Inflammatory Monocytes Drive Influenza A Virus-Mediated Lung Injury in Juvenile Mice

Healthy children are more likely to die of influenza A virus (IAV) infection than healthy adults. However, little is known about the mechanisms underlying the impact of young age on the development of life-threatening IAV infection. We report increased mortality in juvenile mice compared with adult mice at each infectious dose of IAV. Juvenile mice had sustained elevation of type I IFNs and persistent NLRP3 inflammasome activation in the lungs, both of which were independent of viral titer. Juvenile mice, but not adult mice, had increased MCP-1 levels that remained high even after viral clearance. Importantly, continued production of MCP-1 was associated with persistent recruitment of monocytes to the lungs and prolonged elevation of inflammatory cytokines. Transcriptional signatures of recruited monocytes to the juvenile and adult IAV-infected lungs were assessed by RNA-seq. Genes associated with a proinflammatory signature were upregulated in the juvenile monocytes compared with adult monocytes. Depletion of monocytes with anti-CCR2 Ab decreased type I IFN secretion, NLRP3 inflammasome activation, and lung injury in juvenile mice. This suggests an exaggerated inflammatory response mediated by increased recruitment of monocytes to the lung, and not an inability to control viral replication, is responsible for severe IAV infection in juvenile mice. This study provides insight into severe IAV infection in juveniles and identifies key inflammatory monocytes that may be central to pediatric acute lung injury secondary to IAV.

Inhibition of the NOD-Like Receptor Protein 3 Inflammasome Is Protective in Juvenile Influenza A Virus Infection

Influenza A virus (IAV) is a significant cause of life-threatening lower respiratory tract infections in children. Antiviral therapy is the mainstay of treatment, but its effectiveness in this age group has been questioned. In addition, damage inflicted on the lungs by the immune response to the virus may be as important to the development of severe lung injury during IAV infection as the cytotoxic effects of the virus itself. A crucial step in the immune response to IAV is activation of the NOD-like receptor protein 3 (NLRP3) inflammasome and the subsequent secretion of the inflammatory cytokines, interleukin-1β (IL-1β), and interleukin-18 (IL-18). The IAV matrix 2 proton channel (M2) has been shown to be an important activator of the NLRP3 inflammasome during IAV infection. We sought to interrupt this ion channel-mediated activation of the NLRP3 inflammasome through inhibition of NLRP3 or the cytokine downstream from its activation, IL-1β. Using our juvenile mouse model of IAV infection, we show that inhibition of the NLRP3 inflammasome with the small molecule inhibitor, MCC950, beginning 3 days after infection with IAV, improves survival in juvenile mice. Treatment with MCC950 reduces NLRP3 levels in lung homogenates, decreases IL-18 secretion into the alveolar space, and inhibits NLRP3 inflammasome activation in alveolar macrophages. Importantly, inhibition of the NLRP3 inflammasome with MCC950 does not impair viral clearance. In contrast, inhibition of IL-1β signaling with the IL-1 receptor antagonist, anakinra, is insufficient to protect juvenile mice from IAV. Our findings suggest that targeting the NLRP3 inflammasome in juvenile IAV infection may improve disease outcomes in this age group.

The role of vimentin intermediate filaments in the progression of lung cancer

There is an accumulation of evidence in the literature demonstrating the integral role of vimentin intermediate filaments (IFs) in the progression of lung cancers. Vimentin IF proteins have been implicated in many aspects of cancer initiation and progression, including tumorigenesis, epithelial-to-mesenchymal transition (EMT), and the metastatic spread of cancer. Specifically, vimentin IFs have been recognized as an essential component regulating EMT, major signal transduction pathways involved in EMT and tumor progression, cell migration and invasion, the positioning and anchorage of organelles, such as mitochondria, and cell-cell and cell-substrate adhesion. In tumorgenesis, vimentin forms a complex with 14-3-3 and beclin 1 to inhibit autophagy via an AKT-dependent mechanism. Vimentin is a canonical marker of EMT, and recent evidence has shown it to be an important regulator of cellular motility. Transcriptional regulation of vimentin through hypoxia-inducible factor-1 may be a potential driver of EMT. Finally, vimentin regulates 14-3-3 complexes and controls various intracellular signaling and cell cycle control pathways by depleting the availability of free 14-3-3. There are many exciting advances in our understanding of the complex role of vimentin IFs in cancer, pointing to the key role vimentin IFs may play in tumor progression.

