Blood DNA methylation signature of diet quality and association with cardiometabolic traits

AIMS

Diet quality might influence cardiometabolic health through epigenetic changes, but this has been little investigated in adults. Our aims were to identify cytosine-phosphate-guanine (CpG) dinucleotides associated with diet quality by conducting an epigenome-wide association study (EWAS) based on blood DNA methylation (DNAm) and to assess how diet-related CpGs associate with inherited susceptibility to cardiometabolic traits: body mass index (BMI), systolic blood pressure (SBP), triglycerides, type 2 diabetes (T2D), and coronary heart disease (CHD).

METHODS AND RESULTS

Meta-EWAS including 5274 participants in four cohorts from Spain, the USA, and the UK. We derived three dietary scores (exposures) to measure adherence to a Mediterranean diet, to a healthy plant-based diet, and to the Dietary Approaches to Stop Hypertension. Blood DNAm (outcome) was assessed with the Infinium arrays Human Methylation 450K BeadChip and MethylationEPIC BeadChip. For each diet score, we performed linear EWAS adjusted for age, sex, blood cells, smoking and technical variables, and BMI in a second set of models. We also conducted Mendelian randomization analyses to assess the potential causal relationship between diet-related CpGs and cardiometabolic traits. We found 18 differentially methylated CpGs associated with dietary scores (P < 1.08 × 10-7; Bonferroni correction), of which 12 were previously associated with cardiometabolic traits. Enrichment analysis revealed overrepresentation of diet-associated genes in pathways involved in inflammation and cardiovascular disease. Mendelian randomization analyses suggested that genetically determined methylation levels corresponding to lower diet quality at cg02079413 (SNORA54), cg02107842 (MAST4), and cg23761815 (SLC29A3) were causally associated with higher BMI and at cg05399785 (WDR8) with greater SBP, and methylation levels associated with higher diet quality at cg00711496 (PRMT1) with lower BMI, T2D risk, and CHD risk and at cg0557921 (AHRR) with lower CHD risk.

CONCLUSION

Diet quality in adults was related to differential methylation in blood at 18 CpGs, some of which related to cardiometabolic health.

Equilibrative nucleotide transporter ENT3 (SLC29A3): A unique transporter for inherited disorders and cancers

As a crucial gene associated with diseases, the SLC29A3 gene encodes the equilibrative nucleoside transporter 3 (ENT3). ENT3 plays an essential regulatory role in transporting intracellular hydrophilic nucleosides, nucleotides, hydrophilic anticancer and antiviral nucleoside drugs, energy metabolism, subcellular localization, protein stability, and signal transduction. The mutation and inactivation of SLC29A3 are intimately linked to the occurrence, development, and prognosis of various human tumors. Moreover, many hereditary human diseases, such as H syndrome, pigmentary hypertrichosis and non-autoimmune insulin-dependent diabetes mellitus (PHID) syndrome, Faisalabad histiocytosis (FHC), are related to SLC29A3 mutations. This review explores the mechanisms of SLC29A3 mutations and expression alterations in inherited disorders and cancers. Additionally, we compile studies on the inhibition of ENT3, which may serve as an effective strategy to potentiate the anticancer activity of chemotherapy. Thus, the synopsis of genetics, permeant function and drug therapy of ENT3 provides a new theoretical and empirical foundation for the diagnosis, prognosis of evaluation and treatment of various related diseases.

Paediatric diabetes subtypes in a consanguineous population: a single-centre cohort study from Kurdistan, Iraq

AIMS/HYPOTHESIS

Monogenic diabetes is estimated to account for 1-6% of paediatric diabetes cases in primarily non-consanguineous populations, while the incidence and genetic spectrum in consanguineous regions are insufficiently defined. In this single-centre study we aimed to evaluate diabetes subtypes, obtain the consanguinity rate and study the genetic background of individuals with syndromic and neonatal diabetes in a population with a high rate of consanguinity.

METHODS

Data collection was carried out cross-sectionally in November 2021 at the paediatric diabetic clinic, Dr Jamal Ahmad Rashed Hospital, in Sulaimani, Kurdistan, Iraq. At the time of data collection, 754 individuals with diabetes (381 boys) aged up to 16 years were registered. Relevant participant data was obtained from patient files. Consanguinity status was known in 735 (97.5%) participants. Furthermore, 12 families of children with neonatal diabetes and seven families of children with syndromic diabetes consented to genetic testing by next-generation sequencing. Prioritised variants were evaluated using the American College of Medical Genetics and Genomics guidelines and confirmed by Sanger sequencing.

RESULTS

A total of 269 of 735 participants (36.5%) with known consanguinity status were offspring of consanguineous families. An overwhelming majority of participants (714/754, 94.7%) had clinically defined type 1 diabetes (35% of them were born to consanguineous parents), whereas only eight (1.1%) had type 2 diabetes (38% consanguineous). Fourteen (1.9%) had neonatal diabetes (50% consanguineous), seven (0.9%) had syndromic diabetes (100% consanguineous) and 11 (1.5%) had clinically defined MODY (18% consanguineous). We found that consanguinity was significantly associated with syndromic diabetes (p=0.0023) but not with any other diabetes subtype. The genetic cause was elucidated in ten of 12 participants with neonatal diabetes who consented to genetic testing (homozygous variants in GLIS3 [sibling pair], PTF1A and ZNF808 and heterozygous variants in ABCC8 and INS) and four of seven participants with syndromic diabetes (homozygous variants in INSR, SLC29A3 and WFS1 [sibling pair]). In addition, a participant referred as syndromic diabetes was diagnosed with mucolipidosis gamma and probably has type 2 diabetes.

CONCLUSIONS/INTERPRETATION

This unique single-centre study confirms that, even in a highly consanguineous population, clinically defined type 1 diabetes is the prevailing paediatric diabetes subtype. Furthermore, a pathogenic cause of monogenic diabetes was identified in 83% of tested participants with neonatal diabetes and 57% of participants with syndromic diabetes, with most variants being homozygous. Causative genes in our consanguineous participants were markedly different from genes reported from non-consanguineous populations and also from those reported in other consanguineous populations. To correctly diagnose syndromic diabetes in consanguineous populations, it may be necessary to re-evaluate diagnostic criteria and include additional phenotypic features such as short stature and hepatosplenomegaly.

Hyperglycemia with hypogonadism and growth hormone deficiency in a 17-year-old male with H syndrome: the first case report from Syria

BACKGROUND

The nucleoside transport capabilities of the human equilibrative nucleoside transporter-3 (hENT3) are disrupted by mutations in SLC29A3 (10q22.2), which are genes for the nucleoside transporter and are the cause of the unusual autosomal recessive disease known as H syndrome. As a result, histiocytic cells invade a number of organs.

CASE PRESENTATION

A 17-year-old Syrian male was admitted to the internal medicine department with a one-month history of polyuria, polydipsia, general weakness, and pallor. He had a history of progressive bilateral sensorineural hearing loss and failure to gain weight for three years. Physical examination revealed various abnormalities, including scrotal mass, small penis and testicles, absence of pubic and axillary hair, joint abnormalities, short stature, hallux valgus, fibrous protrusion near the navel, and hyperpigmented non-itchy painful skin plaques. Clinical signs along with laboratory test results confirmed hyperglycemia, primary hypogonadism, osteopenia, and growth hormone deficiency. After a review of the relevant medical literature, this patient's presentation of hyperglycemia with hypogonadism, hyperpigmentation, hallux valgus, hearing loss, hematological abnormalities, and short stature suggested the diagnosis of H syndrome. The patient received treatment with insulin and testosterone, leading to a significant improvement in his presenting symptoms.

CONCLUSIONS

H syndrome is a very rare condition, and the fact that the first case has only recently been reported in Syria serves to emphasize how rare it is. H Syndrome should be suspected if a patient has short stature with signs of hyperglycemia and other endocrine and cutaneous abnormalities. We are reporting this case to increase physicians' awareness of this exceedingly rare and unique syndrome.

Loss of function of ENT3 drives histiocytosis and inflammation through TLR-MAPK signaling

Histiocytoses are inflammatory myeloid neoplasms often driven by somatic activating mutations in mitogen-activated protein kinase (MAPK) cascade genes. H syndrome is an inflammatory genetic disorder caused by germ line loss-of-function mutations in SLC29A3, encoding the lysosomal equilibrative nucleoside transporter 3 (ENT3). Patients with H syndrome are predisposed to develop histiocytosis, yet the mechanism is unclear. Here, through phenotypic, molecular, and functional analysis of primary cells from a cohort of patients with H syndrome, we reveal the molecular pathway leading to histiocytosis and inflammation in this genetic disorder. We show that loss of function of ENT3 activates nucleoside-sensing toll-like receptors (TLR) and downstream MAPK signaling, inducing cytokine secretion and inflammation. Importantly, MEK inhibitor therapy led to resolution of histiocytosis and inflammation in a patient with H syndrome. These results demonstrate a yet-unrecognized link between a defect in a lysosomal transporter and pathological activation of MAPK signaling, establishing a novel pathway leading to histiocytosis and inflammation.

