The transcription factors FOXO4 and p53 regulate aging, and their deregulation has been linked to several diseases, including cancer. Under stress conditions, cellular senescence is promoted by p53 sequestration and senescence-associated protein p21 transcriptional upregulation induced by interactions between the FOXO4 Forkhead DNA-binding domain and the p53 transactivation domain. However, the molecular details of these interactions remain unclear. Here, we report that these interactions between p53 and FOXO4 domains are highly heterogeneous. The p53 transactivation domain primarily interacts with the region formed by the N-terminal helical bundle of the FOXO4 Forkhead domain but retains a substantial degree of flexibility in the complex. In addition, NMR data-driven molecular simulations suggest that p53 interacts with FOXO4 through multiple binding modes. Overall, our findings not only provide the structural insights into interactions between FOXO4 and p53 but also highlight their potential as targets for developing senolytic compounds.

• MeSH
• Forkhead Transcription Factors * metabolism   chemistry   genetics   MeSH
• Humans MeSH
• Tumor Suppressor Protein p53 * metabolism   chemistry   genetics   MeSH
• Protein Domains MeSH
• Cell Cycle Proteins * metabolism   chemistry   MeSH
• Molecular Dynamics Simulation MeSH
• Transcription Factors * metabolism   chemistry   genetics   MeSH
• Protein Binding MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Forkhead Transcription Factors * MeSH
• FOXO4 protein, human MeSH Browser
• Tumor Suppressor Protein p53 * MeSH
• Cell Cycle Proteins * MeSH
• TP53 protein, human MeSH Browser
• Transcription Factors * MeSH

Protein radical labeling, like fast photochemical oxidation of proteins (FPOP), coupled to a top-down mass spectrometry (MS) analysis offers an alternative analytical method for probing protein structure or protein interaction with other biomolecules, for instance, proteins and DNA. However, with the increasing mass of studied analytes, the MS/MS spectra become complex and exhibit a low signal-to-noise ratio. Nevertheless, these difficulties may be overcome by protein isotope depletion. Thus, we aimed to use protein isotope depletion to analyze FPOP-oxidized samples by top-down MS analysis. For this purpose, we prepared isotopically natural (IN) and depleted (ID) forms of the FOXO4 DNA binding domain (FOXO4-DBD) and studied the protein-DNA interaction interface with double-stranded DNA, the insulin response element (IRE), after exposing the complex to hydroxyl radicals. As shown by comparing tandem mass spectra of natural and depleted proteins, the ID form increased the signal-to-noise ratio of useful fragment ions, thereby enhancing the sequence coverage by more than 19%. This improvement in the detection of fragment ions enabled us to detect 22 more oxidized residues in the ID samples than in the IN sample. Moreover, less common modifications were detected in the ID sample, including the formation of ketones and lysine carbonylation. Given the higher quality of ID top-down MSMS data set, these results provide more detailed information on the complex formation between transcription factors and DNA-response elements. Therefore, our study highlights the benefits of isotopic depletion for quantitative top-down proteomics. Data are available via ProteomeXchange with the identifier PXD044447.

• MeSH
• DNA MeSH
• Ions MeSH
• Isotopes MeSH
• Proteins * analysis   MeSH
• Tandem Mass Spectrometry * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA MeSH
• Ions MeSH
• Isotopes MeSH
• Proteins * MeSH

Increased FOXO3 nuclear localization is involved in neuroblastoma chemoresistance and tumor angiogenesis. Accordingly, FOXO3 inhibition is a promising strategy for boosting antitumor immune responses and suppressing FOXO3-mediated therapy resistance in cancer cells. However, no FOXO3 inhibitors are currently available for clinical use. Nevertheless, we have recently identified (4-propoxy)phenylpyrimidinylguanidine as a FOXO3 inhibitor in cancer cells in the low micromolar range. Here, we report the synthesis and structure-activity relationship study of a small library of its derivatives, some of which inhibit FOXO3-induced gene transcription in cancer cells in a submicromolar range and are thus 1 order of magnitude more potent than their parent compound. By NMR and molecular docking, we showed that these compounds differ in their interactions with the DNA-binding domain of FOXO3. These results may provide a foundation for further optimizing (4-propoxy)phenylpyrimidinylguanidine and developing therapeutics for inhibiting the activity of forkhead box (FOX) transcription factors and their interactions with other binding partners.

• Publication type
• Journal Article MeSH