CELLULAR GROWTH AND SURVIVAL ARE MEDIATED BY BETA-1 INTEGRINS IN NORMAL HUMAN BREAST EPITHELIUM BUT NOT IN BREAST-CARCINOMA

We previously established a rapid three-dimensional assay for discrimi nation of normal and malignant human breast epithelial cells using a l aminin-rich reconstituted basement membrane. In this assay, normal epi thelial cells differentiate into well-organized acinar structures wher eas tumor cells fail to recapitulate this process and produce large, d isordered colonies. The data suggest that breast acinar morphogenesis and differentiation is regulated by cell-extracellular matrix (ECM) in teractions and that these interactions are altered in malignancy. Here , we investigated the role of ECM receptors (integrins) in these proce sses and report on the expression and function of potential laminin re ceptors in normal and tumorigenic breast epithelial cells. Immmunocyto chemical analysis showed that normal and carcinoma cells in a three-di mensional substratum express profiles of integrins similar to normal a nd malignant breast tissues in situ. Normal cells express alpha 1, alp ha 2, alpha 3, alpha 6, beta 1 and beta 4 integrin subunits, whereas b reast carcinoma cells show variable losses, disordered expression, or downregulation of these subunits. Function-blocking experiments using inhibitory antiintegrin subunit antibodies showed a >5-fold inhibition of the formation of acinar structures by normal cells in the presence of either anti-beta 1 or anti-alpha 3 antibodies, whereas anti-alpha 2 or -alpha 6 had little or no effect. In experiments where collagen t ype I gels were used instead of basement membrane, acinar morphogenesi s was blocked by anti-beta 1 and -alpha 2 antibodies but not by anti-a lpha 3. These data suggest a specificity of integrin utilization depen dent on the ECM ligands encountered by the cell. The interruption of n ormal acinar morphogenesis by anti-integrin antibodies was associated with an inhibition of cell growth and induction of apoptosis. Function -blocking antibodies had no inhibitory effect on the rate of tumor cel l growth, survival or capacity to form colonies. Thus under our cultur e conditions breast acinar formation is at least a two-step process in volving beta 1-integrin-dependent cellular growth followed by polariza tion of the cells into organized structures. The regulation of this pa thway appears to be impaired or lost in the tumor cells, suggesting th at tumor colony formation occurs by independent mechanisms and that lo ss of proper integrin-mediated cell-ECM interaction may be critical to breast tumor formation.