Heat shock protein 90 inhibitors augment endogenous wild-type p53 expression but down-regulate the adenovirally-induced expression by inhibiting a proteasome activity

Our plain-English summary of Heat shock protein 90 inhibitors augment endogenous wild-type p53 expression but down-regulate the adenovirally-induced expression by inhibiting a proteasome activity, by K. Chai, X. Ning, T.T.T. Nguyễn, et al (Oncotarget, 2018).

The study

• Authors: K. Chai, X. Ning, T.T.T. Nguyễn, B. Zhong, T. Morinaga, Z. Li, M. Shingyoji, Y. Tada, K. Tatsumi, H. Shimada, K. Hiroshima, N. Yamaguchi, M. Tagawa
• Journal: Oncotarget
• Published: 2018;9(40):26130-26143
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Heat shock protein 90 (HSP90) inhibitors suppressed MDM4 functions which mediated p53 ubiquitination, and blocked a chaperon function which influenced expression of the client proteins. We examined cytotoxic effects of the inhibitors, 17-allylamino-17-demetheoxygeldanamycin (17-AAG) and 17-dimethylaminoethylamino-17-demethoxy-geldanamycin (17-DMAG), on mesothelioma and investigated combinatory effects of the inhibitors and adenoviruses expressing the wild-type p53 gene (Ad-p53). A majority of mesothelioma lacks p14 and p16 expression, which leads to defective p53 pathway despite bearing the wild-type p53 genotype. The HSP90 inhibitors up-regulated endogenous wild-type p53 expression and induced cell death. Furthermore, the inhibitors increased the endogenous p53 levels that were induced by cisplatin. Nevertheless, the HSP90 inhibitors suppressed Ad-p53-induced exogenous p53 expression primarily at a posttranscriptional level and inhibited the Ad-p53-mediated cell death. HSP90 inhibitors suppressed ubiquitination processes which were involved in p53 degradation, but a proteasome inhibitor, MG-132, prevented the HSP90 inhibitors-induced p53 down-regulation. In contrast, an inhibitor for HSP70 with a chaperon function, pifithrin-μ, did not produce the p53 down-regulation. The HSP90 inhibitors did not suppress expression of Ad receptor molecules but rather increased expression of green fluorescence protein transduced by the same Ad vector. These data collectively indicated that an HSP90 inhibitor possessed a divalent action on p53 expression, as an activator for endogenous wild-type p53 through inhibited ubiquitination and a negative regulator of exogenously over-expressed p53 through the proteasome pathway.

In plain English

This was a laboratory study using human mesothelioma cell lines (MSTO-211H, NCI-H28, NCI-H226, NCI-H2052, NCI-H2452, JMN-1B, EHMES-1, EHMES-10), immortalized mesothelial Met-5A cells and p53-null pancreatic carcinoma AsPC-1 cells. The authors treated cells with the HSP90 inhibitors 17-AAG and 17-DMAG, alone and combined with adenoviruses carrying the wild-type p53 gene (Ad-p53), and measured viability, cell cycle, and protein and mRNA levels. Both inhibitors reduced viability, with 17-DMAG more cytotoxic; mean IC50 values were lower in the p53 non-functional group (17-AAG 98.6 nM, 17-DMAG 10.3 nM) than the p53 functional group (319.8 nM and 39.0 nM), without statistical significance (P = 0.089 and P = 0.086). The inhibitors raised endogenous wild-type p53 and Ser15 phosphorylation and produced PARP cleavage, and added to cisplatin-induced p53. In contrast, they lowered Ad-p53-induced p53 and antagonized Ad-p53 cytotoxicity (combination index above 1 at most fraction-affected points). The proteasome inhibitor MG-132 blocked that down-regulation; separately, the HSP70 inhibitor pifithrin-μ lowered endogenous mutated p53 but did not itself affect Ad-p53-induced p53.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: in vitro laboratory study of human mesothelioma and other cell lines treated with HSP90 inhibitors and adenoviral p53 vectors
• Who was studied: Human mesothelioma cell lines (MSTO-211H, NCI-H28, NCI-H226, NCI-H2052, NCI-H2452, JMN-1B, EHMES-1, EHMES-10), immortalized mesothelial Met-5A cells, and p53-null pancreatic carcinoma AsPC-1 cells; laboratory work in Japan
• Exposure: HSP90 inhibitors 17-AAG and 17-DMAG at various doses, adenoviral vectors (Ad-p53, Ad-LacZ, Ad-EGFP at 3 x 10^4 vp/cell), cisplatin, the proteasome inhibitors MG-132 and lactacystin, the HSP70 inhibitor pifithrin-µ, rapamycin and BAY 11-7082
• Main results:
  • HSP90 inhibitors reduced viability of mesothelioma and Met-5A cells, with 17-DMAG more cytotoxic than 17-AAG
  • Mean IC50 values were lower in the p53 non-functional cell group (17-AAG 98.6 nM; 17-DMAG 10.3 nM) than the p53 functional group (17-AAG 319.8 nM; 17-DMAG 39.0 nM), without statistical significance
  • Susceptibility to the HSP90 inhibitors was not related to MDM4 expression levels
  • In wild-type p53 mesothelioma cells (MSTO-211H, NCI-H28, EHMES-10), the inhibitors increased p53, Ser15 phosphorylation and PARP cleavage
  • In NCI-H28 cells the inhibitors augmented p53 phosphorylation in both cisplatin-untreated and cisplatin-treated cells
  • In JMN-1B cells the inhibitors lowered Ad-p53-induced p53 and its downstream effects, and the combination was antagonistic (combination index above 1)
  • The proteasome inhibitor MG-132 prevented the HSP90 inhibitor-induced p53 down-regulation in Ad-p53-infected and uninfected JMN-1B cells
  • The HSP70 inhibitor pifithrin-µ suppressed endogenous mutated p53 but did not affect Ad-p53-induced p53, and combined with Ad-p53 gave synergistic cytotoxicity in JMN-1B cells
  • HSP90 inhibitors raised CAR and integrin alphaVbeta3 but lowered alphaVbeta5 on JMN-1B cells, and increased Ad-EGFP-transduced GFP intensity and positive cell numbers
  • p53 mRNA from Ad-p53-infected cells was similar at 12 hours with or without inhibitors and only marginally lower later, while protein fell later, indicating a mainly posttranscriptional effect
• The authors' conclusion: The authors concluded that HSP90 inhibitors have a divalent action on p53: augmenting endogenous wild-type p53 while facilitating proteasome-mediated degradation of adenovirally overexpressed p53, so the dual effect must be considered in combination treatments
• Limitations the authors state:
  • The authors did not investigate p53 function in terms of the tetrameric structure, and note that susceptibility of tetrameric p53 should be clarified in a future study
  • No p53-null mesothelioma cells were available, so pancreatic carcinoma AsPC-1 cells were used instead
  • The authors state it is not known why HSP90 inhibitors affected wild-type p53 differently in the two settings

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Cisplatin.

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