Expression of an activated Notch4(int-3) oncoprotein disrupts morphogenesis and induces an invasive phenotype in mammary epithelial cells in vitro

The protein encoded by the Notch4 gene is a member of the Notch/lin-12 fami ly of transmembrane receptor proteins, which have been shown to control cel l fate determination and cell differentiation in a wide variety of organism s. Expression of Notch4(int-3), a truncated form of Notch4 having most of i ts extracellular domain deleted, as a transgene in mice induces the formati on of poorly differentiated mammary carcinomas. To establish whether Notch4 (int-3) has the capacity of subverting normal epithelial architecture, we a ssessed the effect of Notch4(int-3) expression on the in vitro morphogeneti c properties of TAC-2 mammary epithelial cells. When grown in three-dimensi onal collagen gels in the presence of hydrocortisone, both wild-type and La cZ-transfected TAC-2 cells formed alveolar-like structures composed of pola rized epithelial cells surrounding a central lumen. In contrast, TAC-2 cell s programmed to express Notch4(int-3) formed compact cell aggregates devoid of tissue-specific organization. In addition, when grown on the surface of a collagen gel, Notch4(int-3)-expressing TAG-2 cells invaded the underlyin g matrix, whereas TAG-2 LacZ cells remained strictly confined to the gel su rface. Expression of Notch4(int-3) in TAG-2 cells also disrupted contact-in hibition of cell proliferation, resulting in cell multilayering. Our result s suggest that the ability of Notch4(int-3) to subvert normal epithelial mo rphogenesis and to promote invasion of the extracellular matrix contributes significantly to its tumorigenic potential. (C) 2000 Wiley-Liss, Inc.