Study Of Focal Adhesion Kinase (Fak) Functions In Developmental Angiogenesis And Mammary Tumors Utilizing Knockin Technology

Abstract

Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase involved in integrinmediated signal transductions. In adherent cells, FAK co-localizes with integrins in focal contacts, and integrin binding to their extracellular ligands leads to FAK activation and autophosphorylation in a variety of cell types. FAK phosphorylation and its interactions with other molecules trigger several downstream signaling pathways which can regulate various cell functions, including cell migration, proliferation, cell survival and adhesions. Although many in vitro studies utilizing overexpression of FAK mutants have been done to illustrate the functions of the kinase activity or the second C-terminal proline-rich motif of FAK in different cellular functions, very little is known about their roles in vivo either during development or under pathological conditions, like cancer. This thesis utilized genetic knockin technology and for the first time illustrated both kinase-independent and -dependent roles of FAK during developmental angiogenesis and the functions of the second Cterminal proline-rich motif of FAK in mammary tumor growth in vivo. FAK plays an essential role in vascular development as endothelial cells (ECs)specific conditional knockout of FAK (i.e. CFKO mice) leads to embryonic lethality caused by increased apoptosis and other defects in ECs. In order to investigate the mechanisms by which FAK regulates vascular development and angiogenesis in vivo, we created and analyzed an EC-specific conditional FAK kinase-defective mutant knockin (CFKI) mouse model (Chapter 2). Our data suggested that kinase-independent functions of FAK can support EC survival in vascular developmental through E13.5, but is insufficient for maintaining EC functions to allow for completion of embryogenesis. FAK is also important for mammary tumorigenesis and metastasis. Specific deletion of FAK in mammary epithelial cells suppressed mammary tumor formation, growth and metastasis. Here we studied the specific roles of the second C-terminal proline-rich motif of FAK in vivo with knockin mouse models. Our studies revealed that PA mutations of this motif in mammary epithelial tumor cells led to increased cell contact inhibition; whereas in endothelial cells, the specific knockin of this motif resulted in formation of mal-functioning blood vessels (Chapter 3). In summary, by generating various conditional knockin mice models, we identified that FAK could promote mammary tumor growth through distinct mechanisms in different systems.