Fragmentation of Golgi complex and Golgi autoantigens during apoptosis and necrosis

Elevated levels of anti-Golgi antibodies: An early sign of seronegative rheumatoid arthritis

Anti-Golgi antibodies are uncommon antibodies that exhibit specific, polarized cytoplasmic staining on the Hep-2 substrate. The objective of our study was to identify the clinical and laboratory features associated with anti-Golgi antibodies. We examined 4.5 years of data from a Turkish tertiary hospital in this retrospective cohort analysis. The indirect immunofluorescence staining patterns, antinuclear antibody (ANA) titres and clinical data of all patients were obtained from the hospital record system. A total of 146,055 ANAs were detected, of which 224 patients (0.15%) exhibited anti-Golgi antibody staining. In total, 39.4% of diagnosed patients had autoimmune diseases (AIDs). Of the AIDs, 26 (46.4%) were rheumatoid arthritis (RA). This is a very high rate and another remarkable point is that 17 (65.3%) of these patients had seronegative RA. High-titre results (1 ≥ 1/320) were more common in patients with AID. Anti-Ro52 was prevalent in 50% of extractable nuclear antigen (ENA)-positive patients, making it a remarkable finding. The majority of individuals with high-titre anti-Golgi antibodies had AID, particularly RA. The majority of these patients also tested negative for anti-cyclic citrullinated peptide (anti-CCP) and rheumatoid factor (RF). Finally, high-titre anti-Golgi antibodies may be an important serologic marker for seronegative RA in the Turkish population.

Split but merge: Golgi fragmentation in physiological and pathological conditions

The Golgi complex is a highly dynamic and tightly regulated cellular organelle with essential roles in the processing as well as the sorting of proteins and lipids. Its structure undergoes rapid disassembly and reassembly during normal physiological processes, including cell division, migration, polarization, differentiation, and cell death. Golgi dispersal or fragmentation also occurs in pathological conditions, such as neurodegenerative diseases, infectious diseases, congenital disorders of glycosylation diseases, and cancer. In this review, current knowledge about both structural organization and morphological alterations in the Golgi in physiological and pathological conditions is summarized together with the methodologies that help to reveal its structure.

Structural alterations in cell organelles induced by photodynamic treatment with chlorin p6 -histamine conjugate in human oral carcinoma cells probed by 3D fluorescence microscopy

We have explored the intracellular cell organelle's structural alterations after photodynamic treatment with chlorin p₆ -histamine conjugate (Cp₆ -his) in human oral cancer cells. Herein, the cells were treated with Cp₆ -his (10 μm) and counterstained with organelle-specific fluorescence probes to find the site of intracellular localization using confocal microscopy. For photodynamic therapy (PDT), the cells were exposed to ~30 kJ/m² red light (660 ± 20 nm) to induce ~90% cytotoxicity. We used the three-dimensional (3D) image reconstruction approach to analyze the photodynamic damage to cell organelles. The result showed that Cp₆ -his localized mainly in the endoplasmic reticulum (ER) and lysosomes but not in mitochondria and Golgi apparatus (GA). The 3D model revealed that in necrotic cells, PDT led to extensive fragmentation of ER and fragmentation and swelling of GA as well. Results suggest that the indirect damage to GA occurred due to loss of connection between ER and GA. Moreover, in damaged cells with no sign of necrosis, the perinuclear ER appeared condensed and surrounded by several small clumps at the peripheral region of the cell, and the GA was observed to form a single condensed structure. Since these structural changes were associated with apoptotic cell death, it is suggested that the necrotic and apoptotic death induced by PDT with Cp₆ -his is determined by the severity of damage to ER and indirect damage to GA. The results suggest that the indirect damage to cell organelle apart from the sites of photosensitizer localization and the severity of damage at the organelle level contribute significantly to the mode of cell death in PDT.

Dissecting the Mechanism of Action of Spiperone-A Candidate for Drug Repurposing for Colorectal Cancer

Simple Summary

Despite advances in primary and adjuvant treatments, approximately 50% of colorectal cancer (CRC) patients still die from recurrence and metastatic disease. Thus, alternative and more effective therapeutic approaches are expected to be developed. Drug repurposing is increasing interest in cancer therapy, as it represents a cheaper and faster alternative strategy to de novo drug synthesis. Psychiatric medications are promising as a new generation of antitumor drugs. Here, we demonstrate that spiperone—a licensed drug for the treatment of schizophrenia—induces apoptosis in CRC cells. Our data reveal that spiperone’s cytotoxicity in CRC cells is mediated by phospholipase C activation, intracellular calcium homeostasis dysregulation, and irreversible endoplasmic reticulum stress induction, resulting in lipid metabolism alteration and Golgi apparatus damage. By identifying new targetable pathways in CRC cells, our findings represent a promising starting point for the design of novel therapeutic strategies for CRC.

Abstract

Approximately 50% of colorectal cancer (CRC) patients still die from recurrence and metastatic disease, highlighting the need for novel therapeutic strategies. Drug repurposing is attracting increasing attention because, compared to traditional de novo drug discovery processes, it may reduce drug development periods and costs. Epidemiological and preclinical evidence support the antitumor activity of antipsychotic drugs. Herein, we dissect the mechanism of action of the typical antipsychotic spiperone in CRC. Spiperone can reduce the clonogenic potential of stem-like CRC cells (CRC-SCs) and induce cell cycle arrest and apoptosis, in both differentiated and CRC-SCs, at clinically relevant concentrations whose toxicity is negligible for non-neoplastic cells. Analysis of intracellular Ca²⁺ kinetics upon spiperone treatment revealed a massive phospholipase C (PLC)-dependent endoplasmic reticulum (ER) Ca²⁺ release, resulting in ER Ca²⁺ homeostasis disruption. RNA sequencing revealed unfolded protein response (UPR) activation, ER stress, and induction of apoptosis, along with IRE1-dependent decay of mRNA (RIDD) activation. Lipidomic analysis showed a significant alteration of lipid profile and, in particular, of sphingolipids. Damage to the Golgi apparatus was also observed. Our data suggest that spiperone can represent an effective drug in the treatment of CRC, and that ER stress induction, along with lipid metabolism alteration, represents effective druggable pathways in CRC.

Anti-Golgi Antibody as a Potential Indicator for Rheumatoid Arthritis

OBJECTIVE

To reveal the relationship between anti-Golgi antibody (AGA) and clinical diseases through retrospective analysis.

METHODS

The clinical data of 584 cases testing positive for AGA in the past 11 years were collected and retrospectively analyzed.

RESULTS

AGA pattern accounted for .2% of positive ANA results. In total, 35.0% of diagnosed patients had autoimmune diseases (AID), mainly rheumatoid arthritis (RA). High-titer AGA (≧1:1000) was common in AID. In nondiagnosed patients with clinical symptoms, joint pain/muscle pain was the most common.

CONCLUSIONS

Positive AGA with high titer was closely related to RA. Joint pain/muscle pain was the most common symptom in patients who tested AGA positive. Therefore, AGA may be a key indicator of RA in the Chinese population.

