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Biomedical subjects

A T Hewitt

Publications and source records attributed to A T Hewitt.

29 records · Page 2Linked to original sources
PubMed1982

The isolation and partial characterization of chondronectin, an attachment factor for chondrocytes.

We have previously demonstrated that the adhesion of embryonic chick sternal chondrocytes to a type II-collagen substrate is not mediated by fibronectin but rather by a distinct attachment factor which we have named chondronectin. Here we describe the isolation, properties, and biological activity of chondronectin prepared from chicken serum. Chondronectin is shown to be a glycoprotein with an estimated Mr = 180,000. After reduction, it migrates as subunits of Mr = 70,000. Antibodies directed against chondronectin inhibited the attachment of chondrocytes to type II collagen. Chondronectin is immunologically distinct from either fibronectin or laminin. Immunofluorescence studies on frozen sections of embryonic chick sternal cartilage and of cultured sternal chondrocytes showed that chondronectin is cell-associated rather than a major matrix component.

Animals↗
PubMed1982

Immunofluorescence localization of fibronectin in chondrosarcoma cartilage matrix.

In this study, we have compared the extracellular matrix components and the in vitro adhesion characteristics of normal rat epiphysial chondrocytes with those from the Swarm rat chondrosarcoma, which has many of the biochemical characteristics of normal cartilage. With the use of immunofluorescence techniques, tissue slices and chondrocytes in culture were tested for the presence of collagen types I and II, cartilage-characteristic proteoglycan, and fibronectin. Both normal and tumor matrix contained type II collagen and cartilage proteoglycan, but only the tumor matrix contained fibronectin. In culture, tumor-derived chondrocytes continued to accumulate fibronectin in their matrix, even after deposition of type II collagen and proteoglycans, while normal chondrocytes did not. When the attachment characteristics of both types of chondrocytes were compared, tumor chondrocytes required fibronectin for attachment, while normal chondrocytes used another attachment factor that had been identified previously as chondronectin. These studies suggest that, although biochemically similar to normal chondrocytes, tumor chondrocytes are no longer able to express the regulatory mechanisms for fibronectin accumulation.

Animals↗
PubMed1982

The role of chondronectin and cartilage proteoglycan in the attachment of chondrocytes to collagen.

The interaction of cells with collagen has previously been demonstrated to be of importance in the growth and differentiation of various cells (reviewed by Hay 1981; Kleinman, et al 1981). Chondronectin has been demonstrated to be involved in mediating the interaction of chondrocytes with their matrix. Unlike fibronectin, which binds directly to collagen before the cell can interact with this macromolecular complex, chondronectin must interact with cartilage proteoglycan monomer in order to function efficiently as an attachment factor. Figure 4 is a schematic representation of the interaction between chondrocytes and their matrix components. We suggest that if these specific interactions are perturbed by the introduction of some outside factor, the phenotypic expression of the cells could be altered. For example, chondrocytes are not normally associated with fibronectin (Dessau, et al 1978; Stenman, Vaheri 1978). However, if chondrocytes are grown in the presence of fibronectin they will become more fibroblastic and stop making the cartilage-specific molecules of type II collagen and cartilage proteoglycan (Pennypacker, et al 1979; West et al 1979). Consequently, it is possible that the specific interactions seen between chondrocytes, chondronectin, type II collagen, and proteoglycan may be essential for the maintenance of the chondrocyte phenotype.

Animals↗
PubMed1981

Localization of the human fibronectin (FN) gene on chromosome 8 by a specific enzyme immunoassay.

The fibronectin produced by clonal murine-human hybrid cell lines containing various complements of human chromosomes was measured. Human and murine fibronectins were assayed by specific immunoassay, and the production of human fibronectin was correlated with karyology and isozyme markers for specific human chromosomes. The data show a 100% concordance between the expression of human fibronectin and glutathione reductase, a marker for human chromosome 8, indicating that chromosome 8 codes for the fibronectin polypeptide.

Animals↗
PubMed1980

Identification of an adhesion factor for chondrocytes.

The attachment of chondrocytes to collagen substrates is stimulated by serum but not by fibronectin. The active material in serum was partially purified and was shown to be a protein by its sensitivity to trypsin and heat and its chromatographic properties. This factor, which we have named chondronectin, is distinct from fibronectin and does not stimulate fibroblast attachment. Because material with similar attachment-enhancing activity is produced by chondrocytes and is extractable from cartilage, chondronectin may be a chondrocyte-specific attachment protein.

Animals↗
PubMed1978

The involvement of microfilaments and microtubules in the lateral mobility of lectin binding sites of normal and brachypod mouse limb mesenchyme.

It has been demonstrated that differences exist in the lateral mobility of Con A- and WGA-binding sites in the membranes of normal and brachypod mouse limb mesenchymal cells (Hewitt et al., 1978). The work presented here investigates the involvement of microtubules and microfilaments as mediators of binding site mobility in this system. Treatment of cells with colchicine suggests that microtubules are not involved in the mobility of either type of lectin-binding site. Disruption of microfilaments with cytochalasin B prevents the redistribution of Con A-binding sites but not those of WGA. the results were found to be the same for both genotypes. This suggests that the differences which have been found between genotypes are related to some mechanism of restraining the lateral mobility of lectin binding sites other than by attachment to microtubules and microfilaments.

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