Transcriptome screening identifies TIPARP as an antiviral host factor against the Getah virus

IMPORTANCE

Alphaviruses threaten public health continuously, and Getah virus (GETV) is a re-emerging alphavirus that can potentially infect humans. Approved antiviral drugs and vaccines against alphaviruses are few available, but several host antiviral factors have been reported. Here, we used GETV as a model of alphaviruses to screen for additional host factors. Tetrachlorodibenzo-p-dioxin-inducible poly(ADP ribose) polymerase was identified to inhibit GETV replication by inducing ubiquitination of the glycoprotein E2, causing its degradation by recruiting the E3 ubiquitin ligase membrane-associated RING-CH8 (MARCH8). Using GETV as a model virus, focusing on the relationship between viral structural proteins and host factors to screen antiviral host factors provides new insights for antiviral studies on alphaviruses.

H syndrome treated with Tocilizumab: two case reports and literature review

H syndrome is a rare autosomal recessive genetic disorder characterized by the following clinical features: cutaneous hyperpigmentation, hypertrichosis, hepatosplenomegaly, heart anomalies, hearing loss, hypogonadism, short stature, hallux valgus, hyperglycemia, fixed flexion contractures of the toe joints, and the proximal interphalangeal joints. In rare cases, autoinflammatory and lymphoproliferative manifestations have also been reported. This disorder is due to loss-of-function mutations in SLC29A3 gene, which encode the equilibrative nucleoside transporter ENT3. This deficiency leads to abnormal function and proliferation of histiocytes. H syndrome is part of the R-group of histiocytosis. We report two different cases, one was diagnosed in adulthood and the other in childhood. The first case reported is a 37-year-old woman suffering from H syndrome with an autoinflammatory systemic disease that begins in adulthood (fever and diffuse organ's infiltration) and with cutaneous, articular, auditory, and endocrinological manifestations since childhood. The second case reported is a 2-year-old girl with autoinflammatory, endocrine, and cutaneous symptoms (fever, lymphadenopathy, organomegaly, growth delay, and cutaneous hyperpigmentation). Homozygous mutations in SLC29A3 confirmed the diagnosis of H syndrome in both cases. Each patient was treated with Tocilizumab with a significant improvement for lymphoproliferative, autoinflammatory, and cutaneous manifestations. Both cases were reported to show the multiple characteristics of this rare syndrome, which can be diagnosed either in childhood or in adulthood. In addition, an overview of the literature suggested Tocilizumab efficiency.

Neuronal activity-induced, equilibrative nucleoside transporter-dependent, somatodendritic adenosine release revealed by a GRAB sensor

The purinergic signaling molecule adenosine (Ado) modulates many physiological and pathological functions in the brain. However, the exact source of extracellular Ado remains controversial. Here, utilizing a newly optimized genetically encoded GPCR-Activation-Based Ado fluorescent sensor (GRABAdo), we discovered that the neuronal activity-induced extracellular Ado elevation is due to direct Ado release from somatodendritic compartments of neurons, rather than from the axonal terminals, in the hippocampus. Pharmacological and genetic manipulations reveal that the Ado release depends on equilibrative nucleoside transporters but not the conventional vesicular release mechanisms. Compared with the fast-vesicular glutamate release, the Ado release is slow (~40 s) and requires calcium influx through L-type calcium channels. Thus, this study reveals an activity-dependent second-to-minute local Ado release from the somatodendritic compartments of neurons, potentially serving modulatory functions as a retrograde signal.

IFN-stimulated metabolite transporter ENT3 facilitates viral genome release

An increasing amount of evidence emphasizes the role of metabolic reprogramming in immune cells to fight infections. However, little is known about the regulation of metabolite transporters that facilitate and support metabolic demands. In this study, we found that the expression of equilibrative nucleoside transporter 3 (ENT3, encoded by solute carrier family 29 member 3, Slc29a3) is part of the innate immune response, which is rapidly upregulated upon pathogen invasion. The transcription of Slc29a3 is directly regulated by type I interferon-induced signaling, demonstrating that this metabolite transporter is an interferon-stimulated gene (ISG). Suprisingly, we unveil that several viruses, including SARS-CoV-2, require ENT3 to facilitate their entry into the cytoplasm. The removal or suppression of Slc29a3 expression is sufficient to significantly decrease viral replication in vitro and in vivo. Our study reveals that ENT3 is a pro-viral ISG co-opted by some viruses to gain a survival advantage.

Osteopetrosis: Gene-based nosology and significance Dysosteosclerosis

Dysosteosclerosis (DSS) refers to skeletal dysplasias that radiographically feature focal appendicular osteosclerosis with variable platyspondyly. Genetic heterogeneity is increasingly reported for the DSS phenotype and now involves mutations of SLC29A3, TNFRSF11A, TCIRG1, LRRK1, and CSF1R. Typical radiological findings are widened radiolucent long bones with thin cortices yet dense irregular metaphyses, flattened vertebral bodies, dense ribs, and multiple fractures. However, the radiographic features of DSS evolve, and the metaphyseal and/or appendicular osteosclerosis variably fades with increasing patient age, likely due to some residual osteoclast function. Fractures are the principal presentation of DSS, and may even occur in infancy with SLC29A3-associated DSS. Cranial base sclerosis can lead to cranial nerve palsies such as optic atrophy, and may be the initial presentation, though not observed with SLC29A3-associated DSS. Gene-specific extra-skeletal features can be the main complication in some forms of DSS such as CSF1R- associated DSS. Further genetic heterogeneity is likely, especially for X-linked recessive DSS and cases currently with an unknown genetic defect. Distinguishing DSS can be challenging due to variable clinical and radiological features and an evolving phenotype. However, defining the DSS phenotype is important for predicting complications, prognosis, and instituting appropriate health surveillance and treatment.

Genome-wide association study of leprosy in Malawi and Mali

Leprosy is a chronic infection of the skin and peripheral nerves caused by Mycobacterium leprae. Despite recent improvements in disease control, leprosy remains an important cause of infectious disability globally. Large-scale genetic association studies in Chinese, Vietnamese and Indian populations have identified over 30 susceptibility loci for leprosy. There is a significant burden of leprosy in Africa, however it is uncertain whether the findings of published genetic association studies are generalizable to African populations. To address this, we conducted a genome-wide association study (GWAS) of leprosy in Malawian (327 cases, 436 controls) and Malian (247 cases, 368 controls) individuals. In that analysis, we replicated four risk loci previously reported in China, Vietnam and India; MHC Class I and II, LACC1 and SLC29A3. We further identified a novel leprosy susceptibility locus at 10q24 (rs2015583; combined p = 8.81 × 10-9; OR = 0.51 [95% CI 0.40 - 0.64]). Using publicly-available data we characterise regulatory activity at this locus, identifying ACTR1A as a candidate mediator of leprosy risk. This locus shows evidence of recent positive selection and demonstrates pleiotropy with established risk loci for inflammatory bowel disease and childhood-onset asthma. A shared genetic architecture for leprosy and inflammatory bowel disease has been previously described. We expand on this, strengthening the hypothesis that selection pressure driven by leprosy has shaped the evolution of autoimmune and atopic disease in modern populations. More broadly, our data highlights the importance of defining the genetic architecture of disease across genetically diverse populations, and that disease insights derived from GWAS in one population may not translate to all affected populations.

Atypical comorbidities in a child considered to have type 1 diabetes led to the diagnosis of SLC29A3 spectrum disorder

INTRODUCTION

SLC29A3 spectrum disorder is an autosomal, recessively inherited, autoinflammatory, multisystem disorder characterized by distinctive cutaneous features, including hyperpigmentation or hypertrichosis, hepatosplenomegaly, hearing loss, cardiac anomalies, hypogonadism, short stature, and insulin-dependent diabetes.

CASE PRESENTATION

Herein, we report a 6-year-old boy who presented with features resembling type 1 diabetes mellitus, but his clinical course was complicated by IgA nephropathy, pure red cell aplasia, and recurrent febrile episodes. The patient was tested for the presence of pathogenic variants in 53 genes related to monogenic diabetes and found to be compound heterozygous for two SLC29A3 pathogenic variants (p. Arg386Gln and p. Leu298fs).

CONCLUSION

This case demonstrated that SLC29A3 spectrum disorder should be included in the differential diagnosis of diabetes with atypical comorbidities, even when the distinctive dermatological hallmarks of SLC29A3 spectrum disorder are entirely absent.

