Conrad Michaela, Kankipati Harish Nag, Kimpe Marlies, Van Zeebroeck Griet, Zhang Zhiqiang, Thevelein Johan M
Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, B-3001 KU Leuven, Belgium.
Center for Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium.
FEMS Yeast Res. 2017 Aug 1;17(5). doi: 10.1093/femsyr/fox048.
Two nutrient-controlled signalling pathways, the PKA and TOR pathway, play a major role in nutrient regulation of growth as well as growth-correlated properties in yeast. The relationship between the two pathways is not well understood. We have used Gap1 and Pho84 transceptor-mediated activation of trehalase and phosphorylation of fragmented Sch9 as a read-out for rapid nutrient activation of PKA or TORC1, respectively. We have identified conditions in which L-citrulline-induced activation of Sch9 phosphorylation is compromised, but not activation of trehalase: addition of the TORC1 inhibitor, rapamycin and low levels of L-citrulline. The same disconnection was observed for phosphate activation in phosphate-starved cells. The leu2 auxotrophic mutation reduces amino acid activation of trehalase, which is counteracted by deletion of GCN2. Both effects were also independent of TORC1. Our results show that rapid activation of the TOR pathway by amino acids is not involved in rapid activation of the PKA pathway and that effects of Gcn2 inactivation as well as leu2 auxotrophy all act independently of the TOR pathway. Hence, rapid nutrient signalling to PKA and TOR in cells arrested by nutrient starvation acts through parallel pathways.
两种营养物质控制的信号通路，即蛋白激酶A（PKA）和雷帕霉素靶蛋白（TOR）通路，在酵母生长的营养调控以及与生长相关的特性方面发挥着主要作用。这两条通路之间的关系尚未完全明晰。我们利用Gap1和Pho84转感受器介导的海藻糖酶激活以及片段化的Sch9磷酸化，分别作为PKA或TORC1快速营养激活的读数。我们确定了一些条件，在这些条件下，L-瓜氨酸诱导的Sch9磷酸化激活受到损害，但海藻糖酶的激活不受影响：添加TORC1抑制剂雷帕霉素和低水平的L-瓜氨酸。在缺磷细胞中，磷酸盐激活也观察到了同样的脱节现象。亮氨酸营养缺陷型突变降低了海藻糖酶的氨基酸激活，而GCN2缺失可抵消这种作用。这两种效应也都独立于TORC1。我们的结果表明，氨基酸对TOR通路的快速激活不参与PKA通路的快速激活，并且Gcn2失活以及亮氨酸营养缺陷的效应均独立于TOR通路发挥作用。因此，在因营养饥饿而停滞的细胞中，向PKA和TOR的快速营养信号传导通过平行通路起作用。
