AF-6 controls integrin-mediated cell adhesion by regulating Rap1 activation through the specific recruitment of Rap1GTP and SPA-1.

In the present study, we showed that SPA-1, a Rap1 GTPase-activating protein (GAP), was bound to a cytoskeleton-anchoring protein AF-6. SPA-1 and AF-6 were co-immunoprecipitated in the 293T cells transfected with both cDNAs as well as in normal thymocytes. In vitro binding studies using truncated fragments and their mutants suggested ...
that SPA-1 was bound to the PDZ domain of AF-6 via probable internal PDZ ligand motif within the GAP-related domain. The motif was conserved among Rap1 GAPs, and it was shown that rapGAP I was bound to AF-6 comparably with SPA-1. RapV12 was also bound to AF-6 via the N-terminal domain, and SPA-1 and RapV12 were co-immunoprecipitated only in the presence of AF-6, indicating that they could be brought into close proximity via AF-6 in cells. Immunostaining analysis revealed that SPA-1 and RapV12 were co-localized with AF-6 at the cell attachment sites. In HeLa cells expressing SPA-1 in a tetracycline-regulatory manner, expression of AF-6 inhibited endogenous Rap1GTP and beta(1) integrin-mediated cell adhesion to fibronectin in SPA-1-induced conditions, whereas it affected neither of them in SPA-1-repressed conditions. These results suggested that AF-6 could control integrin-mediated cell adhesion by regulating Rap1 activation through the recruitment of both SPA-1 and Rap1GTP via distinct domains.
Mesh Terms:
Animals, Binding Sites, Cell Adhesion, Cytoskeletal Proteins, GTPase-Activating Proteins, Humans, Integrins, Kinesin, Lymphocytes, Mice, Mice, Inbred BALB C, Myosins, Nuclear Proteins, Precipitin Tests, Protein Binding, Protein Structure, Tertiary, Thymus Gland, Transfection, Tumor Cells, Cultured, rap1 GTP-Binding Proteins
J. Biol. Chem.
Date: Apr. 25, 2003
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