Heme oxygenase-1(HO-1) regulates Golgi stress and attenuates endotoxin-induced acute lung injury through hypoxia inducible factor-1α (HIF-1α)/HO-1 signaling pathway

Sepsis caused acute lung injury (ALI) is a kind of serious disease in critically ill patients with very high morbidity and mortality. Recently, it has been demonstrated that Golgi is involved in the process of oxidative stress. However, whether Golgi stress is associated with oxidative stress in septic induced acute lung injury has not been elucidated. In this research, we found that lipopolysaccharide (LPS) induced oxidative stress, apoptosis, inflammation and Golgi morphology changes in acute lung injury both in vivo and in vitro. The knockout of heme oxygenase-1(HO-1) aggravated oxidative stress, inflammation, apoptosis and reduced the expression of Golgi matrix protein 130 (GM130), mannosidase Ⅱ, Golgi-associated protein golgin A1 (Golgin 97), and increased the expression of Golgi phosphoprotein 3 (GOLPH3), which caused the fragmentation of Golgi. Furtherly, the activation of hypoxia inducible factor-1α (HIF-1α)/HO-1 pathway, attenuates Golgi stress and oxidative stress by increasing the levels of GM130, mannosidase Ⅱ, Golgin 97, and decreasing the expression of GOLPH3 both in vivo and in vitro. Therefore, the activation of HO-1 plays a crucial role in alleviating sepsis-induced acute lung injury by regulating Golgi stress, oxidative stress, which may provide a therapeutic target for the treatment of acute lung injury.

From hepatitis C virus immunoproteomics to rheumatology via cross-reactivity in one table

PURPOSE OF REVIEW

To give an overview of molecular and immunologic data that link hepatitis C virus (HCV) infection to rheumatic diseases in the human host.

RECENT FINDINGS

A high level of peptide sharing exists between immunopositive HCV epitopes and human proteins that, when altered, associate with rheumatic manifestations.

SUMMARY

The findings suggest the involvement of HCV infection in the induction of most rheumatic diseases via a mechanism of autoimmune cross-reactivity.

Post-ER Stress Biogenesis of Golgi Is Governed by Giantin

BACKGROUND

The Golgi apparatus undergoes disorganization in response to stress, but it is able to restore compact and perinuclear structure under recovery. This self-organization mechanism is significant for cellular homeostasis, but remains mostly elusive, as does the role of giantin, the largest Golgi matrix dimeric protein.

METHODS

In HeLa and different prostate cancer cells, we used the model of cellular stress induced by Brefeldin A (BFA). The conformational structure of giantin was assessed by proximity ligation assay and atomic force microscopy. The post-BFA distribution of Golgi resident enzymes was examined by 3D SIM high-resolution microscopy.

RESULTS

We detected that giantin is rather flexible than an extended coiled-coil dimer and BFA-induced Golgi disassembly was associated with giantin monomerization. A fusion of the nascent Golgi membranes after BFA washout is forced by giantin re-dimerization via disulfide bond in its luminal domain and assisted by Rab6a GTPase. GM130-GRASP65-dependent enzymes are able to reach the nascent Golgi membranes, while giantin-sensitive enzymes appeared at the Golgi after its complete recovery via direct interaction of their cytoplasmic tail with N-terminus of giantin.

CONCLUSION

Post-stress recovery of Golgi is conducted by giantin dimer and Golgi proteins refill membranes according to their docking affiliation rather than their intra-Golgi location.

Golgi Structure and Function in Health, Stress, and Diseases

The Golgi apparatus is a central intracellular membrane-bound organelle with key functions in trafficking, processing, and sorting of newly synthesized membrane and secretory proteins and lipids. To best perform these functions, Golgi membranes form a unique stacked structure. The Golgi structure is dynamic but tightly regulated; it undergoes rapid disassembly and reassembly during the cell cycle of mammalian cells and is disrupted under certain stress and pathological conditions. In the past decade, significant amount of effort has been made to reveal the molecular mechanisms that regulate the Golgi membrane architecture and function. Here we review the major discoveries in the mechanisms of Golgi structure formation, regulation, and alteration in relation to its functions in physiological and pathological conditions to further our understanding of Golgi structure and function in health and diseases.

CD70 as a target for chimeric antigen receptor T cells in head and neck squamous cell carcinoma

OBJECTIVES

In accordance with the Precision Medicine Initiative, new treatment strategies for head and neck squamous cell carcinoma (HNSCC) are needed to yield better therapeutic outcomes. The purpose of this study was to establish and validate chimeric antigen receptor (CAR)-T cells targets in HNSCC.

METHODS

Putative CAR-T antigens were identified in The Cancer Genome Atlas database. To validate antigen suitability, quantitative RT-PCR, flow cytometry, and immunofluorescent staining were performed. A retroviral human CD70 CAR construct, using truncated CD27 conjugated with 4-1BB and CD3-zeta costimulatory molecules, was used to transduce activated human T cells to generate CD70 CAR-T cells. Cell-based cytotoxicity and cytokine ELISAs were used to measure efficacy of killing.

RESULTS

Nine potential CAR-T targets (CD276, EGFR, MICA, MICB, MAGE-A4, FAP, EPCAM, CD70, B4GALNT1) were identified based on their high expression in tumors compared to flanking control tissues. CD70 was selected for further proof-of-principle analysis based on its differential expression in several tumor subtypes, and showed substantial heterogeneity in individual tumors analyzed. Cell surface CD70 protein and CD70 mRNA were detected from low to high levels in established HNSCC cancer cell lines. CD70 was highly expressed in 4 of 21 tumor biopsies (19%), and 3 of 4 specimens showed strong CD70 expression on the tumor cell surface. CD70-specific CAR-T cells were generated and further demonstrated to recognize and kill CD70-positive HNSCC cells efficiently, but not CD70-negative cancer cells.

CONCLUSION

CD70-specific CAR-T cells specifically recognized and efficiently eliminated CD70-positive HNSCC cells. This study provides the basis for further investigation into CD70 and other CAR-T targets.

Golgi ribbon disassembly during mitosis, differentiation and disease progression

The Golgi apparatus is tightly integrated into the cellular system where it plays essential roles required for a variety of cellular processes. Its vital functions include not only processing and sorting of proteins and lipids, but also serving as a signaling hub and a microtubule-organizing center. Golgi stacks in mammalian cells are interconnected into a compact ribbon in the perinuclear region. However, the ribbon can undergo distinct disassembly processes that reflect the cellular state or environmental demands and stress. For instance, its most dramatic change takes place in mitosis when the ribbon is efficiently disassembled into vesicles through a combination of ribbon unlinking, cisternal unstacking and vesiculation. Furthermore, the ribbon can also be detached and positioned at specific cellular locations to gain additional functionalities during differentiation, or fragmented to different degrees along disease progression or upon cell death. Here, we describe the major morphological alterations of Golgi ribbon disassembly under physiological and pathological conditions and discuss the underlying mechanisms that drive these changes.

Report on the second International Consensus on ANA Pattern (ICAP) workshop in Dresden 2015

The second meeting for the International Consensus on Antinuclear antibody (ANA) Pattern (ICAP) was held on 22 September 2015, one day prior to the opening of the 12th Dresden Symposium on Autoantibodies in Dresden, Germany. The ultimate goal of ICAP is to promote harmonization and understanding of autoantibody nomenclature, and thereby optimizing ANA usage in patient care. The newly developed ICAP website www.ANApatterns.org was introduced to the more than 50 participants. This was followed by several presentations and discussions focusing on key issues including the two-tier classification of ANA patterns into competent-level versus expert-level, the consideration of how to report composite versus mixed ANA patterns, and the necessity for developing a consensus on how ANA results should be reported. The need to establish on-line training modules to help users gain competency in identifying ANA patterns was discussed as a future addition to the website. To advance the ICAP goal of promoting wider international participation, it was agreed that there should be a consolidated plan to translate consensus documents into other languages by recruiting help from members of the respective communities.

