CsoR is a novel Mycobacterium tuberculosis copper-sensing transcriptional regulator

Copper is an essential element that becomes highly cytotoxic when concentrations exceed the capacity of cells to sequester the ion. Here, we identify a new copper-specific repressor (CsoR) of a copper-sensitive operon (cso) in Mycobacterium tuberculosis (Mtb) that is representative of a large, previously uncharacterized family of proteins (DUF156). Electronic and X-ray absorption spectroscopies reveal that CsoR binds a single-monomer mole equivalent of Cu(I) to form a trigonally coordinated (S(2)N) Cu(I) complex. The 2.6-A crystal structure of copper-loaded CsoR shows a homodimeric antiparallel four-helix bundle architecture that represents a novel DNA-binding fold. The Cu(I) is coordinated by Cys36, Cys65' and His61' in a subunit bridging site. Cu(I) binding negatively regulates the binding of CsoR to a DNA fragment encompassing the operator-promoter region of the Mtb cso operon; this results in derepression of the operon in Mtb and the heterologous host Mycobacterium smegmatis. Substitution of Cys36 or His61 with alanine abolishes Cu(I)- and CsoR-dependent regulation in vivo and in vitro. Potential roles of CsoR in Mtb pathogenesis are discussed.     

The small molecule harmine is an antidiabetic cell-type-specific regulator of PPARgamma expression

PPARgamma is the master regulator of adipogenesis and the molecular target of the thiazolidinedione antidiabetic drugs. By screening for compounds that promote adipogenesis, we identified a small molecule that targets the PPARgamma pathway by a distinct mechanism. This molecule, harmine, is not a ligand for the receptor; rather, it acts as a cell-type-specific regulator of PPARgamma expression. Administration of harmine to diabetic mice mimics the effects of PPARgamma ligands on adipocyte gene expression and insulin sensitivity. Unlike thiazolidinediones, however, harmine does not cause significant weight gain or hepatic lipid accumulation. Molecular studies indicate that harmine controls PPARgamma expression through inhibition of the Wnt signaling pathway. This work validates phenotypic screening of adipocytes as a promising strategy for the identification of bioactive small molecules and suggests that regulators of PPARgamma expression may represent a complementary approach to PPARgamma ligands in the treatment of insulin resistance.     

Tip60 acetyltransferase activity is controlled by phosphorylation

Here we show that the phosphorylation of histone acetyltransferase Tip60, a target of human immunodeficiency virus, type 1-encoded transactivator Tat, plays a crucial role in the control of its catalytic activity. Baculovirus-based expression and purification of Tip60 combined with mass spectrometry allowed the identification of serines 86 and 90 as two major sites of phosphorylation in vivo. The phosphorylation of Tip60 was found to modulate its histone acetyltransferase activity. One of the identified phosphorylated serines, Ser-90, was within a consensus cyclin B/Cdc2 site. Ser-90 was specifically phosphorylated in vitro by the cyclin B/Cdc2 complex. Accordingly, the phosphorylation of Tip60 was enhanced after drug-induced arrest of cells in G(2)/M. This G(2)/M-dependent phosphorylation of Tip60 was abolished by treating cells with a specific inhibitor of the cyclin-dependent kinase, roscovitin. All together, these results strongly suggest a G(2)/M-dependent control of Tip60 activity.     

A cell-type-specific alternative splicing regulator shapes synapse properties in a trans-synaptic manner

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Tip60: updates

The maintenance of genome integrity is essential for organism survival. Therefore, eukaryotic cells possess many DNA repair mechanisms in response to DNA damage. Acetyltransferase, Tip60, plays a central role in ATM and p53 activation which are involved in DNA repair. Recent works uncovered the roles of Tip60 in ATM and p53 activation and how Tip60 is recruited to double-strand break sites. Moreover, recent works have demonstrated the role of Tip60 in cancer progression. Here, we review the current understanding of how Tip60 activates both ATM and p53 in response to DNA damage and his new roles in tumorigenesis.