Hungry cells eat ribosomes

作者：Nicole Lebrasseur · 发表于：Journal of Cell Biology · 年份：2008 · DOI：10.1083/JCB.1813RR5 · 研究领域：Biology

Starving cells seem to first gobble up their ribosomes before they start cannibalizing anything and everything, based on results from Claudine Kraft, Matthias Peter, and colleagues (ETH, Zurich, Switzerland). Using a ribosome-specific autophagy pathway, cells might match ribosome number to metabolic needs. Figure 1 Ribosomes (white) end up in the vacuole in starving cells, unless either of the ribophagy proteins Ubp3p (middle) or Bre5p (bottom) is missing. When nutrients are scarce, autophagy allows cells to degrade their internal components and focus on only the essentials. Kraft et al. noticed that one of the first sets of components dumped into vacuoles, where autophagocytosed products are digested, included ribosomes. Their early deposition required several known autophagy genes. Autophagosomes can engulf either bulk cytoplasm, and anything that comes along with it, or only specific elements, such as mitochondria. According to the new results, ribosomes were taken in selectively by a pathway that the authors dubbed ribophagy, which depended on a ubiquitin-cleaving enzyme called Ubp3p and its cofactor, Bre5p. Ubp3p mutant cells die upon nutrient starvation, possibly because of their inability to digest ribosomes—an excellent first option for autophagy, according to Peter. “They're rich in protein and RNA, so they provide plenty of building blocks like amino acids. Maybe the starvation response isn't all-or-none. Cells could first get rid of r...