The Yeast Forkhead Transcription Factors Fkh1 and Fkh2 Regulate Lifespan and Stress Response Together with the Anaphase-Promoting Complex

Abstract

Forkhead box O (FOXO) transcription factors have a conserved function in regulating metazoan lifespan. A key function in this process involves the regulation of the cell cycle and stress responses including free radical scavenging. We employed yeast chronological and replicative lifespan assays, as well as oxidative stress assays, to explore the potential evolutionary conservation of function between the FOXOs and the yeast forkhead box transcription factors FKH1 and FKH2. We report that the deletion of both FKH genes impedes normal lifespan and stress resistance, particularly in stationary phase cells, which are non-responsive to caloric restriction. Conversely, increased expression of the FKHs leads to extended lifespan and improved stress response. Here we show the Anaphase-Promoting Complex (APC) genetically interacts with the Fkh pathway, likely working in a linear pathway under normal conditions, as fkh1Δ fkh2Δ post-mitotic survival is epistatic to that observed in apc5^CA mutants. However, under stress conditions, post-mitotic survival is dramatically impaired in apc5^CA fkh1Δ fkh2Δ, while increased expression of either FKH rescues APC mutant growth defects. This study establishes the FKHs role as evolutionarily conserved regulators of lifespan in yeast and identifies the APC as a novel component of this mechanism under certain conditions, likely through combined regulation of stress response, genomic stability, and cell cycle regulation. Throughout human evolution, one question has remained constant: can we live forever? We are continuously bombarded with products, diets, and exercise regimens that supposedly add years to our life. Is there an alterable program, whether genetic or environmental, that can be tweaked to increase longevity? Medical advances have led to a dramatic increase in average lifespan over the last century. However, the maximum human lifespan has curiously remained constant. Recent research indicates that in many organisms a genetic program exists to control lifespan. The conservation of this genetic lifespan program extends into yeast where numerous longevity genes have been isolated and characterized. Interestingly, mutations that reduce genomic instability, glucose utilization, or oxidative damage extend lifespan in multiple organisms. Here we characterize one such set of genes, the FOXOs. In animals, these genes increase lifespan and suppress tumors, but have yet to be associated with longevity in yeast. By confirming that these genes play a similar role in yeast, we provide a tool to identify downstream factors triggered by the FOXOs, a feat which has not yet been accomplished in other systems. Considering the conservation of these factors, it is likely that our discoveries in yeast will be directly applicable to research into human cancer and aging.