Integrin α6β4 Cooperates with LPA Signaling to Stimulate Rac Through AKAP-Lbc-Mediated RhoA Activation
The α6β4 integrin promotes carcinoma invasion through its ability to promote directed migration and polarization of carcinoma cells. In this study, we explore how the α6β4 integrin cooperates with lysophosphatidic acid (LPA) to activate Rho and Rac small GTPases. Through the use of dominant negative Rho constructs, C3 exotransferase, and Rho kinase inhibitor, we find that Rho is critical for LPA-dependent chemotaxis and lamellae formation. However, utilization of specific Rho isoforms depends on integrin α6β4 expression status. Integrin α6β4-negative MDA-MB-435 cells utilize only RhoC for motility, whereas integrin α6β4-expressing cells utilize RhoC but additionally activate and utilize RhoA for LPA-dependent cell motility and lamellae formation. Notably, the activation of RhoA by cooperative LPA and integrin α6β4 signaling requires the Rho guanine nucleotide exchange factor AKAP-Lbc. We also determine that integrin α6β4 cannot activate Rac1 directly but promotes LPA-mediated Rac1 activation that is dependent on RhoA activity and de novo β1 integrin ligation. Finally, we find that the regulation of Rac1 and RhoA in response to LPA is differentially regulated by phosphodiesterases, PKA, and phosphatidylinositol 3-kinase, thus supporting their spatially distinct compartmentalization. In summary, signaling from integrin α6β4 facilitates LPA-stimulated chemotaxis through preferential activation of RhoA, which, in turn, facilitates activation of Rac1.
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This work was supported by the United States Army Medical Research and Materiel Command Grant DAMD17-98-1-8033 and the National Institutes of Health Grant R01-CA109136.
O'Connor, Kathleen L.; Chen, Min; and Towers, L. Nicole, "Integrin α6β4 Cooperates with LPA Signaling to Stimulate Rac Through AKAP-Lbc-Mediated RhoA Activation" (2012). Markey Cancer Center Faculty Publications. 123.