Hypoxia specifically and reversibly induces the synthesis of ferritin in oligodendrocytes and human oligodendrogliomas.

Neonatal (3 day old) rat oligodendrocytes grown in monolayer culture and exposed to increasingly hypoxic culture conditions showed increased Tran35S-label incorporation into a 22-kDa protein. Reoxygenation of cultures reversed the synthesis of the protein. Amino acid sequencing of a peptide derived from the purified protein revealed a 13 amino acid sequence with complete identity to a human heavy chain subunit of ferritin. This was confirmed by two-dimensional gel electrophoresis, immunoprecipitation, and western blot analysis with antiferritin antibody. In addition, hypoxia was able to induce the synthesis of ferritin in a cell line derived from human oligodendroglioma cells but not in astrocytes or neurons. Actinomycin D (1-15 micrograms/ml) treatment did not block the hypoxic induction of ferritin synthesis, whereas cycloheximide (1 microM) gave complete inhibition. Northern blot analysis showed that ferritin mRNA levels remained unchanged in both control and hypoxic oligodendrocytes and human oligodendroglioma cells, suggesting that the synthesis of ferritin was translationally rather than transcriptionally regulated by hypoxia. In neither oligodendrocytes nor the oligodendroglioma was there any cross-reaction with an antibody to alpha B-crystallin, the 22-kDa protein induced in astrocytes by various types of stress, further suggesting the specificity of hypoxic induction of ferritin in oligodendrocytes.