor for IL-1 or TNF does not necessarily signal a motogenic response in melanoma cells, but induces heterogeneous shifts in beta 1 integrin expression. However, upregulation in alpha 4 and alpha 5 integrin subunits appears to relate to enhanced migration on fibronectin.

Identification of integrin receptors on cultured human bone cells

The interactions of bone cells with their surrounding extracellular microenvironment may be mediated by integrins, a family of heterodimeric glycoproteins consisting of alpha and beta subunits that noncovalently interact to form cell-substratum adhesion receptors. We previously described the integrins on calvarial bone cells in rats with use of polyclonal antibodies against some integrin subunits. In the present study, we expanded this initial characterization by employing a more complete panel of monoclonal antibodies to identify integrins on human bone cells. Minced fragments of trabecular bone obtained during total knee arthroplasty were grown in culture until bone cells became confluent. The cells then were dissociated, plated again, grown to confluence, and assayed for alkaline phosphatase activity, response of cyclic adenosine monophosphate to stimulation with parathyroid hormone, and osteocalcin content. The percentage of the cells that adhered to various substrates was measured; 60-70% adhered to type-I collagen, fibronectin, vitronectin, and poly-D-lysine; 40-50% adhered to type-IV collagen, laminin, and gelatin; and only 10% adhered to fibrinogen. Flow cytometric analysis with anti-integrin monoclonal antibodies and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immunoprecipitates of the human bone cells revealed high levels of alpha 1 beta 1, alpha 3 beta 1, alpha 5, beta 1 and alpha v beta 5 integrins and much lower levels of alpha 2 beta 1, alpha 4 beta 1, alpha v beta 1, and alpha v beta 3 integrins. This description of the integrin repertoire of cultured human bone cells represents the first step toward an understanding of the role played by integrins in the growth, maintenance, and repair of bone.

The distribution of cellular adhesion molecules in pigmented skin lesions

BACKGROUND

The process of multistep tumor development has been studied thoroughly in the development of malignant melanomas. The authors investigated the expression of cellular adhesion molecules in nevomelanocytic lesions to explore a postulated role of adhesion molecules in cell-cell and cell-matrix interactions during tumor development.

METHODS

Sections of 20 nevocellular nevi, 35 dysplastic nevi, 6 melanomas in situ, and 20 malignant melanomas were investigated with respect to their expression of intercellular adhesion molecule-1 (ICAM-1), inducible cell adhesion molecule-110 (INCAM-110)/vascular cell adhesion molecule-1 (VCAM-1), E-selectin, lymphocyte function-associated antigen-1 (LFA-1), and the integrins for very late antigen-(VLA) alpha-(alpha) 2 and VLA-alpha 6; for these studies, monoclonal antibodies were used and indirect immunoperoxidase and immunofluorescence staining methods were performed.

RESULTS

In the transformation from benign to malignant neoplasms, the expression of ICAM-1 was upregulated strongly. The expression of VLA-alpha 2 on tumor cells increased whereas that of VLA-alpha 6 decreased; these alterations corresponded to changes previously observed in their ligands within the extracellular matrix. These results were statistically significant. In addition, ICAM-1, INCAM-110/VCAM-1, and E-selectin were detected in activated endothelial cells, probably as a result of cytokine activation. The ligand for ICAM-1, LFA-1, was confined to mononuclear cells.

CONCLUSIONS

The increase in ICAM-1 and VLA-alpha 2 expression and the decrease of VLA-alpha 6 expression may, in combination with specific matrix alterations, lead to a change in cell-cell and cell-matrix interaction, thereby contributing to the invasive property of melanocytic tumor cells. The neoexpression of INCAM-110/VCAM-1 and E-selectin in pigmented skin lesions may play a role in both infiltrative growth and the generation of a host reaction toward these tumors.

Functional identification of integrin laminin receptors that mediate process outgrowth by human SY5Y neuroblastoma cells

Treatment of the human neuroblastoma cell line SY5Y with nerve growth factor (NGF) induces terminal neuronal differentiation of a subpopulation of cells which can be selected by treatment with a DNA synthesis inhibitor. We have examined the interactions of naive (untreated) and NGF-differentiated SY5Y cells with laminin, and identified integrin receptors that mediate laminin-induced process outgrowth. Differentiated cells displayed a greater capacity for process extension, which correlated with increased expression of integrin laminin receptors. Both naive and differentiated cells expressed integrins alpha 1/beta 1, alpha 2/beta 1, and alpha 3/beta 1 but the differentiated population expressed about 5-fold higher levels of alpha 1/beta 1 and about 2-fold more alpha 2/beta 1 and alpha 3/beta 1 on their surface. Function blocking monoclonal antibodies were used to identify integrin receptors mediating process outgrowth. The anti-alpha 1 monoclonal antibody SR84 was shown to block alpha 1 function and inhibit process outgrowth on laminin. Despite the presence of multiple integrins which have been shown to bind laminin in other cell types, alpha 1/beta 1 mediated the majority of process outgrowth in both naive and differentiated cells, with a minor role played by alpha 3/beta 1. These data indicate that alpha 1/beta 1 function is required for process outgrowth on laminin by SY5Y cells and suggest that increased expression may be a crucial aspect of neuronal differentiation.

