title: Lithocholic acid is an endogenous inhibitor of MDM4 and MDM2.
abstract: The proteins MDM2 and MDM4 are key negative regulators of the tumor suppressor protein p53, which are frequently upregulated in cancer cells. They inhibit the transactivation activity of p53 by binding separately or in concert to its transactivation domain. MDM2 is also a ubiquitin ligase that leads to the degradation of p53. Accordingly, MDM2 and MDM4 are important targets for drugs to inhibit their binding to p53. We found from in silico screening and confirmed by experiment that lithocholic acid (LCA) binds to the p53 binding sites of both MDM2 and MDM4 with a fivefold preference for MDM4. LCA is an endogenous steroidal bile acid, variously reported to have both carcinogenic and apoptotic activities. The comparison of LCA effects on apoptosis in HCT116 p53(+/+) vs. p53(-/-) cells shows a predominantly p53-mediated induction of caspase-3/7. The dissociation constants are in the μM region, but only modest inhibition of binding of MDM2 and MDM4 is required to negate their upregulation because they have to compete with transcriptional coactivator p300 for binding to p53. Binding was weakened by structural changes in LCA, and so it may be a natural ligand of MDM2 and MDM4, raising the possibility that MDM proteins may be sensors for specific steroids.
authors.affiliation: Laboratory for Molecular Design and Pharmaceutical Biophysics, Department of Pharmaceutical and Medicinal Chemistry, Institute of Pharmacy, Eberhard Karls University Tuebingen, Auf der Morgenstelle 8, 72076 Tuebingen, Germany.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Vogel
authors.forename: Matthias R
authors.initials: MR
authors.lastname: Bauer
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Joerger
authors.forename: Rainer
authors.initials: R
authors.lastname: Wilcken
authors.forename: Tobias
authors.initials: T
authors.lastname: Brandt
authors.forename: Dmitry B
authors.initials: DB
authors.lastname: Veprintsev
authors.forename: Trevor J
authors.initials: TJ
authors.lastname: Rutherford
authors.forename: Alan R
authors.initials: AR
authors.lastname: Fersht
authors.forename: Frank M
authors.initials: FM
authors.lastname: Boeckler
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D002846:Chromatography, Affinity; D004926:Escherichia coli; D005454:Fluorescence Polarization; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D008095:Lithocholic Acid / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D014461:Ultracentrifugation
chemical_list: D018797:Cell Cycle Proteins; C482775:MDM4 protein, human; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D008095:Lithocholic Acid; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D053148:Caspase 3; D053179:Caspase 7