Sphingolipid biosynthesis is essential for metabolic rewiring during TH17 cell differentiation.

T helper 17 (TH17) cells are implicated in autoimmune diseases, and several metabolic processes are shown to be important for their development and function. In this study, we report an essential role for sphingolipids synthesized through the de novo pathway in TH17 cell development. Deficiency of SPTLC1, a major subunit of serine palmitoyl transferase enzyme complex that catalyzes the first and rate-limiting step of de novo sphingolipid synthesis, impaired glycolysis in differentiating TH17 cells by increasing intracellular reactive oxygen species (ROS) through enhancement of nicotinamide adenine dinucleotide phosphate oxidase 2 activity. Increased ROS leads to impaired activation of mammalian target of rapamycin C1 and reduced expression of hypoxia-inducible factor 1-alpha and c-Myc-induced glycolytic genes. SPTLCI deficiency protected mice from developing experimental autoimmune encephalomyelitis and experimental T cell transfer colitis. Our results thus show a critical role for de novo sphingolipid biosynthetic pathway in shaping adaptive immune responses with implications in autoimmune diseases.

Specific inhibition of an anticancer target, polo-like kinase 1, by allosterically dismantling its mechanism of substrate recognition.

Polo-like kinase 1 (Plk1) is considered an attractive target for anticancer therapy. Over the years, studies on the noncatalytic polo-box domain (PBD) of Plk1 have raised the expectation of generating highly specific protein-protein interaction inhibitors. However, the molecular nature of the canonical PBD-dependent interaction, which requires extensive water network-mediated interactions with its phospholigands, has hampered efforts to identify small molecules suitable for Plk1 PBD drug discovery. Here, we report the identification of the first allosteric inhibitor of Plk1 PBD, called Allopole, a prodrug that can disrupt intracellular interactions between PBD and its cognate phospholigands, delocalize Plk1 from centrosomes and kinetochores, and induce mitotic block and cancer cell killing. At the structural level, its unmasked active form, Allopole-A, bound to a deep Trp-Phe-lined pocket occluded by a latch-like loop, whose adjoining region was required for securely retaining a ligand anchored to the phospho-binding cleft. Allopole-A binding completely dislodged the L2 loop, an event that appeared sufficient to trigger the dissociation of a phospholigand and inhibit PBD-dependent Plk1 function during mitosis. Given Allopole's high specificity and antiproliferative potency, this study is expected to open an unexplored avenue for developing Plk1 PBD-specific anticancer therapeutic agents.

Protonation-Dependent Sequencing of 5-Formylcytidine in RNA.

Chemical modification of cytidine in noncoding RNAs plays a key role in regulating translation and disease. However, the distribution and dynamics of many of these modifications remain unknown due to a lack of sensitive site-specific sequencing technologies. Here, we report a protonation-dependent sequencing reaction for the detection of 5-formylcytidine (5fC) and 5-carboxycytidine (5caC) in RNA. First, we evaluate how protonation combined with electron-withdrawing substituents alters the molecular orbital energies and reduction of modified cytidine nucleosides, highlighting 5fC and 5caC as reactive species. Next, we apply this reaction to detect these modifications in synthetic oligonucleotides as well as endogenous human transfer RNA (tRNA). Finally, we demonstrate the utility of our method to characterize a patient-derived model of 5fC deficiency, where it enables facile monitoring of both pathogenic loss and exogenous rescue of NSUN3-dependent 5fC within the wobble base of human mitochondrial tRNAMet. These studies showcase the ability of protonation to enhance the reactivity and sensitive detection of 5fC in RNA and more broadly provide a molecular foundation for using optimized sequencing reactions to better understand the role of oxidized RNA cytidine residues in diseases.

Remodelin Is a Cryptic Assay Interference Chemotype That Does Not Inhibit NAT10-Dependent Cytidine Acetylation.

