Rack1, a receptor for activated protein kinase C, interacts with integrin β subunit

Abstract

The integrin β subunit cytoplasmic domains are important for activation-dependent cell adhesion and adhesion-dependent signaling events. We report an interaction between integrin β subunit cytoplasmic domain and Rack1, a Trp-Asp (WD) repeat protein that has been shown to bind activated protein kinase C. The Rack1-binding site on integrin β2 subunit resides within a conserved, membrane-proximal region. In the yeast two-hybrid assay, WD repeats five to seven of Rack1 (Rack1-WD5/7) interact with integrin β1, β2 and β5 cytoplasmic domain. In eukaryotic cells, Rack1 co- immunoprecipitates with at least two different β integrins, β1 integrins in 293T cells and β2 integrins in JY lymphoblastoid cells. Whereas Rack1- /binds integrins constitutively, the association of full-length Rack1 to integrins in vivo requires a treatment with phorbol esters, which promotes cell spreading and adhesion. These findings suggest that Rack1 may link protein kinase C directly to integrins and participate in the regulation of integrin functions.