Hypoxia–Immune-Related Gene SLC19A1 Serves as a Potential Biomarker for Prognosis in Multiple Myeloma

Background

Multiple myeloma (MM) remains an incurable malignant tumor of plasma cells. Increasing evidence has reported that hypoxia and immune status contribute to the progression of MM. In this research, the prognostic value of the hypoxia–immune-related gene SLC19A1 in MM was evaluated by bioinformatics analysis.

Method

RNA-sequencing (RNA-seq) data along with clinical information on MM were downloaded from the Gene Expression Omnibus (GEO) database. Consistent clustering analysis and ESTIMATE algorithms were performed to establish the MM sample subgroups related to hypoxia and immune status, respectively, based on the GSE24080 dataset. The differentially expressed analysis was performed to identify the hypoxia–immune-related genes. Subsequently, a hypoxia–immune-gene risk signature for MM patients was constructed by univariate and multivariate Cox regression analyses, which was also verified in the GSE4581 dataset. Furthermore, the mRNA expression of SLC19A1 was determined using qRT-PCR in 19 MM patients, and the correlations between the genetic expression of SLC19A1 and clinical features were further analyzed.

Result

A total of 47 genes were identified as hypoxia–immune-related genes for MM. Among these genes, SLC19A1 was screened to construct a risk score model that had better predictive power for MM. The constructed prognostic signature based on SLC19A1 was verified in the GSE4581 dataset. All independent prognostic factors (age, β₂-microglobulin, LDH, albumin, MRI, and gene risk score) were used to develop a nomogram that showed a better performance for predicting the survival probability of MM patients for 1–5 years. Furthermore, SLC19A1 was highly expressed in newly diagnosed and relapsed MM patients, and high expression of SLC19A1 is correlated with higher bone marrow aspiration plasma cells and β₂-microglobulin levels in MM patients.

Conclusion

In conclusion, our results suggest that SLC19A1 is aberrantly expressed in MM and highly expressed SLC19A1 might be a biomarker correlated with inferior prognosis. More importantly, we identified SLC19A1 as a hypoxia–immune-related gene in MM. Future functional and mechanistic studies will further clarify the roles of SLC19A1 in MM.

SLC19A1 May Serve as a Potential Biomarker for Diagnosis and Prognosis in Osteosarcoma

BACKGROUND

Osteosarcoma is the most frequent primary malignant tumor of bone. SLC19A1 has been explored as a novel biomarker in some cancers. In this research, the diagnostic and prognostic value of SLC19A1 expression in osteosarcoma was evaluated by bioinformatics analysis. Data were sourced from the Gene Expression Omnibus (GEO) database.

METHODS

Gene expression data and clinical materials of patients with osteosarcoma were collected from GSE42352 and GSE21257 datasets. The mRNA expression of SLC19A1 was compared between osteosarcoma cells and mesenchyme stem cells with the Wilcoxon rank-sum test. Moreover, receiver operating characteristic (ROC) curve analysis was performed to determine the diagnostic merit of SLC19A1 for osteosarcoma. The relationship between SLC19A1 and clinicopathological characteristics was analyzed using logistic regression. Besides, the correlation between SLC19A1 and survival rate was assessed using Kaplan-Meier and Cox regression. The biological functions of SLC19A1 were annotated and evaluated through gene set enrichment analysis (GSEA) and gene set variation analysis (GSVA).

RESULTS

SLC19A1 was significantly highly expressed in osteosarcoma cells (p < 0.001). The ROC curve showed an area under the curve of 0.899, which indicated a high diagnostic value. High SLC19A1 expression showed a negative correlation with Huvos grade [odds ratio (OR) = 0.09 for III vs. I, p = 0.014]. Kaplan-Meier survival analysis showed that the overall survival (OS) of the patients with high SLC19A1 expression was significantly poorer than the low SLC19A1 expression group (p = 0.016). The univariate analysis revealed that high SLC19A1 expression was associated with poor OS [p = 0.013, hazard ratio (HR) = 6.74, 95% CI = 1.49 - 30.46]. The multivariate analysis revealed that SLC19A1 expression (p = 0.014, HR = 8.03, 95% CI = 1.52 - 42.51) was independently correlated with OS. GSEA showed that genes in high expression group of SLC19A1 were enriched in KEGG pathways, including "Glyoxylate and dicarboxylate metabolism", "Oxidative phosphorylation", "Aminoacyl tRNA biosynthesis", "Base excision repair", "Pyrimidine metabolism" and "Proteasome". GSVA further suggested their importance in the progression of osteosarcoma.

CONCLUSIONS

SLC19A1 may be a potential biomarker for diagnosis and prognosis in osteosarcoma.

