Branching morphogenesis of human mammary epithelial cells in collagen gels

Highly stoichiometric, stable, and specific association of integrin alpha3beta1 with CD151 provides a major link to phosphatidylinositol 4-kinase, and may regulate cell migration

Here we describe an association between alpha3beta1 integrin and transmembrane-4 superfamily (TM4SF) protein CD151. This association is maintained in relatively stringent detergents and thus is remarkably stable in comparison with previously reported integrin-TM4SF protein associations. Also, the association is highly specific (i.e., observed in vitro in absence of any other cell surface proteins), and highly stoichiometric (nearly 90% of alpha3beta1 associated with CD151). In addition, alpha3beta1 and CD151 appeared in parallel on many cell lines and showed nearly identical skin staining patterns. Compared with other integrins, alpha3beta1 exhibited a considerably higher level of associated phosphatidylinositol-4-kinase (PtdIns 4-kinase) activity, most of which was removed upon immunodepletion of CD151. Specificity for CD151 and PtdIns 4-kinase association resided in the extracellular domain of alpha3beta1, thus establishing a novel paradigm for the specific recruitment of an intracellular signaling molecule. Finally, antibodies to either CD151 or alpha3beta1 caused a approximately 88-92% reduction in neutrophil motility in response to f-Met-Leu-Phe on fibronectin, suggesting an functionally important role of these complexes in cell migration.

Distribution of integrins during human fetal lung development

Interactions between epithelial cells and the extracellular matrix through integrins play a key role in the development of the lung by modulating branching morphogenesis, epithelial cell polarization, and differentiation. To determine the role of integrins during the different stages of lung development, we investigated the distribution of eight integrin subunits in the trachea and lung from human fetuses. In distal airways, during the early pseudoglandular stage of development, the alpha2-, alpha5-, alpha6-, alphav-, and beta1-subunits were detected in all epithelial cell plasma membranes, and polarized but undifferentiated tracheal epithelial cells expressed alpha3-, alpha6-, and beta1-subunits in the plasma membrane of the cells facing the basement membrane. The alpha6- and beta4-chains were detected along the basal plasma membrane of the basal cells in differentiated tracheal epithelia. The alpha4-subunit was detected in all respiratory cells throughout fetal development. In the submucosal glands, myoepithelial cells expressed the integrin subunits found in the undifferentiated cells of the developing airways, whereas the secretory cells expressed only alpha2-, alpha3-, alpha4-, alpha6-, and beta1-subunits. These results demonstrate differential expression of integrins during lung development and suggest that integrins may play multiple roles in organogenesis and maturation of respiratory surface epithelium and glands.

Isolation of EpH4 mammary epithelial cell subpopulations which differ in their morphogenetic properties

EpH4 is a nontumorigenic cell line derived from spontaneously immortalized mouse mammary gland epithelial cells (Fialka et al., 1996). When grown in collagen gels, EpH4 cells give rise to different types of structures, e.g., solid cords or branching tubes. By removing and subsequently dissociating single three-dimensional colonies of defined morphology, we have isolated six clonal subpopulations of EpH4 cells which display distinct morphogenetic properties in collagen gel cultures. Thus, cells from the H1B clone form branching cords devoid of a central lumen, K3A3 cells form cords enclosing small multifocal lumina, and J3B1 cells form large cavitary structures containing a wide lumen. I3G2 cells form either cords or tubes, depending on the type of serum added to the culture medium. Finally, when grown in serum-free medium, Bela cells form spherical cysts, whereas Be4a cells form long, extensively branched tubes. In additional assays of morphogenesis, i.e., cell sandwiching between two collagen gels or culture on a thick layer of Matrigel (a laminin-rich extracellular matrix), all clones form epithelial-cell lined cavitary structures, except H1B cells which are unable to generate lumina under these conditions. The EpH4 sublines we have isolated provide an in vitro system for studying the mechanisms responsible for lumen formation and branching morphogenesis, as well as for identifying the factors which subvert these developmental processes during mammary carcinogenesis.

