HYPOXIA SPECIFICALLY AND REVERSIBLY INDUCES THE SYNTHESIS OF FERRITININ OLIGODENDROCYTES AND HUMAN OLIGODENDROGLIOMAS

Neonatal (3 day old) rat oligodendrocytes grown in monolayer culture a nd exposed to increasingly hypoxic culture conditions showed increased Tran(35)S-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 ac id sequence with complete identity to a human heavy chain subunit of f erritin. This was confirmed by two-dimensional gel electrophoresis, im munoprecipitation, and western blot analysis with antiferritin antibod y. In addition, hypoxia was able to induce the synthesis of ferritin i n a cell line derived from human oligodendroglioma cells but not in as trocytes or neurons. Actinomycin D (1-15 mu g/ml) treatment did not bl ock the hypoxic induction of ferritin synthesis, whereas cycloheximide (1 mu M) gave complete inhibition. Northern blot analysis showed that ferritin mRNA levels remained unchanged in both control and hypoxic o ligodendrocytes and human oligodendroglioma cells, suggesting that the synthesis of ferritin was translationally rather than transcriptional ly regulated by hypoxia. In neither oligodendrocytes nor the oligodend roglioma was there any crossreaction with an antibody to alpha B-cryst allin, the 22-kDa protein induced in astrocytes by various types of st ress, further suggesting the specificity of hypoxic induction of ferri tin in oligodendrocytes.