p73 Induces Apoptosis via PUMA Transactivation and Bax Mitochondrial Translocation

Abstract

p73, an important developmental gene, shares a high sequence homology with p53 and induces both G 1 cell cycle arrest and apoptosis. However, the molecular mechanisms through which p73 induces apoptosis are unclear. We found that p73-induced apoptosis is mediated by PUMA (p53 up-regulated modulator of apoptosis) induction, which, in turn, causes Bax mitochondrial translocation and cytochrome c release. Overexpression of p73 isoforms promotes cell death and bax promoter transactivation in a time-dependent manner. However, the kinetics of apoptosis do not correlate with the increase of Bax protein levels. Instead, p73-induced mitochondrial translocation of Bax is kinetically compatible with the induction of cell death. p73 is localized in the nucleus and remains nuclear during the induction of cell death, indicating that the effect of p73 on Bax translocation is indirect. The ability of p73 to directly transactivate PUMA and the direct effect of PUMA on Bax conformation and mitochondrial relocalization suggest a molecular link between p73 and the mitochondrial apoptotic pathway. Our data therefore indicate that PUMA-mediated Bax mitochondrial translocation, rather than its direct transactivation, correlates with cell death. Finally, human ⌬Np73, an isoform lacking the amino-terminal transactivation domain, inhibits TAp73-induced as well as p53-induced apoptosis. The ⌬Np73 isoforms seem therefore to act as dominant negatives, repressing the PUMA/Bax system and, thus, finely tuning p73-induced apoptosis. Our findings demonstrate that p73 elicits apoptosis via the mitochondrial pathway using PUMA and Bax as mediators.

Transcriptional upregulation of PUMA modulates endoplasmic reticulum calcium pool depletion-induced apoptosis via Bax activation

“…26 Although our results implicate PUMA to reside upstream of Bax during TG-induced apoptosis, the effect of TG on intracellular Bax translocation is not known. Next, we sought to investigate how TG would affect intracellular Bax distribution.…”

“…25 Recent evidence implicates Bax to be a critical mediator of PUMAdependent apoptosis. 11,26 For example, PUMA has been reported to promote Bax translocation from cytosol towards mitochondria, where Bax affects mitochondrial permeability transition and consequent cytochrome c release. 26 Furthermore, overexpression of exogenous PUMA does not induce apoptosis in Bax-deficient cells.…”

“…11,26 For example, PUMA has been reported to promote Bax translocation from cytosol towards mitochondria, where Bax affects mitochondrial permeability transition and consequent cytochrome c release. 26 Furthermore, overexpression of exogenous PUMA does not induce apoptosis in Bax-deficient cells. 11 Together these findings implicate PUMA to reside upstream of Bax and that Bax could be a key downstream effector of PUMA-mediated apoptotic signals.…”

“…11 Together these findings implicate PUMA to reside upstream of Bax and that Bax could be a key downstream effector of PUMA-mediated apoptotic signals. In view of our recent findings that Bax plays an important role during TG-induced apoptosis 25 and the finding that PUMA and Bax appear to be intimately linked, 11,26 we undertook this study to explore the molecular basis of mutual interactions between Bax and PUMA during TG-mediated apoptosis.…”

Apoptosis and disease: a matter of cell fate

“…The translocation of Bax to the mitochondrion, facilitated by Puma, allows the exit of cytochrome c and activation of the apoptosome 6 (Figure 2). In addition, TAp73 induces ER stress mediated by the direct transactivation of Scotin, 7 a p53-inducible gene cloned by David Lane's group.…”