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MSK1 is activated after oncogene-induced cellular senescence (OIS). MSK1 is recruited to the INK4AB/ARF locus, mediates H3S28 phosphorylation, and contributes to rapid transcriptional activation of p15INK4B and p16INK4A through the displacement of Polycomb complexes. Both ERK and p38α contribute to MSK1 activation in OIS., The tumor suppressor proteins p15INK4B, p16INK4A, and p14ARF, encoded by the INK4AB/ARF locus, are crucial regulators of cellular senescence. The locus is epigenetically silenced by the repressive Polycomb complexes in growing cells but is activated in response to oncogenic stress. Here we show that the mitogen- and stress-activated kinase (MSK1) is up-regulated after RAF1 oncogenic stress and that the phosphorylated (activated) form of MSK1 is significantly increased in the nucleus and recruited to the INK4AB/ARF locus. We show that MSK1 mediates histone H3S28 phosphorylation at the INK4AB/ARF locus and contributes to the rapid transcriptional activation of p15INK4B and p16INK4A in human cells despite the presence of the repressive H3K27me3 mark. Furthermore, we show that upon MSK1 depletion in oncogenic RAF1-expressing cells, H3S28ph presence at the INK4 locus and p15INK4B and p16INK4A expression are reduced. Finally, we show that H3S28-MSK–dependent phosphorylation functions in response to RAF1 signaling and that ERK and p38α contribute to MSK1 activation in oncogene-induced senescence.

The interaction of estrogen receptor alpha (ERalpha) with the consensus LXXLL motifs of transcriptional coactivators provides an entry for functional ERalpha inhibition. Here, synthetic cell-permeable LXXLL peptide probes are brought forward that allow evaluation of the interaction of specific recognition motifs with ERalpha in the context of the cell. The probes feature a nona-arginine tag that facilitates cellular entry and induces probe localization in nucleoli. The nucleoli localization provides an explicit tool for evaluating the LXXLL motif interaction with ERalpha. The probes compete with coactivators, bind ERalpha, and recruit it into the nucleoli. The physical inhibition of the ERalpha-coactivator interaction by the probes is shown to be correlated with the inhibition of ERalpha-mediated gene transcription. This chemical biology approach allows evaluating the ERalpha-coactivator interaction and inhibitor binding directly in cells.

Decoction of Strychnopsis thouarsii is used in the Malagasy traditional medicine to combat malaria. We have shown that this traditional remedy prevents malaria infection by targeting Plasmodium at its early liver stage. Bioassay-guided fractionation of S. thouarsii stem barks extracts, using a rodent Plasmodium yoelii liver stage parasites inhibition assay, led to isolate the new morphinan alkaloid tazopsine (1) together with sinococuline (2) and two other new related morphinan analogs, 10-epi-tazopsine (3) and 10-epi-tazoside (4). Structures were characterized by 2D NMR, MS, and CD spectral analysis. Compounds 1-3 were found to fully inhibit the rodent P. yoelii liver stage parasites in vitro.

The Estrogen Receptors ERα and ERβ bind cofactor proteins via short LXXLL motifs. The exact regulation and selectivity of these interactions remains an open question and the role of post-translational modifications (PTMs) is virtually unexplored. Here, we designed an X(7)-LXXLL-X(7) T7 phage display library and screened this against four ER protein constructs: the 'naked' ERα and ERβ Ligand Binding Domains (LBDs) and the tyrosine phosphorylated ERα (pY537) and ERβ (pY488) LBDs. The site-selective tyrosine phosphorylated protein constructs were obtained via a protein semi-synthesis approach. Phage display screening yielded preferential sets of peptides. LXXLL peptides with a low pI/acidic C-terminus prefer binding to the naked ERβ over the phosphorylated ERβ analogue and ERα constructs. Peptides with a high pI/basic C-terminus show the opposite behaviour. These findings not only show regulation of the ERβ-cofactor interaction via tyrosine phosphorylation, but also suggest that ERβ and its tyrosine 488 phosphorylation play crucial roles in modulating interactions of coactivators to ERα since the natural Steroid Receptor Coactivators (SRCs) feature LXXLL motifs with acidic C-termini, while the repressor protein RIP140 features LXXLL motifs with basic C-termini. This insight provides explanation for ER transcriptional activity and can lead to more focussed targeting of the ER-coactivator interaction.

Chemical protein synthesis allows the generation of milligram quantities of correctly folded and previously inaccessible tyrosine-phosphorylated estrogen receptor a (ERa) and ß (ERß) ligand binding domains. By using this synthetic strategy, the crystal structure of a post-translationally modified nuclear receptor (pY488 ERß) could be obtained for the first time

New imidazo[1,2-a]quinoxaline derivatives have been synthesised by condensation of an appropriate alpha-aminoalcohol with a quinoxaline followed by intramolecular cyclisation and nucleophilic substitutions. Their phosphodiesterase inhibitory activities have been assessed on a preparation of the PDE4 isoform purified from a human alveolar epithelial cell line (A549). These studies showed potent inhibitory properties that emphasize the importance of a methyl amino group at position 4 and a weakly hindered group at position 1.