The nucleoporin Nup153 affects spindle checkpoint activity due to an association with Mad1

The nucleoporin Nup153 is known to play pivotal roles in nuclear import and export in interphase cells and as the cell transitions into mitosis, Nup153 is involved in nuclear envelope breakdown. In this study, we demonstrate that the interaction of Nup153 with the spindle assembly checkpoint protein Mad1 is important in the regulation of the spindle checkpoint. Overexpression of human Nup153 in HeLa cells leads to the appearance of multinucleated cells and induces the formation of multipolar spindles. Importantly, it causes inactivation of the spindle checkpoint due to hypophosphorylation of Mad1. Depletion of Nup153 using RNA interference results in the decline of Mad1 at nuclear pores during interphase and more significantly causes a delayed dissociation of Mad1 from kinetochores in metaphase and an increase in the number of unresolved midbodies. In the absence of Nup153 the spindle checkpoint remains active. In vitro studies indicate direct binding of Mad1 to the N-terminal domain of Nup153. Importantly, Nup153 binding to Mad1 affects Mad1's phosphorylation status, but not its ability to interact with Mad2. Our data suggest that Nup153 levels regulate the localization of Mad1 during the metaphase/anaphase transition thereby affecting its phoshorylation status and in turn spindle checkpoint activity and mitotic exit.

Chromosomal regions associated with prostate cancer risk localize to lamin B-deficient microdomains and exhibit reduced gene transcription

The lamins are major determinants of nuclear shape and chromatin organization and these features are frequently altered in prostate cancer (CaP). Human CaP cell lines frequently have nuclear lobulations, which are enriched in A-type lamins but lack B-type lamins and have been defined as lamin B-deficient microdomains (LDMDs). LDMD frequency is correlated with CaP cell line aggressiveness and increased cell motility. In addition, LNCaP cells grown in the presence of dihydrotestosterone (DHT) show an increased frequency of LDMDs. The LDMDs are enriched in activated RNA polymerase II (Pol IIo) and androgen receptor (AR) and A-type lamins form an enlarged meshwork that appears to co-align with chromatin fibres and AR. Furthermore, fluorescence in situ hybridization and comparative genomic hybridization demonstrated that chromosomal regions associated with CaP susceptibility are preferentially localized to LDMDs. Surprisingly, these regions lack histone marks for transcript elongation and exhibit reduced BrU incorporation, suggesting that Pol II is stalled within LDMDs. Real-time PCR of genes near androgen response elements (AREs) was used to compare transcription between cells containing LDMDs and controls. Genes preferentially localized to LDMDs showed significantly decreased expression, while genes in the main nuclear body were largely unaffected. Furthermore, LDMDs were observed in human CaP tissue and the frequency was correlated with increased Gleason grade. These results imply that lamins are involved in chromatin organization and Pol II transcription, and provide insights into the development and progression of CaP.

