Cai Ying, Wei Yue-Hua
No. 3 People's Hospital Affiliated to Shanghai Jiao Tong University, School of Medicine, Shanghai 201900, China.
Aging (Albany NY). 2015 Feb;7(2):133-43. doi: 10.18632/aging.100727.
The Protein kinase A (PKA) and Sch9 regulates cell growth as well as lifespan in Saccharomyces cerevisiae. Maf1 is a RNA polymerase III (PolIII) inhibitor that tailors 5S rRNA and tRNA production in response to various environmental cues. Both PKA and Sch9 have been shown to phosphorylate Maf1 in vitro at similar amino acids, suggesting a redundancy in Maf1 regulation. However, here we find that activating PKA by bcy1 deletion cannot replace Sch9 for Maf1 phosphorylation and cytoplasmic retention; instead, such modulation lowers Maf1 protein levels. Consistently, loss of MAF1 or constitutive PKA activity reverses the stress resistance and the extended lifespan of sch9Δ cells. Overexpression of MAF1 partially rescues the extended lifespan of sch9Δ in bcy1Δsch9Δ mutant, suggesting that PKA suppresses sch9Δ longevity at least partly through Maf1 abundance. Constitutive PKA activity also reverses the reduced tRNA synthesis and slow growth of sch9Δ, which, however, is not attributed to Maf1 protein abundance. Therefore, regulation of lifespan and growth can be decoupled. Together, we reveal that lifespan regulation by PKA and Sch9 are mediated by Maf1 through distinct mechanisms.
蛋白激酶A（PKA）和Sch9调节酿酒酵母中的细胞生长以及寿命。Maf1是一种RNA聚合酶III（PolIII）抑制剂，可根据各种环境信号调整5S rRNA和tRNA的产生。PKA和Sch9在体外均已被证明可在相似的氨基酸位点磷酸化Maf1，这表明Maf1的调节存在冗余。然而，我们在此发现，通过缺失bcy1激活PKA不能替代Sch9进行Maf1的磷酸化和细胞质滞留；相反，这种调节会降低Maf1蛋白水平。一致地，MAF1的缺失或组成型PKA活性会逆转sch9Δ细胞的抗逆性和延长的寿命。MAF1的过表达部分挽救了bcy1Δsch9Δ突变体中sch9Δ延长的寿命，这表明PKA至少部分通过Maf1丰度抑制sch9Δ的长寿。组成型PKA活性也会逆转sch9Δ中tRNA合成减少和生长缓慢的情况，然而，这并非归因于Maf1蛋白丰度。因此，寿命和生长的调节可以解耦。我们共同揭示，PKA和Sch9对寿命的调节是由Maf1通过不同机制介导的。
