ID: 32013726
Title: Cholesterol derivatives induce dephosphorylation of the histone deacetylases Rpd3/HDAC1 to upregulate autophagy.
Abstract: Histone deacetylases (HDACs) are important for global gene expression and contribute to numerous physiological events. Deacetylase Rpd3 in yeast and its conserved homolog HDAC1 in mammals oppositely regulate autophagy; however, how Rpd3/HDAC1 is regulated to mediate autophagy remains unclear. Here, we showed autophagy occurrence in silkworm (Bombyx mori) required BmRpd3, wherein steroid hormone 20-hydroxyecdysone (20E) signaling regulated its protein level and nuclear localization negatively. Inhibition of MTOR led to dephosphorylation and nucleo-cytoplasmic translocation of BmRpd3/HsHDAC1. Besides, cholesterol, 20E, and 27-hydroxycholesterol could all induce massive dephosphorylation and cytoplasmic localization of BmRpd3/HsHDAC1, and thus autophagy by affecting MTORC1 activity. In addition, three phosphorylation sites (Ser392, Ser421, and Ser423) identified in BmRpd3 were conserved in HsHDAC1. Single or triple phosphorylation-site mutation attenuated the phosphorylation levels of BmRpd3/HsHDAC1, leading to their cytoplasmic localization and autophagy activation. In general, cholesterol derivatives, especially hydroxylated cholesterol, caused dephosphorylation and nucleo-cytoplasmic shuttling of BmRpd3/HsHDAC1 through inhibition of MTOR signaling to facilitate autophagy in B. mori and mammals. These findings improve our understandings of BmRpd3/HsHDAC1-mediated autophagy induced by cholesterol derivatives and shed light on their potential as a therapeutic target for neurodegenerative diseases and autophagy-related studies.Abbreviations: 20E: 20-hydroxyecdysone; 27-OH: 27-hydroxycholesterol; ACTB: actin beta; AMPK: AMP-activated protein kinase; Atg: autophagy-related; BmSqstm1: Bombyx sequestosome 1; CQ: chloroquine; HDAC: histone deacetylase; LMNB: Lamin B1; MTOR: mechanistic target of rapamycin kinase; PE: phosphatidylethanolamine; SQSTM1/p62: sequestosome 1; TUBA1A: tubulin alpha 1a.

ID: 33958580
Title: Small heat-shock protein HSPB3 promotes myogenesis by regulating the lamin B receptor.
Abstract: One of the critical events that regulates muscle cell differentiation is the replacement of the lamin B receptor (LBR)-tether with the lamin A/C (LMNA)-tether to remodel transcription and induce differentiation-specific genes. Here, we report that localization and activity of the LBR-tether are crucially dependent on the muscle-specific chaperone HSPB3 and that depletion of HSPB3 prevents muscle cell differentiation. We further show that HSPB3 binds to LBR in the nucleoplasm and maintains it in a dynamic state, thus promoting the transcription of myogenic genes, including the genes to remodel the extracellular matrix. Remarkably, HSPB3 overexpression alone is sufficient to induce the differentiation of two human muscle cell lines, LHCNM2 cells, and rhabdomyosarcoma cells. We also show that mutant R116P-HSPB3 from a myopathy patient with chromatin alterations and muscle fiber disorganization, forms nuclear aggregates that immobilize LBR. We find that R116P-HSPB3 is unable to induce myoblast differentiation and instead activates the unfolded protein response. We propose that HSPB3 is a specialized chaperone engaged in muscle cell differentiation and that dysfunctional HSPB3 causes neuromuscular disease by deregulating LBR.

