LAP2α preserves genome integrity through assisting RPA deposition on damaged chromatin

The nexus of nuclear envelope dynamics, circular economy and cancer cell pathophysiology

The nuclear envelope (NE) is a critical component in maintaining the function and structure of the eukaryotic nucleus. The NE and lamina are disassembled during each cell cycle to enable an open mitosis. Nuclear architecture construction and deconstruction is a prime example of a circular economy, as it fulfills a highly efficient recycling program bound to continuous assessment of the quality and functionality of the building blocks. Alterations in the nuclear dynamics and lamina structure have emerged as important contributors to both oncogenic transformation and cancer progression. However, the knowledge of the NE breakdown and reassembly is still limited to a fraction of participating proteins and complexes. As cancer cells contain highly diverse nuclei in terms of DNA content, but also in terms of nuclear number, size, and shape, it is of great interest to understand the intricate relationship between these nuclear features in cancer cell pathophysiology. In this review, we provide insights into how those NE dynamics are regulated, and how lamina destabilization processes may alter the NE circular economy. Moreover, we expand the knowledge of the lamina-associated domain region by using strategic algorithms, including Artificial Intelligence, to infer protein associations, assess their function and location, and predict cancer-type specificity with implications for the future of cancer diagnosis, prognosis and treatment. Using this approach we identified NUP98 and MECP2 as potential proteins that exhibit upregulation in Acute Myeloid Leukemia (LAML) patients with implications for early diagnosis.

The expression and role of the Lem-D proteins Ankle2, Emerin, Lemd2, and TMPO in triple-negative breast cancer cell growth

Background

Triple-negative breast cancer (TNBC) is a sub-classification of breast carcinomas, which leads to poor survival outcomes for patients. TNBCs do not possess the hormone receptors that are frequently targeted as a therapeutic in other cancer subtypes and, therefore, chemotherapy remains the standard treatment for TNBC. Nuclear envelope proteins are frequently dysregulated in cancer cells, supporting their potential as novel cancer therapy targets. The Lem-domain (Lem-D) (LAP2, Emerin, MAN1 domain, and Lem-D) proteins are a family of inner nuclear membrane proteins, which share a ~45-residue Lem-D. The Lem-D proteins, including Ankle2, Lemd2, TMPO, and Emerin, have been shown to be associated with many of the hallmarks of cancer. This study aimed to define the association between the Lem-D proteins and TNBC and determine whether these proteins could be promising therapeutic targets.

Methods

GENT2, TCGA, and KM plotter were utilized to investigate the expression and prognostic implications of several Lem-D proteins: Ankle2, TMPO, Emerin, and Lemd2 in publicly available breast cancer patient data. Immunoblotting and immunofluorescent analysis of immortalized non-cancerous breast cells and a panel of TNBC cells were utilized to establish whether protein expression of the Lem-D proteins was significantly altered in TNBC. SiRNA was used to decrease individual Lem-D protein expression, and functional assays, including proliferation assays and apoptosis assays, were conducted.

Results

The Lem-D proteins were generally overexpressed in TNBC patient samples at the mRNA level and showed variable expression at the protein level in TNBC cell lysates. Similarly, protein levels were generally negatively correlated with patient survival outcomes. siRNA-mediated depletion of the individual Lem-D proteins in TNBC cells induced aberrant nuclear morphology, decreased proliferation, and induced cell death. However, minimal effects on nuclear morphology or cell viability were observed following Lem-D depletion in non-cancerous MCF10A cells.

Conclusion

There is evidence to suggest that Ankle2, TMPO, Emerin, and Lemd2 expressions are correlated with breast cancer patient outcomes, but larger patient sample numbers are required to confirm this. siRNA-mediated depletion of these proteins was shown to specifically impair TNBC cell growth, suggesting that the Lem-D proteins may be a specific anti-cancer target.

Consolidating Organometallic Complex Empowers Mitochondria-Directed Chemotherapy against Resistant Cancer via Stemness and Metastasis Inhibition

Cancer treatment has faced severe obstacles due to the smart biological system of cancer cells. Herein, we report a three-in-one agent Ir-CA via attenuation of cancer cell stemness with the down-regulated biomarker CD133 expression from the mitochondria-directed chemotherapy. Over 80% of Ir-CA could accumulate in mitochondria, result in severe mitochondrial dysfunctions, and subsequently initiate mitophagy and cell cycle arrest to kill cisplatin-resistant A549R cells. In vitro and in vivo antimetastatic experiments demonstrated that Ir-CA can effectively inhibit metastasis with down-regulated MMP-2/MMP-9. RNA seq analysis and Western blotting indicated that Ir-CA also suppresses the GSTP1 expression to decrease the intracellular Pt-GS adducts, resulting in the detoxification and resensitization to cisplatin of A549R cells. In vivo evaluation indicated that Ir-CA restrains the tumor growth and has minimal side effects and superior biocompatibility. This work not only provides the first three-in-one agent to attenuate cancer cell stemness and simultaneously realize anticancer, antimetastasis, and conquer metallodrug resistance but also demonstrates the effectiveness of the mitochondria-directed strategy in cancer treatment.