Oncolytic reovirus induces intracellular redistribution of Ras to promote apoptosis and progeny virus release

Reovirus is a naturally oncolytic virus that preferentially replicates in Ras-transformed cells and is currently undergoing clinical trials as a cancer therapeutic. Ras transformation promotes reovirus oncolysis by enhancing virion disassembly during entry, viral progeny production, and virus release through apoptosis; however, the mechanism behind the latter is not well understood. Here, we show that reovirus alters the intracellular location of oncogenic Ras to induce apoptosis of H-RasV12-transformed fibroblasts. Reovirus infection decreases Ras palmitoylation levels and causes accumulation of Ras in the Golgi through Golgi fragmentation. With the Golgi being the site of Ras palmitoylation, treatment of target cells with the palmitoylation inhibitor, 2-bromopalmitate (2BP), prompts a greater accumulation of H-RasV12 in the Golgi, and a dose-dependent increase in progeny virus release and subsequent spread. Conversely, tethering H-RasV12 to the plasma membrane (thereby preventing its movement to the Golgi) allows for efficient virus production, but results in basal levels of reovirus-induced cell death. Analysis of Ras downstream signaling reveals that cells expressing cycling H-RasV12 have elevated levels of phosphorylated JNK (c-Jun N-terminal kinase), and that Ras retained at the Golgi body by 2BP increases activation of the MEKK1/MKK4/JNK signaling pathway to promote cell death. Collectively, our data suggest that reovirus induces Golgi fragmentation of target cells, and the subsequent accumulation of oncogenic Ras in the Golgi body initiates apoptotic signaling events required for virus release and spread.

Infertility in the hyperplasic ovary of freshwater planarians: the role of programmed cell death

Ex-fissiparous planarians produce infertile cocoons or, in very rare cases, cocoons with very low fertility. Here, we describe the features of programmed cell death (PCD) occurring in the hyperplasic ovary of the ex-fissiparous freshwater planarian Dugesia arabica that may explain this infertility. Based on TEM results, we demonstrate a novel extensive co-clustering of cytoplasmic organelles, such as lysosomes and microtubules, and their fusion with autophagosomes during the early stage of oocyte cell death occurring through an autophagic pattern. During a later stage of cell death, the generation of apoptotic vesicles in the cytoplasm can be observed. The immunohistochemical labeling supports the ultrastructural results because it has been shown that the proapoptotic protein bax was more highly expressed in the hyperplasic ovary than in the normal one, whereas the anti-apoptotic protein bcl2 was slightly more highly expressed in the normal ovary compared to the hyperplasic one. TUNEL analysis of the hyperplasic ovary confirmed that the nuclei of the majority of differentiating oocytes were TUNEL-positive, whereas the nuclei of oogonia and young oocytes were TUNEL-negative; in the normal ovary, oocytes are TUNEL-negative. Considering all of these data, we suggest that the cell death mechanism of differentiating oocytes in the hyperplasic ovary of freshwater planarians is one of the most important factors that cause ex-fissiparous planarian infertility. We propose that autophagy precedes apoptosis during oogenesis, whereas apoptotic features can be observed later.

Restoration of compact Golgi morphology in advanced prostate cancer enhances susceptibility to galectin-1-induced apoptosis by modifying mucin O-glycan synthesis

Prostate cancer progression is associated with upregulation of sialyl-T antigen produced by β-galactoside α-2,3-sialyltransferase-1 (ST3Gal1) but not with core 2-associated polylactosamine despite expression of core 2 N-acetylglucosaminyltransferase-L (C2GnT-L/GCNT1). This property allows androgen-refractory prostate cancer cells to evade galectin-1 (LGALS1)-induced apoptosis, but the mechanism is not known. We have recently reported that Golgi targeting of glycosyltransferases is mediated by golgins: giantin (GOLGB1) for C2GnT-M (GCNT3) and GM130 (GOLGA2)-GRASP65 (GORASP1) or GM130-giantin for core 1 synthase. Here, we show that for Golgi targeting, C2GnT-L also uses giantin exclusively whereas ST3Gal1 uses either giantin or GM130-GRASP65. In addition, the compact Golgi morphology is detected in both androgen-sensitive prostate cancer and normal prostate cells, but fragmented Golgi and mislocalization of C2GnT-L are found in androgen-refractory cells as well as primary prostate tumors (Gleason grade 2-4). Furthermore, failure of giantin monomers to be phosphorylated and dimerized prevents Golgi from forming compact morphology and C2GnT-L from targeting the Golgi. On the other hand, ST3Gal1 reaches the Golgi by an alternate site, GM130-GRASP65. Interestingly, inhibition or knockdown of non-muscle myosin IIA (MYH9) motor protein frees up Rab6a GTPase to promote phosphorylation of giantin by polo-like kinase 3 (PLK3), which is followed by dimerization of giantin assisted by protein disulfide isomerase A3 (PDIA3), and restoration of compact Golgi morphology and targeting of C2GnT-L. Finally, the Golgi relocation of C2GnT-L in androgen-refractory cells results in their increased susceptibility to galectin-1-induced apoptosis by replacing sialyl-T antigen with polylactosamine.

IMPLICATIONS

This study demonstrates the importance of Golgi morphology and regulation of glycosylation and provides insight into how the Golgi influences cancer progression and metastasis.

Arf4 is required for Mammalian development but dispensable for ciliary assembly

The primary cilium is a sensory organelle, defects in which cause a wide range of human diseases including retinal degeneration, polycystic kidney disease and birth defects. The sensory functions of cilia require specific receptors to be targeted to the ciliary subdomain of the plasma membrane. Arf4 has been proposed to sort cargo destined for the cilium at the Golgi complex and deemed a key regulator of ciliary protein trafficking. In this work, we show that Arf4 binds to the ciliary targeting sequence (CTS) of fibrocystin. Knockdown of Arf4 indicates that it is not absolutely required for trafficking of the fibrocystin CTS to cilia as steady-state CTS levels are unaffected. However, we did observe a delay in delivery of newly synthesized CTS from the Golgi complex to the cilium when Arf4 was reduced. Arf4 mutant mice are embryonic lethal and die at mid-gestation shortly after node formation. Nodal cilia appeared normal and functioned properly to break left-right symmetry in Arf4 mutant embryos. At this stage of development Arf4 expression is highest in the visceral endoderm but we did not detect cilia on these cells. In the visceral endoderm, the lack of Arf4 caused defects in cell structure and apical protein localization. This work suggests that while Arf4 is not required for ciliary assembly, it is important for the efficient transport of fibrocystin to cilia, and also plays critical roles in non-ciliary processes.

Primary cilia are ubiquitous sensory organelles that play vital roles in an ever-growing class of human diseases termed ciliopathies including obesity, retinal degeneration and polycystic kidney disease. The proper function of the primary cilium relies on a cell's ability to target and concentrate specific receptors to the ciliary membrane – a unique subdomain of the plasma membrane yet little is known about how receptors are trafficked to the primary cilium. Mutations affecting the ciliary localized receptor fibrocystin (PKHD1) cause autosomal recessive polycystic kidney disease, which affects approximately 1∶20,000 individuals. Previously we identified a motif located in the cytoplasmic domain of fibrocystin that is required for its ciliary localization. In this work we demonstrate that the ciliary targeting sequence (CTS) of fibrocystin interacts with the small G protein Arf4 and this interaction is important for the efficient delivery of the CTS to cilia in cultured cells. Disruption of Arf4 in mice results in defects in the non-ciliated visceral endoderm and death at mid-gestation indicating Arf4 has vital functions in addition to ciliary protein trafficking.