Integrin-matrix interactions affect the form of the structures developing from human mammary epithelial cells in collagen or fibrin gels

The HB2 cell line, developed from luminal epithelial cells cultured from milk, forms ball-like structures in collagen gels which show a uniform branching response to hepatocyte growth factor. The alpha2beta1 integrin is the major integrin expressed by luminal epithelial cells, and the role of this integrin in mammary morphogenesis has been analysed using HB2 cells cultured in collagen gels and antibodies which affect integrin function. Selectivity of response was followed by comparing effects on morphogenesis in fibrin, where the alphavbeta1 integrin interacts with the matrix. In the presence of hepatocyte growth factor, using alpha2 and beta1 antibodies in collagen and alphav and beta1 antibodies in fibrin, complete blocking of the cell-matrix interaction inhibits cell survival. With partial blocking of the integrin-ligand interaction, the cells proliferate but form dissociated colonies. Activating antibodies to the beta1 integrin subunit which enhance the matrix interaction dramatically inhibit the branching and motility responses to hepatocyte growth factor. A series of non-blocking alpha2 reactive antibodies also inhibit these responses specifically in or on collagen. Studies with ras-transfected HB2 cells emphasise the importance of the alpha2beta1 collagen interaction in the development of form since HB2ras cells, which express reduced levels of the alpha2beta1 integrin, form dissociated colonies in collagen but not in fibrin. Treatment of HB2ras cells with a beta1 activating antibody, however, induces the formation of compact colonies. Even though the ras-transformants form colonies in agar, complete blocking of the alpha2beta1/collagen interaction does not allow survival in collagen. The results indicate that in mammary morphogenesis, the strength of the interaction of integrins with the extracellular matrix modulates the response to motogenic factors and contributes to the definition of form.

Differentiation and cancer in the mammary gland: shedding light on an old dichotomy

In this brief review, the development of breast cancer is discussed from the vantage of phenotypic differentiation, similar to what has been considered over the years for leukemias and melanomas, both of which express easily visible differentiation markers (Hart and Easty, 1991; Clarke et al., 1995; Lynch, 1995; Sachs, 1996; Sledge, 1996). The review is divided into a theoretical background for human breast differentiation and a discussion of recent experimental results in our laboratories with differentiation of breast epithelial cells. In the theoretical background, in situ markers of differentiation of normal breast and carcinomas are discussed with emphasis on their possible implications for tumor therapy. So far, most of the emphasis regarding differentiation therapy of tumors has been focused on the possible action of soluble factors, such as colony-stimulating factors in leukemias and retinoic acids in solid tumors (Lotan, 1996; Sachs, 1996). However, an emerging and promising new avenue in this area appears to point to additional factors, such as the cellular form and extracellular matrix (ECM) (Bissel et al., 1982; Bissel and Barcellos-Hoff, 1987; Ingber, 1992). The recent interest in these parameters has evolved along with an increasing understanding of the molecular composition of the ECM, and of the molecular basis of the classical findings that normal cell--in contrast to tumor cells--are anchorage dependent for survival and growth (Folkman and Moscona, 1978; Hannigan et al., 1996). We now know that this is the case for epithelial as well as fibroblastic cells, and that interaction with ECM is crucial for such regulation. Indeed, ECM and integrins are emerging as the central regulators of differentiation, apoptosis, and cancer (Boudreau et al., 1995; Boudreau and Bissel, 1996; Werb et al., 1996; Bissell, 1997; Weaver, et al., 1997). In the experimental part, we elaborate on our own recent experiments with functional culture models of the human breast, with particular emphasis on how "normal" and cancer cells could be defined within a reconstituted ECM. Special attention is given to integrins, the prominent ECM receptors. We further discuss a number of recent experimental results, all of which point to the same conclusion: namely that phenotypic reversion toward a more normal state for epithelial tumors is no longer an elusive goal. Thus "therapy by differentiation" could be broadened to include not only blood-borne tumors, but also solid tumors of epithelial origin.

