N-terminal acetylation and replicative age affect proteasome localization and cell fitness during aging

Abstract

Specific degradation of proteins is essential for virtually all cellular processes and is carried out predominantly by the proteasome. The proteasome is important for clearance of damaged cellular proteins. Damaged proteins accumulate over time and excess damaged proteins can aggregate and induce the death of old cells. In yeast, the localization of the proteasome changes dramatically during aging, possibly in response to altered proteasome activity requirements. We followed two key parameters of this process: the distribution of proteasomes in nuclear and cytosolic compartments, and the formation of cytoplasmic aggregate-like structures called proteasome storage granules (PSGs). Whereas replicative young cells efficiently relocalized proteasomes from the nucleus to the cytoplasm and formed PSGs, replicative old cells were less efficient in relocalizing the proteasome and had less PSGs. By using a microscopy-based genome-wide screen, we identified genetic factors involved in these processes. Both relocalization of the proteasome and PSG formation were affected by two of the three N-acetylation complexes. These N-acetylation complexes also had different effects on the longevity of cells, indicating that each N-acetylation complex has different roles in proteasome location and aging.

Intracellular Dynamics of the Ubiquitin-Proteasome-System

“…Their presence protects cells against proteo- and genotoxic stress and confers cell fitness during aging. Post-translation modifications such as N-acetylation also play a role in PSG organization, but their targets are unknown ( Saunier et al , 2013; van Deventer et al , 2015; Weberruss et al , 2013). …”

The biological functions of Naa10 — From amino-terminal acetylation to human disease

“…In agreement with that, overexpression of the Hsp70 protein Ssb1 partially suppressed the temperature sensitivity and derepression of the silent mating type loci caused by NAA15 Δ or NAA10 Δ (Gautschi et al, 2003). Furthermore, disruption of NatA (Naa10 or Naa15) affects general cell fitness as assayed by the ability of cells to restart their cell cycle when nutrients are added after starvation (Aragon et al, 2008; van Deventer et al, 2014). …”

“…This shuttling efficiency ceases with age (impairment of proteasome relocalization and/or PSG formation correlates with replicative age). NatC auxiliary subunit Naa35 was identified in a yeast screen for mutants affecting nuclear-cytoplasmic shuttling during starvation (van Deventer et al, 2014). Additionally, loss of N-acetylation by deletion of the NatC subunits Naa30, Naa35 or Naa38 or a catalytically inactive NatC mutant (Naa30 N123A/Y130A) caused an increased nuclear enrichment/retention of the proteasomes under starvation without affecting PSG formation as visualized by tagging the catalytically active β1-subunit (Pre3) of the proteasome with GFP (van Deventer et al, 2014).…”

“…NatC auxiliary subunit Naa35 was identified in a yeast screen for mutants affecting nuclear-cytoplasmic shuttling during starvation (van Deventer et al, 2014). Additionally, loss of N-acetylation by deletion of the NatC subunits Naa30, Naa35 or Naa38 or a catalytically inactive NatC mutant (Naa30 N123A/Y130A) caused an increased nuclear enrichment/retention of the proteasomes under starvation without affecting PSG formation as visualized by tagging the catalytically active β1-subunit (Pre3) of the proteasome with GFP (van Deventer et al, 2014). Disruption of NatB ( NAA20 Δ and NAA25 Δ) had similar effects but also quenched PSG formation under starvation, whereas disruption of NatA ( NAA10 Δ, NAA15 Δ and NAA50 Δ) had no effects (van Deventer et al, 2014).…”

“…Additionally, loss of N-acetylation by deletion of the NatC subunits Naa30, Naa35 or Naa38 or a catalytically inactive NatC mutant (Naa30 N123A/Y130A) caused an increased nuclear enrichment/retention of the proteasomes under starvation without affecting PSG formation as visualized by tagging the catalytically active β1-subunit (Pre3) of the proteasome with GFP (van Deventer et al, 2014). Disruption of NatB ( NAA20 Δ and NAA25 Δ) had similar effects but also quenched PSG formation under starvation, whereas disruption of NatA ( NAA10 Δ, NAA15 Δ and NAA50 Δ) had no effects (van Deventer et al, 2014). The associated NatB or NatC substrates have not been identified and mutation of the N-terminus of the putative candidates α5 (Pup2), α6 (Pre5), Rpn9, Fub1, Avo2, Hul5 or Nup100, that would prevent acetylation (MX- to MP-mutation), failed to phenotypically mimic cells lacking NatB or NatC.…”