Autophosphorylation-independent and -dependent Functions of Focal Adhesion Kinase during Development

Focal adhesion kinase (FAK) regulates numerous cellular functions and is critical for processes ranging from embryo development to cancer progression. Although autophosphorylation on Tyr-397 appears required for FAK functions in vitro, its role in vivo has not been established. We addressed this question using a mutant mouse (fak Delta) deleted of exon 15, which encodes Tyr-397. The resulting mutant protein FAK(Delta/Delta) is an active kinase expressed at normal levels. Our results demonstrate that the requirement for FAK autophosphorylation varies during development. FAK(Delta/Delta) embryos developed normally up to embryonic day (E) 12.5, contrasting with the lethality at E8.5 of FAK-null embryos. Thus, autophosphorylation on Tyr-397 is not required for FAK to achieve its functions until late mid-gestation. However, FAK(Delta/Delta) embryos displayed hemorrhages, edema, delayed artery formation, vascular remodeling defects, multiple organ abnormalities, and overall developmental retardation at E13.5-14.5, and died thereafter demonstrating that FAK autophosphorylation is also necessary for normal development. Fibroblasts derived from mutant embryos had a normal stellate morphology and expression of focal adhesion proteins, Src family members, p53, and Pyk2. In contrast, in FAK(Delta/Delta) fibroblasts and endothelial cells, spreading and lamellipodia formation were altered with an increased size and number of focal adhesions, enriched in FAK(Delta/Delta). FAK mutation also decreased fibroblast proliferation. These results show that the physiological functions of FAK in vivo are achieved through both autophosphorylation-independent and autophosphorylation-dependent mechanisms.