Comparison of mammalian cell lines expressing distinct isoforms of divalent metal transporter 1 in a tetracycline-regulated fashion.
DMT1 (divalent metal transporter; also known as SLC11A2, DCT1 or Nramp2) is responsible for ferrous iron uptake in the duodenum, iron exit from endosomes during the transferrin cycle and some transferrin-independent iron uptake in many cells. Four protein isoforms differ by starting in exon 1A or 2 and ending with alternative peptides encoded by mRNA that contains or lacks an IRE (iron responsive element; +/-IRE). We have compared 1A/+IRE and 2/-IRE DMT1 during regulated ectopic expression. HEK-293-F (human embryonic kidney-293-fast growing variant) cells were stably transfected with each construct expressed from a tetracycline-regulated CMV promoter. Reverse transcriptase-PCR analysis showed that construct expression responded to doxycycline. Immunofluorescence staining of cells, using antibodies specific for DMT1 isoforms, confirmed an increase in expression in the plasma membrane and cytosolic vesicles after doxycycline treatment, but with isoform specific distributions. Immunoblotting also revealed stimulation of expression. Nevertheless, both DMT1 isoforms performed similarly in assays for functional properties based on 54Mn2+ and 59Fe2+ uptake. Mn incorporation after doxycycline treatment was approximately 10-fold greater than that of untreated cells, while expression in the untreated cells was approximately 5-fold greater than in the untransfected cells. Uptake of Mn depended on addition of doxycycline, with half maximal response at approximately 1 nM doxycycline. Doxycycline-stimulated Mn and Fe uptake was linear with time for 10 min but not over longer periods. Transport exhibited a pH optimum at approximately 5.5 and dependence on incubation temperature and Mn or Fe concentration. The new cell lines should prove useful for research on metal homoeostasis, toxicological studies and efforts to identify distinctive properties of the isoforms.
Garrick
Michael D
MD
Department of Biochemistry, SUNY, Buffalo, NY, 14214, USA. lgarrick@buffalo.edu
Kuo
Hung-Chieh
HC
Vargas
Farida
F
Singleton
Steven
S
Zhao
Lin
L
Smith
Jaime J
JJ
Paradkar
Prasad
P
Roth
Jerome A
JA
Garrick
Laura M
LM
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004318:Doxycycline / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism; D033862:Iron-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D051379:Mice; D020033:Protein Isoforms; D051381:Rats; D013997:Time Factors; D000099236:Solute Carrier Family 11, Member 2
D000900:Anti-Bacterial Agents; D027682:Cation Transport Proteins; D004318:Doxycycline; D007501:Iron; D033862:Iron-Binding Proteins; D008345:Manganese; D020033:Protein Isoforms; D000099236:Solute Carrier Family 11, Member 2