Remodelin is a putative small molecule inhibitor of the RNA acetyltransferase NAT10 which has shown preclinical efficacy in models of the premature aging disease Hutchinson-Gilford Progeria Syndrome (HGPS). Here we evaluate remodelin's assay interference characteristics and effects on NAT10-catalyzed RNA cytidine acetylation. We find the remodelin chemotype constitutes a cryptic assay interference compound, which does not react with small molecule thiols but demonstrates protein reactivity in ALARM NMR and proteome-wide affinity profiling assays. Biophysical analyses find no direct evidence for interaction of remodelin with the NAT10 acetyltransferase active site. Cellular studies verify that N4-acetylcytidine (ac4C) is a nonredundant target of NAT10 activity in human cell lines and find that this RNA modification is not affected by remodelin treatment in several orthogonal assays. These studies display the potential for remodelin's chemotype to interact with multiple protein targets in cells and indicate remodelin should not be applied as a specific chemical inhibitor of NAT10-catalyzed RNA acetylation.

SSSPTA is essential for serine palmitoyltransferase function during development and hematopoiesis.

Serine palmitoyltransferase complex (SPT) mediates the first and rate-limiting step in the de novo sphingolipid biosynthetic pathway. The larger subunits SPTLC1 and SPTLC2/SPTLC3 together form the catalytic core while a smaller third subunit either SSSPTA or SSSPTB has been shown to increase the catalytic efficiency and provide substrate specificity for the fatty acyl-CoA substrates. The in vivo biological significance of these smaller subunits in mammals is still unknown. Here, using two null mutants, a conditional null for ssSPTa and a null mutant for ssSPTb, we show that SSSPTA is essential for embryogenesis and mediates much of the known functions of the SPT complex in mammalian hematopoiesis. The ssSPTa null mutants are embryonic lethal at E6.5 much like the Sptlc1 and Sptlc2 null alleles. Mx1-Cre induced deletion of ssSPTa leads to lethality and myelopoietic defect. Chimeric and competitive bone marrow transplantation experiments show that the defect in myelopoiesis is accompanied by an expansion of the Lin-Sca1+c-Kit+ stem and progenitor compartment. Progenitor cells that fail to differentiate along the myeloid lineage display evidence of endoplasmic reticulum stress. On the other hand, ssSPTb null mice are homozygous viable, and analyses of the bone marrow cells show no significant difference in the proliferation and differentiation of the adult hematopoietic compartment. SPTLC1 is an obligatory subunit for the SPT function, and because Sptlc1-/- and ssSPTa-/- mice display similar defects during development and hematopoiesis, we conclude that an SPT complex that includes SSSPTA mediates much of its developmental and hematopoietic functions in a mammalian model.

Degradation of 5hmC-marked stalled replication forks by APE1 causes genomic instability.

Synthetic lethality between poly(ADP-ribose) polymerase (PARP) inhibition and BRCA deficiency is exploited to treat breast and ovarian tumors. However, resistance to PARP inhibitors (PARPis) is common. To identify potential resistance mechanisms, we performed a genome-wide RNAi screen in BRCA2-deficient mouse embryonic stem cells and validation in KB2P1.21 mouse mammary tumor cells. We found that resistance to multiple PARPi emerged with reduced expression of TET2 (ten-eleven translocation), which promotes DNA demethylation by oxidizing 5-methylcytosine (5mC) to 5-hydroxymethycytosine (5hmC) and other products. TET2 knockdown in BRCA2-deficient cells protected stalled replication forks (RFs). Increasing 5hmC abundance induced the degradation of stalled RFs in KB2P1.21 and human cancer cells by recruiting the base excision repair-associated apurinic/apyrimidinic endonuclease APE1, independent of the BRCA2 status. TET2 loss did not affect the recruitment of the repair protein RAD51 to sites of double-strand breaks (DSBs) or the abundance of proteins associated with RF integrity. The loss of TET2, of its product 5hmC, and of APE1 recruitment to stalled RFs promoted resistance to the chemotherapeutic cisplatin. Our findings reveal a previously unknown role for the epigenetic mark 5hmC in maintaining the integrity of stalled RFs and a potential resistance mechanism to PARPi and cisplatin.

Assessing Endogenous and Exogenous Hormone Exposures and Breast Development in a Migrant Study of Bangladeshi and British Girls.