Concentrative Nucleoside Transporter, CNT, Results in Selective Toxicity of Toyocamycin against Candida albicans

Toyocamycin (TM) is an adenosine-analog antibiotic isolated from Streptomyces toyocaensis. It inhibits Candida albicans, several plant fungal pathogens, and human cells, but many fungi, including Saccharomyces cerevisiae, are much less susceptible to TM. Aiming to clarify why TM and its analogs tubercidin and 5-iodotubercidin are active against C. albicans but not S. cerevisiae, this study focused on the absence of purine nucleoside transport activity from S. cerevisiae. When the concentrative nucleoside transporter (CNT) of C. albicans was expressed in S. cerevisiae, the recombinant strain became sensitive to TM and its analogs. The expression of C. albicans purine nucleoside permease in S. cerevisiae did not result in sensitivity to TM. Clustered regularly interspaced short palindromic repeat-mediated disruption of CNT was performed in C. albicans. The CNTΔ strain of C. albicans became insensitive to TM and its analogs. These data suggest that the toxicity of TM and its analogs toward C. albicans results from their transport via CNT. Interestingly, S. cerevisiae also became sensitive to TM and its analogs if human CNT3 was introduced into cells. These findings enhance our understanding of the mechanisms of action of adenosine analogs toward Candida pathogens and human cells. IMPORTANCE We investigated the mechanism of toxicity of TM and its analogs to C. albicans. Inspired by the effect of the copresence of TM and purine nucleosides on cell growth of C. albicans, we investigated the involvement of CNT in the toxicity mechanism by expressing CNT of C. albicans (CaCNT) in S. cerevisiae and deleting CaCNT in C. albicans. Our examinations clearly demonstrated that CaCNT is responsible for the toxicity of TM to C. albicans. S. cerevisiae expressing the human ortholog of CaCNT also became sensitive to TM and its analogs, and the order of effects of the TM analogs was a little different between CaCNT- and hCNT3-expressing S. cerevisiae. These findings are beneficial for an understanding of the mechanisms of action of adenosine analogs toward Candida pathogens and human cells and also the development of new antifungal drugs.

Inborn Errors of Nucleoside Transporter (NT)-Encoding Genes (SLC28 and SLC29)

The proper regulation of nucleotide pools is essential for all types of cellular functions and depends on de novo nucleotide biosynthesis, salvage, and degradation pathways. Despite the apparent essentiality of these processes, a significant number of rare diseases associated with mutations in genes encoding various enzymes of these pathways have been already identified, and others are likely yet to come. However, knowledge on genetic alterations impacting on nucleoside and nucleobase transporters is still limited. At this moment three gene-encoding nucleoside and nucleobase transporter proteins have been reported to be mutated in humans, SLC29A1, SLC29A3, and SLC28A1, impacting on the expression and function of ENT1, ENT3, and CNT1, respectively. ENT1 alterations determine Augustine-null blood type and cause ectopic calcification during aging. ENT3 deficiency translates into various clinical manifestations and syndromes, altogether listed in the OMIM catalog as histiocytosis-lymphoadenopathy plus syndrome (OMIM#602782). CNT1 deficiency causes uridine-cytidineuria (URCTU) (OMIM#618477), a unique type of pyrimidineuria with an as yet not well-known clinical impact. Increasing knowledge on the physiological, molecular and structural features of these transporter proteins is helping us to better understand the biological basis behind the biochemical and clinical manifestations caused by these deficiencies. Moreover, they also support the view that some metabolic compensation might occur in these disturbances, because they do not seem to significantly impact nucleotide homeostasis, but rather other biological events associated with particular subtypes of transporter proteins.

A Toxoplasma gondii Oxopurine Transporter Binds Nucleobases and Nucleosides Using Different Binding Modes

Toxoplasma gondii is unable to synthesize purines de novo, instead salvages them from its environment, inside the host cell, for which they need high affinity carriers. Here, we report the expression of a T. gondii Equilibrative Nucleoside Transporter, Tg244440, in a Trypanosoma brucei strain from which nucleobase transporters have been deleted. Tg244440 transported hypoxanthine and guanine with similar affinity (K_m ~1 µM), while inosine and guanosine displayed K_i values of 4.05 and 3.30 µM, respectively. Low affinity was observed for adenosine, adenine, and pyrimidines, classifying Tg244440 as a high affinity oxopurine transporter. Purine analogues were used to probe the substrate-transporter binding interactions, culminating in quantitative models showing different binding modes for oxopurine bases, oxopurine nucleosides, and adenosine. Hypoxanthine and guanine interacted through protonated N1 and N9, and through unprotonated N3 and N7 of the purine ring, whereas inosine and guanosine mostly employed the ribose hydroxy groups for binding, in addition to N1H of the nucleobase. Conversely, the ribose moiety of adenosine barely made any contribution to binding. Tg244440 is the first gene identified to encode a high affinity oxopurine transporter in T. gondii and, to the best of our knowledge, the first purine transporter to employ different binding modes for nucleosides and nucleobases.

Comprehensive characterization of purine and pyrimidine transport activities in Trichomonas vaginalis and functional cloning of a trichomonad nucleoside transporter

Trichomoniasis is a common and widespread sexually-transmitted infection, caused by the protozoan parasite Trichomonas vaginalis. T. vaginalis lacks the biosynthetic pathways for purines and pyrimidines, making nucleoside metabolism a drug target. Here we report the first comprehensive investigation into purine and pyrimidine uptake by T. vaginalis. Multiple carriers were identified and characterized with regard to substrate selectivity and affinity. For nucleobases, a high-affinity adenine transporter, a possible guanine transporter and a low affinity uracil transporter were found. Nucleoside transporters included two high affinity adenosine/guanosine/uridine/cytidine transporters distinguished by different affinities to inosine, a lower affinity adenosine transporter, and a thymidine transporter. Nine Equilibrative Nucleoside Transporter (ENT) genes were identified in the T. vaginalis genome. All were expressed equally in metronidazole-resistant and -sensitive strains. Only TvagENT2 was significantly upregulated in the presence of extracellular purines; expression was not affected by co-culture with human cervical epithelial cells. All TvagENTs were cloned and separately expressed in Trypanosoma brucei. We identified the main broad specificity nucleoside carrier, with high affinity for uridine and cytidine as well as purine nucleosides including inosine, as TvagENT3. The in-depth characterization of purine and pyrimidine transporters provides a critical foundation for the development of new anti-trichomonal nucleoside analogues.

PARP7 negatively regulates the type I interferon response in cancer cells and its inhibition triggers antitumor immunity

PARP7 is a monoPARP that catalyzes the transfer of single units of ADP-ribose onto substrates to change their function. Here, we identify PARP7 as a negative regulator of nucleic acid sensing in tumor cells. Inhibition of PARP7 restores type I interferon (IFN) signaling responses to nucleic acids in tumor models. Restored signaling can directly inhibit cell proliferation and activate the immune system, both of which contribute to tumor regression. Oral dosing of the PARP7 small-molecule inhibitor, RBN-2397, results in complete tumor regression in a lung cancer xenograft and induces tumor-specific adaptive immune memory in an immunocompetent mouse cancer model, dependent on inducing type I IFN signaling in tumor cells. PARP7 is a therapeutic target whose inhibition induces both cancer cell-autonomous and immune stimulatory effects via enhanced IFN signaling. These data support the targeting of a monoPARP in cancer and introduce a potent and selective PARP7 inhibitor to enter clinical development.

Rosai-Dorfman Disease and Exocrine Pancreatic Insufficiency in a Patient With a Germline SLC29A3 Mutation

Rosai-Dorfman disease (RDD) typically presents as bulky lymphadenopathy. Somatic mutations in RAS/MAP kinase pathway genes are common but germline mutations are rare. A patient with RDD and exocrine pancreatic insufficiency was found to have a homozygous germline mutation in SLC29A3, which has been associated with the Histiocytosis/Lymphadenopathy Plus Syndrome. His RDD also was positive for a somatic mutation in lymphoid enhancer binding factor 1 (LEF1). The concurrence of RDD and pancreatic insufficiency should raise consideration of SLC29A3 mutations. Other cases will be needed to confirm this observation and a possible contribution of LEF1 to the development of RDD.

Patient with H syndrome, cardiogenic shock, multiorgan infiltration, and digital ischemia

BACKGROUND

H syndrome (HS) is a rare autoinflammatory disease caused by a mutation in the solute carrier family 29, member 3 (SCL29A3) gene. It has a variable clinical presentation and little phenotype-genotype correlation. The pathognomonic sign of HS is cutaneous hyperpigmentation located mainly in the inner thighs and often accompanied by other systemic manifestations. Improvement after tocilizumab treatment has been reported in a few patients with HS. We report the first patient with HS who presented cardiogenic shock, multiorgan infiltration, and digital ischemia.

