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. 2015 Sep 17;22(9):1206-16.
doi: 10.1016/j.chembiol.2015.07.016. Epub 2015 Aug 27.

Small-Molecule Reactivation of Mutant p53 to Wild-Type-like p53 Through the p53-Hsp40 Regulatory Axis

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Small-Molecule Reactivation of Mutant p53 to Wild-Type-like p53 Through the p53-Hsp40 Regulatory Axis

Masatsugu Hiraki et al. Chem Biol. .
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Abstract

TP53 is the most frequently mutated gene in human cancer, and small-molecule reactivation of mutant p53 function represents an important anticancer strategy. A cell-based, high-throughput small-molecule screen identified chetomin (CTM) as a mutant p53 R175H reactivator. CTM enabled p53 to transactivate target genes, restored MDM2 negative regulation, and selectively inhibited the growth of cancer cells harboring mutant p53 R175H in vitro and in vivo. We found that CTM binds to Hsp40 and increases the binding capacity of Hsp40 to the p53 R175H mutant protein, causing a potential conformational change to a wild-type-like p53. Thus, CTM acts as a specific reactivator of the p53 R175H mutant form through Hsp40. These results provide new insights into the mechanism of reactivation of this specific p53 mutant.

Figures

Figure 1
Figure 1. Identification of CTM as a mutant p53 R175H reactivator
(A) H1299-mutant p53 R175H cells with luciferase reporter carrying the p53 DNA binding site of PUMA promoter was generated and tested for luciferase activity with adenovirus (Ad)-GFP or -p53. (B) Screening strategy used in this study. (C) High-throughput chemical screening was performed in duplicate, and relative luciferase activity was calculated. (D) Fractionation of natural extracts #4 and #5 by HPLC methods and luciferase activity assays of resulting fractions of natural extracts. Each natural extract was subjected to HPLC fractionation [#4, fractions 1-7; #5, fractions 1-9]. Each fraction from extracts #4 and #5 was analyzed by luciferase assay using H1299-mutant p53 R175H cells with luciferase reporter carrying the p53 DNA binding site of PUMA promoter. Cells were treated with each fraction at indicated concentrations for 15 hours. Luciferase activity was then measured. Data shown are mean ± S.D. in triplicate and measured at the same time. (E) Chemical structure of chetomin with absolute stereochemistry predicted through optical rotation calculations. (F) Global minimum conformation of chetomin calculated using DFT at the SCRF(chloroform)-wB97XD/6-311++G(d,p) level of theory. See also Table S1. (G) CTM was analyzed by luciferase assay using H1299-mutant p53 R175H cells with luciferase reporter carrying the p53 DNA binding site of PUMA promoter. Cells were treated with CTM at indicated concentrations for 15 hours, after which luciferase activity was measured. Data shown are mean ± S.D. in triplicate and measured at the same time. Adenoviruses Ad-GFP and Ad-p53 were used as negative and positive controls for luciferase assay, respectively. See also Figure S1.
Figure 2
Figure 2. CTM preferentially suppresses cancer cells with p53 R175H and induces p53 target genes
(A) CTM shows high anticancer activity in mutant p53 R175H cells. Normal and cancer cells including p53 wild type, p53 null, mutant p53 R175H and R273H were treated with CTM for 24 hours at indicated concentrations. Cells were stained with Sulforhodamine B and measured for cell viability. Error bars represent the range of duplicates. (B) p53 target genes are highly induced in mutant p53 R175H cells. Cancer cells (R175H: CAL-33, HuCCT1, FAMPAC, KLE and TOV-112D; wild type: HCT116; null: H1299; R273H: PANC-1) with various status of p53 were treated with CTM (150 nM) for indicated times. Total RNA was extracted and subjected to quantitative real-time PCR with specific primers for p21, PUMA and MDM2. HCT116 cells were treated with etoposide (50 μM) for indicated time points as a positive control. Data shown are mean ± S.D. in triplicates and measured at the same time. (C and D) CTM-mediated p53 target protein induction in mutant p53 R175H cells. Cancer cells (R175H: CAL-33, HuCCT1, FAMPAC and KLE; R248Q: OVCAR-3; R273H: A431; wild type: HCT116; null: H1299) with various status of p53 were treated with CTM for 18 hours, and cell lysates were analyzed by western blotting with indicated antibodies. Ad-p53 was used as a positive control.
