Co-translational, Post-translational, and Non-catalytic Roles of N-Terminal Acetyltransferases.

Recent studies of N-terminal acetylation have identified new N-terminal acetyltransferases (NATs) and expanded the known functions of these enzymes beyond their roles as ribosome-associated co-translational modifiers. For instance, the identification of Golgi- and chloroplast-associated NATs shows that acetylation of N termini also happens post-translationally. In addition, we now appreciate that some NATs are highly specific; for example, a dedicated NAT responsible for post-translational N-terminal acetylation of actin was recently revealed. Other studies have extended NAT function beyond Nt acetylation, including functions as lysine acetyltransferases (KATs) and non-catalytic roles. Finally, emerging studies emphasize the physiological relevance of N-terminal acetylation, including roles in calorie-restriction-induced longevity and pathological α-synuclein aggregation in Parkinson's disease. Combined, the NATs rise as multifunctional proteins, and N-terminal acetylation is gaining recognition as a major cellular regulator.

Dynamic RNA acetylation revealed by quantitative cross-evolutionary mapping.

N4-acetylcytidine (ac4C) is an ancient and highly conserved RNA modification that is present on tRNA and rRNA and has recently been investigated in eukaryotic mRNA1-3. However, the distribution, dynamics and functions of cytidine acetylation have yet to be fully elucidated. Here we report ac4C-seq, a chemical genomic method for the transcriptome-wide quantitative mapping of ac4C at single-nucleotide resolution. In human and yeast mRNAs, ac4C sites are not detected but can be induced-at a conserved sequence motif-via the ectopic overexpression of eukaryotic acetyltransferase complexes. By contrast, cross-evolutionary profiling revealed unprecedented levels of ac4C across hundreds of residues in rRNA, tRNA, non-coding RNA and mRNA from hyperthermophilic archaea. Ac4C is markedly induced in response to increases in temperature, and acetyltransferase-deficient archaeal strains exhibit temperature-dependent growth defects. Visualization of wild-type and acetyltransferase-deficient archaeal ribosomes by cryo-electron microscopy provided structural insights into the temperature-dependent distribution of ac4C and its potential thermoadaptive role. Our studies quantitatively define the ac4C landscape, providing a technical and conceptual foundation for elucidating the role of this modification in biology and disease4-6.

NATs at a glance.

Most proteins receive an acetyl group at the N terminus while in their nascency as the result of modification by co-translationally acting N-terminal acetyltransferases (NATs). The N-terminal acetyl group can influence several aspects of protein functionality. From studies of NAT-lacking cells, it is evident that several cellular processes are affected by this modification. More recently, an increasing number of genetic cases have demonstrated that N-terminal acetylation has crucial roles in human physiology and pathology. In this Cell Science at a Glance and the accompanying poster, we provide an overview of the human NAT enzymes and their properties, substrate coverage, cellular roles and connections to human disease.

N-terminal acetyltransferase 6 facilitates enterovirus 71 replication by regulating PI4KB expression and replication organelle biogenesis.

Enterovirus 71 (EV71) is one of the major pathogens causing hand, foot, and mouth disease in children under 5 years old, which can result in severe neurological complications and even death. Due to limited treatments for EV71 infection, the identification of novel host factors and elucidation of mechanisms involved will help to counter this viral infection. N-terminal acetyltransferase 6 (NAT6) was identified as an essential host factor for EV71 infection with genome-wide CRISPR/Cas9 screening. NAT6 facilitates EV71 viral replication depending on its acetyltransferase activity but has little effect on viral release. In addition, NAT6 is also required for Echovirus 7 and coxsackievirus B5 infection, suggesting it might be a pan-enterovirus host factor. We further demonstrated that NAT6 is required for Golgi integrity and viral replication organelle (RO) biogenesis. NAT6 knockout significantly inhibited phosphatidylinositol 4-kinase IIIß (PI4KB) expression and PI4P production, both of which are key host factors for enterovirus infection and RO biogenesis. Further mechanism studies confirmed that NAT6 formed a complex with its substrate actin and one of the PI4KB recruiters-acyl-coenzyme A binding domain containing 3 (ACBD3). Through modulating actin dynamics, NAT6 maintained the integrity of the Golgi and the stability of ACBD3, thereby enhancing EV71 infection. Collectively, these results uncovered a novel mechanism of N-acetyltransferase supporting EV71 infection.IMPORTANCEEnterovirus 71 (EV71) is an important pathogen for children under the age of five, and currently, no effective treatment is available. Elucidating the mechanism of novel host factors supporting viral infection will reveal potential antiviral targets and aid antiviral development. Here, we demonstrated that a novel N-acetyltransferase, NAT6, is an essential host factor for EV71 replication. NAT6 could promote viral replication organelle (RO) formation to enhance viral replication. The formation of enterovirus ROs requires numerous host factors, including acyl-coenzyme A binding domain containing 3 (ACBD3) and phosphatidylinositol 4-kinase IIIß (PI4KB). NAT6 could stabilize the PI4KB recruiter, ACBD3, by inhibiting the autophagy degradation pathway. This study provides a fresh insight into the relationship between N-acetyltransferase and viral infection.