ID: 35239049
Title: CTCF supports preferentially short lamina-associated domains.
Abstract: More than one third of the mammalian genome is in a close association with the nuclear lamina, thus these genomic regions were termed lamina-associated domains (LADs). This association is fundamental for many aspects of chromatin biology including transcription, replication, and DNA damage repair. LADs association with the nuclear envelope is thought to be dependent on two major mechanisms: The first mechanism is the interaction between nuclear membrane proteins such as LBR with heterochromatin modifications that are enriched in LADs chromatin. The second mechanism is based on proteins that bind the borders of the LADs and support the association of the LADs with the nuclear envelope. Two factors were suggested to support the second mechanism: CCCTC-binding factor (CTCF) and YY1 based on their enriched binding to LADs borders. However, this mechanism has not been proven yet at a whole genome level. Here, to test if CTCF supports the LADs landscape, we generated melanoma cells with a partial loss of function (pLoF) of CTCF by the CRISPR-Cas9 system and determined the LADs landscape by lamin B ChIP-seq analysis. We found that under regular growth conditions, CTCF pLoF led to modest changes in the LADs landscape that included an increase in the signal of 2% of the LADs and a decrease in the signal of 8% of the LADs. However, CTCF importance for the LADs landscape was much higher upon induction of a chromatin stress. We induced chromatin stress by inhibiting RNA polymerase II, an intervention that is known to alter chromatin compaction and supercoiling. Notably, only in CTCF pLoF cells, the chromatin stress led to the dissociation of 7% of the LADs from the lamina. The CTCF-dependent LADs had almost three times shorter median length than the non-affected LADs, were enriched in CTCF binding at their borders, and were higher in their facultative-status (cell-type specific). Thus, it appears that CTCF is a key factor in facilitating the association of short facultative LADs with the nuclear lamina upon chromatin stress.

ID: 35453551
Title: Diagnostic and Clinical Value of Specific Autoantibodies against Kelch-like 12 Peptide and Nuclear Envelope Proteins in Patients with Primary Biliary Cholangitis.
Abstract: Primary biliary cholangitis (PBC) is a chronic autoimmune liver disease characterized by the presence of antimitochondrial and antinuclear antibodies in patients’ serum. Here, we analyzed the reactivity of autoantibodies against a novel autoantigen, kelch-like 12 (KLHL12) protein, in a cohort of 138 PBC and 90 non-PBC patients. Additionally, we compared the reactivity of KLHL12 with antinuclear envelope antibodies: anti-gp210, anti-p62, and anti-LBR. Commercially available kits and an ‘in-house’ ELISA were used in the studies. Antinuclear envelope antibodies were detected in 65% of PBC patients and the presence of these antibodies was observed more frequently in patients diagnosed with later stages (III/IV) of PBC, according to Ludwig’s classification (p < 0.05) and were found to correlate with a higher concentration of bilirubin. Overall, anti-KLHL12 antibodies were found more frequently in PBC patients than in non-PBC controls (p < 0.001). Anti-KLHL12 antibodies were detected in 36% of the tested PBC cohort, including PBC patients negative for antimitochondrial antibodies. Presence of anti-KLHL12 was also associated with a higher concentration of bilirubin and correlated with fibrosis (p < 0.05). Anti-KLHL12 antibodies were detected in 30% of PBC individuals positive for antinuclear envelope antibodies, while anti-KLHL12 and antinuclear envelope antibodies were found in 17% of all PBC cases. Concluding, our data confirm that antibodies against the KLHL12 protein are highly specific for PBC and when used in combination with other markers, may significantly increase the diagnosis of PBC.

ID: 35972904
Title: Shared and Distinctive Neighborhoods of Emerin and Lamin B Receptor Revealed by Proximity Labeling and Quantitative Proteomics.
Abstract: Emerin and lamin B receptor (LBR) are abundant transmembrane proteins of the nuclear envelope that are concentrated at the inner nuclear membrane (INM). Although both proteins interact with chromatin and nuclear lamins, they have distinctive biochemical and functional properties. Here, we have deployed proximity labeling using the engineered biotin ligase TurboID (TbID) and quantitative proteomics to compare the neighborhoods of emerin and LBR in cultured mouse embryonic fibroblasts. Our analysis revealed 232 high confidence proximity partners that interact selectively with emerin and/or LBR, 49 of which are shared by both. These included previously characterized NE-concentrated proteins, as well as a host of additional proteins not previously linked to emerin or LBR functions. Many of these are TM proteins of the ER, including two E3 ubiquitin ligases. Supporting these results, we found that 11/12 representative proximity relationships identified by TbID also were detected at the NE with the proximity ligation assay. Overall, this work presents methodology that may be used for large-scale mapping of the landscape of the INM and reveals a group of new proteins with potential functional connections to emerin and LBR.