The role of nuclear lamin B1 in cell proliferation and senescence

Nuclear lamin B1 (LB1) is a major structural component of the nucleus that appears to be involved in the regulation of many nuclear functions. The results of this study demonstrate that LB1 expression in WI-38 cells decreases during cellular senescence. Premature senescence induced by oncogenic Ras also decreases LB1 expression through a retinoblastoma protein (pRb)-dependent mechanism. Silencing the expression of LB1 slows cell proliferation and induces premature senescence in WI-38 cells. The effects of LB1 silencing on proliferation require the activation of p53, but not pRb. However, the induction of premature senescence requires both p53 and pRb. The proliferation defects induced by silencing LB1 are accompanied by a p53-dependent reduction in mitochondrial reactive oxygen species (ROS), which can be rescued by growth under hypoxic conditions. In contrast to the effects of LB1 silencing, overexpression of LB1 increases the proliferation rate and delays the onset of senescence of WI-38 cells. This overexpression eventually leads to cell cycle arrest at the G1/S boundary. These results demonstrate the importance of LB1 in regulating the proliferation and senescence of human diploid cells through a ROS signaling pathway.

Distinct association of the nuclear pore protein Nup153 with A- and B-type lamins

The nuclear envelope (NE) is a double membrane physical barrier, which separates the nucleus from the cytoplasm. Underlying the NE are the nuclear lamins, which in combination with inner nuclear membrane proteins form the lamina. The lamina is crucial for maintaining the structural integrity of the nucleus and for positioning of nuclear pore complexes (NPCs) within the NE. The nucleoporin Nup153 has previously been reported to bind to B-type lamins. However, the specificity of this interaction is not well established. Here we show that Nup153 exhibits multiple binding sites for A- and B-type lamins. Using GST-pull down assays, we found that both the N-terminal domain of Nup153 and its C terminus associate with the Ig-fold domain of A- and B-type lamins. By employing purified Nup153 and lamin proteins in blot overlay assays we revealed that both the N-terminal and the C-terminal domain of Nup153 are directly interacting with the lamins. Moreover, we provide evidence that mutations in the lamin A Ig-fold domain selectively affect Nup153-binding, suggesting that Nup153 may play a role in lamin-associated diseases, known as laminopathies. Together our results indicate a far more intricate interplay between Nup153 and nuclear lamins than previously accepted.

Biomimetic high density lipoprotein nanoparticles for nucleic acid delivery

We report a gold nanoparticle-templated high density lipoprotein (HDL AuNP) platform for gene therapy that combines lipid-based nucleic acid transfection strategies with HDL biomimicry. For proof-of-concept, HDL AuNPs are shown to adsorb antisense cholesterylated DNA. The conjugates are internalized by human cells, can be tracked within cells using transmission electron microscopy, and regulate target gene expression. Overall, the ability to directly image the AuNP core within cells, the chemical tailorability of the HDL AuNP platform, and the potential for cell-specific targeting afforded by HDL biomimicry make this platform appealing for nucleic acid delivery.

Vimentin organization modulates the formation of lamellipodia

The disassembly and withdrawal of vimentin intermediate filaments (VIF) from the plasma membrane induces membrane ruffling and the formation of a lamellipodium. Conversely, lamellipodium formation is inhibited when VIF are present.

Vimentin intermediate filaments (VIF) extend throughout the rear and perinuclear regions of migrating fibroblasts, but only nonfilamentous vimentin particles are present in lamellipodial regions. In contrast, VIF networks extend to the entire cell periphery in serum-starved or nonmotile fibroblasts. Upon serum addition or activation of Rac1, VIF are rapidly phosphorylated at Ser-38, a p21-activated kinase phosphorylation site. This phosphorylation of vimentin is coincident with VIF disassembly at and retraction from the cell surface where lamellipodia form. Furthermore, local induction of photoactivatable Rac1 or the microinjection of a vimentin mimetic peptide (2B2) disassemble VIF at sites where lamellipodia subsequently form. When vimentin organization is disrupted by a dominant-negative mutant or by silencing, there is a loss of polarity, as evidenced by the formation of lamellipodia encircling the entire cell, as well as reduced cell motility. These findings demonstrate an antagonistic relationship between VIF and the formation of lamellipodia.

