Rap1 controls activation of the αMβ2 integrin in a talin-dependent manner

✍ Scribed by Jenson Lim; Aurélien G. Dupuy; David R. Critchley; Emmanuelle Caron

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 386 KB
• Volume: 111
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.22788

✦ Synopsis

The small GTPase Rap1 and the cytoskeletal protein talin regulate binding of C3bi-opsonised red blood cells (RBC) to integrin a M b 2 in phagocytic cells, although the mechanism has not been investigated. Using COS-7 cells transfected with a M b 2 , we show that Rap1 acts on the b 2 and not the a M chain, and that residues 732-761 of the b 2 subunit are essential for Rap1-induced RBC binding. Activation of a M b 2 by Rap1 was dependent on W747 and F754 in the b 2 tails, which are required for talin head binding, suggesting a link between Rap1 and talin in this process. Using talin1 knock-out cells or siRNA-mediated talin1 knockdown in the THP-1 monocytic cell line, we show that Rap1 acts upstream of talin but surprisingly, RIAM knockdown had little effect on integrin-mediated RBC binding or cell spreading. Interestingly, Rap1 and talin influence each other's localisation at phagocytic cups, and co-immunoprecipitation experiments suggest that they interact together. These results show that Rap1-mediated activation of a M b 2 in macrophages shares both common and distinct features from Rap1 activation of a IIb b 3 expressed in CHO cells.