Nitric oxide up-regulates ferritin mRNA level in snail neurons

We cloned and sequenced the ferric ion-binding protein, ferritin, from the nervous system of the pulmonate snail, Helix pomatia. Helix H-ferritin cDNA contains a 519-bp open reading frame (ORF) and predicts an iron-responsive element (IRE) at the 5'-untranslated region (5'-UTR) of the ferritin mRNA. The deduced amino acid sequence revealed 86% similarity with Lymnaea stagn alis ferritin and about 70% similarity with vertebrate H-ferritin. While se creted ferritin isoforms contain a signalling sequence at their N-terminal end, Helix ferritin does not contain this sorting signal indicating that it is restricted to the cytoplasm. The amino acid ligands at positions Glu25, Tyr30, Glu59, Glu60, His63, Glu105 and Gln139 indicate an active ferroxida se site in Helix ferritin. In situ hybridization visualized ferritin mRNA i n neuronal cell bodies but not in the neuropil. In contrast, ferritin-immun oreactive protein was localized in cell bodies and neurites. We further dem onstrate that the NO donors S-nitroso-N-acetylpenicillamine (SNAP), or hydr oxylamine (HA), increase the intracellular ferritin mRNA level by about 55% . In conclusion, our findings show that Helix neurons express an intracellu lar H-ferritin isoform and suggest that iron and NO metabolism are coupled.