Review: nuclear lamins--structural proteins with fundamental functions

Lamin chromatin binding is modulated by interactions of different LAP2α domains with lamins and chromatin

Lamins A and C are components of the lamina at the nuclear periphery and associate with heterochromatin. A distinct, relatively mobile pool of lamin A/C in the nuclear interior associates with euchromatic regions and with lamin-associated polypeptide 2α (LAP2α). Here we show that phosphorylation-dependent impairment of lamin assembly had no effect on its chromatin association, while LAP2α depletion was sufficient to increase chromatin association of lamins. This suggests that complex interactions between LAP2α, chromatin, and lamins regulate lamin chromatin binding. Both the C terminus of LAP2α and its N-terminal LAP2-Emerin-MAN1 (LEM) domain, mediating interaction with lamin A/C indirectly via barrier-to-autointegration factor (BAF), are required for binding to lamins. The N-terminal LEM-like domain of LAP2α, but not its LEM domain, mediates chromatin association of LAP2α and requires LAP2α dimerization via its C terminus. Our data suggest that formation of several LAP2α-, lamin A/C-, and BAF-containing complexes in the nucleoplasm and on chromatin affects lamin chromatin association.

Transcription factor FOXM1 specifies chromatin DNA to extracellular vesicles

Extracellular vesicle DNAs (evDNAs) hold significant diagnostic value for various diseases and facilitate transcellular transfer of genetic material. Our study identifies transcription factor FOXM1 as a mediator for directing chromatin genes or DNA fragments (termed FOXM1-chDNAs) to extracellular vesicles (EVs). FOXM1 binds to MAP1LC3/LC3 in the nucleus, and FOXM1-chDNAs, such as the DUX4 gene and telomere DNA, are designated by FOXM1 binding and translocated to the cytoplasm before being released to EVs through the secretory autophagy during lysosome inhibition (SALI) process involving LC3. Disrupting FOXM1 expression or the SALI process impairs FOXM1-chDNAs incorporation into EVs. FOXM1-chDNAs can be transmitted to recipient cells via EVs and expressed in recipient cells when they carry functional genes. This finding provides an example of how chromatin DNA fragments are specified to EVs by transcription factor FOXM1, revealing its contribution to the formation of evDNAs from nuclear chromatin. It provides a basis for further exploration of the roles of evDNAs in biological processes, such as horizontal gene transfer.Abbreviation: ATG5: autophagy related 5; CCFs: cytoplasmic chromatin fragments; ChIP: chromatin immunoprecipitation; cytoDNA: cytoplasmic DNA; CQ: chloroquine; FOXM1-DBD: FOXM1 DNA binding domain; DUX4:double homeobox 4; EVs: extracellular vesicles; evDNAs: extracellular vesicle DNAs; FOXM1: forkhead box M1; FOXM1-chDNAs: chromatin DNA fragments directed by FOXM1 to EVs; HGT: horizontal gene transfer; LC3-II: lipid modified LC3; LMNB1: lamin B1; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MVBs: multivesicular bodies; M1-binding DNA: a linear DNA containing 72× FOXM1 binding sites; SALI: secretory autophagy during lysosome inhibition; siRNA: small interfering RNA; TetO-DUX4: TetO array-containing DUX4 DNA; TetO: tet operator; TetR: tet repressor.

The structure and function of lamin A/C: Special focus on cardiomyopathy and therapeutic interventions

Lamins are inner nuclear membrane proteins that belong to the intermediate filament family. Lamin A/C lie adjacent to the heterochromatin structure in polymer form, providing skeletal to the nucleus. Based on the localization, lamin A/C provides nuclear stability and cytoskeleton to the nucleus and modulates chromatin organization and gene expression. Besides being the structural protein making the inner nuclear membrane in polymer form, lamin A/C functions as a signalling molecule involved in gene expression as an enhancer inside the nucleus. Lamin A/C regulates various cellular pathways like autophagy and energy balance in the cytoplasm. Its expression is highly variable in differentiated tissues, higher in hard tissues like bone and muscle cells, and lower in soft tissues like the liver and brain. In muscle cells, including the heart, lamin A/C must be expressed in a balanced state. Lamin A/C mutation is linked with various diseases, such as muscular dystrophy, lipodystrophy, and cardiomyopathies. It has been observed that a good number of mutations in the LMNA gene impact cardiac activity and its function. Although several works have been published, there are still several unexplored areas left regarding the lamin A/C function and structure in the cardiovascular system and its pathological state. In this review, we focus on the structural organization, expression pattern, and function of lamin A/C, its interacting partners, and the pathophysiology associated with mutations in the lamin A/C gene, with special emphasis on cardiovascular diseases. With the recent finding on lamin A/C, we have summarized the possible therapeutic interventions to treat cardiovascular symptoms and reverse the molecular changes.

Ion Mobility-Based Enrichment-Free N-Terminomics Analysis Reveals Novel Legumain Substrates in Murine Spleen

Aberrant levels of the asparaginyl endopeptidase legumain have been linked to inflammation, neurodegeneration, and cancer, yet our understanding of this protease is incomplete. Systematic attempts to identify legumain substrates have been previously confined to in vitro studies, which fail to mirror physiological conditions and obscure biologically relevant cleavage events. Using high-field asymmetric waveform ion mobility spectrometry (FAIMS), we developed a streamlined approach for proteome and N-terminome analyses without the need for N-termini enrichment. Compared to unfractionated proteomic analysis, we demonstrate FAIMS fractionation improves N-termini identification by >2.5 fold, resulting in the identification of >2882 unique N-termini from limited sample amounts. In murine spleens, this approach identifies 6366 proteins and 2528 unique N-termini, with 235 cleavage events enriched in WT compared to legumain-deficient spleens. Among these, 119 neo-N-termini arose from asparaginyl endopeptidase activities, representing novel putative physiological legumain substrates. The direct cleavage of selected substrates by legumain was confirmed using in vitro assays, providing support for the existence of physiologically relevant extra-lysosomal legumain activity. Combined, these data shed critical light on the functions of legumain and demonstrate the utility of FAIMS as an accessible method to improve depth and quality of N-terminomics studies.

Male vitellogenin regulates gametogenesis through a testis-enriched big protein in Chrysopa pallens

In insects, vitellogenin (Vg) is generally viewed as a female-specific protein. Its primary function is to supply nutrition to developing embryos. Here, we reported Vg from the male adults of a natural predator, Chrysopa pallens. The male Vg was depleted by RNAi. Mating with Vg-deficient male downregulated female Vg expression, suppressed ovarian development and decreased reproductive output. Whole-organism transcriptome analysis after male Vg knockdown showed no differential expression of the known spermatogenesis-related regulators and seminal fluid protein genes, but a sharp downregulation of an unknown gene, which encodes a testis-enriched big protein (Vcsoo). Separate knockdown of male Vg and Vcsoo disturbed the assembly of spermatid cytoplasmic organelles in males and suppressed the expansion of ovary germarium in mated females. These results demonstrated that C. pallens male Vg signals through the downstream Vcsoo and regulates male and female reproduction.

A novel observation: effect of anionic gelatin nanoparticle on stromal cells

Biocompatible nanoparticles are very popular in health science research. Biomolecule carriers for wound healing and tissue engineering are two main applications among many others. In many instances, these structures come in direct vicinity of cells and govern cell behaviour and responses. In this study, gelatin nano/submicron structures were synthesized by binary nonsolvent aided coacervation (BNAC) method at pH ranging from 3 to 11 with an intention to employ in skin tissue regeneration. Effect of pH over morphology and the surface composition with respect to its ionic composition were studied. Further, the initial toxicity was assessed against peripheral blood mononuclear cells (PBMC). pH 7 was found to be the optimum for synthesis of gelatin nanoparticles (GNPs) with minimum particle size. Positive cell viability of 103.14% for GNPs synthesized at pH 7 was observed. It may be due to the minimum difference between cumulative negative and positive charge (CNCP) ratio of 1.19. Finally, effect of the gelatin nanoparticles over L929 mouse fibroblast cells was assessed through MTT assay. It has resulted in 122.77% cell viability.

