Genetic Dissection of Yeast Bax Inhibitor Function in UPR and Calcium Signaling

Austriaco, Nicanor

Abstract

Bax inhibitor-1 (BI-1) is a six-transmembrane containing endoplasmic reticulum (ER) resident protein that provides cytoprotective functions in both animals and plants. It is up regulated in a variety of different human tumors like anaplastic large cell lymphoma, prostate and breast carcinoma, and acute myeloid leukemia. The precise biological function of Bax inhibitor remains unclear. In mammalian cells, several studies conclude that BI-1 may protect cells from ER-stress induced programmed cell death (PCD) by suppressing the signaling of the unfolded protein response (UPR). It also appears to regulate the concentration of Ca2+ in the ER and the cytosol. Despite these published studies, however, it is still not clear whether (and if it is, how) Bax inhibitor's role in the regulation of the UPRis linked to its role in the regulation of cellular calcium levels. Therefore there is a need to answe a pressing question in the field: Does Bax inhibitor regulate cellular calcium levels by regulating the UPR (or vice versa) or does it accomplish these functions independently? To fill this knowledge gap, my laboratory at Providence College initiated now-published studies to investigate the function of the Saccharomyces cerevisiae Bax inhibitor homolog, which we have called BXI1. In this R15 AREA proposal, we describe genetic - primarily epistatic - experiments that build upon our published data to continue to use the power of yeast genetics to characterize the link between the two functions of Bax inhibitor, the regulation of the UPR and the regulation of calcium signaling. We expect our research program to have a positive impact because these genetic studies should help us not only to better understand Bax inhibitor function in programmed cell death and cancer but also to uncover functional links between the UPR and calcium signaling. Since ER stress and the UPR have been implicated in a variety of human diseases we anticipate that our research program should have a positive impact on fields exploring the biological basis for these and other diseases that involve ER stress and the UPR. Finally, in addition to expanding our knowledge base in ER-stress and cancer more generally and in Bax inhibitor's mechanism of action more specifically, funding the research described in this AREA R15 grant proposal will also allow my laboratory and our department here at Providence College to improve our research infrastructure so that we can continue to train and to prepare talented undergraduate students for successful careers in the biomedical sciences.

Public Health Relevance

Bax inhibitor-1 (BI-1) is a gene that has been linked to several human cancers including lymphoma, leukemia, prostate, and breast cancer. It is a gene that is also found in a diversity of animals, plants, and single celled organisms like yeast and bacteria. It is not clear how the malfunctioning of Bax inhibitor leads to tumor formation. However, there is some experimental data that suggests that this gene is involved in a cell's response to stresses that disrupt protein structure and to changes in calcium levels in its environment. It may also be involved in programmed cell death. We would like to discover how Bax inhibitor works by making yeast mutants lacking Bax inhibitor and combinations of key protein stress and calcium regulatory genes. Studying these mutants with the powerful techniques available with yeast genetics should allow us to pinpoint Bax inhibitor's function within the cell. We expect this research to help us better understand how this gene functions normally during programmed cell suicide, and abnormally during cancer, which could in turn lead to better treatment for patients fighting Bax inhibitor related cancers.