The human mammary gland basement membrane is integral to the polarity of luminal epithelial cells

We show that myoepithelial cell basement membrane derived E3 and E8 domains of laminin-1 are capable of polarizing luminal epithelial cells with regar d to epithelial membrane antigen localization. This event is dependent on t he alpha 6 integrin and results in aggregation and phosphorylation of the t yrosine residues of the focal adhesion kinase complex. We also demonstrate that uncultured normal luminal epithelial cells synthesize normal levels of beta and gamma laminin chains and reduced levels of alpha chains mRNA in c ommon with malignant epithelial cells. In contrast normal myoepithelial cel ls synthesize all three constituent chains of laminin-1. Therefore in breas t cancer the absence of myoepithelial cells could result in a lack of lamin in alpha chains which may contribute to loss of polarity of malignant epith elial cells. (C) 1999 Academic Press.