The tight junction protein ZO-2 localizes to the nucleus and interacts with the heterogeneous nuclear ribonucleoprotein scaffold attachment factor-B.
Zonula occludens proteins (ZOPs), currently comprising ZO-1, ZO-2, and ZO-3, belong to the family of membrane-associated guanylate kinase homologue (MAGUK) proteins that are involved in the organization of epithelial and endothelial intercellular junctions. ZOPs bind to the cytoplasmic C termini of junctional transmembrane proteins linking them to the actin cytoskeleton. They are characterized by several conserved modules, including three PDZ domains, one SH3 domain, and a guanylate kinase-like domain, elements indicating that ZOPs may serve multiple purposes. Interestingly, ZOPs contain some unique motifs not shared by other MAGUK family members, including nuclear localization and nuclear export signals and a leucine zipper-like sequence. Their potential involvement in cell growth and proliferation has been suggested earlier based on the observation that the N-terminal half of ZOPs displays significant similarity to the product of the Drosophila tumor suppressor gene lethal(1)discs-large (dlg). The nuclear targeting of ZOPs in subconfluent epithelial cell cultures is well documented, although the action of the junctional MAGUKs in the nucleus has remained elusive. Here we show for the first time that nuclear ZO-2 directly interacts with the DNA-binding protein scaffold attachment factor-B (SAF-B). Our results from two-hybrid assays and in vivo co-immunoprecipitation studies provide evidence to suggest that ZO-2 associates with the C-terminal portion of SAF-B via its PDZ-1 domain. We further demonstrate that enhanced green fluorescent protein (EGFP)- and DsRed-tagged ZO-2 and SAF-B fusion proteins partially co-localize in nuclei of transfected epithelial cells. As shown by laser confocal microscopy and epifluorescent analysis, nuclear ZO-2 is present in epithelial and endothelial cells, particularly in response to environmental stress conditions. Interestingly, no association of SAF-B with ZO-1 was found, which supports the notion that junctional MAGUKs serve nonredundant functions.
Traweger
Andreas
A
Institute of Molecular Biology, Austrian Academy of Sciences, 5020 Salzburg, Austria.
Fuchs
Renate
R
Krizbai
Istvan A
IA
Weiger
Thomas M
TM
Bauer
Hans-Christian
HC
Bauer
Hannelore
H
D000818:Animals; D015153:Blotting, Western; D002455:Cell Division; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D004285:Dogs; D004727:Endothelium / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D015151:Immunoblotting; D036961:Matrix Attachment Region Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000737:chemistry; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D034521:Nuclear Matrix-Associated Proteins / Q000737:chemistry / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D011960:Receptors, Estrogen; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013696:Temperature; D020798:Two-Hybrid System Techniques; D062827:Zonula Occludens-2 Protein; D001616:beta-Galactosidase / Q000378:metabolism
D036961:Matrix Attachment Region Binding Proteins; D008565:Membrane Proteins; D034521:Nuclear Matrix-Associated Proteins; D011960:Receptors, Estrogen; D011993:Recombinant Fusion Proteins; C109132:SAFB protein, human; C486371:Safb protein, rat; C569046:TJP2 protein, human; C569047:Tjp2 protein, mouse; D062827:Zonula Occludens-2 Protein; D001616:beta-Galactosidase