Unique and shared features of Golgi complex autoantigens

Loss of GM130 does not impair oocyte meiosis and embryo development in mice

Golgi matrix protein 130 (GM130), encoded by GOLGA2, is the classical marker of the Golgi apparatus. It plays important roles in various mitotic events, such as interacting with importin-alpha and liberating spindle assembly factor TPX2 to regulate mitotic spindle formation. A previous study showed that in vitro knockdown of GM130 could regulate the meiotic spindle pole assembly. In the current study, we found that knockout (KO) mice progressively died, had a small body size and were completely infertile. Furthermore, we constructed an oocyte-specific GM130 knockout mouse model (GM130-ooKO) driven by Gdf9-Cre. Through breeding assays, we found that the GM130-ooKO mice showed similar fecundity as control mice. During superovulation assays, the KO and GM130-ooKO mice had comparable numbers of ovulated eggs, oocyte maturation rates and normal polar bodies, similar to the control groups. Thus, this study indicated that deletion of GM130 might have a limited impact on the maturation and morphology of oocytes. This might due to more than one golgin sharing the same function, with others compensating for the loss of GM130.

A Monoclonal Antibody to M-Phase Phosphoprotein 1/Kinesin-Like Protein KIF20B

Kinesin-like protein KIF20B, originally named M-phase phosphoprotein 1 (MPP1), is a plus-end-directed kinesin-related protein that exhibits in vitro microtubule-binding and -bundling properties as well as microtubule-stimulated ATPase activity. It has been characterized as a slow molecular motor that moves toward the plus-end of microtubules. Human autoantibodies directed against KIF20B have been described in up to 25% of patients with idiopathic ataxia and less commonly in other neuropathies and autoinflammatory conditions. One of the limitations of research into the structure and function of KIF20B has been a reliable monoclonal antibody that can be used in a variety of applications. To establish a reference standard for anti-KIF20B immunoassays and facilitate studies on the role of KIF20B in developmental cell biology, we developed an IgG1 monoclonal antibody, 10C7, which reacts with the cognate KIF20B protein in Western immunoblots and in addressable laser bead immunoassays. In HEp2 cells, leptomeningeal pericytes, and transfected HEK293T cells, indirect immunofluorescence studies showed that reactivity was mainly localized to a proportion of interphase nuclei, but during metaphase, it was redistributed throughout the cytoplasm and perichromatin mass. Later in telophase/anaphase, KIF20B was localized to the stem body and midzone of the midbody. 10C7 also showed remarkable staining of a subset of cells in the cerebellum, ovary, and testis tissues. KIF20B was shown to have extensive coiled-coil domains. The monoclonal antibody, 10C7, will be of value to diagnostic laboratory scientists interested in having a reliable reference standard for anti-KIF20B immunoassays as well as cell, molecular, and developmental biology researchers.

Transport carrier tethering - how vesicles are captured by organelles

All cells contain numerous membrane-bound organelles that carry out specific functions. These compartments do not, however, act in isolation. Some are in direct contact via membrane contact sites, while others exchange material via specific vesicles or tubular carriers laden with cargo. The term tethering in the context of this review is used to describe the primary recognition and docking of transport carriers with acceptor organelles that occurs before SNARE engagement and membrane fusion. However, it is important to note that other tethering events occur, for example, between organelles in direct contact, which do not lead to fusion.

Golga5 is dispensable for mouse embryonic development and postnatal survival

Golgins are a family of coiled-coil proteins located at the cytoplasmic surface of the Golgi apparatus and have been implicated in maintaining Golgi structural integrity through acting as tethering factors for retrograde vesicle transport. Whereas knockdown of several individual golgins in cultured cells caused Golgi fragmentation and disruption of vesicle trafficking, analysis of mutant mouse models lacking individual golgins have discovered tissue-specific developmental functions. Recently, homozygous loss of function of GOLGA2, of which previous in vitro studies suggested an essential role in maintenance of Golgi structure and in mitosis, has been associated with a neuromuscular disorder in human patients, which highlights the need for understanding the developmental roles of the golgins in vivo. We report here generation of Golga5-deficient mice using CRISPR/Cas9-mediated genome editing. Although knockdown studies in cultured cells have implicated Golga5 in maintenance of Golgi organization, we show that Golga5 is not required for mouse embryonic development, postnatal survival, or fertility. Moreover, whereas Golga5 is structurally closely related to Golgb1, we show that inactivation of Golga5 does not enhance the severity of developmental defects in Golgb1-deficient mice. The Golga5-deficient mice enable further investigation of the roles and functional specificity of golgins in development and diseases.