Phase II trial of pemetrexed plus bevacizumab for second-line therapy of patients with advanced non-small-cell lung cancer: NCCTG and SWOG study N0426

PURPOSE

To evaluate the efficacy and toxicity of pemetrexed combined with bevacizumab as second-line therapy for patients with advanced non-small-cell lung cancer (NSCLC) and to correlate allelic variants in pemetrexed-metabolizing genes with clinical outcome.

PATIENTS AND METHODS

Patients with previously treated NSCLC received pemetrexed (500 mg/m(2) intravenous) combined with bevacizumab (15 mg/kg intravenous) every 3 weeks. The primary end point, evaluated using a one-stage Fleming design for detecting a true success rate of at least 70%, was the proportion of patients who were progression free and on treatment at 3 months. Polymorphisms in genes responsible for pemetrexed transport (reduced folate carrier [SLC19A1]) and metabolism (folylpolyglutamate synthase [FPGS] and gamma-glutamyl hydrolase [GGH]) evaluated in germline DNA (blood) were correlated with treatment outcome.

RESULTS

Forty-eight evaluable patients (14 females and 34 males) received a median of four cycles (range, one to 20 cycles). The most common grade 3 or 4 nonhematologic adverse events (AEs) were fatigue (13%), dyspnea (10%), and thrombosis (10%). Grade 3 or 4 hematologic AEs were neutropenia (19%) and lymphopenia (13%). Twenty-four (57%; 95% CI, 41% to 72%) of the first 42 patients met the success criteria. Median overall survival (OS) and progression-free survival (PFS) times were 8.6 and 4.0 months, respectively. The exon 6 (2522)C-->T polymorphism in SLC19A1 correlated with 3-month progression-free status (P = .01) and with PFS (P = .05). The IVS1(1307)C-->T polymorphism in GGH correlated with OS (P = .04).

CONCLUSION

The study did not meet its primary end point. However, the median PFS time of 4 months is promising. Pharmacogenetic studies in larger cohorts are needed to definitively identify polymorphisms that predict for survival and toxicity of pemetrexed.

Significance of thymidylate synthase for resistance to pemetrexed in lung cancer

Pemetrexed (MTA) is a multitargeted antifolate with promising clinical activity in lung cancer. We exposed the small cell lung cancer cell line PC6 to stepwise-increasing pemetrexed concentrations of 0.4, 1.6, and 4.0 microm, and established three pemetrexed-resistant lung cancer cell lines: PC6/MTA-0.4, PC6/MTA-1.6, and PC6/MTA-4.0 cells. To investigate the mechanisms of acquired resistance to pemetrexed, we measured the expression levels of the thymidylate synthase (TS), reduced folate carrier (RFC), and folylpoly-gamma-glutamate synthetase (FPGS) genes. TS gene expression was significantly increased in PC6/MTA-1.6 and PC6/MTA-4.0 cells relative to parental cells in a pemetrexed dose-dependent manner. In contrast, the levels of RFC gene expression in PC6/MTA-0.4 cells and FPGS in PC6/MTA-1.6 cells were significantly decreased, whereas the levels of both genes were restored in PC6/MTA-4.0 cells. Knockdown of TS expression using siRNA enhanced pemetrexed cytotoxicity in PC6/MTA-4.0 cells. The expression level of the TS gene was significantly correlated with the concentration of pemetrexed for 50% cell survival (IC(50)) in 11 non-small cell lung cancer cell lines. These results suggest that the alteration of molecular pharmacological factors in relation with pemetrexed resistance is dose-dependent, and that up-regulation of the expression of the TS gene may have an important role in the acquired resistance to pemetrexed. In addition, TS may be a predictive marker for pemetrexed sensitivity in lung cancer.

Alternative transcripts of rat slc19a1: Cloning, genomic organisation, tissue specific promoters and alternative splicing

Recently, the rat genome project revealed the genomic sequence of slc19a1, coding for the methotrexate carrier-1, identical to the reduced folate carrier-1 of humans, on rat chromosome 20. At the same time, we have cloned and analysed the complete or partial cDNAs of now at least six different transcripts from rat liver and kidneys. Alignment with the genomic sequence revealed seven exons. The first two non-coding exons, exon I and Ia were used alternatively in kidneys and liver, respectively, suggesting usage of alternative promoters. Three minor mRNA forms resulted from absent splicing of intron III, a shortened exon III (exon IIIa), and a shortened exon IV (exon IVa). The minor transcripts were predicted to result in translation products with 7 or 6 instead of 12 transmembrane domains (TMDs) and a peptide mass of 38, 39 and 40 kDa instead of 58 kDa.

A80G polymorphism of reduced folate carrier 1 (RFC1) and C776G polymorphism of transcobalamin 2 (TC2) genes in Down's syndrome etiology

CONTEXT AND OBJECTIVE

There is evidence that polymorphisms of genes involved in folate metabolism may be associated with higher risk that mothers may bear a Down's syndrome (DS) child. This study therefore had the objective of investigating the A80G polymorphism of the reduced folate carrier 1 (RFC1) gene and the C776G polymorphism of the transcobalamin 2 (TC2) gene as maternal risk factors for DS among Brazilian women.

