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

Abstract

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.

Human ribosomal protein L9 is a Bax suppressor that promotes cell survival in yeast

“…Accordingly, it often remains difficult to dissociate ribosomal from extra-ribosomal function for individual ribosomal proteins (Warner & McIntosh, 2009). We previously reported the identification of a number of novel pro-survival sequences by screening mammalian cDNA expression libraries in the yeast Saccharomyces cerevisiae undergoing Bax-mediated cell death (Yang et al, 2006;Clapp et al, 2012a). One of the unreported cDNAs identified in our Bax screen encodes human ribosomal protein L9 (hRPL9).…”

Does the Ingestion of Isoxaflutole Herbicide Affect the Midgut and Salivary Glands of Pentatomidae Predators?

“…While apoptosis is important for the survival of multicellular organisms because it eliminates damaged or infected cells which can interfere with the body's normal function, in excess it may impair the overall functioning of tissues (Portt et al, 2011;Clapp Does the ingestion of isoxaflutole herbicide affect the midgut ... et al, 2012), damaging important processes in digestion and, consequently, P. nigrispinus' role of predation and survival.…”

Contemporary, yeast-based approaches to understanding human genetic variation

“…Despite the anecdotal success of cross-species complementation and the development of humanized yeast as models for studies on Parkinson’s and apoptosis [46,47], systematic approaches have only recently been made practical by advances in clone libraries and vector engineering. For example, the human ORFeome collection is an ongoing project that together with the Mammalian Gene Collection has assembled a clone library of sequence-confirmed human cDNAs for over 90% of genes, including a growing assortment of splice variants [48,49].…”