Fibroblast surface antigen (SF): molecular properties, distribution in vitro and in vivo, and altered expression in transformed cells

Ail protein binds ninth type III fibronectin repeat (9FNIII) within central 120-kDa region of fibronectin to facilitate cell binding by Yersinia pestis

The Yersinia pestis adhesin molecule Ail interacts with the extracellular matrix protein fibronectin (Fn) on host cells to facilitate efficient delivery of cytotoxic Yop proteins, a process essential for plague virulence. A number of bacterial pathogens are known to bind to the N-terminal region of Fn, comprising type I Fn (FNI) repeats. Using proteolytically generated Fn fragments and purified recombinant Fn fragments, we demonstrated that Ail binds the centrally located 120-kDa fragment containing type III Fn (FNIII) repeats. A panel of monoclonal antibodies (mAbs) that recognize specific epitopes within the 120-kDa fragment demonstrated that mAb binding to (9)FNIII blocks Ail-mediated bacterial binding to Fn. Epitopes of three mAbs that blocked Ail binding to Fn were mapped to a similar face of (9)FNIII. Antibodies directed against (9)FNIII also inhibited Ail-dependent cell binding activity, thus demonstrating the biological relevance of this Ail binding region on Fn. Bacteria expressing Ail on their surface could also bind a minimal fragment of Fn containing repeats (9-10)FNIII, and this binding was blocked by a mAb specific for (9)FNIII. These data demonstrate that Ail binds to (9)FNIII of Fn and presents Fn to host cells to facilitate cell binding and delivery of Yops (cytotoxins of Y. pestis), a novel interaction, distinct from other bacterial Fn-binding proteins.

Differentiation of primary human submandibular gland cells cultured on basement membrane extract

There is no effective treatment for the loss of functional salivary tissue after irradiation for head and neck cancer or the autoimmune disease Sjögren's syndrome. One possible approach is the regeneration of salivary glands from stem cells. The present study aimed to investigate whether small pieces of human submandiblar gland tissue contain elements necessary for the reconstruction of salivary rudiments in vitro via acinar and ductal cell differentiation. Primary submandibular gland (primary total human salivary gland; PTHSG) cells were isolated from human tissue and cultured in vitro using a new method in which single cells form an expanding epithelial monolayer on plastic substrates. Differentiation, morphology, number, and organization of these cells were then followed on basement membrane extract (BME) using RNA quantitation (amylase, claudin-1 (CLN1), CLN3, kallikrein, vimentin), immunohistochemistry (amylase and occludin), viability assay, and videomicroscopy. On the surface of BME, PTHSG cells formed acinotubular structures within 24 h, did not proliferate, and stained for amylase. In cultures derived from half of the donors, the acinar markers amylase and CLN3 were upregulated. The PTHSG culture model suggests that human salivary gland may be capable of regeneration via reorganization and differentiation and that basement membrane components play a crucial role in the morphological and functional differentiation of salivary cells.

Maxillary fibrosarcoma with extracellular immuno-characterization

Maxillary fibrosarcoma of a 31-year-old female is described with special reference to immunofluorescent characterization of the extracellular matrix. Following extractions, endodontic treatment and occlusal adjustment the tumour was operated on. The spindle-shaped tumour cells displayed a herring-bone pattern. The tumour was diagnosed as a fibrosarcoma and graded as poorly differentiated. Immunostaining for the specific type I collagen was positive throughout the tumour matrix, whereas staining for type III collagen was faint and occasional, and did not definitely codistribute with reticulin. Staining for type IV collagen and fibronectin in the tumour matrix was negative.

Properties and fate of plasma fibronectin bound to the tissue culture substratum

Plasma fibronectin (pFn) is a serum protein which, when adsorbed to a glass or plastic substratum, mediates the adhesion of fibroblasts in culture. We have studied some of the details of its adsorption and subsequent fate. By using 125I-labeled pFn, we show that a substratum incubated with pFn adsorbs approximately 0.4 microgram/cm2 pFn (a monomolecular layer), and one incubated with medium containing serum adsorbs approximately 7 ng/cm2 pFn (a 12-fold enrichment relative to a random selection of the soluble proteins). SDS-polyacrylamide gel electrophoresis (SDS-PAGE) suggests the bound serum proteins (eluted with SDS) are primarily BSA and beta-globulins. The bound pFn adheres so tightly, though, that most resists elution, as assayed 1) with pFn radioiodinated before binding, 2) with pFn radioiodinated after binding, or 3) by the cell spreading activity of the bound pFn retained after SDS treatment. Under culture conditions, there is a continuous "turnover" of substratum-bound pFn: soluble pFn can bind to a serum-coated substratum, while bound pFn is gradually removed by incubation with serum proteins. The presence of fibroblasts increases the rate of this removal several-fold. By SDS-PAGE the material removed (as well as that eluted from the substratum with SDS after cell detachment) is intact pFn or large (possibly proteolytically generated) fragments. Thus, pFn binds preferentially to the tissue culture substratum, but can be removed subsequently by the combined action of cells and other serum proteins.