CASE PRESENTATION

8-year-old boy born to consanguineous parents of Moroccan origin who was admitted to the intensive care unit during the Coronavirus Disease-2019 (COVID-19) pandemic with tachypnoea, tachycardia, and oliguria. Echocardiography showed dilated cardiomyopathy and severe systolic dysfunction compatible with cardiogenic shock. Additionally, he presented with multiple organ dysfunction syndrome. SARS-CoV-2 polymerase chain reaction (PCR) and antibody detection by chromatographic immunoassay were negative. A previously ordered gene panel for pre-existing sensorineural hearing loss showed a pathological mutation in the SCL29A3 gene compatible with H syndrome. Computed tomography scan revealed extensive alveolar infiltrates in the lungs and multiple poor defined hypodense lesions in liver, spleen, and kidneys; adenopathy; and cardiomegaly with left ventricle subendocardial nodules. Invasive mechanical ventilation, broad antibiotic and antifungal coverage showed no significant response. Therefore, Tocilizumab as compassionate use together with pulsed intravenous methylprednisolone was initiated. Improvement was impressive leading to normalization of inflammation markers, liver and kidney function, and stabilising heart function. Two weeks later, he was discharged and has been clinically well since then on two weekly administration of Tocilizumab.

CONCLUSIONS

We report the most severe disease course produced by HS described so far in the literature. Our patient's manifestations included uncommon, new complications such as acute heart failure with severe systolic dysfunction, multi-organ cell infiltrate, and digital ischemia. Most of the clinical symptoms of our patient could have been explained by SARS-CoV-2, demonstrating the importance of a detailed differential diagnosis to ensure optimal treatment. Although the mechanism of autoinflammation of HS remains uncertain, the good response of our patient to Tocilizumab makes a case for the important role of IL-6 in this syndrome and for considering Tocilizumab as a first-line treatment, at least in severely affected patients.

Overexpression of uracil permease and nucleoside transporter from Bacillus amyloliquefaciens improves cytidine production in Escherichia coli

Cytidine is an important raw material for nucleic acid health food and genetic engineering research. In recent years, it has shown irreplaceable effects in anti-virus, anti-tumor, and AIDS drugs. Its biosynthetic pathway is complex and highly regulated. In this study, overexpression of uracil permease and a nucleoside transporter from Bacillus amyloliquefaciens related to cell membrane transport in Escherichia coli strain BG-08 was found to increase cytidine production in shake flask cultivation by 1.3-fold (0.91 ± 0.03 g/L) and 1.8-fold (1.26 ± 0.03 g/L) relative to that of the original strain (0.70 ± 0.03 g/L), respectively. Co-overexpression of uracil permease and a nucleoside transporter further increased cytidine yield by 2.7-fold (1.59 ± 0.05 g/L) compared with that of the original strain. These results indicate that the overexpressed uracil permease and nucleoside transporter can promote the accumulation of cytidine, and the two proteins play a synergistic role in the secretion of cytidine in Escherichia coli.

Glomerular involvement in children with H syndrome

BACKGROUND

H syndrome is a multisystem inflammatory disease caused by mutations in the SLC29A3 gene (OMIM #602782). The protein product, hENT3, is a nucleoside transporter essential for DNA salvage synthesis. Clinical manifestations are hyperpigmentation, hypertrichosis, hepatosplenomegaly, hearing loss, heart anomalies, hypogonadism, short stature, skeletal deformities, and diabetes mellitus. Laboratory findings are consistent with inflammatory processes. Structural kidney anomalies have been described in 6% of patients.

CASE REPORTS

Three family members with genetically diagnosed H syndrome (c.1279G>A, p.Gly427Ser). Two of them presented with hypoalbuminemia and nephrotic range proteinuria. Kidney ultrasound was normal. Kidney biopsy performed in one patient presenting with generalized peripheral pitting edema revealed membranous nephropathy. Different treatments including ACE inhibitors, corticosteroids, and immunomodulatory agents failed to improve the clinical outcome.

CONCLUSIONS

Generalized peripheral pitting edema and glomerulopathy broaden the clinical spectrum of H syndrome. Periodic bloodwork and urinalysis are recommended.

Post-Transcriptional Regulation of PARP7 Protein Stability Is Controlled by Androgen Signaling

Poly-ADP-ribose polymerases (PARPs) are enzymes that catalyze ADP-ribosylation and play critical roles in normal and disease settings. The PARP family member, PARP7, is a mono-ADP-ribosyltransferase that has been suggested to play a tumor suppressive role in breast, ovarian, and colorectal cancer. Here, we have investigated how androgen signaling regulates PARP7 homeostasis in prostate cancer cells, where PARP7 is a direct target gene of AR. We found that the PARP7 protein is extremely short-lived, with a half-life of 4.5 min. We show that in addition to its transcriptional regulation by AR, PARP7 is subject to androgen-dependent post-transcriptional regulation that increases its half-life to 25.6 min. This contrasts with PARP1, PARP2, PARP9, and PARP14, which do not display rapid turnover and are not regulated by androgen signaling. Androgen- and AR-dependent stabilization of PARP7 leads to accumulation in the nucleus, which we suggest is a major site of action. Mutations in the catalytic domain, the Cys3His1 zinc finger, and WWE (tryptophan-tryptophan-glutamate) domains in PARP7 each reduce the degradation rate of PARP7, suggesting the overall structure of the protein is tuned for its rapid turnover. Our finding that PARP7 is regulated by AR signaling both transcriptionally and post-transcriptionally in prostate cancer cells suggests the dosage of PARP7 protein is subject to tight regulation.

Autoinflammation in addition to combined immunodeficiency: SLC29A3 gene defect

INTRODUCTION

H Syndrome is an autosomal recessive (AR) disease caused by defects in SLCA29A3 gene. This gene encodes the equilibrative nucleoside transporter, the protein which is highly expressed in spleen, lymph node and bone marrow. Autoinflammation and autoimmunity accompanies H Syndrome (HS).

AIM

The aim was to further elucidate the mechanisms of disease by molecular studies in a patient with SLC29A3 gene defect.

PATIENT AND METHODS

Mitochondrial dysfunction, lysosomal integrity, cytokine response in response to stimulation with different pattern recognition receptor ligands, and circulating cell-free mitochondrial-DNA(ccf-mtDNA) level in plasma were analyzed compared to controls to understand the cellular triggers of autoinflammation. RNA sequencing (RS) analyses were also performed in monocytes before/after culture with lipopolysaccharide.

RESULTS

Patient had progressive destructive arthropathy in addition to clinical findings due to combined immunodeficiency. Pure red cell aplasia (PRCA), vitiligo, diabetes, multiple autoantibody positivity, lymphopenia, increased acute phase reactants were present. Recent thymic emigrants (RTE), naïve T cells were decreased, effector memory CD4 + T cells, nonclassical inflammatory monocytes were increased. Patient's peripheral blood mononuclear cells secreted more IL-1β and IL-6, showed lysosomal disruption and significant mitochondrial dysfunction compared to healthy controls. Plasma ccf-mtDNA level was significantly elevated compared to age-matched controls (p < 0.05). RNA sequencing studies revealed decreased expression of NLR Family Caspase Recrument-Domain Containing 4(NLRC4), 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4(PFKFB4), serine dehydratase(SDS), heparan sulfate(Glucosamine) 3-O-sulfotransferase 1(HS3ST1), neutral cholesterol ester hydrolase 1 (NCEH1), and interleukin-8 (IL-8) in patient's monocytes compared to controls. Longstanding PRCA, which is possibly autoimmune, resolved after initiating monthly intravenous immunoglobulins (IVIG) and low dose steroids to the patient.

CONCLUSION

Although autoinflammation and autoimmunity are reported in HS, by functional analyses we here show in the present patient that over-active inflammasome pathway in HS might be related with mitochondrial and lysosomal dysfunction. Increased plasma ccf-mtDNA may be used as a biomarker of inflammasomopathy in HS. HS should be included in the classification of primary immunodeficiency diseases.

Type 1 diabetes genetic risk score discriminates between monogenic and Type 1 diabetes in children diagnosed at the age of <5 years in the Iranian population

AIM

To examine the extent to which discriminatory testing using antibodies and Type 1 diabetes genetic risk score, validated in European populations, is applicable in a non-European population.

METHODS

We recruited 127 unrelated children with diabetes diagnosed between 9 months and 5 years from two centres in Iran. All children underwent targeted next-generation sequencing of 35 monogenic diabetes genes. We measured three islet autoantibodies (islet antigen 2, glutamic acid decarboxylase and zinc transporter 8) and generated a Type 1 diabetes genetic risk score in all children.

RESULTS

We identified six children with monogenic diabetes, including four novel mutations: homozygous mutations in WFS1 (n=3), SLC19A2 and SLC29A3, and a heterozygous mutation in GCK. All clinical features were similar in children with monogenic diabetes (n=6) and in the rest of the cohort (n=121). The Type 1 diabetes genetic risk score discriminated children with monogenic from Type 1 diabetes [area under the receiver-operating characteristic curve 0.90 (95% CI 0.83-0.97)]. All children with monogenic diabetes were autoantibody-negative. In children with no mutation, 59 were positive to glutamic acid decarboxylase, 39 to islet antigen 2 and 31 to zinc transporter 8. Measuring zinc transporter 8 increased the number of autoantibody-positive individuals by eight.

