Repetitive disruptions of the nuclear envelope invoke temporary loss of cellular compartmentalization in laminopathies

Abstract

The nuclear lamina provides structural support to the nucleus and has a central role in nuclear organization and gene regulation. Defects in its constituents, the lamins, lead to a class of genetic diseases collectively referred to as laminopathies. Using live cell imaging, we observed the occurrence of intermittent, non-lethal ruptures of the nuclear envelope in dermal fibroblast cultures of patients with different mutations of lamin A/C. These ruptures, which were absent in normal fibroblasts, could be mimicked by selective knockdown as well as knockout of LMNA and were accompanied by the loss of cellular compartmentalization. This was demonstrated by the influx of cytoplasmic transcription factor RelA and regulatory protein Cyclin B1 into the nucleus, and efflux of nuclear transcription factor OCT1 and nuclear structures containing the promyelocytic leukemia (PML) tumour suppressor protein to the cytoplasm. While recovery of enhanced yellow fluorescent protein-tagged nuclear localization signal in the nucleus demonstrated restoration of nuclear membrane integrity, part of the mobile PML structures became permanently translocated to the cytoplasm. These satellite PML structures were devoid of the typical PML body components, such as DAXX, SP100 or SUMO1. Our data suggest that nuclear rupture and loss of compartmentalization may add to cellular dysfunction and disease development in various laminopathies.

Oxydative stress alters nuclear shape through lamins dysregulation

“…Indeed, it has been reported that a disruption in the integrity of the nuclear membrane allows the passage of components and even organelles from the cytoplasm to the nucleus. 51 Consequently, the presence of mitochondria in the nucleoplasm should increase nuclear ROS to a level that can damage DNA.…”

Consequences of a tight squeeze: Nuclear envelope rupture and repair

“…[6][7][8][9][10][11] NE ruptures can also be detected by monitoring fluorescent proteins tagged with a nuclear export signal (NES), which only enter the nucleus during NE rupture and are exported back into the cytoplasm once NE integrity is restored. 6,10 In addition to these fluorescent reporters, evidence of NE rupture comes from mitochondria and ribosomes that become mislocalized to the nucleus, and promyelocytic leukemia (PML) nuclear bodies found in the cytoplasm of cells that exhibited NE rupture. 6,7 In cells cultured on rigid substrates, spontaneous NE rupture is observed in circa 5% of cells over a 24 h period.…”

“…6,10 In addition to these fluorescent reporters, evidence of NE rupture comes from mitochondria and ribosomes that become mislocalized to the nucleus, and promyelocytic leukemia (PML) nuclear bodies found in the cytoplasm of cells that exhibited NE rupture. 6,7 In cells cultured on rigid substrates, spontaneous NE rupture is observed in circa 5% of cells over a 24 h period. 6,7,9 Depletion of lamins or expression of disease-causing lamin mutants that impair nuclear lamina stability increases NE rupture rates.…”

ESCRTs breach the nuclear border

“…24 In multicellular eukaryotes, massive membrane remodeling occurs during mitotic NE-disassembly and post-mitotic NE reformation; we wonder how ESCRT-III will function in these contexts. Moreover, the capacity of ESCRT-III to repair plasma membrane wounds 15,16 raises the possibility that it might also be capable of repairing the transient NE-ruptures that have been observed in several cancer cell lines 56,57 and in cells containing laminopathy mutations, 58 a model consistent with the growing role of ESCRT-III in membrane homeostasis and quality control.…”