ID: 36124691
Title: Nuclear envelope protein lamin B receptor protects the genome from chromosomal instability and tumorigenesis.
Abstract: Lamin B Receptor (LBR) is an inner nuclear membrane protein that assembles the nuclear envelope post mitosis. Here we show that LBR depletion induces mitotic defects accompanied by recurrent chromosomal losses. In addition, LBR knockdown results in nuclear aberrations such as nuclear blebs and micronuclei, with chromosomes showing higher frequency of losses, being enriched within the micronucleus. Furthermore, doxycycline-induced conditional depletion of LBR significantly increased tumor volumes that form within the subcutaneous xenografts of mice. Of note, the tumor-derived primary cells recapitulated chromosomal losses and gains, revealing a novel role for LBR as a tumor suppressor. Co-immunoprecipitation of LBR uncovered an association of LBR with telomere-associated factors. Interestingly, qPCR array-based gene expression profiling showed a significant upregulation of telomere repeat-binding factor 1 (TRF1) upon LBR depletion. Remarkably, TRF1 knockdown in the background of LBR depletion maintains chromosomal stability, unraveling a novel mechanism involving LBR and TRF in the maintenance of chromosomal stability in colorectal cancer cells.

ID: 36598800
Title: Differentiation-dependent changes in lamin B1 dynamics and lamin B receptor localization.
Abstract: The nuclear lamina serves important roles in chromatin organization and structural support, and lamina mutations can result in laminopathies. Less is known about how nuclear lamina structure changes during cellular differentiation-changes that may influence gene regulation. We examined the structure and dynamics of the nuclear lamina in human-induced pluripotent stem cells (iPSCs) and differentiated germ layer cells, focusing on lamin B1. We report that lamin B1 dynamics generally increase as iPSCs differentiate, especially in mesoderm and ectoderm, and that lamin B receptor (LBR) partially redistributes from the nucleus to cytoplasm in mesoderm. Knocking down LBR in iPSCs led to an increase in lamin B1 dynamics, a change that was not observed for ELYS, emerin, or lamin B2 knockdown. LBR knockdown also affected expression of differentiation markers. These data suggest that differentiation-dependent tethering of lamin B1 either directly by LBR or indirectly via LBR-chromatin associations impacts gene expression.

ID: 36611919
Title: SR Protein Kinase 1 Inhibition by TAF15.
Abstract: Although SRPKs were discovered nearly 30 years ago, our understanding of their mode of regulation is still limited. Regarded as constitutively active enzymes known to participate in diverse biological processes, their prominent mode of regulation mainly depends on their intracellular localization. Molecular chaperones associate with a large internal spacer sequence that separates the bipartite kinase catalytic core and modulates the kinases' partitioning between the cytoplasm and nucleus. Besides molecular chaperones that function as anchoring proteins, a few other proteins were shown to interact directly with SRPK1, the most-studied member of SRPKs, and alter its activity. In this study, we identified TAF15, which has been involved in transcription initiation, splicing, DNA repair, and RNA maturation, as a novel SRPK1-interacting protein. The C-terminal RGG domain of TAF15 was able to associate with SRPK1 and downregulate its activity. Furthermore, overexpression of this domain partially relocalized SRPK1 to the nucleus and resulted in hypophosphorylation of SR proteins, inhibition of splicing of a reporter minigene, and inhibition of Lamin B receptor phosphorylation. We further demonstrated that peptides comprising the RGG repeats of nucleolin, HNRPU, and HNRNPA2B1, were also able to inhibit SRPK1 activity, suggesting that negative regulation of SRPK1 activity might be a key biochemical property of RGG motif-containing proteins.

