Starting from a yeast phenotypic screening performed on 21 compounds, we described the identification of two small molecules (9 and 18) able to significantly reduce the S. cerevisiae cell growth, thus miming the effect of GCN5 deletion mutant. Tested on a GCN5-dependent gene transcription assay, compounds 9 and 18 gave a high reduction of the reporter activity. In S. cerevisiae histone H3 terminal tails assay, the H3 acetylation levels were highly reduced by treatment with 0.6-1 mM 9, while 18 was effective only at 1.5 mM. In human leukemia U937 cell line, at 1 mM 9 and 18 showed effects on cell cycle (arrest in G1 phase, 9), apoptosis (9), and granulocytic differentiation (18). When tested on U937 cell nuclear extracts to evaluate their histone acetyltransferase (HAT) inhibitory action, both compounds were able to reduce the enzyme activity when used at 500 microM. Another quinoline, compound 22, was synthesized with the aim to improve the activity observed with 9 and 18. Tested in the HAT assay, 22 was able to reduce the HAT catalytic action at 50 and 25 microM, thereby being comparable to anacardic acid, curcumin, and MB-3 used as references. Finally, in U937 cells, compounds 9 and 18 used at 2.5 mM were able to reduce the extent of the acetylation levels of histone H3 (9) and alpha-tubulin (9 and 18). In the same assay, 22 at lower concentration (100 microM) showed the same hypoacetylating effects with both histone and non-histone substrates.

DNA is acquiring a primary role in material development, self-assembling by design into complex supramolecular aggregates, the building block of a new-materials world. Using DNA nanoconstructs to translate sophisticated theoretical intuitions into experimental realizations by closely matching idealized models of colloidal particles is a much less explored avenue. Here we experimentally show that an appropriate selection of competing interactions enciphered in multiple DNA sequences results into the successful design of a one-pot DNA hydrogel that melts both on heating and on cooling. The relaxation time, measured by light scattering, slows down dramatically in a limited window of temperatures. The phase diagram displays a peculiar re-entrant shape, the hallmark of the competition between different bonding patterns. Our study shows that it is possible to rationally design biocompatible bulk materials with unconventional phase diagrams and tuneable properties by encoding into DNA sequences both the particle shape and the physics of the collective response.

Blue light-induced transcription in Neurospora crassa is regulated by the White Collar-1 (WC-1) photoreceptor. We report that residue K14 of histone H3 associated with the light-inducible albino-3 (al-3) promoter becomes transiently acetylated after photoinduction. This acetylation depends on WC-1. The relevance of this chromatin modification was directly evaluated in vivo by construction of a Neurospora strain with a mutated histone H3 gene (hH3 K14Q ). This strain phenocopies a wc-1 blind mutant and shows a strong reduction of light-induced transcriptional activation of both al-3 and vivid (vvd), another light-inducible gene. We mutated Neurospora GCN Five (ngf-1), which encodes a homologue of the yeast HAT Gcn5p, to generate a strain impaired in H3 K14 acetylation and found that it was defective in photoinduction. Together, our findings reveal a direct link between histone modification and light signaling in Neurospora and contribute to the developing understanding of the molecular mechanisms operating in light-inducible gene activation.

No abstract

Acetylation is a key modulator of genome accessibility through decondensation of the chromatin structure. The balance between acetylation and opposite deacetylation is, in fact, a prerequisite for several cell functions and differentiation. To find modulators of the histone acetyltransferase Gcn5p, we performed a phenotypic screening on a set of newly synthesized molecules derived from thiazole in budding yeast Saccharomyces cerevisiae. We selected compounds that induce growth inhibition in yeast strains deleted in genes encoding known histone acetyltransferases. A novel molecule CPTH2, cyclopentylidene-[4-(4'-chlorophenyl)thiazol-2-yl)hydrazone, was selected based on its inhibitory effect on the growth of a gcn5Delta strain. We demonstrated a specific chemical-genetic interaction between CPTH2 and HAT Gcn5p, indicating that CPTH2 inhibits the Gcn5p dependent functional network. CPTH2 inhibited an in vitro HAT reaction, which is reverted by increasing concentration of histone H3. In vivo, it decreased acetylation of bulk histone H3 at the specific H3-AcK14 site. On the whole, our results demonstrate that CPTH2 is a novel HAT inhibitor modulating Gcn5p network in vitro and in vivo.

Purpose: We previously identified novel thiazole derivatives able to reduce histone acetylation and histone acetyltransferase (HAT) activity in yeast. Among these compounds, 3-methylcyclopentylidene-[4-(4 0 -chlorophenyl)thiazol-2-yl]hydrazone (CPTH6) has been selected and used throughout this study.Experimental Design: The effect of CPTH6 on histone acetylation, cell viability and differentiation, cellcycle distribution, and apoptosis in a panel of acute myeloid leukemia and solid tumor cell lines has been evaluated.Results: Here, we showed that CPTH6 leads to an inhibition of Gcn5 and pCAF HAT activity. Moreover, it inhibits H3/H4 histones and a-tubulin acetylation of a panel of leukemia cell lines. Concentration-and time-dependent inhibition of cell viability, paralleled by accumulation of cells in the G 0 /G 1 phase and depletion from the S/G 2 M phases, was observed. The role of mitochondrial pathway on CPTH6-induced apoptosis was shown, being a decrease of mitochondrial membrane potential and the release of cytochrome c, from mitochondria to cytosol, induced by CPTH6. Also the involvement of Bcl-2 and Bcl-xL on CPTH6-induced apoptosis was found after overexpression of the two proteins in leukemia cells. Solid tumor cell lines from several origins were shown to be differently sensitive to CPTH6 treatment in terms of cell viability, and a correlation between the inhibitory efficacy on H3/H4 histones acetylation and cytotoxicity was found. Differentiating effect on leukemia and neuroblastoma cell lines was also induced by CPTH6.Conclusions: These results make CPTH6 a suitable tool for discovery of molecular targets of HAT and, potentially, for the development of new anticancer therapies, which warrants further investigations.

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Neurospora and higher eukaryotes share a common mechanism for the signal transduction of environmental stimuli. A scenario is given in which the Neurospora WC-1 photoreceptor represents a function orthologous to that of vertebrate nuclear receptors, acting through the association with the HAT NGF-1 via a vertebrate-like LXXLL motif.