Characterization of two cDNAs encoding folate-binding proteins from L1210 murine leukemia cells. Increased expression associated with a genomic rearrangement.
L1210 murine leukemic cells grown under conditions of continuous low folate concentrations acquire increased levels of a high affinity/low capacity folate-binding protein (FBP). Using an oligonucleotide probe complementary to the human FBP, we have cloned and sequenced two murine FBP cDNAs isolated from a library constructed using a L1210 subline adapted for growth on low levels of 5-formyltetrahydrofolate. The encoding proteins, designated FBP1 and FBP2, have predicted Mr values of 29,415 and 28,821, respectively. These proteins share significant sequence identity with each other (70%) and with the deduced sequences of the human- and bovine-encoded FBPs (68-79%). Southern blot analysis of the low folate-adapted cell line revealed that, while neither of the two FBP-encoding genes was amplified, the FBP1 genomic locus had undergone rearrangement. On Northern blot analysis, this rearrangement was reflected in the enhanced expression (greater than 100-fold) of a FBP1-specific transcript which was 200 nucleotides shorter than the corresponding L1210 parental transcript. The increased expression of this transcript coincided with the increased expression of a membrane protein (Mr = 38,000) which could be affinity-labeled with a N-hydroxysuccinimide ester of [3H]folate. Accordingly, the FBP1 transcript appears to encode the high affinity/low capacity FBP. Compared to parental L1210 cells, expression of the FBP2-encoding transcript was unchanged in this cell line and, while the exact nature of the protein is unclear, FBP2 may represent a fetal form of the FBP.
Brigle
K E
KE
Department of Medicine, Virginia Commonwealth University, Medical College of Virginia, Richmond 23298.
Westin
E H
EH
Houghton
M T
MT
Goldman
I D
ID
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D015152:Blotting, Northern; D015139:Blotting, Southern; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D004247:DNA; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism; D005786:Gene Expression Regulation; D015321:Gene Rearrangement; D006031:Glycosylation; D007942:Leukemia, Experimental; D051379:Mice; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D011956:Receptors, Cell Surface; D015183:Restriction Mapping; D016415:Sequence Alignment; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D004247:DNA; D005492:Folic Acid