Our previous study identified two alternate non-coding upstream exons (A and B) in the human reduced folate carrier (hRFC) gene, each controlled by a separate promoter. Each minimal promoter was regulated by unique cis-elements and transcription factors, including stimulating protein (Sp) 1 and Sp3 and the basic leucine zipper family of proteins, suggesting opportunities for cell- and tissue-specific regulation. Studies were performed to explore the expression patterns of hRFC in human tissues and cell lines. Levels of hRFC transcripts were measured on a multi-tissue mRNA array from 76 human tissues and tumour cell lines and on a multi-tissue Northern blot of representative tissues, each probed with full-length hRFC cDNA. hRFC transcripts were ubiquitously expressed, with the highest level in placenta and the lowest level in skeletal muscle. By rapid amplification of cDNA 5′-ends assay from nine tissues and two cell lines, hRFC transcripts containing both A and B 5′-untranslated regions (UTRs) were identified. However, five additional 5′-UTRs (designated A1, A2, C, D and E) were detected, mapping over 35kb upstream from the hRFC translation start site. The 5′-UTRs were characterized by multiple transcription start sites and/or alternative splice forms. At least 18 unique hRFC transcripts were detected. A novel promoter was localized to a 453bp fragment, including 442 upstream of exon C and 11bp of exon C. A 346bp repressor flanked the 3′-end of this promoter. Our results suggest an intricate regulation of hRFC gene expression involving multiple promoters and non-coding exons. Moreover, they provide a transcriptional framework for understanding the role of hRFC in the pathophysiology of folate deficiency and antifolate drug selectivity.
The human reduced folate carrier gene is ubiquitously and differentially expressed in normal human tissues: identification of seven non-coding exons and characterization of a novel promoter
- Views Icon Views
- Share Icon Share
- Cite Icon Cite
Johnathan R. WHETSTINE, Robin M. FLATLEY, Larry H. MATHERLY; The human reduced folate carrier gene is ubiquitously and differentially expressed in normal human tissues: identification of seven non-coding exons and characterization of a novel promoter. Biochem J 1 November 2002; 367 (3): 629–640. doi: https://doi.org/10.1042/bj20020512
Download citation file: