Reversible nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase upon serum depletion

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH; E.C. 1.2.1.12) functions a s a glycolytic enzyme within the cytoplasm, but beside its metabolic functi on it is involved in early steps of apoptosis, which trigger the translocat ion of GAPDH into the nucleus. As apoptosis can be induced by serum withdra wal, which otherwise causes cell cycle arrest, the linkage between serum de privation, cell cycle and nuclear transport of GAPDH has been investigated. The intracellular distribution of GAPDH was monitored by confocal laser sc anning microscopy of either immune-stained NIH 3T3 fibroblasts or of cells overexpressing GFP-tagged GAPDH. Serum withdrawal led to an accumulation of GAPDH in the nucleus. In contrast to investigations published so far, this nuclear translocation was a reversible process: cytoplasmic location of en dogenous GAPDH or of GFP-GAPDH could be recovered upon serum addition to ar rested cells and was not inhibited by cycloheximide treatment. In addition, the nuclear import upon serum depletion had no influence neither on the ca talytic activity nor on the expression level of GAPDH. The nuclear export o f GFP-GAPDH in serum-deprived cells could be stimulated by serum or directl y by the growth factors EGF or PDGF. The transport process is not regulated via an initiation of cell cycle arrest, as olomoucine, which causes G(1)-a rrest neither stimulated nuclear accumulation nor prevented nuclear export after serum addition to serum-depleted cultures. Moreover, SV40-transformed 3T3 cells transported GAPDH into the nucleus upon serum deprivation, thoug h the expression of the viral large T-antigen enabled growth factor-indepen dent cell proliferation in this cell line. The recruitment of GAPDH to the cytoplasm upon serum stimulation of arrested cells was not impaired by the inhibition of the MAPK signalling pathway with PD 098059. However, further analysis of the growth factor signalling pathway,vith specific inhibitors r evealed that nuclear export was prevented by LY 294002, an inhibitor of the PI-3 kinase. PI3K links the growth factor signalling pathway with cell dea th via the repression of an apoptotic inducer. Thus, the nuclear accumulati on of GAPDH upon growth factor depletion is a reversible process not relate d directly to cell cycle and likely triggered by survival signals.