TOR1AIP1-Associated Nuclear Envelopathies

Human TOR1AIP1 encodes LAP1, a nuclear envelope protein expressed in most human tissues, which has been linked to various biological processes and human diseases. The clinical spectrum of diseases related to mutations in TOR1AIP1 is broad, including muscular dystrophy, congenital myasthenic syndrome, cardiomyopathy, and multisystemic disease with or without progeroid features. Although rare, these recessively inherited disorders often lead to early death or considerable functional impairment. Developing a better understanding of the roles of LAP1 and mutant TOR1AIP1-associated phenotypes is paramount to allow therapeutic development. To facilitate further studies, this review provides an overview of the known interactions of LAP1 and summarizes the evidence for the function of this protein in human health. We then review the mutations in the TOR1AIP1 gene and the clinical and pathological characteristics of subjects with these mutations. Lastly, we discuss challenges to be addressed in the future.

α7 Nicotinic acetylcholine receptors regulate translocation of HIF-1α to the cell nucleus and mitochondria upon hypoxia

Nicotinic acetylcholine receptors (nAChRs), initially characterized as ligand-gated ion channels mediating fast synaptic transmission, are now found in many non-excitable cells and mitochondria where they function in ion-independent manner and regulate vital cellular processes like apoptosis, proliferation, cytokine secretion. Here we show that the nAChRs of α7 subtype are present in the nuclei of liver cells and astrocytoma U373 cell line. As shown by lectin ELISA, the nuclear α7 nAChRs are mature glycoproteins that follow the standard rout of post-translational modifications in Golgi; however, their glycosylation profile is non-identical to that of mitochondrial nAChRs. They are exposed on the outer nuclear membrane and are found in combination with lamin B1. The nuclear α7 nAChRs are up-regulated in liver within 1 h after partial hepatectomy and in H₂O₂-treated U373 cells. As shown both in silico and experimentally, the α7 nAChR interacts with hypoxia-inducible factor HIF-1α and this interaction is impaired by α7-selective agonists PNU282987 and choline or type 2 positive allosteric modulator PNU120596, which prevent HIF-1α accumulation in the nuclei. Similarly, HIF-1α interacts with mitochondrial α7 nAChRs in U373 cells treated with dimethyloxalylglycine. It is concluded that functional α7 nAChRs influence HIF-1α translocation into the nucleus and mitochondria upon hypoxia.

Nanoengineered sonosensitive platelets for synergistically augmented sonodynamic tumor therapy by glutamine deprivation and cascading thrombosis

Ultrasound (US)-activated sonodynamic therapy (SDT) stands for a distinct antitumor modality because of its attractive characteristics including intriguing noninvasiveness, desirable safety, and high tissue penetration depth, which, unfortunately, suffers from compromised therapeutic efficacy due to cancer cell-inherent adaptive mechanisms, such as glutathione (GSH) neutralization response to reactive oxygen species (ROS), and glutamine addictive properties of tumors. In this work, we developed a biological sonosensitive platelet (PLT) pharmacytes for favoring US/GSH-responsive combinational therapeutic of glutamine deprivation and augmented SDT. The amino acid transporter SLC6A14 blockade agent α-methyl-_DL-tryptophan (α-MT)-loaded and MnO₂-coated porphyrinic metal-organic framework (MOF) nanoparticles were encapsulated in the PLTs through the physical adsorption of electrostatic attraction and the intrinsic endocytosis of PLTs. When the sonosensitive PLT pharmacytes reached tumor sites through their natural tendencies to TME, US stimulated the PLTs-loaded porphyrinic MOF to generate ROS, resulting in morphological changes of the PLTs and the release of nanoparticles. Subsequently, intracellular high concentration of GSH and extracellular spatio-temporal controlled US irradiation programmatically triggered the release of α-MT, which enabled the synergistically amplified SDT by inducing amino acid starvation, inhibiting mTOR, and mediating ferroptosis. In addition, US stimulation achieved the targeted activation of PLTs at tumor vascular site, which evolved from circulating PLTs to dendritic PLTs, effectively blocking the blood supply of tumors through thrombus formation, and revealing the encouraging potential to facilitate tumor therapeutics.

Recruitment of a splicing factor to the nuclear lamina for its inactivation

Precursor messenger RNA splicing is a highly regulated process, mediated by a complex RNA-protein machinery, the spliceosome, that encompasses several hundred proteins and five small nuclear RNAs in humans. Emerging evidence suggests that the spatial organization of splicing factors and their spatio-temporal dynamics participate in the regulation of splicing. So far, methods to manipulate the spatial distribution of splicing factors in a temporally defined manner in living cells are missing. Here, we describe such an approach that takes advantage of a reversible chemical dimerizer, and outline the requirements for efficient, reversible re-localization of splicing factors to selected sub-nuclear compartments. In a proof-of-principle study, the partial re-localization of the PRPF38A protein to the nuclear lamina in HEK293T cells induced a moderate increase in intron retention. Our approach allows fast and reversible re-localization of splicing factors, has few side effects and can be applied to many splicing factors by fusion of a protein tag through genome engineering. Apart from the systematic analysis of the spatio-temporal aspects of splicing regulation, the approach has a large potential for the fast induction and reversal of splicing switches and can reveal mechanisms of splicing regulation in native nuclear environments.

Through the use of a reversible chemical dimerizer, the splicing factor PRPF38A is re-localized to the nuclear lamina, paving the way for a systematic analysis of spatio-temporal splicing regulation.

SARS-Cov-2 spike protein fragment 674-685 protects mitochondria from releasing cytochrome c in response to apoptogenic influence

In spite of numerous studies, many details of SARS-Cov-2 interaction with human cells are still poorly understood. The 674–685 fragment of SARS-Cov-2 spike protein is homologous to the fragment of α-cobratoxin underlying its interaction with α7 nicotinic acetylcholine receptors (nAChRs). The interaction of 674–685 peptide with α7 nAChR has been predicted in silico. In the present paper we confirm this prediction experimentally and investigate the effect of SARS-Cov-2 spike protein peptide on mitochondria, which express α7 nAChRs to regulate apoptosis-related events. We demonstrate that SARS-Cov-2 spike protein peptide 674–685 competes with the antibody against 179–190 fragment of α7 nAChR subunit for the binding to α7-expressing cells and mitochondria and prevents the release of cytochrome c from isolated mitochondria in response to 0.5 mM H₂O₂ but does not protect intact U373 cells against apoptogenic effect of H₂O_2. Our data suggest that the α7 nAChR-binding portion of SARS-Cov-2 spike protein prevents mitochondria-driven apoptosis when the virus is uncoated inside the cell and, therefore, supports the infected cell viability before the virus replication cycle is complete.

Mitochondrial α7 nicotinic acetylcholine receptors are displaced from complexes with VDAC1 to form complexes with Bax upon apoptosis induction

Nicotinic acetylcholine receptors (nAChRs) mediate fast synaptic transmission in muscles and autonomic ganglia and regulate cytokine and neurotransmitter release in the brain and non-excitable cells. The α7 nAChRs localized in the outer membrane of mitochondria regulate cytochrome c release stimulated by apoptosis-inducing agents. However, the mechanisms through which nAChRs influence mitochondrial permeability remain obscure. Here we put an aim to explore the interaction of nAChRs with voltage-dependent anion channels (VDAC1) and pro-apoptotic protein Bax in the course of apoptosis induction. By using molecular modeling in silico, it was shown that both Bax and VDAC1 can bind within the 4th transmembrane portion (M4) of nAChR subunits. Experimentally, α7 nAChR-Bax and α7 nAChR-VDAC1 complexes were identified by sandwich ELISA in mitochondria isolated from astrocytoma U373 cells. Stimulating apoptosis of U373 cells by H₂O₂ disrupted α7-VDAC complexes and favored formation of α7-Bax complexes accompanied by cytochrome c release from mitochondria. α7-selective agonist PNU282987 or type 2 positive allosteric modulator PNU120596 disrupted α7-Bax and returned α7 nAChR to complex with VDAC1 resulting in attenuation of cytochrome c release. It is concluded that mitochondrial nAChRs regulate apoptosis-induced mitochondrial channel formation by modulating the interplay of apoptosis-related proteins in mitochondria outer membrane.