Expanded in vivo substrate profile of the yeast N-terminal acetyltransferase NatC.

N-terminal acetylation is a conserved protein modification among eukaryotes. The yeast Saccharomyces cerevisiae is a valuable model system for studying this modification. The bulk of protein N-terminal acetylation in S. cerevisiae is catalyzed by the N-terminal acetyltransferases NatA, NatB, and NatC. Thus far, proteome-wide identification of the in vivo protein substrates of yeast NatA and NatB has been performed by N-terminomics. Here, we used S. cerevisiae deleted for the NatC catalytic subunit Naa30 and identified 57 yeast NatC substrates by N-terminal combined fractional diagonal chromatography analysis. Interestingly, in addition to the canonical N-termini starting with ML, MI, MF, and MW, yeast NatC substrates also included MY, MK, MM, MA, MV, and MS. However, for some of these substrate types, such as MY, MK, MV, and MS, we also uncovered (residual) non-NatC NAT activity, most likely due to the previously established redundancy between yeast NatC and NatE/Naa50. Thus, we have revealed a complex interplay between different NATs in targeting methionine-starting N-termini in yeast. Furthermore, our results showed that ectopic expression of human NAA30 rescued known NatC phenotypes in naa30Δ yeast, as well as partially restored the yeast NatC Nt-acetylome. Thus, we demonstrate an evolutionary conservation of NatC from yeast to human thereby underpinning future disease models to study pathogenic NAA30 variants. Overall, this work offers increased biochemical and functional insights into NatC-mediated N-terminal acetylation and provides a basis for future work to pinpoint the specific molecular mechanisms that link the lack of NatC-mediated N-terminal acetylation to phenotypes of NatC deletion yeast.

NAT10 mediated ac4C acetylation driven m6A modification via involvement of YTHDC1-LDHA/PFKM regulates glycolysis and promotes osteosarcoma.

The dynamic changes of RNA N6-methyladenosine (m6A) during cancer progression participate in various cellular processes. However, less is known about a possible direct connection between upstream regulator and m6A modification, and therefore affects oncogenic progression. Here, we have identified that a key enzyme in N4-acetylcytidine (ac4C) acetylation NAT10 is highly expressed in human osteosarcoma tissues, and its knockdown enhanced m6A contents and significantly suppressed osteosarcoma cell growth, migration and invasion. Further results revealed that NAT10 silence inhibits mRNA stability and translation of m6A reader protein YTHDC1, and displayed an increase in glucose uptake, a decrease in lactate production and pyruvate content. YTHDC1 recognizes differential m6A sites on key enzymes of glycolysis phosphofructokinase (PFKM) and lactate dehydrogenase A (LDHA) mRNAs, which suppress glycolysis pathway by increasing mRNA stability of them in an m6A methylation-dependent manner. YTHDC1 partially abrogated the inhibitory effect caused by NAT10 knockdown in tumor models in vivo, lentiviral overexpression of YTHDC1 partially restored the reduced stability of YTHDC1 caused by lentiviral depleting NAT10 at the cellular level. Altogether, we found ac4C driven RNA m6A modification can positively regulate the glycolysis of cancer cells and reveals a previously unrecognized signaling axis of NAT10/ac4C-YTHDC1/m6A-LDHA/PFKM in osteosarcoma. Video Abstract.

Acetylcytidine modification of Amotl1 by N-acetyltransferase 10 contributes to cardiac fibrotic expansion in mice after myocardial infarction.

