Fusicoccins (FCs) exhibit variousc ellular activities in mammalian cells, but detailso ft he mechanism of action are not fully understood. In this study,w esynthesized two pairs of model derivatives of FCs differing only in the presence and absence of a1 2-hydroxyl group and evaluated their binding to a1 4-3-3 protein together with various mode 1a nd mode 3p hosphopeptide ligands. Our results demonstrate that the 12-hydroxyl group hampersb inding to 14-3-3 with mode 1p hospholigands,p resumably due to steric repulsion with the i+ +2r esidue. Furthermore, cellbased evaluations showedt hat only non-substituted FCs exhibit significant cytotoxicity and all 12-hydroxyl derivatives were inactive, demonstrating ac lear correlation with their ability to form ternary complexes with 14-3-3 and am ode 1 ligand.T hese results suggest that binding to 14-3-3 and a partner protein(s) possessing am ode 1s equence plays a role in the mechanism of action of 12-non-substituted FCs.[a] Prof.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.1002/chem.201804428:Experimental details for synthesis, in vitro evaluation,and cell-based experiments.
KY02111 is a widely used small molecule that boosts cardiomyogenesis of the mesoderm cells derived from pluripotent stem cells, yet its molecular mechanism of action remains elusive. The present study resolves the initially perplexing effects of KY02111 on Wnt signaling and subsequently identifies squalene synthase (SQS) as a molecular target of KY02111 and its optimized version, KY‐I. By disrupting the interaction of SQS with cardiac ER‐membrane protein TMEM43, KY02111 impairs TGFβ signaling, but not Wnt signaling, and thereby recapitulates the clinical mutation of TMEM43 that causes arrhythmogenic right ventricular cardiomyopathy (ARVC), an inherited heart disease that involves a substitution of myocardium with fatty tissue. These findings reveal a heretofore undescribed role of SQS in TGFβ signaling and cardiomyogenesis. KY02111 may find its use in ARVC modeling as well as serve as a chemical tool for studying TGFβ/SMAD signaling.
We accidentally found that YM-53601, a known small-molecule inhibitor of squalene synthase (SQS), selectively depletes SQS from mammalian cells upon ultraviolet (UV) irradiation. Further analyses indicate that the photo-depletion of SQS requires its short peptide segment located at the COOH terminus. Remarkably, when the 27-amino acid peptide was fused to GFP or unrelated proteins at either NH2 or COOH termini, such fusion proteins were selectively depleted when the cells are treated both with YM-53601 and UV exposure. Product analysis and ESR experiments suggest that the UV irradiation promotes a homolytic C-O bond cleavage of the aryl ether group in YM-53601. It is likely that the radical species generated from UVactivated YM-53601 abstract hydrogen atoms from the SQS peptide, leading to the photolysis of the entire protein. The pair of the SQS peptide and YM-53601 discovered in the present study paves the way for designing a new small-molecule-controlled optogenetic tool.
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