Molecular mechanisms and therapeutic implications of tetrandrine and cepharanthine in T cell acute lymphoblastic leukemia and autoimmune diseases

Inappropriately activated T cells mediate autoimmune diseases and T cell acute lymphoblastic leukemia (T-ALL). Glucocorticoid and chemotherapeutic agents have largely extended lives of these patients. However, serious side effects and drug resistance often limit the prognosis of considerable number of the patients. The efficient treatment of autoimmune diseases or T-ALL with drug resistance remains an important unmet demand clinically. Bisbenzylisoquinoline alkaloids tetrandrine and cepharanthine have been applied for the treatment of certain types of autoimmune diseases and cancers, while studies on their action mechanisms and their further applications combined with glucocorticoids or chemotherapeutic agents remains to be expanded. This review introduced molecular mechanisms of tetrandrine and cepharanthine in T cells, including their therapeutic implications. Both tetrandrine and cepharnthine influence the growth of activated T cells via several kinds of signaling pathways, such as NF-κB, caspase cascades, cell cycle, MAPK, and PI3K/Akt/mTOR. According to recent preclinical and clinical studies, P-glycoprotein inhibitory effect of tetrandrine and cepharnthine could play a significant role on T cell-involved refractory diseases. Therefore, tetrandrine or cepharanthine combined with glucocorticoid or other anti-leukemia drugs would bring a new hope for patients with glucocorticoid-resistant autoimmune disease or refractory T-ALL accompanied with functional P-glycoprotein. In conclusion, bisbenzylisoquinoline alkaloids tetrandrine and cepharanthine can regulate several signaling pathways in abnormally activated T cells with low toxicity. Bisbenzylisoquinoline alkaloids deserve to be paid more attention as a lead compound to develop new drugs for the treatment of T cell-involved diseases in the future.

The power from within - understanding the driving forces of neutrophil extracellular trap formation

Neutrophil extracellular traps (NETs) are one of the most intriguing discoveries in immunological research of the past few years. After their first description in 2004, the number of research articles on how NETs affect immunodefense, and also how they contribute to an ever-growing number of diseases, has skyrocketed. However, tempting as it may seem to plunge into pharmaceutical approaches to tamper with NET formation, our understanding of this complex process is still incomplete. Important concepts such as the context-dependent dual functions of NETs, in that they are both inflammatory and anti-inflammatory, or the major intra- and extracellular forces driving NET formation, are only emerging. In this Review, we summarize key aspects of our current understanding of NET formation (also termed NETosis), emphasize biophysical aspects and focus on three key principles - rearrangement and destabilization of the plasma membrane and the cytoskeleton, alterations and disassembly of the nuclear envelope, and chromatin decondensation as a driving force of intracellular reorganization.

Dysfunction of iPSC-derived endothelial cells in human Hutchinson-Gilford progeria syndrome

Children with Hutchinson-Gilford progeria syndrome (HGPS) succumb to myocardial infarction and stroke in their teen years. Endothelial dysfunction is an early event in more common forms of atherosclerosis. Endothelial pathobiology may contribute to HGPS, but a comprehensive characterization of endothelial function in HGPS has not been performed. iPSCs derived from fibroblasts of HGPS patients or unaffected relatives were differentiated into endothelial cells (ECs). Immunofluorescent signal of the pluripotent stem cell markers SSEA4, Oct4, Sox2 and TRAI-60 was similar in HGPS or control iPSCs. Following the differentiation, FACS analysis and immunocytochemistry for CD31 and CD144 revealed a smaller percentage of ECs from HGPS iPSCs. Immunostaining for Lamin A revealed nuclear dysmorphology in HGPS iPSC-ECs. Furthermore, these cells were significantly larger and rounded, and they proliferated less, features which are typical of senescent endothelial cells. HGPS iPSC-ECs manifested less Dil-Ac-LDL uptake; less DAF-2DA staining for nitric oxide generation and formed fewer networks in matrigel in vitro. In immunodeficient mice injected with iPSC-ECs, HGPS iPSC-ECs generated a sparser vascular network compared to the control, with reduced capillary number. Telomere length (T/S ratio) of HGPS iPSC-EC was reduced as assessed by mmqPCR. iPSC-ECs derived from HGPS patients have dysmorphic appearance, abnormal nuclear morphology, shortened telomeres, reduced replicative capacity and impaired functions in vitro and in vivo. Targeting the endothelial abnormality in patients with HGPS may provide a new therapeutic avenue for the treatment of this condition. Abbreviations: HGPS: Hutchinson-Gilford progeria syndrome; ZMPSTE24: Zinc metallopeptidase STE24; FTI: Farnesyltransferase inhibitors; VSMCs: Vascular smooth muscle cells; iPSC: Induced pluripotent stem cells; EC: Endothelial cells; hTERT: Human telomerase reverse transcriptase; VEGF: vascular endothelial growth factor; DAF-FM DA: 3-Amino, 4-aminomethyl-2',7'-difluorofluorescein diacetate; BMP4: Bone Morphogenetic Protein 4; mmqPCR: mono chrome multiplex PCR; SCG: single-copy gene; CSI: Cell shape index.

Chromatin dynamics governed by a set of nuclear structural proteins

During the past three decades, the study of nuclear and chromatin organization has become of great interest. The organization and dynamics of chromatin are directly responsible for many functions including gene regulation, genome replication, and maintenance. In order to better understand the details of these mechanisms, we need to understand the role of specific proteins that take part in these processes. The genome in the nucleus is organized in different length scales, ranging from the bead-like nucleosomes through topological associated domains up to chromosome territories. The mechanisms that maintain these structures, however, remain to be fully elucidated. Previous works highlighted the significance of lamin A, an important nucleoplasmic protein; however, there are other nuclear structural proteins that are also important for chromatin organization. Studying the organizational aspects of the nucleus is a complex task, and different methods have been developed and adopted for this purpose, including molecular and imaging methods. Here we describe the use of the live-cell imaging method and demonstrate that the dynamics of the nucleus is strongly related to its organizational mechanisms. We labeled different genomic sites in the nucleus and measured the effect of nuclear structural proteins on their dynamics. We studied lamin A, BAF, Emerin, lamin B, CTCF, and Cohesin and discuss how each of them affect chromatin dynamics. Our findings indicate that lamin A and BAF have a significant effect on chromosomes dynamics, while other proteins mildly affect the type of the diffusion while the volume of motion is not affected.

The Genomic Health of Human Pluripotent Stem Cells: Genomic Instability and the Consequences on Nuclear Organization

Human pluripotent stem cells (hPSCs) are increasingly used for cell-based regenerative therapies worldwide, with embryonic and induced pluripotent stem cells as potential treatments for debilitating and chronic conditions, such as age-related macular degeneration, Parkinson's disease, spinal cord injuries, and type 1 diabetes. However, with the level of genomic anomalies stem cells generate in culture, their safety may be in question. Specifically, hPSCs frequently acquire chromosomal abnormalities, often with gains or losses of whole chromosomes. This review discusses how important it is to efficiently and sensitively detect hPSC aneuploidies, to understand how these aneuploidies arise, consider the consequences for the cell, and indeed the individual to whom aneuploid cells may be administered.

Automatic directional analysis of cell fluorescence images and morphological modeling of microfilaments

Cytoskeleton and nucleus are two important anatomic components in eukaryotic cells. Cell fluorescence images are employed to study their realignment and deformation during cell extrusion. Quantitative analysis and modeling of cell orientation are investigated in this paper. For orientation measurement, alignment orientation of microfilaments is calculated using structure tensor method. Nuclei is segmented and fitted to ellipses in nuclei images. Based on the fitted ellipse, orientation and aspect ratio of each nucleus are computed. A morphological model is proposed to describe the movement of microfilaments quantitatively. The parameters of the model are determined by in-plane stresses obtained by numerical simulation. The proposed automatic orientation measurement algorithms can help to analyze the relationship between cell orientation and stress qualitatively. The proposed morphological model is the first model to quantitatively describe the relationship of microfilament movement with stress. Experimental results show that cell and nucleus tend to align along in-plane maximum shear stress and the proposed morphological model is a reasonable model for cell movement. The modeling of cell behavior under different stress can facilitate biomedical research such as tissue engineering and cancer analysis. Graphical abstract ᅟ.

