The heat-shock protein Apg-2 binds to the tight junction protein ZO-1 and regulates transcriptional activity of ZONAB.
The tight junction adaptor protein ZO-1 regulates intracellular signaling and cell proliferation. Its Src homology 3 (SH3) domain is required for the regulation of proliferation and binds to the Y-box transcription factor ZO-1-associated nucleic acid binding protein (ZONAB). Binding of ZO-1 to ZONAB results in cytoplasmic sequestration and hence inhibition of ZONAB's transcriptional activity. Here, we identify a new binding partner of the SH3 domain that modulates ZO-1-ZONAB signaling. Expression screening of a cDNA library with a fusion protein containing the SH3 domain yielded a cDNA coding for Apg-2, a member of the heat-shock protein 110 (Hsp 110) subfamily of Hsp70 heat-shock proteins, which is overexpressed in carcinomas. Regulated depletion of Apg-2 in Madin-Darby canine kidney cells inhibits G(1)/S phase progression. Apg-2 coimmunoprecipitates with ZO-1 and partially localizes to intercellular junctions. Junctional recruitment and coimmunoprecipitation with ZO-1 are stimulated by heat shock. Apg-2 competes with ZONAB for binding to the SH3 domain in vitro and regulates ZONAB's transcriptional activity in reporter gene assays. Our data hence support a model in which Apg-2 regulates ZONAB function by competing for binding to the SH3 domain of ZO-1 and suggest that Apg-2 functions as a regulator of ZO-1-ZONAB signaling in epithelial cells in response to cellular stress.
Tsapara
Anna
A
Division of Cell Biology, Institute of Ophthalmology, University College London, London EC1V 9EL, UK.
Matter
Karl
K
Balda
Maria S
MS
D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004285:Dogs; D004847:Epithelial Cells / Q000166:cytology; D016193:G1 Phase / Q000502:physiology; D005786:Gene Expression Regulation; D050957:HSP110 Heat-Shock Proteins / Q000737:chemistry / Q000172:deficiency / Q000378:metabolism*; D006979:Hyperthermia, Induced; D008565:Membrane Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D011485:Protein Binding; D016196:S Phase / Q000502:physiology; D015398:Signal Transduction; D019108:Tight Junctions / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics*; D062826:Zonula Occludens-1 Protein
D004268:DNA-Binding Proteins; D050957:HSP110 Heat-Shock Proteins; D008565:Membrane Proteins; D010750:Phosphoproteins; D014157:Transcription Factors; C409302:ZONAB protein, Canis familiaris; D062826:Zonula Occludens-1 Protein