Timing of breast development (or thelarche) and its endogenous and exogenous determinants may underlie global variation in breast cancer incidence. The study objectives were to characterize endogenous estrogen levels and bisphenol A (BPA) exposure using a migrant study of adolescent girls and test whether concentrations explained differences in thelarche by birthplace and growth environment. Estrogen metabolites (EM) and BPA-glucuronide (BPA-G) were quantified in urine spot samples using liquid chromatography tandem mass spectrometry (LC-MS/MS) from a cross-sectional study of Bangladeshi, first- and second-generation Bangladeshi migrants to the UK, and white British girls aged 5-16 years (n = 348). Thelarche status at the time of interview was self-reported and defined equivalent to Tanner Stage ≥2. We compared geometric means (and 95% confidence interval (CIs)) of EM and BPA-G using linear regression and assessed whether EM and BPA-G explained any of the association between exposure to the UK and the age at thelarche using hazard ratios and 95% confidence intervals. Average EM decreased with exposure to the UK, whereas BPA-G increased and was significantly higher among white British (0.007 ng/mL, 95% CI: 0.0024-0.0217) and second-generation British-Bangladeshi girls (0.009 ng/mL, 95% CI: 0.0040-0.0187) compared to Bangladeshi girls (0.002 ng/mL, 95% CI: 0.0018-0.0034). Two of four EM ratios (16-pathway/parent and parent/all pathways) were significantly associated with thelarche. The relationship between exposure to the UK and thelarche did not change appreciably after adding EM and BPA-G to the models. While BPA-G is often considered a ubiquitous exposure, our findings suggest it can vary based on birthplace and growth environment, with increasing levels for girls who were born in or moved to the UK. Our study did not provide statistically significant evidence that BPA-G or EM concentrations explained earlier thelarche among girls who were born or raised in the UK.

A Systems Chemoproteomic Analysis of Acyl-CoA/Protein Interaction Networks.

Acyl-coenzyme A (CoA)/protein interactions are essential for life. Despite this importance, their global scope and selectivity remains undefined. Here, we describe CATNIP (CoA/AcetylTraNsferase Interaction Profiling), a chemoproteomic platform for the high-throughput analysis of acyl-CoA/protein interactions in endogenous proteomes. First, we apply CATNIP to identify acetyl-CoA-binding proteins through unbiased clustering of competitive dose-response data. Next, we use this method to profile the selectivity of acyl-CoA/protein interactions, leading to the identification of specific acyl-CoA engagement signatures. Finally, we apply systems-level analyses to assess the features of protein networks that may interact with acyl-CoAs, and use a strategy for high-confidence proteomic annotation of acetyl-CoA-binding proteins to identify a site of non-enzymatic acylation in the NAT10 acetyltransferase domain that is likely driven by acyl-CoA binding. Overall, our studies illustrate how chemoproteomics and systems biology can be integrated to understand the roles of acyl-CoA metabolism in biology and disease.

Sptlc1 is essential for myeloid differentiation and hematopoietic homeostasis.

Serine palmitoyltransferase (SPT) long-chain base subunit 1 (SPTLC1) is 1 of the 2 main catalytic subunits of the SPT complex, which catalyzes the first and rate-limiting step of sphingolipid biosynthesis. Here, we show that Sptlc1 deletion in adult bone marrow (BM) cells results in defective myeloid differentiation. In chimeric mice from noncompetitive BM transplant assays, there was an expansion of the Lin- c-Kit+ Sca-1+ compartment due to increased multipotent progenitor production, but myeloid differentiation was severely compromised. We also show that defective biogenesis of sphingolipids in the endoplasmic reticulum (ER) leads to ER stress that affects myeloid differentiation. Furthermore, we demonstrate that transient accumulation of fatty acid, a substrate for sphingolipid biosynthesis, could be partially responsible for the ER stress. Independently, we find that ER stress in general, such as that induced by the chemical thapsigargin or the fatty acid palmitic acid, compromises myeloid differentiation in culture. These results identify perturbed sphingolipid metabolism as a source of ER stress, which may produce diverse pathological effects related to differential cell-type sensitivity.

Glutamine synthetase is necessary for sarcoma adaptation to glutamine deprivation and tumor growth.

