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Molecular and Cellular Biology, March 2000, p. 1956-1969, Vol. 20, No. 6
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Rap1 Is a Potent Activation Signal for Leukocyte Function-Associated Antigen 1 Distinct from Protein Kinase C and Phosphatidylinositol-3-OH Kinase

Koko Katagiri,1,2 Masakazu Hattori,3 Nagahiro Minato,3 Shin-kichi Irie,2 Kiyoshi Takatsu,1,* and Tatsuo Kinashi1,*

Department of Immunology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108,1 Institute of Biomatrix, Nippi Inc., Adachi-ku, Tokyo 120,2 and Department of Immunology and Cell Biology, Graduate School of Medicine, Kyoto University, Kyoto 606-8501,3 Japan

Received 28 September 1999/Returned for modification 23 November 1999/Accepted 15 December 1999

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 , beta I, beta II, 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.

* Corresponding author. Mailing address for Kiyoshi Takatsu: Department of Immunology, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108, Japan. Phone: 81-3-5449-5265. Fax: 81-3-5449-5407. E-mail: takatsuk{at}ims.u-tokyo.ac.jp. Present address for Tatsuo Kinashi: Bayer-chair Department of Molecular Immunology, Graduate School of Medicine, Kyoto University, Yoshida-konoe, Sakyo-ku, Kyoto 606-8501, Japan. Phone: 81-75-771-8159. Fax: 81-75-771-8184. E-mail: tkinashi{at}mfour.med.kyoto-u.ac.jp.

Molecular and Cellular Biology, March 2000, p. 1956-1969, Vol. 20, No. 6
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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