Mutations in theRAD27andSGS1genes differentially affect the chronological and replicative lifespan of yeast cells growing on glucose and glycerol

Abstract

The Sgs1 protein from Saccharomyces cerevisiae is a member of the RecQ helicases. Defects in RecQ helicases result in premature aging phenotypes in both yeasts and humans, which appear to be promoted by replicative stress. Yeast rad27 mutants also suffer from premature aging. As the human Rad27p and Sgs1p homologs interact, a similar interaction between the yeast proteins could be important for promoting longevity in S. cerevisiae. We tested the contribution of a potential interaction between Rad27p and Sgs1p to longevity by analyzing lifespan and parameters associated with longevity in rad27 and sgs1 mutants. The carbon source supporting growth also modulated longevity as evaluated by replicative and chronological lifespan measurements. Growth on glycerol promoted chronological lifespan, while maximum replicative lifespan was obtained with glucose-supported growth. In comparison to the individual mutants, the sgs1 rad27 double mutant displayed a shortened replicative lifespan and was also more sensitive to DNA-damaging agents. In addition to promoting replicative lifespan, the activity of Rad27p was critical for achieving full chronological lifespan. The rad27 mutants exhibited increased oxidative stress levels along with an elevated spontaneous mutation rate. Removal of Sgs1p activity additionally increased the oxidative stress and spontaneous mutation rate in rad27 mutants without affecting the chronological lifespan.

DNA replication stress-induced loss of reproductive capacity inS. cerevisiaeand its inhibition by caloric restriction

“…2A), consistent with prior reports that rad27Δ cells lose reproductive capacity at an earlier time point in CLS experiments in unbuffered medium. 26,27 In contrast, rad27Δ cells cultured in buffered SC medium prepared with 10% glucose exhibited a substantially shorter reproductive capacity compared with wild-type cells at day 7, and the reproductive capacity of rad27Δ cells was reduced cells undergoing programmed cell death marked by DNA degradation that resulted in cells with a sub G 1 content of DNA (Fig. 3B).…”

“…28 Although sgs1Δ cells have been reported to exhibit a shorter replicative lifespan (RLS) 29 and CLS, 30 it has also been reported that sgs1Δ cells do not exhibit a shorter CLS. 26,31 sgs1Δ cells more frequently undergo adaptive regrowth in stationary phase, which complicates CLS measurements. For example, in early stationary phase, sgs1Δ cells initially exhibit a substantial reduction in reproductive capacity compared with wild-type cells, but at later time points differences in reproductive capacity are masked by adaptive regrowth.…”

“…25 Therefore, inactivation of RAD27 causes replication stress, which likely contributes to the shorter CLS detected in rad27Δ compared with wild-type cells. 26,27 To determine whether glucose signaling enhances replication stress induced in stationary phase cells in the absence of HU, we compared the reproductive capacity of stationary phase wild-type and rad27Δ cells cultured in buffered SC medium that initially contained either 2 or 10% glucose.…”

Cryptococcus neoformans constitutes an ideal model organism to unravel the contribution of cellular aging to the virulence of chronic infections

“…From genetically manipulated S. cerevisiae strains, large numbers of senescent cells can also be isolated [18–20]. From several large scale studies, it has been concluded that replicative and chronological aging are linked [21,22], but other studies in S. cerevisiae involving mutants also suggest that the two are controlled independently [2,23–25]. …”

Maintenance of Yeast Genome Integrity by RecQ Family DNA Helicases

“…A contribution of Sgs1 to BER is less likely. Sgs1 functionally interacts with the 5 flap-endonuclease Rad27, which besides its well-understood function in Okazaki fragment maturation also plays a role in long-patch BER [202,209]. Sgs1 also functionally interacts with the ROS-scavenging enzyme Tsa1, which suppresses genome rearrangements and is required for normal growth in the absence of Sgs1 [210].…”