The Tor and Sin3-Rpd3 complex regulate expression of the mitophagy receptor protein Atg32

Abstract

When mitophagy is induced in Saccharomyces cerevisiae, the mitochondrial outer membrane protein ScAtg32 interacts with the cytosolic adaptor protein ScAtg11. ScAtg11 then delivers the mitochondria to the pre-autophagosomal structure for autophagic degradation. Despite the importance of ScAtg32 for mitophagy, the expression and functional regulation of ScAtg32 are poorly understood. In this study, we identified and characterized the ScAtg32 homolog in Pichia pastoris (PpAtg32). Interestingly, we found that PpAtg32 was barely expressed before induction of mitophagy and was rapidly expressed after induction of mitophagy by starvation. Additionally, PpAtg32 was phosphorylated when mitophagy was induced. We found that PpAtg32 expression was suppressed by Tor and the downstream PpSin3-PpRpd3 complex. Inhibition of Tor by rapamycin induced PpAtg32 expression, but could neither phosphorylate PpAtg32 nor induce mitophagy. Based on these findings, we conclude that the Tor and PpSin3-PpRpd3 pathway regulates PpAtg32 expression, but not PpAtg32 phosphorylation.

Protein N-terminal Acetylation by the NatA Complex Is Critical for Selective Mitochondrial Degradation

“…Recently, the Ume6-Sin3-Rpd3 complex, a transcriptional regulator, has been reported to suppress Atg32 expression (27). It remains possible that NatA might acetylate Sin3 and Rpd3 containing a serine and a valine at the second amino acid position, respectively.…”

Mechanistic insights into selective autophagy pathways: lessons from yeast

“…By contrast, some SARs, such as Atg32 in P. pastoris 71 (which is responsible for mitochondrial degradation), as well as Atg39 and Atg40 in S. cerevisiae 33 (which mediate ER-phagy), are not expressed in vegetative conditions. Their expression is only induced when cells encounter nitrogen starvation or are treated with rapamycin, which indicates a regulation of the expression of these receptors by TORC1 signalling 93 .…”

“…Interestingly, mitophagy can be induced by shifting yeast cells from a glucose-rich medium to a glucose-minimal medium without nitrogen; this type of induced mitophagy also depends on SAR phosphorylation 59,61,70 . Finally, the SAR is not phosphorylated and mitophagy is not induced if only TORC1 is inactivated by rapamycin in glucose-rich media 71 .…”

“…In support of this finding, it has been revealed that Atg32 expression in P. pastoris and S. cerevisiae is inhibited by TORC1 and a complex comprising Sin3 and Rpd3 (REF. 71). Atg32 levels increase dramatically when TORC1 is inhibited or when the Rpd3 or Sin3 proteins are absent, suggesting that these proteins suppress ATG32 gene transcription.…”

ER fatalities—The role of ER-mitochondrial contact sites in yeast life and death decisions

“…Importantly, Rim15, a transcription factor that is negatively regulated by TORC1, PKA and Sch9, indirectly upregulates ATG gene expression including ATG32 following nitrogen starvation [78]. In addition, activated Rim15 also suppresses the Ume6–Sin3–Rpd3 transcriptional repressor complex following nitrogen starvation leading to elevated ATG32 transcription in both S. cerevisiae [79] and P. pastoris [80]. The combination of enhanced ATG32 expression and Atg32 protein phosphorylation is important as failure to do either reduces mitophagic efficiency.…”