Multiple, conserved iron-responsive elements in the 3'-untranslated region of transferrin receptor mRNA enhance binding of iron regulatory protein 2.
Synthesis of proteins for iron homeostasis is regulated by specific, combinatorial mRNA/protein interactions between RNA stem-loop structures (iron-responsive elements, IREs) and iron-regulatory proteins (IRP1 and IRP2), controlling either mRNA translation or stability. The transferrin receptor 3'-untranslated region (TfR-3'-UTR) mRNA is unique in having five IREs, linked by AU-rich elements. A C-bulge in the stem of each TfR-IRE folds into an IRE that has low IRP2 binding, whereas a loop/bulge in the stem of the ferritin-IRE allows equivalent IRP1 and IRP2 binding. Effects of multiple IRE interactions with IRP1 and IRP2 were compared between the native TfR-3'-UTR sequence (5xIRE) and RNA with only 3 or 2 IREs. We show 1) equivalent IRP1 and IRP2 binding to multiple TfR-IRE RNAs; 2) increased IRP-dependent nuclease resistance of 5xIRE compared with lower IRE copy-number RNAs; 3) distorted TfR-IRE helix structure within the context of 5xIRE, detected by Cu-(phen)(2) binding/cleavage, that coincides with ferritin-IRE conformation and enhanced IRP2 binding; and 4) variable IRP1 and IRP2 expression in human cells and during development (IRP2-mRNA predominated). Changes in TfR-IRE structure conferred by the full length TfR-3'-UTR mRNA explain in part evolutionary conservation of multiple IRE-RNA, which allows TfR mRNA stabilization and receptor synthesis when IRP activity varies, and ensures iron uptake for cell growth.
Children's Hospital Oakland Research Institute, The Research Institute of the Children's Hospital and Medical Center Oakland, 5700 Martin Luther King, Jr. Way, Oakland, California 94609-1673, USA.
Ronit
R
Erlitzki
Joanne C
JC
Long
Elizabeth C
EC
Theil
D020413:3' Untranslated Regions / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D015152:Blotting, Northern; D017124:Conserved Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics; D017931:DNA Primers; D006801:Humans; D007501:Iron / Q000378:metabolism; D035941:Iron Regulatory Protein 1 / Q000235:genetics; D035942:Iron Regulatory Protein 2 / Q000378:metabolism*; D007700:Kinetics; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D011990:Receptors, Transferrin / Q000235:genetics*
D020413:3' Untranslated Regions; D017931:DNA Primers; D012333:RNA, Messenger; D011990:Receptors, Transferrin; D004247:DNA; D007501:Iron; D035941:Iron Regulatory Protein 1; D035942:Iron Regulatory Protein 2