Disruption of Epithelial Cell-Matrix Interactions Induces Apoptosis

Cell-matrix interactions have major effects upon phenotypic features such as gene regulation, cytoskeletal structure, differentiation, and aspects of cell growth control. Programmed cell death (apoptosis) is crucial for maintaining appropriate cell number and tissue organization. It was therefore of interest to determine whether cell-matrix interactions affect apoptosis. The present report demonstrates that apoptosis was induced by disruption of the interactions between normal epithelial cells and extracellular matrix. We have termed this phenomenon "anoikis" Overexpression of bcl-2 protected cells againstanoikis. Cellular sensitivity to anoikis was apparently regulated: (a) anoikis did not occur in normal fibroblasts; (b) it was abrogated in epithelial cells by transformation with v-Ha-ras, v-src, or treatment with phorbol ester; (c) sensitivity to anoikis was conferred upon HTI080 cells or v-Ha-ms-transformed MDCK ceils by reversetransformation with adenovirus Ela; (d) anoikis in MDCK cells was alleviated by the motility factor, scatter factor. The results suggest that the circumvention of anoikis accompanies the acquisition of anchorage independence or cell motility. C ELL-matrix interactions have major effects upon phenotypic features such as gene regulation; cytoskeletal structure, differentiation, and aspects of cell growth control (Adams and Watt, 1993; Blau and Baltimore, 1991; Ingber, 1993). In particular, determination of anchorage dependence is an important function of cell-matrix interactions. The restriction of cell proliferation to matrixinteracting cells serves to prevent dysplasia; the circumvention of anchorage dependence plays an important role in tumorigenesis (Stoker et al., 1968). In previous studies, the growth arrest induced by suspension of fibroblasts was found to be reversible (Folkman and Moscona, 1978; Ben-Ze'ev et al., 1980). However, the fate of other cell types challenged similarly was not examined. Programmed cell death (apoptosis; Tomei and Cope, 1991; M. Raft, 1992; Lee et al., 1993; Marx, 1993; Barinaga, 1993; Vaux, 1993) is crucial for maintaining appropriate cell number and tissue organization in certain cell types such as lymphocytes and neurons. We considered that possibility that, for certain cell types, lack of matrix attachment could stringently restrict inappropriate cell growth by inducing apoptosis. Without apoptosis, detached cells could possibly reattach to inappropriately localized matrices, including the matrix that they would eventually synthesize themselves, and resume growth. However, apoptosis occurring in detached cells would abrogate this escape mechanism. Address all correspondence to S. M. Frisch, La Jolla Cancer Research Foundation, 10901 N. Torrey Pines Road, La Jolla, CA 92037. This article reports that a form of apoptosis that we call "anoikis" was induced by the disruption of cell-matrix interactions in two model epithelial cell lines. The authenticity of the apoptotic form of cell death was demonstrated by several criteria. Regulation of apoptosis thus appears to be a new function for cell-matrix interactions. Aside from attachment to extraceUular matrix, epithelial cells are linked to each other via tight junctions, adherens junctions and desmosomes (Farquhar and Palade, 1963). These cells form the frst tissues to emerge in the embryo. Mesenchymal cells differentiate from the embryonic epithelia (Hay, 1990). Unlike the stationary epithelial cells, mesenchymal cells are invasive, motile, and do not adhere to each other. Certain tissue remodeling events, as well as oncogenic transformation, recapitulate the transition from epithelial to mesenchymal phenotype (Zuk et al., 1989; Behrens et al., 1991; Schmidt et al., 1993). We reasoned that cell motility or transformation might require matrix-independent survival. Because anoikis would be incompatible with these phenotypes, we tested the prediction that cell motility factors, transformation or fibroblastic (motile) phenotypes might confer resistance to anoikis. Evidence confirming these predictions is presented. Transformation or treatment with a cell motility factor conferred resistance to anoikis, while reverse-transformation conferred sensitivity; normal fibroblasts were resistant. These results suggest that the acquisition of anchorage-independent or motile phenotypes alleviates anoikis. Cellular sensitivity to anoikis can therefore be regulated. © The Rockefeller University Press, 0021-9525/94/02/619/8 $2.00 The Journal of Ce|l Biology, Volume 124, Number 4, February 1994 619-626 619 on July 9, 2017 jcb.rress.org D ow nladed fom Materials and Methods