Collective cell polarization and alignment on curved surfaces

Curvature as an important topological parameter of 3D extra-cellular matrix has drawn growing attention in recent years. But the underlying mechanism that curvature influences cell behaviors has remained unknown. In this study, we seeded cells on semi-cylindrical and hemispheric surfaces and tested cell alignment and polarization. We found that the surface curvature has profound effect on cell behaviors. With the decrease of diameter of the cylinder/sphere (i.e. increase of curvature), the cells would more preferentially align and polarize with large aspect ratio in the axial/peripheral direction. And the behaviors of the alignment and polarization were position-dependent. For example, at the end of the cylinder, the cells preferred to align circumferentially; while in the interior region, the cells preferred to align in the axial direction. We showed that the cell polarization and alignment were closely correlated with the in-plane stresses in cell layer. That is, the cell polarization and alignment were controlled by the maximum shear stress, which drove cells to align and polarize along the maximum principal stress. The curvature could influence the magnitude of the maximum shear stress and thus regulate cell behaviors. This study provided important insights into the mechanisms of surface curvature influencing cell behaviors in tissue morphogenesis. In addition, our theory of the stress dependent cellular polarity provides a generalized interpretation of the curvature and edge effects which might be extended to understand other steric effects in cell behaviors.

MAFb protein confers intrinsic resistance to proteasome inhibitors in multiple myeloma

Background

Multiple myeloma (MM) patients with t(14;20) have a poor prognosis and their outcome has not improved following the introduction of bortezomib (Bzb). The mechanism underlying the resistance to proteasome inhibitors (PIs) for this subset of patients is unknown.

Methods

IC50 of Bzb and carfilzomib (CFZ) in human myeloma cell lines (HMCLs) were established by MTT assay. Gene Expression profile (GEP) analysis was used to determine gene expression in primary myeloma cells. Immunoblotting analysis was performed for MAFb and caspase family proteins. Immunofluorescence staining was used to detect the location of MAFb protein in MM cells. Lentiviral infections were used to knock-down MAFb expression in two lines. Apoptosis detection by flow cytometry and western blot analysis was performed to determine the molecular mechanism MAFb confers resistance to proteasome inhibitors.

Results

We found high levels of MAFb protein in cell lines with t(14;20), in one line with t(6;20), in one with Igλ insertion into MAFb locus, and in primary plasma cells from MM patients with t(14;20). High MAFb protein levels correlated with higher IC50s of PIs in MM cells. Inhibition of GSK3β activity or treatment with Bzb or CFZ prevented MAFb protein degradation without affecting the corresponding mRNA level indicating a role for GSK3 and proteasome inhibitors in regulation of MAFb stability. Silencing MAFb restored sensitivity to Bzb and CFZ, and enhanced PIs-induced apoptosis and activation of caspase-3, − 8, − 9, PARP and lamin A/C suggesting that high expression of MAFb protein leads to insensitivity to proteasome inhibitors.

Conclusion

These results highlight the role of post-translational modification of MAFb in maintaining its protein level, and identify a mechanism by which proteasome inhibitors induced stabilization of MAFb confers resistance to proteasome inhibitors, and provide a rationale for the development of targeted therapeutic strategies for this subset of patients.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4602-4) contains supplementary material, which is available to authorized users.

Mitochondrial Nicotinic Acetylcholine Receptors Support Liver Cells Viability After Partial Hepatectomy

Nicotinic acetylcholine receptors (nAChRs) expressed on the cell plasma membrane are ligand-gated ion channels mediating fast synaptic transmission, regulating neurotransmitter and cytokine release and supporting the viability of many cell types. The nAChRs expressed in mitochondria regulate the release of pro-apoptotic factors, like cytochrome c, in ion channel-independent manner. Here we show that α3β2, α7β2, and α9α10 nAChR subtypes are up-regulated in rat liver mitochondria 3–6 h after partial hepatectomy resulting in increased sustainability of mitochondria to apoptogenic effects of Ca²⁺ and H₂O₂. In contrast, laparotomy resulted in down-regulation of all nAChR subunits, except α9, and decreased mitochondria sustainability to apoptogenic effects of Ca²⁺ and H₂O₂. Experiments performed in liver mitochondria from α3+/-, α7-/-, β4-/-, α7β2-/-, or wild-type C57Bl/6J mice demonstrated that the decrease of α3 or absence of α7 or α7/β2 subunits in mitochondria is compensated with β4 and α9 subunits, which could be found in α3β4, α4β4, α9β4, and α9α10 combinations. Mitochondria from knockout mice maintained their sustainability to Ca²⁺ but were differently regulated by nAChR subtype-specific ligands: PNU-282987, methyllycaconitine, dihydro-β-erythroidine, α-conotoxin MII, and α-conotoxin PeIA. It is concluded that mitochondrial nAChRs play an important role in supporting the viability of hepatic cells and, therefore, may be a pharmacological target for pro-survival therapy. The concerted action of multiple nAChR subtypes controlling either CaKMII- or Src-dependent signaling pathways in mitochondria ensures a reliable protection against apoptogenic factors of different nature.

Parameterization of Palmitoylated Cysteine, Farnesylated Cysteine, Geranylgeranylated Cysteine, and Myristoylated Glycine for the Martini Force Field

Peripheral membrane proteins go through various post-translational modifications that covalently bind fatty acid tails to specific amino acids. These post-translational modifications significantly alter the lipophilicity of the modified proteins and allow them to anchor to biological membranes. Over 1000 different proteins have been identified to date that require such membrane-protein interactions to carry out their biological functions, including members of the Src and Ras superfamilies that play key roles in cell signaling and carcinogenesis. We have used all-atom simulations with the CHARMM36 force field to parameterize four of the most common post-translational modifications for the Martini 2.2 force field: palmitoylated cysteine, farnesylated cysteine, geranylgeranylated cysteine, and myristoylated glycine. The parameters reproduce the key features of clusters of configurations of the different anchors in lipid membranes as well as the water-octanol partitioning free energies of the anchors, which are crucial for the correct reproduction of the expected biophysical behavior of peripheral membrane proteins at the membrane-water interface. Implementation in existing Martini setup tools facilitates the use of the new parameters.

The Natural Antiangiogenic Compound AD0157 Induces Caspase-Dependent Apoptosis in Human Myeloid Leukemia Cells

Evasion of apoptosis is a hallmark of cancer especially relevant in the development and the appearance of leukemia drug resistance mechanisms. The development of new drugs that could trigger apoptosis in aggressive hematological malignancies, such as AML and CML, may be considered a promising antileukemic strategy. AD0157, a natural marine pyrrolidinedione, has already been described as a compound that inhibits angiogenesis by induction of apoptosis in endothelial cells. The crucial role played by defects in the apoptosis pathways in the pathogenesis, progression and response to conventional therapies of several forms of leukemia, moved us to analyze the effect of this compound on the growth and death of leukemia cells. In this work, human myeloid leukemia cells (HL60, U937 and KU812F) were treated with AD0157 ranging from 1 to 10 μM and an experimental battery was applied to evaluate its apoptogenic potential. We report here that AD0157 was highly effective to inhibit cell growth by promotion of apoptosis in human myeloid leukemia cells, and provide evidence of its mechanisms of action. The apoptogenic activity of AD0157 on leukemia cells was verified by an increased chromatin condensation and DNA fragmentation, and confirmed by an augmentation in the apoptotic subG1 population, translocation of the membrane phosphatidylserine from the inner face of the plasma membrane to the cell surface and by cleavage of the apoptosis substrates PARP and lamin-A. In addition, AD0157 in the low micromolar range significantly enhanced the activities of the initiator caspases-8 and -9, and the effector caspases-3/-7 in a dose-dependent manner. Results presented here throw light on the apoptogenic mechanism of action of AD0157, mediated through caspase-dependent cascades, with an especially relevant role played by mitochondria. Altogether, these results suggest the therapeutic potential of this compound for the treatment of human myeloid leukemia.