TGF-alpha can act as morphogen and/or mitogen in a colon-cancer cell line

Transforming growth factor alpha (TGF-alpha) has multifunctional biological effects on a variety of mesenchymal and epithelial cells. It is a potent mitogen for a number of normal and transformed cell types, regulates extracellular matrix (ECM) production and promotes breast, kidney and lung morphogenesis. To clarify the role of ECM proteins in the morphogenetic and mitogenic effects of TGF-alpha, we have used a human colon carcinoma cell line (SW1222) which expresses EGF receptor. Here we show that TGF-alpha at 1 ng/ml increases the proliferation of SW1222 cells, but only when they are cultured on plastic rather than collagen-coated plates. Higher concentrations of TGF-alpha (10 ng/ml) did not increase cell proliferation but significantly enhanced the crypt-like glandular differentiation when cells were grown in 3-dimensional collagen gel (p = 0.027). These effects were accompanied by increased expression of alpha 2 beta 1 and alpha 3 beta 1 integrin molecules, which are receptors for extracellular matrix proteins, and by a statistically significant increase in binding of SW1222 cells to type-1 collagen. The effects of TGF-alpha both on binding to type-1 collagen and on morphological differentiation in 3-dimensional collagen gel were inhibited by monoclonal antibodies recognizing the alpha 2 beta 1 integrin. These data indicate that the morphogenetic or mitogenic activities of TGF-alpha are critically dependent on cellular interactions with extracellular matrix proteins and are primarily mediated by the alpha 2 beta 1 integrin receptor. Inappropriate expression of this growth factor, seen in tumours whose cell-matrix interactions are greatly impaired, could have deleterious effects on the maintenance of normal tissue architecture and growth control.

The growth-supportive effect of thrombospondin (TSP1) and the expression of TSP1 by human MG-63 osteoblastic cells are both inhibited by dexamethasone

Thrombospondin (TSP) is a 450-kDa extracellular matrix glycoprotein which supports the growth of human MG-63 osteoblastic cells [Abbadia et al., FEBS Lett., 329 (1993) 341-346]. In this study, we describe the effect of the glucocorticoid, dexamethasone, on cell proliferation and TSP expression by MG-63 cells. Using a serum-free mitogenesis assay, dexamethasone (25 to 500 nM) caused a dose-dependent decrease in [3H]thymidine incorporation by MG-63 cells in culture, reaching 40% inhibition of cell proliferation at a concentration of 250 nM. Similarly, the stimulatory effect of TSP (500 ng/ml) on proliferation of MG-63 cells was totally abolished in the presence of dexamethasone (250 nM). In situ hybridization indicated that TSP mRNA level in dexamethasone-treated MG-63 cells decreased compared to quiescent cells. As judged by fluorescence-activated cell sorting analysis, dexamethasone treatment of MG-63 cells resulted in a 50 to 70% decrease in TSP cell surface expression compared to quiescent cells. Secretion of TSP in the culture fluid of dexamethasone-treated MG-63 cells also decreased by 40% while, under similar experimental conditions, a 180% increase in alkaline phosphatase activity was observed in dexamethasone-treated cells. Because glucocorticoids induce osteoporosis in vivo and reduce proliferation of osteoblasts in vitro, our results argue for an important role of TSP during bone formation.

