Isolation and characterization of epinectin, a novel adhesion protein for epithelial cells

Activity of heat shock genes' promoters in thermally contrasting animal species

Heat shock gene promoters represent a highly conserved and universal system for the rapid induction of transcription after various stressful stimuli. We chose pairs of mammalian and insect species that significantly differ in their thermoresistance and constitutive levels of Hsp70 to compare hsp promoter strength under normal conditions and after heat shock (HS). The first pair includes the HSPA1 gene promoter of camel (Camelus dromedarius) and humans. It was demonstrated that the camel HSPA1A and HSPA1L promoters function normally in vitro in human cell cultures and exceed the strength of orthologous human promoters under basal conditions. We used the same in vitro assay for Drosophila melanogaster Schneider-2 (S2) cells to compare the activity of the hsp70 and hsp83 promoters of the second species pair represented by Diptera, i.e., Stratiomys singularior and D. melanogaster, which dramatically differ in thermoresistance and the pattern of Hsp70 accumulation. Promoter strength was also monitored in vivo in D. melanogaster strains transformed with constructs containing the S. singularior hsp70 ORF driven either by its own promoter or an orthologous promoter from the D. melanogaster hsp70Aa gene. Analysis revealed low S. singularior hsp70 promoter activity in vitro and in vivo under basal conditions and after HS in comparison with the endogenous promoter in D. melanogaster cells, which correlates with the absence of canonical GAGA elements in the promoters of the former species. Indeed, the insertion of GAGA elements into the S. singularior hsp70 regulatory region resulted in a dramatic increase in promoter activity in vitro but only modestly enhanced the promoter strength in the larvae of the transformed strains. In contrast with hsp70 promoters, hsp83 promoters from both of the studied Diptera species demonstrated high conservation and universality.

The laminin receptor and basement membrane dissolution: role in tumour metastasis

Tumour invasion and metastasis is a complex process involving multiple interactions of tumour cells with host cellular and extracellular elements. Metastasizing tumour cells traverse basement membranes at many stages in the metastatic cascade. Immunohistology studies demonstrate that the basement membranes are defective in all human malignant epithelial neoplasms studied to date. The basement membrane is absent in regions of microinvasion and adjacent to actively invading tumour cells. In contrast, benign neoplasms retain a continuous basement membrane. This distinction may have diagnostic value in surgical pathology. Tumour cells are hypothesized to traverse basement membranes by a three-step process: attachment, local degradation of the basement membrane by type IV collagenase and other proteases, and locomotion. The first step may be mediated in part by specific cell surface receptors which bind to laminin in the basement membrane. The laminin receptor has been purified from a series of different human carcinomas. The receptor has an Mr of 67 000 and a binding coefficient of 2 nM. The content of unoccupied receptors is markedly augmented in invasive human breast cancer compared to benign controls.

Limited cell attachment time as a method to synchronize cells grown in monolayer culture

A novel method of synchronizing monolayer tissue culture cells is described. By limiting the period of attachment of trypsinized cells and the subsequent removal of unattached cells a G1 population of cells is isolated. Evaluation of the degree of synchrony has been carried out by measuring the labeling index and incorporation of [3H]thymidine into DNA. Further conformation of synchrony, as well as a comparison with synchrony by isoleucine deprivation, was obtained by flow cytometry. The expected peak in DNA synthesis rate following limited attachment was observed. This peak becomes more prominent and shifts to earlier times with shorter attachment intervals. The synchronization method described is simple, rapid, yields a substantial number of cells, and is applicable to many cell lines.

Epithelial and neural localization and heparin binding of the cell-substratum adhesion molecule, epinectin

Epinectin, a cell-substratum adhesion promoting molecule, was first isolated from the extracellular matrix of A431 human squamous carcinoma cells. In order to determine the biologic significance of epinectin, we determined the distribution of epinectin in various rat epithelial tissues by indirect immunofluorescence microscopy. Polyclonal antibodies to epinectin stained basal cells and basilar regions of skin, urinary bladder, and vagina. There was predominantly cytoplasmic staining along with amorphous extracellular staining. Strong staining was also noted in sebaceous glands and hair follicles. The immunoreactivity for epinectin in the skin was distinct from that for fibronectin, laminin, and type IV collagen. Antibodies to epinectin also stained subpopulations of neurons in the cerebrum and cerebellum. Epinectin antibodies strongly stained the cytoplasm of some pineal cells and cells of the pars intermedia of the pituitary. The distribution of epinectin suggests a role not only in epithelial cell-substratum adhesion, but in neuronal cell function. Heparan sulfate is known to be involved in the binding of several adhesion promoting molecules to cell surfaces. In order to assess the mechanism of adhesion of epinectin to cells, we measured the binding of 3H-heparin to epinectin. Binding of 3H-heparin was concentration dependent and inhibitable with cold heparin.

Biochemical characterization of the epithelial basement membrane antigen defined by the monoclonal antibody KF-1

The KF-1 monoclonal antibody has been shown to identify a noncollageneous component of the lamina densa of the basement membrane zone of human skin. In the present work, the monoclonal antibody and the antigen were further characterized. KF-1 monoclonal antibody is an IgG3 immunoglobulin with no binding to staphylococcal protein A. Two squamous carcinoma cell lines--namely, TR131 and TR146--quantitatively express the antigen. Immunofluorescence techniques showed that the antigen is a cell surface antigen, is sensitive to Triton X-100 extraction, and is concentrated in cell areas from which actin fibers are excluded. Immunoblot analysis showed that this monoclonal antibody identifies a 72 kD polypeptide present in TR131 cell extract as well as in cultured human keratinocyte cell extract.

