Membrane-associated guanylate kinase with inverted orientation (MAGI)-1/brain angiogenesis inhibitor 1-associated protein (BAP1) as a scaffolding molecule for Rap small G protein GDP/GTP exchange protein at tight junctions.
BACKGROUND
Membrane-associated guanylate kinase (MAGUK) with inverted orientation (MAGI)-1/brain angiogenesis inhibitor 1-associated protein (BAP1), is a member of the MAGUK family that has multiple PDZ domains and interacts with many transmembrane proteins, including receptors and channels, through these domains. MAGI-1/BAP1 is ubiquitously expressed and localized at tight junctions in epithelial cells. It is an isoform of the neurone-specific synaptic scaffolding molecule (S-SCAM), which is known to interact with NMDA receptors and neuroligins. We have recently found that S-SCAM also interacts with a signalling molecule, a GDP/GTP exchange protein (GEP) that is specific for Rap1 small G protein, Rap GEP, which has also recently been referred to as RA-GEF/PDZ-GEFI/CNras-GEF. In this study, we have examined whether MAGI-1/BAP1 also interacts with and serves as a scaffolding molecule for Rap GEP at tight junctions in epithelial cells.


RESULTS
MAGI-1/BAP1 similarly interacted with Rap GEP in cell-free and intact cell systems. A Northern blot analysis revealed that Rap GEP was expressed in most tissues examined. However, neither postsynaptic density (PSD)-95/synapse-associated protein (SAP) 90 (another member of the MAGUK family) nor SAP97/human discs-large tumour suppressor gene product (another ubiquitously expressed MAGUK localizing to adherens junctions in epithelial cells and the isoform of PSD-95/SAP90) interacted with Rap GEP.


CONCLUSIONS
These results indicate that MAGI-1/BAP1 serves as a scaffolding molecule for Rap GEP at tight junctions in epithelial cells.
Mino
A
A
Department of Molecular Biology and Biochemistry, Osaka University Graduate School of Medicine/Faculty of Medicine, Suita 565-0871, Japan.
Ohtsuka
T
T
Inoue
E
E
Takai
Y
Y
D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D020533:Angiogenesis Inhibitors / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000098:blood supply / Q000378:metabolism; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism*; D015815:Cell Adhesion Molecules; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism*; D002460:Cell Line; D000074288:Discs Large Homolog 1 Protein; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D051528:Guanylate Kinases; D006801:Humans; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009703:Nucleoside-Phosphate Kinase / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D000074407:SAP90-PSD95 Associated Proteins; D019108:Tight Junctions / Q000378:metabolism*; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D020533:Angiogenesis Inhibitors; D002352:Carrier Proteins; D015815:Cell Adhesion Molecules; D015816:Cell Adhesion Molecules, Neuronal; C513314:DLG1 protein, human; D000074288:Discs Large Homolog 1 Protein; D020662:Guanine Nucleotide Exchange Factors; C114103:Magi2 protein, rat; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C403525:RAPGEF2 protein, human; D000074407:SAP90-PSD95 Associated Proteins; D009703:Nucleoside-Phosphate Kinase; D051528:Guanylate Kinases; C113338:MAGI1 protein, human; D019204:GTP-Binding Proteins; D020827:rap1 GTP-Binding Proteins