The half-life of the transcript encoding the folate receptor alpha in KB cells is reduced by cytosolic proteins expressed in folate-replete and not in folate-depleted cells.
The KB cell, a transformed human cell line, constitutively expresses a high level of the glycosylphosphatidylinositol (GPI) anchored folate receptor protein alpha (FR alpha) and thereby can grow in medium containing <1 nM folate. When transferred from a folate-replete (FR) medium to one folate-deficient (FD), intracellular folate diminishes about 50-fold and expression of the FR alpha increases 6-fold. This up-regulation is mediated by a 4.5-fold increase in the initial transcription rate and a 2.4-fold prolongation of the mRNA half-life that together provide a higher level of the steady-state mRNA abundance. An RNA gel -shift assay of a 5' region of the mRNA that includes all of the non-coding and 24 nt of coding sequence, and a 3' region comprised only of coding sequence, identified unique complexes with cytosolic proteins from the FR-KB cells that were not observed with the cytosol from FD-KB cells. It appears, therefore, that expression of these folate-dependent cytosolic trans-active proteins function to maintain a shorter half-life of the mRNA in the FR-KB cells by binding to 5' and 3' cis elements, reducing the stability of this transcript.
Sadasivan
Easwara
E
Department of Medicine, Division of Hematology-Oncology, State University of New York, SUNY Downstate College of Medicine (Box #20), 450 Clarkson Avenue, Brooklyn, NY 11203, USA.
Regec
Annette
A
Rothenberg
Sheldon P
SP
D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D024202:Electrophoretic Mobility Shift Assay; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006207:Half-Life; D006801:Humans; D020871:RNA Stability / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D005492:Folic Acid