Abstract LB-494: Forcing integrin signaling perturbs mammary morphogenesis

Abstract The extracellular matrix and its receptors regulate tissue development and homeostasis and perturbations in this dialogue contribute to the pathogenesis of cancer. In the mammary gland β1 integrin modulates branching morphogenesis and directs tissue-specific differentiation so that expression of a dominant-negative or the conditional knockdown of β1 integrin compromises mammary epithelial cell (MEC) proliferation, survival and migration to disrupt branching and acinar differentiation (Streuli et al. J Cell Biol. 1991). Consistently, breast tumors are associated with elevated β1 integrin signaling through focal adhesion kinase (FAK) and ablation of β1 integrin or FAK expression prevents tumor progression and inhibits metastasis (White et al. Cancer Cell. 2004, Pylayeva et al. J Clin Invest. 2009, Provenzano et al. Am J Pathol. 2008). Nevertheless, whether integrin-dependent signaling promotes cell proliferation, survival and migration to drive mammary epithelial branching and whether this enhanced signaling would be sufficient to drive tumorigenesis in vivo has yet to be determined. We developed a novel β1 integrin mutant V737N in which the neutral transmembrane amino acid glycine was replaced with a highly charged asparagine (Paszek et al. Cancer Cell. 2005). This integrin mutant promotes the assembly of focal adhesions and potentiates FAK and ERK activity in fibroblasts and mammary epithelial cells even when the cells interact with a compliant ECM. The mutant integrin also enhances cell survival and promotes invasion of premalignant MECs within compliant three dimensional (3D) gels and promotes tumor growth in vivo. To further explore the impact of enhanced focal adhesion assembly on tissue morphogenesis and tumorigenesis we conditionally knocked in V737N integrin mutant into the ROSA26 locus using PBigT vector. These mice were crossed into the MMTV-Cre mice to induce expression of V737N β1 integrin in the luminal MECs and effects on developmental branching morphogenesis were assessed. Data showed that the mammary glands of 10 week old virgin V737N β1 integrin mice were larger and heavier as compared to age matched controls. Whole mount analysis revealed a profound precocious branching morphogenesis in the number 4 mammary glands that was characterized by elevated numbers of tertiary branches with prominent terminal end buds. Moreover, immunohistochemistry of the mammary epithelial cells showed evidence of elevated proliferation. These findings suggest that forced assembly of integrin focal adhesions is sufficient for mammary epithelial cell proliferation and migration. Further studies are underway to explore whether enhancing focal adhesion assembly potentiates integrin and growth factor signaling and if this compromises tissue specific differentiation and/or promotes malignancy. Supported by: NCI SPORE P50 CA058207, NCI R01 CA138818-01A1, NCI R01 CA140663-01-A2, DOD W81XWH-05-1-0330 and NCI U54 CA143836-01 to VMW. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-494. doi:1538-7445.AM2012-LB-494