Two synergistic activation mechanisms of alpha 2 beta 1 integrin-mediated collagen binding

: Connors WL, Jokinen J, White DJ, Puranen JS, Kankaanpaa P, Upla P, Tulla M, Johnson MS, Heino J

Publisher: AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC

: 2007

: Journal of Biological Chemistry

: JOURNAL OF BIOLOGICAL CHEMISTRY

: J BIOL CHEM

: 282

: 19

: 14675

: 14683

: 9

: 0021-9258

DOI: https://doi.org/10.1074/jbc.M700759200

Activation of protein kinase C by 12-O-tetradecanoylphorbol-13-acetate (TPA) induces ligand-independent aggregation of a cell surface collagen receptor, alpha 2 beta 1 integrin. Concomitantly, TPA increases the avidity of alpha 2 beta 1 for collagen and the number of conformationally activated alpha 2 beta 1 integrins. The structural change was shown using a monoclonal antibody 12F1 that recognizes the "open" active) conformation of the inserted domain in the alpha 2 subunit (alpha 2I). Amino acid residue Glu-336 in alpha 2 subunit is proposed to mediate the interaction between alpha 2I domain and beta 1 subunit. Glu-336 seems to regulate a switch between open and "closed" conformations, since the mutation alpha 2E336A inhibited the TPA-related increase in the number of 12F1 positive integrins. E336A also reduced cell adhesion to collagen. However, E336A did not prevent the TPA-related increase in adhesion to collagen or alpha 2 beta 1 aggregation. Thus, alpha 2 beta 1 integrin avidity is regulated by two synergistic mechanisms, first an alpha 2E336-dependent switch to the open alpha 2I conformation, and second an alpha 2E336-independent mechanism temporally associated with receptor aggregation.