ID: 37223461
Title: Phosphorylation Promotes the Accumulation of PERIOD Protein Foci.
Abstract: Circadian clock drives the 24-h rhythm in our behavior and physiology. The molecular clock consists of a series of transcriptional/translational feedback loops operated by a number of clock genes. A very recent study reported that the clock protein PERIOD (PER) is organized into discrete foci at the nuclear envelope in fly circadian neurons, which is believed to be important for controlling the subcellular localization of clock genes. Loss of inner nuclear membrane protein lamin B receptor (LBR) leads to disruption of these foci, but how they are regulated is yet unknown. Here, we found that PER foci are likely phase-separated condensates, the formation of which is mediated by intrinsically disordered region in PER. Phosphorylation promotes the accumulation of these foci. Protein phosphatase 2A, which is known to dephosphorylate PER, hampers the accumulation of the foci. On the other hand, the circadian kinase DOUBLETIME (DBT) which phosphorylates PER enhances the accumulation of the foci. LBR likely facilitates PER foci accumulation by destabilizing the catalytic subunit of protein phosphatase 2A, MICROTUBULE STAR (MTS). In conclusion, here, we demonstrate a key role for phosphorylation in promoting the accumulation of PER foci, while LBR modulates this process by impinging on the circadian phosphatase MTS.

ID: 38185834
Title: Fly clock, my clock, and lamin B receptor.
Abstract: In the fruit fly Drosophila melanogaster, circadian rhythm was disrupted when the inner nuclear membrane protein lamin B receptor (LBR) was depleted from its clock neurons (Proc. Natl. Acad. Sci. USA 118, e2019756118. 2021; https://doi.org/10. 1073/pnas.2019756118 and Research 6, 0139, 2023; https://doi.org/10.34133/research.0139). Ordinarily, the clock proteinPERIOD (PER) forms foci close to the inner nuclear membrane in the circadian clock's repression phase. The size, number, and location of foci near the nuclear membrane oscillate with a 24-h rhythm. When LBR was absent the foci did not form. The PER foci bring per and other clock genes close to the nuclear envelope, where their transcription is silenced. Then, in the circadian clock's activation phase, the PER protein gradually gets degraded and the foci disappear. The clock genes, including per, relocate to the nucleus interior where they resume transcription. Rhythmic re-positioning of clock genes between nucleus periphery and interior, correlates with their repression and activation in the circadian cycle. Absence of LBR disrupted this rhythm. Phosphorylation of PER promoted the formation of foci whereas dephosphorylation by protein phosphatase 2A causedthem to disappear. LBR promoted focus formation by destabilizing the catalytic subunit of protein phosphatase 2A. The lbr gene is no stranger to this journal. The first hint that vertebrate LBR is also a sterol biosynthesis enzyme, specifically, a sterol C14 reductase, was reported here (J. Genet. 73, 33-41, 1994; https://www.ias.ac.in/article/fulltext/jgen/073/01/0033-0041). Mutations in the human Lbr gene cause a range of phenotypes--from the relatively benign Pelger-Huet anomaly to the perinatally lethal Greenberg skeletal dysplasia.Drosophila, like all insects, is a sterol auxotroph. The fly orthologue of vertebrate lbr genes encodes a protein (dLBR) that shares several properties with vertebrate LBR proteins, with one notable exception. While human LBR complemented theyeast Saccharomyces cerevisiae erg24 mutant which lacks sterol C14 reductase activity, dLBR did not (J. Cell. Sci. 117, 2015-28, 2004; https://doi.org/10.1242/jcs.01052). Despite not possessing sterol reductase activity, dLBR retains significant sequence homology with vertebrate LBRs which have this activity. An undergraduate summer trainee in my laboratory obtained early (unpublished) evidence that dLBR lost sterol reductase activity during evolution. She transferred adult drosophila flies to vials containing a medium made of agar, dextrose, and dried and powdered mycelium of the filamentous fungus Neurospora crassa. On medium made with wild-type mycelium, theflies mated, laid eggs, hatched larvae, and developed pupae which eclosed progeny adult flies. The life cycle was no different than on 'regular' fly food composed of agar, dextrose and yeast extract. However, on a medium made with mycelium from a sterol C14 reductase null mutant, the flies laid eggs which hatched and released larvae, but the larvae failed to pupate, and no adult progeny flies emerged. This was because the fly lacks a sterol C14 reductase. The wild-type sterol, ergosterol, is a precursor of the steroid hormone ecdysone needed for molting and metamorphosis. Can expression of vertebrate LBR in dLBR-depleted fly clock neurons restore circadian rhythm? Can expression of vertebrate LBR enable flies to complete their life cycle on mutant Neurospora medium? Does LBR regulate the vertebrate clock in a like manner? If yes, then is the sterol reductase activity dispensable in this role? These are some questions that came to my mind on a recent morning walk. The walk itself was a much-cherished outcome of my circadian clock.