The dynamic properties of intermediate filaments during organelle transport

Intermediate filament (IF) dynamics during organelle transport and their role in organelle movement were studied using Xenopus laevis melanophores. In these cells, pigment granules (melanosomes) move along microtubules and microfilaments, toward and away from the cell periphery in response to alpha-melanocyte stimulating hormone (alpha-MSH) and melatonin, respectively. In this study we show that melanophores possess a complex network of vimentin IFs which interact with melanosomes. IFs form an intricate, honeycomb-like network that form cages surrounding individual and small clusters of melanosomes, both when they are aggregated and dispersed. Purified melanosome preparations contain a substantial amount of vimentin, suggesting that melanosomes bind to IFs. Analyses of individual melanosome movements in cells with disrupted IF networks show increased movement of granules in both anterograde and retrograde directions, further supporting the notion of a melanosome-IF interaction. Live imaging reveals that IFs, in turn, become highly flexible as melanosomes disperse in response to alpha-MSH. During the height of dispersion there is a marked increase in the rate of fluorescence recovery after photobleaching of GFP-vimentin IFs and an increase in vimentin solubility. These results reveal a dynamic interaction between membrane bound pigment granules and IFs and suggest a role for IFs as modulators of granule movement.

The A- and B-type nuclear lamin networks: microdomains involved in chromatin organization and transcription

The nuclear lamins function in the regulation of replication, transcription, and epigenetic modifications of chromatin. However, the mechanisms responsible for these lamin functions are poorly understood. We demonstrate that A- and B-type lamins form separate, but interacting, stable meshworks in the lamina and have different mobilities in the nucleoplasm as determined by fluorescence correlation spectroscopy (FCS). Silencing lamin B1 (LB1) expression dramatically increases the lamina meshwork size and the mobility of nucleoplasmic lamin A (LA). The changes in lamina mesh size are coupled to the formation of LA/C-rich nuclear envelope blebs deficient in LB2. Comparative genomic hybridization (CGH) analyses of microdissected blebs, fluorescence in situ hybridization (FISH), and immunofluorescence localization of modified histones demonstrate that gene-rich euchromatin associates with the LA/C blebs. Enrichment of hyperphosphorylated RNA polymerase II (Pol II) and histone marks for active transcription suggest that blebs are transcriptionally active. However, in vivo labeling of RNA indicates that transcription is decreased, suggesting that the LA/C-rich microenvironment induces promoter proximal stalling of Pol II. We propose that different lamins are organized into separate, but interacting, microdomains and that LB1 is essential for their organization. Our evidence suggests that the organization and regulation of chromatin are influenced by interconnections between these lamin microdomains.

The highly conserved nuclear lamin Ig-fold binds to PCNA: its role in DNA replication

This study provides insights into the role of nuclear lamins in DNA replication. Our data demonstrate that the Ig-fold motif located in the lamin C terminus binds directly to proliferating cell nuclear antigen (PCNA), the processivity factor necessary for the chain elongation phase of DNA replication. We find that the introduction of a mutation in the Ig-fold, which alters its structure and causes human muscular dystrophy, inhibits PCNA binding. Studies of nuclear assembly and DNA replication show that lamins, PCNA, and chromatin are closely associated in situ. Exposure of replicating nuclei to an excess of the lamin domain containing the Ig-fold inhibits DNA replication in a concentration-dependent fashion. This inhibitory effect is significantly diminished in nuclei exposed to the same domain bearing the Ig-fold mutation. Using the crystal structures of the lamin Ig-fold and PCNA, molecular docking simulations suggest probable interaction sites. These findings also provide insights into the mechanisms underlying the numerous disease-causing mutations located within the lamin Ig-fold.