Despite a growing body of knowledge about the genomic landscape and molecular pathogenesis of sarcomas, translation of basic discoveries into targeted therapies and significant clinical gains has remained elusive. Renewed interest in altered metabolic properties of cancer cells has led to an exploration of targeting metabolic dependencies as a novel therapeutic strategy. In this study, we have characterized the dependency of human pediatric sarcoma cells on key metabolic substrates and identified a mechanism of adaptation to metabolic stress by examining proliferation and bioenergetic properties of rhabdomyosarcoma and Ewing sarcoma cells under varying concentrations of glucose and glutamine. While all cell lines tested were completely growth-inhibited by lack of glucose, cells adapted to glutamine deprivation, and restored proliferation following an initial period of reduced growth. We show that expression of glutamine synthetase (GS), the enzyme responsible for de novo glutamine synthesis, increased during glutamine deprivation, and that pharmacological or shRNA-mediated GS inhibition abolished proliferation of glutamine-deprived cells, while having no effect on cells grown under normal culture conditions. Moreover, the GS substrates and glutamine precursors glutamate and ammonia restored proliferation of glutamine-deprived cells in a GS-dependent manner, further emphasizing the necessity of GS for adaptation to glutamine stress. Furthermore, pharmacological and shRNA-mediated GS inhibition significantly reduced orthotopic xenograft tumor growth. We also show that glutamine supports sarcoma nucleotide biosynthesis and optimal mitochondrial bioenergetics. Our findings demonstrate that GS mediates proliferation of glutamine-deprived pediatric sarcomas, and suggest that targeting metabolic dependencies of sarcomas should be further investigated as a potential therapeutic strategy.

Acetylation of Cytidine in mRNA Promotes Translation Efficiency.

Generation of the "epitranscriptome" through post-transcriptional ribonucleoside modification embeds a layer of regulatory complexity into RNA structure and function. Here, we describe N4-acetylcytidine (ac4C) as an mRNA modification that is catalyzed by the acetyltransferase NAT10. Transcriptome-wide mapping of ac4C revealed discretely acetylated regions that were enriched within coding sequences. Ablation of NAT10 reduced ac4C detection at the mapped mRNA sites and was globally associated with target mRNA downregulation. Analysis of mRNA half-lives revealed a NAT10-dependent increase in stability in the cohort of acetylated mRNAs. mRNA acetylation was further demonstrated to enhance substrate translation in vitro and in vivo. Codon content analysis within ac4C peaks uncovered a biased representation of cytidine within wobble sites that was empirically determined to influence mRNA decoding efficiency. These findings expand the repertoire of mRNA modifications to include an acetylated residue and establish a role for ac4C in the regulation of mRNA translation.

A Chemical Signature for Cytidine Acetylation in RNA.

N4-acetylcytidine (ac4C) is a highly conserved modified RNA nucleobase whose formation is catalyzed by the disease-associated N-acetyltransferase 10 (NAT10). Here we report a sensitive chemical method to localize ac4C in RNA. Specifically, we characterize the susceptibility of ac4C to borohydride-based reduction and show this reaction can cause introduction of noncognate base pairs during reverse transcription (RT). Combining borohydride-dependent misincorporation with ac4C's known base-sensitivity provides a unique chemical signature for this modified nucleobase. We show this unique reactivity can be used to quantitatively analyze cellular RNA acetylation, study adapters responsible for ac4C targeting, and probe the timing of RNA acetylation during ribosome biogenesis. Overall, our studies provide a chemical foundation for defining an expanding landscape of cytidine acetyltransferase activity and its impact on biology and disease.

Profiling Cytidine Acetylation with Specific Affinity and Reactivity.

The human acetyltransferase NAT10 has recently been shown to catalyze formation of N4-acetylcytidine (ac4C), a minor nucleobase known to alter RNA structure and function. In order to better understand the role of RNA acetyltransferases in biology and disease, here we report the development and application of chemical methods to study ac4C. First, we demonstrate that ac4C can be conjugated to carrier proteins using optimized protocols. Next, we describe methods to access ac4C-containing RNAs, enabling the screening of anti-ac4C antibodies. Finally, we validate the specificity of an optimized ac4C affinity reagent in the context of cellular RNA by demonstrating its ability to accurately report on chemical deacetylation of ac4C. Overall, these studies provide a powerful new tool for studying ac4C in biological contexts, as well as new insights into the stability and half-life of this highly conserved RNA modification. More broadly, they demonstrate how chemical reactivity may be exploited to aid the development and validation of nucleobase-targeting affinity reagents designed to target the emerging epitranscriptome.

