Regulation of normal and malignant cellular processes by the cytoskeletal scaffold, cortactin

The ability of a cell to control diverse physiological processes in response to environmental cues requires exquisite control of multiple signaling cascades. Scaffold proteins orchestrate the assembly of multi-molecular signaling complexes in particular spatiotemporal patterns to generate specific biological responses. Cortactin is an actin-binding scaffold that regulates normal cellular functions, including migration, adhesion, and vesicle trafficking; misregulation of cortactin is linked to tumor progression and oncogenic transformation. Thus, studies addressing the mechanisms by which cortactin contributes to normal and malignant processes are important for understanding how cortactin may promote tumor progression. The work described in this dissertation investigates roles for cortactin in epithelial and fibroblast motility, transendothelial migration, and v-Src-induced transformation.; Specifically, this dissertation shows first that not only overexpression of full-length cortactin, but overexpression of either the cortactin N-terminal half or C-terminal half enhanced the migration and disrupted differentiation of mammary epithelial cells. Further, the cortactin C-terminus was necessary and sufficient for N-WASP activation and actin polymerization in vitro, and cortactin-enhanced cell migration required N-WASP. Second, the requirement for cortactin and its phosphorylation by Src family kinases during leukocyte transendothelial migration was explored. In vitro transendothelial migration assays demonstrated that Src family kinase activity, as well as cortactin expression and tyrosine phosphorylation, were required in the endothelium for polymorphonuclear cell transmigration. Finally, the potential role of cortactin in mediating cellular transformation by v-Src was investigated. These studies demonstrated a requirement for cortactin in v-Src-induced podosome formation. Cortactin knockdown also enhanced the ability of v-Src-transformed cells to form colonies in soft agar and increased their proliferation, suggesting cortactin may negatively regulate v-Src-induced anchorage-independent growth and proliferation, in addition to promoting an invasive phenotype.; Taken together, the work presented in this dissertation furthers the understanding of the molecular mechanisms by which the scaffold, cortactin, regulates processes in normal and malignant cells. These findings contribute to a broader appreciation of the multiple potential roles for cortactin in tumor progression, including effects on cellular transformation and tumor cell invasion and migration, as well as possible cell non-autonomous effects to promote tumor metastasis via modulation of the barrier function of surrounding tissues and vasculature.