The acute box cis-element in human heavy ferritin mRNA 5'-untranslated region is a unique translation enhancer that binds poly(C)-binding proteins.

Abstract

Intracellular levels of the light (L) and heavy (H) ferritin subunits are regulated by iron at the level of message translation via a modulated interaction between the iron regulatory proteins (IRP1 and IRP2) and a 5'-untranslated region. Iron-responsive element (IRE). Here we show that iron and interleukin-1beta (IL-1beta) act synergistically to increase H- and L-ferritin expression in hepatoma cells. A GC-rich cis-element, the acute box (AB), located downstream of the IRE in the H-ferritin mRNA 5'-untranslated region, conferred a substantial increase in basal and IL-1beta-stimulated translation over a similar time course to the induction of endogenous ferritin. A scrambled version of the AB was unresponsive to IL-1. Targeted mutation of the AB altered translation; reverse orientation and a deletion of the AB abolished the wild-type stem-loop structure and abrogated translational enhancement, whereas a conservative structural mutant had little effect. Labeled AB transcripts formed specific complexes with hepatoma cell extracts that contained the poly(C)-binding proteins, iso-alphaCP1 and -alphaCP2, which have well defined roles as translation regulators. Iron influx increased the association of alphaCP1 with ferritin mRNA and decreased the alphaCP2-ferritin mRNA interaction, whereas IL-1beta reduced the association of alphaCP1 and alphaCP2 with H-ferritin mRNA. In summary, the H-ferritin mRNA AB is a key cis-acting translation enhancer that augments H-subunit expression in Hep3B and HepG2 hepatoma cells, in concert with the IRE. The regulated association of H-ferritin mRNA with the poly(C)-binding proteins suggests a novel role for these proteins in ferritin translation and iron homeostasis in human liver.

• Authors: Andrew M Thomson, Catherine M Cahill, Hyun-Hee Cho, Kristin D Kassachau, Michael R Epis, Kenneth R Bridges, Peter J Leedman, Jack T Rogers
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 280 Issue 34 Pg. 30032-45 (Aug 26 2005) ISSN: 0021-9258 [Print] United States
• PMID: 15967798 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• 5' Untranslated Regions
• Interleukin-1
• Pregnancy Proteins
• RNA, Messenger
• Recombinant Proteins
• Poly C
• Ferritins
• Iron
• FTH1 protein, human
• Oxidoreductases
• Luciferases
• Chloramphenicol O-Acetyltransferase

Topics

• 5' Untranslated Regions
• Base Sequence
• Carcinoma, Hepatocellular (metabolism)
• Cell Line, Tumor
• Chloramphenicol O-Acetyltransferase (metabolism)
• Cytoplasm (metabolism)
• Dose-Response Relationship, Drug
• Enhancer Elements, Genetic
• Ferritins (chemistry, metabolism)
• Genes, Reporter
• Humans
• Immunoblotting
• Immunoprecipitation
• Interleukin-1 (metabolism)
• Iron (chemistry, metabolism)
• Liver (metabolism)
• Luciferases (metabolism)
• Molecular Sequence Data
• Oxidoreductases
• Plasmids (metabolism)
• Poly C (chemistry)
• Pregnancy Proteins (metabolism)
• Protein Binding
• Protein Biosynthesis
• Protein Structure, Secondary
• Protein Structure, Tertiary
• RNA, Messenger (metabolism)
• Recombinant Proteins (chemistry)
• Reverse Transcriptase Polymerase Chain Reaction
• Time Factors
• Transfection
• Ultraviolet Rays