Janssen, A. F. | bioRxiv Science

bioRxiv2023

A Novel Role for CSA in the Regulation of Nuclear Envelope Integrity: Uncovering a Non-Canonical Function

Cockayne syndrome (CS) is an autosomal recessive premature ageing condition mainly characterized by microcephaly, growth failure, and neurodegeneration. It is caused by mutations in ERCC6 or ERCC8 genes which encode for Cockayne Syndrome B (CSB) and Cockayne Syndrome A (CSA) proteins, respectively. CSA and CSB have well-characterised roles in transcription-coupled nucleotide excision repair (TC-NER), responsible for the removal of bulky DNA lesions, including those caused by UV irradiation. Here, we report that CSA knockout cells and CSA patient cells (CS-A) carrying a loss-of-function mutation in the ERCC8 gene exhibit defects in nuclear envelope (NE) integrity. NE dysfunction is a characteristic phenotype of cells from progeroid disorders caused by mutation in NE proteins, such as Hutchinson-Gilford Progeria Syndrome (HGPS). However, it has never been reported in Cockayne Syndrome. We observed that CS-A cells displayed reduced levels of LAP2-emerin-MAN1 (LEM)-domain 2 (LEMD2) at the NE resulting in decreased formation of LEMD2-lamin A/C complexes. In addition, loss of CSA function caused increased actin stress fibers that contributed to enhanced mechanical stress to the NE. Altogether, these led to NE blebbing and ruptures in interphase, causing activation of the innate/immune cGAS/STING signaling pathway. Disrupting the linker of the nucleoskeleton and cytoskeleton (LINC) complex that is responsible for anchoring the cytoskeleton to the NE, rescued the NE phenotypes and reduced the activation of cGAS/STING pathway. This work has revealed a previously uncharacterized role for CSA in regulating NE integrity and shed light on mechanisms that may further explain some of the clinical phenotypes observed in CS patients such as neuroinflammation. This is to our knowledge, the first study showing NE dysfunction in a progeroid syndrome caused by mutations in a DNA damage repair protein, reinforcing the connection between NE deregulation and ageing.

cell biology↗

bioRxiv2021

Direct observation of aggregate-triggered selective autophagy

Degradation of aggregates by selective autophagy is important as damaged proteins may impose a threat to cellular homeostasis. Although the core components of the autophagy machinery are well-characterized, the spatiotemporal regulation of many selective autophagy processes, including aggrephagy, remains largely unexplored. Furthermore, because most live-cell imaging studies have so far focused on starvation-induced autophagy, little is known about the dynamics of aggrephagy. Here, we describe the development and application of the mKeima-PIM assay, which enables live-cell observation of autophagic turnover and degradation of inducible protein aggregates in conjunction with key autophagy players. This allowed us to quantify the relative timing and duration of different steps of aggrephagy and revealed the short-lived nature of the autophagosome. The assay furthermore showed the spatial distribution of omegasome formation, highlighting that autophagy initiation is directly instructed by the cargo. Moreover, we found that nascent autophagosomes mostly remain immobile until acidification occurs. Thus, our assay provides new insights into the spatiotemporal regulation and dynamics of aggrephagy.

cell biology↗