Disease relevance of Slc19a1

• At 38 weeks, RFC1(+/-) mice developed local inflammatory lesions with or without epithelial dysplasia as well as adenocarcinomas, which were larger relative to RFC1(+/+) mice [1].
• In conclusion, Folbp1 and RFC1 genetically modified mice exhibit distinct changes in colonocyte phenotype and therefore have utility as models to examine the role of folate homeostasis in colon cancer development [1].
• It is concluded that genetic modifications at the Folbp1 and RFC loci confers no particular sensitivity to arsenic toxicity compared to wild-type controls, thus disproving the working hypothesis that decreased methylating capacity of the genetically modified mice would put them at increased risk for arsenic-induced reproductive toxicity [2].
• Embryonic lethality and neural tube defect (NTD) frequency in Folbp1 mice was dose-dependent and differed from the RFC mice; however, no genotype-related differences were observed [2].
• L1210 leukemia cells transport reduced folates and methotrexate via a well defined reduced folate carrier system and, in the absence of low folate selective pressure, do not express an alternate endocytotic route mediated by cell surface folate receptors [3].

High impact information on Slc19a1

• The small lymphocyte non-RFC required a longer time than the medium lymphocyte RFC effector cell to produce maximum activity [4].
• Microarray analysis of colonic mucosa showed distinct changes in gene expression specific to Folbp1 or RFC1 ablation [1].
• In contrast, subtle changes in folate homeostasis resulted from targeted deletion of RFC1 (RFC1(+/-)) [1].
• These animals had reduced (P < 0.05) colonic RFC1 mRNA and exhibited a 2-fold reduction in the plasma S-adenosylmethionine/S-adenosylhomocysteine [1].
• Colonic cell proliferation was increased in RFC1(+/-) mice relative to RFC1(+/+) mice [1].

Chemical compound and disease context of Slc19a1

• This laboratory previously described an L1210 leukemia cell line, MTXrA, with acquired resistance to methotrexate (MTX) due to the loss of mobility of the reduced folate carrier [3].
• These data suggest that RFC1 may be one of the alternative transport routes available for TMP in some tissues when THTR-1 is mutated in the autosomal recessive disorder thiamine-responsive megaloblastic anemia [5].
• Activity of a novel anti-folate (PDX, 10-propargyl 10-deazaaminopterin) against human lymphoma is superior to methotrexate and correlates with tumor RFC-1 gene expression [6].
• The modulation of thiamin accumulation by RFC1 in murine leukemia cells suggests that this carrier may play a role in thiamin homeostasis and could serve as a modifying factor in thiamin nutritional deficiency as well as when the high affinity thiamin transporter is mutated [7].

Biological context of Slc19a1

• The RFC heterozygotes tended to have higher plasma levels of S-adenosylhomocysteine (SAH) than did the wild-type controls, although this effect was not robust [2].
• RFC-1 gene copy number also decreased, and the mean length of the HSR in these revertants declined 1.6- to 5-fold [8].
• Transfection of the parental reduced folate carrier into MTXrA cells resulted in a cell line which exhibited a complete restoration of methotrexate uptake and an enhanced sensitivity to methotrexate [9].
• Structure and regulation of the murine reduced folate carrier gene: identification of four noncoding exons and promoters and regulation by dietary folates [10].
• These RFC1(-)/- mice showed a marked absence of erythropoiesis in bone marrow, spleen, and liver along with lymphoid depletion in the splenic white pulp and thymus [11].

Anatomical context of Slc19a1

• Decreased expression of the reduced folate carrier and folypolyglutamate synthetase is the basis for acquired resistance to the pemetrexed antifolate (LY231514) in an L1210 murine leukemia cell line [12].
• The increase in pH-dependent influx during maturation was associated with an increase in RFC-1 gene expression in the form of a 2.5-kilobase RNA transcript and 58-kDa brush-border membrane protein detected by folate-based affinity labeling and with anti-mouse RFC-1 peptide antibodies [13].
• RFC-1 gene expression regulates folate absorption in mouse small intestine [13].
• In the present study, we demonstrate that transport of thiamine monophosphate (TMP), an important thiamine metabolite present in plasma and cerebrospinal fluid, is mediated by RFC1 in L1210 murine leukemia cells [5].
• In the E9.0 to E11.5 mouse embryo RFC is widely detectable, with intense signal localized to cell populations in the neural tube, craniofacial region, limb buds and heart [14].

Associations of Slc19a1 with chemical compounds

• This was evidenced by the increase in Vmax for [3H]MTX (methotrexate) influx and a commensurate increase in the amount of the 46 kilodalton (kDa) transport protein and reduced folate carrier (RFC-1) mRNA [8].
• The concentrative advantage for RFC1 (the ratio of [MTX]i in MTXrA-R16 to L1210 cells) increased from 1.8 at 0.1 microM MTX to 3.8 at an [MTX]e level of 30 microM [15].
• Rescue of embryonic lethality in reduced folate carrier-deficient mice by maternal folic acid supplementation reveals early neonatal failure of hematopoietic organs [11].
• In an ongoing study of structure-function relationships of the murine reduced folate carrier 1 (RFC1), a glutamate to lysine mutation at amino acid 45 was identified in a methotrexate (MTX)-resistant L1210 clonal variant in which MTX and 5-formyltetrahydrofolate (5-CHO-THF) influx was markedly decreased [16].
• The data suggest that substitution of a positive for a negative amino acid at position 45 results in the loss of RFC1 mobility in the absence of small inorganic anions that bind to, and neutralize the positive charge on, the lysine residue [16].

Regulatory relationships of Slc19a1

• FR-alpha expressed at sufficient levels can mediate influx of MTX and folates into cells at rates comparable to the reduced folate carrier and hence has pharmacologic and physiologic importance [3].
• RESULTS: In the mouse, RFC transcripts and protein are expressed in the E10.0 placenta and yolk sac [14].

Other interactions of Slc19a1

• The data indicate that resistance to pemetrexed in the MTA-13 cell line was due to changes in both RFC and FPGS expression, two proteins that act in tandem to regulate polyglutamation of folates and antifolates in cells, resulting in cellular depletion of these active pemetrexed congeners [12].
• The present work demonstrates that RFC is present in placenta and yolk sac and provides the first evidence that it is expressed in the neural tube, craniofacial region, limb buds and heart during organogenesis [14].

Analytical, diagnostic and therapeutic context of Slc19a1

• The results of Southern and Northern blotting showed that the RFC-1 gene copy number and RNA transcript level were markedly increased (30-35 fold) in L1210/R83 cells [8].
• Fluorescence in situ hybridization (FISH) analysis revealed that the HSR-like segment in these cells was the site of amplified RFC-1 genes [8].
• We now report on the sequence analysis of cDNAs encoding the reduced folate carrier from this line and identify a single mutation that results in the substitution of a proline for an alanine in a highly conserved transmembrane region of the protein [9].
• RT-PCR analysis for the expression of genes involved in folate metabolism demonstrated that increased sensitivity to PDX correlated with higher RFC-1 gene expression with no difference in FPGS or FPGH levels, suggesting that measurement of tumor RFC-1 gene expression level may be a predictor of response to PDX [6].
• Role of the amino acid 45 residue in reduced folate carrier function and ion-dependent transport as characterized by site-directed mutagenesis [17].

References