Monolayer and three-dimensional cell culture and living tissue culture of gallbladder epithelium

Several models for preparing and isolating human and animal gallbladder epithelial cells, including low-grade gallbladder carcinoma cells, as well as proposed systems for culturing these isolated epithelial cells are reviewed here. Several reports concerning tissue culture of the gallbladder are also reviewed. The cell culture systems are divided into monolayer cell culture on collagen-coated or uncoated culture dishes or other culture substrate and three-dimensional cell culture in collagen gel. To prepare and isolate gallbladder epithelial cells, digestion of the gallbladder mucosa, abrasion of the mucosal epithelial cells, and excision of epithelial outgrowth of mucosal explants are applied. In monolayer cell culture, most of the specific biological features of isolated and cultured cells characteristic to the gallbladder are gradually lost after several passages, though quantitative and objective analyses of the pathophysiology of cultured cells and their secretory substances can be performed. Tissue culture using explants of the gallbladder has mainly been used for physiological studies of the gallbladder, such as investigating the transport of water and electrolytes. In this tissue culture system, quantitative assessment is difficult, though the original and specific biological and histological characteristics of the gallbladder are retained. Three-dimensional collagen gel culture could be an ideal model combining monolayer cell culture and tissue culture systems, and create controllable conditions or environments when several biologically active substances, such as growth factors, proinflammatory cytokines and adhesion molecules, are added to the culture medium. Advantages and shortcomings of individual cultivation models are discussed, and selecting the culture model most appropriate to the purpose of the study will facilitate investigations of the biology and pathogenetic mechanisms of gallbladder diseases such as cholelithiasis.

Ezrin is an effector of hepatocyte growth factor-mediated migration and morphogenesis in epithelial cells

The dissociation, migration, and remodeling of epithelial monolayers induced by hepatocyte growth factor (HGF) entail modifications in cell adhesion and in the actin cytoskeleton through unknown mechanisms. Here we report that ezrin, a membrane-cytoskeleton linker, is crucial to HGF-mediated morphogenesis in a polarized kidney-derived epithelial cell line, LLC-PK1. Ezrin is a substrate for the tyrosine kinase HGF receptor both in vitro and in vivo. HGF stimulation causes enrichment of ezrin recovered in the detergent-insoluble cytoskeleton fraction. Overproduction of wild-type ezrin, by stable transfection in LLC-PK1 cells, enhances cell migration and tubulogenesis induced by HGF stimulation. Overproduction of a truncated variant of ezrin causes mislocalization of endogenous ezrin from microvilli into lateral surfaces. This is concomitant with altered cell shape, characterized by loss of microvilli and cell flattening. Moreover, the truncated variant of ezrin impairs the morphogenic and motogenic response to HGF, thus suggesting a dominant-negative mechanism of action. Site-directed mutagenesis of ezrin codons Y145 and Y353 to phenylalanine does not affect the localization of ezrin at microvilli, but perturbs the motogenic and morphogenic responses to HGF. These results provide evidence that ezrin displays activities that can control cell shape and signaling.

Expression of hepatocyte growth factor/scatter factor and its receptor, MET, suggests roles in human embryonic organogenesis

Hepatocyte growth factor/scatter factor (HGF/SF) is secreted by mesenchymal cells and elicits proliferation, motility, differentiation, and morphogenesis of epithelia and other cells. These effects are mediated by binding to MET, a receptor tyrosine kinase. Genetically engineered mice lacking HGF/SF die in utero due to a failure of placental and hepatocyte differentiation, but little information exists regarding the expression of this signaling system in human development. Using reverse transcriptase-polymerase chain reaction, Western blots, and immunohistochemistry, we report that HGF/SF and MET are expressed during critical early periods of human organogenesis from 6 to 13 wk of gestation. Organs that expressed both genes included liver, metanephric kidney, intestine, and lung, each of which develop by inductive interactions between mesenchyme and epithelia. Of all organs studied, the placenta contained the highest levels of HGF/SF protein, and MET was detected in trophoblastic cells of chorionic villi as early as the 5th wk of gestation. Finally, examination of a human multicystic dysplastic kidney demonstrated that malformed, hyperproliferative tubules expressed MET, whereas HGF/SF protein was immunolocalized to the same epithelia and also to the surrounding undifferentiated cells. Hence HGF/SF might be an important growth factor in normal human embryogenesis and may additionally play a role in human organ malformations.

