Role of BI-1 Protein in Breast Cancer Apoptosis
Creators: name: University Of California Office Of The President
Publisher: name: University of California Office of the President
publisherIdentifier: https://ror.org/00dmfq477
publisherIdentifierScheme: ROR
Year: 2024

description: Defects in apoptotic (programmed cell death) mechanisms play an important role in pathogenesis and progression of breast cancer. However, relatively little is known about which apoptosis-regulating genes are expressed in tumors of mammary epithelial origin. The Reed laboratory at The Burnham Institute has recently discovered a novel anti-apoptotic protein, called BI-1 (Bax Inhibitor-1), which appears to regulate a cell death pathway linked to stress in the endoplasmic reticulum. The endoplasmic reticulum is a network of tubules, vesicles and sacs that are interconnected inside of the cell's cytoplasm. One key function of the endoplasmic reticulum is to store calcium. The endoplasmic reticulum is known to trigger an apoptosis pathway that may be relevant to a variety of diseases, including breast cancer. BI-1 is an endoplasmic reticulum-resident protein that suppresses apoptosis induction by specific types of stimuli, predominantly linked to endoplasmic reticulum-stress situations. Indeed, endoplasmic reticulum stress results in caspase activation and apoptosis, both of which are blocked by BI-1 over-expression. Elevated BI-1 expression also inhibits calcium efflux from the endoplasmic reticulum. We have evidence indicating that BI-1 expression is elevated in a significant proportion of breast cancer cell lines, and we also observed that hypoxia (low tumor oxygen concentration) is a potent inducer of BI-1 expression. 
 
 
 
 
 
 
 
 We will test the hypothesis that BI-1 is an important regulator of cell death pathways linked to endoplasmic reticulum stress. We will: (i) dissect the point in apoptotic pathways where BI-1 blocks cell death induced by endoplasmic reticulum stress; (ii) determine the effects of BI-1 on endoplasmic reticulum -dependent functions such as calcium and protein sequestration; (iii) define the role of BI-1 in hypoxia; (iv) determine the role of BI-1 in breast cancer oncogenesis using mouse xenograft models; and (v) characterize the expression of BI-1 protein in human breast cancer clinical samples. Transmission electron microscopy will be used to evaluate the ultrastructure of the endoplasmic reticulum and Golgi in cells with varying amounts of BI-1. Caspase activation and activity we will be performed by immunoblotting and using selective flurogenic peptide substrates, respectively. Cell death will be monitored by propidium dye uptake/Annexin V assay. Intracellular calcium concentrations will be monitored by video time-lapse "deconvolution microscopy" using a calcium -sensitive fluorescent dye, such as Fura-2. Fluorescently-tagged endoplasmic reticulum luminal proteins will be employed for determining whether proteins are release into the cytosol. Hypoxia-induced increases in BI-1 will be determined by using nuclear "run-on" assays. Immunostaining will be used to analyze expression of BI-1 in breast cancer specimens.
 
 
 
 
 
 
 
 By using BI-1 as a "window" into this poorly understood endoplasmic reticulum-apoptosis pathway, we eventually hope to devise strategies for bypassing roadblocks to cell death that commonly arise in cancers. From a therapy perspective, our research could assist in devising strategies to allow cancers to become more sensitive to chemotherapy. Finally, BI-1 expression could be useful a predictive "biomarker" for cancer progression or therapy options for patients.