DESIGN AND SETTING

Analytical cross-sectional study with control group, at Faculdade de Medicina de São José do Rio Preto (Famerp).

METHODS

Sixty-seven mothers of DS individuals with free trisomy 21, and 113 control mothers, were studied. Molecular analysis of the polymorphisms was performed by means of the polymerase chain reaction with restriction fragment length polymorphism (PCR-RFLP), followed by electrophoresis on 2% agarose gel.

RESULTS

The frequencies of the polymorphic alleles were 0.51 and 0.52 for RFC1 80G, and 0.34 and 0.34 for TC2 776G, in the case and control groups, respectively. Thus, there were no differences between the groups in relation to either the allele or the genotype frequency, for both polymorphisms (P = 0.696 for RFC1 A80G; P = 0.166 for TC2 C776G; P = 0.268 for combined genotypes).

CONCLUSION

There was no evidence of any association between the RFC1 A80G and TC2 C776G polymorphisms and the maternal risk of DS in the sample evaluated.

Polymorphisms and methylation of the reduced folate carrier in osteosarcoma

High-dose methotrexate is a standard component in the treatment of osteogenic sarcoma. Impaired methotrexate uptake associated with decreased reduced folate carrier expression is a common mechanism of methotrexate resistance in osteogenic sarcoma samples. We investigated whether promoter methylation and polymorphisms in the 3' untranslated region are involved in regulating reduced folate carrier expression. In a cohort of 66 osteogenic sarcoma specimens, quantitative methylation-specific polymerase chain reaction and single-strand conformation polymorphism were performed. We found detectable levels of promoter methylation in 84.3% of samples. When related to the reduced folate carrier mRNA levels, a trend was observed that reduced folate carrier expression is lower in samples (median, 0.7) with greater than 10% DNA methylation as compared with those (median, 2.3) with less than 10% DNA methylation. The heterozygous polymorphisms of 2582 T/G and 2617C/T in the 3' untranslated region showed reduced folate carrier expression (median, 0.9) as compared with the wild-type 2582T and 2617C (median, 4.2). The data suggest promoter methylation and polymorphisms in the 3' untranslated region of the reduced folate carrier may be involved in its transcriptional regulation in osteogenic sarcoma. Further study is required to confirm this finding.

The reduced folate carrier (RFC) is cytotoxic to cells under conditions of severe folate deprivation. RFC as a double edged sword in folate homeostasis

The reduced folate carrier (RFC), a bidirectional anion transporter, is the major uptake route of reduced folates essential for a spectrum of biochemical reactions and thus cellular proliferation. However, here we show that ectopic overexpression of the RFC, but not of folate receptor alpha, a high affinity unidirectional folate uptake route serving here as a negative control, resulted in an approximately 15-fold decline in cellular viability in medium lacking folates but not in folate-containing medium. Moreover to explore possible mechanisms of adaptation to folate deficiency in various cell lines that express the endogenous RFC, we first determined the gene expression status of the following genes: (a) RFC, (b) ATP-driven folate exporters (i.e. MRP1, MRP5, and breast cancer resistance protein), and (c) folylpoly-gamma-glutamate synthetase and gamma-glutamate hydrolase (GGH), enzymes catalyzing folate polyglutamylation and hydrolysis, respectively. Upon 3-7 days of folate deprivation, semiquantitative reverse transcription-PCR analysis revealed a specific approximately 2.5-fold decrease in RFC mRNA levels in both breast cancer and T-cell leukemia cell lines that was accompanied by a consistent fall in methotrexate influx, serving here as an RFC transport activity assay. Likewise a 2.4-fold decrease in GGH mRNA levels and approximately 19% decreased GGH activity was documented for folate-deprived breast cancer cells. These results along with those of a novel mathematical biomodeling devised here suggest that upon severe short term (i.e. up to 7 days) folate deprivation RFC transport activity becomes detrimental as RFC, but not ATP-driven folate exporters, efficiently extrudes folate monoglutamates out of cells. Hence down-regulation of RFC and GGH may serve as a novel adaptive response to severe folate deficiency.

Impairments in antifolate transport are common in retinoblastoma tumor samples

BACKGROUND

Many patients with retinoblastoma have a genetic predisposition to cancer and external beam radiation therapy and alkylating agent chemotherapy may increase their risk of secondary malignancy. Identification of effective chemotherapy agents for retinoblastoma that are not associated with an elevated risk of secondary malignancy would be beneficial.

PROCEDURE

Twenty-six specimens of fresh retinoblastoma tumor cells were studied in vitro with a PT430 competitive displacement assay. Differential displacement of the PT430 by methotrexate and not trimetrexate was considered indicative of a defect in reduced folate carrier (RFC)-mediated transport. Elevations in the accumulation of PT430 were considered indicative of dihydrofolate reductase (DHFR) amplification.

