Regulatory roles of NAT10 in airway epithelial cell function and metabolism in pathological conditions.

N-acetyltransferase 10 (NAT10), a nuclear acetyltransferase and a member of the GNAT family, plays critical roles in RNA stability and translation processes as well as cell proliferation. Little is known about regulatory effects of NAT10 in lung epithelial cell proliferation. We firstly investigated NTA10 mRNA expression in alveolar epithelial types I and II, basal, ciliated, club, and goblet/mucous epithelia from heathy and patients with chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, lung adenocarcinoma, para-tumor tissue, and systemic sclerosis, respectively. We selected A549 cells for representative of alveolar epithelia or H1299 and H460 cells as airway epithelia with different genetic backgrounds and studied dynamic responses of NAT10-down-regulated epithelia to high temperature, lipopolysaccharide, cigarette smoking extract (CSE), drugs, radiation, and phosphoinositide 3-kinase (PI3K) inhibitors at various doses. We also compared transcriptomic profiles between alveolar and airway epithelia, between cells with or without NAT10 down-regulation, between early and late stages, and between challenges. The present study demonstrated that NAT10 expression increased in human lung epithelia and varied among epithelial types, challenges, and diseases. Knockdown of NAT10 altered epithelial mitochondrial functions, dynamic responses to LPS, CSE, or PI3K inhibitors, and transcriptomic phenomes. NAT10 regulates biological phenomes, and behaviors are more complex and are dependent upon multiple signal pathways. Thus, NAT10-associated signal pathways can be a new alternative for understanding the disease and developing new biomarkers and targets.

Conditional depletion of the acetyltransferase Tip60 protects against the damaging effects of myocardial infarction.

Injury from myocardial infarction (MI) and consequent post-MI remodeling is accompanied by massive loss of cardiomyocytes (CM), a cell type critical for contractile function that is for all practical purposes non-regenerable due to its profound state of proliferative senescence. Identification of factors that limit CM survival and/or constrain CM renewal provides potential therapeutic targets. Tip60, a pan-acetyltransferase encoded by the Kat5 gene, has been reported to activate apoptosis as well as multiple anti-proliferative pathways in non-cardiac cells; however, its role in CMs, wherein it is abundantly expressed, remains unknown. Here, using mice containing floxed Kat5 alleles and a tamoxifen-activated Myh6-MerCreMer recombinase transgene, we report that conditional depletion of Tip60 in CMs three days after MI induced by permanent coronary artery ligation greatly improves functional recovery for up to 28 days. This is accompanied by diminished scarring, activation of cell-cycle transit markers in CMs within the infarct border and remote zones, reduced expression of cell-cycle inhibitors pAtm and p27, and reduced apoptosis in the remote regions. These findings implicate Tip60 as a novel, multifactorial target for limiting the damaging effects of ischemic heart disease.

Fatty acid transport protein 4 (FATP4) prevents light-induced degeneration of cone and rod photoreceptors by inhibiting RPE65 isomerase.

Although rhodopsin is essential for sensing light for vision, it also mediates light-induced apoptosis of photoreceptors in mouse. RPE65, which catalyzes isomerization of all-trans retinyl fatty acid esters to 11-cis-retinol (11cROL) in the visual cycle, controls the rhodopsin regeneration rate and photoreceptor susceptibility to light-induced degeneration. Mutations in RPE65 have been linked to blindness in affected children. Despite such importance, the mechanism that regulates RPE65 function remains unclear. Through unbiased expression screening of a bovine retinal pigment epithelium (RPE) cDNA library, we have identified elongation of very long-chain fatty acids-like 1 (ELOVL1) and fatty acid transport protein 4 (FATP4), which each have very long-chain fatty acid acyl-CoA synthetase (VLCFA-ACS) activity, as negative regulators of RPE65. We found that the VLCFA derivative lignoceroyl (C24:0)-CoA inhibited synthesis of 11cROL, whereas palmitoyl (C16:0)-CoA promoted synthesis of 11cROL. We further found that competition of FATP4 with RPE65 for the substrate of RPE65 was also involved in the mechanisms by which FATP4 inhibits synthesis of 11cROL. FATP4 was predominantly expressed in RPE, and the FATP4-deficient RPE showed significantly higher isomerase activity. Consistent with these results, the regeneration rate of 11-cis-retinaldehyde and the recovery rate for rod light sensitivity were faster in FATP4-deficient mice than wild-type mice. Moreover, FATP4-deficient mice displayed increased accumulation of the cytotoxic all-trans retinaldehyde and hypersusceptibility to light-induced photoreceptor degeneration. Our findings demonstrate that ELOVL1, FATP4, and their products comprise the regulatory elements of RPE65 and play important roles in protecting photoreceptors from degeneration induced by light damage.

