Nuclear Translocation of Glyceraldehyde‐3‐Phosphate Dehydrogenase Isoforms During Neuronal Apoptosis

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Abstract
: Treatment with cytosine β‐d‐arabinoside (AraC ; 300 μM) induced a time‐dependent accumulation of glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) protein in nuclei purified from cultured cerebellar granule cells, with a concomitant degradation of lamin B1, a nuclear membrane protein and a substrate of CPP32/caspase‐3. Moreover, Asp‐Glu‐Val‐Asp‐fluoromethyl ketone (DEVD‐fmk), a CPP32‐selective antagonist, dosedependently suppressed AraC‐induced apoptosis of these neurons. Nuclear accumulation of GAPDH protein was associated with a progressive decrease in the activity of uracil‐DNA glycosylase (UDG), one of the nuclear functions of GAPDH. The nuclear dehydrogenase activity of GAPDH was initially increased after treatment and then decreased parallel to UDG activity. Six GAPDH isoforms were detected in the nuclei of AraC‐treated cells. The more alkaline isoforms, 1‐3, constituted the bulk of the nuclear GAPDH, and the remaining isoforms, 4‐6, were the minor species. Levels of all six isoforms were increased after treatment with AraC for 16 h ; a 4‐h treatment increased levels of only isoforms 4 and 5. Thus, it appears that various GAPDH isoforms are differentially regulated and may have distinct apoptotic roles. Pretreatment with GAPDH antisense oligonucleotide blocked the nuclear translocation of GAPDH isoforms, and the latter process occurred concurrently with a decrease in cytosolic GAPDH isoforms. Sodium nitroprusside‐induced NAD labeling of nuclear GAPDH showed a 60% loss of GAPDH labeling after AraC treatment, suggesting that the active site of GAPDH may be covalently modified, denatured, or improperly folded. The unfolded protein response elicited by denatured GAPDH may contribute to AraC‐induced neuronal death.