RESULTS

In 9 of the 26 (35%) samples, displacement by methotrexate was less than half the displacement by trimetrexate indicative of a defect in the RFC. In 5 of the 26 (19%) samples, trimetrexate did not displace the PT430. In 7 of 26 (27%) samples, the peak PT430 accumulation was suggestive of DHFR overexpression. Overall 9 of 26 (35%) samples had no evidence of a transport defect or DHFR overexpression and would be anticipated to be potentially sensitive to methotrexate. In 15 of the 26 (58%), no defects existed in trimetrexate displacement or DHFR overexpression and would be anticipated to be potentially sensitive to trimetrexate.

CONCLUSION

These results would support consideration of a phase II study to determine the effectiveness of trimetrexate for recurrent intra-ocular retinoblastoma.

A humanized mouse model for the reduced folate carrier

The ubiquitously expressed reduced folate carrier (RFC) or SLC19A1 is recognized to be an essential transport system for folates in mammalian cells and tissues. In addition to its generalized role as a folate transporter, RFC provides specialized tissue functions including absorption across intestinal/colonic epithelia, transport across the basolateral membrane of renal proximal tubules, transplacental transport of folates, and folate transport across the blood-brain barrier. The human RFC (hRFC) gene is regulated by five major upstream non-coding regions (designated A1/A2, A, B, C, and D), each transcribed from a unique promoter. Altogether, at least 14 distinct hRFC transcripts can be envisaged in which different 5' untranslated regions (UTRs) are fused to a common splice acceptor region (positions -1 to -49) within the first coding exon with a common 1776bp coding sequence. The 5' non-coding regions are characterized by alternate transcription start sites, multiple splice forms, and selective tissue distributions. Alternate 5' UTRs impact mRNA stabilities and translation efficiencies, and result in synthesis of modified hRFC proteins translated from upstream AUGs. In this report, we describe production and characterization of transgenic mice (TghRFC1) containing a functional hRFC gene and of humanized mice in which the mRFC gene is inactivated and an active hRFC gene has been introduced. The mice appear to be healthy and to breed well. Analysis of tissue specificity of expression in both the TghRFC1 and humanized hRFC mice by real-time RT-PCR demonstrates that the hRFC gene is expressed with a specificity closely resembling that seen in human tissues. For the humanized hRFC mice, levels of B and A1/A2 5' UTRs predominated in all mice/tissues, thus resembling results in normal human tissues. Lower levels of A and C 5' UTRs were also detected. The availability of humanized mouse models for hRFC will permit investigators to address critical unanswered questions pertinent to human health and disease. These include the ability to analyze the hRFC gene in vivo, to control dietary and other environmental conditions that may impact levels of gene expression, and to control the genetics of the mice in order to assess the effects of hRFC gene alterations on tissue folate uptake and distribution, none of which can be easily achieved in human populations.

Folate receptor and human reduced folate carrier expression in HepG2 cell line exposed to fumonisin B1 and folate deficiency

Fumonisin B1 (FB1) induces apoptosis and decreases the cellular uptake of 5-methyltetrahydrofolate. Two folate transporters (folate receptor, FR, and Reduced Folate Carrier, hRFC1) are involved in the cell uptake of folate. We aimed to study whether FB1 modifies the expression of the FR and the hRFC1 and whether its apoptotic effect is influenced by folate. Incubation of HepG2 cells with FB1 induced apoptosis in concentration and time-dependent manner in complete medium (experimental control medium, ECM), as well as in folate-depleted medium (FDM). FDM increased the toxicity of FB1 as the cells developed apoptosis within 24 h at 1 microM of FB1 instead of 100 microM in ECM. Whereas FR protein expression in cells grown in ECM was significantly inhibited after apoptosis event, protein expression of the hRFC1 was rather increased. The hrfc1 transcription was decreased in the treated cells. Under folate-deficient conditions, dramatic changes were observed on both transcriptional and post-transcriptional expression of the two transporters. FDM alone reduced FR protein expression by 12 +/- 2% and 43 +/- 1% at 48 and 72 h, respectively. The 5-methytetrahydrofolate attenuates apoptosis in a greater extent than the folic acid. However, its effects in preventing decrease of both folate transporters have not been observed. In conclusion, this study shows that the changes in the expression of FR after FB1 addition are probably a consequence of the FB1 toxicity. The response to FB1 by HepG2 cell lines is influenced by folate status and by folate form. 5-methyltetrahydrofolate appears to be more effective in preventing apoptosis than folic acid.