Cardiac fibrosis is a pathological scarring process that impairs cardiac function. N-acetyltransferase 10 (Nat10) is recently identified as the key enzyme for the N4-acetylcytidine (ac4C) modification of mRNAs. In this study, we investigated the role of Nat10 in cardiac fibrosis following myocardial infarction (MI) and the related mechanisms. MI was induced in mice by ligation of the left anterior descending coronary artery; cardiac function was assessed with echocardiography. We showed that both the mRNA and protein expression levels of Nat10 were significantly increased in the infarct zone and border zone 4 weeks post-MI, and the expression of Nat10 in cardiac fibroblasts was significantly higher compared with that in cardiomyocytes after MI. Fibroblast-specific overexpression of Nat10 promoted collagen deposition and induced cardiac systolic dysfunction post-MI in mice. Conversely, fibroblast-specific knockout of Nat10 markedly relieved cardiac function impairment and extracellular matrix remodeling following MI. We then conducted ac4C-RNA binding protein immunoprecipitation-sequencing (RIP-seq) in cardiac fibroblasts transfected with Nat10 siRNA, and revealed that angiomotin-like 1 (Amotl1), an upstream regulator of the Hippo signaling pathway, was the target gene of Nat10. We demonstrated that Nat10-mediated ac4C modification of Amotl1 increased its mRNA stability and translation in neonatal cardiac fibroblasts, thereby increasing the interaction of Amotl1 with yes-associated protein 1 (Yap) and facilitating Yap translocation into the nucleus. Intriguingly, silencing of Amotl1 or Yap, as well as treatment with verteporfin, a selective and potent Yap inhibitor, attenuated the Nat10 overexpression-induced proliferation of cardiac fibroblasts and prevented their differentiation into myofibroblasts in vitro. In conclusion, this study highlights Nat10 as a crucial regulator of myocardial fibrosis following MI injury through ac4C modification of upstream activators within the Hippo/Yap signaling pathway.

A nonsense variant in the N-terminal acetyltransferase NAA30 may be associated with global developmental delay and tracheal cleft.

Most human proteins are N-terminally acetylated by N-terminal acetyltransferases (NATs), which play crucial roles in many cellular functions. The NatC complex, comprising the catalytic subunit NAA30 and the auxiliary subunits NAA35 and NAA38, is estimated to acetylate up to 20% of the human proteome in a co-translational manner. Several NAT enzymes have been linked to rare genetic diseases, causing developmental delay, intellectual disability, and heart disease. Here, we report a de novo heterozygous NAA30 nonsense variant c.244C>T (p.Q82*) (NM_001011713.2), which was identified by whole exome sequencing in a 5-year-old boy presenting with global development delay, autism spectrum disorder, hypotonia, tracheal cleft, and recurrent respiratory infections. Biochemical studies were performed to assess the functional impact of the premature stop codon on NAA30's catalytic activity. We find that NAA30-Q82* completely disrupts the N-terminal acetyltransferase activity toward a classical NatC substrate using an in vitro acetylation assay. This finding corresponds with structural modeling showing that the truncated NAA30 variant lacks the entire GNAT domain, which is required for catalytic activity. This study suggests that defective NatC-mediated N-terminal acetylation can cause disease, thus expanding the spectrum of NAT variants linked to genetic disease.

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.

Activated SIRT1 contributes to DPT-induced glioma cell parthanatos by upregulation of NOX2 and NAT10.