Nuclear lamins: major factors in the structural organization and function of the nucleus and chromatin

Over the past few years it has become evident that the intermediate filament proteins, the types A and B nuclear lamins, not only provide a structural framework for the nucleus, but are also essential for many aspects of normal nuclear function. Insights into lamin-related functions have been derived from studies of the remarkably large number of disease-causing mutations in the human lamin A gene. This review provides an up-to-date overview of the functions of nuclear lamins, emphasizing their roles in epigenetics, chromatin organization, DNA replication, transcription, and DNA repair. In addition, we discuss recent evidence supporting the importance of lamins in viral infections.

Mutant nuclear lamin A leads to progressive alterations of epigenetic control in premature aging

The premature aging disease Hutchinson-Gilford Progeria Syndrome (HGPS) is caused by a mutant lamin A (LADelta50). Nuclei in cells expressing LADelta50 are abnormally shaped and display a loss of heterochromatin. To determine the mechanisms responsible for the loss of heterochromatin, epigenetic marks regulating either facultative or constitutive heterochromatin were examined. In cells from a female HGPS patient, histone H3 trimethylated on lysine 27 (H3K27me3), a mark for facultative heterochromatin, is lost on the inactive X chromosome (Xi). The methyltransferase responsible for this mark, EZH2, is also down-regulated. These alterations are detectable before the changes in nuclear shape that are considered to be the pathological hallmarks of HGPS cells. The results also show a down-regulation of the pericentric constitutive heterochromatin mark, histone H3 trimethylated on lysine 9, and an altered association of this mark with heterochromatin protein 1alpha (Hp1alpha) and the CREST antigen. This loss of constitutive heterochromatin is accompanied by an up-regulation of pericentric satellite III repeat transcripts. In contrast to these decreases in histone H3 methylation states, there is an increase in the trimethylation of histone H4K20, an epigenetic mark for constitutive heterochromatin. Expression of LADelta50 in normal cells induces changes in histone methylation patterns similar to those seen in HGPS cells. The epigenetic changes described most likely represent molecular mechanisms responsible for the rapid progression of premature aging in HGPS patients.

A mitotic lamin B matrix induced by RanGTP required for spindle assembly

Mitotic spindle morphogenesis is a series of highly coordinated movements that lead to chromosome segregation and cytokinesis. We report that the intermediate filament protein lamin B, a component of the interphase nuclear lamina, functions in spindle assembly. Lamin B assembled into a matrix-like network in mitosis through a process that depended on the presence of the guanosine triphosphate-bound form of the small guanosine triphosphatase Ran. Depletion of lamin B resulted in defects in spindle assembly. Dominant negative mutant lamin B proteins that disrupt lamin B assembly in interphase nuclei also disrupted spindle assembly in mitosis. Furthermore, lamin B was essential for the formation of the mitotic matrix that tethers a number of spindle assembly factors. We propose that lamin B is a structural component of the long-sought-after spindle matrix that promotes microtubule assembly and organization in mitosis.

Intermediate filament proteins participate in signal transduction

How timely transport of chemical signals between the distal end of long axonal processes and the cell bodies of neurons occurs is an interesting and unresolved issue. Recently, Perlson et al. presented evidence that cleavage products of newly synthesized vimentin, an intermediate filament (IF) protein, interact with mitogen-activated protein (MAP) kinases at sites of axon injury. These IF fragments appear to be required for the transport of these kinases to the cell body along microtubule tracks. The truncated vimentin is instrumental in signal propagation as it provides a scaffold that brings together activated MAP kinases (such as Erk 1 and Erk2), as well as importin beta and cytoplasmic dynein. The authors propose that this all-in-one transport complex has the extraordinary ability to travel towards the cell body and enter the nucleus where the kinases activate and influence gene expression so that a neuron can generate a timely response to injury.

