Modulation of breast cancer cell adhesion, invasion, epidermal growth factor signaling, and anchorage-independent growth by β-parvin: Implications in cancer therapy

5039 Invasion and metastasis involves dysregulation of integrin-mediated cell adhesion and migration. Integrin-linked kinase (ILK) is a serine/threonine kinase that is required for integrin adhesion. β-parvin (PARVB) is an ILK-binding protein that is involved in the regulation of cell anchorage. Interestingly, the PARVB gene is located in a region of chromosome 22q13 that is deleted in breast cancer patients. We hypothesize that PARVB is a potential tumor suppressor, and that PARVB-deficiencies contribute to tumorigenesis through altered integrin-mediated cell adhesion, invasion, signaling, and tumor growth. By western blot analysis, we show that PARVB is deficient in the highly invasive human breast cancer cell line MDA-MB-231. To study the role of PARVB in cell invasion and metastasis, we first investigated its effects on breast cancer cell adhesion. Intriguingly, MDA-MB-231 cells that stably express myc-PARVB exhibit a significant increase in ability to bind to collagen I. Since highly metastatic cells are less adherent, the finding that PARVB promotes cell-substrate adherence, and hence, decreases metastatic capability, supports an anti-cancer role for PARVB. Another feature of invasive cancer cells is increased migratory potential. Consistent with a tumor suppressor role, PARVB inhibits EGF-induced MDA-MB-231 cell invasion through matrigel. In addition, PARVB abrogates MDA-MB-231 anchorage-independent growth in soft agar, thus, further supporting a role of PARVB in tumor growth suppression. Our preliminary results suggest that PARVB expression does not affect MDA-MB-231 cell cycle distribution or suspension-induced apoptosis (anoikis). Since EGF induces breast cancer cell migration, we also examined the role of PARVB in EGF receptor tyrosine kinase (RTK) signaling by immunoblot analysis using a phospho-specific antibody for GSK3β, an ILK substrate. Remarkably, PARVB inhibits EGF-stimulated GSK3β serine 9 phosphorylation, suggesting a novel point of cross-talk between RTK and integrin signaling. Studies using ILK adenovirus and RNAi to overexpress and inhibit ILK expression, respectively, are in progress to assess the role of ILK in RTK signaling in the PARVB stables. To determine whether PARVB inhibits tumor development in vivo, the ability of myc-PARVB breast cancer cells to develop tumors and metastasize in nude mice will be evaluated. Our study will elucidate the novel functions of PARVB, and provide new insights into therapeutic approaches for treatments of invasive and metastatic breast cancers.