Detection of integrins in formalin-fixed, paraffin-embedded tissues

Integrins are heterodimeric transmembrane receptors, which are expressed in many cells. In vitro experiments have demonstrated that integrins may be important in tumor progression and organ development. The functions of integrins were previously studied in cell cultures and their tissue expression was detected by immunofluorescence or immunoperoxidase in frozen sections. The purpose of this study was to determine the optimal conditions for detection of integrins in formalin-fixed, paraffin-embedded tissues. We utilized microwave heating and enzyme digestion in routinely processed, surgically removed tissues. Our results demonstrate that integrins can be reliably detected in archival material. This approach will facilitate further investigation of the role played by integrins in human malignancies and in developmental processes.

Separated human breast epithelial and myoepithelial cells have different growth factor requirements in vitro but can reconstitute normal breast lobuloalveolar structure

In order to investigate the specific factors controlling the growth of normal breast cell types, purified populations of human breast epithelial and myoepithelial cells from reduction mammoplasties were grown in primary culture in three defined media and their response to foetal calf serum (FCS), epidermal growth factor (EGF) and basic fibroblast growth factor (FGF2) measured using MTT growth assays. Epithelial and myoepithelial cells differed markedly in their growth requirements. Whereas epithelial cell survival was dependent on the presence of FCS, myoepithelial cell growth was dramatically inhibited by serum. EGF and FGF2 were mitogenic for epithelial cells but not myoepithelial cells, the addition of insulin being the only essential supplement required for myoepithelial cell growth. Heparin inhibited FGF2-stimulated epithelial cell growth but also basal myoepithelial cell proliferation and this inhibition could be overcome by the addition of EGF. Neutralizing antibodies to EGF also inhibited basal myoepithelial cell growth. This suggests the possibility of an autocrine role for a heparin-binding member of the EGF family in the growth of myoepithelial cells. Purified cells combined to form lobuloalveolar structures when incubated in a reconstituted basement membrane matrix (Matrigel) in the presence of EGF and FGF2.

The role of laminin-5 and its receptors in mammary epithelial cell branching morphogenesis

In vivo, normal mammary epithelial cells utilize hemidesmosome attachment devices to adhere to stroma. However, analyses of a potential role for hemidesmosomes and their components in mammary epithelial tissue morphogenesis have never been attempted. MCF-10A cells are a spontaneously immortalized line derived from mammary epithelium and possess a number of characteristics of normal mammary epithelial cells including expression of hemidesmosomal associated proteins such as the two bullous pemphigoid antigens, alpha 6 beta 4 integrin and its ligand laminin-5. More importantly, MCF-10A cells readily assemble mature hemidesmosomes when plated onto uncoated substrates. When maintained on matrigel, like their normal breast epithelial cell counterparts, MCF-10A cells undergo a branching morphogenesis and assemble hemidesmosomes at sites of cell-matrigel interaction. Function blocking antibodies specific for human laminin-5 and the alpha subunits of its two known receptors (alpha 3 beta 1 and alpha 6 beta 4 integrin) not only inhibit hemidesmosome assembly by MCF-10A cells but also impede branching morphogenesis induced by matrigel. Our results imply that the hemidesmosome, in particular those subunits comprising its laminin-5/integrin 'backbone', play an important role in morphogenetic events. We discuss these results in light of recent evidence that hemidesmosomes are sites involved in signal transduction.

