Puma (p53 up-regulated modulator of apoptosis) is a BH3-only protein member of the Bcl-2 family that controls apoptosis by regulating the release of pro-apoptotic factors from mitochondria. Previously, we reported that sodium arsenite (NaAsO2) induces Puma-dependent apoptosis in cortical neurons in a p53-independent manner. The following evidence shows that p53-independent Puma activation by NaAsO2 is mediated by the p53-related protein TAp73: (i) NaAsO2 causes TAp73 alpha accumulation and increases p53-independent expression of p73 target genes; (ii) two p53 response elements in the Puma promoter are required for NaAsO2-mediated activation of a Puma reporter construct; (iii) expression of the inhibitory Delta Np73 alpha and Delta Np73 beta isoforms decreases NaAsO2-mediated induction of Puma and other p53-family target genes in a p53-null background; (iv) Delta Np73 alpha and Delta Np73 beta expression protects the neurons from NaAsO2-dependent apoptosis. Interestingly, although ER stressors also induce p53-independent, Puma-dependent apoptosis, they do not increase TAp73 expression while NaAsO2 does not induce notable endoplasmic reticulum (ER) stress. In contrast, DNA damaging agents, okadaic acid, and H2O2 all induce apoptosis in a strictly Puma- and p53-dependent manner. Hence, the pivotal position of Puma as mediator of apoptosis in cortical neurons is because of the availability of at least three independent signalling pathways that ensure its activation.
- ER stress
- sodium arsenite