Nicotinic Acetylcholine Receptor α9 and α10 Subunits Are Expressed in the Brain of Mice

The α9 and α10 nicotinic acetylcholine receptor (nAChR) subunits are likely to be the evolutionary precursors to the entire cys-loop superfamily of ligand-gated ion channels, which includes acetylcholine, GABA, glycine and serotonin ionotropic receptors. nAChRs containing α9 and α10 subunits are found in the inner ear, dorsal root ganglia and many non-excitable tissues, but their expression in the central nervous system has not been definitely demonstrated. Here we show the presence of both α9 and α10 nAChR subunits in the mouse brain by RT-PCR and immunochemical approaches with a range of nAChR subunit-selective antibodies, which selectivity was demonstrated in the brain preparations of α7−/−, α9−/− and α10−/− mice. The α9 and α10 RNA transcripts were found in medulla oblongata (MO), cerebellum, midbrain (MB), thalamus and putamen (TP), somatosensory cortex (SC), frontal cortex (FC) and hippocampus. High α9-selective signal in ELISA was observed in the FC, SC, MO, TP and hippocampus and α10-selective signal was the highest in MO and FC. The α9 and α10 proteins were found in the brain mitochondria, while their presence on the plasma membrane has not been definitely confirmed The α7-, α9- and α10-selective antibodies stained mainly neurons and hypertrophied astrocytes, but not microglia. The α9- and α10-positive cells formed ordered structures or zones in cerebellum and superior olive (SO) and were randomly distributed among α7-positive cells in the FC; they were found in CA1, CA3 and CA4, but not in CA2 region of the hippocampus. The α9 and α10 subunits were up-regulated in α7−/− mice and both α7 and α9 subunits were down-regulated in α10−/− mice. We conclude that α9 and α10 nAChR subunits are expressed in distinct neurons of the mouse brain and in the brain mitochondria and are compensatory up-regulated in the absence of α7 subunits.

Molecular cloning and characterization of the genes encoding the proteins of Zika virus

Zika virus (ZIKV) encodes a precursor protein (also called polyprotein) of about 3424 amino acids that is processed by proteases to generate 10 mature proteins and a small peptide. In the present study, we characterized the chemical features, suborganelle distribution and potential function of each protein using Flag-tagged protein expression system. Western blot analysis revealed the molecular weight of the proteins and the polymerization of E, NS1, and NS3 proteins. In addition, we performed multi-labeled fluorescent immunocytochemistry and subcellular fractionation to determine the subcellular localization of these proteins in host cells. We found that 1) the capsid protein colocalizes with 3 different cellular organelles: nucleoli, Golgi apparatus, and lipid droplet; NS2b and NS4a are associated with the Golgi apparatus; 2) the capsid and NS1proteins distribute in both cytoplasm and nucleus, NS5 is a nuclear protein; 3) NS3 protein colocalizes with tubulin and affects Lamin A; 4) Envelope, PrM, and NS2a proteins co-localize with the endoplasmic reticulum; 5) NS1 is associated with autophagosomes and NS4b is related to early endosome; 6) NS5 forms punctate structures in the nucleus that associate with splicing compartments shown by SC35, leading to reduction of SC35 protein level and trafficking of SC35 from the nucleus to the cytoplasm. These data suggest that ZIKV generates 10 functional viral proteins that exhibit distinctive subcellular distribution in host cells.

A novel de novo mutation in Lamin A/C gene in Emery Dreifuss Muscular Dystrophy patient with atrial paralysis

We present a 26 year old female Indonesian patient with full spectrum Emery Dreifuss Muscular Dystrophy (EDMD) characterized with contracture of elbows, heel cord and pelvic muscle wasting and weakness and atrial paralysis, as rare cardiac findings in EDMD . A novel de novo pathogenic heterozygous missense mutation (NM_170707.3: c.122G>T, p.Arg41Leu) in exon 1 was detected. Preventing atrial paralytic patients from systemic embolism is important. Early diagnosis, intervention, targeted management and counseling are necessary for a better health and life quality of individuals with EDMD.

Atomic force microscopy and lamins: A review study towards future, combined investigations

In the last decades, atomic force microscopy (AFM) underwent a rapid and stunning development, especially for studying mechanical properties of biological samples. The numerous discoveries relying to this approach, have increased the credit of AFM as a versatile tool, and potentially eligible as a diagnostic equipment. Meanwhile, it has become strikingly evident that lamins are involved on the onset and development of certain diseases, including cancer, Hutchinson-Gilford progeria syndrome, cardiovascular pathologies, and muscular dystrophy. A new category of pathologies has been defined, the laminopathies, which are caused by mutations in the gene encoding for A-type lamins. As the majority of medical issues, lamins, and all their related aspects can be considered as a quite complex problem. Indeed, there are many facets to explore, and this definitely requires a multidisciplinary approach. One of the most intriguing aspects concerning lamins is their remarkable contribute to cells mechanics. Over the years, this has led to the speculation of the so-called "structural hypothesis", which attempts to elucidate the etiology and some features of the laminopathies. Among the various techniques tried to figure out the role of lamins in the cells mechanics, the AFM has been already successfully applied, proving its versatility. Therefore, the present work aims both to highlight the qualities of AFM and to review the most relevant knowledge about lamins, in order to promote the study of the latter, taking advantage from the former. Microsc. Res. Tech. 80:97-108, 2017. © 2016 Wiley Periodicals, Inc.

MAF protein mediates innate resistance to proteasome inhibition therapy in multiple myeloma

Multiple myeloma (MM) patients with the t(14;16) translocation have a poor prognosis, and unlike other molecular subgroups, their outcome has not improved with the introduction of bortezomib (Bzb). The mechanism underlying innate resistance of MM to Bzb is unknown. In the present study, we have investigated how MAF overexpression impacts resistance to proteasome inhibitor (PI) therapy (Bzb and carfilzomib). High levels of MAF protein were found in t(14;16) cell lines; cell lines from the t(4;14) subgroup had intermediate levels, whereas cell lines from the other subgroups had low levels. High expression of MAF protein in t(14;16) was associated with significantly higher PI half-maximum inhibitory concentration values compared with other molecular subgroups. PI exposure abrogated glycogen synthase kinase 3β (GSK3β)-mediated degradation of MAF protein, resulting in increased MAF protein stability and PI resistance. Subsequent studies using loss-of-function and gain-of-function models showed that silencing MAF led to increased sensitivity to PIs, enhanced apoptosis, and activation of caspase-3, -7, -8, -9, poly (ADP-ribose) polymerase, and lamin A/C. In contrast, overexpression of MAF resulted in increased resistance to PIs and reduced apoptosis. These results define the role of MAF and GSK3 in the resistance of t(14;16) MM to PIs and identifies a novel mechanism by which MAF protein levels are regulated by PIs, which in turn confers resistance to PIs.

B-type nuclear lamin and the nuclear pore complex Nup107-160 influences maintenance of the spindle envelope required for cytokinesis in Drosophila male meiosis

In higher eukaryotes, nuclear envelope (NE) disassembly allows chromatin to condense and spindle microtubules to access kinetochores. The nuclear lamina, which strengthens the NE, is composed of a polymer meshwork made of A- and B-type lamins. We found that the B-type lamin (Lam) is not fully disassembled and continues to localize along the spindle envelope structure during Drosophila male meiosis I, while the A-type lamin (LamC) is completely dispersed throughout the cytoplasm. Among the nuclear pore complex proteins, Nup107 co-localized with Lam during this meiotic division. Surprisingly, Lam depletion resulted in a higher frequency of cytokinesis failure in male meiosis. We also observed the similar meiotic phenotype in Nup107-depleted cells. Abnormal localization of Lam was found in the Nup-depleted cells at premeiotic and meiotic stages. The central spindle microtubules became abnormal and recruitment of a contractile ring component to the cleavage sites was disrupted in Lam-depleted cells and Nup107-depleted cells. Therefore, we speculate that both proteins are required for a reinforcement of the spindle envelope, which supports the formation of central spindle microtubules essential for cytokinesis in Drosophila male meiosis.

Mechanobiology of Chromatin and the Nuclear Interior

The view of the cell nucleus has evolved from an isolated, static organelle to a dynamic structure integrated with other mechanical elements of the cell. Both dynamics and integration appear to contribute to a mechanical regulation of genome expression. Here, we review physical structures inside the nucleus at different length scales and the dynamic reorganization modulated by cellular forces. First, we discuss nuclear organization focusing on self-assembly and disassembly of DNA structures and various nuclear bodies. We then discuss the importance of connections from the chromatin fiber through the nuclear envelope to the rest of the cell as they relate to mechanobiology. Finally, we discuss how cell stimulation, both chemical and physical, can alter nuclear structures and ultimately cellular function in healthy cells and in some model diseases. The view of chromatin and nuclear bodies as mechanical entities integrated with force generation from the cytoskeleton combines polymer physics with cell biology and medicine.