Danhong injection: A modulator for Golgi structural stability after cerebral ischemia-reperfusion injury

The cerebral ischemia-reperfusion model was established using the suture occlusion method, and rats were intraperitoneally given 8 mL/kg Danhong injection once a day prior to model establishment. Rat brain tissues were harvested at 6, 24, 48, 72 hours after reperfusion. Immunohistochemical staining showed that transforming growth factor-β1 expression increased, while Golgi matrix protein GM130 expression decreased after cerebral ischemia-reperfusion. Danhong injection was shown to significantly up-regulate the expression of transforming growth factor-β1 and GM130, and expression levels peaked at 7 days after reperfusion. At 7 days after cerebral ischemia-reperfusion, Golgi morphology was damaged in untreated rats, while Golgi morphology breakage was not observed after intervention with Danhong injection. These experimental findings indicate that Danhong injection can up-regulate the expression of transforming growth factor-β1 and GM130, and maintain Golgi stability, thus playing a neuroprotective role in rats after cerebral ischemia-reperfusion.

Toxoplasma gondii salvages sphingolipids from the host Golgi through the rerouting of selected Rab vesicles to the parasitophorous vacuole

The obligate intracellular protozoan Toxoplasma gondii actively invades mammalian cells and, upon entry, forms its own membrane-bound compartment, named the parasitophorous vacuole (PV). Within the PV, the parasite replicates and scavenges nutrients, including lipids, from host organelles. Although T. gondii can synthesize sphingolipids de novo, it also scavenges these lipids from the host Golgi. How the parasite obtains sphingolipids from the Golgi remains unclear, as the PV avoids fusion with host organelles. In this study, we explore the host Golgi-PV interaction and evaluate the importance of host-derived sphingolipids for parasite growth. We demonstrate that the PV preferentially localizes near the host Golgi early during infection and remains closely associated with this organelle throughout infection. The parasite subverts the structure of the host Golgi, resulting in its fragmentation into numerous ministacks, which surround the PV, and hijacks host Golgi-derived vesicles within the PV. These vesicles, marked with Rab14, Rab30, or Rab43, colocalize with host-derived sphingolipids in the vacuolar space. Scavenged sphingolipids contribute to parasite replication since alterations in host sphingolipid metabolism are detrimental for the parasite's growth. Thus our results reveal that T. gondii relies on host-derived sphingolipids for its development and scavenges these lipids via Golgi-derived vesicles.

The canonical NF-κB pathway differentially protects normal and human tumor cells from ROS-induced DNA damage

DNA damage responses (DDR) invoke senescence or apoptosis depending on stimulus intensity and the degree of activation of the p53-p21(Cip1/Waf1) axis; but the functional impact of NF-κB signaling on these different outcomes in normal vs. human cancer cells remains poorly understood. We investigated the NF-κB-dependent effects and mechanism underlying reactive oxygen species (ROS)-mediated DDR outcomes of normal human lung fibroblasts (HDFs) and A549 human lung cancer epithelial cells. To activate DDR, ROS accumulation was induced by different doses of H(2)O(2). The effect of ROS induction caused a G2 or G2-M phase cell cycle arrest of both human cell types. However, ROS-mediated DDR eventually culminated in different end points with HDFs undergoing premature senescence and A549 cancer cells succumbing to apoptosis. NF-κB p65/RelA nuclear translocation and Ser536 phosphorylation were induced in response to H(2)O(2)-mediated ROS accumulation. Importantly, blocking the activities of canonical NF-κB subunits with an IκBα super-repressor or suppressing canonical NF-κB signaling by IKKβ knock-down accelerated HDF premature senescence by up-regulating the p53-p21(Cip1/Waf1) axis; but inhibiting the canonical NF-κB pathway exacerbated H(2)O(2)-induced A549 cell apoptosis. HDF premature aging occurred in conjunction with γ-H2AX chromatin deposition, senescence-associated heterochromatic foci and beta-galactosidase staining. p53 knock-down abrogated H(2)O(2)-induced premature senescence of vector control- and IκBαSR-expressing HDFs functionally linking canonical NF-κB-dependent control of p53 levels to ROS-induced HDF senescence. We conclude that IKKβ-driven canonical NF-κB signaling has different functional roles for the outcome of ROS responses in the contexts of normal vs. human tumor cells by respectively protecting them against DDR-dependent premature senescence and apoptosis.

Induction of cytoplasmic rods and rings structures by inhibition of the CTP and GTP synthetic pathway in mammalian cells

Background

Cytoplasmic filamentous rods and rings (RR) structures were identified using human autoantibodies as probes. In the present study, the formation of these conserved structures in mammalian cells and functions linked to these structures were examined.

Methodology/Principal Findings

Distinct cytoplasmic rods (∼3–10 µm in length) and rings (∼2–5 µm in diameter) in HEp-2 cells were initially observed in immunofluorescence using human autoantibodies. Co-localization studies revealed that, although RR had filament-like features, they were not enriched in actin, tubulin, or vimentin, and not associated with centrosomes or other known cytoplasmic structures. Further independent studies revealed that two key enzymes in the nucleotide synthetic pathway cytidine triphosphate synthase 1 (CTPS1) and inosine monophosphate dehydrogenase 2 (IMPDH2) were highly enriched in RR. CTPS1 enzyme inhibitors 6-diazo-5-oxo-L-norleucine and Acivicin as well as the IMPDH2 inhibitor Ribavirin exhibited dose-dependent induction of RR in >95% of cells in all cancer cell lines tested as well as mouse primary cells. RR formation by lower concentration of Ribavirin was enhanced in IMPDH2-knockdown HeLa cells whereas it was inhibited in GFP-IMPDH2 overexpressed HeLa cells. Interestingly, RR were detected readily in untreated mouse embryonic stem cells (>95%); upon retinoic acid differentiation, RR disassembled in these cells but reformed when treated with Acivicin.

Conclusions/Significance

RR formation represented response to disturbances in the CTP or GTP synthetic pathways in cancer cell lines and mouse primary cells and RR are the convergence physical structures in these pathways. The availability of specific markers for these conserved structures and the ability to induce formation in vitro will allow further investigations in structure and function of RR in many biological systems in health and diseases.

The golgin coiled-coil proteins of the Golgi apparatus

A number of long coiled-coil proteins are present on the Golgi. Often referred to as "golgins," they are well conserved in evolution and at least five are likely to have been present in the last common ancestor of all eukaryotes. Individual golgins are found in different parts of the Golgi stack, and they are typically anchored to the membrane at their carboxyl termini by a transmembrane domain or by binding a small GTPase. They appear to have roles in membrane traffic and Golgi structure, but their precise function is in most cases unclear. Many have binding sites for Rab family GTPases along their length, and this has led to the suggestion that the golgins act collectively to form a tentacular matrix that surrounds the Golgi to capture Rab-coated membranes in the vicinity of the stack. Such a collective role might explain the lack of cell lethality seen following loss of some of the genes in human familial conditions or mouse models.

Golgi positioning

The Golgi apparatus in mammalian cells is positioned near the centrosome-based microtubule-organizing center (Fig. 1). Secretory cargo moves inward in membrane carriers for delivery to Golgi membranes in which it is processed and packaged for transport outward to the plasma membrane. Cytoplasmic dynein motor proteins (herein termed dynein) primarily mediate inward cargo carrier movement and Golgi positioning. These motors move along microtubules toward microtubule minus-ends embedded in centrosomes. Centripetal motility is controlled by a host of regulators whose precise functions remain to be determined. Significantly, a specific Golgi receptor for dynein has not been identified. This has impaired progress toward elucidation of membrane-motor-microtubule attachment in the periphery and, after inward movement, recycling of the motor for another round. Pericentrosomal positioning of the Golgi apparatus is dynamic. It is regulated during critical cellular processes such as mitosis, differentiation, cell polarization, and cell migration. Positioning is also important as it aligns the Golgi along an axis of cell polarity. In certain cell types, this promotes secretion directed to the proximal plasma membrane domain thereby maintaining specializations critical for diverse processes including wound healing, immunological synapse formation, and axon determination.