Parthanatos is a type of programmed cell death dependent on hyper-activation of poly (ADP-ribose) polymerase 1 (PARP-1). SIRT1 is a highly conserved nuclear deacetylase and often acts as an inhibitor of parthanatos by deacetylation of PARP1. Our previous study showed that deoxypodophyllotoxin (DPT), a natural compound isolated from the traditional herb Anthriscus sylvestris, triggered glioma cell death via parthanatos. In this study, we investigated the role of SIRT1 in DPT-induced human glioma cell parthanatos. We showed that DPT (450 nmol/L) activated both PARP1 and SIRT1, and induced parthanatos in U87 and U251 glioma cells. Activation of SIRT1 with SRT2183 (10 µmol/L) enhanced, while inhibition of SIRT1 with EX527 (200 µmol/L) or knockdown of SIRT1 attenuated DPT-induced PARP1 activation and glioma cell death. We demonstrated that DPT (450 nmol/L) significantly decreased intracellular NAD+ levels in U87 and U251 cells. Further decrease of NAD+ levels with FK866 (100 µmol/L) aggravated, but supplement of NAD+ (0.5, 2 mmol/L) attenuated DPT-induced PARP1 activation. We found that NAD+ depletion enhanced PARP1 activation via two ways: one was aggravating ROS-dependent DNA DSBs by upregulation of NADPH oxidase 2 (NOX2); the other was reinforcing PARP1 acetylation via increase of N-acetyltransferase 10 (NAT10) expression. We found that SIRT1 activity was improved when being phosphorylated by JNK at Ser27, the activated SIRT1 in reverse aggravated JNK activation via upregulating ROS-related ASK1 signaling, thus forming a positive feedback between JNK and SIRT1. Taken together, SIRT1 activated by JNK contributed to DPT-induced human glioma cell parthanatos via initiation of NAD+ depletion-dependent upregulation of NOX2 and NAT10.

NAT10-mediated RNA acetylation enhances HNRNPUL1 mRNA stability to contribute cervical cancer progression.

N4-acetylcytidine (ac4C) is a lately discovered nucleotide modification that has been shown to be closely implicated in cancer. N-acetyltransferase10(NAT10) acts as an enzyme that regulates mRNA acetylation modifications. Currently, the role of NAT10-mediated RNA acetylation modification in cervical cancer remains to be elucidated. On the basis of transcriptome analysis of TCGA and GEO open datasets (GSE52904, GSE29570, GSE122697), NAT10 is upregulated in cervical cancer tissues and correlated with poor prognosis. Knockdown of NAT10 suppressed the cell proliferation, invasion, and migration of cervical cancer cells. The in vivo oncogenic function of NAT10 was also confirmed in xenograft models. Combined RNA-seq and acRIP-seq analysis revealed HNRNPUL1 as the target of NAT10 in cervical cancer. NAT10 positively regulate HNRNPUL1 expression by promoting ac4C modification and stability of HNRNPUL1 mRNA. Furthermore, depletion of HNRNPUL1 suppressed the cell division, invasion, and migration of cervical cancer. HNRNPUL1 overexpression partially restored cellular function in cervical cancer cells with NAT10 knockdown. Thus, this study demonstrates that NAT10 contributes to cervical cancer progression by enhancing HNRNPUL1 mRNA stability via ac4C modification, and NAT10-ac4C-HNRNPUL1 axis might be a potential target for cervical cancer therapy.

The versatile interactome of chloroplast ribosomes revealed by affinity purification mass spectrometry.

In plant cells, chloroplast gene expression is predominantly controlled through post-transcriptional regulation. Such fine-tuning is vital for precisely orchestrating protein complex assembly as for the photosynthesis machinery and for quickly responding to environmental changes. While regulation of chloroplast protein synthesis is of central importance, little is known about the degree and nature of the regulatory network, mainly due to challenges associated with the specific isolation of transient ribosome interactors. Here, we established a ribosome affinity purification method, which enabled us to broadly uncover putative ribosome-associated proteins in chloroplasts. Endogenously tagging of a protein of the large or small subunit revealed not only interactors of the holo complex, but also preferential interactors of the two subunits. This includes known canonical regulatory proteins as well as several new proteins belonging to the categories of protein and RNA regulation, photosystem biogenesis, redox control and metabolism. The sensitivity of the here applied screen was validated for various transiently interacting proteins. We further provided evidence for the existence of a ribosome-associated Nα-acetyltransferase in chloroplasts and its ability to acetylate substrate proteins at their N-terminus. The broad set of ribosome interactors underscores the potential to regulate chloroplast gene expression on the level of protein synthesis.

Acetylation of MORC2 by NAT10 regulates cell-cycle checkpoint control and resistance to DNA-damaging chemotherapy and radiotherapy in breast cancer.

