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.
Erlitzki
Ronit
R
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.
Long
Joanne C
JC
Theil
Elizabeth C
EC
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