Nuclear envelope (NE) ruptures are emerging observations in Lamin-related dilated cardiomyopathy, an adult-onset disease caused by loss-of-function mutations in Lamin A/C, a nuclear lamina component. Here, we test a prevailing hypothesis that NE ruptures trigger the pathological cGAS-STING cytosolic DNA-sensing pathway using a mouse model of Lamin cardiomyopathy. The reduction of Lamin A/C in cardio-myocyte of adult mice causes pervasive NE ruptures in cardiomyocytes, preceding inflammatory transcription, fibrosis, and fatal dilated cardiomyopathy. NE ruptures are followed by DNA damage accumulation without causing immediate cardiomyocyte death. However, cGAS-STING-dependent inflammatory signaling remains inactive. Deleting cGas or Sting does not rescue cardiomyopathy in the mouse model. The lack of cGAS-STING activation is likely due to the near absence of cGAS expression in adult cardiomyocytes at baseline. Instead, extracellular matrix (ECM) signaling is activated and predicted to initiate pro-inflammatory communication from Lamin-reduced cardiomyocytes to fibroblasts. Our work nominates ECM signaling, not cGAS-STING, as a potential inflammatory contributor in Lamin cardiomyopathy.

In eukaryotic cells, the nuclear envelope (NE) is a membrane partition between the nucleus and the cytoplasm to compartmentalize nuclear contents. It plays an important role in facilitating nuclear functions including transcription, DNA replication and repair. In mammalian cells, the NE breaks down and then reforms during cell division, and in interphase it is restored shortly after the NE rupture induced by mechanical force. In this way, the partitioning effect is regulated through dynamic processes throughout the cell cycle. A failure in rebuilding the NE structure triggers the mixing of nuclear and cytoplasmic contents, leading to catastrophic consequences for the nuclear functions. Whereas the precise details of molecular mechanisms for NE reformation during cell division and NE restoration in interphase are still being investigated, here, we mostly focus on mammalian cells to describe key aspects that have been identified and to discuss the crosstalk between them.

The integrity of the nuclear envelope (NE) is essential for maintaining the structural stability of the nucleus. Rupture of the NE has been frequently observed in cancer cells, especially in the context of mechanical challenges, such as physical confinement and migration. However, spontaneous NE rupture events, without any obvious physical challenges to the cell, have also been described. The molecular mechanism(s) of these spontaneous NE rupture events remain to be explored. Here, we show that DNA damage and subsequent ATR activation leads to NE rupture. Upon DNA damage, lamin A/C is phosphorylated in an ATR-dependent manner, leading to changes in lamina assembly and, ultimately, NE rupture. In addition, we show that cancer cells with intrinsic DNA repair defects undergo frequent events of DNA-damage-induced NE rupture, which renders them extremely sensitive to further NE perturbations. Exploiting this NE vulnerability could provide a new angle to complement traditional, DNA-damage-based chemotherapy.

The microtubule-associated protein tau is an abundant component of neurons of the central nervous system. In Alzheimer\'s disease and other neurodegenerative tauopathies, tau is found hyperphosphorylated and aggregated in neurofibrillary tangles. To obtain a better understanding of the cellular perturbations that initiate tau pathogenesis, we performed a CRISPR-Cas9 screen for genetic modifiers that enhance tau aggregation. This initial screen yielded three genes, BANF1, ANKLE2, and PPP2CA, whose inactivation promotes the accumulation of tau in a phosphorylated and insoluble form. In a complementary screen, we identified three additional genes, LEMD2, LEMD3, and CHMP7, that, when overexpressed, provide protection against tau aggregation. The proteins encoded by the identified genes are mechanistically linked and recognized for their roles in the maintenance and repair of the nuclear envelope. These results implicate the disruption of nuclear envelope integrity as a possible initiating event in tauopathies and reveal targets for therapeutic intervention.

Nuclear rupture has long been associated with deficits or defects in lamins, with recent results also indicating a role for actomyosin stress, but key physical determinants of rupture remain unclear. Here, lamin-B filaments stably interact with the nuclear membrane at sites of low Gaussian curvature yet dilute at high curvature to favor rupture, whereas lamin-A depletion requires high strain-rates. Live-cell imaging of lamin-B1 gene-edited cancer cells is complemented by fixed-cell imaging of rupture in: iPS-derived progeria patients cells, cells within beating chick embryo hearts, and cancer cells with multi-site rupture after migration through small pores. Data fit a model of stiff filaments that detach from a curved surface.Rupture is modestly suppressed by inhibiting myosin-II and by hypotonic stress, which slow the strain-rates. Lamin-A dilution and rupture probability indeed increase above a threshold rate of nuclear pulling. Curvature-sensing mechanisms of proteins at plasma membranes, including Piezo1, might thus apply at nuclear membranes.Summary statement: High nuclear curvature drives lamina dilution and nuclear envelope rupture even when myosin stress is inhibited. Stiff filaments generally dilute from sites of high Gaussian curvature, providing mathematical fits of experiments.

During metastasis, invading tumor cells and circulating tumor cells (CTC) face multiple mechanical challenges during migration through narrow pores and cell squeezing. However, little is known on the importance and consequences of mechanical stress for tumor progression and success in invading a new organ. Recently, several studies have shown that cell constriction can lead to nuclear envelope rupture (NER) during interphase. This loss of proper nuclear compartmentalization has a profound effect on the genome, being a key driver for the genome evolution needed for tumor progression. More than just being a source of genomic alterations, the transient nuclear envelope collapse can also support metastatic growth by several mechanisms involving the innate immune response cGAS/STING pathway. In this review we will describe the importance of the underestimated role of cellular squeezing in the progression of tumorigenesis. We will describe the complexity and difficulty for tumor cells to reach the metastatic site, detail the genomic aberration diversity due to NER, and highlight the importance of the activation of the innate immune pathway on cell survival. Cellular adaptation and nuclear deformation can be the key to the metastasis success in many unsuspected aspects.