Occurrence of fibronectin on the primary mesenchyme cell surface during migration in the sea urchin embryo

The distribution of fibronectin in situ in the sea urchin embryo was examined by using indirect immunofluorescence with an antibody raised against human plasma fibronectin. Fibronectin was detected on the surfaces of primary mesenchyme cells in the mid-mesenchyme blastula stage, when these cells are migratory. However, it was not detected on these cells at the early mesenchyme blastula or early gastrula stages. Also, it was not detected in the blastocoel nor on the basal surface of the blastular wall. The migration of the primary mesenchyme cells is therefore correlated with a stage-dependent occurrence of cell surface-associated fibronectin.

Effects of sodium butyrate on the membrane glycoconjugates of murine sarcoma virus-transformed rat cells

The temporal relationship between butyrate-induced cellular flattening of murine sarcoma virus-transformed rat cells (MSV-NRK) and alterations in certain surface-associated biochemical markers of transformation, e.g., surface glycopeptides, glycolipids, fibronectin, hexose uptake, and cell-substrate adhesion was examined. The induction of elevated levels of the ganglioside GM3 and of a GDla-like ganglioside were observed to precede or to parallel cellular flattening. Likewise, enhanced incorporation of radioisotopically labeled fucose into a novel fucose-containing component, i.e., glucopyranosyl (1 leads to 3) fucopyranosyl-threonine, was also observed to occur at an early stage of cellular flattening. In contrast, a shift in the molecular weight distribution of trypsin-sensitive, surface fucopeptides was observed to occur at a late stage of cellular flattening. Moreover, surface fibronectin was not detectable in the butyrate-flattened MSV-NRK cells despite the fact that the cells manifested significantly enhanced cell-substrate adhesion. Thus, butyrate appears to be a useful tool for understanding the sequential changes associated with expression of the transformed phenotype of MSV-NRK cells.

The reversal immune surveillance hypothesis

The proposed reveral immune surveillance hypothesis is based on the identification primarily of self and secondarily of foreignness, unlike the original hypothesis that is based on the identification of foreignness per se. The proposed system is considered to have evolved from the invertebrates through to the vertebrates to become more complex in the mammals, and involves the identification of cell types by lymphocytes through the cell type surface pattern and major histocompatibility antigens. The identification of self and associated foreignness by the immune system is required for the regulation of cell differentiation and replication, and because of this design, the ability of the immune system to destroy foreignness can be regarded as a natural consequence. The reversal immune surveillance hypothesis explains why spontaneously occurring tumours may not be antigenic, in the sense of eliciting their own destruction, and is consistent with the destruction of tumour cells that display significant amounts of viral antigens or gross antigenic changes induced by carcinogenic agents. It is also able to explain the stimulation and inhibition of tumour development.

Distribution of a major connective tissue protein, fibronectin, in normal human tissues

Fibronectin is a major surface-associated glycoprotein of cultured fibroblasts and it is also present in human plasma. Antiserum specific for human fibronectin was used to study the distribution of fibronectin in normal adult human tissues. The protein was detected (a) characteristically in various basement membranes including capillary walls: (b) around individual smooth muscle cells and in the sarcolemma of striated muscle fibers; and (c) in the stroma of lymphatic tissue and as thin fibers in loose connective tissue. The distribution of fibronectin was distinct from that of collagen and elastic fibers, but was very similar to reticulin, as demonstrated by conventional histological staining. The results indicate that fibronectin is a major component of connective tissue matrix. The distribution also indicates that most types of adherent cells abut fibronectin-containing structures. This supports the possible role of fibronectin in cell-cell and cell-matrix interactions in tissues.

Distribution of a major surface-associated glycoprotein, fibronectin, in cultures of adherent cells

Fibronectin was present in media and cell layers of cultures of adherent cells from human skin, kidney, lung, chest wall, liver, and heart. Cell-surface fibronectin, visualized by immunofluorescence, was in dense fibrillar (cultures from lung), discrete fibrillar (e.g., cultures from skin), or punctate (some cultures from kidney) structures. The subunit sizes of cell-surface fibronectin and fibronectin soluble in medium appeared identical in sodium dodecyl sulfate-polyacrylamide gels. To explain the polymorphism of cell-surface fibronectin, there must be chemical differences among the fibronectins synthesized by different cell strains or factors in the cell layer which influence fibronectin binding and aggregation.

Connective tissue origin of the amyloid-related protein SAA

Protein SAA is a serum protein related to the major constituent of secondary amyloid fibrils, protein AA, and has been suggested to be a precursor of the amyloid protein AA. In the present study, the origin of SAA was investigated by studying human fetal tissues and cultured human fetal fibroblasts with the indirect immunofluorescence technique. Anti-SAA antibodies reacted strongly with cultured fibroblasts producing a fine fibrillary cytoplasmic staining and with extracellular fibrils in loose connective tissues and vessel walls. The reactions were specifically inhibited by absorption with degraded amyloid material, isolated protein AA, isolated protein SAA, and sera from patients with elevated levels of SAA. In contrast, no inhibition was seen with amyloid fibril material devoid of AA protein or by human sera in which SAA was not detectable by double-diffusion tests. These observations showed that SAA-like material is produced by fibroblasts and indicate that it is a normal constituent of developing extracellular connective tissue fibers.