Protein Kinase A and Sch9 Cooperatively Regulate Induction of Autophagy inSaccharomyces cerevisiae

Abstract

Autophagy is a highly conserved, degradative process in eukaryotic cells. The rapamycin-sensitive Tor kinase complex 1 (TORC1) has a major role in regulating induction of autophagy; however, the regulatory mechanisms are not fully understood. Here, we find that the protein kinase A (PKA) and Sch9 signaling pathways regulate autophagy cooperatively in yeast. Autophagy is induced in cells when PKA and Sch9 are simultaneously inactivated. Mutant alleles of these kinases bearing a mutation that confers sensitivity to the ATP-analogue inhibitor C3-1-naphthyl-methyl PP1 revealed that autophagy was induced independently of effects on Tor kinase. The PKA-Sch9-mediated autophagy depends on the autophagy-related 1 kinase complex, which is also essential for TORC1-regulated autophagy, the transcription factors Msn2/4, and the Rim15 kinase. The present results suggest that autophagy is controlled by the signals from at least three partly separate nutrient-sensing pathways that include PKA, Sch9, and TORC1.

Ume6 transcription factor is part of a signaling cascade that regulates autophagy

“…For example, when cells are grown on acetate as the sole carbon source in conditions of nitrogen limitation, Rim15 promotes Ume6 phosphorylation and disrupts the association of Sin3 and Rpd3 with the complex, thus relieving transcriptional repression of the target genes (12). In addition, we have shown that Rim15 is a positive regulator of autophagy (17,18), although its relevant target(s) had not been identified. Therefore, we decided to investigate a potential role for Rim15 in Ume6-regulated Atg8 induction.…”

“…Rim15 plays an important role in integrating many nutrient-regulatory signals and, therefore, plays a central role in regulating autophagy (17,22). Rim15 is negatively regulated through direct phosphorylation by cAMP-dependent protein kinase A (PKA) and Sch9 in the presence of glucose and nitrogen (23,24) and is involved in the autophagy induction that occurs upon PKA-Sch9 inactivation (18). PKA and Sch9 are upstream sensors that act to negatively regulate autophagy; however, the downstream components in this signaling pathway are unknown, and how PKA and Sch9 signaling affects the autophagy machinery to regulate autophagosome formation has not been elucidated previously.…”

Life in the midst of scarcity: adaptations to nutrient availability in Saccharomyces cerevisiae

“…Also Pho85-Pho80, which phosphorylates Rim15 at Thr 1075 , controls the nuclear export of Rim15. PDS post-diauxic shift, STRE stressresponsive element combined inactivation of Sch9 and PKA appeared to additively stimulate autophagy, indicating that also for autophagy Sch9 and PKA act, at least in part, in parallel to the TORC1 pathways (Yorimitsu et al 2007). …”

“…These studies revealed that autophagy is induced in yeast cells upon the simultaneous inactivation of Sch9 and PKA (Yorimitsu et al 2007). This induction required the Atg1 kinase complex and was only in part dependent on the presence of Rim15 and Msn2/4.…”

“…For instance, both kinases have an additive effect for the expression of proteins required for nucleotide metabolism but they exert opposite effects on the expression on proteins involved in detoxification or proteolysis . In addition, they independently determine the sensitivity of yeast cells for the ATP-analogue 1NM-PP1 as illustrated by the observation that a mutant with combined analogue-sensitive sch9 as tpk1 as tpk2 as tpk3 as alleles is more sensitive than the single sch9 as mutant or the tpk1 as tpk2 as tpk3 as strain (Yorimitsu et al 2007;Huber et al 2009;Lee et al 2009). …”