CONCLUSIONS

The present study provides the first evidence that Type 1 diabetes genetic risk score can be used to distinguish monogenic from Type 1 diabetes in an Iranian population with a large number of consanguineous unions. This test can be used to identify children with a higher probability of having monogenic diabetes who could then undergo genetic testing. Identification of these individuals would reduce the cost of treatment and improve the management of their clinical course.

Functional disruption of pyrimidine nucleoside transporter CNT1 results in a novel inborn error of metabolism with high excretion of uridine and cytidine

Genetic defects in the pyrimidine nucleoside transporters of the CNT transporter family have not yet been reported. Metabolic investigations in a patient with infantile afebrile tonic-clonic seizures revealed increased urinary uridine and cytidine excretion. Segregation of this metabolic trait in the family showed the same biochemical phenotype in a healthy older brother of the index. Whole exome sequencing revealed biallelic mutations in SLC28A1 encoding the pyrimidine nucleoside transporter CNT1 in the index and his brother. Both parents and unaffected sibs showed the variant in heterozygous state. The transporter is expressed in the kidneys. Compelling evidence is available for the disrupting effect of the mutation on the transport function thus explaining the increased excretion of the pyrimidine nucleosides. The exome analysis also revealed a pathogenic mutation in PRRT2 in the index, explaining the epilepsy phenotype in infancy. At present, both the index (10 years) and his older brother are asymptomatic. Mutations in SLC28A1 cause a novel inborn error of metabolism that can be explained by the disrupted activity of the pyrimidine nucleoside transporter CNT1. This is the first report describing a defect in the family of CNT concentrative pyrimidine nucleoside transporter proteins encoded by the SLC28 gene family. In all likelihood, the epilepsy phenotype in the index is unrelated to the SLC28A1 defect, as this can be fully explained by the pathogenic PRRT2 variant. Clinical data on more patients are required to prove whether pathogenic mutations in SLC28A1 have any clinical consequences or are to be considered a benign metabolic phenotype.

Sclerosing bone dysplasias with hallmarks of dysosteosclerosis in four patients carrying mutations in SLC29A3 and TCIRG1

The osteopetroses and related sclerosing bone dysplasias can have a broad range of manifestations. Especially in the milder forms, sandwich vertebrae are an easily recognizable and reliable radiological hallmark. We report on four patients from three families presenting with sandwich vertebrae and platyspondyly. The long bone phenotypes were discordant with one patient showing modeling defects and patchy osteosclerosis, while the second displayed only metaphyseal sclerotic bands, and the third and fourth had extreme metaphyseal flaring with uniform osteosclerosis. Two of the four patients had experienced pathological fractures, two had developmental delay, but none showed cranial nerve damage, hepatosplenomegaly, or bone marrow failure. According to these clinical features the diagnoses ranged between intermediate autosomal recessive osteopetrosis and dysosteosclerosis. After exclusion of mutations in CLCN7 we performed gene panel and exome sequencing. Two novel mutations in SLC29A3 were found in the first two patients. In the third family a TCIRG1 C-terminal frameshift mutation in combination with a mutation at position +4 in intron 2 were detected. Our study adds two cases to the small group of individuals with SLC29A3 mutations diagnosed with dysosteosclerosis, and expands the phenotypic variability. The finding that intermediate autosomal recessive osteopetrosis due to TCIRG1 splice site mutations can also present with platyspondyly further increases the molecular heterogeneity of dysosteosclerosis-like sclerosing bone dysplasias.

Characterization of drug resistance-associated TevAT1 gene of Trypanosoma evansi from Philippine water buffaloes (Bubalus bubalis)

This study detected and characterized the TevAT1 gene of Trypanosoma evansi isolates from Philippine water buffaloes (Bubalus bubalis). A total of 68 blood samples from Philippine water buffaloes were subjected to DNA extraction and PCR assay was performed using RoTat 1.2 gene to detect T. evansi. Those samples positive for T. evansi subsequently underwent another PCR assay to detect the presence of TevAT1 gene. Trypanosoma evansi was detected in 26.47% (18/68) blood samples in which distributed throughout the main islands of the country (4 from Luzon, 2 from Visayas and 12 from Mindanao). However, only 10 of these samples were positive for TevAT1 gene. Sequence alignment of the TevAT1 gene from local isolates showed no single nucleotide polymorphisms when compared to other strains in various countries. Those T. evansi without the gene of interest could be possibly resistant to some trypanocidal drugs but this needs to be further investigated in-vitro or in-vivo.

Three UDP-xylose transporters participate in xylan biosynthesis by conveying cytosolic UDP-xylose into the Golgi lumen in Arabidopsis

UDP-xylose (UDP-Xyl) is synthesized by UDP-glucuronic acid decarboxylases, also termed UDP-Xyl synthases (UXSs). The Arabidopsis genome encodes six UXSs, which fall into two groups based upon their subcellular location: the Golgi lumen and the cytosol. The latter group appears to play an important role in xylan biosynthesis. Cytosolic UDP-Xyl is transported into the Golgi lumen by three UDP-Xyl transporters (UXT1, 2, and 3). However, while single mutants affected in the UDP-Xyl transporter 1 (UXT1) showed a substantial reduction in cell wall xylose content, a double mutant affected in UXT2 and UXT3 had no obvious effect on cell wall xylose deposition. This prompted us to further investigate redundancy among the members of the UXT family. Multiple uxt mutants were generated, including a triple mutant, which exhibited collapsed vessels and reduced cell wall thickness in interfascicular fiber cells. Monosaccharide composition, molecular weight, nuclear magnetic resonance, and immunolabeling studies demonstrated that both xylan biosynthesis (content) and fine structure were significantly affected in the uxt triple mutant, leading to phenotypes resembling those of the irx mutants. Pollination was also impaired in the uxt triple mutant, likely due to reduced filament growth and anther dehiscence caused by alterations in the composition of the cell walls. Moreover, analysis of the nucleotide sugar composition of the uxt mutants indicated that nucleotide sugar interconversion is influenced by the cytosolic UDP-Xyl pool within the cell. Taken together, our results underpin the physiological roles of the UXT family in xylan biosynthesis and provide novel insights into the nucleotide sugar metabolism and trafficking in plants.

Flow Cytometric Analysis of Nucleoside Transporters Activity in Chemoresistant Prostate Cancer Model

BACKGROUND

Nucleoside analogues represent a relevant class of antimetabolites used for therapy of various types of cancer. However, their effectivity is limited by drug resistance. The nucleoside transport capability of tumour cells is considered to be a determinant of the clinical outcome of treatment regimens using antimetabolites. Due to hydrophilic properties of antimetabolites, their transport across the plasma membrane is mediated by two families of transmembrane proteins, the SLC28 family of cation-linked concentrative nucleoside transporters (hCNTs) and SLC29 family of energy-independent equilibrative nucleoside transporters (hENTs). Loss of functional nucleoside transporters has been associated with reduced efficacy of antimetabolites and their derivatives and treatment failure in diverse malignancies including solid tumours, such as pancreatic adenocarcinoma.

MATERIAL AND METHODS

The effectivity and kinetics of antimetabolite uptake were analysed using control and docetaxel-resistant PC3 cells. For this purpose, fluorescent nucleoside analogue probe uridine-furane and inhibitor of nucleoside transporters, S-(4-nitrobenzyl) -6-thioinosine were exploited. Combination of flow cytometry, confocal microscopy and real-time quantitative polymerase chain reaction methodology were used for the analysis.

RESULTS

Here we utilized flow cytometric assay for analysis of nucleoside transporters activity employing fluorescent nucleoside analogue, uridine-furane. We have determined the long-time kinetics of uridine-furane incorporation and quantified its levels in the parental prostate cancer cell line PC3 and its chemoresistant derivative. Finally, we have shown an association between the activity and mRNA expression of nucleoside transporters and sensitivity to various nucleoside analogues.

CONCLUSION

Fluorescent techniques can serve as an effective tool for the detection of nucleoside transporter activity which has the potential for application in clinical oncology.Key words: nucleoside transporter proteins - drug resistance - prostatic neoplasm - chemotherapy.

A semi-synthetic organism that stores and retrieves increased genetic information

Since at least the last common ancestor of all life on Earth, genetic information has been stored in a four-letter alphabet that is propagated and retrieved by the formation of two base pairs. The central goal of synthetic biology is to create new life forms and functions, and the most general route to this goal is the creation of semi-synthetic organisms whose DNA harbours two additional letters that form a third, unnatural base pair. Previous efforts to generate such semi-synthetic organisms culminated in the creation of a strain of Escherichia coli that, by virtue of a nucleoside triphosphate transporter from Phaeodactylum tricornutum, imports the requisite unnatural triphosphates from its medium and then uses them to replicate a plasmid containing the unnatural base pair dNaM-dTPT3. Although the semi-synthetic organism stores increased information when compared to natural organisms, retrieval of the information requires in vivo transcription of the unnatural base pair into mRNA and tRNA, aminoacylation of the tRNA with a non-canonical amino acid, and efficient participation of the unnatural base pair in decoding at the ribosome. Here we report the in vivo transcription of DNA containing dNaM and dTPT3 into mRNAs with two different unnatural codons and tRNAs with cognate unnatural anticodons, and their efficient decoding at the ribosome to direct the site-specific incorporation of natural or non-canonical amino acids into superfolder green fluorescent protein. The results demonstrate that interactions other than hydrogen bonding can contribute to every step of information storage and retrieval. The resulting semi-synthetic organism both encodes and retrieves increased information and should serve as a platform for the creation of new life forms and functions.

