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pubmed:abstractText |
The small GTPase Rap1 and the cytoskeletal protein talin regulate binding of C3bi-opsonised red blood cells (RBC) to integrin ?(M)?(2) in phagocytic cells, although the mechanism has not been investigated. Using COS-7 cells transfected with ?(M)?(2), we show that Rap1 acts on the ?(2) and not the ?(M) chain, and that residues 732-761 of the ?(2) subunit are essential for Rap1-induced RBC binding. Activation of ?(M)?(2) by Rap1 was dependent on W747 and F754 in the ?(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 ?(M)?(2) in macrophages shares both common and distinct features from Rap1 activation of ?(IIb)?(3) expressed in CHO cells.
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pubmed:affiliation |
Centre for Molecular Microbiology and Infection, Division of Cell and Molecular Biology, Imperial College London, London, UK. jensons_blog@yahoo.co.uk
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