Hypoxia induces synthesis of a novel 22-kDa protein in neonatal rat oligodendrocytes.
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 Tran35S-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 Tran35S-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 [alpha-32P]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.(ABSTRACT TRUNCATED AT 250 WORDS)
Qi
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Department of Pediatrics, Joseph P. Kennedy Jr. Mental Retardation Research Center, University of Chicago, Illinois 60637.
Dawson
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D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D015153:Blotting, Western; D002478:Cells, Cultured; D006160:Guanosine Triphosphate / Q000737:chemistry; D006360:Heat-Shock Proteins / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism*; D008970:Molecular Weight; D004676:Myelin Basic Protein / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000302:isolation & purification; D009836:Oligodendroglia / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D006360:Heat-Shock Proteins; D004676:Myelin Basic Protein; D009419:Nerve Tissue Proteins; D006160:Guanosine Triphosphate