“…Although the exact function and mechanism of the protease(s) with respect to specific cellular alterations are unclear, many of the effects of the proteolytic activity appear to reside at the cell surface. Thus, when exogenous proteases are added to cultures of normal cells, alterations in the growth rate, agglutinability, adhesiveness, and morphology of the cells are observed (5,9,13,29,37,53,58); conversely, when specific protease inhibitors are added to cultures of transformed cells, the opposite effects on the cells' growth rate, agglutinability, adhesiveness, and morphology are observed (21,22,52,64); and finally, specific polypeptide alterations, temporally related to the onset of malignant transformation, have been detected on the surface of transformed ceils (10,25,27,28,62,65). It has been inferred from these studies that proteolytic activity may be enhanced in cultures of transformed cells and may be involved in both the initiation and the uninterrupted maintenance of characteristic changes on the surface membrane of the malignant cell.…”