Involvement of protein kinase C and protein tyrosine kinase pathways in tumor necrosis factor-alpha-induced clustering of ovarian theca-interstitial cells

Tumor necrosis factor-alpha (TNF) induces clustering of theca-interstitial cells (TIC) isolated from immature, hypophysectomized rats, while inhibiting luteinizing hormone (LH)-stimulated androstenedione in vitro. Stimulators of PKC, 1-oleoyl-2-acetyl-sn-glycerol (OAG, 50 and 100 microM) and phorbol-12-myristate-13-acetate (PMA, 50 nM), caused TIC clustering by 6 days in vitro. Clustering induced by these compounds resembled that induced by TNF. The protein kinase inhibitor, staurosporine at 1 and 10 nM, impaired TNF-induced TIC clustering for 6 days, as did the protein kinase inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperizine dihydrochloride (H-7); conversely, the protein kinase inhibitor, chelerythrine chloride (0.1, 1.0 or 10 microM), did not attenuate TNF-directed clustering. The protein kinase inhibitors did not reverse the suppression of LH-stimulated androstenedione by TNF. Inhibitors of the EGF receptor PTK, A23 (10, 50, or 100 microM) and A46 (0.1, 1.0, 10, or 50 microM), impaired TNF-induced TIC clustering, while TNF suppression of LH-directed androstenedione was unaffected. EGF-induced TIC clustering was also impaired by A46, while A23 was less effective. Both A23 and A46 blocked EGF attenuation of LH-directed androstenedione after 4 days. When challenged with TNF (1 ng/ml) or PMA (50 nM), PKC activity increased in TIC. A23 (50 microM) and A46 (10 microM) each alone blocked the TNF-associated increase in PKC activity; however, PKC activity attributable to PMA was unaffected by A46. Together, these results suggest that TNF-induced TIC clustering involves activation of PTK which directs subsequent increases in PKC activity; however, mechanisms by which TNF inhibits LH-stimulated steroidogenesis remains elusive.

Integrin-type extracellular matrix receptors in cancer and inflammation

The integrins are a large family of cell adhesion receptors, involved in cell-cell and cell-matrix interactions. At present, 20 different integrin heterodimers are known. Integrins participate in a complex apparatus anchoring cells to their surroundings and transducting signals into the cells. These signals regulate many important aspects of cell behaviour, including growth, differentiation, and phenotype. This is an overview of the molecular and cellular biology of the integrin-type extracellular matrix receptors. Integrins may play a central role in the healing process of tissue injuries, and in many diseases, especially in human cancer.

Studies on human porin. IX. Immunolocalization of porin and CFTR channels in human surface respiratory epithelium

The expression of the voltage-dependent anion channel (VDAC) "Porin 31 HL" and its cellular and subcellular immunocytochemical localization in the human respiratory epithelium were studied with monoclonal and polyclonal antibodies using immunofluorescence and immunogold labelling with light (LM) and transmission electron microscopy (TEM), respectively. Porin was identified in the apical domain of the ciliated cells and in the basal cells of the respiratory epithelium. Immunogold labelling was present in the apical plasma membrane and subapical vesicles of the ciliated cells. In pre-embedded freshly dissociated surface epithelial cells, porin could also be identified with TEM at the outer part of the plasma membrane of basal cells. By LM double immunolabelling, both porin and cystic fibrosis transmembrane conductance regulator (CFTR) were identified in the apical domain of ciliated cells but not in basal cells where CFTR was never identified. On Western blots of solubilized total membrane protein preparations from the same frozen surface epithelial respiratory cells, the antibodies recognized a group of 3 proteins of 31, 60 and 130-140 kDa with a strong reactivity for a 31 kDa protein, corresponding to the porin and a protein of 170 kDa which is consistent with mature CFTR. These results suggest that porin might be part of a multi-component chloride channel complex which could interact with CFTR.

Expression of beta 1 integrins in non-neoplastic mammary epithelium, fibroadenoma and carcinoma of the breast

beta 1 Integrins were examined immunohistochemically in normal and mastopathic mammary glands, 12 benign tumours and 90 carcinomas of the breast using monoclonal antibodies against beta 1 and alpha 1 to alpha 6 subunits. When compared with epithelial cells of non-neoplastic mammary glands and of benign tumours, carcinoma cells showed considerable quantitative changes in the pattern of alpha 2, alpha 3 and alpha 6 subunit expression. In contrast, the distribution pattern of beta 1, alpha 1, alpha 4 and alpha 5 antigens corresponded to the situation observed in non-neoplastic mammary gland epithelium in most instances. An abnormal expression of alpha 2 was found in 71.0% of the carcinomas ranging from a remarkably low number of alpha 2-positive tumour cells in 27.5% of the cases to a complete absence of the alpha 2 molecule in 43.5% of the carcinomas. Of the carcinomas 39.9% exhibited quantitative changes in alpha 3 expression with an abnormally low content of alpha 3-positive neoplastic cells in 15.4% and a complete absence of this molecule in 24.5% of the cases. Expression of alpha 6 was abnormal in 73.2% of the carcinomas, consisting in a greater number of alpha 6-negative tumour cells in 31.9% and in a complete absence of alpha 6 in 41.3% of the tumours. The abnormally low expression/absence of alpha 2 and alpha 3 subunits correlated with oestrogen receptor negativity (P < 0.033 and P < 0.04, respectively). In addition, abnormally low expression/absence of alpha 2 correlated with poor differentiation of the tumours (P < 0.014). The quantitative changes in the expression pattern of beta 1-associated alpha subunits in breast carcinomas may cause a disturbed cell-cell and/or cell-matrix interaction that increases the invasive and migratory property of the tumour cells.