Functions and dysfunctions of the nuclear lamin Ig-fold domain in nuclear assembly, growth, and Emery-Dreifuss muscular dystrophy

The non-alpha-helical C terminus of Xenopus lamin B3 (LB3T) inhibits the polymerization of lamin B3 in vitro and prevents the assembly of nuclei in Xenopus egg interphase extracts. To more precisely define the functions of LB3T in nuclear assembly, we have expressed subdomains of LB3T and determined their effects on nuclear assembly in Xenopus extracts. The results demonstrate that the Ig-fold motif (LB3T-Ig) is sufficient to inhibit lamin polymerization in vitro. Addition of the LB3T-Ig to egg extracts before the introduction of chromatin prevents chromatin decondensation and the assembly of the lamina, membranes, and pore complexes comprising the nuclear envelope. When added to assembled nuclei, LB3T-Ig prevents the further incorporation of lamin B3 into the endogenous lamina and blocks nuclear growth. The introduction of a point mutation in LB3T-Ig (R454W; LB3T-IgRW), known to cause Emery-Dreifuss muscular dystrophy when present in lamin A, does not inhibit lamin polymerization, chromatin decondensation, or nuclear assembly and growth. These results shed light on the specific alterations in lamin functions attributable to a known muscular dystrophy mutation and provide an experimental framework for revealing the effects of other mutations causing a wide range of laminopathies.

The nuclear lamina comes of age

Many nuclear proteins form lamin-dependent complexes, including LEM-domain proteins, nesprins and SUN-domain proteins. These complexes have roles in chromatin organization, gene regulation and signal transduction. Some link the nucleoskeleton to cytoskeletal structures, ensuring that the nucleus and centrosome assume appropriate intracellular positions. These complexes provide new insights into cell architecture, as well as a foundation for the understanding of the molecular mechanisms that underlie the human laminopathies - clinical disorders that range from Emery-Dreifuss muscular dystrophy to the accelerated ageing seen in Hutchinson-Gilford progeria syndrome.

Nuclear lamins: building blocks of nuclear structure and function

The cell nucleus is surrounded by a complex membranous envelope which separates the nucleoplasm from the cytoplasm. Unlike the cytoplasm, the nucleoplasm is not subdivided into membrane-bound compartments, which allows for the efficient segregation of a wide range of complex metabolic activities. In the absence of such membrane compartmentalization, the nucleus is faced with the daunting task of efficiently segregating and interconnecting an enormous array of critically important functions. These include the assembly of the large multi-component complexes or 'factories' involved in DNA replication and transcription. These structures are dynamic as they are assembled and disassembled both spatially and temporally at different times, implying the existence of an infrastructure or nucleoskeleton responsible for establishing and maintaining a complex nuclear architecture. There is increasing evidence that the nuclear lamins are essential elements of this nuclear infrastructure, and that their proper assembly and organization are required for numerous essential nuclear functions. Our goal has been to determine the roles of the nuclear lamins in vital nuclear processes including DNA replication and transcription. The hypothesis directing our investigations is that the lamins form a 3D network that courses throughout the nucleoplasm providing an infrastructure for the assembly and distribution of numerous multicomponent complexes involved in a wide range of nuclear functions.

Accumulation of mutant lamin A causes progressive changes in nuclear architecture in Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder, commonly caused by a point mutation in the lamin A gene that results in a protein lacking 50 aa near the C terminus, denoted LADelta50. Here we show by light and electron microscopy that HGPS is associated with significant changes in nuclear shape, including lobulation of the nuclear envelope, thickening of the nuclear lamina, loss of peripheral heterochromatin, and clustering of nuclear pores. These structural defects worsen as HGPS cells age in culture, and their severity correlates with an apparent increase in LADelta50. Introduction of LADelta50 into normal cells by transfection or protein injection induces the same changes. We hypothesize that these alterations in nuclear structure are due to a concentration-dependent dominant-negative effect of LADelta50, leading to the disruption of lamin-related functions ranging from the maintenance of nuclear shape to regulation of gene expression and DNA replication.

