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A more recent version of this article appeared on March 1, 2006
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Submitted on June 8, 2005
Revised on December 20, 2005
Accepted on December 28, 2005
Division of Cell Biology, Institute of Ophthalmology, University College London, London EC1V 9EL, United Kingdom
Monitoring Editor: Asma Nusrat
The tight junction adaptor protein ZO-1 regulates intracellular signaling and cell proliferation. Its SH3 domain is required for the regulation of proliferation and binds to the Y-box transcription factor 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 Hsp110 subfamily of Hsp70 heat shock proteins, which is overexpressed in carcinomas. Regulated depletion of Apg-2 in MDCK cells inhibits G1/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.
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