A re-evaluation of anti-NA-14 antibodies in patients with primary Sjögren's syndrome: Significant role of interferon-γ in the production of autoantibodies against NA-14

Novel autoantibodies against nuclear antigen of 14 kDa (NA-14)/Sjögren's syndrome nuclear antigen-1 (SSNA-1) are predominantly recognized in sera of patients with primary Sjögren's syndrome (pSS). However, the detailed characteristics of the anti-NA-14 antibody remain unknown. Here, we sought to clarify the characteristics of anti-SSNA-1/NA-14 antibodies and the mechanisms of autoantibody production using sera from patients with connective tissue diseases (including pSS), autoimmune sera reacting with standard autoantigens (SS-A/Ro and/or SS-B/La, ds DNA, Scl-70 and Jo-1), and normal healthy controls (NHCs). Anti-NA-14 antibodies were predominantly recognized in sera from patients with pSS and in autoimmune sera reacting with thSS-A/Ro and/or -SS-B/Lo. Indirect immunofluorescence analysis showed that NA-14 was strongly expressed in mitotic-phase cells. Patients with pSS having anti-NA-14 antibodies exhibited significant elevation of serum IP-10 and BAFF compared to that in patients with pSS without anti-NA-14 antibodies and NHCs. Thus, our data demonstrated that anti-NA-14 antibodies could be classified as novel autoantibodies reacting with mitosis-related autoantigens predominantly recognized in pSS. Moreover, interferon-γ played an important role in the production of anti-NA-14 autoantibodies as patients with pSS having anti-NA-14 antibodies exhibited increased serum levels of IP-10 and BAFF.

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.

Finding the Golgi: Golgin Coiled-Coil Proteins Show the Way

The Golgi apparatus lies at the centre of the secretory pathway. It consists of a series of flattened compartments typically organised into a stack that, in mammals, is connected to additional stacks to form a Golgi ribbon. The Golgi is responsible for the maturation and modification of proteins and lipids, and receives and exports vesicles to and from multiple destinations within the cell. This complex trafficking network requires that only the correct vesicles fuse with the correct destination membrane. Recently, a group of coiled-coil proteins called golgins were shown to not only capture incoming vesicles but to also provide specificity to the tethering step. This raises many interesting questions about how they interact with other components of membrane traffic, some of which may also contribute to specificity.

Coexistence of Autoantibodies against the Golgi Complex and Ro52 Antigen in a Patient with Nonspecific Interstitial Pneumonia

Nonspecific interstitial pneumonia (NSIP) is often associated with connective tissue diseases (CTD). The diagnosis of NSIP was confirmed in a 63-year-old man by high-resolution computed tomography and an open lung biopsy. Anti-Golgi complex autoantibodies (AGA) and anti-Ro52 antibodies were simultaneously detected at high concentrations. Autoantibodies to aminoacyl-tRNA synthetases (ARS) were negative. The patient was treated with corticosteroids for six months. During the seven-year follow-up, NSIP had a slow progression and patient had not developed the clinical features of CTD. The present study potentially demonstrates that the autoimmune process elicited by AGA and/or Ro/SSA may play a role in promoting idiopathic NSIP independently of the typical ARS routes, which has not been reported thus far.

