Genetic Characterization of Bax Inhibitor (BXI1) Function in the Budding Yeast, Saccharomyces (2012 - Present)

Investigator:  Nicanor Austriaco, Providence College

Abstract:  Apoptosis is both an important physiological process and a significant anti-tumor defense mechanism in multicellular organisms. Cells that bypass apoptosis in response to oncogenic stimuli can undergo malignant transformation. Some have even called the ability to evade programmed cell death a “hallmark of cancer”. For the past four years, my laboratory at Providence College has studied BXI1, a novel gene in the budding yeast, Saccharomyces cerervisiae, which is homologous to human Bax Inhibitor-1 (BI-1), a gene whose expression is upregulated in a variety of human cancers. BI-1 has been linked to endoplasmic reticulum function and ER stress-associated apoptosis, though its precise mechanism of action is still not known. We have confirmed that yeast cells lacking BXI1 are more susceptible to ethanol-induced and to glucoseinduced programmed cell death. Moreover, they are not only more sensitive to drugs that induce ER stress, but also have a decreased unfolded protein response as measured with a UPRE-lacZ reporter. Finally, we have discovered that deleting BXI1 diminishes the calcium signaling response in response to the accumulation of unfolded proteins in the ER as measured by a calcineurin-dependent CDRE-lacZ reporter. In toto, our data suggests that the Bxi1p, like its metazoan homologs, is an ER-localized protein that links the unfolded protein response and programmed cell death. This proposal outlines a genetic strategy to illuminate BXI1 function by characterizing a bxi1 ire1 double mutant. IRE1 encodes the ER resident transmembrane kinase and ribonuclease that regulates the yeast UPR.

It will exploit the primary advantage of the yeast system over its mammalian counterpart as a model system for programmed cell death: Yeast cells are amenable to genetic analysis that allows investigators to identify rapidly molecular pathways underlying a biological process. The goal of the project is to determine if BXI1 regulates either the unfolded protein response and/or the calcineurin-dependent calcium response via an IRE1-mediated mechanism. We will test the following hypothesis: BXI1 and IRE1 act in concert to regulate the UPR and calcium response pathways in yeast.