The overall 5-year survival rate of patients with head and neck squamous cell carcinoma (HNSCC) is less than 50%, and ~75% of human HNSCC cases have mutations in the tumor suppressor p53. The vast majority of p53 mutations are missense mutations that show oncogenic activities, with strong correlation with poor prognosis in patients with HNSCC. Recent evidence indicates that stabilization of mutant p53 (mutp53) in tumors is crucial for its oncogenic activities, while its knockdown attenuates tumor progression. Although there are numerous publications on the function and regulation of wild-type p53 (wtp53), little is known about mechanisms controlling mutp53 levels in tumors and the workable strategies that induce mutp53 degradation. The goal of this proposal is to discover efficient strategies to specifically degrade mutp53 in HNSCC and elucidate the underlying mechanisms. To identify compounds that reduce mutp53 levels, we performed high throughput screening of chemical libraries and identified ?statins?, a class of drugs that inhibit cholesterol production, as degradation inducers of structurally misfolded mutp53 proteins. Statins showed minimal effects on wtp53 and DNA contact mutp53 with native structure. Reduction in mevalonte-5-phosphate (MVP), but not other metabolites in the mevalonate (MV) pathway, triggered mutp53 degradation by CHIP ubiquitin ligase in a protein prenylation-independent manner. Statins also inhibited binding of mutp53 to DNAJA1, a molecular chaperone of the Hsp40 family which plays a role in refolding of misfolded proteins. Indeed, mutp53 degradation by statins was nullified by MVP supplementation, as well as by DNAJA1 overexpression. These data suggest that MVP positively regulates the DNAJA1-mutp53 binding and that DNAJA1 stabilizes misfolded mutp53. However, it is still unclear how reduced MVP leads to inhibition of DNAJA1-mutp53 binding. Based on our compelling preliminary data showing that reduction in MVP by knockdown of mevalonate kinase (MVK) increased acetylation of mutp53, we hypothesize that acetylation of mutp53 upon MVP reduction inhibits the mutp53-DNAJA1 binding, which promotes mutp53 degradation, leading to tumor suppression. We will test this hypothesis and establish the role of DNAJA1 in the malignant progression of HNSCC cells.
In Aim 1, we will determine the mechanism by which reduced MVP leads to inhibited binding of mutp53 with DNAJA1 to induce mutp53 degradation and tumor suppression.
In Aim 2, we will test the hypothesis that DNAJA1 promotes HNSCC progression in a misfolded mutp53-dependent manner.
In Aim 3, we will characterize potential DNAJA1 inhibitors identified through molecular docking studies for their abilities to bind to DNAJA1, induce mutp53 degradation, and reduce the malignant properties of HNSCC cells. Completion of this study will reveal a novel mechanism of mutp53 stabilization via unexpected functional link between MVP and DNAJA1 and will establish the MV pathway and DNAJA1 as novel therapeutic targets for mutp53-carrying cancers. This study may also identify a DNAJA1 inhibitor as a potential compound that can be used for HNSCC therapy.
Human head and neck squamous cell carcinoma (HNSCC) is the top 3rd human cancer carrying p53 mutations which accelerate tumor progression when stabilized. Our study is expected to provide compelling mechanistic evidence that reduction in mevalonte-5-phosphate, a metabolite in the cholesterol synthesis pathway, by cholesterol-lowering drugs ?statins?, leads to inhibited mutant p53-DNAJA1 interaction, mutant p53 degradation and attenuated tumor progression. Thus, this study will reveal crucial roles of DNAJA1 in malignant progression of HNSCC via stabilization of mutant p53 and will establish DNAJA1 as a novel therapeutic target for HNSCC.