Serial Free Bisphenol A and Bisphenol A Glucuronide Concentrations in Neonates.

OBJECTIVE: To determine the balance of metabolism of free bisphenol A (BPA) to the inactive conjugate, BPA glucuronide (BPAG), in neonates. STUDY DESIGN: Free BPA and BPAG concentrations were measured in 78 urine samples collected between December 2012 and August 2013 from a cohort of 44 healthy full term (≥ 37 weeks' gestation) neonates at 2 intervals (3-6 days and 7-27 days of age). A questionnaire was administered at the time of sample collection. Neonates recruited into the study were born in an urban, tertiary care hospital. RESULTS: Only BPAG was detected in the urine samples; concentrations ranged from <0.1 µg/L to 11.21 µg/L (median: 0.27 µg/L). Free BPA concentrations were below the limit of quantification of 0.1 µg/L. Age, but not sex or type of diet, was significantly associated with urinary BPAG concentration (P = .002). CONCLUSIONS: Our results illustrate widespread BPA exposure in healthy full-term neonates and efficient conjugation of BPA to its readily excretable and biologically inactive form (BPAG) as early as 3 days of age. Factors other than type of diet may be important contributors to BPA exposure in neonates.

Urinary bisphenol A-glucuronide and postmenopausal breast cancer in Poland.

PURPOSE: Concerns regarding a possible link between bisphenol A (BPA) and breast cancer have been mounting, but studies in human populations are lacking. We evaluated the association between the major urinary BPA metabolite [BPA-glucuronide (BPA-G)] and postmenopausal breast cancer risk in a large population-based case-control study conducted in two cities in Poland (2000-2003); we further explored the association of BPA-G levels with known postmenopausal breast cancer risk factors in our control population. METHODS: We analyzed creatinine-adjusted urinary BPA-G levels among 575 postmenopausal cases matched on age and study site to 575 controls without breast cancer using a recently developed assay. Odds ratios and 95 % confidence intervals were used to estimate the association between urinary BPA-G level and breast cancer using conditional logistic regression. Among controls, geometric mean BPA-G levels were compared across categories of breast cancer risk factors using linear regression models. RESULTS: There was no indication that increased BPA-G was associated with postmenopausal breast cancer (p-trend = 0.59). Among controls, mean BPA-G was higher among women reporting extended use of menopausal hormones, a prior screening mammogram, and residence in Warsaw. Other comparisons across strata of postmenopausal breast cancer risk factors were not related to differences in BPA-G. CONCLUSIONS: Urinary BPA-G, measured at the time of diagnosis, is not linked to postmenopausal breast cancer.

Prospective evaluation of serum sarcosine and risk of prostate cancer in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial.

Metabolomic profiling has identified, sarcosine, a derivative of the amino acid glycine, as an important metabolite involved in the etiology or natural history of prostate cancer. We examined the association between serum sarcosine levels and risk of prostate cancer in 1122 cases (813 non-aggressive and 309 aggressive) and 1112 controls in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Sarcosine was quantified using high-throughput liquid chromatography-mass spectrometry. A significantly increased risk of prostate cancer was observed with increasing levels of sarcosine (odds ratio [OR] for the highest quartile of exposure [Q4] versus the lowest quartile [Q1] = 1.30, 95% confidence interval [CI]: 1.02, 1.65; P-trend 0.03). When stratified by disease aggressiveness, we observed a stronger association for non-aggressive cases (OR for Q4 versus Q1 = 1.44, 95% CI: 1.11, 1.88; P-trend 0.006) but no association for aggressive prostate cancer (OR for Q4 versus Q1 = 1.03, 95% CI: 0.73, 1.47; P-trend 0.89). Although not statistically significant, temporal analyses showed a stronger association between sarcosine and prostate cancer for serum collected closer to diagnosis, suggesting that sarcosine may be an early biomarker of disease. Interestingly, the association between sarcosine and prostate cancer risk was stronger among men with diabetes (OR = 2.66, 95% CI: 1.04, 6.84) compared with those without reported diabetes (OR = 1.23, 95% CI: 0.95-1.59, P-interaction = 0.01). This study found that elevated levels of serum sarcosine are associated with an increased prostate cancer risk and evidence to suggest that sarcosine may be an early biomarker for this disease.

