The iron transporter DMT1 is expressed in Caco-2 cells and is required for pH-dependent Fe²⁺ uptake across the apical membrane of these cells (Tandy et al. 2000). There are two functional splice variants of DMT1, one containing an iron responsive element (IRE) in the 3Ì untranslated region, the other lacking this IRE (Lee et al. 1998). It has been suggested that the presence of the IRE should permit iron-dependent regulation of DMT1 mRNA. Thus the purpose of our current study was to investigate the effects of non-haem iron on the expression of the DMT1 splice variants.

Caco-2 cells were cultured in DMEM containing 20 % fetal bovine serum for 21 days. Medium was supplemented with 100 µM FeCl₃ for the final 24 h of the culture period. Total RNA was extracted from cells using Trizol reagent and was subjected to RT-PCR using a Roche Lightcycler real-time PCR system and isoform-specific primers. Data are expressed in arbitrary units (a.u.) as means ± S.E.M. of six experiments and have been normalised to GAPDH expression. Statistical analysis utilised Student’s unpaired t test and differences were considered significant at P < 0.05.

Expression of DMT1 (+IRE) and DMT1 (non-IRE) was similar in fully differentiated cells (+IRE, 24.6 ± 4.8 a.u. vs. non-IRE, 18.3 ± 1.4 a.u.). Following 24 h treatment with iron, the +IRE isoform was significantly decreased -73.5 %, 6.5 ± 1.4 a.u., P < 0.001), whereas non-IRE levels remained unchanged (-6.5 %, 17.1 ± 2.3 a.u., P > 0.6). These findings are consistent with the suggested role of the IRE in the regulation of DMT1 by non-haem iron, and agree with our previous findings that DMT1 protein expression in the apical membrane and pH-dependent Fe²⁺ uptake are both decreased in Caco-2 cells cultured in iron-supplemented medium (Tandy et al. 2000).

This work was supported by BBSRC (grant number 90/D13400).