Altered folate-binding protein mRNA stability in KB cells grown in folate-deficient medium.
Folate-binding protein (FBP), a high-affinity folate receptor, is responsible for cellular accumulation of folate and folate analogs such as methotrexate in human KB (nasopharyngeal carcinoma) cells. Both FBP and FBP mRNA increase 3- to 5-fold when KB cells are grown in folate-deficient (less than 10 nM folate) medium (KB-FD), compared with growth in standard folate-replete medium containing at least 2 microM folate (KB-FR). The possible mechanisms of enhanced FBP gene expression in KB-FD were examined in this study. Southern blot analysis revealed no significant change in the FBP gene organization or copy number in the KB-FD DNA. While hypomethylation of the FBP gene was observed in KB-FD DNA, relative to KB-FR DNA, exposure of KB-FR to the DNA methylation inhibitors did not result in elevated FBP mRNA levels. The transcriptional rate of the FBP gene was the same in KB-FR and KB-FD. RNA half-life studies indicated that the half-life of FBP mRNA in KB-FD was increased approximately 2.5-fold, compared with KB-FR. Thus, the increase in the steady-state levels of FBP mRNA in KB-FD can be attributed partly to increased FBP mRNA stability.
Hsueh
C T
CT
Department of Experimental Therapeutics, Grace Cancer Drug Center, Roswell Park Cancer Institute, Buffalo, NY 14263.
Dolnick
B J
BJ
D002352:Carrier Proteins / Q000032:analysis* / Q000235:genetics; D002460:Cell Line; D003470:Culture Media; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000494:pharmacology; D005494:Folic Acid Deficiency / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D008745:Methylation; D012333:RNA, Messenger / Q000032:analysis*; D011956:Receptors, Cell Surface; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D003470:Culture Media; D058973:Folate Receptors, GPI-Anchored; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D005492:Folic Acid