The EGF receptor ligand amphiregulin controls cell division via FoxM1

Epidermal growth factor receptor (EGFR) is central to epithelial cell physiology, and deregulated EGFR signaling has an important role in a variety of human carcinomas. Here we show that silencing of the EGF-related factor amphiregulin (AREG) markedly inhibits the expansion of human keratinocytes through mitotic failure and accumulation of cells with ⩾ 4n DNA content. RNA-sequencing-based transcriptome analysis revealed that tetracycline-mediated AREG silencing significantly altered the expression of 2331 genes, 623 of which were not normalized by treatment with EGF. Interestingly, genes irreversibly upregulated by suppression of AREG overlapped with genes involved in keratinocyte differentiation. Moreover, a significant proportion of the irreversibly downregulated genes featured upstream binding sites recognized by forkhead box protein M1 (FoxM1), a key transcription factor in the control of mitosis that is widely dysregulated in cancer. The downregulation of FoxM1 and its target genes preceded mitotic arrest. Constitutive expression of FoxM1 in AREG knockdown cells normalized cell proliferation, reduced the number of cells with ⩾ 4n DNA content and rescued expression of FoxM1 target genes. These results demonstrate that AREG controls G2/M progression and cytokinesis in keratinocytes via activation of a FoxM1-dependent transcriptional program, suggesting new avenues for treatment of epithelial cancer.

Glucotoxic and diabetic conditions induce caspase 6-mediated degradation of nuclear lamin A in human islets, rodent islets and INS-1 832/13 cells

Nuclear lamins form the lamina on the interior surface of the nuclear envelope, and regulate nuclear metabolic events, including DNA replication and organization of chromatin. The current study is aimed at understanding the role of executioner caspase 6 on lamin A integrity in islet β-cells under duress of glucotoxic (20 mM glucose; 24 h) and diabetic conditions. Under glucotoxic conditions, glucose-stimulated insulin secretion and metabolic cell viability were significantly attenuated in INS-1 832/13 cells. Further, exposure of normal human islets, rat islets and INS-1 832/13 cells to glucotoxic conditions leads to caspase 6 activation and lamin A degradation, which is also observed in islets from the Zucker diabetic fatty rat, a model for type 2 diabetes (T2D), and in islets from a human donor with T2D. Z-Val-Glu-Ile-Asp-fluoromethylketone, a specific inhibitor of caspase 6, markedly attenuated high glucose-induced caspase 6 activation and lamin A degradation, confirming that caspase 6 mediates lamin A degradation under high glucose exposure conditions. Moreover, Z-Asp-Glu-Val-Asp-fluoromethylketone, a known caspase 3 inhibitor, significantly inhibited high glucose-induced caspase 6 activation and lamin A degradation, suggesting that activation of caspase 3 might be upstream to caspase 6 activation in the islet β-cell under glucotoxic conditions. Lastly, we report expression of ZMPSTE24, a zinc metallopeptidase involved in the processing of prelamin A to mature lamin A, in INS-1 832/13 cells and human islets; was unaffected by high glucose. We conclude that caspases 3 and 6 could contribute to alterations in the integrity of nuclear lamins leading to metabolic dysregulation and failure of the islet β-cell.

Cancer cell migration in 3D tissue: negotiating space by proteolysis and nuclear deformability

Efficient tumor cell invasion into the surrounding desmoplastic stroma is a hallmark of cancer progression and involves the navigation through available small tissue spaces existent within the dense stromal network. Such navigation includes the reciprocal adaptation of the moving tumor cell, including the nucleus as largest and stiffest organelle, to pre-existent or de-novo generated extracellular matrix (ECM) gaps, pores and trails within stromal compartments. Within the context of migration, we briefly summarize physiological and tumor-related changes in ECM geometries as well as tissue proteolysis. We then focus on mechanisms that ensure the successful translocation of a nucleus through a confining pore by cytoskeleton-mediated coupling, as well as regulators of cell and nuclear deformability such as chromatin organization and nuclear lamina expression. In summary, understanding dynamic nuclear mechanics during migration in response to confined space will add to a better conceptual appreciation of cancer invasion and progression.

Lamins: nuclear intermediate filament proteins with fundamental functions in nuclear mechanics and genome regulation

Lamins are intermediate filament proteins that form a scaffold, termed nuclear lamina, at the nuclear periphery. A small fraction of lamins also localize throughout the nucleoplasm. Lamins bind to a growing number of nuclear protein complexes and are implicated in both nuclear and cytoskeletal organization, mechanical stability, chromatin organization, gene regulation, genome stability, differentiation, and tissue-specific functions. The lamin-based complexes and their specific functions also provide insights into possible disease mechanisms for human laminopathies, ranging from muscular dystrophy to accelerated aging, as observed in Hutchinson-Gilford progeria and atypical Werner syndromes.

BGLF4 kinase modulates the structure and transport preference of the nuclear pore complex to facilitate nuclear import of Epstein-Barr virus lytic proteins

BGLF4 kinase, the only Ser/Thr protein kinase encoded by the Epstein-Barr virus (EBV) genome, phosphorylates multiple viral and cellular substrates to optimize the cellular environment for viral DNA replication and the nuclear egress of nucleocapsids. Previously, we found that nuclear targeting of BGLF4 is through direct interaction with the FG repeat-containing nucleoporins (FG-Nups) Nup62 and Nup153 independently of cytosolic transport factors. Here, we investigated the regulatory effects of BGLF4 on the structure and biological functions of the nuclear pore complex (NPC). In EBV-positive NA cells, the distribution of FG-Nups was modified during EBV reactivation. In transfected cells, BGLF4 changed the staining pattern of Nup62 and Nup153 in a kinase activity-dependent manner. Detection with anti-phospho-Ser/Thr-Pro MPM-2 antibody demonstrated that BGLF4 induced the phosphorylation of Nup62 and Nup153. The nuclear targeting of importin β was attenuated in the presence of BGLF4, leading to inhibition of canonical nuclear localization signal (NLS)-mediated nuclear import. An in vitro nuclear import assay revealed that BGLF4 induced the nuclear import of larger molecules. Notably, we found that BGLF4 promoted the nuclear import of several non-NLS-containing EBV proteins, including the viral DNA-replicating enzymes BSLF1, BBLF2/3, and BBLF4 and the major capsid protein (VCA), in cotransfected cells. The data presented here suggest that BGLF4 interferes with the normal functions of Nup62 and Nup153 and preferentially helps the nuclear import of viral proteins for viral DNA replication and assembly. In addition, the nuclear import-promoting activity was found in cells expressing the BGLF4 homologs of another two gammaherpesviruses but not those from alpha- and betaherpesviruses.

IMPORTANCE

During lytic replication, many EBV genome-encoded proteins need to be transported into the nucleus, not only for viral DNA replication but also for the assembly of nucleocapsids. Because nuclear pore complexes are effective gateways that control nucleocytoplasmic traffic, most EBV proteins without canonical NLSs are retained in the cytoplasm until they form complexes with their NLS-containing partners for nuclear targeting. In this study, we found that EBV BGLF4 protein kinase interacts with the Nup62 and Nup153 and induces the redistribution of FG-Nups. BGLF4 modulates the function of the NPC to inhibit the nuclear import of host NLS-containing proteins. Simultaneously, the nuclear import of non-NLS-containing EBV lytic proteins was enhanced, possibly through phosphorylation of Nup62 and Nup153, nuclear pore dilation, or microtubule reorganization. Overall, our data suggest that BGLF4-induced modification of nuclear pore transport may block nuclear targeting of cellular proteins and increase the import of viral proteins to promote viral lytic replication.

Proteomic analysis of chicken peripheral blood mononuclear cells after infection by Newcastle disease virus

Characteristic clinical manifestations of Newcastle disease include leukopenia and immunosuppression. Peripheral blood mononuclear cells (PBMCs) are the main targets of Newcastle disease virus (NDV) infection. To survey changes in proteomic expression in chicken PBMCs following NDV infection, PBMC proteins from 30 chickens were separated using two- dimensional electrophoresis (2-DE) and subjected to mass spectrometry analysis. Quantitative intensity analysis showed that the expression of 78 proteins increased more than two-fold. Thirty-five proteins exhibited consistent changes in expression and 13 were identified as unique proteins by matrix assisted laser desorption ionization-time of flight mass spectrometer/mass spectrometer including three that were down-regulated and 10 that were up-regulated. These proteins were sorted into five groups based on function: macromolecular biosynthesis, cytoskeleton organization, metabolism, stress responses, and signal transduction. Furthermore, Western blot analysis confirmed the down-regulation of integrin-linked kinase expression and up-regulation of lamin A production. These data provide insight into the in vivo response of target cells to NDV infection at the molecular level. Additionally, results from this study have helped elucidate the molecular pathogenesis of NDV and may facilitate the development of new antiviral therapies as well as innovative diagnostic methods.