ID: 38712240
Title: Neutrophils secrete exosome-associated DNA to resolve sterile acute inflammation.
Abstract: Acute inflammation, characterized by a rapid influx of neutrophils, is a protective response that can lead to chronic inflammatory diseases when left unresolved. Secretion of LTB 4 -containing exosomes is required for effective neutrophil infiltration during inflammation. In this study, we show that neutrophils release nuclear DNA in a non-lytic, rapid, and repetitive manner, via a mechanism distinct from suicidal NET release and cell death. The packaging of nuclear DNA occurs in the lumen of nuclear envelope (NE)-derived multivesicular bodies (MVBs) that harbor the LTB 4 synthesizing machinery and is mediated by the lamin B receptor (LBR) and chromatin decondensation. Disruption of secreted exosome-associated DNA (SEAD) in a model of sterile inflammation in mouse skin amplifies and prolongs the presence of neutrophils, impeding the onset of resolution. Together, these findings advance our understanding of neutrophil functions during inflammation and the physiological significance of NETs, with implications for novel treatments for inflammatory disorders.

ID: 39252008
Title: Calpain-1 weakens the nuclear envelope and promotes the release of neutrophil extracellular traps.
Abstract: The inducers of neutrophil extracellular trap (NET) formation are heterogeneous and consequently, there is no specific pathway or signature molecule indispensable for NET formation. But certain events such as histone modification, chromatin decondensation, nuclear envelope breakdown, and NET release are ubiquitous. During NET formation, neutrophils drastically rearrange their cytoplasmic, granular and nuclear content. Yet, the exact mechanism for decoding each step during NET formation still remains elusive. Here, we investigated the mechanism of nuclear envelope breakdown during NET formation. Immunofluorescence microscopic evaluation revealed a gradual disintegration of outer nuclear membrane protein nesprin-1 and alterations in nuclear morphology during NET formation. MALDI-TOF analysis of NETs that had been generated by various inducers detected the accumulation of nesprin-1 fragments. This suggests that nesprin-1 degradation occurs before NET release. In the presence of a calpain-1, inhibitor nesprin-1 degradation was decreased in calcium driven NET formation. Microscopic evaluation confirmed that the disintegration of the lamin B receptor (LBR) and the collapse of the actin cytoskeleton occurs in early and later phases of NET release, respectively. We conclude that the calpain-1 degrades nesprin-1, orchestrates the weakening of the nuclear membrane, contributes to LBR disintegration, and promoting DNA release and finally, NETs formation.

ID: 40355051
Title: Novel LBR pathogenic variants with loss of sterol reductase activity participate in the pathogenesis of skeletal dysplasia via dysregulating canonical Wnt pathway.
Abstract: Biallelic pathogenic variants in the lamin B receptor (LBR) with impaired sterol reductase function are associated with the development of perinatal lethal Greenberg dysplasia (GRBGD) and mild nonfatal skeletal dysplasia with or without Pelger-Huet anomaly (PHASK), as well as other related hereditary skeletal dysplasia. However, the underlying molecular mechanism remains unclear. In this study, we found two novel pathogenic variants of LBR, namely missense mutation (c.1011 T > G, NM_002296.4; p.Cys337Trp, NP_002287.2) and LBR gene deletion (Chr1q42.12 (225,515,082-225,633,464), NC_000001.10). LBR is a novel substrate of FBW7, which is degraded by GSK3β/FBW7-mediated proteasome pathway and whose C337W mutation promotes its degradation through enhanced interaction with FBW7. Wild-type but not C337W mutant LBR is upregulated by WNT3A-mediated inactivation of GSK3β/FBW7 axis and then participated in WNT3A-activated Wnt pathway through its mediated cholesterol synthesis. MC3T3-E1 cells with Lbr knockdown or cholesterol removal exhibited reduced mineralized nodules in the presence of WNT3A, but addition of cholesterol in the culture medium reversed this phenotype. Collectively, we detected two novel variants in LBR and our study revealed for the first time that disruption of cholesterol synthesis by LBR impairs Wnt pathway and thus disrupts the cell osteogenic differentiation, providing new insights into the pathogenesis of skeletal dysplasia caused by LBR variation.

