Selective expression of folate receptor β and its possible role in methotrexate transport in synovial macrophages from patients with rheumatoid arthritis
✍ Scribed by Noriko Nakashima-Matsushita; Toshio Homma; Su Yu; Takemasa Matsuda; Nobuhiko Sunahara; Tadashi Nakamura; Michishi Tsukano; Manohar Ratnam; Takami Matsuyama
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 249 KB
- Volume
- 42
- Category
- Article
- ISSN
- 0004-3591
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✦ Synopsis
Objective. To investigate the expression of folate receptors (FR) and reduced folate carrier (RFC) and determine their relevance to methotrexate (MTX) transport in synovial mononuclear cells (SMC) from patients with rheumatoid arthritis (RA).
Methods. Levels of FR and RFC messenger RNA (mRNA) were examined by reverse transcriptasepolymerase chain reaction (RT-PCR) in SMC from RA patients and peripheral blood mononuclear cells from healthy donors. Expression of FR- mRNA and protein was determined by Northern blot and Western blot analyses in RA SMC and monocyte/macrophage-lineage cells. FR- expression and folic acid binding capacity on the cell surface were examined by flow cytometric analysis and 3 H-folic acid binding analysis. Studies of the inhibition of 3 H-MTX uptake in the presence of unlabeled folic acid were performed to investigate the uptake of MTX through FR in RA SMC.
Results. RT-PCR, Northern blot, and Western blot analyses showed that FR- mRNA and protein were expressed selectively in activated monocytes and CD14؉ RA SMC. These cells exhibited folic acid binding capacity. Furthermore, the FR- protein was shown to have folic acid binding capacity. Uptake of 3 H-MTX through RA SMC was significantly inhibited in the presence of unlabeled folic acid.
Conclusion. These results demonstrate that FR- expression is selectively elevated in RA synovial macrophages and suggest that MTX is transported through FR- in RA synovial macrophages. The findings suggest that folate antagonists with higher affinity for FR- would be useful in the treatment of RA.