Report of the First International Consensus on Standardized Nomenclature of Antinuclear Antibody HEp-2 Cell Patterns 2014-2015

During the 12th International Workshop on Autoantibodies and Autoimmunity held in Sao Paulo, Brazil, on August 28, 2014, a full day session was devoted to establishing a consensus on the nomenclature of staining patterns observed in the antinuclear antibody (ANA) indirect immunofluorescence test on HEp-2 cells. The current report summarizes the collective agreements with input from the host Brazilian and international communities that represented research, clinical, and diagnostic service laboratories. Patterns are categorized in three major groups (nuclear, cytoplasmic, and mitotic patterns) and each pattern has been defined and described in detail. The consensus nomenclature and representative patterns are made available online at the international consensus on antinuclear antibody pattern (ICAP) website (www.ANApatterns.org). To facilitate continuous improvement and input, specific comments on ICAP are encouraged and these will be discussed in subsequent ICAP meetings. The ultimate goal with the establishment of the ICAP is to promote harmonization and understanding of autoantibody test nomenclature, as well as interpretation guidelines for ANA testing, thereby optimizing usage in patient care.

Report of the First International Consensus on Standardized Nomenclature of Antinuclear Antibody HEp-2 Cell Patterns 2014-2015

During the 12th International Workshop on Autoantibodies and Autoimmunity held in Sao Paulo, Brazil, on August 28, 2014, a full day session was devoted to establishing a consensus on the nomenclature of staining patterns observed in the antinuclear antibody (ANA) indirect immunofluorescence test on HEp-2 cells. The current report summarizes the collective agreements with input from the host Brazilian and international communities that represented research, clinical, and diagnostic service laboratories. Patterns are categorized in three major groups (nuclear, cytoplasmic, and mitotic patterns) and each pattern has been defined and described in detail. The consensus nomenclature and representative patterns are made available online at the international consensus on antinuclear antibody pattern (ICAP) website (www.ANApatterns.org). To facilitate continuous improvement and input, specific comments on ICAP are encouraged and these will be discussed in subsequent ICAP meetings. The ultimate goal with the establishment of the ICAP is to promote harmonization and understanding of autoantibody test nomenclature, as well as interpretation guidelines for ANA testing, thereby optimizing usage in patient care.

High-Throughput Analysis of Plasma Hybrid Markers for Early Detection of Cancers

Biomarkers for the early detection of cancer in the general population have to perform with high sensitivity and specificity in order to prevent the costs associated with over-diagnosis. There are only a few current tissue or blood markers that are recommended for generalized cancer screening. Despite the recognition that combinations of multiple biomarkers will likely improve their utility, biomarker panels are usually limited to a single class of molecules. Tissues and body fluids including plasma and serum contain not only proteins, DNA and microRNAs that are differentially expressed in cancers but further cancer specific information might be gleaned by comparing different classes of biomolecules. For example, the level of a certain microRNA might be related to the level of a particular protein in a cancer specific manner. Proteins might have cancer-specific post-translational modifications (e.g., phosphorylation or glycosylation) or lead to the generation of autoantibodies. Most currently approved biomarkers are glycoproteins. Autoantibodies can be produced as a host's early surveillance response to cancer-specific proteins in pre-symptomatic and pre-diagnostic stages of cancer. Thus, measurement of the level of a protein, the level of its glycosylation or phosphorylation and whether autoantibodies are produced to it can yield multi-dimensional information on each protein. We consider specific proteins that show consistent cancer-specific changes in two or three of these measurements to be "hybrid markers". We hypothesize these markers will suffer less variation between different individuals since one component can act to "standardize" the other measurement. As a proof of principle, a 180 plasma sample set consisting of 120 cases (60 colon cancers and 60 adenomas) and 60 controls were analyzed using our high-density antibody array for changes in their protein, IgG-complex and sialyl-Lewis A (SLeA) modified proteins. At p < 0.05, expression changes in 1,070 proteins, 49 IgG-complexes (11 present in the protein list) and 488 Lewis X-modified proteins (57 on the protein list) were observed. The biomarkers significant on both lists are potential hybrid markers. Thus, plasma hybrid markers have the potential to create a new class of early detection markers of cancers.

