MTHFR

MTHFR Gene Polymorphism in Breast Cancer Patients Receiving CMF Regimen... 

Fig. 14.10 Folate metabolism and role of MTHFR. Genetically reduced MTHFR activity affects the distribution between folate species required for protein and DNA synthesis. Higher availabil ity of 5,10-methylenetetrahydrofolate (CH2THF) potentiates the TS inhibition by 5-FdUMP, the active metabolite of 5-FU. Hey, homocysteine Met, methionine CH3HF, 5-methyltetrahydrofolate TS, thymidylate synthase 5-FdUMP, fluorodeoxyuridine monophosphate.

Toffoli G, Veronesi A, Boiocchi M et al. MTHFR gene polymorphism and se-... 

Ueland PM, Hustad S, Schneede J et al. Biological and clinical implications of the MTHFR C677T polymorphism. 

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the NAD(P)H-dependent reduction of 5,10-methylenetetrahydrofolate (CH2-THF) to 5-methyltetrahydrofolate (CH3-THF). CH3-THF then serves as a methyl donor for the synthesis of methionine. The MTHFR proteins and genes from mammalian liver and E. coli have been characterized,12"15 and MTHFR genes have been identified in S. cerevisiae16 and other organisms. The MTHFR of E. coli (MetF) is a homotetramer of 33-kDa subunits that prefers NADH as reductant,12 whereas mammalian MTHFRs are homodimers of 77-kDa subunits that prefer NADPH and are allosterically inhibited by AdoMet.13,14 Mammalian MTHFRs have a two-domain structure the amino-terminal domain shows 30% sequence identity to E. coli MetF, and is catalytic the carboxyterminal domain has been implicated in AdoMet-mediated inhibition of enzyme activity.13,14... 

The MTHFRs of Arabidopsis and maize have recently been cloned by genomics-based approaches, based on homology with the enzymes from other organisms.17 Like mammalian MTHFRs, the plant enzymes were found to be homodimers of two-domain subunits that are homologous to the mammalian enzymes throughout both domains. However, when the recombinant plant proteins were expressed in yeast, they were found to differ radically from the mammalian MTHFRs in both their pyridine nucleotide preference and their regulatory properties plant enzymes prefer NADH to NADPH, and they are insensitive to AdoMet.17... 

In order to estimate the flux through the SMM cycle and to explore its function, a computer model of methionine metabolism in mature Arabidopsis rosette leaves was developed based on data from radiotracer experiments and on metabolite contents. This model suggested that the cycle serves to stop accumulation of AdoMet, rather than to prevent depletion of free methionine, as proposed by Mudd and Datko.54 Because plants lack the AdoMet feedbacks on MTHFR and AdoMet synthetase that regulate AdoMet pool size in other eucaryotes, the SMM cycle may be the main mechanism whereby plants achieve short-term control of AdoMet level. MMT knockouts of maize and Arabidopsis recently became available, and these can now be used to further investigate the role of the SMM cycle, and to test the predictions of the model. 

GOYETTE, P., PAI, A., MILOS, R., FROSST, P., TRAN, P., CHEN, Z., CHAN, M.,.ROZEN, R., Gene structure of human and mouse methylenetetrahydrofolate reductase (MTHFR), Mamm. Genome, 1998,9,652-656. 

MTHFR = methylene tetrahydrofolate reductase DHFR = dihydrofolate reductase SAM = S-adenosyl methionine... 

Chapman, J., Wang, N., Treves, T.A., Korczyn, A.D., Borstein, N.M. (1998) ACE, MTHFR, factor V Leiden, and APOE polymorphisms in patients with vascular and Alzheimer s dementia. Stroke, 29, 1401-1404. 

Fig. 14.1 Cellular pathway of methotrexate. ABCBl, ABCCl-4, ABC transporters ADA, adenosine deaminase ADP, adenosine diphosphate AICAR, aminoimidazole carboxamide ribonucleotide AMP, adenosine monophosphate ATIC, AICAR transformylase ATP, adenosine triphosphate SjlO-CH -THF, 5,10-methylene tetrahydrofolate 5-CHj-THF, 5-methyl tetrahydro-folate DHFR, dihydrofolate reductase dTMP, deoxythymidine monophosphate dUMP, deoxy-uridine monophosphate FAICAR, 10-formyl AICAR FH, dihydrofolate FPGS, folylpolyglutamyl synthase GGH, y-glutamyl hydrolase IMP, inosine monophosphate MTHFR, methylene tetrahydrofolate reductase MTR, methyl tetrahydrofolate reductase MTX-PG, methotrexate polyglutamate RFCl, reduced folate carrier 1 TYMS, thymidylate synthase. Italicized genes have been targets of pharmacogenetic analyses in studies published so far. (Reproduced from ref. 73 by permission of John Wiley and Sons Inc.)...

The MTHFR gene is a 19-kb gene located on chromosome 1 (lp36.3). Of the several MTHFR polymorphisms that have been identified (23), two polymorphisms, the C677T and A1298C polymorphisms, have been well studied for their influence on MTX s clinical effects. The C677T polymorphism leads to an alanine-to-valine... 

MTHFR Important in C677T Thermolabile Increased GI side 27... 

Berkun, Y., Levartovsky, D., Rubinow, A., et al. (2004) Methotrexate related adverse effects in patients with rheumatoid arthritis are associated with the A1298C polymorphism of the MTHFR gene. Annals of the Rheumatic Diseases. 63, 227-231. 

Kalemi TG, Lambropoulos AF, Gueorguiev M et al (2005) The association of p53 mutations and p53 codon 72, Her 2 codon 655 and MTHFR C677T polymorphisms with breast cancer in Northern Greece. Cancer Lett 222 57-65... 

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