The nucleoskeleton: lamins and actin are major players in essential nuclear functions

The nucleoskeleton is composed of many interacting structural proteins that provide the framework for DNA replication, transcription and a variety of other nuclear functions. For example, the type-V intermediate filament proteins, the lamins, and their associated proteins (e.g. Lap2alpha) play important roles in DNA replication and transcription. Furthermore, actin, actin-related proteins and other actin-associated proteins likewise appear to be important in nuclear functions because they are components of chromatin-remodeling complexes and are involved in mRNA synthesis, processing and transport. Newly described nuclear proteins that contain both actin- and lamin-binding domains could be involved in regulating molecular crosstalk between these two types of nucleoskeletal proteins. This range of activities might help to explain why genetic defects in some of the nucleoskeletal proteins contribute to an ever-expanding list of human diseases.

LAP2 binds to BAF.DNA complexes: requirement for the LEM domain and modulation by variable regions

LAP2 belongs to a family of nuclear membrane proteins sharing a 43 residue LEM domain. All LAP2 isoforms have the same N-terminal 'constant' region (LAP2-c), which includes the LEM domain, plus a C-terminal 'variable' region. LAP2-c polypeptide inhibits nuclear assembly in Xenopus extracts, and binds in vitro to barrier-to-autointegration factor (BAF), a DNA-bridging protein. We tested 17 Xenopus LAP2-c mutants for nuclear assembly inhibition, and binding to BAF and BAF small middle dotDNA complexes. LEM domain mutations disrupted all activities tested. Some mutations outside the LEM domain had no effect on binding to BAF, but disrupted activity in Xenopus extracts, suggesting that LAP2-c has an additional unknown function required to inhibit nuclear assembly. Mutagenesis results suggest that BAF changes conformation when complexed with DNA. The binding affinity of LAP2 was higher for BAF small middle dotDNA complexes than for BAF, suggesting that these interactions are physiologically relevant. Nucleoplasmic domains of Xenopus LAP2 isoforms varied 9-fold in their affinities for BAF, but all isoforms supershifted BAF small middle dotDNA complexes. We propose that the LEM domain is a core BAF-binding domain that can be modulated by the variable regions of LAP2 isoforms.

TPEN, a Zn2+/Fe2+ chelator with low affinity for Ca2+, inhibits lamin assembly, destabilizes nuclear architecture and may independently protect nuclei from apoptosis in vitro

We used Xenopus egg extracts to examine the effects of TPEN, a chelator with strong affinities for Zn2+, Fe2+, and Mn2+, on nuclear assembly in vitro. At concentrations above 1 mM, TPEN blocked the assembly of the nuclear lamina and produced nuclei that were profoundly sensitive to stress-induced balloon-like 'shedding' of nuclear membranes away from chromatin-associated membranes. TPEN-arrested nuclei were also defective for DNA replication, which could be explained as secondary to the lack of a lamina. Imaging of TPEN-arrested nuclei by field emission in-lens scanning electron microscopy (FEISEM) revealed clustered, structurally-perturbed nuclear pore complexes. TPEN-arrested nuclei were defective in the accumulation of fluorescent karyophilic proteins. All detectable effects caused by TPEN were downstream of the effects of BAPTA, a Ca2+/Zn2+ chelator that blocks pore complex assembly at two distinct early stages. Surprisingly, TPEN-arrested nuclei, but not control nuclei, remained active for replication in apoptotic extracts, as assayed by [32P]-dCTP incorporation into high molecular weight DNA, suggesting that TPEN blocks a metal-binding protein(s) required for nuclear destruction during programmed cell death.

