Two antisera were raised in goats against material shed by two different mammary epithelial cell lines into serum-free culture medium. These antisera, when added to the medium of intact, growing mouse mammary tumor cells in the absence of complement, cause distinct and dramatic alterations in cell morphology and adhesiveness. One antiserum (anti-SFM I) causes mouse mammary tumor epithelial cells to round and detach from the substratum. Treatment with the other antiserum (anti-SFM II) does not affect cell-substratum interactions, but causes the cells to convert from an epitheloid to a fibroblastic morphology. Statistical analysis of transmission electron micrographs of control and antibody-treated cells indicates that treatment with anti-SFM II is associated with a substantial reduction in the extent of intercellular junctions, particularly desmosomes. To identify the components with which the two antisera interact, nonionic detergent extracts of mouse mammary tumor cells were fractionated, and the ability of various fractions to block the morphological effects of either antiserum was determined. The whole Nonidet P40 (NP40) extract of the epithelial cells blocked the effects of both antisera. After the extract was subjected to ion exchange and lectin affinity chromatography, two separate fractions were obtained. One fraction blocks and anti-SFM I induced rounding and detachment of cells from the substratum. The second fraction blocks the effects of both antisera. The isolation of the former fraction, which has highly restricted number of components, represents a significant first step toward identifying the surface membrane molecule(s) involved in cell-substratum adhesion in epithelial cells.

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