ID: 41002030
Title: Coordinated control of genome-nuclear lamina interactions by topoisomerase 2B and lamin B receptor.
Abstract: Lamina-associated domains (LADs) are megabase-sized genomic regions anchored to the nuclear lamina (NL). Factors controlling the interactions of the genome with the NL have largely remained elusive. Here, we identified DNA topoisomerase 2 beta (TOP2B) as a regulator of these interactions. TOP2B binds predominantly to inter-LAD (iLAD) chromatin and its depletion results in a partial loss of genomic partitioning between LADs and iLADs, suggesting that this enzyme might protect specific iLADs from interacting with the NL. TOP2B depletion affects LAD interactions with lamin B receptor (LBR) more than with lamins. LBR depletion phenocopies the effects of TOP2B depletion, despite the different positioning of the two proteins in the genome. This suggests a complementary mechanism for organizing the genome at the NL. Indeed, co-depletion of TOP2B and LBR causes partial LAD/iLAD inversion, reflecting changes typical of oncogene-induced senescence. We propose that a coordinated axis controlled by TOP2B in iLADs and LBR in LADs maintains the partitioning of the genome between the NL and the nuclear interior.

ID: 41059452
Title: A Family of LBR Biallelic Pathogenic Variants Resulting in Rhizomelic Skeletal Dysplasia with Pelger-Huët Anomaly.
Abstract: The lamin-B receptor (LBR) gene has two primary functions: maintaining the structural integrity of the nuclear envelope and playing a role in cholesterol biosynthesis. Heterozygous variants in the LBR gene have been associated with Pelger-Huët anomaly (PHA, OMIM #169400), while homozygous or compound heterozygous mutations have been associated with rhizomelic skeletal dysplasia, with or without PHA (OMIM #618019) and Greenberg dysplasia (OMIM #215140). We report a 4-year-old boy presenting with short stature and short limbs and his mother exhibiting milder findings. Genetic analysis revealed a heterozygous c.1640A>G (p.Asn547Ser) and c.43C>T (p.Arg15*) variants in the LBR gene in both the boy and his mother. The father was identified as a heterozygous carrier of the c.43C>T (p.Arg15*) variant. Peripheral blood smears confirmed the PHA in the patient and his parents. The phenotypic differences observed between the mother and male child in our study highlight the genetic variability and regressive nature of LBR-related skeletal dysplasias. This report shows the complexity of LBR-related phenotypes and expands the clinical spectrum of LBR mutations in rhizomelic skeletal dysplasia with PHA.

ID: 41735607
Title: LBR and LAP2 mediate heterochromatin tethering to the nuclear periphery to preserve genome homeostasis.
Abstract: In most eukaryotic cells, euchromatin is localized in the nuclear interior, whereas heterochromatin is enriched at the nuclear envelope (NE). This conventional chromatin organization is established by heterochromatin tethering to the NE; however, its importance for cellular homeostasis is largely unexplored. One tether is constituted by the lamin B receptor (LBR) in mammals, but the enigmatic nature of other redundant tethers has hampered functional analyses. Here we demonstrate that downregulation of abundant, ubiquitous NE proteins can induce the global detachment of heterochromatin from the NE and its repositioning to the nuclear interior. We identify LBR and lamina-associated polypeptide 2 (LAP2) as key factors for peripheral heterochromatin positioning in differentiated and pluripotent mammalian cells. Their long-term loss leads to changes in three-dimensional chromatin organization and a reduction in repressive epigenetic marks, especially H3K27me3. These changes are associated with massive deregulation of gene expression, activation of antiviral innate immunity, and defects in cell fate determination.

