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

Abstract

PUMA, a key mediator of p53-induced apoptosis, is a BH3-only domain proapoptotic protein that localizes to mitochondria and interacts with antiapoptotic Bcl-2 and Bcl-X L . Recent evidence implicates Bax to be an important mediator of PUMA-activated apoptotic signals. We have previously demonstrated that Bax deficiency significantly affects thapsigargin (TG)-mediated endoplasmic reticulum calcium pool depletion-induced apoptosis. We now present evidence that TG upregulates PUMA expression and that although Baxdeficient cells exhibit resistance to TG, Bax deficiency does not attenuate TG upregulation of PUMA expression. Furthermore, TG transcriptionally upregulates PUMA expression in a p53-independent manner and that PUMA-deficient cells are more resistant to undergo TG-induced apoptosis than the PUMA-proficient counterparts. Thus, our results demonstrate that TG engages PUMA and Bax for full transduction of apoptotic signals and both PUMA and Bax appear to exist in the same TG-activated apoptotic pathway in which PUMA may reside upstream of Bax.

Endoplasmic reticulum stress-induced apoptosis requires bax for commitment and Apaf-1 for execution in primary neurons

“…4 Our results showing the transcriptional upregulation of Puma following ER stress are in agreement with other studies. 15,36 Although Puma was initially identified as a p53-regulated BH3-only gene, p53-deficient neurons were still able to upregulate Puma and did not show any resistance to ER stress-induced apoptosis (Supplementary Figure 3). Thus, whereas transcription factors c-Jun and p53 do not appear to be important for ER stress-induced DP5 and Puma upregulation, this upregulation could be mediated by alternative transcription factors such as FOXO3a, which is known to be activated in neurons in response to other apoptotic stimuli.…”

Cellular response to endoplasmic reticulum stress: a matter of life or death

“…145,146 Conversely, ER stress itself can upregulate or otherwise activate several 'BH3-only' proapoptotic members of the Bcl-2 family, including Bim, 147 BIK, [148][149][150][151] and PUMA. 152,153 Therefore, efferent signaling from the stressed ER can engage the Bcl-2 death machinery directly.…”

The endoplasmic reticulum in apoptosis and autophagy: role of the BCL-2 protein family

“…Ectopic expression of ER-targeted BIM also induced apoptosis, which was inhibited by suppression of caspase-12 (Morishima et al, 2004). Finally, PUMA and NOXA are also upregulated during ER stress, both have been found at the ER, and both play a role in ER Ca 2 þ release (Reimertz et al, 2003;Luo et al, 2005;Rao et al, 2006;Shibue et al, 2006;Kieran et al, 2007;Nickson et al, 2007;Hassan et al, 2008). PUMAmediated apoptosis has been linked to activation of caspase-12 and is reduced by caspase-12 knockdown or deficiency (Shibue et al, 2006).…”

“…In addition, BAX/BAK doubleknockout (DKO) cells are resistant to ER stress-induced apoptosis, a phenotype that is only partially reversed by reintroduction of mitochondria-targeted BAX/BAK . As well, a number of BH3-only proteins, including BAD (Elyaman et al, 2002), PUMA (Luo et al, 2005), NOXA , BID (Gao et al, 2005;Upton et al, 2008) and BIM Puthalakath et al, 2007;Szegezdi et al, 2008) have been linked to ER stress-initiated cell death.…”

“…For example, ERrestricted BCL-2 and BCL-xL can inhibit apoptosis initiated by diverse stimuli (Hacki et al, 2000;Germain et al, 2005;Mathai et al, 2005;Bhatt et al, 2008) and BAX/BAK (Nutt et al, 2002b;Zong et al, 2003;Chami et al, 2004), as well as a number of BH3-only proteins (Elyaman et al, 2002;Gao et al, 2005;Luo et al, 2005;Armstrong et al, 2007;Hetz et al, 2007;Puthalakath et al, 2007;Szegezdi et al, 2008;Upton et al, 2008) can promote apoptosis through their activity at the ER. BCL-2 family proteins at the ER regulate apoptosis through both direct modulation of signaling pathways leading to caspase activation and through the modulation of ER Ca 2 þ signaling (Oakes et al, 2006;Rong and Distelhorst, 2008).…”