MORC family CW-type zinc finger 2 (MORC2) is an oncogenic chromatin-remodeling enzyme with an emerging role in DNA repair. Here, we report a novel function for MORC2 in cell-cycle checkpoint control through an acetylation-dependent mechanism. MORC2 is acetylated by the acetyltransferase NAT10 at lysine 767 (K767Ac) and this process is counteracted by the deacetylase SIRT2 under unperturbed conditions. DNA-damaging chemotherapeutic agents and ionizing radiation stimulate MORC2 K767Ac through enhancing the interaction between MORC2 and NAT10. Notably, acetylated MORC2 binds to histone H3 phosphorylation at threonine 11 (H3T11P) and is essential for DNA damage-induced reduction of H3T11P and transcriptional repression of its downstream target genes CDK1 and Cyclin B1, thus contributing to DNA damage-induced G2 checkpoint activation. Chemical inhibition or depletion of NAT10 or expression of an acetylation-defective MORC2 (K767R) forces cells to pass through G2 checkpoint, resulting in hypersensitivity to DNA-damaging agents. Moreover, MORC2 acetylation levels are associated with elevated NAT10 expression in clinical breast tumor samples. Together, these findings uncover a previously unrecognized role for MORC2 in regulating DNA damage-induced G2 checkpoint through NAT10-mediated acetylation and provide a potential therapeutic strategy to sensitize breast cancer cells to DNA-damaging chemotherapy and radiotherapy by targeting NAT10.

Inhibition of N-Acetyltransferase 10 Suppresses the Progression of Prostate Cancer through Regulation of DNA Replication.

Cancer suppression through the inhibition of N-acetyltransferase 10 (NAT10) by its specific inhibitor Remodelin has been demonstrated in a variety of human cancers. Here, we report the inhibitory effects of Remodelin on prostate cancer (PCa) cells and the possible associated mechanisms. The prostate cancer cell lines VCaP, LNCaP, PC3, and DU145 were used. The in vitro proliferation, migration, and invasion of cells were measured by a cell proliferation assay, colony formation, wound healing, and Transwell assays, respectively. In vivo tumor growth was analyzed by transplantation into nude mice. The inhibition of NAT10 by Remodelin not only suppressed growth, migration, and invasion in vitro, but also the in vivo cancer growth of prostate cancer cells. The involvement of NAT10 in DNA replication was assessed by EdU labeling, DNA spreading, iPOND, and ChIP-PCR assays. The inhibition of NAT10 by Remodelin slowed DNA replication. NAT10 was detected in the prereplication complex, and it could also bind to DNA replication origins. Furthermore, the interaction between NAT10 and CDC6 was analyzed by Co-IP. The altered expression of NAT10 was measured by immunofluorescence staining and Western blotting. Remodelin markedly reduced the levels of CDC6 and AR. The expression of NAT10 could be altered under either castration or noncastration conditions, and Remodelin still suppressed the growth of in vitro-induced castration-resistant prostate cancers. The analysis of a TCGA database revealed that the overexpression of NAT10, CDC6, and MCM7 in prostate cancers were correlated with the Gleason score and node metastasis. Our data demonstrated that Remodelin, an inhibitor of NAT10, effectively inhibits the growth of prostate cancer cells under either no castration or castration conditions, likely by impairing DNA replication.

Extended N-Terminal Acetyltransferase Naa50 in Filamentous Fungi Adds to Naa50 Diversity.

Most eukaryotic proteins are N-terminally acetylated by a set of Nα acetyltransferases (NATs). This ancient and ubiquitous modification plays a fundamental role in protein homeostasis, while mutations are linked to human diseases and phenotypic defects. In particular, Naa50 features species-specific differences, as it is inactive in yeast but active in higher eukaryotes. Together with NatA, it engages in NatE complex formation for cotranslational acetylation. Here, we report Naa50 homologs from the filamentous fungi Chaetomium thermophilum and Neurospora crassa with significant N- and C-terminal extensions to the conserved GNAT domain. Structural and biochemical analyses show that CtNaa50 shares the GNAT structure and substrate specificity with other homologs. However, in contrast to previously analyzed Naa50 proteins, it does not form NatE. The elongated N-terminus increases Naa50 thermostability and binds to dynein light chain protein 1, while our data suggest that conserved positive patches in the C-terminus allow for ribosome binding independent of NatA. Our study provides new insights into the many facets of Naa50 and highlights the diversification of NATs during evolution.

[Overexpression of NAT10 induced platinum drugs resistance in breast cancer cell].