H syndrome: 5 new cases from the United States with novel features and responses to therapy

BACKGROUND

H Syndrome is an autosomal recessive disorder characterized by cutaneous hyperpigmentation, hypertrichosis, and induration with numerous systemic manifestations. The syndrome is caused by mutations in SLC29A3, a gene located on chromosome 10q23, which encodes the human equilibrative transporter 3 (hENT3). Less than 100 patients with H syndrome have been described in the literature, with the majority being of Arab descent, and only a few from North America.

CASE PRESENTATION

Here we report five pediatric patients from three medical centers in the United States who were identified to have H syndrome by whole exome sequencing. These five patients, all of whom presented to pediatric rheumatologists prior to diagnosis, include two of Northern European descent, bringing the total number of Caucasian patients described to three. The patients share many of the characteristics previously reported with H syndrome, including hyperpigmentation, hypertrichosis, short stature, insulin-dependent diabetes, arthritis and systemic inflammation, as well as some novel features, including selective IgG subclass deficiency and autoimmune hepatitis. They share genetic mutations previously described in patients of the same ethnic background, as well as a novel mutation. In two patients, treatment with prednisone improved inflammation, however both patients flared once prednisone was tapered. In one of these patients, treatment with tocilizumab alone resulted in marked improvement in systemic inflammation and growth. The other had partial response to prednisone, azathioprine, and TNF inhibition; thus, his anti-TNF biologic was recently switched to tocilizumab due to persistent polyarthritis. Another patient improved on Methotrexate, with further improvement after the addition of tocilizumab.

CONCLUSION

H syndrome is a rare autoinflammatory syndrome with pleiotropic manifestations that affect multiple organ systems and is often mistaken for other conditions. Rheumatologists should be aware of this syndrome and its association with arthritis. It should be considered in patients with short stature and systemic inflammation, particularly with cutaneous findings. Some patients respond to treatment with biologics alone or in combination with other immune suppressants; in particular, treatment of systemic inflammation with IL-6 blockade appears to be promising. Overall, better identification and understanding of the pathophysiology may help devise earlier diagnosis and better treatment strategies.

Review of Rosai-Dorfman Disease: New Insights into the Pathogenesis of This Rare Disorder

Rosai-Dorfman disease (RDD) is a rare histiocytosis typically with bilateral painless cervical lymphadenopathy. Laboratory data are nonspecific, and the presence of emperipolesis in large foamy S-100+ CD1a- histiocytes is the prominent histologic feature. The pathogenesis of RDD still remains elusive. According to published studies, we propose that RDD cells might represent intermediate recruiting monocytes with differentiation blockade. Both disturbance of homoeostasis and inherent genomic alterations could contribute to initiation of the disorder through signal transduction. Several inflammatory molecules such as macrophage colony-stimulating factor, IL-1β, IL-6, and tumor necrosis factor-α also play a pivotal role in the development of this rare entity. Additional studies are needed to further elucidate the essence of the disease.

A Versatile Strategy for Production of Membrane Proteins with Diverse Topologies: Application to Investigation of Bacterial Homologues of Human Divalent Metal Ion and Nucleoside Transporters

Membrane proteins play key roles in many biological processes, from acquisition of nutrients to neurotransmission, and are targets for more than 50% of current therapeutic drugs. However, their investigation is hampered by difficulties in their production and purification on a scale suitable for structural studies. In particular, the nature and location of affinity tags introduced for the purification of recombinant membrane proteins can greatly influence their expression levels by affecting their membrane insertion. The extent of such effects typically depends on the transmembrane topologies of the proteins, which for proteins of unknown structure are usually uncertain. For example, attachment of oligohistidine tags to the periplasmic termini of membrane proteins often interferes with folding and drastically impairs expression in Escherichia coli. To circumvent this problem we have employed a novel strategy to enable the rapid production of constructs bearing a range of different affinity tags compatible with either cytoplasmic or periplasmic attachment. Tags include conventional oligohistidine tags compatible with cytoplasmic attachment and, for attachment to proteins with a periplasmic terminus, either tandem Strep-tag II sequences or oligohistidine tags fused to maltose binding protein and a signal sequence. Inclusion of cleavage sites for TEV or HRV-3C protease enables tag removal prior to crystallisation trials or a second step of purification. Together with the use of bioinformatic approaches to identify members of membrane protein families with topologies favourable to cytoplasmic tagging, this has enabled us to express and purify multiple bacterial membrane transporters. To illustrate this strategy, we describe here its use to purify bacterial homologues of human membrane proteins from the Nramp and ZIP families of divalent metal cation transporters and from the concentrative nucleoside transporter family. The proteins are expressed in E. coli in a correctly folded, functional state and can be purified in amounts suitable for structural investigations.

Dipyridamole analogs as pharmacological inhibitors of equilibrative nucleoside transporters. Identification of novel potent and selective inhibitors of the adenosine transporter function of human equilibrative nucleoside transporter 4 (hENT4)

To identify needed human equilibrative nucleoside transporter 4 (hENT4) inhibitors, we cloned and stably expressed the recombinant protein in PK15NTD (nucleoside transporter deficient) cells, and, investigated its interaction with a series of dipyridamole analogs synthesized in our laboratory. Compounds were tested in this newly established hENT4 expressing system as well in previous stably expressed hENT1 and hENT2 expressing systems. Of the dipyridamole analogs evaluated, about one fourth of the compounds inhibited hENT4 with higher potencies than dipyridamole. The most potent of them, Compound 30 displayed an IC₅₀ of 74.4 nM, making it about 38 times more potent than dipyridamole (IC₅₀=2.8 μM), and selectivities of about 80-fold and 20-fold relative to ENT1 and ENT2, respectively. Structure-activity relationship showed nitrogen-containing monocyclic rings and noncyclic substituents at the 4- and 8-positions of the pyrimido[5,4-d]pyrimidine were important for the inhibitory activity against hENT4. The most potent and selective hENT4 inhibitors tended to have a 2,6-di(N-monohydroxyethyl) substitution on the pyrimidopyrimidine ring system. The inhibitors of hENT4 identified in this study are the most selective and potent inhibitors of hENT4 adenosine transporter function to date, and should serve as useful pharmacological/biochemical tools and/or potential leads for ENT4-based therapeutics. Also, the new hENT4-expressing PK15 cell line established will serve as a useful screening tool for the discovery and design of hENT4 ligands.

Generalized pure cutaneous Rosai-Dorfman disease: a link between inflammation and cancer not associated with mitochondrial DNA and SLC29A3 gene mutation?

Recently, we described a case of generalized pure cutaneous Rosai-Dorfman disease in a 43-year-old Asian man in JAMA. The lesions distributed on nearly all of the skin of the whole body, except for mucous sites. Molecular, immunophenotypic, and sequencing analyses seem to define it as a histiocytic-mesenchymal transition and intermediate proliferative histiocytosis not associated with mtDNA large deletion and pathogenic mutation, as well as the SLC29A3 gene mutation.

Discovering thiamine transporters as targets of chloroquine using a novel functional genomics strategy

Chloroquine (CQ) and other quinoline-containing antimalarials are important drugs with many therapeutic benefits as well as adverse effects. However, the molecular targets underlying most such effects are largely unknown. By taking a novel functional genomics strategy, which employs a unique combination of genome-wide drug-gene synthetic lethality (DGSL), gene-gene synthetic lethality (GGSL), and dosage suppression (DS) screens in the model organism Saccharomyces cerevisiae and is thus termed SL/DS for simplicity, we found that CQ inhibits the thiamine transporters Thi7, Nrt1, and Thi72 in yeast. We first discovered a thi3Δ mutant as hypersensitive to CQ using a genome-wide DGSL analysis. Using genome-wide GGSL and DS screens, we then found that a thi7Δ mutation confers severe growth defect in the thi3Δ mutant and that THI7 overexpression suppresses CQ-hypersensitivity of this mutant. We subsequently showed that CQ inhibits the functions of Thi7 and its homologues Nrt1 and Thi72. In particular, the transporter activity of wild-type Thi7 but not a CQ-resistant mutant (Thi7^T287N) was completely inhibited by the drug. Similar effects were also observed with other quinoline-containing antimalarials. In addition, CQ completely inhibited a human thiamine transporter (SLC19A3) expressed in yeast and significantly inhibited thiamine uptake in cultured human cell lines. Therefore, inhibition of thiamine uptake is a conserved mechanism of action of CQ. This study also demonstrated SL/DS as a uniquely effective methodology for discovering drug targets.

