Bax induces activation of the unfolded protein response by inducing HAC1 mRNA splicing in Saccharomyces cerevisiae.

Bax, a multidomain pro-apoptotic Bcl-2 protein, localizes to the endoplasmic reticulum (ER), where it regulates ER stress-induced apoptosis. Adaptation to ER stress depends on the activation of an integrated signal transduction pathway known as the unfolded protein response (UPR). This study examined the death-inducing activity of Bax and its ability to induce UPR signalling pathways in yeast. We observed that inhibition of global translation in yeast cells expressing Bax correlated with Bax-induced cell death. Using a lacZ reporter containing several UPR cis-activating regulatory elements, we also found that Bax directly activated the UPR. Furthermore, this correlated with the splicing of HAC1 mRNA, a gene involved in UPR activation. Bax induced expression of representative UPR target genes such as KAR2, DER1 and GCN4. Finally, we found that Ire1p function is critical for Bax-induced cell death.