Expression of the Human Placental Folate Receptor Transcript is Regulated in Human Tissues

Abstract

The primary structures of the human KB cell (FR-KB1) folate receptor (FR) and of a human placental (FR-P2) FR, proteins important in cellular accumulation of folates, have been deduced from cDNA sequences. Herein, we report a novel human FR cDNA (FR-P3) isolated from a placental library and the chromosomal organization of the human FR-P3 gene. Compared to the FR-P2 cDNA, the composite 1084 base-pair (bp) FR-P3 cDNA is homologous, but contains a unique 5' terminus and sequence differences within the open reading frame (ORF) and at the exon I-II junction. Polymerase chain reaction and RNase protection assays demonstrate that the FR-P3 cDNA represents the major transcript, and suggest that the FR-P2 cDNA is encoded by an independent FR gene. The nucleotide sequences of two non-overlapping human genomic clones contain the FR-P3 gene, which spans 5148 bp, is composed of five exons, and is polymorphic relative to 5' restriction sites. The transcript size (1084 bp) predicted from structural analysis of the FR-P3 gene correlates with the size (1100 bp) determined by Northern blots. Based on RNase protection assays, both FR-P3 and FR-KB1 transcripts are expressed in human fetal and adult tissues, and the abundance of each transcript varies among the tissues studied. These results indicate that the FR transcripts are products of independent, conserved genes; that neither FR gene is preferentially expressed during fetal development; and that specific FR transcripts are differentially expressed in human tissues, suggesting that transcription of each FR gene is regulated independently. The isolation of the FR-P3 gene will permit functional analysis of the cis and trans regulatory elements of the FR-P3 gene and the mechanisms involved in tissue-specific FR gene expression.

The role of folate receptor α in cancer development, progression and treatment: Cause, consequence or innocent bystander?

“…47 In contrast, the FOLR2 and FOLR3 genes each consist of 5 exons, 4 introns and 1 promoter that encodes a single transcript. 20,51,67,68 Regulation of FOLR1 gene expression and protein…”

Selective expression of folate receptor ? and its possible role in methotrexate transport in synovial macrophages from patients with rheumatoid arthritis

“…RNA blots were hybridized with 32 P-dCTP-labeled cDNA probes in RapidHyb buffer (Amersham) at 58°C for 2 hours. The FR-␤-specific probe had a sequence that corresponded to ϩ665 to ϩ933 of the cDNA (32), and the CD14-specific probe was as previously described (25). Washing of RNA blots was performed in 2ϫ saline-sodium citrate (SSC)/1% sodium dodecyl sulfate (SDS) at room temperature for 20 minutes, 1ϫ SSC/ 0.1% SDS at 65°C for 15 minutes, and finally 0.5ϫ SSC/0.1% SDS at 65°C for 15 minutes.…”

Neural Tube and Craniofacial Defects With Special Emphasis On Folate Pathway Genes

“…While the placenta is known to contain FRox as well as FRI (Elwood, 1989; Lacey et alc., 1989;Campbell et al, 1991;Antony, 1992; Weitman et al, 1992a,b;Willis et al, 1992;Ross et al, 1993;Prasad et al, 1994), a-receptors have also been localized to the bronchiolar epithelium, bronchial epithelium, pneumocytes in the lung, and in the kidney on the brush border membrane of the proximal tubules (Selhub et al, 1987;Antony, 1992;Weitman et al, 1992b;Birn et al, 1993;Page et al, 1993). Other tissues containing folate receptors include the choroid plexus, thyroid, and oviduct epithelium, although the exact isoform remains unknown due to their high degree of homology (Selhub et al, 1987;Holm et al, 1991;Antony, 1992;Weitman et al, 1992a;Page et al, 1993 Fan et al, 1992), and from 80 to 120 kDa in human cells (Matherly et al, 1991(Matherly et al, , 1994Freisheim et al, 1992). Differences in the extent of glycosylation between the human and murine carriers may account for the disparity in their apparent sizes (Matherly et al, 1991).…”

“…This is especially true given the high concentration of these receptors on the maternal placenta (Weitman et al, 1992a,b), as well as the syncytiotrophoblast and fetal neuro-epithelium. Since most embryonic cells lack folate receptors (Page et al, 1993), the presence of the receptors in these tissues is highly suggestive of a critical role for folate in the normal morphogenetic events involved in neural tube closure (NTC (Orr and Kamen, 1995). Fetuses with such mutations would be significantly compromised in their ability to harvest sufficient folate from the placenta to ensure an adequate supply during embryogenesis.…”