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Hypoxia Induces Synthesis of a Novel 22‐kDa Protein in Neonatal Rat Oligodendrocytes
Author(s) -
Qi Yan,
Dawson Glyn
Publication year - 1992
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1992.tb11002.x
Subject(s) - biology , blot , calpain , g protein , oligodendrocyte , biochemistry , heat shock protein , cell fractionation , leupeptin , cytoskeleton , microbiology and biotechnology , myelin basic protein , immunoprecipitation , protein subunit , protease , myelin , cell , signal transduction , enzyme , neuroscience , gene , central nervous system
Neonatal (3‐day‐old) rat oligodendrocytes grown in monolayer culture and exposed to increasingly hypoxic culture conditions showed a dramatic reduction in myelin basic protein synthesis but no significant inhibition of Tran 35 S‐label incorporation into oligodendrocyte proteins in general or into structural proteins such as actin. However, there was a dramatic increase in synthesis of a novel 22‐kDa protein. Reoxygenation of cultures reversed the synthesis of the 22‐kDa protein, and thiol and calpain protease inhibitors (EP‐459 and leupeptin) did not prevent synthesis of the protein, suggesting that it did not result from proteolysis. The 22‐kDa protein (which we have called hypoxin ) was coimmunoprecipitated by a polyclonal antibody to actin but did not react with the anti‐actin antibody on western blots. The synthesis of hypoxin accounted for up to 50% of the Tran 35 S‐label incorporated into immunoprecipitated protein, suggesting that it plays a major role in the cell's response to hypoxia. Subcellular fractionation revealed that the 22‐kDa protein was largely associated with the cytosolic/cytoskeletal compartment. However, it is unlikely to be one of the cytoskeleton‐associated Rho or Rac low‐molecular‐mass (20–24 kDa) GTP‐binding proteins because it did not bind [α‐ 32 P]GTP on western blots. Oligodendrocytes did not synthesize a 22‐kDa protein in response to heat shock but did synthesize the typical 70‐ and 90‐kDa heat‐shock proteins. The novel aspects of this protein were further emphasized by the fact that increased synthesis of this 22‐kDa protein was not detected in cultured embryonic chick neurons, rat astrocytes, mouse, rat, or human gliomas, and oligodendrogliomas subjected to similar periods of hypoxia. Thus the induction of the hypoxin appears specific for nontransformed oligodendrocytes subjected to hypoxic injury.