Interaction of the integrin β1 cytoplasmic domain with ICAP-1 protein

In a yeast two-hybrid screen, a protein named ICAP-1 (beta(1) integrin cytoplasmic domain associated protein) associated with the integrin beta(1) cytoplasmic tail but not with tails from three other integrin beta subunits (beta(2), beta(3), and beta(5)) or from seven different a subunits, Likewise in human cells, ICAP-1 associated specifically with the beta(1) but not beta(2), beta(3), Or beta(5) tails. The carboxyl-terminal 14 amino acids of beta(1) were critical for ICAP-1 interaction. ICAP-1 is a ubiquitously expressed protein of 27 and 31 kDa, with the smaller form being preferentially solubilized by Triton X-100. Phosphorylation of both 27- and 31-kDa forms was constitutive but was increased by 1.5-2-fold upon cell spreading on fibronectin, compared with poly-L-lysine. Also, ICAP-1 contributes to beta(1) integrin-dependent migration because (i) ICAP-1 transfection markedly increased chemotactic migration of COS7 cells through fibronectin-coated but not vitronectin-coated porous filters, and (ii) support of beta(1)-dependent cell migration (in Chinese hamster ovary cells transfected with various wild type and mutant beta(1) forms) correlated with ICAP-1 association. In summary, ICAP-1 (i) associates specifically with beta(1) integrins, (ii) is phosphorylated upon beta(1) integrin-mediated adhesion, and (iii) may regulate beta(1) dependent cell migration.