The Torsin/ NEP1R1-CTDNEP1/ Lipin axis regulates nuclear envelope lipid metabolism for nuclear pore complex insertion

Abstract

<jats:title>Abstract</jats:title><jats:p>Torsin ATPases of the endoplasmic reticulum (ER) and nuclear envelope (NE) lumen inhibit Lipin-mediated phosphatidate (PA) to diacylglycerol (DAG) conversion by an unknown mechanism. This excess PA metabolism is implicated in <jats:italic>TOR1A</jats:italic>/TorsinA diseases, but it is unclear whether it explains why Torsin concomitantly affects nuclear structure, lipid droplets (LD), organelle and cell growth. Here a fly miniscreen identified that Torsins affect these events via the NEP1R1-CTDNEP1 phosphatase complex. Further, Torsin homo-oligomerization rather than ATPase activity was key to function. NEP1R1-CTDNEP1 activates Lipin by dephosphorylation. We show that Torsin prevents CTDNEP1 from accumulating in the NE and excludes Lipin from the nucleus. Moreover, this repression of nuclear PA metabolism is required for interphase nuclear pore biogenesis. We conclude that Torsin is an upstream regulator of the NEP1R1-CTDNEP1/ Lipin pathway. This connects the ER/NE lumen with PA metabolism, and affects numerous cellular events including it has a previously unrecognized role in nuclear pore biogenesis.</jats:p><jats:sec><jats:title>Highlights</jats:title><jats:list list-type="bullet"><jats:list-item><jats:p>Nuclear envelope PA-DAG-TAG synthesis is independently regulated by Torsin and Torip/LAP1</jats:p></jats:list-item><jats:list-item><jats:p>Torsin removes CTDNEP1 from the nuclear envelope and excludes Lipin from the nucleus</jats:p></jats:list-item><jats:list-item><jats:p>Excess nuclear envelope NEP1R1-CTDNEP1/ Lipin activity impairs multiple aspects of NPC biogenesis</jats:p></jats:list-item><jats:list-item><jats:p>NEP1R1-CTDNEP1/ Lipin inhibition prevents cellular defects associated with <jats:italic>TOR1A</jats:italic> and <jats:italic>TOR1AIP1</jats:italic> / LAP1 disease</jats:p></jats:list-item></jats:list></jats:sec>

Drosophila STING protein has a role in lipid metabolism

“…Next, we used adult flies expressing GFP-tagged dSTING under the native dSTING promoter to examine the localization of dSTING, ACC and FASN in the fat body, main lipid synthesizing organ in Drosophila. The ER (as judged by the ER marker Calnexin) extended throughout fat body cells, with most prominent staining at the cell periphery and in the perinuclear region as was shown before (Jacquemyn et al, 2020) (Figure 6A,A'). GFP-dSTING mainly co-localized with Calnexin at the cortex.…”

Drosophila STING protein has a role in lipid metabolism

“…Next, we used adult flies expressing GFP-tagged dSTING under native dSTING promoter to examine the localization of dSTING, ACC and FAS in the fat body, main lipid synthesizing organ in Drosophila. ER (as judged by ER marker Calnexin) extended throughout fat body cells, with most prominent staining at the cell periphery and in perinuclear region as was shown before (J acquemyn et al 2020) ( Figure 7A ). GFP-dSTING mainly co-localized with Calnexin at the cortex ( Figure 7A ).…”

Direct binding of ESCRT protein Chm7 to phosphatidic acid–rich membranes at nuclear envelope herniations

“…Such an idea fits with work exploring the biogenesis of similar herniations in human cells with a loss of function of the AAA+ ATPase TorsinA ( Goodchild et al, 2005 ; Laudermilch et al, 2016 ). As data grow linking these herniations to defective NPC assembly ( Laudermilch et al, 2016 ; Pappas et al, 2018 ; Rampello et al, 2020 ), so does evidence that they are a product of defective lipid metabolism; in fact, recent work suggests that TorsinA may inhibit Lipin ( Grillet et al, 2016 ; Cascalho et al, 2020 ; Jacquemyn et al, 2020 Preprint ). Second, and as follows, while ultimately too much PA may be deleterious ( Fig.…”