Comparison of O-linked carbohydrate chains in MUC-1 mucin from normal breast epithelial cell lines and breast carcinoma cell lines. Demonstration of simpler and fewer glycan chains in tumor cells

MUC-1 mucin is considered to be aberrantly glycosylated in breast, ovary, and other carcinomas in comparison with mucin from corresponding normal tissues. In order to clarify these differences in glycosylation, we have compared the O-linked carbohydrate chains from MUC-1 immunoprecipitated from [3H]GlcN-labeled breast epithelial cell lines (MMSV1-1, MTSV1-7, and HB-2) derived from cells cultured from human milk, with three breast cancer cell lines (MCF-7, BT-20, and T47D). Analysis by high pH anion chromatography showed that the normal cell lines had a higher ratio of GlcN/GalN and more complex oligosaccharide profiles than the cancer cell lines. Structural analyses were carried out on the oligosaccharides from MTSV1-7 and T47D MUC-1, and the following structures were proposed. MUC-1 from T47D had rather a simple glycosylation pattern, with NeuAcalpha2-3Galbeta1-3GalNAc-ol, Galbeta1-3GalNAc-ol, and GalNAc-ol predominating; in contrast, MUC-1 from MTSV1-7 had more complex structures, including a number of disialo, core 2 species, i.e. NeuAcalpha2-3Galbeta1-4GlcNAcbeta1-6[NeuAcalpha2 -3Galbeta1-3]GalNAc- ol and NeuAcalpha2-3Galbeta1-4GlcNAcbeta1-6[NeuAcalpha2 -3Galbeta1-4GlcNAcbet a1-3Galbeta1-3]GalNAc-ol. Double-labeling experiments with [3H]GlcN and 14C-aminoacids and analysis of GalNAc or GalNAc-ol:protein ratios in MUC-1 showed that there was also a significant difference in the degree of glycosylation of the mucin between the two cell types. We conclude that MUC-1 from breast cancer cell lines has simpler, and fewer, carbohydrate chains than MUC-1 from normal breast epithelial cells, and that these differences, combined or separately, explain the differential tumor specificity of some MUC-1 antibodies and T cells.

Alpha 3 beta 1 integrin has a crucial role in kidney and lung organogenesis

A mutation was targeted to the murine alpha3 integrin gene. Homozygous mutant mice survived to birth, but died during the neonatal period. The mutation caused abnormal kidney and lung development. Mutant kidneys displayed decreased branching of the medullary collecting ducts, although the number of nephrons was not altered. Proximal tubules exhibited two distinct subsets of abnormalities, with the epithelial cells either containing excess lysosomes or becoming microcystic. In addition, glomerular development was markedly affected. In mutant kidneys, the extent of branching of glomerular capillary loops was decreased, with capillary lumina being wider than normal. The glomerular basement membrane was disorganized and glomerular podocytes were unable to form mature foot processes. Branching of the bronchi in lungs of mutant mice was also decreased and the large bronchi extended to the periphery. These results indicate a role for integrin receptors in basement membrane organization and branching morphogenesis.

Alpha 2 beta 1 integrin is required for the collagen and FGF-1 induced cell dispersion in a rat bladder carcinoma cell line

We have investigated the role of integrins in the epithelial to mesenchymal transition (EMT) induced by either collagen or fibroblast growth factor-1 (FGF-1) in the rat bladder carcinoma cell line NBT-II. The major collagen-binding receptor is the alpha 2 beta 1 integrin. An increase in expression of alpha 2 beta 1 integrin coincided with EMT induced by either collagen or FGF-1. When both inducers were present, a further increase in alpha 2 expression was observed which correlated with an enhancement in the speed of locomotion. Overexpression of human alpha 2 in NBT-II cells did not trigger EMT but rendered cells more sensitive to the dispersing effect of collagen and FGF-1. Anti-human alpha 2 blocking antibodies affected cell scattering and motility induced by either collagen or FGF-1. These data demonstrate that alpha 2 beta 1 integrin is the mediator of the cell scattering effect induced by collagen. They also indicate that a functional alpha 2 integrin is essential for the motile behavior of NBT-II cells during the FGF-1 induced EMT.

