Identification of prothymosin-α1, the necrosis–apoptosis switch molecule in cortical neuronal cultures

Abstract

We initially identified a nuclear protein, prothymosin-α1 (ProTα), as a key protein inhibiting necrosis by subjecting conditioned media from serum-free cultures of cortical neurons to a few chromatography steps. ProTα inhibited necrosis of cultured neurons by preventing rapid loss of cellular adenosine triphosphate levels by reversing the decreased membrane localization of glucose transporters but caused apoptosis through up-regulation of proapoptotic Bcl2-family proteins. The apoptosis caused by ProTα was further inhibited by growth factors, including brain-derived neurotrophic factor. The ProTα-induced cell death mode switch from necrosis to apoptosis was also reproduced in experimental ischemia-reperfusion culture experiments, although the apoptosis level was markedly reduced, possibly because of the presence of growth factors in the reperfused serum. Knock down of PKCβII expression prevented this cell death mode switch. Collectively, these results suggest that ProTα is an extracellular signal protein that acts as a cell death mode switch and could be a promising candidate for preventing brain strokes with the help of known apoptosis inhibitors.

Prothymosin-α1 prevents necrosis and apoptosis following stroke

“…Therefore, the finding by Shiau et al 17 is unlikely related to the ProTa-induced cell death inhibition in this study. Furthermore, in our previous study, 3 there was no significant difference in the survival activity between ProTa and its mutant lacking C-terminal NLS.…”

“…As macrophages are equipped with receptors recognizing PS, erythrocytes exposing PS at their cell surface will be rapidly recognized, engulfed and degraded. 3 While the requirement for Ca 2 þ entry in the induction of cell death was shown for all these three cell death forms, 2 only ionomycin-induced cell death was found to be dependent on activation of m-calpain, 1 a Ca 2 þ -dependent protease.…”

“…1 Recently, we found that ProTa is released upon necrotic stress and protects cells from neuronal death through activation of a putative G i/o -coupled receptor coupled to phospholipase C and protein kinase Cb II . 3 Letters to the Editor Results represent the incidence of activated caspase 3 (green) and PI staining (red). *Po0.05.…”

“…This finding contrasts with our recent study, in which ProTa was shown to inhibit necrosis by restoring the reduced membrane translocation of glucose transporters under ischemic conditions in a primary culture of cortical neurons, but to cause apoptosis through upregulation of proapoptotic Bax and Bim. 3 However, complete inhibition of cell death was observed when ischemic neurons were cotreated with ProTa and antiapoptotic neurotrophins, the expression levels of which are upregulated in in vivo ischemic models. 15 In fact, the treatment with anti-BDNF or anti-EPO IgG (1 mg each) into the subarachnoid space through a parietal bone, 30 min before MCAO stress, reversed ProTainhibited apoptosis, but not necrosis (Figures 1p and q).…”

“…Since the appearance of PS plays a key role in the recognition of RBCs, 3 we investigated the kinetics of PS exposure on the surface of TG2-null RBCs following addition of ionomycin. The exposure of PS was delayed modestly in TG2-null erythrocytes during Ca 2 þ -induced death (Figure 1b).…”