Recently, we isolated from human blood a protein named epibolin, which supports the spreading of mature epidermal cells in vitro. An antibody to epibolin blocks the cell-spreading activity of whole plasma (or serum). Using one cell line derived from a human tongue squamous carcinoma, we gathered evidence that epibolin also is necessary for the spread of these cancer cells in tissue culture. To test the generality of the epibolin effect on cancer cells and probe its mechanisms of action, the following studies are being undertaken. Using an in vitro assay, the dependence of several different human squamous, cancer-cell lines (HN1-5) on epibolin and antiepibolin for spreading will be determined. How epibolin affects cell morphology will be studied with time by phase contrast, interference reflection, and scanning and transmission electron microscopies. To separate cell spreading from cell migration, in vitro motility studies (by time-lapse cinemicrography) will be conducted using purified epibolin and each cell line. The location of the spreading protein on spread cells will be measured by indirect immunofluorescence using purified antibodies to epibolin. Finally, to test for domain structure of epibolin, its cancer-cell-spreading activity will be assayed after fragmenting the molecule and isolating the pieces by standard biochemical procedures. By understanding the serum component that supports cancer-cell spreading and how it acts, we hope to gain insight into the process of cancer invasion and metastasis and thereby acquire some means of controlling cancer dissemination. As we started studies on the spreading of various epithelial and cancer cell lines and their in vitro dependence on proteins (epibolin) in media, we observed something that we had anticipated in our original research proposal: some cell lines showed epibolin-dependent spreading and others showed protein- and epibolin-independent spreading. We observed that the protein-independence or dependence could be induced even in differentiated keratinocytes by manipulating the growth conditions of these cells. We learned that confluent cells require protein to spread but subconfluent cells spread to a considerable degree in the absence of protein. It appears subconfluent cells and those cancer cells that spread in the absence of protein do so because they make their own protein substrate. Defining that substrate is currently one of our efforts. Studies on the epibolin mechanism on epidermal-cell and cancer-cell spreading are currently in progress. The morphological and immunofluorescence studies will be conducted during the coming research year. (J)
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