SPECIFIC PROTEINS SYNTHESIZED IN HUMAN-LYMPHOCYTES DURING HYPOXIA

Hypoxia is a severe stress factor to which man and most other mammalian species are capable of adapting. However, the cellular mechanisms that enable cells to tolerate decreases in ambient oxygen tension are still unknown. We have previously shown that hypoxia induces the synthesis of unique proteins (molecular mass 38, 52, 74, 76 kDa) in human aortic endothelial cells and lymphocytes. In this study we investigated the specificity of hypoxia on the upregulation of these hypoxic stress proteins (HYP) in human peripheral blood lymphocytes and the role of calcium in this response. S-35-methionine pulse-labeling studies using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two-dimensional electrophoresis and autoradiography demonstrated that normobaric hypoxia (4% O2-5% CO2-91% N2) enhanced synthesis of HYP, whereas heat-shock protein synthesis was not affected. Heat shock (42-degrees-C) and cold stress (4-degrees-C) did, however, induce synthesis of heat-shock protein but not HYP. The 38-kDa HYP is the major protein for which synthesis is upregulated by hypoxia. Its isoelectric point (pI) is 3.5-4.0, and it is localized in the cytosol. The 52-kDa HYP has a pI of > 6.5, and it is also localized in the cytosol. The 74- and 76-kDa HYPs appear to be membrane bound. In addition to hypoxia, an increase in calcium concentration in the culture media (25-50 mM) enhanced synthesis of HYP. An ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)/Ca2+ binding complex, when added to blood lymphocytes during exposure to hypoxia, significantly inhibited HYP synthesis. On the basis of the similarity of molecular masses, pI, localization in the cytosol, and Ca2+ dependence of HYP expression, we suggest that HYP 38 and 52 may be isoenzymes of inositol 1,4,5-triphosphate 3-kinase, an enzyme that regulates phosphoinositol turnover and intracellular calcium concentration in cells.