REGULATION OF ENDOTHELIAL-CELL GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE EXPRESSION BY HYPOXIA

Exposure of endothelial cells (EC) to hypoxia results in the increased expression of a distinct set of proteins with molecular masses of 56, 47, 39, 36, and 34 kDa. Their induction appears to be unique to EC an d the stress of decreased oxygen tension. To understand the mechanism( s) and significance of the up-regulation of these proteins we have ide ntified the 36-kDa protein by limited amino-terminal amino acid sequen cing. The 21-amino acid sequence from the bovine protein exhibited 90. 5% identity with the human sequence of the glycolytic enzyme glycerald ehyde-3-phosphate dehydrogenase (GAPDH). Northern blot analysis showed that the time course and extent of EC GAPDH mRNA up-regulation correl ated with the increase in 36-kDa protein synthesis. Nuclear runoff ana lysis demonstrated that this increase in GAPDH expression is regulated , in part, at the transcriptional level; however, the increase in the rate of transcription did not account for the entire mRNA accumulation , suggesting that GAPDH, like other hypoxia-regulated proteins, is pos ttranscriptionally regulated. Subcellular fractionation of hypoxic EC showed up-regulation of the 36-kDa protein in the cytoplasmic fraction and, to a lesser extent, in the nuclear fraction. The up-regulation o f GAPDH in EC may be related to their relative hypoxia tolerance. Alte rnatively, the upregulation of GAPDH in EC during hypoxia may be relat ed to the potential nonglycolytic functions of this enzyme.