Reciprocal interactions between beta 1-integrin and epidermal growth factor receptor in three-dimensional basement membrane breast cultures: A different perspective in epithelial biology

Anchorage and growth factor independence are cardinal features of the trans formed phenotype. Although it is logical that the two pathways must be core gulated in normal tissues to maintain homeostasis, this has not been demons trated directly. We showed previously that down-modulation of beta 1-integr in signaling reverted the malignant behavior of a human breast tumor cell l ine (T4-2) derived from phenotypically normal cells (HMT-3522) and led to g rowth arrest in a three-dimensional (3D) basement membrane assay in which t he cells formed tissue-like acini (14), Here, we show that there is a bidir ectional cross-modulation of beta 1-integrin and epidermal growth factor re ceptor (EGFR) signaling via the mitogen-activated protein kinase (MAPK) pat hway. The reciprocal modulation does not occur in monolayer (2D) cultures, Antibody-mediated inhibition of either of these receptors in the tumor cell s, or inhibition of MAPK kinase, induced a concomitant downregulation of bo th receptors, followed by growth-arrest and restoration of normal breast ti ssue morphogenesis, Cross-modulation and tissue morphogenesis were associat ed with attenuation of EGF-induced transient MAPK activation. To specifical ly test EGFR and beta 1-integrin interdependency, EGFR was overexpressed in nonmalignant cells, leading to disruption of morphogenesis and a compensat ory up-regulation of beta 1-integrin expression, again only in 3D, Our resu lts indicate that when breast cells are spatially organized as a result of contact with basement membrane, the signaling pathways become coupled and b idirectional. They further explain,why breast cells fail to differentiate i n monolayer cultures in which these events are mostly uncoupled. Moreover, in a subset of tumor cells in,which these pathways are misregulated but fun ctional, the cells could be "normalized" by manipulating either pathway.