Epidermal growth factor stimulation of the human gastrin promoter requires Sp1

Growth factors coordinately regulate a variety of different genes to stimulate cellular proliferation. In the stomach, gastrin, epidermal growth factor (EGF), and transforming growth factor-alpha all mediate gastric mucosal homeostasis by promoting cell renewal. We have previously shown that EGF and phorbol esters stimulate the human gastrin promoter through a novel GC-rich DNA element 5'-(68)GGGGCGGGGTGGGGGG-53 called gERE (gastrin EGF response element). In this report, we show that three factors bind to this element, the transcription factor Sp1 and two fast migrating complexes designated gastrin EGF response proteins (gERP 1 and 2). To understand how these factors bind and confer EGF responsiveness, mutations of gERE were tested in vitro for protein binding and in vivo for promoter activation. Both gel shift assays and UV cross-linking studies revealed that the factors bind to overlapping domains, Sp1 to the 5' half-site and gERP 1 and 2 to the 3' half-site. Placing either the 5' or 3' mutations upstream of a minimal gastrin promoter abolished EGF induction. Therefore both the 5' and 3' domains were required to confer EGF induction. Collectively, these results demonstrate that complex interactions between Sp1 and other factors binding to overlapping gERE half-sites confer EGF responsiveness to the gastrin promoter.

Increased cell-substrate adhesion accompanies conditional reversion to the normal phenotype in ras-oncogene-transformed NIH-3T3 cells

We recently reported (1991, Mol. Cell Biol. 11, 3699-3710) that depletion of c-myc protein by myc antisense sequences in ras-transformed NIH-3T3 cells reverses several of the malignant characteristics of these cells. These include transformed morphology, growth in soft agar, and ability to form tumors in athymic mice. In the present study we examined the same cells for in vitro adhesive behavior. Cells depleted of c-myc protein by antisense transfection showed no change in attachment to fibronectin-coated dishes as compared to ras-transformed NIH-3T3 cells but had greatly increased resistance to trypsin/EDTA-mediated release from the substratum after attachment. In concomitant studies, the cells were examined for fibronectin biosynthesis and cell surface fibronectin. There was no overall change in fibronectin biosynthesis in the c-myc antisense transfected cells as compared to the ras-transformed NIH-3T3. However, immunofluorescence staining revealed increased amount of surface fibronectin associated with the antisense c-myc-expressing transfectants. Taken together, these data indicate that the conditional reacquisition of the nonmalignant phenotype in ras-transformed NIH-3T3 cells by selected depletion of c-myc protein is associated with an increase in cell-substrate adhesion. This, in turn, is associated with an increase in surface fibronectin.

Mesangial cell killing by leukocytes: Role of leukocyte oxidants and proteolytic enzymes

Mesangial cells from human and rat kidney were examined for sensitivity to killing by neutrophils. Cells from both species were sensitive to killing by phorbol myristate acetate-stimulated neutrophils. Catalase was highly protective while superoxide dismutase was less protective and a number of protease inhibitors were not protective. Strong protection was also observed with the iron chelators, deferoxamine and phenanthroline, and with the hydroxyl radical scavengers, dimethylthiourea and 5,5-dimethyl-1-pyrroline N-oxide. Pretreatment of the mesangial cells with deferoxamine followed by washing also provided protection. Mesangial cells were also killed by reagent hydrogen peroxide (H2O2) but were much less sensitive to injury by direct application of proteolytic enzymes. The ability of H2O2 to injure mesangial cells was prevented by pre-incubation of the H2O2 with human leukocyte myeloperoxidase. These data suggest that killing is due primarily to the generation of H2O2 by the stimulated neutrophils and its further reduction in an iron-catalyzed reaction. The hydroxyl radical may be the reduction product that actually mediates lethal injury but lack of scavenger specificity prevents definitively concluding this. Mesangial cell killing by activated neutrophils could be significantly inhibited by monoclonal antibodies to CD11/CD18 molecules, suggesting that close contact between the target and effector cells is required for cytotoxicity. Although qualitatively similar to endothelial cells, the mesangial cells appeared to be quantitatively more oxidant sensitive than previously examined human and rat endothelial cells. Taken together, these data show that mesangial cells from rat and human are sensitive to leukocyte-induced injury and that injury results via an oxidant pathway.(ABSTRACT TRUNCATED AT 250 WORDS)