Objective: To observe the platinum drugs resistance effect of N-acetyltransferase 10 (NAT10) overexpression in breast cancer cell line and elucidate the underlining mechanisms. Methods: The experiment was divided into wild-type (MCF-7 wild-type cells without any treatment) group, NAT10 overexpression group (H-NAT10 plasmid transfected into MCF-7 cells) and NAT10 knockdown group (SH-NAT10 plasmid transfected into MCF-7 cells). The invasion was detected by Transwell array, the interaction between NAT10 and PARP1 was detected by co-immunoprecipitation. The impact of NAT10 overexpression or knockdown on the acetylation level of PARP1 and its half-life was also determined. Immunostaining and IP array were used to detect the recruitment of DNA damage repair protein by acetylated PARP1. Flow cytometry was used to detect the cell apoptosis. Results: Transwell invasion assay showed that the number of cell invasion was 483.00±46.90 in the NAT10 overexpression group, 469.00±40.50 in the NAT10 knockdown group, and 445.00±35.50 in the MCF-7 wild-type cells, and the differences were not statistically significant (P>0.05). In the presence of 10 µmol/L oxaliplatin, the number of cell invasion was 502.00±45.60 in the NAT10 overexpression group and 105.00±20.50 in the NAT10 knockdown group, both statistically significant (P<0.05) compared with 219.00±31.50 in wild-type cells. In the presence of 10 µmol/L oxaliplatin, NAT10 overexpression enhanced the binding of PARP1 to NAT10 compared with wild-type cells, whereas the use of the NAT10 inhibitor Remodelin inhibited the mutual binding of the two. Overexpression of NAT10 induced PARP1 acetylation followed by increased PARP1 binding to XRCC1, and knockdown of NAT10 expression reduced PARP1 binding to XRCC1. Overexpression of NAT10 enhanced PARP1 binding to LIG3, while knockdown of NAT10 expression decreased PARP1 binding to LIG3. In 10 µmol/L oxaliplatin-treated cells, the γH2AX expression level was 0.38±0.02 in NAT10 overexpressing cells and 1.36±0.15 in NAT10 knockdown cells, both statistically significant (P<0.05) compared with 1.00±0.00 in wild-type cells. In 10 µmol/L oxaliplatin treated cells, the apoptosis rate was (6.54±0.68)% in the NAT10 overexpression group and (12.98±2.54)% in the NAT10 knockdown group, both of which were statistically significant (P<0.05) compared with (9.67±0.37)% in wild-type cells. Conclusion: NAT10 overexpression enhances the binding of NAT10 to PARP1 and promotes the acetylation of PARP1, which in turn prolongs the half-life of PARP1, thus enhancing PARP1 recruitment of DNA damage repair related proteins to the damage sites, promoting DNA damage repair and ultimately the survival of breast cancer cells.

Remodelin, a N-acetyltransferase 10 (NAT10) inhibitor, alters mitochondrial lipid metabolism in cancer cells.

Remodelin is a small molecule inhibitor of N-acetyltransferase 10 (NAT10), reported to reverse the effect of cancer conditions such as epithelial to mesenchymal transition, hypoxia, and drug resistance. We analysed RNA seq data of siNAT10 and found many metabolic pathways were altered, this made us perform unbiased metabolic analysis. Here we performed untargeted metabolomics in Remodelin treated cancer cells using high-performance liquid chromatography-tandem mass spectrometry. Statistical analysis revealed a total number of 138 of which 52 metabolites were significantly modified in Remodelin treated cells. Among the most significantly altered metabolites, we identified metabolites related with mitochondrial fatty acid elongation (MFAE) and mitochondrial beta-oxidation such as lauroyl-CoA, cholesterol, triglycerides, (S)-3-hydroxyhexadecanoyl-CoA, and NAD+ . Furthermore, assessment showed alteration in expression of Enoyl-CoA hydratase, short chain 1, mitochondrial (ECHS1), and Mitochondrial trans-2-enoyl-CoA reductase (MECR) genes, associated with MFAE pathway. We also found statistically significant decrease in total cholesterol and triglycerides in Remodelin treated cancer cells. Overall, our results showed that Remodelin alters mitochondrial fatty acid metabolism and lipid accumulation in cancer cells. Finally, we validated these results in NAT10 knockdown cancer cells and found that NAT10 reduction results in alteration in gene expression associated with mitochondrial fatty acid metabolism, clearly suggesting the possible role of NAT10 in maintaining mitochondrial fatty acid metabolism.