Developmental regulation of murine integrin beta 1 subunit- and Hsc73-encoding genes in mammary gland: sequence of a new mouse Hsc73 cDNA

A partial integrin beta 1 subunit-encoding cDNA (Itg beta 1) and a new heat-shock protein 70-like-encoding cDNA (Hsc73) homologous to rat Hsc73 were cloned by differential display and RT-PCR from mouse mammary gland. Their developmental regulation during pregnancy, lactation and involution is reported. The Itg beta 1 mRNA content was stable in the first half of gestation, decreased to a minimum during lactation and increased markedly in early involution. Hsc73 gene expression was high in the first half of gestation and decreased to a minimum during lactation. The possible significance of the two observed patterns of expression is discussed.

Cell adhesion molecules in the normal and cancerous mammary gland

Loss of normal tissue morphology is one of the first changes seen in the development of solid malignant tumours, including breast cancers. Since cell adhesion molecules play a crucial role in maintaining normal tissue architecture, investigations into the molecular mechanisms involved in the morphological changes occurring in malignancy that focus on the expression and function of cell adhesion molecules in malignant progression are extremely relevant. This review discusses the cadherin and integrin families of adhesion molecules which have been shown to be extremely important in the cell-cell and cell-matrix interactions of epithelial cells. Immunohistochemical studies using tissue and tumour sections indicate that a reduction in levels of expression or function of both types of cell adhesion molecules is indeed observed in many breast cancers. A specific and crucial role for these molecules in the maintenance of normal morphological differentiation has been demonstrated in vitro, where the noninvasive differentiated phenotype correlates with the normal functioning of E-Cadherin and alpha 2 beta 1 integrin. Further in vitro evidence suggests that in mammary epithelial cells, oncogenes may be upstream regulators of both the expression and function of E-Cadherin, the alpha 2 beta 1 integrin, and other epithelial specific molecules important for maintaining epithelial differentiation. In this way they could manifest their effects on the tumorigeneic potential of epithelial cells.

Hepatocyte growth factor/scatter factor expression and c-met in primary breast cancer

Hepatocyte growth factor/scatter factor (HGF/SF) is a fibroblast-derived cytokine whose receptor is encoded by c-met. Activation of c-met promotes tumour cell proliferation, dissociation, invasiveness and angiogenesis. Aberrant expression of HGF/SF or c-met may play a role in tumour progression. HGF/SF and c-met were determined in 73 breast cancers (median follow up: 61 months) and 10 samples of tumour-free breast tissue. HGF/SF was detected at significantly higher concentrations in breast cancers (median 350, range 58-1604 ng per 100 mg total protein) when compared with normal breast tissue (median 108, range 66-213 ng per 100 mg total protein) (P < 0.001). C-met was detected in all 10 samples of tumour-free breast tissue and in 26 breast cancers. HGF/SF concentrations correlated with disease relapse (P < 0.001) and reduced overall survival (P < 0.001). Tumours with detectable c-met correlated significantly with disease-relapse (P = 0.012). Multivariate analysis demonstrated a significant interaction between HGF/SF and c-met in relation to disease-relapse (P = 0.014). These results suggest a biological interaction involving HGF/SF and c-met in promoting tumour progression in breast cancer.

The hepatocyte growth factor/scatter factor (HGF/SF) receptor, met, transduces a morphogenetic signal in renal glomerular fibromuscular mesangial cells

Previous studies have demonstrated that hepatocyte growth factor/scatter factor (HGF/SF) is secreted by mesenchymal cells and that it elicits motility, morphogenesis and proliferation of epithelia expressing the met receptor. We now report that HGF/SF may act as an autocrine factor in fibromuscular renal mesangial cells. These cells mechanically support glomerular endothelia, control the rate of plasma ultrafiltration and are implicated in the pathogenesis of a variety of chronic renal diseases. We detected met protein in the vascular stalk of metanephric glomeruli and in the mature mesangium. Mesangial lines from a mouse transgenic for a temperature-sensitive simian virus 40 T antigen expressed met mRNA and protein, and recombinant HGF/SF phosphorylated the met receptor tyrosine kinase. Cells were immortal in the permissive condition and HGF/SF enhanced proliferation in a defined medium. In the absence of the immortalising protein, division ceased and recombinant HGF/SF caused multipolar cells to become bipolar. The factor diminished stress fibres, their focal contacts and immunostaining for extracellular fibronectin, hence suggesting reduced substratum adhesion and enhanced motility. Mesangial lines also expressed HGF/SF mRNA and secreted bioactive factor; immunocytochemistry showed both ligand and receptor in individual cells. HGF/SF blocking antibody aggregated the cells, suggesting that mesangial-derived factor affects basal cell conformation in an autocrine manner. We conclude that mesangial cells express both HGF/SF and met, and the factor induces morphogenesis of cultured mesangial cells. Therefore HGF/SF may have an autocrine role in mesangial biology but further studies are now required to investigate the potential importance of the factor in vivo.