Intermediate filaments: a dynamic network that controls cell mechanics

In humans the superfamily of intermediate filament (IF) proteins is encoded by more than 70 different genes, which are expressed in a cell- and tissue-specific manner. IFs assemble into approximately 10 nm-wide filaments that account for the principal structural elements at the nuclear periphery, nucleoplasm, and cytoplasm. They are also required for organizing the microtubule and microfilament networks. In this review, we focus on the dynamics of IFs and how modifications regulate it. We also discuss the role of nuclear IF organization in determining nuclear mechanics as well as that of cytoplasmic IFs organization in maintaining cell stiffness, formation of lamellipodia, regulation of cell migration, and permitting cell adhesion.

Glucotoxic conditions induce endoplasmic reticulum stress to cause caspase 3 mediated lamin B degradation in pancreatic β-cells: protection by nifedipine

Nuclear lamins form the lamina on the interior of the nuclear envelope, and are involved in the regulation of various cellular processes, including DNA replication and chromatin organization. Despite this evidence, little is known about potential alterations in nuclear metabolism, specifically lamin structure and integrity in isolated β-cells subjected to stress conditions, including chronic exposure to hyperglycemia (i.e., glucotoxicity). Herein, we investigated effects of glucotoxic conditions on the catalytic activation of caspase 3 and the associated degradation of one of its substrate proteins, namely lamin-B. We report that incubation of insulin-secreting INS-1 832/13 cells, normal rat islets or human islets under glucotoxic conditions (20 mM; 12-48 h) results in the degradation of native lamin B leading to accumulation of the degraded products in non-relevant cellular compartments, including cytosol. Moreover, the effects of high glucose on caspase 3 activation and lamin B degradation were mimicked by thapsigargin, a known inducer of endoplasmic reticulum stress (ER stress). Nifedipine, a known blocker of calcium channel activation, inhibited high glucose-induced caspase 3 activation and lamin B degradation in these cells. 4-Phenyl butyric acid, a known inhibitor of ER stress, markedly attenuated glucose-induced CHOP expression (ER stress marker), caspase 3 activation and lamin B degradation. We conclude that glucotoxic conditions promote caspase 3 activation and lamin B degradation, which may, in part, be due to increased ER stress under these conditions. We also provide further evidence to support beneficial effects of calcium channel blockers against metabolic dysfunction of the islet β-cell induced by hyperglycemic conditions.

Altered dynamics of ubiquitin hybrid proteins during tumor cell apoptosis

The ubiquitin hybrid genes Uba80 and Uba52 encode ubiquitin (Ub), which is fused to the ribosomal proteins S27a (RPS27a) and L40 (RPL40), respectively. Here, we show that these genes are preferentially over-expressed during hepatoma cell apoptosis. Experiments using the tet-inducible transgenic system revealed that over-expression of the ubiquitin hybrid genes sensitized the cells to apoptosis. Further analysis suggested that Ub, and not RPS27a or RPL40, was associated with apoptotic cell death. Cleavage-resistant mutation analysis revealed that the N-terminal portion and the last two amino acids (GG) of Ub are critical for cleavage at the junction between the two protein moieties. An apoptogenic stimulus enhances the nuclear targeting and aggregation of Ub in the nucleus, resulting in histone H2A deubiquitylation followed by abnormal ubiquitylation of the nuclear envelope and the lamina. These events accompany the apoptotic nuclear morphology in the late stage of apoptosis. Each fused RP is localized in the nucleoli. These results suggest a role for Ub hybrid proteins in the altered nuclear dynamics of Ub during tumor cell apoptosis induced by apoptogenic stimuli.

Deregulated LAP2α expression in cervical cancer associates with aberrant E2F and p53 activities

Lamina-associated polypeptide 2 alpha (LAP2α) plays a role in maintaining nuclear structure, in nuclear assembly/disassembly, and in transcriptional regulation. Elevated LAP2α mRNA expression has been previously reported to associate with certain cancer types. The aim of this study was to investigate LAP2α expression in cervical cancer and transformed cells and to identify factors that associate with its differential expression. LAP2α expression was found to be elevated in cervical cancer tissue by microarray, qRT-PCR, and immunofluorescence analyses. LAP2α also showed elevated expression in cervical cancer cell lines and in transformed fibroblasts compared with normal cells. To determine factors associated with elevated LAP2α in cervical cancer, the effect of inhibiting HPV E7 and E6 oncoproteins was investigated. E7 inhibition resulted in a decrease in phosphorylated Rb and an associated decrease in LAP2α, suggesting a role for E2F in regulating LAP2α expression. This finding was confirmed by inhibiting DP1, a co-activator of E2F, which resulted in decreased LAP2α levels. Inhibition of E6 resulted in elevated p53 and an associated decrease in LAP2α, suggesting that p53 associates with the negative regulation of LAP2α expression. This hypothesis was tested by inhibiting p53 in normal cells, and a resultant increase in LAP2α expression was observed. In conclusion, this study provides evidence for elevated LAP2α expression in cervical cancer and suggests that E2F and p53 activities associate with the positive and negative regulation of LAP2α expression, respectively.

Chromosome remodeling and differentiation of tetraploid embryos during preimplantation development

Although it is known that the tetraploid embryo contributes only to the placenta, the question of why tetraploid embryos differentiate into placenta remains unclear. To study the effect of electrofusion on the development of mouse tetraploid oocytes, mouse two-cell embryos were fused and cultured in vitro in Chatot-Ziomek-Bavister medium. After electrofusion, two chromosome sets from the tetraploid blastomere were individually duplicated before nuclear fusion. At 8-10 hr after electrofusion, each chromosome set was condensing and the nuclear membrane was breaking down. Around 12-14 hr after electrofusion, the two chromosome sets had combined together and had reached the second mitotic metaphase, at this point with 8n sets of chromosomes. Interestingly, we discovered that expression of OCT4, an inner cell mass cells biomarker, is lost by the tetraploid expanded blastocysts, but that CDX2, a trophectoderm cells biomarker, is strongly expressed at this stage. This observation provides evidence clarifying why tetraploid embryos contribute only to trophectoderm.

Distinct effects of nuclear membrane localization on gene transcription silencing in Drosophila S2 cells and germ cells

Nuclear envelope proteins have important roles in chromatin organization and signal-dependent transcriptional regulation. A previous study reported that the inner nuclear membrane protein, Otefin (Ote), was essential for germline stem cell (GSC) maintenance via interaction with Smad complex. The interaction of Ote with the Smad complex recruits the bam locus to the nuclear periphery and subsequently results in bam transcriptional silencing, revealing that nuclear peripheral localization is essential for bam gene regulation. However, it remains unknown whether the nuclear peripheral localization is sufficient for bam silencing. To address this issue, we have established a tethering system, in which the Gal4 DNA binding domain (DBD) of the Flag:Gal4 DBD:Ote▵LEM fusion protein physically interacts with the Gal4 binding sites upstream of bamP-gfp to artificially recruit the reporter gene gfp to the nuclear membrane. Our data demonstrated that the nuclear peripheral localization seemed to affect the expression of the target naked gene in S2 cells. By contrast, in Drosophila germ cells, the nuclear membrane localization was not sufficient for gene silencing.

The nuclear envelope

The nuclear envelope (NE) is a highly regulated membrane barrier that separates the nucleus from the cytoplasm in eukaryotic cells. It contains a large number of different proteins that have been implicated in chromatin organization and gene regulation. Although the nuclear membrane enables complex levels of gene expression, it also poses a challenge when it comes to cell division. To allow access of the mitotic spindle to chromatin, the nucleus of metazoans must completely disassemble during mitosis, generating the need to re-establish the nuclear compartment at the end of each cell division. Here, I summarize our current understanding of the dynamic remodeling of the NE during the cell cycle.

