Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148, USA.
G3 (Bethesda). 2021 Jul 14;11(7). doi: 10.1093/g3journal/jkab134.
Nutrient sensing is important for cell growth, aging, and longevity. In Saccharomyces cerevisiae, Sch9, an AGC-family protein kinase, is a major nutrient sensing kinase homologous to mammalian Akt and S6 kinase. Sch9 integrates environmental cues with cell growth by functioning downstream of TORC1 and in parallel with the Ras/PKA pathway. Mutations in SCH9 lead to reduced cell growth in dextrose medium; however, reports on the ability of sch9Δ mutants to utilize non-fermentable carbon sources are inconsistent. Here, we show that sch9Δ mutant strains cannot grow on non-fermentable carbon sources and rapidly accumulate suppressor mutations, which reverse growth defects of sch9Δ mutants. sch9Δ induces gene expression of three transcription factors required for utilization of non-fermentable carbon sources, Cat8, Adr1, and Hap4, while sch9Δ suppressor mutations, termed sns1 and sns2, strongly decrease the gene expression of those transcription factors. Despite the genetic suppression interactions, both sch9Δ and sns1 (or sns2) homozygous mutants have severe defects in meiosis. By screening mutants defective in sporulation, we identified additional sch9Δ suppressor mutants with mutations in GPB1, GPB2, and MCK1. Using library complementation and genetic analysis, we identified SNS1 and SNS2 to be IRA2 and IRA1, respectively. Furthermore, we discovered that lifespan extension in sch9Δ mutants is dependent on IRA2 and that PKA inactivation greatly increases basal expression of CAT8, ADR1, and HAP4. Our results demonstrate that sch9Δ leads to complete loss of growth on non-fermentable carbon sources and mutations in MCK1 or genes encoding negative regulators of the Ras/PKA pathway reverse sch9Δ mutant phenotypes.
营养感应对于细胞生长、衰老和长寿非常重要。在酿酒酵母中，Sch9 是一种 AGC 家族蛋白激酶，是与哺乳动物 Akt 和 S6 激酶同源的主要营养感应激酶。Sch9 通过作为 TORC1 的下游分子和与 Ras/PKA 途径平行发挥作用，将环境线索与细胞生长整合在一起。SCH9 的突变导致在葡萄糖培养基中细胞生长减少；然而，关于 sch9Δ 突变体利用非发酵碳源的能力的报告不一致。在这里，我们表明 sch9Δ 突变株不能在非发酵碳源上生长，并且迅速积累抑制突变，这些抑制突变逆转了 sch9Δ 突变体的生长缺陷。sch9Δ 诱导非发酵碳源利用所需的三个转录因子的基因表达，Cat8、Adr1 和 Hap4，而 sch9Δ 抑制突变体，称为 sns1 和 sns2，强烈降低这些转录因子的基因表达。尽管存在遗传抑制相互作用，但 sch9Δ 和 sns1（或 sns2）纯合突变体在减数分裂中都有严重缺陷。通过筛选孢子形成缺陷的突变体，我们鉴定出了其他在 GPB1、GPB2 和 MCK1 中具有突变的 sch9Δ 抑制突变体。通过文库互补和遗传分析，我们鉴定出 SNS1 和 SNS2 分别为 IRA2 和 IRA1。此外，我们发现 IRA2 在 sch9Δ 突变体中的寿命延长中起作用，并且 PKA 失活大大增加了 CAT8、ADR1 和 HAP4 的基础表达。我们的结果表明，sch9Δ 导致在非发酵碳源上完全丧失生长能力，并且 MCK1 或编码 Ras/PKA 途径负调节剂的基因的突变逆转了 sch9Δ 突变体的表型。