Neutrophils are the most abundant circulating white blood cells and one of the major cell types of the innate immune system. Neutrophil extracellular traps (NETs) are a result of the extracellular release of nuclear chromatin from the ruptured nuclear envelope and plasma membrane. The externalized chromatin is an ancient defense weapon for animals to entrap and kill microorganisms in the extracellular milieu, thus protecting animals ranging from lower invertebrates to higher vertebrates. Although the externalized chromatin has the advantage of acting as anti-infective to protect against infections, extracellular chromatin might be problematic in higher vertebrate animals as they have an adaptive immune system that can trigger further immune or autoimmune responses. NETs and their associated nuclear and/or cytoplasmic components may induce sterile inflammation, immune, and autoimmune responses, leading to various human diseases. Though important in human pathophysiology, the cellular and molecular mechanisms of NET formation (also called NETosis) are not well understood. Given that nuclear chromatin forms the backbone of NETs, the nucleus is the root of the nuclear DNA extracellular traps. Thus, nuclear chromatin decondensation, along with the rupture of nuclear envelope and plasma membrane, is required for nuclear chromatin extracellular release and NET formation. So far, most of the literature focuses on certain signaling pathways, which are involved in NET formation but without explanation of cellular events and morphological changes described above. Here, we have summarized emerging evidence and discuss new mechanistic understanding, with our perspectives, in NET formation in neutrophils.

Cancer metastasis, i.e., the spreading of tumor cells from the primary tumor to distant organs, is responsible for the vast majority of cancer deaths. In the process, cancer cells migrate through narrow interstitial spaces substantially smaller in cross-section than the cell. During such confined migration, cancer cells experience extensive nuclear deformation, nuclear envelope rupture, and DNA damage. The molecular mechanisms responsible for the confined migration-induced DNA damage remain incompletely understood. Although in some cell lines, DNA damage is closely associated with nuclear envelope rupture, we show that, in others, mechanical deformation of the nucleus is sufficient to cause DNA damage, even in the absence of nuclear envelope rupture. This deformation-induced DNA damage, unlike nuclear-envelope-rupture-induced DNA damage, occurs primarily in S/G2 phase of the cell cycle and is associated with replication forks. Nuclear deformation, resulting from either confined migration or external cell compression, increases replication stress, possibly by increasing replication fork stalling, providing a molecular mechanism for the deformation-induced DNA damage. Thus, we have uncovered a new mechanism for mechanically induced DNA damage, linking mechanical deformation of the nucleus to DNA replication stress. This mechanically induced DNA damage could not only increase genomic instability in metastasizing cancer cells but could also cause DNA damage in non-migrating cells and tissues that experience mechanical compression during development, thereby contributing to tumorigenesis and DNA damage response activation.

Micronuclei are extra-nuclear bodies mainly derived from ana-telophase lagging chromosomes/chromatins (LCs) that are not incorporated into primary nuclei at mitotic exit. Unlike primary nuclei, most micronuclei are enclosed by nuclear envelope (NE) that is highly susceptible to spontaneous and irreparable rupture. Ruptured micronuclei act as triggers of chromothripsis-like chaotic chromosomal rearrangements and cGAS-mediated innate immunity and inflammation, raising the view that micronuclei play active roles in human aging and tumorigenesis. Thus, understanding the ways in which micronuclear envelope (mNE) goes awry acquires increased importance. Here, we review the data to present a general framework for this question. We firstly describe NE reassembly after mitosis and NE repair during interphase. Simultaneously, we briefly discuss how mNE is organized and how mNE rupture controls the fate of micronuclei and micronucleated cells. As a focus of this review, we highlight current knowledge about why mNE is rupture-prone and irreparable. For this, we survey observations from a series of elegant studies to provide a systematic overview. We conclude that the birth of rupture-prone and irreparable micronuclei may be the cumulative effects of their intracellular geographic origins, biophysical properties, and specific mNE features. We propose that DNA damage and immunogenicity in micronuclei increase stepwise from altered mNE components, mNE rupture, and refractory to repair. Throughout our discussion, we note interesting issues in mNE fragility that have yet to be resolved.

The nuclear lamina is essential for the structural integration of the nuclear envelope. Nuclear envelope rupture and chromatin externalization is a hallmark of the formation of neutrophil extracellular traps (NETs). NET release was described as a cellular lysis process; however, this notion has been questioned recently. Here, we report that during NET formation, nuclear lamin B is not fragmented by destructive proteolysis, but rather disassembled into intact full-length molecules. Furthermore, we demonstrate that nuclear translocation of PKCα, which serves as the kinase to induce lamin B phosphorylation and disassembly, results in nuclear envelope rupture. Decreasing lamin B phosphorylation by PKCα inhibition, genetic deletion, or by mutating the PKCα consensus sites on lamin B attenuates extracellular trap formation. In addition, strengthening the nuclear envelope by lamin B overexpression attenuates NET release in vivo and reduces levels of NET-associated inflammatory cytokines in UVB-irradiated skin of lamin B transgenic mice. Our findings advance the mechanistic understanding of NET formation by showing that PKCα-mediated lamin B phosphorylation drives nuclear envelope rupture for chromatin release in neutrophils.