High impact information on RFT1

• These studies, done with N(5)-methyltetrahydrofolate (the predominant folate derivative in blood) and folate as substrates, have shown that RFT-1 functions in a Na(+)- and C1(-)-independent manner [1].
• NO is elevated in diabetes, and therefore in the present study the alteration of RFT-1 activity in RPE under conditions of high glucose was investigated [2].
• Nitric oxide (NO) significantly decreases the activity of RFT-1 in cultured RPE cells [2].
• METHODS: Human ARPE-19 cells were incubated in media containing 5 mM glucose plus 40 mM mannitol (control) or 45 mM glucose for varying periods and the activity of RFT-1 was assessed by determining the uptake of [3H]-N(5)-methyltetrahydrofolate (MTF) [2].
• The activity of RFT-1 and expression of mRNA encoding RFT-1 were analyzed also in RPE of streptozotocin-induced diabetic mice [2].

Anatomical context of RFT1

• However, a cocktail of three ITs prepared from RFT11, WT1 and RFT1 gave superior and consistent killing (mean 99.9%; range 99.8-100%) of peripheral blood T cells from six donors [3].
• In RPE, RFT-1 is localized to the apical membrane and is thought to transport folate from RPE to photoreceptor cells [4].
• Treatment of ARPE-19 cells, a human RPE cell line, with Hcy at concentrations higher than 50 microM led to a significant decrease in RFT-1 activity [4].
• The differential polarized distribution of the folate receptor alpha (FR alpha) in the basal membrane and reduced-folate transporter (RFT-1) in the apical membrane was demonstrated previously in the retinal pigment epithelium (RPE) [5].

Associations of RFT1 with chemical compounds

• Reduced-folate transporter-1 (RFT-1) transports reduced-folates, such as N5-methyltetrahydrofolate (MTF), the predominant circulating form of folate [4].
• Regulation of reduced-folate transporter-1 (RFT-1) by homocysteine and identity of transport systems for homocysteine uptake in retinal pigment epithelial (RPE) cells [4].

Physical interactions of RFT1

• The presence of FR alpha in the basal membrane was demonstrable by folate binding and that of RFT-1 in the apical membrane by blockade of folate transport by RFT-1-specific antibody [5].

Other interactions of RFT1

• The immunotoxin prepared from RFT1 (CD5) was the next most efficient toxin and the immunotoxin prepared from RFT8 (CD8) was the least toxic [3].
• CONCLUSIONS: Excess folate levels downregulate RFT-1 in RPE [6].
• Based on this, we hypothesized that folate would enter the RPE via FR alpha and exit the cell via RFT-1 [5].

Analytical, diagnostic and therapeutic context of RFT1

• Laser-scanning confocal microscopy using antibodies specific for RFT-1 demonstrated an apical distribution of this protein in cultured human and intact mouse RPE, which contrasts with the basolateral distribution of FRalpha in these cells [1].
• Semiquantitative RT-PCR demonstrated that the mRNA encoding RFT-1 was decreased significantly in RPE of diabetic mice [2].
• The levels of mRNA encoding RFT-1 were determined by RT-PCR and protein levels by Western blot analysis [2].

References