Figure 3
Figure 3. Mutant p53 reactivation effect of CTM is mediated through p53 R175H
(A) Knockdown of mutant p53 R175H impairs induction of p53 target genes by CTM. Cells were transfected with siRNA (si control or sip53) and treated with CTM for 18 hours. Overexpression of mutant p53 R175H increased protein expression level of p53 target genes. H1299 (p53-null) cells were transfected with pcDNA3-empty or mutant p53 R175H plasmid. Stable cells were treated with CTM for 18 hours. HCT116 p53−/− cells overexpressing mutant p53 R175H or R273H by tetracycline-inducible system were treated with CTM (150 nM) for 18 hours. Mutant p53 was overexpressed by doxycycline for 48 hours prior to CTM treatment. (B) ChIP analysis shows that CTM treatment restores the transactivation function of p53 in mutant p53 R175H cells. Cells were treated with DMSO, etoposide (50 μM), or CTM (200 nM) and cross-linked. Sheared chromatin was immunoprecipitated with p53 antibody. Eluted DNA was examined by quantitative real-time PCR using primers that specifically target p53 binding site in the promoter. Data shown are mean ± S.D. in triplicate. See also Figure S2.
Figure 4
Figure 4. CTM restores p53 wild type-like properties in mutant p53 R175H
(A) p53 level is decreased upon CTM treatment due to MDM2 negative regulation in mutant p53 R175H cells, but not in mutant p53 R275H and R248Q cells. Cells were treated with Nutlin-3 and/or CTM at indicated concentrations and time. (B) CTM treatment increased MDM2 protein level and binding capacity to p53 protein in R175H cells. Cells were treated with etoposide, CTM and/or Nutlin-3 as described, and co-immunoprecipitation was performed with cell lysate using anti-p53 or -MDM2 antibody. Inputs and co-IP were analyzed with indicated antibodies. See also Figure S3.
Figure 5
Figure 5. CTM suppresses tumor growth in vivo in a p53 R175H mutant dependent manner
Various types of p53 cells were used for xenograft model-(A) TOV-112D (p53-R175H) and CAL-33 (p53 -R175H), (B) A431 (p53-R273H), (C) H1299 (p53-null). Tumors were allowed to grow to 50 mm3 before intraperitoneal injection of DMSO or CTM at 1 mg/kg/day for indicated days. Tumor volume and weight were measured. Examined mice numbers are as follows: TOV-112D (DMSO control: n=7, and CTM-treated: n=6), CAL-33 (DMSO control: n=9, and CTM-treated: n=9), A431 (DMSO control: n=6, and CTM-treated: n=6), H1299 (DMSO control: n=8, and CTM-treated: n=8). Data shown are mean ± S.D. Student's t-test, *P<0.001, **P<0.005.
Figure 6
Figure 6. Binding of CTM to the Hsp40 protein is required for the CTM-mediated reactivation of mutant p53 R175H
(A) Hsp40 expression is increased and its binding capacity to mutant p53 is enhanced upon CTM treatment in CAL-33 (R175H) cells. Cells were treated with CTM (200 nM) for 8 hours and co-immunoprecipitation was performed with cell lysate using anti-p53 antibody. Inputs and co-IP were analyzed with indicated antibodies. (B) Hsp40 depletion impairs protein induction of p53 target genes upon chetomin treatment. CAL-33 cells were transfected with siRNA (si control and si-p53) and treated with CTM for 18 hours. Cell lysates were analyzed by western blotting. (C) CTM treatment increases the binding capacity of Hsp40 protein to mutant p53 R175H in vitro. Top panel: Recombinant proteins of mutant p53 R175H (250 nM) and His-Hsp40 (1 μM) were incubated with or without CTM at increasing concentrations (1, 2 and 4 μM), and pull-down assays were performed with anti-p53 antibody DO1, which recognizes both wild type and mutant p53. Bottom panel: Recombinant proteins of His-mutant p53 R175H (55 nM) and His-Hsp40 (1 μM) were incubated with or without CTM (4 μM), and pull-down assays were performed with either anti-p53 antibody DO1 or anti-p53 antibody PAb1620 (wild type-specific). (D) CTM binds to Hsp40 in a concentration-dependent manner. Physical interaction between CTM and Hsp40, mt-p53 R175H, or Hsp70 was tested through Biacore assay. A 2-fold dilution series of CTM, ranging from 0 μM to 40 μM, was tested for binding. In addition, physical interaction between Hsp40 and either NSC319726 (40 μM) or etoposide (40 μM) was tested through Biacore assay. Each series of experiment was tested in duplicates. See also Figure S4-S6 and Table S5.

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