Differential gene expression and developmental competence in in vitro produced bovine embryos

The embryonic developmental block occurs at the 8-cell stage in cattle and is characterized by a lengthening of the cell cycle and an increased number of embryos that stop development. The maternal-embryonic transition arises at the same stage resulting in the transcription of many genes. Gene expression studies during this stage may contribute to the understanding of the physiological mechanisms involved in the maternal-embryonic transition. Herein we identified genes differentially expressed between embryos with high or low developmental competence to reach the blastocyst stage using differential display PCR. Embryos were analysed according to developmental kinetics: fast cleavage embryos showing 8 cells at 48 h post insemination (hpi) with high potential of development (F8), and embryos with slow cleavage presenting 4 cells at 48 hpi (S4) and 8 cells at 90 hpi (S8), both with reduced rates of development to blastocyst. The fluorescence DDPCR method was applied and allowed the recovery of 176 differentially expressed bands with similar proportion between high and low development potential groups (52% to F8 and 48% in S4 and S8 groups). A total of 27 isolated fragments were cloned and sequenced, confirming the expected primer sequences and allowing the identification of 27 gene transcripts. PI3KCA and ITM2B were chosen for relative quantification of mRNA using real-time PCR and showed a kinetic and a time-related pattern of expression respectively. The observed results suggest the existence of two different embryonic genome activation mechanisms: fast-developing embryos activate genes related to embryonic development, and slow-developing embryos activate genes related to cellular survival and/or death.

Neurons sense nanoscale roughness with nanometer sensitivity

The interaction between cells and nanostructured materials is attracting increasing interest, because of the possibility to open up novel concepts for the design of smart nanobiomaterials with active biological functionalities. In this frame we investigated the response of human neuroblastoma cell line (SH-SY5Y) to gold surfaces with different levels of nanoroughness. To achieve a precise control of the nanoroughness with nanometer resolution, we exploited a wet chemistry approach based on spontaneous galvanic displacement reaction. We demonstrated that neurons sense and actively respond to the surface nanotopography, with a surprising sensitivity to variations of few nanometers. We showed that focal adhesion complexes, which allow cellular sensing, are strongly affected by nanostructured surfaces, leading to a marked decrease in cell adhesion. Moreover, cells adherent on nanorough surfaces exhibit loss of neuron polarity, Golgi apparatus fragmentation, nuclear condensation, and actin cytoskeleton that is not functionally organized. Apoptosis/necrosis assays established that nanoscale features induce cell death by necrosis, with a trend directly related to roughness values. Finally, by seeding SH-SY5Y cells onto micropatterned flat and nanorough gold surfaces, we demonstrated the possibility to realize substrates with cytophilic or cytophobic behavior, simply by fine-tuning their surface topography at nanometer scale. Specific and functional adhesion of cells occurred only onto flat gold stripes, with a clear self-alignment of neurons, delivering a simple and elegant approach for the design and development of biomaterials with precise nanostructure-triggered biological responses.

Acyl-coenzyme A binding domain containing 3 (ACBD3; PAP7; GCP60): an emerging signaling molecule

Golgi body-mediated signaling has been linked to its fragmentation and regeneration during the mitotic cycle of the cell. During this process, Golgi-resident proteins are released to the cytosol and interact with other signaling molecules to regulate various cellular processes. Acyl-coenzyme A binding domain containing 3 protein (ACBD3) is a Golgi protein involved in several signaling events. ACBD3 protein was previously known as peripheral-type benzodiazepine receptor and cAMP-dependent protein kinase associated protein 7 (PAP7), Golgi complex-associated protein of 60kDa (GCP60), Golgi complex-associated protein 1 (GOCAP1), and Golgi phosphoprotein 1 (GOLPH1). In this review, we present the gene ontology of ACBD3, its relations to other Acyl-coenzyme A binding domain containing (ACBD) proteins, and its biological function in steroidogenesis, apoptosis, neurogenesis, and embryogenesis. We also discuss the role of ACBD3 in asymmetric cell division and cancer. New findings about ACBD3 may help understand this newly characterized signaling molecule and stimulate further research into its role in molecular endocrinology, neurology, and stem cell biology.

Autoantibody to NA14 is an independent marker primarily for Sjogren's syndrome

Nuclear Autoantigen of 14 kDa (NA14) was originally identified using the serum of a Sjögren's syndrome (SS) patient as probe in screening a human testis cDNA expression library. To date there is no report in the systematic analysis of the prevalence of autoantibodies to NA14. In this study, anti-NA14 was determined in several rheumatic diseases from independent cohorts in the US and Japan. The prevalence of anti-NA14 were 18/132 (13.6%) in primary SS, 0/50 (0%) secondary SS, 2/100 (2%) SLE, 1/43 (2.3%) scleroderma, 0/54 (0%) rheumatoid arthritis, 1/29 (3.4%) polymyositis/dermatomyositis, and 0/58 (0%) normal healthy controls. The frequencies of anti-NA14 positive sera in primary SS are statistically greater than normal healthy controls (p=0.006), secondary SS (p=0.044), and other rheumatic diseases. Furthermore, among 11 anti-NA14 positive primary SS sera, 4/11 (36.3%) sera were negative for both anti-SS-A/Ro and SS-B/La antibodies. Thus anti-NA14 autoantibodies may be useful for the discrimination of primary versus secondary SS and serve as a diagnostic marker for primary SS especially in seronegative (anti-SS-A/Ro and anti-SS-B/La antibodies negative) patients with SS.

Co-clustering of Golgi complex and other cytoplasmic organelles to crescentic region of half-moon nuclei during apoptosis

Early apoptosis is defined by stereotypic morphological changes, especially evident in the nucleus, where chromatin condenses and compacts, and assumes a globular, half-moon or crescent-shaped morphology. Accumulating evidence suggests that cytoplasmic organelles such as mitochondria and the Golgi complex are major sites of integration of pro-apoptotic signaling. In this study, cytoplasmic organelles including Golgi complex, mitochondria, endosomes, lysosomes, and peroxisomes were shown to condense at the same unique region adjacent to the crescentic nucleus during a relatively early stage of apoptosis induced by staurosporine or other agents. The co-clustering phenomenon may be caused by shrinkage of cytoplasm during apoptosis although cytoskeletal markers actin and tubulin were not condensed and appeared excluded. These data suggest the co-clustering of cytoplasmic organelles plays an interesting role during the progression of the apoptotic process. It is possible that modification of pro-apoptotic proteins may arise as a result of the interplay of these cytoplasmic organelles.

Autoantibodies from mice exposed to Libby amphibole asbestos bind SSA/Ro52-enriched apoptotic blebs of murine macrophages

Asbestos exposure is associated with increased autoimmune responses in humans. For example, in Libby, MT where significant asbestos exposure has occurred due to an asbestos-contaminated vermiculite mine near the community, residents have developed increased autoimmune responses compared to an unexposed population. However, the exact mechanism by which Libby amphibole asbestos generates autoimmune responses is unclear. A murine model of amphibole asbestos-induced autoimmunity was recently established, and one of the targets of the autoantibodies (AAs) was the SSA/Ro52 autoantigen. The purpose of this study was to determine whether the SSA/Ro52 autoantigen is exposed at the surface of cells as a result of asbestos exposure as a possible mechanism leading to antigenicity. Our results indicate that Libby asbestos induces apoptosis in murine macrophages as determined by phosphatidylserine exposure, cleavage of poly(ADP-ribose) polymerase and morphological changes such as nuclear condensation. Moreover, asbestos-induced apoptosis results in the formation of apoptotic cell surface blebs enriched in SSA/Ro52 as determined by confocal microscopy. Most importantly, apoptotic cell surface blebs are recognized by AAs from mice exposed to amphibole asbestos suggesting that these cell surface structures may be antigenic when presented in a pro-inflammatory context. This study supports the hypothesis that the induction of apoptosis plays a key role in environmentally induced autoimmunity through cell surface exposure of a known autoantigen.

