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Protein acetylation regulates both PU.1 transactivation and Ig kappa 3' enhancer activity.

Igkappa gene expression and chromatin structure change during B cell development. At the pre-B cell stage, the locus is relatively hypoacetylated on histone H3, whereas it is hyperacetylated at the plasma cell stage. We find in this study that the histone deacetylase inhibitor, trichostatin A (TSA) stimulated 3' enhancer activity through the PU.1 binding site. TSA also stimulated PU.1 transactivation potential. PU.1 activity was increased by the coactivator acetyltransferase protein, p300, and p300 physically interacted with PU.1 residues 7-30. PU.1 served as a substrate for p300 and was acetylated on lysine residues 170, 171, 206, and 208. Mutation of PU.1 lysines 170 and 171 did not affect PU.1 DNA binding, but did lower the ability of PU.1 to activate transcription in association with p300. Lysine 170 was acetylated in pre-B cells and plasmacytoma cells, but TSA treatment did not stimulate PU.1 acetylation at this residue arguing that a second mechanism can stimulate 3' enhancer activity. Using chromatin immunoprecipitation assays we found that TSA caused preferential acetylation of histone H3 at the 3' enhancer. The relevance of these studies for PU.1 function in transcription and hemopoietic development is discussed.

3' Untranslated Regions↗

Inhibition of the growth of Ureaplasma urealyticum by a new urease inhibitor, flurofamide.

Flurofamide (N-[diaminophosphinyl]-4-fluorobenzamide), a urease inhibitor, was a potent inhibitor of the growth of Ureaplasma urealyticum. As little as 10 microM flurofamide (2 micrograms/ml) prevented any growth, but U. urealyticum survived for about eight hours before colony counts become undetectable. Flurofamide was a specific inhibitor of U. urealyticum since it did not inhibit growth of four Mycoplasma species or Acholeplasma hippikon. Flurofamide was 1,000 times more active than acetohydroxamic acid and thus has promise as a chemotherapeutic agent and a biochemical tool.

Acholeplasma↗

Effect of acetohydroxamic acid on rumen urease activity in vitro.

Acetohydroxamic acid at a concentration of 1 X 10(-6) M, 6 X 10(-5) M, and 1 X 10(-3) M inhibited urease of intact rumen microbes in vitro by 11%, 50%, and 74%. Inhibition of rumen urease by the acid reached equilibrium state, unlike jack bean urease. Inhibition was maximum over a broad range of pH (8 to 10) and it did not resemble the pH activity profile of rumen urease. Sulfhydryl compounds did not reverse the inhibition; however, addition of these compounds prior to acetohydroxamic acid addition prevented inhibition. The nature of inhibition was noncompetitive with inhibitor constant 4.8 X 10(-5) M. Acetohydroxamic acid at a concentration that produced 50% urease inhibition did not affect rumen cellulase and proteolytic enzymes in vitro. The complex of acetohydroxamic acid-rumen urease is dissociable on dialysis.

Animals↗

Activation of carcinogenic arylhydroxamic acids by human tissues.

Incubation of the carcinogenic arylhydroxamic acids N-hydroxy-N-2-fluorenylacetamide or N-hydroxy-N-4-biphenylacetamide and tRNA with 105,000 times g supernatants of homogenates of human small intestine, liver, or colon led to formation of arylamine-substituted nucleic acid adducts. These data indicated that enzymes of human tissues could activate arylhydroxamic acids by N leads to O acyl transfer. The unstable N-acetoxyarylamines formed by these enzymes reacted spontaneously with the tRNA to give covalently linked adducts with the nucleic acid.

Acyltransferases↗

The role of peptide deformylase in protein biosynthesis: a proteomic study.

Recently we investigated the influence of classical and emerging antibiotics on the proteome of Bacillus subtilis including in our studies actinonin, a potent novel inhibitor of peptide deformylase. The protein synthesis pattern under actinonin treatment changed so dramatically that a direct comparison to the control pattern was impossible. Dual channel imaging revealed that actinonin treatment caused the majority of newly synthesised proteins to accumulate in spots different from the ones usually observed, indicating a more acidic isoelectric point. Two strategies were used to investigate the nature of the charge shift. In the first place, protein patterns of a conditional peptide deformylase mutant under nonrepressing and repressing conditions were compared. Secondly, several protein pairs excised from two-dimensional (2-D) gels of the peptide deformylase mutant, exponentially growing untreated wild-type and the actinonin treated wild-type were investigated with matrix-assisted laser desorption/ionization and electrospray ionization (ESI) time of flight mass spectrometry (TOF MS) for the existence of N-terminal formylation. Under nonrepressing conditions the mutant protein pattern resembled that of the wild-type. The loss of peptide deformylase activity under repressing conditions led to the same pI shift observed for actinonin treatment in the wild-type. Quadrupole TOF-MS on 11 protein pairs proved that the remaining N-terminal formyl residue was indeed responsible for the charge shift. Eight of these protein pairs were also present on 2-D gels of exponentially growing B. subtilis, where the more acidic, still formylated protein species represented the smaller parts.

Amidohydrolases↗

Inhibition of IL-8 gene expression in Caco-2 cells by compounds which induce histone hyperacetylation.

Ulcerative colitis, an idiopathic inflammatory disease of the colonic mucosa, can be effectively treated by enemas containing short chain fatty acids (SCFA) such as butyrate, propionate, and acetate. The molecular mechanisms that lead to this response have not been well characterized. It is well known that intestinal inflammation leads to an alteration in patterns of epithelial differentiation with an increase in epithelial proliferation and an expansion of cell populations in an undifferentiated state. SCFAs such as butyrate are capable of inhibiting cell proliferation and inducing a differentiated phenotype in vitro. The Caco-2 colon cancer cell line was used to study the effect of SCFAs and the process of cellular differentiation on the expression of the pro-inflammatory cytokine, interleukin 8 (IL-8). SCFAs and trichostatin A, structurally unrelated compounds which both induce histone hyperacetylation, both led to a dose-dependent inhibition of IL-8 gene expression. Furthermore, spontaneous differentiation of Caco-2 cells by growth to a post-confluent state also inhibited the expression of IL-8. A possible mechanism by which SCFAs may be effective in the treatment of ulcerative colitis may be through their ability to increase histone acetylation states and inhibit the production of pro-inflammatory substances by the intestinal epithelium.

Acetylation↗

Cloning, sequencing, and characterization of the Azospirillum brasilense fhuE gene.

The fhuE gene of Escherichia coli encodes the FhuE protein, which is a receptor protein in the coprogen-mediated siderophore iron-transport system. A fhuE gene homologue from Azospirillum brasilense, a nitrogen-fixing soil bacterium that lives in association with the roots of cereal grasses, was cloned, sequenced, and characterized. The A. brasilense fhuE encodes a protein of 802 amino acids with a predicted molecular weight of approximately 87 kDa. The deduced amino-acid sequence showed a high level of homology to the sequences of all the known fhuE gene products. The fhuE mutant was sensitive to iron starvation and defective in coprogen-mediated iron uptake. The mutant failed to express one membrane protein of approximately 78 kDa that was induced by iron starvation in the wild type. Complementation studies showed that the A. brasilense fhuE gene, when present on a low-copy number plasmid, could restore the functions of the mutant. Mutation in fhuE gene did not affect nitrogen fixation.

Amino Acid Sequence↗