NONNEURONAL ENOLASE IS AN ENDOTHELIAL HYPOXIC STRESS PROTEIN

The hypoxia-associated proteins (HAPs) are five cell associated stress proteins (M(r) 34, 36, 39, 47, and 57) upregulated in cultured vascul ar endothelial cells (EC) exposed to hypoxia, While hypoxic exposure o f other cell types induces heat shock and glucose-regulated proteins, EC preferentially up-regulate HAPs. In order to identify the 47 kDa HA P, protein from hypoxic bovine EC lysates was isolated, digested with trypsin, and sequenced. Significant identity was found with enolase, a glycolytic enzyme. Western analyses confirmed that non-neuronal enola se (NNE) is up-regulated in hypoxic EC. Western analysis of subcellula r fractions localized NNE primarily to the cytoplasm and confirmed tha t it was up-regulated 2.3-fold by hypoxia. Interestingly, NNE also app eared in the nuclear fraction of EC but was unchanged by hypoxia. Nort hern analyses revealed that NNE mRNA hypoxic up-regulation began at 1- 2 h, peaked at 18 h, persisted for 48 h, and returned to base line aft er return to 21% O-2 for 24 h, Hypoxia maximally up-regulated NNE mRNA levels 3.4-fold, While hypoxic up-regulation of NNE may have a protec tive effect by augmenting anaerobic metabolism, we speculate that enol ase may contribute to EC hypoxia tolerance through one or more of its nonglycolytic functions.