Organelle intermixing and membrane scrambling in cell death

In many cell types, intracellular organelles are involved along the progression of cell death. While many studies have focused on individual organelles such as mitochondria, evidence has accumulated that different organelles are simultaneously engaged in dynamic changes induced by death signaling before nuclear alterations are evident. This chapter examines approaches to evaluate dynamic aspects of organelle changes and intermixing during apoptosis. The methods presented here, which have been adapted from approaches used in the field of membrane traffic, enable the evaluation of mitochondrial intermixing with other organelles and the centrifugal movements of internal membranes that are associated, in particular, with death receptor-mediated apoptosis.

Sulfated glycosphingolipid as mediator of phagocytosis: SM4s enhances apoptotic cell clearance and modulates macrophage activity

Sulfoglycolipids are present on the surface of a variety of cells. The sulfatide SM4s is increased in lung, renal, and colon cancer and is associated with an adverse prognosis, possibly due to a low immunoreactivity of the tumor. As macrophages significantly contribute to the inflammatory infiltrate in malignancies, we postulated that SM4s may modulate macrophage function. We have investigated the effect of SM4s on the uptake of apoptotic tumor cells, macrophage cytokine profile, and receptor expression. Using flow cytometry and microscopic analyses, we found that coating apoptotic murine carcinoma cells from the colon and kidney with SM4s promoted their phagocytosis by murine macrophages up to 3-fold ex vivo and in vivo. This increased capacity was specifically inhibited by preincubation of macrophages with oxidized or acetylated low density lipoprotein and maleylated albumin, indicating involvement of scavenger receptors in this interaction. The uptake of SM4s-coated apoptotic cells significantly enhanced macrophage production of TGF-beta1, expression of P-selectin, and secretion of IL-6. These data suggest that SM4s within tumors may promote apoptotic cell removal and alter the phenotype of tumor-associated macrophages.

Identification of a redox-sensitive cysteine in GCP60 that regulates its interaction with golgin-160

Golgin-160 is ubiquitously expressed in vertebrates. It localizes to the cytoplasmic side of the Golgi and has a large C-terminal coiled-coil domain. The noncoiled-coil N-terminal head domain contains Golgi targeting information, a cryptic nuclear localization signal, and three caspase cleavage sites. Caspase cleavage of the golgin-160 head domain generates different fragments that can translocate to the nucleus by exposing the nuclear localization signal. We have previously shown that GCP60, a Golgi resident protein, interacts weakly with the golgin-160 head domain but has a strong interaction with one of the caspase-generated golgin-160 fragments (residues 140-311). This preferential interaction increases the Golgi retention of the golgin-160 fragment in cells overexpressing GCP60. Here we studied the interaction of golgin-160-(140-311) with GCP60 and identified a single cysteine residue in GCP60 (Cys-463) that is critical for the interaction of the two proteins. Mutation of the cysteine blocked the interaction in vitro and disrupted the ability to retain the golgin-160 fragment at the Golgi in cells. We also found that Cys-463 is redox-sensitive; in its reduced form, interaction with golgin-160 was diminished or abolished, whereas oxidation of the Cys-463 by hydrogen peroxide restored the interaction. In addition, incubation with a nitric oxide donor promoted this interaction in vitro. These findings suggest that nuclear translocation of golgin-160-(140-311) is a highly coordinated event regulated not only by cleavage of the golgin-160 head but also by the oxidation state of GCP60.

beta4GalT-II increases cisplatin-induced apoptosis in HeLa cells depending on its Golgi localization

beta1,4-Galactosyltransferase II (beta4GalT-II) is one of the enzymes transferring galactose to the terminal N-acetylglucosamine of complex-type N-glycans and its expression is significantly altered during oncogenesis with unknown functions. Here, we reported for the first time the pro-apoptotic role of beta4GalT-II in tumor cells. The level of beta4GalT-II mRNA expression was obviously decreased during HeLa cell apoptosis induced by cisplatin. Interestingly, the ectopic expression of beta4GalT-II in HeLa cells markedly increased apoptosis and cleavage of PARP induced by cisplatin as well as the expression of pro-apoptotic protein Bax. Furthermore, deletion of Golgi localization domain abolished the apoptotic role of beta4GalT-II in HeLa cells. Collectively, these results suggest that beta4GalT-II increases HeLa cell apoptosis induced by cisplatin depending on its Golgi localization, which indicates that beta4GalT-II might contribute to the therapeutic efficiency of cisplatin for cervix cancer.

New Insights into Membrane Trafficking and Protein Sorting

Protein transport in the secretory and endocytic pathways is a multistep process involving the generation of transport carriers loaded with defined sets of cargo, the shipment of the cargo-loaded transport carriers between compartments, and the specific fusion of these transport carriers with a target membrane. The regulation of these membrane-mediated processes involves a complex array of protein and lipid interactions. As the machinery and regulatory processes of membrane trafficking have been defined, it is increasingly apparent that membrane transport is intimately connected with a number of other cellular processes, such as quality control in the endoplasmic reticulum (ER), cytoskeletal dynamics, receptor signaling, and mitosis. The fidelity of membrane trafficking relies on the correct assembly of components on organelles. Recruitment of peripheral proteins plays a critical role in defining organelle identity and the establishment of membrane subdomains, essential for the regulation of vesicle transport. The molecular mechanisms for the biogenesis of membrane subdomains are also central to understanding how cargo is sorted and segregated and how different populations of transport carriers are generated. In this review we will focus on the emerging themes of organelle identity, membrane subdomains, regulation of Golgi trafficking, and advances in dissecting pathways in physiological systems.

GCP60 preferentially interacts with a caspase-generated golgin-160 fragment

Golgin-160, a ubiquitous protein in vertebrates, localizes to the cytoplasmic face of the Golgi complex. Golgin-160 has a large coiled-coil C-terminal domain and a non-coiled-coil N-terminal ("head") domain. The head domain contains important motifs, including a nuclear localization signal, a Golgi targeting domain, and three aspartates that are recognized by caspases during apoptosis. Some of the caspase cleavage products accumulate in the nucleus when overexpressed. Expression of a non-cleavable form of golgin-160 impairs apoptosis induced by some pro-apoptotic stimuli; thus cleavage of golgin-160 appears to play a role in apoptotic signaling. We used a yeast two-hybrid assay to screen for interactors of the golgin-160 head and identified GCP60 (Golgi complex-associated protein of 60 kDa). Further analysis demonstrated that GCP60 interacts preferentially with one of the golgin-160 caspase cleavage fragments (residues 140-311). This strong interaction prevented the golgin-160 fragment from accumulating in the nucleus when this fragment and GCP60 were overexpressed. In addition, cells overexpressing GCP60 were more sensitive to apoptosis induced by staurosporine, suggesting that nuclear-localized golgin-160-(140-311) might promote cell survival. Our results suggest a potential mechanism for regulating the nuclear translocation and potential functions of golgin-160 fragments.