Polymorphisms in Folate, Pyrimidine, and Purine Metabolism Are Associated with Efficacy and Toxicity of Methotrexate in Psoriasis

Methotrexate is the gold standard therapy for moderate to severe psoriasis, but there is marked interpersonal variation in its efficacy and toxicity. We hypothesized that in psoriasis patients, specific common polymorphisms in folate, pyrimidine, and purine metabolic enzymes are associated with methotrexate efficacy and/or toxicity. DNA from 203 retrospectively recruited psoriasis patients treated with methotrexate was collected and genotyped by restriction endonuclease digestion or length polymorphism assays. The reduced folate carrier (RFC) 80A allele and the thymidylate synthase (TS) 3'-untranslated region (3'-UTR) 6 bp deletion were associated with methotrexate-induced toxicity (P=0.025 and P=0.025, respectively). RFC 80A and 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (ATIC) 347G were associated with methotrexate discontinuation (P=0.048 and P=0.038). The TS 5'-UTR 28 bp 3R polymorphism correlated with poor clinical outcome (P=0.029), however, this was not the case when patients with palmoplantar pustular psoriasis were not included in the analysis. Stronger associations between specific polymorphisms and methotrexate-induced toxicity and discontinuation were found in a subanalysis of patients on methotrexate not receiving folic acid supplementation. We have demonstrated preliminary evidence that specific polymorphisms of enzymes involved in folate, pyrimidine, and purine metabolism could be useful in predicting clinical response to methotrexate in patients with psoriasis.

Effect of folate oversupplementation on folate uptake by human intestinal and renal epithelial cells

BACKGROUND

Folic acid [corrected] plays an essential role in cellular metabolism. Its deficiency can lead to neural tube defects. However, optimization of body folate homeostasis can reduce the incidence of neural tube defects and may decrease the risk of Alzheimer and cardiovascular diseases and cancer. Hence, food fortification and intake of supplemental folate are widespread.

OBJECTIVE

We examined the effects of long-term folate oversupplementation on the physiologic markers of intestinal and renal folate uptake processes.

DESIGN

Human-derived intestinal Caco-2 and renal HK-2 epithelial cells were maintained (5 generations) in a growth medium oversupplemented (100 micromol folic acid/L) or maintained under sufficient conditions (0.25 and 9 micromol folic acid/L).

RESULTS

Carrier-mediated uptake of (3)H-folic acid (2 micromol/L) at buffer pH 5.5 (but not buffer pH 7.4) by Caco-2 and HK-2 cells maintained under the folate-oversupplemented condition was significantly (P<0.01) and specifically lower than in cells maintained under the folate-sufficient condition. This reduction in folic acid uptake was associated with a significant decrease in the protein and mRNA levels of the human reduced-folate carrier (hRFC) and a decrease in the activity of the hRFC promoter. It was also associated with a decrease in mRNA levels of the proton-coupled folate transporter/heme carrier protein 1 (PCFT/HCP1) and folate receptor (FR).

CONCLUSIONS

Long-term oversupplementation with folate leads to a specific and significant down-regulation in intestinal and renal folate uptake, which is associated with a decrease in message levels of hRFC, PCFT/HCP1, and FR. This regulation appears to be mediated via a transcriptional mechanism, at least for the hRFC system.

Associations of common polymorphisms in the thymidylate synthase, reduced folate carrier and 5-aminoimidazole-4-carboxamide ribonucleotide transformylase/inosine monophosphate cyclohydrolase genes with folate and homocysteine levels and venous thrombosis risk

BACKGROUND

Folate is important in purine and thymidylate synthesis and, via homocysteine remethylation, facilitates S-adenosylmethionine-dependent transmethylation. Low folate availability leads to hyperhomocysteinemia, which is a risk factor for arterial vascular disease and venous thrombosis. Genetic variation in folate-metabolizing genes may affect folate availability and hence confer a greater risk of venous thrombosis.

METHODS

We genotyped the thymidylate synthase (TYMS) 28-bp repeat and 6-bp deletion, and the reduced folate carrier (RFC1) 80G>A and AICAR transformylase/inosine monophosphate (IMP) cyclohydrolase (ATIC) 346C>G polymorphisms in population-based controls (n=431), and assessed their effect on plasma total homocysteine (tHcy), and serum and red blood cell (RBC) folate. We investigated the associations between these variants and disease risk in a retrospective case-control study on recurrent venous thrombosis (n=173) as well.

RESULTS

None of the genotypes, alone or in combination, were associated with major changes in tHcy. However, the TYMS 28-bp repeat was associated with serum and RBC folate levels. We found no evidence that the genetic variants studied were associated with recurrent venous thrombosis risk.

CONCLUSIONS

The TYMS 28-bp repeat and 6-bp deletion, and RFC1 80G>A and ATIC 346C>G polymorphisms are not associated with tHcy, but we did observe an association between the TYMS 28-bp repeat and serum and RBC folate in a general population. None of the polymorphisms was associated with recurrent venous thrombosis risk.