Specific association of CD63 with the VLA-3 and VLA-6 integrins

We screened monoclonal antibodies to cell-surface proteins and selected an antibody, called 6H1, that recognizes a putative integrin-associated protein. The 6H1 monoclonal antibody (mAb) indirectly coprecipitated alpha 3 beta 1 and/or alpha 6 beta 1, but not alpha 2 beta 1, or alpha 5 beta 1 from Brij 96 detergent lysates of multiple cell lines. Large scale purification using the 6H1 mAb yielded a single protein of 45-60 kDa with an amino-terminal sequence that exactly matched CD63. Confirming that the 6H1 mAb recognized the CD63 protein, 6H1 and a known anti-CD63 mAb yielded identical coprecipitation results and identical colocalization into lysosomal granules containing cathepsin D. Furthermore, we used an established anti-CD63 mAb to detect this protein in an alpha 3 beta 1 immunoprecipitate, and also we observed VLA-3 and CD63 colocalization in cellular "footprints." Notably, the cytoplasmic domain of alpha 3 was neither required nor sufficient for CD63 association, suggesting that it occurred elsewhere within the alpha 3 beta 1 complex. Knowledge of these specific CD63-alpha 3 beta 1 and CD63-alpha 6 beta 1 biochemical associations should lead to critical insights into the specialized functions of alpha 3 beta 1, alpha 6 beta 1, and CD63.

Regulation of Wnt5a mRNA expression in human mammary epithelial cells by cell shape, confluence, and hepatocyte growth factor

The Wnts are a family of genes with a role in cell fate and morphological development in numerous embryonic and adult tissues. In mouse mammary tissue a subset of the Wnts have a function in the normal development of the gland, and aberrant expression of Wnts normally silent in this tissue causes mammary carcinomas. We have previously shown that Wnt5a expression is elevated in the epithelial component of proliferative lesions of human breast and have therefore examined the regulation of Wnt5a mRNA expression in the human mammary epithelial cell line HB2, which has a luminal phenotype and thus represents the most commonly transformed cell type in human breast cancer. Wnt5a was up-regulated 30-fold at confluence. This up-regulation was induced specifically by confluence and not by the growth arrest that accompanied it. In addition, Wnt5a was down-regulated 3-fold by changes in cell shape associated with the transition from growth on a two-dimensional surface (flat cell morphology) to growth in three-dimensional gels (spherical cell morphology). Cytoskeletal disruption with non-toxic doses of colchicine also induced a spherical morphology and brought about a dose-dependent down-regulation of Wnt5a. Wnt5a was also down-regulated 10-fold during the hepatocyte growth factor-induced branching of HB2 cell aggregates in collagen gels. The down-regulation of Wnt5a preceded the branching process. A similar result was obtained with primary human breast epithelial populations and the breast cancer cell line MDA468. We conclude that regulation of Wnt5a expression is a down-stream effect of signaling by hepatocyte growth factor. These results are consistent with a role for Wnt5a in mammary epithelial cell motility and are in accord with Xwnt5a's function in embryonal cell migration. If Wnt5a's function in human mammary epithelial cells is similar to that of Xwnt5a, its up-regulation at confluence may be a mechanism for inhibition of cell migration beyond confluence.