Interfering TRIB3 protects the blood brain barrier through PI3K/Akt pathway to alleviate cerebral ischemia-reperfusion injury in diabetes mellitus mice.

This study aimed to treat diabetic cerebral ischemia-reperfusion injury (CI/RI) by affecting blood brain barrier (BBB) permeability and integrity. The CI/RI model in DM mice and a high glucose (HG) treated oxygen and glucose deprivation/reoxygenation (OGD/R) brain endothelial cell model were established for the study. Evans blue (EB) staining was used to evaluate the permeability of BBB in vivo. TTC staining was used to analyze cerebral infarction. The location and expression of tribbles homolog 3 (TRIB3) in endothelial cells were detected by immunofluorescence. Western blotting was used to detect the protein expressions of TRIB3, tight junction molecules, adhesion molecules, phosphorylated protein kinase B (p-AKT) and AKT. The levels of pro-inflammatory cytokines were detected by qRT-PCR. Trans-epithelial electrical resistance (TEER) and fluorescein isothiocyanate (FITC)-dextran were used to measure vascular permeability in vitro. TRIB3 ubiquitination and acetylation levels were detected. Acetyltransferase bound to TRIB3 were identified by immunoprecipitation. TRIB3 was localized in cerebral endothelial cells and was highly expressed in diabetic CI/R mice. The BBB permeability in diabetic CI/R mice and HG-treated OGD/R cells was increased, while the junction integrity was decreased. Interference with TRIB3 in vitro reduces BBB permeability and increases junction integrity. In vivo interfering with TRIB3 reduced cerebral infarction volume, BBB permeability and inflammation levels, and upregulated p-AKT levels. The phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin reversed the effects of TRIB3-interfering plasmid. In vitro HG treatment induced TRIB3 acetylation through acetyltransferase p300, which in turn reduced ubiquitination and stabilized TRIB3. Interfering TRIB3 protects BBB by activating PI3K/AKT pathway and alleviates brain injury, which provides a new target for diabetic CI/RI.

Effects of putrescine on oxidative stress, spermidine/spermine-N(1)-acetyltransferase, inflammation and energy levels in liver and serum in rats with brain ischemia-reperfusion.

We aimed to examine the effects of brain ischemia-reperfusion (IR) especially on serum parameters or liver enzymes, free radicals, cytokines, oxidatively damaged DNA, spermidine/spermine N-1-acetyltransferase (SSAT). The effects of addition of putrescine on IR will be evaluated in terms of inflammation and oxidant-antioxidant balance in liver.The study was conducted on 46 male Albino Wistar rats weighing 200-250 g. The rats were grouped into: 1-Sham group (n = 6). 2-IR group (n = 8): The carotid arteries were ligated for 30-min and reperfusion was achieved for 30-min under general anesthesia. 3-Ischemia + putrescine + reperfusion group (IPR) (n = 8): Unlike the IR group, a single dose of 250 µmol kg-1 putrescine was given by gavage at the beginning of reperfusion. In putrescine treatment groups in addition to the procedures performed in the IR group a total of 4 doses of 250 µmol kg-1 putrescine were given at 12-h intervals, with the first dose immediately after 30-min reperfusion (4-IR+putrescine group (IR+P1) (n = 8)); 3 h after the 30-min reperfusion (5-IR+putrescine group (IR+P2) (n = 8)); 6 h after the 30-min reperfusion (6-IR+putrescine group (IR+P3) (n = 8)). ALT, AST, ATP, NO, SSAT, 8-OHdG levels were analyzed in the serum, and liver samples. NF-κB and IL-6 levels were analyzed in the liver samples.Brain IR causes inflammatory, oxidative and DNA damage in the liver, and putrescine supplementation through gavage reduces liver damage by showing anti-inflammatory and antioxidant effects.