Human reduced folate carrier: translation of basic biology to cancer etiology and therapy

This review attempts to provide a comprehensive overview of the biology of the physiologically and pharmacologically important transport system termed the "reduced folate carrier" (RFC). The ubiquitously expressed RFC has unequivocally established itself as the major transport system in mammalian cells and tissues for a group of compounds including folate cofactors and classical antifolate therapeutics. Loss of RFC expression or function may have potentially profound pathophysiologic consequences including cancer. For chemotherapeutic antifolates used for cancer such as methotrexate or pemetrexed, synthesis of mutant RFCs or loss of RFC transcripts and proteins results in antifolate resistance due to incomplete inhibition of cellular enzyme targets and insufficient substrate for polyglutamate synthesis. Since RFC was first cloned in 1994, tremendous advances have been made in understanding the complex transcriptional and posttranscriptional regulation of RFC, in identifying structurally and functionally important domains and amino acids in the RFC molecule as a prelude to establishing the mechanism of transport, and in characterizing the molecular defects in RFC associated with loss of transport in antifolate resistant cell line models. Many of the insights gained from laboratory models of RFC portend opportunities for modulating carrier expression in drug resistant tumors, and for designing a new generation of agents with improved transport by RFC or substantially enhanced transport by other folate transporters over RFC. Many of the advances in the basic biology of RFC in cell line models are now being directly applied to human cancers in the clinical setting, most notably pediatric acute lymphoblastic leukemia and osteogenic sarcoma.

Genetic polymorphisms in the one-carbon metabolism pathway and breast cancer risk: a population-based case-control study and meta-analyses

Epidemiological evidence suggests that intake of folate and other B-vitamins and genetic variants in the one-carbon metabolism pathway could influence the risk of breast cancer. Previous studies have focused on 2 polymorphisms in the methylenetetrahydrofolate gene (MTHFR A222V and E429A); however, findings are inconclusive. In a large population-based case-control study in Poland (2,386 cases, 2,502 controls), we investigated the association between breast cancer risk and 13 polymorphisms in 6 one-carbon metabolism genes (MTHFR, MTR, MTRR, CBS, SHMT1 and SLC19A1). Data suggested an association between a nonsynonymous change in the gene coding for methionine synthase (MTR D919G) and reduced breast cancer risk: OR (95% CI) = 0.84 (0.73-0.96) and 0.85 (0.62-1.15) for heterozygous and homozygote variant genotypes, respectively, compared with common homozygotes; p-trend = 0.01, false discovery rate = 0.14. We found no significant associations between other variants and breast cancer risk, including MTHFR A222V or E429A. Meta-analyses including published studies of MTHFR A222V (8,330 cases and 10,825 controls) and E429A (6,521 cases and 8,515 controls) supported the lack of an overall association; however, studies suggested an increase in risk among premenopausal women. In conclusion, this report does not support a substantial overall association between the evaluated polymorphisms in the one-carbon metabolism pathway and breast cancer risk.

Cloning and functional characterization of a folate transporter from the nematode Caenorhabditis elegans

Two putative orthologs to the human reduced folate carrier (hRFC), folt-1 and folt-2, which share a 40 and 31% identity, respectively, with the hRFC sequence, have been identified in the Caenorhabditis elegans genome. Functional characterization of the open reading frame of the putative folt-1 and folt-2 showed folt-1 to be a specific folate transporter. Transport of folate by folt-1 expressed in a heterologous expression system showed an acidic pH dependence, saturability (apparent K(m) of 1.23 +/- 0.18 microM), a similar degree of inhibition by reduced and substituted folate derivatives, sensitivity to the anti-inflammatory drug sulfasalazine (apparent K(i) of 0.13 mM), and inhibition by anion transport inhibitors, e.g., DIDS. Knocking down (silencing) or knocking out the folt-1 gene led to a significant inhibition of folate uptake by intact living C. elegans. We also cloned the 5'-regulatory region of the folt-1 gene and confirmed promoter activity of the construct in vivo in living C. elegans. With the use of the transcriptional fusion construct (i.e., folt-1::GFP), the expression pattern of folt-1 in different tissues of living animal was found to be highest in the pharynx and intestine. Furthermore, folt-1::GFP expression was developmentally and adaptively regulated in vivo. These studies demonstrate for the first time the existence of a specialized folate uptake system in C. elegans that has similar characteristics to the folate uptake process of the human intestine. Thus C. elegans provides a genetically tractable model that can be used to study integrative aspects of the folate uptake process in the context of the whole animal level.

Prognostic role of the reduced folate carrier, the major membrane transporter for methotrexate, in childhood acute lymphoblastic leukemia: a report from the Children's Oncology Group

PURPOSE

The value of measuring expression of individual genes relevant to particular chemotherapy drugs and encoding metabolizing enzymes, transporters, or drug targets, as predictors of treatment response and outcome in pediatric acute lymphoblastic leukemia (ALL), remains controversial.