Human fibronectin contains distinct adhesion- and motility-promoting domains for metastatic melanoma cells

The active migration of tumor cells through extracellular matrices has been proposed to play a role in certain aspects of metastasis. Metastatic tumor cells migrate in vitro in response to substratum-bound adhesive glycoproteins such as fibronectin. The present studies use affinity-purified proteolytic fragments of fibronectin to determine the nature of adhesion- and/or motility-promoting domains within the protein. Two distinct fragments were identified with cell adhesion-promoting activities. By a number of criteria, the adhesive activity promoted by these two fragments was distinct. One fragment, a 75-kD tryptic fragment purified by monoclonal antibody chromatography, promoted the adhesion, spreading, and haptotactic motility of melanoma cells. Experiments using a synthetic cell attachment peptide in solution indicated that at least part of the attachment activity exhibited by the 75-kD fragment is mediated by the sequence arg-gly-asp-ser. It was not possible to demonstrate migration-stimulating activity using a small (11.5 kD) peptic fragment containing this sequence (Pierschbacher, M.D., E. G. Hayman, and E. Ruoslahti, 1981, Cell, 26:259-267) suggesting that another cell-binding activity within the 75 kD fragment distinct from arg-gly-asp-ser might be required for motility. The second fragment that stimulated melanoma adhesion was a 33-kD tryptic/catheptic carboxyl-terminal heparin-binding fragment, which is localized to the A chain of fibronectin. This fragment promotes adhesion and spreading but not the motility of these cells. Melanoma adhesion to this heparin-binding fragment was sensitive to the effects of cycloheximide, which contrasted adhesion to the haptotaxis-promoting fragment. Importantly, these studies illustrate that haptotaxis in response to fibronectin is not due to simple adhesion gradients of this protein. The results are discussed in light of a model for multiple distinct cell surface constituents mediating cell adhesion and motility on fibronectin.

Cell adhesion to low-Mr proteins extractable from mineralized and soft connective tissues

Guanidinium chloride (4 M) containing proteinase inhibitors was used to extract proteins from porcine calvariae and long bones. The extracted proteins were separated on polyacrylamide slab gels and transferred electrophoretically to nitrocellulose strips. Proteins with cell-adhesion properties were identified by incubating the strips with cells and staining with Amido Black. In addition to binding to fibronectin, both bone cells and fibroblast-like cells adhered to proteins of Mr approximately 30 000 and approximately 14 000-17 000. 4 M-Guanidinium chloride extracts of porcine skin and gingiva yielded cell-binding proteins with similar Mr values. These data suggest that these low-Mr proteins may have a general cell-adhesion function in both soft and mineralized connective tissues.

Human spreading factor: synthesis and response by HepG2 hepatoma cells in culture

Human serum spreading factor (SF) is a cell adhesion and spreading-promoting glycoprotein purified from serum or plasma that mediates effects in a wide variety of animal cell culture systems. HepG2 human hepatoma cells were found to synthesize and secrete SF into culture medium. Quantitative immunoassay of the protein indicated a concentration of about 1 microgram/ml in 48 hr-conditioned medium from confluent cultures. Although fibronectin also was synthesized and secreted into the culture medium, HepG2 cell spreading was observed in response to human serum SF, but not in response to human plasma fibronectin. Immunoprecipitation of SF from culture medium of cells metabolically-labeled with leucine, fucose or glucosamine identified a single form of the molecule of approximately 70,000 daltons. Treatment of cultures with tunicamycin inhibited incorporation of fucose and glucosamine into immunoprecipitated SF, but did not prevent synthesis and secretion of the protein. Electrophoretic analysis and cell spreading assays showed that SF secreted by tunicamycin-treated HepG2 cells was of molecular weight (mw) approximately 60,000, and was biologically active.

The role of cell adhesion proteins--laminin and fibronectin--in the movement of malignant and metastatic cells

Metastasizing tumor cells must traverse diverse extracellular matrices during dissemination. Extracellular matrices consist of two basic types, interstitial stroma and basement membranes. Extracellular matrices are chemically complex structures that interact with cell surfaces by a number of mechanisms. There has been a great deal of effort in recent years to understand the molecular nature of extracellular matrices, especially as it relates to the adhesion of normal and malignant cell types. Adhesive noncollagenous glycoproteins, such as laminin and fibronectin, serve pivotal roles in basement membrane and stromal matrices, respectively. These proteins participate in establishing the architecture of extracellular matrices as well as in attaching to the surface of cells and affecting cellular phenotype. This phenotypic effect ranges from adhesion and motility to growth and differentiation. Changes in adhesive characteristics and motility of cells have long been suspected to play a role in mediating the spread of malignant neoplasms. This article is designed to review extracellular matrix constituents that are currently known that can mediate the adhesion and motility of malignant neoplasms. The adhesion of normal and malignant cells to matrices is a complex process mediated by several distinct mechanisms which are initially manifested by changes in cytoskeletal architecture. The topic of normal and malignant cell adhesion to matrices will also be discussed in this regard, since any explanation of tumor cell migration must account for the complex dynamic interactions of the cell surface with the substratum as well as with the cytoskeleton. Finally, current efforts designed to understand the molecular nature of tumor cell:matrix interactions that contribute to metastatic behavior will also be discussed. The rationale behind these studies is that selective inhibition of specific tumor:extracellular matrix interactions can provide an avenue for therapeutic intervention of metastatic cancer.