Iron differentially stimulates translation of mitochondrial aconitase and ferritin mRNAs in mammalian cells. Implications for iron regulatory proteins as regulators of mitochondrial citrate utilization.
Utilization of mRNAs containing iron-responsive elements (IREs) is modulated by iron-regulated RNA-binding proteins (iron regulatory proteins). We examine herein whether iron differentially affects translation of ferritin and mitochondrial aconitase (m-Acon) mRNAs because they contain a similar but not identical IRE in their 5'-untranslated regions. First, we demonstrate that m-Acon synthesis is iron-regulated in mammalian cells. In HL-60 cells, hemin (an iron source) stimulated m-Acon synthesis 3-fold after 4 h compared with cells treated with an iron chelator (Desferal). Furthermore, hemin stimulated m-Acon synthesis 2-4-fold in several cell lines. Second, we show that iron modulates the polysomal association of m-Acon mRNA. We observed m-Acon mRNA in both ribonucleoprotein and polyribosomal fractions of HL-60 cells. Hemin significantly increased the polyribosomal association and decreased the ribonucleoprotein abundance of m-Acon mRNA in HL-60 cells. Third, our results indicate that iron differentially regulates translation of m-Acon and ferritin mRNAs. A dose response to hemin in HL-60 cells elicited a 2-2.4-fold increase in m-Acon synthesis within 5 h compared with untreated cells, whereas ferritin synthesis was stimulated 20-100-fold. We conclude that iron modulates m-Acon synthesis at the translational level and that iron regulatory proteins appear to differentially affect translation of IRE-containing mRNAs.[1]References
- Iron differentially stimulates translation of mitochondrial aconitase and ferritin mRNAs in mammalian cells. Implications for iron regulatory proteins as regulators of mitochondrial citrate utilization. Schalinske, K.L., Chen, O.S., Eisenstein, R.S. J. Biol. Chem. (1998) [Pubmed]
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