EXPERIMENTAL DESIGN

In a case-control population of 91 pediatric B-precursor ALL patients [42 relapsed within 4 years (cases) and 49 did not relapse (controls)], we used real-time reverse transcription-PCR to measure transcript levels for 20 genes relevant to chemotherapy with the five major drugs used to treat this disease, including asparaginase, 6-mercaptopurine, methotrexate, prednisone, and vincristine. Results were confirmed in a separate case-control population of 26 patients.

RESULTS

Only the human reduced folate carrier (hRFC) gene, encoding the major membrane transporter for methotrexate, showed a significant difference in median transcript levels between the 42 cases and the 49 controls (P = 0.0278, Wilcoxon test). Using cutoffs for hRFC expression levels (based on Akaike information criterion), there were statistically significant associations between hRFC transcripts and treatment relapse (P = 0.0052). hRFC-B, corresponding to the major hRFC transcript form in ALL, was also measured by real-time reverse transcription-PCR and was prognostic. The association between treatment relapse and hRFC levels was validated in a separate study population of 14 cases and 12 controls from an earlier case-control study (P = 0.0221).

CONCLUSIONS

Our results strongly suggest the prognostic importance of hRFC gene expression to treatment outcomes in pediatric ALL. They validate our previous studies of hRFC transcriptional regulation in pediatric ALL and provide further compelling evidence for the critical role for methotrexate in the successful treatment of this disease.

Transcription regulatory polymorphism -43T>C in the 5'-flanking region of SLC19A1 gene could affect rheumatoid arthritis patient response to methotrexate therapy

The reduced folate carrier (RFC) protein (SLC19A1-gene) has central role in the uptake and intracellular accumulation of folates. In this respect, we investigate whether SLC19A1 genetic variations could affect rheumatoid arthritis (RA) patient response to antifolate treatment. One hundred six unrelated RA patients were enrolled in this study. Polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) was used as the screening method for genetic variants. Unusual SSCP patterns were characterized by direct sequencing of the PCR products and subsequently restriction assays were established. Western blot analysis of RFC protein was performed in respect of the identified SLC19A1 genotypes. Patient response to methotrexate (MTX) was evaluated using disease activity for 28 joint indices score, American College of Rheumatology 20% and 50% scores. No mutation was found in the SLC19A1 gene, but three polymorphic variants: the -43T>C in the 5'-flanking sequence to the ATG-transcription start site; and the 80G>A (R27H) and 696C>T (P232P) in the coding gene sequence. The wild type alleles of the three polymorphisms were in strict linkage disequilibrium. Western blot analysis revealed that the non-wild type allele of polymorphism -43T>C is associated with low RFC protein expression levels. Furthermore, the genotypic analysis of the functional polymorphic variant -43T>C revealed to be insufficient to predict patient response to MTX therapy. According to recent literature, several transport systems account for folate membrane transport. Additionally, in previous studies discrepancies have been reported to exist between the same genetic variants and their use in prediction of patient response to MTX therapy. Therefore, the present genotypic-phenotypic association study of a functional polymorphism revealed the need of a complex genotypic analysis in order to predict patient response to folate antagonists' therapy.

No association between common polymorphisms in genes of folate and homocysteine metabolism and the risk of Down's syndrome among French mothers

The cause of the non-disjunction leading to trisomy 21 remains unclear. Recent evidence has suggested that 5, 10-methylenetetrahydrofolate reductase (MTHFR) and/or methionine synthase reductase (MTRR) might contribute to the maternal risk of trisomy 21. The purpose of the present study was to analyse these findings among the French population and to investigate whether common polymorphisms in genes of the folate and homocysteine pathway, including the MTHFR 677C>T, MTHFR 1298A>C, the methionine synthase (MTR) 2756A>G, the cystathionine β-synthase (CBS) 844Ins68 and the reduced folate carrier (RFC-1) 80G>A polymorphisms, contribute to the risk of trisomy 21. The risk was studied by analysing independent and combined genotypes in 119 case mothers and 119 control mothers. The MTHFR 677T, MTHFR 1298C, MTR2756G, MTRR66G, CBSIns68+ and the RFC-1 80G allele frequencies were not significantly different among French case mothers, compared with control mothers. The risk of having a child with trisomy 21 did not appear to be linked to polymorphisms in genes associated with folate and homocysteine metabolism.

Molecular basis for decreased folylpoly-γ-glutamate synthetase expression in a methotrexate resistant CCRF-CEM mutant cell line

A CCRF-CEM mutant, CEM-p, has been shown to exhibit resistance to methotrexate due to decreased methotrexate polyglutamate accumulation. To ascertain the mechanism(s) responsible for this phenotype, we analyzed FPGS and SLC19A1 mRNA expression, examined FPGS promoter activity, and determined nucleotide sequence of the FPGS promoter and full length cDNA from CCRF-CEM and CEM-p cells. We identified in FPGS from CEM-p cells three amino acid substitutions that altered the ATP binding P-loop, glutamate/folate binding, and a conserved domain located at the carboxyl-terminal. Our data demonstrated for the first time the importance of the highly conserved domain (VTGSLHLVGGV) located at the carboxyl-terminal for FPGS activity.

