title: Targeting p53 via JNK pathway: a novel role of RITA for apoptotic signaling in multiple myeloma.
abstract: The low frequency of p53 alterations e.g., mutations/deletions (∼10%) in multiple myeloma (MM) makes this tumor type an ideal candidate for p53-targeted therapies. RITA is a small molecule which can induce apoptosis in tumor cells by activating the p53 pathway. We previously showed that RITA strongly activates p53 while selectively inhibiting growth of MM cells without inducing genotoxicity, indicating its potential as a drug lead for p53-targeted therapy in MM. However, the molecular mechanisms underlying the pro-apoptotic effect of RITA are largely undefined. Gene expression analysis by microarray identified a significant number of differentially expressed genes associated with stress response including c-Jun N-terminal kinase (JNK) signaling pathway. By Western blot analysis we further confirmed that RITA induced activation of p53 in conjunction with up-regulation of phosphorylated ASK-1, MKK-4 and c-Jun. These results suggest that RITA induced the activation of JNK signaling. Chromatin immunoprecipitation (ChIP) analysis showed that activated c-Jun binds to the activator protein-1 (AP-1) binding site of the p53 promoter region. Disruption of the JNK signal pathway by small interfering RNA (siRNA) against JNK or JNK specific inhibitor, SP-600125 inhibited the activation of p53 and attenuated apoptosis induced by RITA in myeloma cells carrying wild type p53. On the other hand, p53 transcriptional inhibitor, PFT-α or p53 siRNA not only inhibited the activation of p53 transcriptional targets but also blocked the activation of c-Jun suggesting the presence of a positive feedback loop between p53 and JNK. In addition, RITA in combination with dexamethasone, known as a JNK activator, displays synergistic cytotoxic responses in MM cell lines and patient samples. Our study unveils a previously undescribed mechanism of RITA-induced p53-mediated apoptosis through JNK signaling pathway and provides the rationale for combination of p53 activating drugs with JNK activators in the treatment of MM.
authors.affiliation: Division of Molecular and Cellular Biology, Toronto General Hospital Research Institute, Toronto, Ontario, Canada.
authors.forename: Manujendra N
authors.initials: MN
authors.lastname: Saha
authors.forename: Hua
authors.initials: H
authors.lastname: Jiang
authors.forename: Yijun
authors.initials: Y
authors.lastname: Yang
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Zhu
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Wang
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Schimmer
authors.forename: Lugui
authors.initials: L
authors.lastname: Qiu
authors.forename: Hong
authors.initials: H
authors.lastname: Chang
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D005663:Furans / Q000494:pharmacology*; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009101:Multiple Myeloma / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D005663:Furans; C118989:NSC 652287; D016159:Tumor Suppressor Protein p53; D048031:JNK Mitogen-Activated Protein Kinases