ID: 41757046
Title: Antagonistic contributions of A-type and B-type lamins to LBR localization and dynamics.
Abstract: Lamin B receptor (LBR) is an inner nuclear membrane (INM) protein that plays crucial roles in maintaining nuclear architecture and organization of peripheral heterochromatin. Lamins and LBR both contribute to chromatin tethering at the nuclear periphery, and the expression of LBR and A-type lamins is tightly regulated during development to ensure a faithful transition between different chromatin tethering modalities. Despite its well-established association with B-type lamins, the contributions of individual lamin isoforms to LBR localization and anchorage have not been systematically examined. Here, we used mouse embryonic fibroblasts (MEFs) lacking all endogenous lamins (triple lamin knockout: TKO) to assess how specific lamin isoforms and domains regulate LBR subcellular localization and mobility. Whereas ectopic expression of either lamin B1 or lamin B2 was sufficient to tether LBR to the nuclear envelope in TKO cells, expression of lamin A increased the lateral mobility of LBR at the nuclear membrane, resulting in its displacement from the nuclear envelope to the ER. The lamin A-induced displacement of LBR was mediated by phosphorylation of LBR. Overexpression of lamin A in wild-type MEFs similarly increased LBR phosphorylation and promoted its displacement from the nuclear envelope. Collectively, these findings define isoform-specific and antagonistic roles for A-type and B-type lamins in regulating LBR anchorage at the nuclear envelope. In addition, they indicate a lamin A-dependent mechanism that may reflect a broader developmental process, since LBR and lamin A sequentially tether peripheral heterochromatin during development.

ID: 42017968
Title: Tau oligomerization induces nuclear lamina invagination and chromatin remodeling in Alzheimer's disease.
Abstract: The aggregation of the microtubule-associated protein tau into oligomeric complexes is strongly correlated with the onset and progression of neurodegeneration in Alzheimer's disease (AD). Increasing evidence implicates nuclear membrane disruption in AD and related tauopathies; however, whether this is a cause or consequence of neurodegeneration remains unresolved. Here, we show that nuclear lamina disruption emerges at the early Braak stages, coinciding with the initial formation of pathological tau aggregates in post-mortem AD brain tissue. Using the tauopathy mouse model (P301S PS19), we demonstrate that oligomeric tau (oTau) directly binds to the Lamin B Receptor (LBR), inducing nuclear envelope invaginations as revealed by electron microscopy. These structural alterations are accompanied by chromatin remodeling and gene expression dysregulation. To dissect the underlying mechanism, we employed a light-inducible OptoTau system (4R1N Tau::mCherry::Cry2Olig) in human iPSC-derived neurons, enabling real-time visualization of tau aggregation dynamics. This system revealed selective recruitment of oTau to the nuclear envelope and direct interactions with LBR and Lamin B2, leading to nuclear deformation and activation of the protein translational stress response. Together, these findings identify nuclear membrane disruption as an early and potentially causative event in tau-mediated neurodegeneration, establishing a mechanistic link between tau oligomerization, nuclear stress, and chromatin remodeling. Targeting nuclear destabilization may offer new therapeutic avenues for mitigating AD pathogenesis.

ID: 42153377
Title: Antagonistic contributions of A-type and B-type lamins to LBR localization and dynamics.
Abstract: Lamin B receptor (LBR) is an inner nuclear membrane protein that organizes peripheral heterochromatin and cooperates with lamins to tether chromatin at the nuclear periphery. However, how individual lamin isoforms regulate LBR localization and anchorage remains unclear. Using mouse embryonic fibroblasts lacking all endogenous lamins, we examined how individual lamin isoforms regulate LBR behavior. Expression of lamin B1 or B2 was sufficient to anchor LBR at the nuclear envelope, whereas lamin A expression increased LBR mobility and led to its displacement from the nuclear envelope. This effect was mediated by phosphorylation of LBR and was recapitulated by lamin A overexpression in wild-type cells. Collectively, these findings define isoform-specific and antagonistic roles for A-type and B-type lamins in regulating LBR anchorage at the nuclear envelope. In addition, they indicate a lamin A-dependent mechanism that may reflect a broader developmental process, since LBR and lamin A sequentially tether peripheral heterochromatin during development.