By using a novel SL/DS methodology in the model organism yeast, we discovered that the antimalarial drug CQ inhibits thiamine transporters and consequently causes thiamine (vitamin B1) deficiency and growth defects. This mechanism of action (MOA) is conserved in human cells and possibly also in other organisms. Given that both thiamine deficiency and treatment with CQ cause retinal, neurological, and cardiovascular disorders in humans, our results suggest that thiamine deficiency might be a root cause of some of CQ's adverse effects, which might be preventable with concomitant dietary thiamine supplementation. Such a MOA by CQ could also be responsible for its therapeutic effects against malarial parasites, which need exogenous thiamine for survival. Such a possibility needs to be investigated before dietary thiamine supplementation can be used to prevent CQ's adverse effects.

A mild form of SLC29A3 disorder: a frameshift deletion leads to the paradoxical translation of an otherwise noncoding mRNA splice variant

We investigated two siblings with granulomatous histiocytosis prominent in the nasal area, mimicking rhinoscleroma and Rosai-Dorfman syndrome. Genome-wide linkage analysis and whole-exome sequencing identified a homozygous frameshift deletion in SLC29A3, which encodes human equilibrative nucleoside transporter-3 (hENT3). Germline mutations in SLC29A3 have been reported in rare patients with a wide range of overlapping clinical features and inherited disorders including H syndrome, pigmented hypertrichosis with insulin-dependent diabetes, and Faisalabad histiocytosis. With the exception of insulin-dependent diabetes and mild finger and toe contractures in one sibling, the two patients with nasal granulomatous histiocytosis studied here displayed none of the many SLC29A3-associated phenotypes. This mild clinical phenotype probably results from a remarkable genetic mechanism. The SLC29A3 frameshift deletion prevents the expression of the normally coding transcripts. It instead leads to the translation, expression, and function of an otherwise noncoding, out-of-frame mRNA splice variant lacking exon 3 that is eliminated by nonsense-mediated mRNA decay (NMD) in healthy individuals. The mutated isoform differs from the wild-type hENT3 by the modification of 20 residues in exon 2 and the removal of another 28 amino acids in exon 3, which include the second transmembrane domain. As a result, this new isoform displays some functional activity. This mechanism probably accounts for the narrow and mild clinical phenotype of the patients. This study highlights the 'rescue' role played by a normally noncoding mRNA splice variant of SLC29A3, uncovering a new mechanism by which frameshift mutations can be hypomorphic.

Uridine metabolism in HIV-1-infected patients: effect of infection, of antiretroviral therapy and of HIV-1/ART-associated lipodystrophy syndrome

Background

Uridine has been advocated for the treatment of HIV-1/HAART-associated lipodystrophy (HALS), although its metabolism in HIV-1-infected patients is poorly understood.

Methods

Plasma uridine concentrations were measured in 35 controls and 221 HIV-1-infected patients and fat uridine in 15 controls and 19 patients. The diagnosis of HALS was performed following the criteria of the Lipodystrophy Severity Grading Scale. Uridine was measured by a binary gradient-elution HPLC method. Analysis of genes encoding uridine metabolizing enzymes in fat was performed with TaqMan RT-PCR.

Results

Median plasma uridine concentrations for HIV-1-infected patients were 3.80 µmol/l (interquartile range: 1.60), and for controls 4.60 µmol/l (IQR: 1.8) (P = 0.0009). In fat, they were of 6.0 (3.67), and 2.8 (4.65) nmol/mg of protein, respectively (P = 0.0118). Patients with a mixed HALS form had a median plasma uridine level of 4.0 (IC95%: 3.40–4.80) whereas in those with isolated lipoatrophy it was 3.25 (2.55–4.15) µmol/l/l (P = 0.0066). The expression of uridine cytidine kinase and uridine phosphorylase genes was significantly decreased in all groups of patients with respect to controls. A higher expression of the mRNAs for concentrative nucleoside transporters was found in HIV-1-infected patients with respect to healthy controls.

Conclusions

HIV-1 infection is associated with a decrease in plasma uridine and a shift of uridine to the adipose tissue compartment. Antiretroviral therapy was not associated with plasma uridine concentrations, but pure lipoatrophic HALS was associated with significantly lower plasma uridine concentrations.

Mutations in SLC29A3, encoding an equilibrative nucleoside transporter ENT3, cause a familial histiocytosis syndrome (Faisalabad histiocytosis) and familial Rosai-Dorfman disease

The histiocytoses are a heterogeneous group of disorders characterised by an excessive number of histiocytes. In most cases the pathophysiology is unclear and treatment is nonspecific. Faisalabad histiocytosis (FHC) (MIM 602782) has been classed as an autosomal recessively inherited form of histiocytosis with similarities to Rosai-Dorfman disease (RDD) (also known as sinus histiocytosis with massive lymphadenopathy (SHML)). To elucidate the molecular basis of FHC, we performed autozygosity mapping studies in a large consanguineous family and identified a novel locus at chromosome 10q22.1. Mutation analysis of candidate genes within the target interval identified biallelic germline mutations in SLC29A3 in the FHC kindred and in two families reported to have familial RDD. Analysis of SLC29A3 expression during mouse embryogenesis revealed widespread expression by e14.5 with prominent expression in the central nervous system, eye, inner ear, and epithelial tissues including the gastrointestinal tract. SLC29A3 encodes an intracellular equilibrative nucleoside transporter (hENT3) with affinity for adenosine. Recently germline mutations in SLC29A3 were also described in two rare autosomal recessive disorders with overlapping phenotypes: (a) H syndrome (MIM 612391) that is characterised by cutaneous hyperpigmentation and hypertrichosis, hepatomegaly, heart anomalies, hearing loss, and hypogonadism; and (b) PHID (pigmented hypertrichosis with insulin-dependent diabetes mellitus) syndrome. Our findings suggest that a variety of clinical diagnoses (H and PHID syndromes, FHC, and familial RDD) can be included in a new diagnostic category of SLC29A3 spectrum disorder.

The histiocytoses are a group of systemic disorders usually confined to childhood and are caused by an excessive number of histiocytes which phagocytose other cells and process antigens. Although nearly a century has passed since histiocytic disorders were recognised, their pathophysiology remains largely unclear, and treatment is nonspecific. The identification of SLC29A3 mutations as the molecular basis for a familial form of syndromic histiocytosis (FHC/RDD) confirms a direct link between Faisalabad histiocytosis and Rosai-Dorfman disease and links these disorders to other SLC29A3-associated phenotypes.

Purification and properties of theEscherichia colinucleoside transporter NupG, a paradigm for a major facilitator transporter sub-family

NupG from Escherichia coli is the archetype of a family of nucleoside transporters found in several eubacterial groups and has distant homologues in eukaryotes, including man. To facilitate investigation of its molecular mechanism, we developed methods for expressing an oligohistidine-tagged form of NupG both at high levels (>20% of the inner membrane protein) in E. coli and in Xenopus laevis oocytes. In E. coli recombinant NupG transported purine (adenosine) and pyrimidine (uridine) nucleosides with apparent K(m) values of approximately 20-30 microM and transport was energized primarily by the membrane potential component of the proton motive force. Competition experiments in E. coli and measurements of uptake in oocytes confirmed that NupG was a broad-specificity transporter of purine and pyrimidine nucleosides. Importantly, using high-level expression in E. coli and magic-angle spinning cross-polarization solid-state nuclear magnetic resonance, we have for the first time been able directly to measure the binding of the permeant ([1'-(13)C]uridine) to the protein and to assess its relative mobility within the binding site, under non-energized conditions. Purification of over-expressed NupG to near homogeneity by metal chelate affinity chromatography, with retention of transport function in reconstitution assays, was also achieved. Fourier transform infrared and circular dichroism spectroscopy provided further evidence that the purified protein retained its 3D conformation and was predominantly alpha-helical in nature, consistent with a proposed structure containing 12 transmembrane helices. These findings open the way to elucidating the molecular mechanism of transport in this key family of membrane transporters.

Functional redundancy of two nucleoside transporters of the ENT family (CeENT1, CeENT2) required for development ofCaenorhabditis elegans

The genome of Caenorhabditis elegans encodes multiple homologues of the two major families of mammalian equilibrative and concentrative nucleoside transporters. As part of a programme aimed at understanding the biological rationale underlying the multiplicity of eukaryote nucleoside transporters, we have now demonstrated that the nematode genes ZK809.4 (ent-1) and K09A9.3 (ent-2) encode equilibrative transporters, which we designate CeENT1 and CeENT2 respectively. These transporters resemble their human counterparts hENT1 and hENT2 in exhibiting similar broad permeant specificities for nucleosides, while differing in their permeant selectivities for nucleobases. They are insensitive to the classic inhibitors of mammalian nucleoside transport, nitrobenzylthioinosine, dilazep and draflazine, but are inhibited by the vasoactive drug dipyridamole. Use of green fluorescent protein reporter constructs indicated that the transporters are present in a limited number of locations in the adult, including intestine and pharynx. Their potential roles in these tissues were explored by using RNA interference to disrupt gene expression. Although disruption of ent-1 or ent-2 expression alone had no effect, simultaneous disruption of both genes yielded pronounced developmental defects involving the intestine and vulva.