Urinary free bisphenol A and bisphenol A-glucuronide concentrations in newborns.

Infants are exposed to the endocrine disruptor bisphenol A (BPA) through breast milk and baby formula. Detoxication by conjugation of BPA may be limited in infants. We demonstrate BPA exposure in 11 neonates and 1 young infant, but find no evidence of a low capacity for BPA conjugation.

Global proteomics and metabolomics in cancer biomarker discovery.

Chromatography and electrophoresis have been used for the last half-century to separate small and large molecules. Advances in MS instrumentation and techniques for sample introduction into the mass analyzer (i.e. matrix-assisted laser desorption/ionization and electrospray ionization), chromatography in all its formats and modes and two-dimensional gel electrophoresis, including two-dimensional difference gel electrophoresis, enabled the separation of complex biological mixtures, such as the proteome and the metabolome, in a biological sample. These advances have made it possible to identify compounds that can be used to discriminate between two samples taken from healthy and diseased individuals. The objective is to find proteins or metabolites that can be used as a clinical test for the early diagnosis, prognosis and monitoring of the disease and the outcome of therapy. In this manuscript, we present an overview of what has been achieved in the search for biomarkers, with emphasis on cancer, using separation science and MS.

A reproducible and high-throughput HPLC/MS method to separate sarcosine from α- and ß-alanine and to quantify sarcosine in human serum and urine.

While sarcosine was recently identified as a potential urine biomarker for prostate cancer, further studies have cast doubt on its utility to diagnose this condition. The inconsistent results may be due to the fact that alanine and sarcosine coelute on an HPLC reversed-phase column and the mass spectrometer cannot differentiate between the two isomers, since the same parent/product ions are generally used to measure them. In this study, we developed a high-throughput liquid chromatography-mass spectrometry (LC-MS) method that resolves sarcosine from alanine isomers, allowing its accurate quantification in human serum and urine. Assay reproducibility was determined using the coefficient of variation (CV) and intraclass correlation coefficient (ICC) in serum aliquots from 10 subjects and urine aliquots from 20 subjects across multiple analytic runs. Paired serum/urine samples from 42 subjects were used to evaluate sarcosine serum/urine correlation. Both urine and serum assays gave high sensitivity (limit of quantitation of 5 ng/mL) and reproducibility (serum assay, intra- and interassay CVs < 3% and ICCs > 99%; urine assay, intra-assay CV = 7.7% and ICC = 98.2% and interassay CV = 12.3% and ICC = 94.2%). In conclusion, this high-throughput LC-MS method is able to resolve sarcosine from α- and ß-alanine and is useful for quantifying sarcosine in serum and urine samples.

Quantitation of free and total bisphenol A in human urine using liquid chromatography-tandem mass spectrometry.

Bisphenol A (BPA) is employed in the synthesis of polycarbonate plastics and epoxy resins and is widely used in consumer products including as a coating for the inside of almost all food and beverage containers and thermal-imaging paper. Bisphenol A is considered to have important health implications because it possesses weak estrogenic activity and can leach from storage containers resulting in its consumption by both humans and animals. It is metabolized in the body and excreted into urine as a glucuronide derivative. In this report, we present an accurate, selective, sensitive, and reproducible high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method for the quantitation of BPA in human urine, which is not prone to exogenous contamination. BPA-glucuronide is hydrolyzed enzymatically, extracted with toluene, derivatized with dansyl chloride, and the BPA-(dansyl)(2) derivative is analyzed using reversed-phase HPLC/MS/MS. Calibration was linear to 50 ng/mL with a limit of quantitation of 50 pg/mL and a limit of detection of 5 pg/mL.