Research on the resistance of isoviolanthin to hydrogen peroxide-triggered injury of skin keratinocytes based on Transcriptome sequencing and molecular docking.

Apoptosis of skin keratinocytes is closely associated with skin problems in humans and natural flavonoids have shown excellent biological activity. Hence, the study of flavonoids against human keratinocyte apoptosis has aroused the interest of numerous researchers. In this study, methyl thiazolyl tetrazolium (MTT) assay and Western blots were used to investigate the skin-protective effect of isoviolanthin, a di-C-glycoside derived from Dendrobium officinale, on hydrogen peroxide (H2O2)-triggered apoptosis of skin keratinocytes. Transcriptome sequencing (RNA-Seq) was used to detect the altered expression genes between the model and treatment group and qRT-PCR was used to verify the accuracy of transcriptome sequencing results. Finally, molecular docking was used to observe the binding ability of isoviolanthin to the selected differential genes screened by transcriptome sequencing. Our results found isoviolanthin could probably increase skin keratinocyte viability, by resisting against apoptosis of skin keratinocytes through downregulating the level of p53 for the first time. By comparing transcriptome differences between the model and drug administration groups, a total of 2953 differential expression genes (DEGs) were identified. Enrichment analysis showed that isoviolanthin may regulate these pathways, such as DNA replication, Mismatch repair, RNA polymerase, Fanconi anemia pathway, Cell cycle, p53 signaling pathway. Last, our results found isoviolanthin has a strong affinity for binding to KDM6B, CHAC2, ESCO2, and IPO4, which may be the potential target for treating skin injuries induced by reactive oxide species. The current study confirms isoviolanthin potential as a skin protectant. The findings may serve as a starting point for further research into the mechanism of isoviolanthin protection against skin damage caused by reactive oxide species (e.g., hydrogen peroxide).

A Therapeutically Targetable NOTCH1-SIRT1-KAT7 Axis in T-cell Leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is a NOTCH1-driven disease in need of novel therapies. Here, we identify a NOTCH1-SIRT1-KAT7 link as a therapeutic vulnerability in T-ALL, in which the histone deacetylase SIRT1 is overexpressed downstream of a NOTCH1-bound enhancer. SIRT1 loss impaired leukemia generation, whereas SIRT1 overexpression accelerated leukemia and conferred resistance to NOTCH1 inhibition in a deacetylase-dependent manner. Moreover, pharmacologic or genetic inhibition of SIRT1 resulted in significant antileukemic effects. Global acetyl proteomics upon SIRT1 loss uncovered hyperacetylation of KAT7 and BRD1, subunits of a histone acetyltransferase complex targeting H4K12. Metabolic and gene-expression profiling revealed metabolic changes together with a transcriptional signature resembling KAT7 deletion. Consistently, SIRT1 loss resulted in reduced H4K12ac, and overexpression of a nonacetylatable KAT7-mutant partly rescued SIRT1 loss-induced proliferation defects. Overall, our results uncover therapeutic targets in T-ALL and reveal a circular feedback mechanism balancing deacetylase/acetyltransferase activation with potentially broad relevance in cancer. SIGNIFICANCE: We identify a T-ALL axis whereby NOTCH1 activates SIRT1 through an enhancer region, and SIRT1 deacetylates and activates KAT7. Targeting SIRT1 shows antileukemic effects, partly mediated by KAT7 inactivation. Our results reveal T-ALL therapeutic targets and uncover a rheostat mechanism between deacetylase/acetyltransferase activities with potentially broader cancer relevance. This article is highlighted in the In This Issue feature, p. 1.

Overexpression of the chromosomally encoded aminoglycoside acetyltransferase eis confers kanamycin resistance in Mycobacterium tuberculosis.