Dual lysine and N-terminal acetyltransferases reveal the complexity underpinning protein acetylation.

Protein acetylation is a highly frequent protein modification. However, comparatively little is known about its enzymatic machinery. N-α-acetylation (NTA) and ε-lysine acetylation (KA) are known to be catalyzed by distinct families of enzymes (NATs and KATs, respectively), although the possibility that the same GCN5-related N-acetyltransferase (GNAT) can perform both functions has been debated. Here, we discovered a new family of plastid-localized GNATs, which possess a dual specificity. All characterized GNAT family members display a number of unique features. Quantitative mass spectrometry analyses revealed that these enzymes exhibit both distinct KA and relaxed NTA specificities. Furthermore, inactivation of GNAT2 leads to significant NTA or KA decreases of several plastid proteins, while proteins of other compartments were unaffected. The data indicate that these enzymes have specific protein targets and likely display partly redundant selectivity, increasing the robustness of the acetylation process in vivo. In summary, this study revealed a new layer of complexity in the machinery controlling this prevalent modification and suggests that other eukaryotic GNATs may also possess these previously underappreciated broader enzymatic activities.

NAA80 is actin's N-terminal acetyltransferase and regulates cytoskeleton assembly and cell motility.

Actin, one of the most abundant proteins in nature, participates in countless cellular functions ranging from organelle trafficking and pathogen motility to cell migration and regulation of gene transcription. Actin's cellular activities depend on the dynamic transition between its monomeric and filamentous forms, a process exquisitely regulated in cells by a large number of actin-binding and signaling proteins. Additionally, several posttranslational modifications control the cellular functions of actin, including most notably N-terminal (Nt)-acetylation, a prevalent modification throughout the animal kingdom. However, the biological role and mechanism of actin Nt-acetylation are poorly understood, and the identity of actin's N-terminal acetyltransferase (NAT) has remained a mystery. Here, we reveal that NAA80, a suggested NAT enzyme whose substrate specificity had not been characterized, is Nt-acetylating actin. We further show that actin Nt-acetylation plays crucial roles in cytoskeletal assembly in vitro and in cells. The absence of Nt-acetylation leads to significant differences in the rates of actin filament depolymerization and elongation, including elongation driven by formins, whereas filament nucleation by the Arp2/3 complex is mostly unaffected. NAA80-knockout cells display severely altered cytoskeletal organization, including an increase in the ratio of filamentous to globular actin, increased filopodia and lamellipodia formation, and accelerated cell motility. Together, the results demonstrate NAA80's role as actin's NAT and reveal a crucial role for actin Nt-acetylation in the control of cytoskeleton structure and dynamics.

Formation of mammalian preribosomes proceeds from intermediate to composed state during ribosome maturation.

In eukaryotes, ribosome assembly is a rate-limiting step in ribosomal biogenesis that takes place in a distinctive subnuclear organelle, the nucleolus. How ribosomes get assembled at the nucleolar site by forming initial preribosomal complexes remains poorly characterized. In this study, using several human and murine cell lines, we developed a method for isolation of native mammalian preribosomal complexes by lysing cell nuclei through mild sonication. A sucrose gradient fractionation of the nuclear lysate resolved several ribonucleoprotein (RNP) complexes containing rRNAs and ribosomal proteins. Characterization of the RNP complexes with MS-based protein identification and Northern blotting-based rRNA detection approaches identified two types of preribosomes we named here as intermediate preribosomes (IPRibs) and composed preribosome (CPRib). IPRib complexes comprised large preribosomes (105S to 125S in size) containing the rRNA modification factors and premature rRNAs. We further observed that a distinctive CPRib complex consists of an 85S preribosome assembled with mature rRNAs and a ribosomal biogenesis factor, Ly1 antibody-reactive (LYAR), that does not associate with premature rRNAs and rRNA modification factors. rRNA-labeling experiments uncovered that IPRib assembly precedes CPRib complex formation. We also found that formation of the preribosomal complexes is nutrient-dependent because the abundances of IPRib and CPRib decreased substantially when cells were either deprived of amino acids or exposed to an mTOR kinase inhibitor. These findings indicate that preribosomes form via dynamic and nutrient-dependent processing events and progress from an intermediate to a composed state during ribosome maturation.