Roles of immunoglobulin-like loops of junctional cell adhesion molecule 4; involvement in the subcellular localization and the cell adhesion.
BACKGROUND
Membrane-associated guanylate kinase with inverted domain structure-1 (MAGI-1) is a scaffolding protein at tight junctions (TJs). We have recently identified junctional adhesion molecule 4 (JAM4) as a MAGI-1-interacting protein. JAM4 belongs to the immunoglobulin superfamily and mediates Ca2+-independent adhesion. In this study, we examined the subcellular localization of JAM4 in various tissues and the involvement of JAM4 in the localization of MAGI-1. Moreover, we investigated into roles of immunoglobulin-like loops (Ig-loops) of JAM4.


RESULTS
JAM4 was localized at TJs but also on apical membranes of epithelial cells in jejunum, ileum, and renal proximal tubules. In Madine Darby canine kidney (MDCK) cells, the localization of JAM4 at TJs depended on the first Ig-loop and did not require the MAGI-1-interacting region. JAM4 determined the subcellular localization of MAGI-1 in MDCK cells. In ileum, however, MAGI-1 was localized at TJs where JAM4 was not detected. Both of Ig-loops were necessary for homophilic interactions, but cis interactions depended on the first Ig-loop.


CONCLUSIONS
JAM4 may be primarily targeted to apical membranes, and subsequently recruited to TJs through the first Ig-loop-mediated molecular interaction. JAM4 determines the localization of MAGI-1 in MDCK cells, but the in vivo localization of MAGI-1 does not necessarily depend on JAM4.
Tajima
Makiko
M
Graduate School of Medicine, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan.
Hirabayashi
Susumu
S
Yao
Ikuko
I
Shirasawa
Madoka
M
Osuga
Junichi
J
Ishibashi
Shun
S
Fujita
Toshiro
T
Hata
Yutaka
Y
D000818:Animals; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000032:analysis* / Q000737:chemistry* / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D016764:Cell Polarity; D004285:Dogs; D051528:Guanylate Kinases; D007136:Immunoglobulins / Q000737:chemistry*; D051379:Mice; D009703:Nucleoside-Phosphate Kinase / Q000032:analysis; D051381:Rats; D019108:Tight Junctions / Q000737:chemistry
D015815:Cell Adhesion Molecules; D007136:Immunoglobulins; D009703:Nucleoside-Phosphate Kinase; D051528:Guanylate Kinases