Integrin α6β4 promotes migration, invasion through Tiam1 upregulation, and subsequent Rac activation

The lethality of pancreatic adenocarcinoma stems from an elevated incidence of tumor cell invasion and metastasis that are mediated by mechanisms not yet understood. Recent studies indicate that the proinvasive integrin α6β4 is highly upregulated in pancreatic adenocarcinomas. To assess the importance of this integrin in pancreatic cancer cell migration and invasion, cell lines were screened for integrin α6β4 expression by immunoblotting and fluorescence-activated cell sorting and their ability to migrate and invade toward hepatocyte growth factor (HGF). We found that cell surface expression of the α6β4 integrin correlated with the cells' ability to migrate and invade toward HGF. When cells expressing high levels of integrin α6β4 were treated with small interfering RNA targeting α6 or β4 integrin subunits, we observed a reduction in cell migration and invasion. Furthermore, the activity of the small GTPase Rac1 was stimulated by α6β4 integrin expression and was necessary for HGF-stimulated chemotaxis. We discovered that expression of the Rac-specific nucleotide exchange factor, Tiam1 (T-lymphoma invasion and metastasis), was upregulated in cells overexpressing the integrin α6β4 and required for the elevated Rac1 activity in these cells. We conclude that the integrin α6β4 promotes the migratory and invasive phenotype of pancreatic carcinoma cells through the Tiam1-Rac1 pathway in part through the upregulation of Tiam1.