Identification of kinectin as a novel Behçet's disease autoantigen

There has been some evidence that Behçet's disease (BD) has a significant autoimmune component but the molecular identity of putative autoantigens has not been well characterized. In the initial analysis of the autoantibody profile in 39 Chinese BD patients, autoantibodies to cellular proteins were uncovered in 23% as determined by immunoblotting. We have now identified one of the major autoantibody specificities using expression cloning. Serum from a BD patient was used as a probe to immunoscreen a λZAP expression cDNA library. Candidate autoantigen cDNAs were characterized by direct nucleotide sequencing and their expressed products were examined for reactivity to the entire panel of BD sera using immunoprecipitation. Reactivity was also examined with normal control sera and disease control sera from patients with lupus and Sjögren's syndrome. Six independent candidate clones were isolated from the cDNA library screen and were identified as overlapping partial human kinectin cDNAs. The finding that kinectin was an autoantigen was verified in 9 out of 39 (23%) BD patient sera by immunoprecipitation of the in vitro translation products. Sera from controls showed no reactivity. The significance of kinectin as a participant in autoimmune pathogenesis in BD and the potential use of autoantibody to kinectin in serodiagnostics are discussed.

Golgins and GTPases, giving identity and structure to the Golgi apparatus

In this review we will focus on the recent advances in how coiled-coil proteins of the golgin family give identity and structure to the Golgi apparatus in animal cells. A number of recent studies reveal a common theme for the targeting of golgins containing the ARL-binding GRIP domain, and the related ARF-binding GRAB domain. Similarly, other golgins such as the vesicle tethering factor p115 and Bicaudal-D are targeted by the Rab GTPases, Rab1 and Rab6, respectively. Together golgins and their regulatory GTPases form a complex network, commonly known as the Golgi matrix, which organizes Golgi membranes and regulates membrane trafficking.

Fragmentation of the Golgi apparatus induced by the overexpression of wild-type and mutant human tau forms in neurons

Tau is a microtubule-associated protein enriched in the axonal compartment. In several neurodegenerative diseases including Alzheimer's disease, hyperphosphorylated tau accumulates in the somatodendritic compartment, self-aggregates, and forms neurofibrillary tangles. A fragmentation of the neuronal Golgi apparatus (GA) was also observed in Alzheimer's disease. In the present study, we examined the effect of overexpressing human tau on the organization of the neuronal GA in rat hippocampal cultures and in JNPL3 mice expressing tau mutant P301L. GA fragmentation was noted in a significantly higher percentage of hippocampal neurons overexpressing wild-type human tau than in control neurons over-expressing green fluorescent protein (GFP) alone. Most importantly, in neurons overexpressing mutant forms of human tau (P301L, V337M, or R406W), the percentage of neurons with a fragmented GA was 10% higher than that of neurons overexpressing wild-type human tau. In JNPL3 mice, a significantly higher percentage of motor neurons presented a fragmented GA compared to control mice. Interestingly, fragmentation of the GA was more frequent in neurons containing an accumulation and aggregation of hyperphosphorylated tau in the cell body than in neurons without these features. In both primary hippocampal neurons and JNPL3 mice, the tau-induced GA fragmentation was not caused by apoptosis. The pre-sent results implicate tau in GA fragmentation and show that this event occurs before the formation of neurofibrillary tangles.

Unique and shared features of Golgi complex autoantigens

Here we summarize recent advances in the characterization of autoimmune antigens associated with the Golgi complex. All Golgi autoantigens identified to date are high molecular weight proteins rich in coiled-coil domains and localized to the cytoplasmic face of the Golgi cisternae. The characteristic features of these Golgi autoantigens are interestingly similar to selected human autoantigens reported in other intracellular compartments such as endosome, centrosome, and centromere. The implication of this class of autoantigens in autoimmunity is discussed.

Caspase-resistant Golgin-160 disrupts apoptosis induced by secretory pathway stress and ligation of death receptors

Golgin-160 is a coiled-coil protein on the cytoplasmic face of the Golgi complex that is cleaved by caspases during apoptosis. We assessed the sensitivity of cell lines stably expressing wild-type or caspase-resistant golgin-160 to several proapoptotic stimuli. Cells expressing a caspase-resistant mutant of golgin-160 were strikingly resistant to apoptosis induced by ligation of death receptors and by drugs that induce endoplasmic reticulum (ER) stress, including brefeldin-A, dithiothreitol, and thapsigargin. However, both cell lines responded similarly to other proapoptotic stimuli, including staurosporine, anisomycin, and etoposide. The caspase-resistant golgin-160 dominantly prevented cleavage of endogenous golgin-160 after ligation of death receptors or induction of ER stress, which could be explained by a failure of initiator caspase activation. The block in apoptosis in cells expressing caspase-resistant golgin-160 could not be bypassed by expression of potential caspase cleavage fragments of golgin-160, or by drug-induced disassembly of the Golgi complex. Our results suggest that some apoptotic signals (including those initiated by death receptors and ER stress) are sensed and integrated at Golgi membranes and that golgin-160 plays an important role in transduction of these signals.

Golgi structure in stress sensing and apoptosis

The Golgi complex in mammalian cells is composed of polarized stacks of flattened cisternal membranes. Stacks are connected by tubules forming a reticular network of membranes closely associated with the microtubule-organizing center. While the Golgi structure is important for the efficient processing of secretory cargo, the organization of the mammalian Golgi complex may indicate potential functions in addition to the processing and sorting of cargo. Similar to the endoplasmic reticulum stress response pathway, the Golgi complex may initiate signaling pathways to alleviate stress, and if irreparable, trigger apoptosis. Here, we review recent experimental evidence suggesting that the elaborate structure of the Golgi complex in mammalian cells may have evolved to sense and transduce stress signals.

Golgi fragmentation during Fas-mediated apoptosis is associated with the rapid loss of GM130

During apoptosis, the Golgi complex becomes fragmented and key proteins (e.g., GRASP65 and p115) are targets for caspase cleavage. GM130, an integral membrane protein, contributes to the maintenance of Golgi structure and facilitates membrane fusion with secretory vesicles. We show that GM130 levels decrease during Fas-induced apoptosis but not during staurosporine-induced apoptosis while in both models p115 levels remain unaffected. We conclude that GM130 is rapidly diminished during Fas-mediated apoptosis associated with Golgi fragmentation in contrast to previous studies which have suggested that loss of GM130 during apoptosis is a late event.

Organellar proteomics reveals Golgi arginine dimethylation

The Golgi complex functions to posttranslationally modify newly synthesized proteins and lipids and to sort them to their sites of function. In this study, a stacked Golgi fraction was isolated by classical cell fractionation, and the protein complement (the Golgi proteome) was characterized using multidimensional protein identification technology. Many of the proteins identified are known residents of the Golgi, and 64% of these are predicted transmembrane proteins. Proteins localized to other organelles also were identified, strengthening reports of functional interfacing between the Golgi and the endoplasmic reticulum and cytoskeleton. Importantly, 41 proteins of unknown function were identified. Two were selected for further analysis, and Golgi localization was confirmed. One of these, a putative methyltransferase, was shown to be arginine dimethylated, and upon further proteomic analysis, arginine dimethylation was identified on 18 total proteins in the Golgi proteome. This survey illustrates the utility of proteomics in the discovery of novel organellar functions and resulted in 1) a protein profile of an enriched Golgi fraction; 2) identification of 41 previously uncharacterized proteins, two with confirmed Golgi localization; 3) the identification of arginine dimethylated residues in Golgi proteins; and 4) a confirmation of methyltransferase activity within the Golgi fraction.