The emergence of multidrug-resistant (MDR) tuberculosis (TB) highlights the urgent need to understand the mechanisms of resistance to the drugs used to treat this disease. The aminoglycosides kanamycin and amikacin are important bactericidal drugs used to treat MDR TB, and resistance to one or both of these drugs is a defining characteristic of extensively drug-resistant TB. We identified mutations in the -10 and -35 promoter region of the eis gene, which encodes a previously uncharacterized aminoglycoside acetyltransferase. These mutations led to a 20-180-fold increase in the amount of eis leaderless mRNA transcript, with a corresponding increase in protein expression. Importantly, these promoter mutations conferred resistance to kanamycin [5 microg/mL < minimum inhibitory concentration (MIC)

The Acetyltransferase KAT5 Inhibitor NU 9056 Promotes Apoptosis and Inhibits JAK2/STAT3 Pathway in Extranodal NK/T Cell Lymphoma.

BACKGROUND: Extranodal natural killer/T cell lymphoma (ENKTL) is an aggressive malignant non- Hodgkin's lymphoma (NHL) with a poor prognosis. Therefore, novel therapeutic biomarkers and agents must be identified for the same. KAT5 inhibitor, NU 9056, is a small molecule that can inhibit cellular proliferation; however, its role in ENKTL has not been studied. OBJECTIVE: The present study investigated the effect of NU 9056 in ENKTL cells and explored the possible molecular mechanism for its antitumour effect. METHODS: The role of NU 9056 in ENKTL cells was investigated through the Cell Counting Kit-8 assay, flow cytometry, Western blot, and real-time quantitative polymerase chain reaction assay. RESULTS: NU 9056 inhibited ENKTL cell proliferation and induced G2/M phase arrest. NU 9056 also induced apoptosis by upregulating DR4, DR5, and caspase 8 expressions. Additionally, NU 9056 increased the expression of Bax, Bid, and cytochrome C and decreased the expression of Bcl-2, Mcl-1, and XIAP. Furthermore, NU 9056 activated endoplasmic reticulum (ER) stress and inhibited the JAK2/STAT3 signalling pathway. The p38 mitogen-activated protein kinase (MAPK) signalling pathway was also activated by NU 9056, and the ERK signalling pathway was suppressed in natural killer/T cell lymphoma cells. CONCLUSION: NU 9056 inhibited cell proliferation, arrested cell cycle in the G2/M phase, and induced apoptosis through the stimulation of ER stress, thus inhibiting the JAK2/STAT3 signalling pathway and regulating MAPK pathways in ENKTL cells.

Elevation of N-acetyltransferase 10 in hippocampal neurons mediates depression- and anxiety-like behaviors.

Major depressive disorder (MDD) is one of the most debilitating and severe mental diseases globally. Increasing evidence has shown that epigenetics is critical for understanding brain function and brain disorders, including MDD. N-acetyltransferase 10 (NAT10), acting on histones, mRNA and other substrates, has been reported to be involved in epigenetic events, including histone acetylation and mRNA modifications. NAT10 is highly expressed in the brain. However, the potential effects of NAT10 on MDD are still unknown. Here, we exploited chronic mild stress (CMS) to induce anxiety- and depression-like behaviors in mice and found that the expression of NAT10 in the mouse hippocampus was upregulated after CMS treatment. Inhibition of NAT10 by pharmacological methods produced anxiolytic- and antidepressant-like effects. Neuron-specific overexpression of NAT10 in the hippocampus resulted in anxiety- and depression-like behaviors, accompanied by higher SIRT1 protein levels, and lower dendritic spine densities. Overall, it was found that elevation of NAT10 in hippocampal neurons is involved in the occurrence of anxiety- and depression-like behaviors, suggesting that NAT10 could be a potential new target for developing anxiolytics and antidepressants.

Long noncoding RNA ZFPM2-AS1 regulates renal cell carcinoma progression via miR-130a-3p/ESCO2.

