A
protein with a molecular mass of 27kDa 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 Ca(2+), (2) a blocker of non-selective
cation channels, (3) a blocker of Na(+)/Ca(2+) exchangers, (4) an inhibitor of Ca(2+)/
calmodulin-dependent protein kinases, and (5) an inhibitor of c-jun/AP-1 activation.