Thaller, D. J. | Search bioRxiv

bioRxiv2021

Atg39 selectively captures inner nuclear membrane into lumenal vesicles for delivery to the autophagosome

Mechanisms that turnover components of the nucleus and inner nuclear membrane (INM) remain to be fully defined. We explore how components of the INM are selected by a cytosolic autophagy apparatus through a transmembrane nuclear envelope-localized cargo adaptor, Atg39. A split-GFP reporter shows that Atg39 localizes to the outer nuclear membrane (ONM) and thus targets the INM across the nuclear envelope lumen. Consistent with this, sequence elements that confer both nuclear envelope localization and a membrane remodeling activity are mapped to the Atg39 lumenal domain; these lumenal motifs are required for the autophagy-mediated degradation of an integral INM protein. Interestingly, correlative light and electron tomography shows that the overexpression of Atg39 leads to the expansion of the ONM and the enclosure of a network of INM-derived vesicles in the nuclear envelope lumen. Thus, we propose an outside-in model of nucleophagy where INM is delivered into vesicles in the nuclear envelope lumen, which can be targeted by the autophagosome.

cell biology↗

bioRxiv2020

Heh2/Man1 may be an evolutionarily conserved sensor of NPC assembly state

Integral membrane proteins of the Lap2-emerin-MAN1 (LEM) family have emerged as important components of the inner nuclear membrane (INM) required for the functional and physical integrity of the nuclear envelope. However, like many INM proteins, there is limited understanding of the biochemical interaction networks that enable LEM protein function. Here, we show that Heh2/Man1 can be affinity purified with major scaffold components of the nuclear pore complex (NPC), specifically the inner ring complex, in evolutionarily distant yeasts. Interactions between Heh2 and nucleoporins is mediated by its C-terminal winged-helix (WH) domain and are distinct from interactions required for INM targeting. Disrupting interactions between Heh2 and the NPC leads to NPC clustering. Interestingly, Heh2s association with NPCs can also be broken by knocking out Nup133, a component of the outer ring that does not physically interact with Heh2. Thus, Heh2s association with NPCs depends on the structural integrity of both major NPC scaffold complexes. We propose a model in which Heh2 acts as a sensor of NPC assembly state, which may be important for NPC quality control mechanisms and the segregation of NPCs during cell division.

cell biology↗