Proteostasis, the process of balancing protein production with protein degradation is vital to normal cell function. Defects within the mechanisms that control proteostasis lead to increased content of a specialized insoluble protein fraction that forms dense aggregates within the cell. We have previously implicated the S. cerevisiae metacaspase Yca1 as an active participant in maintaining proteostasis, whereby Yca1 acts to limit aggregate content. Here, we further characterized the proteostasis role of Yca1 by conducting proteomic analysis of the insoluble protein fraction in wildtype and yca1 knockout cells, under normal and heat stressed conditions. Our findings suggest that the composition of insoluble protein fraction is non-specific and comprises a wide array of protein species rather than a limited repertoire of aggregate susceptible proteins or peptides. Interestingly, the loss of Yca1 led to a significant decrease of proteins that control ribosome biogenesis and protein synthesis within the insoluble fraction, indicating that the cell may invoke a compensatory mechanism to limit protein production during stress, a feature dependent on Yca1 activity. Finally, we noted that protein degradation factors such as Cdc48 co-localize with Yca1 to the insoluble fraction, supporting the hypothesis that Yca1 may act primarily to dissolve or reduce accumulated aggregates.
"On the other hand, the ability of metacaspase to both promote and antagonize different cell cycle checkpoints has been demonstrated, representing an early form of the proliferation/ differentiation regulatory activity exhibited by metazoan caspases . YCA1 also contributes to the fitness and adaptability of growing yeast through clearance of insoluble protein aggregates   and has been implicated in the regulation of antioxidant status and mitochondrial respiration   . The concept of non-apoptotic roles of metacaspase has been expanded in our previous work in which we have performed a comparative analysis between wild type and Δyca1 cells using combined proteomic and metabolomic approach. "
[Show abstract][Hide abstract] ABSTRACT: The two metacaspases PaMCA1 and PaMCA2 of the fungal aging model Podospora anserina have previously been demonstrated to be involved in the control of programmed cell death (PCD) and lifespan. In order to identify specific pathways and components which are controlled by the activity of these enzymes, we set out to characterize them further. Heterologous overexpression in E. coli of the two metacaspase genes resulted in the production of proteins which aggregate and form inclusion bodies from which the active protein has been recovered via refolding in appropriate buffers. The renaturated proteins are characterized by an arginine-specific activity and are active in caspase-like self-maturation leading to the generation of characteristic small protein fragments. Both activities are dependent on the presence of calcium. Incubation of the two metacaspases with recombinant poly(ADP-ribose) polymerase (PARP), a known substrate of mammalian caspases, let to the identification of PARP as a substrate of the two P. anserina proteases. Using double mutants in which PaParp is overexpressed and PaMca1 is either overexpressed or deleted, we provide evidence for in vivo degradation of PaPARP by PaMCA1. These results support the idea that the substrate profiles of caspases and metacaspases are at least partially overlapping. Moreover, they link PCD and DNA maintenance in the complex network of molecular pathways involved in aging and lifespan control.
[Show abstract][Hide abstract] ABSTRACT: How do cells age and die? For the past 20 years, the budding yeast, Saccharomyces cerevisiae, has been used as a model organism to uncover the genes that regulate lifespan and cell death. More recently, investigators have begun to interrogate the other yeasts, the fission yeast, Schizosaccharomyces pombe, and the human fungal pathogen, Candida albicans, to determine if similar longevity and cell death pathways exist in these organisms. After summarizing the longevity and cell death phenotypes in S. cerevisiae, this mini-review surveys the progress made in the study of both aging and programed cell death (PCD) in the yeast models, with a focus on the biology of S. pombe and C. albicans. Particular emphasis is placed on the similarities and differences between the two types of aging, replicative aging, and chronological aging, and between the three types of cell death, intrinsic apoptosis, autophagic cell death, and regulated necrosis, found in these yeasts. The development of the additional microbial models for aging and PCD in the other yeasts may help further elucidate the mechanisms of longevity and cell death regulation in eukaryotes.
FEMS Yeast Research 10/2013; 14(1). DOI:10.1111/1567-1364.12113 · 2.82 Impact Factor
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