Reduced folate carrier-1 80G>A polymorphism affects methotrexate treatment outcome in rheumatoid arthritis

The folate antagonist methotrexate (MTX) is a drug currently used in the treatment of rheumatoid arthritis (RA). MTX enters the cells through the reduced folate carrier (RFC-1) and is activated to polyglutamates. Previous studies have shown that RFC-1 expression may influence the efficacy of therapy with MTX. The studies suggest that G80A polymorphism in RFC-1 is associated with altered folate/antifolate levels and the subjects carrying homozygous mutant 80AA genotype tend to have higher plasma folate and MTX concentrations and higher erythrocyte polyglutamate levels compared with those with the wild type or heterozygous genotype. It is possible that this polymorphism might influence MTX treatment outcome in patients with RA. In the present study, we examined the association between RFC-1 G80A polymorphism and treatment outcome in patients with RA administered MTX. The study was carried out on 174 patients diagnosed with RA treated with MTX (7.5-15.0 mg weekly) plus low doses of methylprednisone. The RFC-1 80G>A polymorphism (resulting in a histidine-to-arginine substitution at codon 27 of RFC-1) was detected using a polymerase chain reaction-restriction fragment length polymorphism method. The probability of remission of RA symptoms was 3.32-fold higher in carriers of 80AA genotype as compared with patients with 80GG genotype (P=0.021, OR=3.32, 95% CI: 1.26-8.79). The frequency of A allele among MTX responders was 62.1, compared to 47.8% in a group of poor MTX responders (P=0.013, OR=1.78, 95% CI: 1.13-2.81). Moreover, the increase of aminotransferase activity was noted more frequently in carriers of 80AA genotype. The present data suggest that evaluation of RFC-1 gene 80G>A polymorphism may be a useful tool to optimize MTX therapy in patients with RA.

Effects of 5' untranslated region diversity on the posttranscriptional regulation of the human reduced folate carrier

The human RFC (hRFC) gene is regulated by five major 5' non-coding exons, characterized by alternate transcription start sites and splice forms. The result is up to 14 hRFC transcripts for which different 5' untranslated regions (UTRs) are fused to a common coding sequence. By in vitro translation assays with hRFC constructs corresponding to the major transcript forms, most of the forms were translated poorly. Upon expression of the 5'UTR-hRFC constructs in hRFC-null HeLa cells, a range of steady state hRFC proteins and transcripts were detected that reflected relative transcript stabilities and, to a lesser extent, translation efficiencies. Transcripts including 5' UTRs derived from non-coding exon A encoded a modified hRFC protein translated from an upstream initiation site. When this modified hRFC protein was expressed in hRFC-null K562 cells, there were only minor differences in surface targeting, stability, or transport function from wild type hRFC. Our results demonstrate an important role for posttranscriptional determinants of cellular hRFC levels and activity.

Metabolic endophenotype and related genotypes are associated with oxidative stress in children with autism

Autism is a behaviorally defined neurodevelopmental disorder usually diagnosed in early childhood that is characterized by impairment in reciprocal communication and speech, repetitive behaviors, and social withdrawal. Although both genetic and environmental factors are thought to be involved, none have been reproducibly identified. The metabolic phenotype of an individual reflects the influence of endogenous and exogenous factors on genotype. As such, it provides a window through which the interactive impact of genes and environment may be viewed and relevant susceptibility factors identified. Although abnormal methionine metabolism has been associated with other neurologic disorders, these pathways and related polymorphisms have not been evaluated in autistic children. Plasma levels of metabolites in methionine transmethylation and transsulfuration pathways were measured in 80 autistic and 73 control children. In addition, common polymorphic variants known to modulate these metabolic pathways were evaluated in 360 autistic children and 205 controls. The metabolic results indicated that plasma methionine and the ratio of S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH), an indicator of methylation capacity, were significantly decreased in the autistic children relative to age-matched controls. In addition, plasma levels of cysteine, glutathione, and the ratio of reduced to oxidized glutathione, an indication of antioxidant capacity and redox homeostasis, were significantly decreased. Differences in allele frequency and/or significant gene-gene interactions were found for relevant genes encoding the reduced folate carrier (RFC 80G > A), transcobalamin II (TCN2 776G > C), catechol-O-methyltransferase (COMT 472G > A), methylenetetrahydrofolate reductase (MTHFR 677C > T and 1298A > C), and glutathione-S-transferase (GST M1). We propose that an increased vulnerability to oxidative stress (endogenous or environmental) may contribute to the development and clinical manifestations of autism.