In a recently developed human breast cancer model, treatment of tumor cells in a 3-dimensional culture with inhibitory β1-integrin antibody or its Fab fragments led to a striking morphological and functional reversion to a normal phenotype. A stimulatory β1-integrin antibody proved to be ineffective. The newly formed reverted acini re-assembled a basement membrane and re-established E-cadherin–catenin complexes, and re-organized their cytoskeletons. At the same time they downregulated cyclin D1, upregulated p21cip,waf-1, and stopped growing. Tumor cells treated with the same antibody and injected into nude mice had significantly reduced number and size of tumors in nude mice. The tissue distribution of other integrins was also normalized, suggesting the existence of intimate interactions between the different integrin pathways as well as adherens junctions. On the other hand, nonmalignant cells when treated with either α6 or β4 function altering antibodies continued to grow, and had disorganized colony morphologies resembling the untreated tumor colonies. This shows a significant role of the α6/β4 heterodimer in directing polarity and tissue structure. The observed phenotypes were reversible when the cells were disassociated and the antibodies removed. Our results illustrate that the extracellular matrix and its receptors dictate the phenotype of mammary epithelial cells, and thus in this model system the tissue phenotype is dominant over the cellular genotype.

†These authors contributed equally to this workHere we show that cells lacking focal adhesion kinase (FAK) are refractory to motility signals from platelet-derived and epidermal growth factors (PDGF and EGF respectively), and that stable re-expression of FAK rescues these defects. FAK associates with activated PDGF-and EGF-receptor (PDGFR and EGFR) signalling complexes, and expression of the band-4.1-like domain at the FAK amino terminus is sufficient to mediate an interaction with activated EGFR. However, efficient EGF-stimulated cell migration also requires FAK to be targeted, by its carboxy-terminal domain, to sites of integrin-receptor clustering. Although the kinase activity of FAK is not needed to promote PDGF-or EGF-stimulated cell motility, kinase-inactive FAK is transphosphorylated at the indispensable Src-kinase-binding site, FAK Y397, after EGF stimulation of cells. Our results establish that FAK is an important receptor-proximal link between growth-factorreceptor and integrin signalling pathways.ransmembrane integrins bind to extracellular matrix proteins and generate important signals that regulate cell proliferation and migration events stimulated by receptors for soluble growth factors. Integrin and growth-factor signalling pathways can interact through several mechanisms, from membrane-proximal clustering of the two receptor types 1,2 to the activation of common downstream signalling pathways [3][4][5] . Although there is a wealth of knowledge regarding the signalling pathways activated by both integrin and growth-factor receptors, little is known about how these signals are integrated by cells and whether there are common receptor-proximal control points that synchronize the execution of biological functions such as cell motility.FAK is a non-receptor protein-tyrosine kinase (PTK) that indirectly localizes to sites of integrin-receptor clustering through Cterminal-domain-mediated interations 6 with integrin-associated proteins such as paxillin 7,8 and talin 9 . FAK becomes phosphorylated at seven to eight different tyrosine residues in vivo after engagement of integrin with matrix proteins 10

Establishment of the human placenta requires that fetal cytotrophoblast stem cells in anchoring chorionic villi become invasive. These cytotrophoblasts aggregate into cell columns and invade both the uterine interstitium and vasculature, anchoring the fetus to the mother and establishing blood flow to the placenta. Cytotrophoblasts colonizing spiral arterioles replace maternal endothelium as far as the first third of the myometrium. We show here that differentiating cytotrophoblasts transform their adhesion receptor phenotype so as to resemble the endothelial cells they replace. Cytotrophoblasts in cell columns show reduced E-cadherin staining and express VE-(endothelial) cadherin, platelet-endothelial adhesion molecule-1, vascular endothelial adhesion molecule-1, and ␣ 4-integrins. Cytotrophoblasts in the uterine interstitium and maternal vasculature continue to express these receptors, and, like endothelial cells during angiogenesis, also stain for ␣ V ␤ 3. In functional studies, ␣ V ␤ 3 and VE-cadherin enhance, while E-cadherin restrains, cytotrophoblast invasiveness. Cytotrophoblasts expressing ␣ 4 integrins bound immobilized VCAM-1 in vitro, suggesting that this receptor-pair could mediate cytotrophoblast-endothelium or cytotrophoblast-cytotrophoblast interactions in vivo, during endovascular invasion. In the pregnancy disorder preeclampsia, in which endovascular invasion remains superficial, cytotrophoblasts fail to express most of these endothelial markers (Zhou et al., 1997. J. Clin. Invest. 99:2152-2164.), suggesting that this adhesion phenotype switch is required for successful endovascular invasion and normal placentation. ( J. Clin. Invest. 1997.

In human pregnancy, placental cytotrophoblasts that invade the uterus downregulate the expression of adhesion receptors that are characteristic of their epithelial origin, and upregulate the expression of adhesion receptors that are expressed by vascular cells. We suggest that this transformation could be critical to endovascular invasion, the process whereby cytotrophoblasts invade the uterine spiral arterioles and line their walls (Zhou et al. J. Clin. Invest. 1997. 99: 2139-2151.). To better understand the in vivo significance of these findings, we tested the hypothesis that in preeclampsia, an important disease of pregnancy in which endovascular invasion is abrogated, cytotrophoblasts fail to adopt a vascular adhesion phenotype. In experiments described here we stained placental bed biopsy specimens from age-matched control pregnancies and from those complicated by preeclampsia with antibodies that recognize adhesion molecules that are normally modulated during this transformation. In preeclampsia, differentiating/invading cytotrophoblasts fail to express properly many of these molecules, including integrin, cadherin, and Ig superfamily members. These results suggest that preeclampsia is associated with failure of cytotrophoblasts to mimic a vascular adhesion phenotype. The functional consequences of this abnormality are unknown, but are likely to affect negatively cytotrophoblast endovascular invasion and uterine arteriole remodeling, thereby compromising blood flow to the maternal-fetal interface. ( J. Clin. Invest. 1997. 99:2152-2164.)