Hypoxia up-regulates glyceraldehyde-3-phosphate dehydrogenase in mouse brain capillary endothelial cells: involvement of Na +/Ca 2+ exchanger

Abstract

The molecular regulatory mechanisms and the characterization of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in hypoxia were studied in a mouse brain capillary endothelial cell line, MBEC4. Activation of GAPDH gene expression by hypoxia was suppressed by an intracellular Ca 2+ chelator and inhibited by a non-selective cation channel blocker or a Na +/Ca 2+ exchanger (NCX) blocker. Sequencing of reverse transcription-PCR products demonstrated that MBEC4 expressed an mRNA encoding NCX3, which functions even under cellular ATP-depleted conditions, in addition to mRNAs encoding NCX1 and NCX2. The inhibition of Ca 2+/calmodulin-dependent protein kinases or c-Jun/AP-1 activation caused a significant decrease in the activation of GAPDH mRNA by hypoxia. These results suggest that hypoxia stimulates Ca 2+ influx through non-selective cation channels and causes the reverse operation of the three NCX isoforms, and consequently, increased intracellular Ca 2+ up-regulates GAPDH gene expression through an AP-1-dependent pathway. Furthermore, subcellular fractionation experiments showed that hypoxia increased GAPDH proteins not only in the cytosolic fraction, but also in the nuclear and particulate fractions, in which GAPDH should play no roles in glycolysis. However, the GAPDH activity did not rise in proportion to the increase of GAPDH protein by hypoxia even in the cytosolic fraction. These results suggest that not all hypoxia-induced GAPDH molecules contribute to glycolysis.