Integrin α5 is required for survival of normal and ErbB2/Neu expressing mammary epithelial cells

A87

The extracellular matrix (ECM) plays a key role in establishing tissue architecture and regulating homeostasis as cells that loose contact with matrix undergo cell death (referred to as anoikis). Certain oncogenes provide protection from anoikis that is critical during tumorigenesis by allowing cells to survive outside the natural microenvironment and disrupt tissue architecture. We are interested in understanding how oncogenes regulate anoikis at the cellular level but also during disruption of tissue architecture using in vitro 3D culture models. Key components in ECM signaling include the integrin receptors, thus we have begun to examine changes in integrin expression during anoikis and by oncogenes that allow anoikis resistance and disrupt mammary 3D morphogenesis. Using the normal mammary epithelial cell line, MCF-10A, we have found that the integrin α5 is specifically upregulated during anoikis and 3D morphogenesis. We hypothesize that induction of integrin α5 enhances cell survival during anoikis. Indeed, targeting integrin α5 with siRNA oligos, but not control oligos, causes increased sensitivity to anoikis of MCF-10A cells. Moreover, we find that MCF-10A cells overexpressing breast cancer causing oncogenes, such as ErbB2/Neu highly upregulate integrin α5 levels compared to control cells. Abrogation of integrin α5 but not integrin α3, via siRNA oligos, in oncogenic ErbB2 expressing cells inhibited colony formation in soft agar suggesting a critical role for integrin α5 in tumorigenesis. This effect on ErbB2-anchorage independence may be due to block of ErbB2-mediated survival signaling as we find that inhibition of integrin α5 in ErbB2 expressing cells causes inhibition of the Erk-MAP kinase pathway leading to induction of the apoptotic protein Bim and activation of caspase-3. Thus, integrin α5 is a major regulator of anoikis sensitivity in normal mammary epithelial cells and key mediator of anchorage independence by the ErbB2-MAP kinase pathway and may be a potential therapeutic target in breast cancers overexpressing ErbB2/Neu oncogene.