Nuclear envelope-vacuole contacts mitigate nuclear pore complex assembly stress

Abstract

The intricacy of nuclear pore complex (NPC) biogenesis imposes risks of failure that can cause defects in nuclear transport and nuclear envelope morphology, however, cellular mechanisms utilized to alleviate NPC assembly stress are not well-defined. In the budding yeast Saccharomyces cerevisiae, we demonstrate that NVJ1-and MDM1-enriched nuclear envelope (NE)-vacuole contacts increase when NPC assembly is compromised in several nup mutants, including nup116ΔGLFG cells. These interorganelle nucleus-vacuole junctions (NVJs) cooperate with lipid droplets to maintain viability and enhance NPC formation in assembly mutants. Additionally, NVJs function with ATG1 to promote vacuole-dependent remodeling in nup116ΔGLFG cells, which also correlates with proper NPC formation. Importantly, NVJs significantly improve the physiology of NPC assembly mutants, despite having only negligible effects when NPC biogenesis is unperturbed. Collectively, these results define how NE-vacuole interorganelle contacts coordinate responses to mitigate deleterious cellular effects caused by disrupted NPC assembly. SummaryHow cells respond to deleterious effects imposed by disrupted nuclear pore complex (NPC) assembly are not well-defined. The authors demonstrate nuclear envelope-vacuole interactions expand in response to perturbed NPC assembly to promote viability, nuclear envelope remodeling, and proper NPC biogenesis.

Direct PA-binding by Chm7 is required for nuclear envelope surveillance at herniations

“…Such an idea would be consistent with the emerging role of PA in several other membrane fusion events, e.g. COPI vesicle formation (Yang et al, 2008; Park et al, 2019) and exocytosis (Zeniou-Meyer et al, 2007; Miner et al, 2017) among many others (Corrotte et al, 2006; Nakanishi et al, 2006; Liu et al, 2007; Yang et al, 2008; Giridharan et al, 2013; Bates et al, 2014; Adachi et al, 2016; Starr et al, 2016), and could ultimately underlie genetic relationships defined between PA-metabolism and nup genes (Siniossoglou et al, 1998; Tange et al, 2002; Santos-Rosa et al, 2005; Costanzo et al, 2016; Lord and Wente, 2020) and those that link lipid metabolism more generally to nuclear envelope function (Gorjánácz and Mattaj, 2009; Domart et al, 2012; Bahmanyar et al, 2014; Grillet et al, 2016; Romanauska and Köhler, 2018; Ventimiglia et al, 2018; Kinugasa et al, 2019; Barbosa et al, 2019; Kume et al, 2019; Lee et al, 2020; Penfield et al, 2020). Definitively testing such a model requires more effective tools to precisely toggle PA levels with nanometer precision; recently developed light-inducible tools might provide a way forward here in the future (Tei and Baskin, 2020).…”

Remodelling of Nucleus-Vacuole Junctions During Metabolic and Proteostatic Stress

“…Still, the proteome of expanded NVJs is not known yet and will most likely differ depending on the specific cellular status. For instance, proteostatic stress restricted to the nuclear envelope or ER stress drive reshaping and expansion of the NVJs, but a general induction of protein misfolding via heat shock does not affect NVJ appearance (Hariri et al., 2018; Lord and Wente, 2020).…”

“…In this line, Snd3 is released from enlarged NVJ patches in starved cells within minutes after glucose is replenished (Tosal-Castano et al., 2021). Whether Snd3 might for instance be involved in the interplay between NVJs and LDs, which is suggested to mitigate proteostatic stress in the nuclear envelope to sustain viability (Lord and Wente, 2020), remains to be shown. As a specific relocalization of Snd3 to the NVJ foci in these conditions was not observed, this protein might respond selectively to nutritional cues.…”

“…Lord and Wente recently reported that the presence of NVJs was crucial to remove misassembled nuclear pore complexes (NPCs). Using mutants deficient in the assembly of NPCs, multi-subunit complexes composed of several nucleoporins that facilitate nucleocytoplasmic transport, the authors could show that NVJs are critical to sustain cellular fitness upon perturbation of NPC assembly (Figure 3) (Lord and Wente, 2020). In contrast to metazoans, yeast undergoes a closed mitosis, thus NPCs have to be inserted into the intact nuclear envelope during interphase in a complex process (Boettcher and Barral, 2013).…”

“…Thus, the LD population decorating the periphery of the ER-vacuole contact zone might be in a prime position to sequester misfolded proteins from the ER and facilitate efficient microphagic removal due to the close proximity to the vacuole. Accordingly, not only LD biogenesis and NVJ formation but also Atg1 as key autophagy regulator were required for degradation of NPC assembly intermediates (Lord and Wente, 2020). One might speculate that NVJ-mediated spatial organisation of LDs aids in localized protein removal and subsequent vacuolar engulfment, supporting the proteasome in the turnover of misfolded proteins from the ER upon persisting stress.…”