Ubiquitin-proteasome-mediated cyclin C degradation promotes cell survival following nitrogen starvation

Mol Biol Cell. 2020 May 1;31(10):1015-1031. doi: 10.1091/mbc.E19-11-0622. Epub 2020 Mar 11.

Abstract

Environmental stress elicits well-orchestrated programs that either restore cellular homeostasis or induce cell death depending on the insult. Nutrient starvation triggers the autophagic pathway that requires the induction of several Autophagy (ATG) genes. Cyclin C-cyclin-dependent kinase (Cdk8) is a component of the RNA polymerase II Mediator complex that predominantly represses the transcription of stress-responsive genes in yeast. To relieve this repression following oxidative stress, cyclin C translocates to the mitochondria where it induces organelle fragmentation and promotes cell death prior to its destruction by the ubiquitin-proteasome system (UPS). Here we report that cyclin C-Cdk8, together with the Ume6-Rpd3 histone deacetylase complex, represses the essential autophagy gene ATG8. Similar to oxidative stress, cyclin C is destroyed by the UPS following nitrogen starvation. Removing this repression is important as deleting CNC1 allows enhanced cell growth under mild starvation. However, unlike oxidative stress, cyclin C is destroyed prior to its cytoplasmic translocation. This is important as targeting cyclin C to the mitochondria induces both mitochondrial fragmentation and cell death following nitrogen starvation. These results indicate that cyclin C destruction pathways are fine tuned depending on the stress and that its terminal subcellular address influences the decision between initiating cell death or cell survival pathways.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Autophagy / drug effects
  • Autophagy-Related Protein 8 Family / genetics
  • Autophagy-Related Protein 8 Family / metabolism
  • Cell Survival / drug effects
  • Cyclin C / metabolism*
  • Cyclin-Dependent Kinase 8 / metabolism
  • Gene Expression Regulation, Fungal / drug effects
  • Hydrogen Peroxide / toxicity
  • Mitochondria / drug effects
  • Mitochondria / metabolism
  • Mitochondrial Dynamics / drug effects
  • Models, Biological
  • Nitrogen / deficiency*
  • Oxidative Stress / drug effects
  • Proteasome Endopeptidase Complex / metabolism*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Saccharomyces cerevisiae / cytology*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / growth & development
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism
  • Sirolimus / pharmacology
  • Stress, Physiological / drug effects
  • Ubiquitin / metabolism*

Substances

  • Autophagy-Related Protein 8 Family
  • Cyclin C
  • RNA, Messenger
  • Saccharomyces cerevisiae Proteins
  • Ubiquitin
  • Hydrogen Peroxide
  • Cyclin-Dependent Kinase 8
  • Proteasome Endopeptidase Complex
  • Nitrogen
  • Sirolimus