DNA replication and replication stress response in the context of nuclear architecture

The DNA replication process needs to be coordinated with other DNA metabolism transactions and must eventually extend to the full genome, regardless of chromatin status, gene expression, secondary structures and DNA lesions. Completeness and accuracy of DNA replication are crucial to maintain genome integrity, limiting transformation in normal cells and offering targeting opportunities for proliferating cancer cells. DNA replication is thus tightly coordinated with chromatin dynamics and 3D genome architecture, and we are only beginning to understand the underlying molecular mechanisms. While much has recently been discovered on how DNA replication initiation is organised and modulated in different genomic regions and nuclear territories-the so-called "DNA replication program"-we know much less on how the elongation of ongoing replication forks and particularly the response to replication obstacles is affected by the local nuclear organisation. Also, it is still elusive how specific components of nuclear architecture participate in the replication stress response. Here, we review known mechanisms and factors orchestrating replication initiation, and replication fork progression upon stress, focusing on recent evidence linking genome organisation and nuclear architecture with the cellular responses to replication interference, and highlighting open questions and future challenges to explore this exciting new avenue of research.

Replication Protein A1 is essential for DNA damage repair during mammalian oogenesis

Persistence of unrepaired DNA damage in oocytes is detrimental and may cause genetic aberrations, miscarriage, and infertility. RPA, an ssDNA-binding complex, is essential for various DNA-related processes. Here we report that RPA plays a novel role in DNA damage repair during postnatal oocyte development after meiotic recombination. To investigate the role of RPA during oogenesis, we inactivated RPA1 (replication protein A1), the largest subunit of the heterotrimeric RPA complex, specifically in oocytes using two germline-specific Cre drivers (Ddx4-Cre and Zp3-Cre). We find that depletion of RPA1 leads to the disassembly of the RPA complex, as evidenced by the absence of RPA2 and RPA3 in RPA1-deficient oocytes. Strikingly, severe DNA damage occurs in RPA1-deficient GV-stage oocytes. Loss of RPA in oocytes triggered the canonical DNA damage response mechanisms and pathways, such as activation of ATM, ATR, DNA-PK, and p53. In addition, the RPA deficiency causes chromosome misalignment at metaphase I and metaphase II stages of oocytes, which is consistent with altered transcript levels of genes involved in cytoskeleton organization in RPA1-deficient oocytes. Absence of the RPA complex in oocytes severely impairs folliculogenesis and leads to a significant reduction in oocyte number and female infertility. Our results demonstrate that RPA plays an unexpected role in DNA damage repair during mammalian folliculogenesis.

Innate immunity mediator STING modulates nascent DNA metabolism at stalled forks in human cells

Background: The cGAS/STING pathway, part of the innate immune response to foreign DNA, can be activated by cell's own DNA arising from the processing of the genome, including the degradation of nascent DNA at arrested replication forks, which can be upregulated in cancer cells. Recent evidence raises a possibility that the cGAS/STING pathway may also modulate the very processes that trigger it, e.g., DNA damage repair or processing of stalled forks. Methods: We manipulated STING levels in human cells by depleting or re-expressing it, and assessed the effects of STING on replication using microfluidics-assisted replication track analysis, or maRTA, a DNA fiber assay, as well as immuno-precipitation of nascent DNA, or iPOND. We also assessed STING subcellular distribution and its ability to activate. Results: Depletion of STING suppressed and its re-expression in STING-deficient cancer cells upregulated the degradation of nascent DNA at arrested replication forks. Replication fork arrest was accompanied by the STING pathway activation, and a STING mutant that does not activate the pathway failed to upregulate nascent DNA degradation. cGAS was required for STING's effect on degradation, but this requirement could be bypassed by treating cells with a STING agonist. Cells expressing inactive STING had a reduced level of RPA on parental and nascent DNA of arrested forks and a reduced CHK1 activation compared to cells with the wild type STING. STING also affected unperturbed fork progression in a subset of cell lines. STING fractionated to the nuclear fractions enriched for structural components of chromatin and nuclear envelope, and furthermore, it associated with the chromatin of arrested replication forks as well as post-replicative chromatin. Conclusion: Our data highlight STING as a determinant of stalled replication fork integrity, thus revealing a novel connection between the replication stress and innate immune responses.