Hypoxic up-regulation of triosephosphate isomerase expression in mouse brain capillary endothelial cells

A protein with a molecular mass of 27 kDa was induced by hypoxia in a mouse brain capillary endothelial cell line and identified as triosephosphate isomerase (TPI) by amino-terminal sequencing. Hypoxia caused an elevation of the TPI protein level, concomitant with an increase of the TPI mRNA level. However, hypoxia resulted in an insufficient elevation of TPI activity level, compared to an increase of TPI protein level. When cells expressing the recombinant TPI protein with histidine tag were exposed to hypoxia and the TPI protein was affinity-purified, the catalytic activity (specific activity) of the TPI protein purified from hypoxic cells was substantially lower than that obtained from normoxic cells. In addition, three TPI isoforms with an electrophoretic multiplicity were found; two of the three isoforms were substantially increased in response to the hypoxia, but the level of the most acidic isoform was barely changed. The induction of TPI gene expression by hypoxia was suppressed by (1) a chelator of intracellular Ca2+, (2) a blocker of non-selective cation channels, (3) a blocker of Na+/Ca2+ exchangers, (4) an inhibitor of Ca2+/calmodulin-dependent protein kinases, and (5) an inhibitor of c-jun/AP-1 activation.