Translational regulation of ferritin synthesis in rat spleen: Effects of iron and inflammation

Abstract

Translational control of ferritin synthesis was studied in rat spleen, and compared with that for liver, heart and brain, in response to iron and inflammation. Spleen concentrations of total RNA in the ribonucleoprotein (mRNP) fraction was comparable to that for liver, while polyribosomal RNA was less. Both fractions were ten-fold lower in heart and brain. In untreated animals, the mRNP fraction of all tissues had the largest portion of the ferritin mRNA, as determined by slot blot hybridization with 32P-labeled cDNA for the L subunit. Acute treatment with ferric ammonium citrate shifted the spleen ferritin mRNA to the polyribosome fraction. This was also so in liver but not in the heart and brain which took up much less iron. The findings were confirmed by hybridization studies of mRNPs and polyribosomes separated in sucrose gradients. Turpentine-induced inflammation also caused a shift in ferritin mRNA from the mRNP to the polyribosome fraction of spleen and liver, over 12 h. We conclude that as in liver, spleen ferritin synthesis is under translational control by iron, and that both tissues also respond to inflammation by shifting of ferritin mRNA to the polyribosomes.