Predictive value of antinuclear antibodies in autoimmune diseases classified by clinical criteria: Analytical study in a specialized health institute, one year follow-up

Introduction: Determination of antinuclear antibodies (ANA) by indirect immunofluorescence (IIF) is usually the initial test for the diagnosis of systemic rheumatic diseases (SRD). Assigning predictive values to positive and negative results of the test is vital because lack of knowledge about ANAs and their usefulness in classification criteria of SRD leads to inappropriate use. Methods: Retrospective study, ANA tests requested by different specialties, correlation to patients' final diagnosis. Results: The prevalence of autoimmune disease was relatively low in our population yielding a low PPV and a high NPV for the ANA test. 40% of the patients had no clinical criteria applied prior to test. Coexistence of two or more autoimmune disorders affects prevalence and predictive values. Conclusion: Application of the test after careful evaluation for clinical criteria remarkably improves the positive likelihood ratio for the diagnosis.

Prevalence and clinical significance of rare antinuclear antibody patterns

While some of the more frequent antinuclear (auto)antibodies (ANA) patterns such as homogenous nuclear staining have been extensively studied, the prevalence and clinical significance of rare antinuclear antibody patterns are not well understood. For the purpose of this review, we defined rare patterns as patterns occurring in less than 1% of patients that test positive on indirect immunofluorescence. The prevalence of different ANA patterns was determined in 68,128 consecutive patients who attended the outpatient clinic or were hospitalized at the University Hospitals Leuven over a 14-year period (1998-2011). To avoid bias, we only included the first sample for each patient and patients who tested positive in the period 1980-1997 were excluded. There were 9268 patients who tested positive for ANA. With the exception of the clinical association of anti-multiple nuclear dots (at higher titers) and anti-nuclear envelope autoantibodies with autoimmune liver disease, there was no good clinical association of rare ANA patterns with the diagnosis of auto-immune disorders. The most important non-autoimmune cause of rare ANA patterns was carcinoma, particularly in patients with rare cell-cycle related ANAs.

Low prevalence of autoantibodies to CENP-H, -I, -K, -L, -M, -N, -T and -U in a Japanese cohort of anti-centromere positive samples

OBJECTIVE

The constituents of the centromere region, centromere protein (CENP)-A, -B, and -C, are mainly targeted by anticentromere antibodies (ACA). Many other proteins also assemble around CENP-A nucleosomes in interphase nuclei to form the interphase centromere complex (ICEN). CENP-H, -I, -K, -L, -M, -N, -T, and -U have been reported as the constitutive components of ICEN. In this study, we examined the reactivities of ACA to the 8 CENPs for the purpose of investigating their autoantigenicity.

METHODS

Sera from 95 patients with ACA were tested by western blotting (WB) and enzyme-linked immunosorbent assay (ELISA) with the recombinant C-terminal of CENP-B (Ct-CENP-B). Next, the sera were examined for autoantibodies against the 8 CENPs by WB with each recombinant protein. Furthermore, the coiled-coil motifs and granzyme B (GB) cleavage for various CENPs were analyzed with computer tools.

RESULTS

Out of 95 ACA-positive sera, 85 and 93 sera were positive for anti-Ct-CENP-B antibodies in WB and in ELISA, respectively. In WB using the 8 CENPs, no sera reacted to any other 7 CENPs, except 1 serum, which reacted weakly to CENP-T. We were unable to find any obvious relationships between the autoantigenicity of CENPs and coiled-coil-forming probabilities or potential substrates for GB.

CONCLUSION

This study demonstrates that ACA rarely target the 8 CENPs, in contrast to CENP-B. Protein structures might not contribute in a major way to the autoantigenicity of CENPs.

Characterization for anti-cytoplasmic antibodies specificity by morphological and molecular techniques

PURPOSE

The aim of our study was the characterization of anti-cytoplasmic antibodies by home-made morphological and biochemical techniques. Indeed, indirect immunofluorescence (IIF) on HEp-2 cell line is not always exhaustive in relation to the complexity of the antigens involved.

METHODS

Nine serum samples with anti-cytoplasmic antibodies (2 anti-Golgi apparatus, 3 with diffuse pattern and 4 with lysosome/endosome-like pattern) were tested with fluorescent confocal microscopy, Western blot analysis and, when necessary, with electron microscopy technique.