Previous studies reported that long noncoding RNA (lncRNA) ZFPM2-AS1 is upregulated in renal cell carcinoma (RCC). However, the biological role of lncRNA ZFPM2-AS1 in RCC has not been explored. In this study, we investigated the role of lncRNA ZFPM2-AS1 in the progression of RCC. Quantitative real-time polymerase chain reaction was used for gene expression analysis, and functional assays including Cell Counting Kit-8 assay, flow cytometry-based apoptosis assay and transwell migration assays were performed to examine the malignant phenotypes. The functional interaction between ZFPM2-AS1 or miR-130A-3P and their targets was detected by dual-luciferase reporter assay. We found that the expressions of ZFPM2-AS1 and ESCO2 were upregulated in RCC tissues and cells, whereas miR-130a-3p was downregulated. The expression level of ZFPM2-AS1 is significantly associated with advanced TNM, distant metastasis, lymphatic metastasis, and a poor overall survival in RCC patients. Silencing ZFPM2-AS1 in RCC cells suppressed cell proliferation, invasion, and migration, and induced cell apoptosis. ZFPM2-AS1 interacted with miR-130A-3P and negatively regulated its expression in RCC cells. We further showed that ESCO2 was a downstream target of miR-130a-3p. Both miR-130a-3p inhibitor and ESCO2 overexpression could rescue the inhibitory effects of ZFPM2-AS1 knockdown in RCC cells. Together, our study demonstrates that ZFPM2-AS1 plays an oncogenic role in RCC progression via the miR-130a-3p/ESCO2 axis.

Curcumin-induced histone hypoacetylation: the role of reactive oxygen species.

Curcumin (Cur), a well-known dietary pigment derived from Curcuma longa, is a promising anticancer drug, but its in vivo target molecules remain to be clarified. Here we report that exposure of human hepatoma cells to Cur led to a significant decrease of histone acetylation. Histone acetyltransferase (HAT) and histone deacetylase (HDAC) are the enzymes controlling the state of histone acetylation in vivo. Cur treatment resulted in a comparable inhibition of histone acetylation in the absence or presence of trichostatin A (the specific HDAC inhibitor), and showed no effect on the in vitro activity of HDAC. In contrast, the domain negative of p300 (a most potent HAT protein) could block the inhibition of Cur on histone acetylation; and the Cur treatment significantly inhibited the HAT activity both in vivo and in vitro. Thus, it is HAT, but not HDAC that is involved in Cur-induced histone hypoacetylation. At the same time, exposure of cells to low or high concentrations of Cur diminished or enhanced the ROS generation, respectively. And the promotion of ROS was obviously involved in Cur-induced histone hypoacetylation, since Cur-caused histone acetylation and HAT activity decrease could be markedly diminished by the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) or their combination, but not by their heat-inactivated forms. The data presented here prove that HAT is one of the in vivo target molecules of Cur; through inhibiting its activity, Cur induces histone hypoacetylation in vivo, where the ROS generation plays an important role. Considering the critical roles of histone acetylation in eukaryotic gene transcription and the involvement of histone hypoacetylation in the lose of cell viability caused by high concentrations of Cur, these results open a new door for us to further understand the molecular mechanism involved in the in vivo function of Cur.

Regulation of distinct biological activities of the NF-kappaB transcription factor complex by acetylation.

Although the proximal cytoplasmic signaling events that control the activation of the NF-kappaB transcription factor are understood in considerable detail, the subsequent intranuclear events that regulate the strength and duration of the NF-kappaB-mediated transcriptional response remain poorly defined. Recent studies have revealed that NF-kappaB is subject to reversible acetylation and that this posttranslational modification functions as an intranuclear molecular switch to control NF-kappaB action. In this review, we summarize this new and fascinating mechanism through which the pleiotropic effects of NF-kappaB are regulated within the cells. NF-kappaB is a heterodimer composed of p50 and RelA subunits. Both subunits are acetylated at multiple lysine residues with the p300/CBP acetyltransferases playing a major role in this process in vivo. Further, the acetylation of different lysines regulates different functions of NF-kappaB, including transcriptional activation, DNA binding affinity, IkappaBalpha assembly, and subcellular localization. Acetylated forms RelA are subject to deacetylation by histone deacetylase 3 (HDAC3). This selective action of HDAC3 promotes IkappaBalpha binding and rapid CRM1-dependent nuclear export of the deacetylated NF-kappaB complex, which terminates the NF-kappaB response and replenishes the cytoplasmic pool of latent NF-kappaB/IkappaBalpha complexes. This readies the cell for the next NF-kappaB-inducing stimulus. Thus, reversible acetylation of RelA serves as an important intranuclear regulatory mechanism that further provides for dynamic control of NF-kappaB action.

