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Heidelberg, Germany—It sounds like Mission Impossible: Follow the changes taking place in a cell by identifying the thousands of different proteins the cell produces and watching how they ebband flow over time. But a growing band of researchers believes that improved analytical techniques may soon make such an approach feasible, and they haveeven coined a new term for it: proteome research. Prototype systems that screen and analyze thousands of proteins at a time look promising.

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Fibronectin (FN ; also called large external transformation-sensitive [LETS] protein or cell-surface protein [CSP]) is a large cell-surface glycoprotein that is frequently observed to be either absent or greatly reduced on the surfaces of malignant cells grown in vitro . Because FN may be a useful molecular marker of cellular malignancy, we have carried out an extensive screening to test the specific association among the degree ofexpression of FN, anchorage-independent growth, and tumorigenicity in the athymic nude mouse . A variety of diploid cell strains and established cell lines were tested for the expression of surface FN by indirect immunofluorescence using rabbit antisera against human cold insoluble globulin, rodent plasma FN, or chicken cell-surface FN . Concomitantly, the cells were assayed for tumor formation in nude mice and for the ability to form colonies in methylcellulose . Tumorigenic cells often showed very low surface fluorescence, confirming earlier reports . However, many highly tumorigenic fibroblast lines from several species stained strongly with all three antisera . In contrast, the anchorage-independent phenotype was nearly always associated with tumorigenicity in -35 cell lines examined in this study . In another series of expriments, FNpositive but anchorage-independent cells were grown as tumors in nude mice and then reintroduced into culture . In five of the six tumor-derived cell lines, cellsurface FN was not significantly reduced ; one such cell line showed very little surface FN .Our data thus indicate that the loss of cell-surface FN is not a necessary step in the process of malignant transformation and that the growth of FN-positive cells as tumors does not require a prior selection in vivo for FN-negative subpopulations .KEY WORDS fibronectin . cell studied in vitro . These generally include decreased transformation . anchorage independencesensitivity to factors which restrict the growth of tumorigenicity . nude mouse normal cells, such as low serum concentration (8, 47), lack of a solid surface for anchorage (26, 52, Malignant transformation of animal cells involves 53), and contact inhibition (6,57,58) . In addition changes in many cellular properties which can be to their greater cellular growth autonomy in vitro, J . CELL BIOLOGY