RESULTS

Confirmation of the IIF staining pattern was performed in confocal microscopy by comparison with the respective antibody marker. The anti-endoplasmatic reticulum positivity was also confirmed by electron microscopy evaluation. Both anti-lysosome/endosome and anti-endoplasmatic reticulum positivity have been definitely identified by Western blot through clear reactivity with calreticulin and LC3B, respectively.

CONCLUSIONS

These results do not aim at representing a standard routine laboratory procedure. Electron microscopy evaluation cannot be proposed as a routine approach, but confocal microscopy technique may be offered in centralized reference laboratories. Newer technologies, especially multiplex immunoassay, can also lead to an easier identification of these autoantibodies, without recurring to a home-made immunoblotting. Only with a complete characterization we will be able to define the clinical relevance of anti-cytoplasmic antibodies, which are still considered as "esoteric" and not as "diagnostic" antibodies.

Tales of tethers and tentacles: golgins in plants

As plant Golgi bodies move through the cell along the actin cytoskeleton, they face the need to maintain their polarized stack structure whilst receiving, processing and distributing protein cargo destined for secretion. Structural proteins, or Golgi matrix proteins, help to hold cisternae together and tethering factors direct cargo carriers to the correct target membranes. This review focuses on golgins, a protein family containing long coiled-coil regions, summarizes their known functions in animal cells and highlights recent findings about plant golgins and their putative roles in the plant secretory pathway.

Human proteins with affinity for dermatan sulfate have the propensity to become autoantigens

The mystery of why and how a small, seemingly disparate subset of all self molecules become functional autoantigens holds a key to understanding autoimmune diseases. Here and in a companion article in this issue, we show that affinity of self molecules to the glycosaminoglycan dermatan sulfate (DS) is a common property of autoantigens and leads to a specific autoreactive B-1a cell response. Autoimmune ANA/ENA reference sera react preferentially with DS affinity-fractionated cellular proteins. Studying patients with autoimmune diseases, we discovered patient-specific complex autoantigen patterns that are far richer and more diverse than previously thought, indicating significant pathological heterogeneity even within traditionally defined clinical entities, such as systemic lupus erythematosus. By shotgun sequencing of DS affinity-enriched proteomes extracted from cell lines, we identified approximately 200 autoantigens, both novel and previously linked to autoimmunity, including several well-known families of autoantigens related to the nucleosome, ribonucleoproteins, the cytoskeleton, and heat shock proteins. Using electron microscopy, we recognized direct interaction with dead cells as an origin of autoantigenic association of DS with self molecules. DS affinity may be a unifying property of the human autoantigen-ome (ie, totality of self molecules that can serve as functional autoantingens) and thus provides a promising tool for discovery of autoantigens, molecular diagnosis of autoimmune diseases, and development of cause-specific therapies.

Redefining the Scl-70 indirect immunofluorescence pattern: autoantibodies to DNA topoisomerase I yield a specific compound immunofluorescence pattern

Objectives. To report on a novel IIF pattern specifically associated with antibodies to DNA topo I.

Methods. A novel compound IF pattern, designated Scl-70 pattern, was characterized in routine ANA-HEp-2 IIF screening. Within the last 3 years, all serum samples presenting the Scl-70 pattern at the ANA-HEp2 IIF screening were tested for anti-topo I reactivity. Conversely, 16 serum samples with known anti-topo I reactivity and affinity-purified anti-topo I antibody preparations were tested for the Scl-70 pattern.

Results. The Scl-70 pattern comprised the staining of five cellular regions: nucleus, nucleolus and cytoplasm in interphase cells; nucleolar organizing region (NOR) and chromosomes in mitotic cells. All 81 serum samples selected as Scl-70 pattern reacted with topo I. All 16 anti-topo I samples and antibody preparations reproduced the Scl-70 pattern. This compound IF pattern was consistently observed in different commercial HEp-2 cell slides and in home-made slides with HEp-2 cells and human fibroblasts fixed with alternative protocols. Double IIF experiments demonstrated the co-localization of topo I and human upstream binding factor at the NOR.

