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Published 6 August 2001. doi:10.1083/jcb.200103047
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© The Rockefeller University Press, 0021-9525/2001/8/491 $5.00
The Journal of Cell Biology, Volume 154, Number 3, August 6, 2001 491-498

Report

Junctional adhesion molecule (JAM) binds to PAR-3

: a possible mechanism for the recruitment of PAR-3 to tight junctions



Masahiko Itoh1, Hiroyuki Sasaki3, Mikio Furuse1, Harunobu Ozaki2, Toru Kita2 and Shoichiro Tsukita1

1 Department of Cell Biology, Faculty of Medicine, Kyoto University, Kyoto 606-8501, Japan
2 Department of Geriatric Medicine, Faculty of Medicine, Kyoto University, Kyoto 606-8501, Japan
3 KAN Research Institute, Inc., Chudoji, Kyoto 600-8317, Japan

Address correspondence to Shoichiro Tsukita, Department of Cell Biology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan. Tel.: 81-75-753-4372. Fax: 81-75-753-4660. E-mail: htsukita{at}mfour.med.kyoto-u.ac.jp

At tight junctions (TJs), claudins with four transmembrane domains are incorporated into TJ strands. Junctional adhesion molecule (JAM), which belongs to the immunoglobulin superfamily, is also localized at TJs, but it remains unclear how JAM is integrated into TJs. Immunoreplica electron microscopy revealed that JAM showed an intimate spatial relationship with TJ strands in epithelial cells. In L fibroblasts expressing exogenous JAM, JAM was concentrated at cell–cell adhesion sites, where there were no strand-like structures, but rather characteristic membrane domains free of intramembranous particles were detected. These domains were specifically labeled with anti-JAM polyclonal antibody, suggesting that JAM forms planar aggregates through their lateral self-association. Immunofluorescence microscopy and in vitro binding assays revealed that ZO-1 directly binds to the COOH termini of claudins and JAM at its PDZ1 and PDZ3 domains, respectively. Furthermore, another PDZ-containing polarity-related protein, PAR-3, was directly bound to the COOH terminus of JAM, but not to that of claudins. These findings led to a molecular architectural model for TJs: small aggregates of JAM are tethered to claudin-based strands through ZO-1, and these JAM aggregates recruit PAR-3 to TJs. We also discuss the importance of this model from the perspective of the general molecular mechanisms behind the recruitment of PAR proteins to plasma membranes.

Key Words: JAM; PAR-3; claudin; ZO-1; tight junction


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