Rap1 is a potent activation signal for leukocyte function-associated antigen 1 distinct from protein kinase C and phosphatidylinositol-3-OH kinase.
To identify the intracellular signals which increase the adhesiveness of leukocyte function-associated antigen 1 (LFA-1), we established an assay system for activation-dependent adhesion through LFA-1/intercellular adhesion molecule 1 ICAM-1 using mouse lymphoid cells reconstituted with human LFA-1 and then introduced constitutively active forms of signaling molecules. We found that the phorbol myristate acetate (PMA)-responsive protein kinase C (PKC) isotypes (alpha, betaI, betaII, and delta) or phosphatidylinositol-3-OH kinase (PI 3-kinase) itself activated LFA-1 to bind ICAM-1. H-Ras and Rac activated LFA-1 in a PI 3-kinase-dependent manner, whereas Rho and R-Ras had little effect. Unexpectedly, Rap1 was demonstrated to function as the most potent activator of LFA-1. Distinct from H-Ras and Rac, Rap1 increased the adhesiveness independently of PI 3-kinase, indicating that Rap1 is a novel activation signal for the integrins. Rap1 induced changes in the conformation and affinity of LFA-1 and, interestingly, caused marked LFA-1/ICAM-1-mediated cell aggregation. Furthermore, a dominant negative form of Rap1 (Rap1N17) inhibited T-cell receptor-mediated LFA-1 activation in Jurkat T cells and LFA-1/ICAM-1-dependent cell aggregation upon differentiation of HL-60 cells into macrophages, suggesting that Rap1 is critically involved in physiological processes. These unique functions of Rap1 in controlling cellular adhesion through LFA-1 suggest a pivotal role as an immunological regulator.
Katagiri
K
K
Department of Immunology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108, Japan.
Hattori
M
M
Minato
N
N
Irie
S k
Sk
Takatsu
K
K
Kinashi
T
T
D000818:Animals; D018922:HL-60 Cells; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D019169:Jurkat Cells; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D015398:Signal Transduction; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D020827:rap1 GTP-Binding Proteins