Conclusions. The Scl-70 pattern belongs to the group of compound IF patterns that hold strong association with the respective autoantibody specificities, such as that observed with centromere protein F (CENP-F) and nuclear mitotic apparatus-1 (NuMA-1) protein. The identification of the Scl-70 pattern at routine ANA-HEp-2 IIF screening may lead to implementation of specific tests for the identification of anti-topo I antibodies. In addition, the Scl-70 pattern outlines cellular domains other than those previously reported for topo I, which is of interest for further understanding the roles of this enzyme in cell biology.

Clinical interpretation of antinuclear antibody tests in systemic rheumatic diseases

Autoantibody tests have been used extensively in diagnosis and follow-up of patients in rheumatology clinics. Immunofluorescent antinuclear antibody test using HEp-2 cells is still considered the gold standard for screening of autoantibodies, and most of specific autoantibodies are currently tested by ELISA as a next step. Among the many autoantibody specificities described, some have been established as clinically useful diagnostic markers and are included in the classification criteria of diseases. Despite a long history of routine tests and attempts to standardize such assays, there are still limitations and problems that clinicians need to be aware of. Clinicians should be able to use autoantibody tests more efficiently and effectively with a basic knowledge on the significance of and potential problems in autoantibody tests.

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.

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.

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.

Global approaches to study Golgi function

Enormous insights into Golgi function have been provided by yeast genetics, biochemical assays and immuno-labeling methods and the emerging picture is of a very complex organelle with multiple levels of regulation. Despite many elegant experimental approaches, it remains unclear what mechanisms transport secretory proteins and lipids through the Golgi, and even the basic structure of the organelle is debated. Recently, new, global approaches such as proteomics and functional genomics have been applied to study the Golgi and its matrix. The data produced reveals great complexity and has potential to help address major unresolved questions concerning Golgi function.

Cis-Golgi matrix proteins move directly to endoplasmic reticulum exit sites by association with tubules

The role of cis-medial Golgi matrix proteins in retrograde traffic is poorly understood. We have used imaging techniques to understand the relationship between the cis-medial Golgi matrix and transmembrane proteins during retrograde traffic in control and brefeldin A (BFA)-treated cells. All five of the cis-medial matrix proteins tested were associated with retrograde tubules within 2-3 min of initiation of tubule formation. Then, at later time points (3-10 min), transmembrane proteins are apparent in the same tubules. Strikingly, both the matrix proteins and the transmembrane proteins moved directly to endoplasmic reticulum (ER) exit sites labeled with p58 and Sec13, and there seemed to be a specific interaction between the ER exit sites and the tips or branch points of the tubules enriched for the matrix proteins. After the initial interaction, Golgi matrix proteins accumulated rapidly (5-10 min) at ER exit sites, and Golgi transmembrane proteins accumulated at the same sites approximately 2 h later. Our data suggest that Golgi cis-medial matrix proteins participate in Golgi-to-ER traffic and play a novel role in tubule formation and targeting.

GMx33 associates with the trans-Golgi matrix in a dynamic manner and sorts within tubules exiting the Golgi

The trans-Golgi matrix consists of a group of proteins dynamically associated with the trans-Golgi and thought to be involved in anterograde and retrograde Golgi traffic, as well as interactions with the cytoskeleton and maintenance of the Golgi structure. GMx33 is localized to the cytoplasmic face of the trans-Golgi and is also present in a large cytoplasmic pool. Here we demonstrate that GMx33 is dynamically associated with the trans-Golgi matrix, associating and dissociating with the Golgi in seconds. GMx33 can be locked onto the trans-Golgi matrix by GTPgammaS, indicating that its association is regulated in a GTP-dependent manner like several other Golgi matrix proteins. Using live-cell imaging we show that GMx33 exits the Golgi associated with tubules and within these tubules GMx33 segregates from transmembrane proteins followed by fragmentation of the tubules into smaller tubules and vesicles. Within vesicles produced by an in vitro budding reaction, GMx33 remains segregated in a matrixlike tail region that sometimes contains Golgin-245. This trans-matrix often links a few vesicles together. Together these data suggest that GMx33 is a member of the trans-Golgi matrix and offer clues regarding the role of the trans-Golgi matrix in sorting and exit from the Golgi.

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.