Rotenone induces disassembly of the Golgi apparatus in the rat dopaminergic neuroblastoma B65 cell line

It has been reported that the Golgi apparatus (GA) is fragmented in some neurodegenerative diseases. However, the significance of the GA fragmentation or disassembly in neurodegeneration is still obscure. To clarify the involvement of this organelle in apoptosis of neuronal cells, we examined the morphological changes in the GA induced by rotenone, a pesticide that produces selective dopaminergic neurodegeneration. In dopaminergic neuroblastoma B65 cells, a 5-day rotenone treatment (50 nM) promoted cell damage. Rotenone-treated cells showed round nuclei, diffuse signals of the GA and cytosolic redistribution of cytochrome c. Nevertheless, these type of cells without nuclear fragmentation did not show any caspase-3 expression. These results indicate that rotenone induces disassembly of the GA in the early stages of the apoptotic process.

Silica-exposed mice generate autoantibodies to apoptotic cells

Silica exposure has been associated with development of autoantibodies and systemic autoimmune disease, but mechanisms leading to these events are unknown. This study tested the hypothesis that autoantibodies associated with silica exposure may recognize epitopes on apoptotic macrophages. Serum was obtained from New Zealand mixed (NZM) mice, in which instillation of silica significantly increased production of autoantibodies. Sera were selected that were shown, by indirect immunofluorescence (IIF), to be positive or negative for antinuclear antibodies (ANA) following silica or saline exposure, respectively. Apoptosis was induced in MH-S murine macrophages using silica or cycloheximide. The ability of the autoantibodies to preferentially recognize apoptotic cells was tested using IIF and ELISA. Apoptotic cells, but not live cells, were shown to stain with serum from ANA-positive mice, but not from ANA-negative serum. In addition, binding of antibodies from ANA-positive mice was shown to be significantly greater on cellular lysates from apoptotic cells, but not necrotic or live cell lysates using an ELISA based assay. Finally, inhibition of apoptosis with a broad spectrum caspase inhibitor, Boc-D-FMK, blocked the increased binding by the autoantibodies. These results suggest that autoantibodies from mice with silica-exacerbated autoimmune responses recognize specific epitopes on apoptotic macrophages. It is therefore possible that silica-induced apoptosis may exacerbate autoimmune responses by exposing antigenic epitopes to the immune system.

Lymphoid Hyperplasia Resulting in Immune Dysregulation Is Caused by Porcine Reproductive and Respiratory Syndrome Virus Infection in Neonatal Pigs

Amid growing evidence that numerous viral infections can produce immunopathology, including nonspecific polyclonal lymphocyte activation, the need to test the direct impact of an infecting virus on the immune system of the host is crucial. This can best be tested in the isolator piglet model in which maternal and other extrinsic influences can be excluded. Therefore, neonatal isolator piglets were colonized with a benign Escherichia coli, or kept germfree, and then inoculated with wild-type porcine reproductive and respiratory syndrome virus (PRRSV) or sham medium. Two weeks after inoculation, serum IgM, IgG, and IgA levels were 30- to 50-, 20- to 80-, and 10- to 20-fold higher, respectively, in animals receiving virus vs sham controls, although <1% was virus specific. PRRSV-infected piglets also had bronchial tree-associated lymph nodes and submandibular lymph nodes that were 5-10 times larger than colonized, sham-inoculated animals. Size-exclusion fast performance liquid chromatography revealed that PRRSV-infected sera contained high-molecular-mass fractions that contained IgG, suggesting the presence of immune complexes. Lesions, inflammatory cell infiltration, glomerular deposits of IgG, IgM, and IgA, and Abs of all three isotypes to basement membrane and vascular endothelium were observed in the kidneys of PRRSV-infected piglets. Furthermore, autoantibodies specific for Golgi Ags and dsDNA could be detected 3-4 wk after viral inoculation. These data demonstrate that PRRSV induces B cell hyperplasia in isolator piglets that leads to immunologic injury and suggests that the isolator piglet model could serve as a useful model to determine the mechanisms of virus-induced immunopathology in this species.

Sequestration of p53 in the cytoplasm by adenovirus type 12 E1B 55-kilodalton oncoprotein is required for inhibition of p53-mediated apoptosis

The adenovirus E1B 55-kDa protein is a potent inhibitor of p53-mediated transactivation and apoptosis. The proposed mechanisms include tethering the E1B repression domain to p53-responsive promoters via direct E1B-p53 interaction. Cytoplasmic sequestration of p53 by the 55-kDa protein would impose additional inhibition on p53-mediated effects. To investigate further the role of cytoplasmic sequestration of p53 in its inhibition by the E1B 55-kDa protein we systematically examined domains in both the Ad12 55-kDa protein and p53 that underpin their colocalization in the cytoplasmic body and show that the N-terminal transactivation domain (TAD) of p53 is essential for retaining p53 in the cytoplasmic body. Deletion of amino acids 11 to 27 or even point mutation L22Q/W23S abolished the localization of p53 to the cytoplasmic body, whereas other parts of TAD and the C-terminal domain of p53 are dispensable. This cytoplasmic body is distinct from aggresome associated with overexpression of some proteins, since it neither altered vimentin intermediate filaments nor associated with centrosome or ubiquitin. Formation of this structure is sensitive to mutation of the Ad12 55-kDa protein. Strikingly, mutation S476/477A near the C terminus of the Ad12 55-kDa protein eliminated the formation of the cytoplasmic body. The equivalent residues in the Ad5 55-kDa protein were shown to be critical for its ability to inhibit p53. Indeed, Ad12 55-kDa mutants that cannot form a cytoplasmic body can no longer inhibit p53-mediated effects. Conversely, the Ad12 55-kDa protein does not suppress p53 mutant L22Q/W23S-mediated apoptosis. Finally, we show that E1B can still sequester p53 that contains the mitochondrial import sequence, thereby potentially preventing the localization of p53 to mitochondria. Thus, cytoplasmic sequestration of p53 by the E1B 55-kDa protein plays an important role in restricting p53 activities.

Giantin is the major Golgi autoantigen in human anti-Golgi complex sera

Anti-Golgi complex antibodies (AGAs) are primarily associated with systemic lupus erythematosus and Sjögren's syndrome. Here we report on the immunoreactivity of AGAs against five Golgi autoantigens (giantin, golgin-245, golgin-160, golgin-95/GM130, and golgin-97) and provide data from epitope mapping on the most common Golgi autoantigen, namely giantin. A total of 80 human sera containing AGAs, as defined by indirect immunofluorescence on HEp-2 cells, were analyzed by ELISA using recombinant autoantigens and immunoprecipitation. The proportion of AGA sera that reacted with the five Golgi autoantigens was correlated with the molecular mass of the Golgi antigens. Autoantibodies to giantin, the largest Golgi autoantigen, were the predominant AGAs, being found in 50% of the AGA sera. Epitope mapping of giantin was performed using six recombinant fragments spanning the entire protein. Antigiantin-positive sera with low titer autoantibodies recognized epitopes in the carboxyl-terminal fragments that are proximal to the Golgi membrane, whereas higher titer sera exhibited strong reactivity to amino-terminal and central domains that are likely to extend from the Golgi membrane into the cytoplasm. Our working hypothesis is that aberrantly expressed Golgi complex autoantigens may be released into the immune system when cells undergo lysis. By virtue of a carboxyl-terminal transmembrane domain, giantin is likely to be more stably associated with the cytoplasmic face of the Golgi complex than are other golgins, which are peripheral proteins. The stable association of giantin with the putative released Golgi complex may contribute to its preferential autoantigenicity.