|Ph.D Student||Saadon Ilona|
|Subject||Biochemical Characterization of the Interaction between the|
bZIP Repressors, JDP2 and ATF3, and HDACs
|Department||Department of Medicine||Supervisor||Professor Ami Aronheim|
|Full Thesis text|
The c-Jun Dimerization Protein-2 (JDP2), is a basic leucine zipper (bZIP) protein displaying a high degree of homology with the stress inducible Activating Transcription Factor 3 (ATF3). Both proteins bind to TPA-response element (TRE) and Cyclic-AMP-response element (CRE) and repress transcription by multiple mechanisms.
Histone deacetylases (HDACs) play a key role in gene inactivation by deacetylating specific lysine residues on histones resulting in chromatin condensation. HDAC6 was isolated in our laboratory using the yeast Ras Recruitment System (RRS) as an interacting protein of JDP2 and ATF3. We hypothesize that the observed interaction between the bZIP proteins with HDAC6 is a part of their ability to repress transcription. Therefore, we aimed to characterize the association between the bZIP repressor proteins and HDAC proteins and reveal its biological relevance. In this study, we describe the association of JDP2 and ATF3 with HDACs 1-6 and HDAC10. The association of HDAC3 and HDAC6 with JDP2 and ATF3 occurs via direct protein-protein interactions. Mapping the association domain within JDP2 and ATF3 with various HDACs revealed that the N-terminal bZIP motif of JDP2 and ATF3 N-terminal as well as the basic domains are necessary and sufficient for the interaction with all HDACs in a manner that is independent of coiled-coil dimerization. Class I HDACs associate with the bZIP repressors via the deacetylase (DAC) conserved domain whereas the Class IIb HDAC6 associates through its C-terminal unique Binder of ubiquitin Zn finger (BUZ) domain. One of the JDP2 and ATF3 common target genes is the ATF3 itself. Both JDP2 and ATF3 repress the ATF3 promoter via binding to both CRE and non-canonical ATF/CRE sites within the ATF3 promoter. We demonstrate that the transcription of ATF3 is significantly enhanced in mouse embryo fibroblast (MEF) cells treated with the potent histone deacetylase inhibitor, trichostatin A (TSA). The TSA-induced up-regulation of ATF3 transcription was significantly reduced in MEF cells lacking both ATF3 and JDP2.
Collectively, we propose that the recruitment of multiple HDAC members to JDP2 and
ATF3 is part of their transcription repression mechanism.