Expression of integrin receptors and their role in adhesion, spreading and migration of normal human melanocytes

Integrin receptors of human melanocytes in vivo and of melanocytes isolated and cultured from in vitro reconstituted normal human epidermis were investigated. Melanocytes were studied by high-resolution immunocytochemistry of in situ epidermis and were found to expose only the integrin subunits alpha 3, alpha 6, alpha v and beta 1 on their plasma membrane surface. Instead, cultured normal melanocytes expressed alpha 3 beta 1, alpha 5 beta 1, alpha 6 beta 1 and alpha v beta 3, which were immunoprecipitated from both metabolically and surface-labeled cells. Beta 1 integrins were diffused on the adhesion surface, while alpha v beta 3 was clustered in focal contacts both in control cells and upon dendrite induction with phorbol 12-myristate 13-acetate (PMA). The functional roles of integrins were studied in vitro by cell adhesion, spreading and migration assays. The sum of the data indicated that, in normal human melanocytes: (i) adhesion to defined substrata is mainly mediated by specific beta 1 integrins; (ii) spreading is mainly modulated by alpha v beta 3; (iii) the beta 1 and beta 3 heterodimers cooperate in regulating migration. The in vitro expression of two integrins (alpha v beta 3 and alpha 5 beta 1) that are not exposed in situ, and their role in the spreading and migratory properties of melanocytes, strongly suggest that they are involved in regenerating a normally pigmented epidermis during wound healing by controlling melanocyte spreading and migration over a provisional matrix. Tumor promoters, such as PMA, selectively increased the expression of alpha 3 beta 1. We suggest that this integrin might be involved in melanocyte migration on the newly formed basement membrane during wound healing as well as in intercellular recognition of adjacent keratinocytes.

Expression of functional alpha 4 beta 1 integrin by human dermal fibroblasts

Fibroblasts interact with the extracellular matrix through cell-surface receptors belonging to the integrin family. In this report, we present evidence that cultured normal human fibroblasts express the integrin alpha 4 beta 1 and that this receptor facilitates fibroblast attachment to fibronectin. Fluorescence-activated cell sorter analysis and immunoprecipitation with monoclonal antibodies demonstrated that normal dermal fibroblasts express the alpha 4-subunit on the cell surface, primarily in association with the beta 1-subunit. Cell-attachment assays demonstrated that normal human fibroblasts can attach to the 40-kDa fibronectin fragment containing the type III connecting segment domain recognized by alpha 4 beta 1. Adhesion to this fragment was inhibited by anti-alpha 4 antibody. Furthermore, our results indicate that alpha 4 beta 1 collaborates with another fibronectin receptor, alpha 5 beta 1, during fibroblast attachment to full-length fibronectin. The region of fibronectin recognized by alpha 5 beta 1 contains the amino acid sequence arg-gly-asp (RGD). A short synthetic RGD peptide, or the 120-kDa fibronectin fragment containing the RGD sequence, only partially inhibited attachment to full-length fibronectin, suggesting that fibroblasts utilize more than the RGD recognition sequence for binding to fibronectin. Accordingly, RGD peptide combined with anti-alpha 4 antibody produced more potent inhibition of cell attachment than either reagent alone. These observations show for the first time that functional alpha 4 beta 1 fibronectin receptor is not restricted to lymphoid cells and transformed cells.

Signal transduction by integrin receptors for extracellular matrix: cooperative processing of extracellular information

Adhesion receptors allow cells to interact with a dynamic and information-rich environment of extracellular matrix molecules. The integrin family of adhesion receptors transduces signals from the extracellular matrix that regulate growth, gene expression and differentiation, as well as cell shape, motility and cytoskeletal architecture. Recent data support the hypothesis that integrins transduce signals cooperatively with other classes of adhesion receptors or with growth factor receptors. Furthermore, the ability of integrins to interact with the cytoskeleton appears to be fundamental to their mechanism for signal transduction.

The junction between cytokines and cell adhesion

Several aspects of the interactions between growth factors and cell adhesion are described. Recent advances in the field come from the identification of molecules resembling growth factors or growth factor receptors, which bear cell adhesion motifs as well as molecules participating in both cell growth control and adhesion.