Untangling the Roles of Anti-Apoptosis in Regulating Programmed Cell Death using Humanized Yeast Cells

Genetically programmed cell death (PCD) mechanisms, including apoptosis, are important for the survival of metazoans since it allows, among things, the removal of damaged cells that interfere with normal function. Cell death due to PCD is observed in normal processes such as aging and in a number of pathophysiologies including hypoxia (common causes of heart attacks and strokes) and subsequent tissue reperfusion. Conversely, the loss of normal apoptotic responses is associated with the development of tumors. So far, limited success in preventing unwanted PCD has been reported with current therapeutic approaches despite the fact that inhibitors of key apoptotic inducers such as caspases have been developed. Alternative approaches have focused on mimicking anti-apoptotic processes observed in cells displaying increased resistance to apoptotic stimuli. Hormesis and pre-conditioning are commonly observed cellular strategies where sub-lethal levels of pro-apoptotic stimuli lead to increased resistance to higher or lethal levels of stress. Increased expression of anti-apoptotic sequences is a common mechanism mediating these protective effects. The relevance of the latter observation is exemplified by the observation that transgenic mice overexpressing anti-apoptotic genes show significant reductions in tissue damage following ischemia. Thus strategies aimed at increasing the levels of anti-apoptotic proteins, using gene therapy or cell penetrating recombinant proteins are being evaluated as novel therapeutics to decrease cell death following acute periods of cell death inducing stress. In spite of its functional and therapeutic importance, more is known regarding the processes involved in apoptosis than anti-apoptosis. The genetically tractable yeast Saccharomyces cerevisiae has emerged as an exceptional model to study multiple aspects of PCD including the mitochondrial mediated apoptosis observed in metazoans. To increase our knowledge of the process of anti-apoptosis, we screened a human heart cDNA expression library in yeast cells undergoing PCD due to the conditional expression of a mammalian pro-apoptotic Bax cDNA. Analysis of the multiple Bax suppressors identified revealed several previously known as well as a large number of clones representing potential novel anti-apoptotic sequences. The focus of this review is to report on recent achievements in the use of humanized yeast in genetic screens to identify novel stress-induced PCD suppressors, supporting the use of yeast as a unicellular model organism to elucidate anti-apoptotic and cell survival mechanisms

Somatic loss of PIK3R1 may sensitize breast cancer to inhibitors of the MAPK pathway

Purpose: The PI3K pathway, which includes the PI3K catalytic subunits p110α (PIK3CA) and the PI3K regulatory subunit p85α (PIK3R1), is the most frequently altered pathway in cancer. We encountered a breast cancer patient whose tumor contained a somatic alteration in PIK3R1. Some commercial sequencing platforms suggest that somatic mutations in PIK3R1 may sensitize cancers to drugs that inhibit the mammalian target of rapamycin (mTOR). However, a review of the preclinical and clinical literature did not find evidence substantiating that hypothesis. The purpose of this study was to knock out PIK3R1 in order to determine the optimal therapeutic approach for breast cancers lacking p85α. Methods: We created an isogenic cellular system by knocking out both alleles of the PIK3R1 gene in the non-tumorigenic human breast cell line MCF-10A. Knockout cells were compared with wild-type cells by measuring growth, cellular signaling, and response to drugs. Results: We observed hyperphosphorylation of MEK in these knockouts, which sensitized PIK3R1-null cells to a MEK inhibitor, trametinib. However, they were not sensitized to the mTOR inhibitor, everolimus. Conclusions: Our findings suggest that breast cancers with loss of p85α may not respond to mTOR inhibition, but may be sensitive to MEK inhibition