ID: 42554236
Title: MODY Mutations in Transcription Factors HNF1A and HNF1B Affect the Production of Interferon Signaling Proteins: Evidence at the Proteome Level.
Abstract: This discovery study investigated the impact of MODY-associated mutations in hepatocyte nuclear factors HNF1A and HNF1B on the cellular proteome, aiming to identify affected pathways and advance understanding of diabetes pathogenesis. Human induced pluripotent stem cells (hiPSCs) carrying the HNF1A frameshift mutation (p.Pro291fsinsC) were differentiated into pancreatic progenitors, and renal proximal tubule epithelial cells (RPTECs) were engineered to overexpress HNF1B with the S148L point mutation. Label-free quantitative proteomics was performed using data-dependent and data-independent acquisition on Orbitrap and timsTOF mass spectrometers. Pathway enrichment was analyzed using Qiagen IPA, Hallmark gene sets, and STRING networks. Comprehensive proteome coverage (over 7000 proteins) revealed consistent downregulation of oxidative phosphorylation, mitochondrial function, and interferon signaling pathways. Both models exhibited suppression of innate immune responses, with overlapping downregulated proteins, including members of the OAS, IFIT, and MX1 families. Using label-free proteomics, we show that MODY-associated mutations in HNF1A and HNF1B suppress mitochondrial function and interferon signaling and are additionally associated with reduced abundance of predicted targets such as A1CF as well as diabetes-related proteins including SCGN, supporting their role in diabetes pathogenesis.

ID: 42554525
Title: TagR, a newly identified member of the MarR family of transcriptional regulators, represses the NRPS operon in Klebsiella oxytoca.
Abstract: Toxigenic Klebsiella oxytoca strains produce the pyrrolobenzodiazepine enterotoxins tilimycin (TM) and tilivalline (TV), which contribute to the development of antibiotic-associated hemorrhagic colitis. The biosynthesis of these toxins depends on the nonribosomal peptide synthetase (NRPS) operon located within the til pathogenicity island. Although several global and signal-responsive regulators of NRPS operon expression have been identified, the regulatory network governing enterotoxin biosynthesis remains incompletely characterized. In this study, we identified a previously unrecognized transcriptional regulator encoded within the til pathogenicity island of K. oxytoca. This protein, designated TagR (Tilivalline-associated genes repressor), is a member of the MarR family and acts as a negative regulator of NRPS operon expression. Structural prediction, molecular dynamics simulations, and biochemical analyses demonstrated that TagR exhibits the characteristic architecture of MarR family regulators and forms a stable homodimer. Deletion of tagR led to significant upregulation of the NRPS-associated genes npsA, thdA, and npsB, while complementation restored transcriptional repression. Electrophoretic mobility shift assays confirmed that TagR binds directly and specifically to the regulatory region upstream of the NRPS operon, supporting a mechanism of direct transcriptional repression. Consistent with these findings, loss of TagR significantly increased the cytotoxicity of K. oxytoca culture supernatants toward HeLa cells. Collectively, these results identify TagR as a direct repressor of the NRPS operon and expand the regulatory framework governing enterotoxin biosynthesis in toxigenic K. oxytoca. This study provides new insight into the transcriptional control of virulence-associated genes and establishes TagR as a previously unrecognized component of the regulatory network controlling TM and TV production.IMPORTANCEElucidating the mechanisms by which toxigenic Klebsiella oxytoca regulates enterotoxin production is critical for understanding the pathogenesis of antibiotic-associated hemorrhagic colitis. TagR is identified as a previously unrecognized MarR family regulator that directly represses the nonribosomal peptide synthetase (NRPS) operon responsible for tilimycin (TM) and tilivalline (TV) biosynthesis. This discovery uncovers a novel regulatory mechanism governing toxin production and offers new perspectives on virulence regulation in this emerging intestinal pathogen.