Constitutive activation of transcription and binding of coactivator by estrogen-related receptors 1 and 2.

In this report, we demonstrate that, in contrast to most previously characterized nuclear receptors, hERR1 and hERR2 (human estrogen receptor-related protein 1 and -2) are constitutive activators of the classic estrogen response element (ERE) as well as the palindromic thyroid hormone response element (TRE(pal)) but not the glucocorticoid response element (GRE). This intrinsically activated state of hERR1 and hERR2 resides in the ligand-binding domains of the two genes and is transferable to a heterologous receptor. In addition, we show that members of the p160 family of nuclear receptor coactivators, ACTR (activator of thyroid and retinoic acid receptors), GRIP1 (glucocorticoid receptor interacting protein 1), and SRC-1 (steroid receptor coactivator 1), potentiate the transcriptional activity by hERR1 and hERR2 in mammalian cells, and that both orphan receptors bind the coactivators in a ligand-independent manner. Together, these results suggest that hERR1 and hERR2 activate gene transcription through a mechanism different from most of the previously characterized steroid hormone receptors.

Defining the orphan functions of lysine acetyltransferases.

Long known for their role in histone acetylation, recent studies have demonstrated that lysine acetyltransferases also carry out distinct "orphan" functions. These activities impact a wide range of biological phenomena including metabolism, RNA modification, nuclear morphology, and mitochondrial function. Here, we review the discovery and characterization of orphan lysine acetyltransferase functions. In addition to highlighting the evidence and biological role for these functions in human disease, we discuss the part emerging chemical tools may play in investigating this versatile enzyme superfamily.

Trichostatin A induces apoptosis of p815 mastocytoma cells in histone acetylation- and mitochondria-dependent fashion.

Although inhibition of histone deacetylase has been demonstrated to induce apoptosis of various cancer cells, there is no report on its effect on mast cell demise to date. Here we studied whether a histone deacetylase inhibitor Trichostatin A (TSA) produces apoptosis in p815 mastocytoma cells. TSA prominently increased the amount of acetylated histones, H3, H4, H2A and H2B, in p815 mastocytoma cells. TSA reduced the viability of p815 mastocytoma cells, and many apoptotic manifestations such as generation of DNA fragmentation, activation of caspase-3, cleavage of poly (ADP-ribose) polymerase (PARP), and increase of DNA hypoploidy proved that the reduction of viability resulted from apoptosis. Whereas TSA treatment increased the expression level of Bad, it decreased the level of Bcl-2, Bcl-xL, and X-linked inhibitor of apoptosis protein. The reduction of mitochondrial membrane potential, the release of cytochrome c and Smac/DIABLO to cytosol, and mitochondrial localization of Bad were also shown. Taken together, TSA induces apoptosis on p815 mastocytoma cells in histone acetylation- and mitochondria-dependent fashion. Our data therefore provide the possibility that TSA could be considered as a novel therapeutic strategy for mastocytoma from its apoptosis-inducing activity.

Influence of nitroreductase and O-acetyltransferase on the mutagenicity of substituted nitrobenzothiophenamines in Salmonella typhimurium.

