Localization of membrane-associated guanylate kinase (MAGI)-1/BAI-associated protein (BAP) 1 at tight junctions of epithelial cells

Abstract

Membrane-associated guanylate kinase (MAGI)-1/BAIassociated protein (BAP) 1 and Synapse-associated protein (SAP) 97/human Discs-large tumor suppressor gene (hDLG) are ubiquitous isoforms of synaptic scaolding molecule (S-SCAM) and Postsynaptic density (PSD)-95/SAP90, both of which are implicated in the structures of synapses, respectively. SAP97/hDLG is localized at epithelial junctions and may function as a scaolding protein, but the subcellular localization or the function of MAGI-1/BAP1 has not been clari®ed. In intestinal epithelial cells, MAGI-1/BAP1 was localized at tight junctions, whereas SAP97/hDLG was localized diusely at cell ± cell junctions. In Madine Darby canine kidney (MDCK) cells, MAGI-1/BAP1 was colocalized with ZO-1, whereas SAP97/hDLG was colocalized with E-cadherin. In MDCK cells, dominant active and negative mutants of Rac1 small G protein changed the amounts of SAP97/hDLG at cell ± cell junctions, but not that of MAGI-1/BAP1. When MDCK cells were switched to a low Ca 2+ medium, E-cadherin disappeared from the plasma membrane, and cells were dissociated. The phorbol 12-myristate 13-acetate-treatment after the low Ca 2+ switch induced a tight junction-like structure. MAGI-1/BAP1 was recruited with ZO-1 to this structure, but SAP97/hDLG or E-cadherin was not. These ®ndings suggest that MAGI-1/BAP1 is a component of tight junctions of epithelial cells, and that its role is dierent from that of SAP97/hDLG.

Analysis of the expression and localisation of a LAP protein, human scribble, in the normal and neoplastic epithelium of uterine cervix

“…Drosophila scribble and hScrib have the conserved amino-acid sequence, especially in LRRs and PDZ domains, which propose an identical function for these two homologues. Another PDZ-domain protein, Drosophila Discs-Large, localises at the septate junction, but its human homologue hDlg localises at the basolateral membrane, and not just at the tight junction (Ide et al, 1999). These data are in line with our data with respect to the localisations of scribble at the septate junction in Drosophila embryonic epithelia and those of hScrib at the broad basolateral wall in the mammalian epithelial cells.…”

Identification of MAGI1 as a tumor-suppressor protein induced by cyclooxygenase-2 inhibitors in colorectal cancer cells

“…Through its PDZ domains MAGI1 associates with a variety of PDZ-binding molecules such as N-methyl-Daspartate receptors (Hirao et al, 1998), d-catenin (Ide et al, 1999), brain specific angiogenesis inhibitor 1 (BAI-1) (Mino et al, 2000), mNET1 (Dobrosotskaya, 2001), phosphatase and tensin homologue (PTEN) (Kotelevets et al, 2005) and b-catenin (Dobrosotskaya and James, 2000;Kawajiri et al, 2000). In epithelial cells MAGI1 localizes at adherens junctions in complex with b-catenin/ E-cadherin (Dobrosotskaya and James, 2000;Kawajiri et al, 2000) as well as at tight junctions (Ide et al, 1999). MAGI1 suppresses the invasiveness of Madin-Darby Canine Kidney (MDCK) cells by recruiting PTEN to cell-cell contacts and decreasing phosphatidylinositol-3-OH kinase signaling (Kotelevets et al, 2005).…”

Direct binding of the human homologue of the Drosophila disc large tumor suppressor gene to seven-pass transmembrane proteins, tumor endothelial marker 5 (TEM5), and a novel TEM5-like protein

“…hDlg localizes at cell-cell adhesion sites (Matsumine et al, 1996;Reuver and Garner, 1998;Ide et al, 1999). Cell adhesion molecules interact directly or indirectly with many junction-associated proteins and regulate their localization.…”

“…Since hDlg is ubiquitously expressed, hDlg may scaffold other molecules in other cell types (Lue et al, 1994). In epithelial cells, hDlg localizes at cell-cell junctions (Matsumine et al, 1996;Reuver and Garner, 1998;Ide et al, 1999). Thus, hDlg may be involved in the localization of some transmembrane proteins at the cell-cell junctions in epithelial cells.…”