Transcobalamin codon 259 polymorphism in HT-29 and Caco-2 cells and in Caucasians: relation to transcobalamin and homocysteine concentration in blood.
Transcobalamin (TC) is the plasma transporter that delivers vitamin B(12) to cells. We have already reported that HT-29 and Caco-2 cells secrete different TC variants. HT-29 secretes 2 TC isoproteins (codon 259-Pro/Arg [259-P/R]), exhibiting unequal concentrations (TC 259-P > TC 259-R), and Caco-2 cells only secrete the phenotype 259-R. We investigated the relation between phenotypic and genetic TC polymorphism in HT-29 cells transfected with Caco-2 TC complementary DNA and in 159 healthy Caucasians. We found that codon 259-R is buried and, thus, the genetic polymorphism provides no explanation why the TCs from HT-29 and Caco-2 cells have different isoelectric points in nondenaturing isoelectric focusing (IEF). The newly translated TC in HT-29 cells from the Caco-2 complementary DNA recombinant plasmid had the same isoelectric point as the TC constitutively expressed in HT-29 cells, suggesting that TC phenotypic variability involves a specific cell folding of the protein. The codon 259 polymorphism was found to have a biallelic distribution: homozygotes P = 34.6%, heterozygotes R/P = 47.8%, and homozygotes R = 17.6%. In heterozygous samples, the IEF showed that the TC 259-P/TC 259-R ratio = 1.6. The blood apo-TC concentration of 259-P homozygous Caucasians was significantly higher than that of homozygous 259-R (P <.0001) and heterozygous (P <.0006) Caucasians. The heterozygotes 259-R/P had homocysteine concentration significantly higher than the homozygotes 259-R and 259-P (P =.02 and P =.01, respectively). In conclusion, TC codon-259 polymorphism affects TC plasma concentration and may interfere in vitamin B(12) cellular availability and homocysteine metabolism.
Namour
F
F
Laboratoire de Pathologie Cellulaire et Moléculaire en Nutrition, INSERM 0014, Faculté de Médecine de Nancy, Vandoeuvre Cedex France.
Olivier
J
J
Abdelmouttaleb
I
I
Adjalla
C
C
Debard
R
R
Salvat
C
C
Guéant
J
J
D000328:Adult; D000368:Aged; D019943:Amino Acid Substitution; D018938:Caco-2 Cells; D003062:Codon / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D005492:Folic Acid / Q000097:blood; D005602:France; D015972:Gene Expression Regulation, Neoplastic; D005787:Gene Frequency; D005838:Genotype; D019073:HT29 Cells; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000097:blood / Q000235:genetics*; D010641:Phenotype; D011110:Polymorphism, Genetic; D014155:Transcobalamins / Q000032:analysis / Q000235:genetics*; D014158:Transcription, Genetic; D014162:Transfection; D014805:Vitamin B 12 / Q000097:blood; D044465:White People / Q000235:genetics*
D003062:Codon; D018076:DNA, Complementary; D009363:Neoplasm Proteins; D014155:Transcobalamins; D006710:Homocysteine; D005492:Folic Acid; D014805:Vitamin B 12