The mutagenic activity of 17 substituted (aryl)(2-nitrobenzo[b]thiophen-3yl)amines has been evaluated in the Ames test with different isogenic strains of Salmonella typhimurium, that varied in their expression of nitroreductase and O-acetyltransferase. Active derivatives induced frameshift mutations in TA98 strain, and differences in the chemical structure resulted in up to 15-fold changes in mutagenic activity. The non-mutagenic compounds are the unsubstituted parent compound and derivatives with para-chloro, para-fluoro, para-diethylamino, meta-bromo and para-dimethylamino groups. They do not show any activity even in strains with higher level of nitroreductase or O-acetyltransferase. The addition of S9 fraction decreases the mutagenic potential or gives comparable results to those obtained without metabolic activation. For electron-donating substituents, the meta-isomers display the greatest mutagenic potency, whereas the transfer of the group to the para-position leads to less active or unactive molecules. All active nitrobenzothiophenes are substrates for bacterial nitroreductase and O-acetyltransferase, as shown by the reduced mutagenicity in the deficient strains and increased mutagenicity in the corresponding overproducing bacteria. Previous reports have pointed out interest in nitrothiophene analogues with para-chloro and para-fluoro substituents as promising anti-inflammatory drugs. The present study further enhances the putative interest in these derivatives, based on absence of mutagenicity.

Bioconversion of ribostamycin (SF-733). II. Isolation and structure of 3-N-acetylribostamycin, a microbiologically inactive product of ribostamycin produced by Streptomyces ribosidificus.

The isolation and structure determination of 3-N-acetylribostamycin, a microbiologically inactive derivative, produced enzymatically from ribostamycin by Streptomyces ribosidificus is described. The location of the acetyl group was established by mass and NMR spectrometry of the new compound and its derivatives, and by optical rotation studies conducted on N-ethoxycarbonyl-2-deoxystreptamine. The latter compound was obtained by partial acid hydrolysis of tri-N-ethoxycarbonyl-N-acetylribostamycin.

Mechanism of resistance to aminoglycoside antibiotics in nebramycin-producing Streptomyces tenebrarius.

Streptomyces tenebrarius ISP 5477, which produces nebramycins, was highly resistant to the following aminoglycoside antibiotics: neamine, ribostamycin, butirosin A, neomycin B, paromomycin, kanamycin A, dibekacin, gentamicin C complex, lividomycin A, istamycin B and streptomycin. Polyphenylalanine synthesis on the ribosomes of this strain was highly resistant to neamine, ribostamycin, butirosin A, kanamycins A, B and C, dibekacin, gentamicin C complex and istamycin B, moderately resistant to lividomycin A and streptomycin, but sensitive to neomycin B and paromomycin. Moreover, cell free extract of the strain contained phosphotransferase and N-acetyltransferase. The former enzyme was confirmed to be an aminoglycoside 6-phosphotransferase which inactivated streptomycin; the latter inactivated kanamycins B and C, dibekacin, neamine, neomycin B, paromomycin, lividomycin A, butirosin A and ribostamycin, but did not inactivate kanamycin A, gentamicin C complex and sagamicin, suggesting an aminoglycoside 2'-acetyltransferase. These results indicated that the high resistance of S. tenebrarius ISP 5477 to a wide range of aminoglycoside antibiotics is due to ribosomal resistance and to the inactivating enzymes, aminoglycoside N-acetyltransferase(s) and aminoglycoside 6-phosphotransferase.

Role of aminoglycoside 6'-acetyltransferase in a novel multiple aminoglycoside resistance of an actinomycete strain #8: inactivation of aminoglycosides with 6'-amino group except arbekacin and neomycin.

From a rare actinomycete strain #8 isolated from soil as arbekacin (ABK) resistant, we cloned a gene segment (0.9 kb) conferring multiple resistance to aminoglycoside (AG) antibiotics with 6'-NH2 including semisynthetic ones except ABK and neomycin (NM). Enzymatic modification using cell free extracts from Streptomyces lividans TK21/pANT-S2 carrying the cloned gene revealed that the gene coded for an AG 6'-acetyltransferase [AAC(6')] capable of acetylating all of the tested AGs with 6'-NH2 including semisynthetic ones and astromicin. The substrate specificity of the enzyme was thus similar to that of AAC(6')-Ie of Enterococcus faecalis. Antibiotic assay revealed a weak but clear antibiotic activity of 6'-N-acetylABK (8% of ABK activity) in contrast with substantial inactivation by the AAC(6') of the other AGs including amikacin and isepamicin. The NM acetylation by the AAC(6') also did not result in NM inactivation. It seems thus likely that AAC(6')-dependent resistance to ABK and NM, if it emerges, will remain at low level.