|Ph.D Student||Weidenfeld Keren|
|Subject||Characterization of JDP2 Function and Regulation|
|Department||Department of Medicine||Supervisor||Professor Ami Aronheim|
|Full Thesis text|
Activating Protein-1 (AP-1) is a dimeric transcription factor composed of Jun, Fos, and ATF subunits. All AP-1 members share Basic and leucine zipper (bZIP) domain, responsible for specific DNA binding and dimerization, respectively. AP-1 mediates transcription of genes which regulates central cellular processes, via binding to TPA-response element (TRE) and Cyclic-AMP-response element (CRE).
c-Jun Dimerization Protein-2 (JDP2) is a member of the AP-1 family and has an established role in counteracting its activity.
JDP2 is closely related to another AP-1 member-Activating Factor-3 (ATF3). Both are capable of binding to TRE and CRE sequences resulting in the repression of transcription as homodimers. While ATF3 is induced upon cell stimulation, JDP2 is ubiquitously expressed and phosphorylated at Threonine-148 by c-Jun N-terminal kinase (JNK) and p38 following cell stimuli. Both proteins exhibit pro- and anti-oncogenic properties depending on cell type and context.
Our research focuses on characterization of JDP2 function and regulation.
We identified the inducible bZIP transcription factor C/EBP homologue protein10 (CHOP10) as JDP2 interacting protein. CHOP10 mediates cell cycle arrest and/or apoptosis in response to nutrient deprivation and Endoplasmic-Reticulum stress, and interact with ATF3.
JDP2-CHOP10 heterodimers enhance transcription from promoters containing TRE, but not from those containing CRE. JDP2-CHOP10 association involves the leucine zipper motifs of both proteins, and displays an altered DNA binding specificity compared with JDP2 homodimer. Over-expression of JDP2 results in increased cell viability following ER stress and counteracts CHOP10 pro-apoptotic activity.
Additionally, we have identified ATF3 as a target gene for JDP2 repression.
JDP2 regulates ATF3 promoter through binding to both the consensus ATF/CRE site and non-canonical ATF site implicated in ATF3 auto-repression activity. Following either serum or ER stress, ATF3 expression is potentiated in JDP2-KO fibroblast cells as compared with wild type cells, suggesting that JDP2 plays a role in the determination of the ATF3 adaptive cellular threshold response to different stress insults and growth stimuli.
Finally, we studied the biological consequence of JDP2 phosphorylation. JDP2 protein level is dramatically reduced in response to signals that activates JNK. Substitution of Threonine-148 with the phosphomimetic glutamic acid residue destabilizes the expression of JDP2 protein, and conversely, replacement of Thr148 with alanine residue stabilizes JDP2 expression in the presence of cell stimuli. JNK inhibition completely abrogates JDP2 destabilization in response to serum. Proteasome inhibition partially rescues JDP2 phosphorylation dependent degradation, suggesting that JDP2 phosphorylation on Thr148 by JNK targets JDP2 to a proteasome mediated degradation.