Temporal proteomic analysis of IGF-1R signalling in MCF-7 breast adenocarcinoma cells

Dysregulation of the insulin-like growth factor 1 receptor signalling network is implicated in tumour growth and resistance to chemotherapy. We explored proteomic changes resulting from insulin-like growth factor 1 stimulation of MCF-7 adenocarcinoma cells as a function of time. Quantitative analysis using iTRAQ reagents and 2-D LC-MS/MS analysis of three biological replicates resulted in the identification of 899 proteins (p<or=0.05) with an estimated mean false-positive rate of 2.6%. Quantitative protein expression was obtained from 681 proteins. Further analysis by supervised k-means clustering identified five temporal clusters, which were submitted to the FuncAssociate server to assign overrepresented gene ontology terms. Proteins associated with vesicle transport were significantly overrepresented. We further analyzed our data set for proteins showing temporal significance using the software, extraction and analysis of differential gene expression, resulting in 20 significantly and temporally changing proteins (p<or=0.1). These significant proteins play roles in, among others, altered glucose metabolism (lactate dehydrogenase A and pyruvate kinase M1/M2) and cellular stress (nascent polypeptide-associated complex subunit alpha and heat shock (HSC70) proteins). We used multiple reaction monitoring to validate these interesting proteins and have revealed several differences in relative peptide expression corresponding to protein isoforms and variants.

Eimeria bovis-induced modulation of the host cell proteome at the meront I stage

The proteome of Eimeria bovis meront I-carrying host cells was analyzed by two-dimensional gel electrophoresis (2DE) at 14 days p.i. and compared to non-infected control cells. A total of 221 protein spots were modulated in their abundance in E. bovis-infected host cells and were subsequently analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectometry (MALDI-TOF-MS). These analyses identified 104 proteins in total with 25 host cell proteins being up-regulated and 79 proteins being down-regulated in E. bovis-infected host cells. Moreover, 20 newly expressed proteins were identified exclusively in E. bovis-infected host cells and were most likely of parasite origin. Parasite-induced differences in protein abundance concerned distinct functional categories, with most proteins being involved in host cell metabolism, cell structure, protein fate and gene transcription. Some of the modulated molecules also indicated regulatory processes on the level of host cell stress response (HSP70, HSP90), host cell apoptosis (caspase 8) and actin elongation/depolymerization (α-actinin-1, gelsonin, tropomodulin-3, transgelin). Since merozoites I were already released shortly after cell sampling, the current data reflect the situation at the end of first merogony. This is the first proteomic approach on E. bovis-infected host cells that was undertaken to gain a rather broad insight into Eimeria-induced host cell modulation. The data processed in this investigation should provide a useful basis for more detailed analyses concerning Eimeria-host cell interactions.

Dynamic chromatin organization during foregut development mediated by the organ selector gene PHA-4/FoxA

Central regulators of cell fate, or selector genes, establish the identity of cells by direct regulation of large cohorts of genes. In Caenorhabditis elegans, foregut (or pharynx) identity relies on the FoxA transcription factor PHA-4, which activates different sets of target genes at various times and in diverse cellular environments. An outstanding question is how PHA-4 distinguishes between target genes for appropriate transcriptional control. We have used the Nuclear Spot Assay and GFP reporters to examine PHA-4 interactions with target promoters in living embryos and with single cell resolution. While PHA-4 was found throughout the digestive tract, binding and activation of pharyngeally expressed promoters was restricted to a subset of pharyngeal cells and excluded from the intestine. An RNAi screen of candidate nuclear factors identified emerin (emr-1) as a negative regulator of PHA-4 binding within the pharynx, but emr-1 did not modulate PHA-4 binding in the intestine. Upon promoter association, PHA-4 induced large-scale chromatin de-compaction, which, we hypothesize, may facilitate promoter access and productive transcription. Our results reveal two tiers of PHA-4 regulation. PHA-4 binding is prohibited in intestinal cells, preventing target gene expression in that organ. PHA-4 binding within the pharynx is limited by the nuclear lamina component EMR-1/emerin. The data suggest that association of PHA-4 with its targets is a regulated step that contributes to promoter selectivity during organ formation. We speculate that global re-organization of chromatin architecture upon PHA-4 binding promotes competence of pharyngeal gene transcription and, by extension, foregut development.

Central regulators of cell fate establish the identity of cells by direct regulation of large cohorts of genes. In Caenorhabditis elegans, foregut (or pharynx) identity relies on the FoxA transcription factor PHA-4, which activates different target genes in different cellular environments. An outstanding question is how PHA-4 distinguishes between target genes for appropriate transcriptional control. Here we examine PHA-4 interactions with target promoters in living embryos and with single-cell resolution. While PHA-4 was found throughout the digestive tract, binding and activation of pharyngeally expressed promoters was restricted to a subset of pharyngeal cells and excluded from the intestine. An RNAi screen identified emerin (emr-1) as a negative regulator of PHA-4 binding within the pharynx. Upon promoter association, PHA-4 induced large-scale chromatin de-compaction, which, we hypothesize, facilitates promoter access. Our results reveal two tiers of PHA-4 regulation. PHA-4 binding is prohibited in intestinal cells and is limited in the pharynx by the nuclear lamina component EMR-1/emerin. The data suggest that association of PHA-4 with its targets is a regulated step that contributes to promoter selectivity during organ formation. We speculate that global re-organization of chromatin architecture upon PHA-4 binding promotes competence of pharyngeal gene transcription and, by extension, foregut development.

Role of the endoplasmic reticulum chaperone BiP, SUN domain proteins, and dynein in altering nuclear morphology during human cytomegalovirus infection

The process of assembly and egress of human cytomegalovirus (HCMV) virions requires significant morphological alterations of the nuclear and cytoplasmic architecture. In the studies presented we show that the nuclear periphery is dramatically altered, especially near the cytoplasmic assembly compartment, where the nuclear lamina is specifically rearranged, the outer nuclear membrane is altered, and the nucleus becomes permeable to large molecules. In addition, the tethering of the inner and outer nuclear membranes is lost during infection due to a decrease in levels of the SUN domain proteins. We previously demonstrated that the endoplasmic reticulum protein BiP functions as a component of the assembly compartment and disruption of BiP causes the loss of assembly compartment integrity. In this study we show that the depletion of BiP, and the loss of assembly compartment integrity, results in the loss of virally induced lamina rearrangement and morphology of the nucleus that is characteristic of HCMV infection. BiP functions in lamina rearrangement through its ability to affect lamin phosphorylation. Depletion of BiP and disruption of the assembly compartment result in the loss of lamin phosphorylation. The dependency of lamin phosphorylation on BiP correlates with an interaction between BiP and UL50. Finally, we confirm previous data (S. V. Indran, M. E. Ballestas, and W. J. Britt, J. Virol. 84:3162-3177, 2010) suggesting an involvement of dynein in assembly compartment formation and extend this observation by showing that when dynein is inhibited, the nuclear morphology characteristic of an HCMV infection is lost. Our data suggest a highly integrated assembly-egress continuum.

Designing, optimizing, and implementing high-throughput siRNA genomic screening with glioma cells for the discovery of survival genes and novel drug targets

A major challenge for the treatment of cancers, such as glioblastoma multiforme (GBM), has been resistance to radiation and cancer chemotherapeutics. Short interfering RNA (siRNA) based screening may facilitate the identification of genes and pathways essential for cancer cell survival and could enable a more targeted therapeutic approach for the treatment of GBM. Although the commercial availability of siRNA libraries has expanded greatly, detailed methods for the implementation and analysis of genome-scale screens are largely lacking. To annotate the essential genes and pathways for glioma cell survival, we designed, optimized, and implemented a high-throughput siRNA screen in the highly drug and radiation resistant T98G glioma cell line. We developed a rapid, readily available, and simple strategy to optimize siRNA transfection assays in a 384-well plate format based on immunofluorescence studies and inhibition of the non-essential, endogenous gene lamin A/C. We used these transfection conditions to successfully screen a library of 1056 siRNAs targeting 352 unique human genes in a cell-based one gene per well format to identify the genes essential for glioma cell survival and assess the quality of the screening conditions prior to large-scale screening. After developing and applying a median-based outlier detection algorithm for post-screen analysis, we identified the Ras oncogene family member RAN as an essential gene for glioma cell survival. Successful implementation and analysis of this siRNA screen validates our transfection optimization approach and provides guidance for the rapid development of high-throughput siRNA screens in human glioma cells.