Decreased nucleoside transport and hENT1 transporter expression in beta-thalassemia major

OBJECTIVE

This study investigated nucleoside transport activity and transporter polypeptide expression in erythrocytes from beta-thalassemia major patients to determine if inhibition of transport activity is a sensitive indicator of oxidative membrane damage.

MATERIALS AND METHODS

Blood samples were obtained from 54 patients, diagnosed as having beta-thalassemia major prior to therapeutic transfusion, and 20 normal subjects. Uptake of (3)H-uridine into washed erythrocytes was measured at room temperature using short incubation periods (5 s) and a rapid inhibitor oil stop protocol. Erythrocyte membranes were analyzed by SDS-PAGE and nucleoside (hENT1) and glucose (GLUT-1) transporter polypeptides quantitated on immunoblots.

RESULTS

Uridine uptake was significantly lower in beta-thalassemic cells than in normal erythrocytes (20.03 +/- 1.08 pmol/10(8) cells/ 5 s, mean +/- SEM, n = 31, vs. 31.15 +/- 1.21 pmol/10(8) cells/5 s, n = 20; p < 0.0001). Expression of hENT1 was significantly lower in beta-thalassemic cells (23.90 +/- 1.01 arbitrary units, n = 54) than in controls (101.20 +/- 2.43 arbitrary units, n = 20; p < 0.001) but expression of GLUT-1 was not changed appreciably (101.80 +/- 2.43 arbitrary units, n = 54, for thalassemic cells; 102.60 +/- 3.02 arbitrary units, n = 20, for control cells; p = 0.87).

CONCLUSIONS

Erythrocytes from beta-thalassemia major patients showed decreased uridine transport which was associated with decreased nucleoside transporter expression. The process(es) mediating a selective decrease in hENT1 polypeptides in beta-thalassemia major was/were not determined.

Duplicated paralogous genes subject to positive selection in the genome of Trypanosoma brucei

Background

Whole genome studies have highlighted duplicated genes as important substrates for adaptive evolution. We have investigated adaptive evolution in this class of genes in the human parasite Trypanosoma brucei, as indicated by the ratio of non-synonymous (amino-acid changing) to synonymous (amino acid retaining) nucleotide substitution rates.

Methodology/Principal Findings

We have identified duplicated genes that are most rapidly evolving in this important human parasite. This is the first attempt to investigate adaptive evolution in this species at the codon level. We identify 109 genes within 23 clusters of paralogous gene expansions to be subject to positive selection.

Conclusions/Significance

Genes identified include surface antigens in both the mammalian and insect host life cycle stage suggesting that competitive interaction is not solely with the adaptive immune system of the mammalian host. Also surface transporters related to drug resistance and genes related to developmental progression are detected. We discuss how adaptive evolution of these genes may highlight lineage specific processes essential for parasite survival. We also discuss the implications of adaptive evolution of these targets for parasite biology and control.

Genotypic and phenotypic characterization of Trypanosoma brucei gambiense isolates from Ibba, South Sudan, an area of high melarsoprol treatment failure rate

Resistance of trypanosomes to melarsoprol is ascribed to reduced uptake of the drug via the P2 nucleoside transporter. The aim of this study was to look for evidence of drug resistance in Trypanosoma brucei gambiense isolates from sleeping sickness patients in Ibba, South Sudan, an area of high melarsoprol failure rate. Eighteen T. b. gambiense stocks were phenotypically and only 10 strains genotypically characterized. In vitro, all isolates were sensitive to melarsoprol, melarsen oxide, and diminazene. Infected mice were cured with a 4 day treatment of 2.5mg/kg bwt melarsoprol, confirming that the isolates were sensitive. The gene that codes for the P2 transporter, TbATI, was amplified by PCR and sequenced. The sequences were almost identical to the TbAT1(sensitive) reference, except for one point mutation, C1384T resulting in the amino acid change proline-462 to serine. None of the described TbAT1(resistant)-type mutations were detected. In a T. b. gambiense sleeping sickness focus where melarsoprol had to be abandoned due to the high incidence of treatment failures, no evidence for drug resistant trypanosomes or for TbAT1(resistant)-type alleles of the P2 transporter could be found. These findings indicate that factors other than drug resistance contribute to melarsoprol treatment failures.

Cellular localization and functional characterization of the equilibrative nucleoside transporters of antitumor nucleosides

Nucleoside transporters play an important role in the disposition of nucleosides and their analogs. To elucidate the relationship between chemosensitivity to antitumor nucleosides and the functional expression of equilibrative nucleoside transporters (ENT), we established stable cell lines of human fibrosarcoma HT-1080 and gastric carcinoma TMK-1 that constitutively overexpressed green fluorescent protein-tagged hENT1, hENT2, hENT3 and hENT4. Both hENT1 and hENT2 were predictably localized to the plasma membrane, whereas hENT3 and hENT4 were localized to the intracellular organelles. The chemosensitivity of TMK-1 cells expressing hENT1 and hENT2 to cytarabine and 1-(3-C-ethynyl-beta-D-ribopentofuranosyl) cytosine increased markedly in comparison to that of mock cells. However, no remarkable changes in sensitivity to antitumor nucleosides were observed in cell lines that expressed both hENT3 and hENT4. These data suggest that hENT3 and hENT4, which are mainly located in the intracellular organelles, are not prominent nucleoside transporters like hENT1 and hENT2, which are responsible for antitumor nucleoside uptake.

Differential regulation of mouse equilibrative nucleoside transporter 1 (mENT1) splice variants by protein kinase CK2

Nucleosides are accumulated by cells via a family of equilibrative transport proteins (ENTs). An alternative splice variant of the most common subtype of mouse ENT (ENT1) has been identified which is missing a protein kinase CK2 (casein kinase 2) consensus site (Ser(254)) in the central intracellular loop of the protein. We hypothesized that this variant (mENT1a) would be less susceptible to modulation by CK2-mediated phosphorylation compared to the variant containing the serine at position 254 (mENT1b). Each splice variant was transfected into nucleoside transporter deficient PK15 cells, and stable transfectants assessed for their ability to bind the ENT1-selective probe [(3)H]nitrobenzylthioinosine (NBMPR) and to mediate the cellular uptake of [(3)H]2-chloroadenosine, with or without treatment with the CK2 selective inhibitor, 4,5,6,7-tetrabromobenzotriazole (TBB). mENT1a had a higher affinity for NBMPR relative to mENT1b - measured both directly by the binding of [(3)H]NBMPR, and indirectly via inhibition of [(3)H]2-chloroadenosine influx by NBMPR. Furthermore, incubation of mENT1b-expressing cells with 10 microM TBB for 48 h decreased both the K(D) and B(max) of [(3)H]NBMPR binding, as well as the V(max) of 2-chloroadenosine uptake, whereas similar treatment of mENT1a-expressing cells with TBB had no effect. PK15 cells transfected with hENT1, which has Ser(254), was similar to mENT1b in its response to TBB. In conclusion, inhibition of CK2 activity, or deletion of Ser(254) from mENT1, enhances transporter affinity for the inhibitor, NBMPR, and reduces the number of ENT1 proteins functioning at the level of the plasma membrane.

Review of recent studies on resistance to cytotoxic deoxynucleoside analogues

Cytotoxic deoxynucleoside analogues are widely used in the treatment of haematological malignancies and solid tumours. Their metabolism and mechanisms of action are relatively well known, but with ongoing technological development, a continuous flow of scientific data is constantly adding new knowledge to this field. Thus, what was already a well-developed area some years ago has continued its expansion and become a better understood part of medical sciences. In order to keep abreast of the latest advances on cellular and clinical resistance to deoxynucleoside analogues, we have reviewed the recent literature and provide here an update on the subject. We have particularly focused on changes in gene products involved in the metabolic pathway of these drugs, such as membrane transporters, kinases, deaminases and 5'-nucleotidases. We also gave an overview on the chemical and biological development of modified deoxynucleoside analogues such as conjugates and pronucleotides.

Pharmacogenomics of gemcitabine: can genetic studies lead to tailor-made therapy?

Gemcitabine is a deoxycytidine analogue that has a broad spectrum of antitumour activity in many solid tumours including pancreatic cancer. We have recently carried out a pharmacogenomic study in cancer patients treated with gemcitabine, and found that one genetic polymorphism of an enzyme involved in gemcitabine metabolism can cause interindividual variations in the pharmacokinetics and toxicity of this agent. In this paper, we review recent genetic studies of gemcitabine, and discuss the possibility of individualised cancer chemotherapy based on a pharmacogenomic approach.