CMTM4 is a subunit of the IL-17 receptor and mediates autoimmune pathology

Interleukin-17A (IL-17A) is a key mediator of protective immunity to yeast and bacterial infections but also drives the pathogenesis of several autoimmune diseases, such as psoriasis or psoriatic arthritis. Here we show that the tetra-transmembrane protein CMTM4 is a subunit of the IL-17 receptor (IL-17R). CMTM4 constitutively associated with IL-17R subunit C to mediate its stability, glycosylation and plasma membrane localization. Both mouse and human cell lines deficient in CMTM4 were largely unresponsive to IL-17A, due to their inability to assemble the IL-17R signaling complex. Accordingly, CMTM4-deficient mice had a severe defect in the recruitment of immune cells following IL-17A administration and were largely resistant to experimental psoriasis, but not to experimental autoimmune encephalomyelitis. Collectively, our data identified CMTM4 as an essential component of IL-17R and a potential therapeutic target for treating IL-17-mediated autoimmune diseases.

The BBSome assembly is spatially controlled by BBS1 and BBS4 in human cells

Bardet-Biedl syndrome (BBS) is a pleiotropic ciliopathy caused by dysfunction of primary cilia. More than half of BBS patients carry mutations in one of eight genes encoding for subunits of a protein complex, the BBSome, which mediates trafficking of ciliary cargoes. In this study, we elucidated the mechanisms of the BBSome assembly in living cells and how this process is spatially regulated. We generated a large library of human cell lines deficient in a particular BBSome subunit and expressing another subunit tagged with a fluorescent protein. We analyzed these cell lines utilizing biochemical assays, conventional and expansion microscopy, and quantitative fluorescence microscopy techniques: fluorescence recovery after photobleaching and fluorescence correlation spectroscopy. Our data revealed that the BBSome formation is a sequential process. We show that the pre-BBSome is nucleated by BBS4 and assembled at pericentriolar satellites, followed by the translocation of the BBSome into the ciliary base mediated by BBS1. Our results provide a framework for elucidating how BBS-causative mutations interfere with the biogenesis of the BBSome.

Systematic analysis of the IL-17 receptor signalosome reveals a robust regulatory feedback loop

IL‐17 mediates immune protection from fungi and bacteria, as well as it promotes autoimmune pathologies. However, the regulation of the signal transduction from the IL‐17 receptor (IL‐17R) remained elusive. We developed a novel mass spectrometry‐based approach to identify components of the IL‐17R complex followed by analysis of their roles using reverse genetics. Besides the identification of linear ubiquitin chain assembly complex (LUBAC) as an important signal transducing component of IL‐17R, we established that IL‐17 signaling is regulated by a robust negative feedback loop mediated by TBK1 and IKKε. These kinases terminate IL‐17 signaling by phosphorylating the adaptor ACT1 leading to the release of the essential ubiquitin ligase TRAF6 from the complex. NEMO recruits both kinases to the IL‐17R complex, documenting that NEMO has an unprecedented negative function in IL‐17 signaling, distinct from its role in NF‐κB activation. Our study provides a comprehensive view of the molecular events of the IL‐17 signal transduction and its regulation.

TBK1 and IKKε prevent TNF-induced cell death by RIPK1 phosphorylation

The linear-ubiquitin chain assembly complex (LUBAC) modulates signalling via various immune receptors. In tumour necrosis factor (TNF) signalling, linear (also known as M1) ubiquitin enables full gene activation and prevents cell death. However, the mechanisms underlying cell death prevention remain ill-defined. Here, we show that LUBAC activity enables TBK1 and IKKε recruitment to and activation at the TNF receptor 1 signalling complex (TNFR1-SC). While exerting only limited effects on TNF-induced gene activation, TBK1 and IKKε are essential to prevent TNF-induced cell death. Mechanistically, TBK1 and IKKε phosphorylate the kinase RIPK1 in the TNFR1-SC, thereby preventing RIPK1-dependent cell death. This activity is essential in vivo, as it prevents TNF-induced lethal shock. Strikingly, NEMO (also known as IKKγ), which mostly, but not exclusively, binds the TNFR1-SC via M1 ubiquitin, mediates the recruitment of the adaptors TANK and NAP1 (also known as AZI2). TANK is constitutively associated with both TBK1 and IKKε, while NAP1 is associated with TBK1. We discovered a previously unrecognized cell death checkpoint that is mediated by TBK1 and IKKε, and uncovered an essential survival function for NEMO, whereby it enables the recruitment and activation of these non-canonical IKKs to prevent TNF-induced cell death.

Strong homeostatic TCR signals induce formation of self-tolerant virtual memory CD8 T cells

Virtual memory T cells are foreign antigen‐inexperienced T cells that have acquired memory‐like phenotype and constitute 10–20% of all peripheral CD8⁺ T cells in mice. Their origin, biological roles, and relationship to naïve and foreign antigen‐experienced memory T cells are incompletely understood. By analyzing T‐cell receptor repertoires and using retrogenic monoclonal T‐cell populations, we demonstrate that the virtual memory T‐cell formation is a so far unappreciated cell fate decision checkpoint. We describe two molecular mechanisms driving the formation of virtual memory T cells. First, virtual memory T cells originate exclusively from strongly self‐reactive T cells. Second, the stoichiometry of the CD8 interaction with Lck regulates the size of the virtual memory T‐cell compartment via modulating the self‐reactivity of individual T cells. Although virtual memory T cells descend from the highly self‐reactive clones and acquire a partial memory program, they are not more potent in inducing experimental autoimmune diabetes than naïve T cells. These data underline the importance of the variable level of self‐reactivity in polyclonal T cells for the generation of functional T‐cell diversity.

LUBAC is essential for embryogenesis by preventing cell death and enabling haematopoiesis

The Linear Ubiquitin chain Assembly Complex (LUBAC) is required for optimal gene activation and prevention of cell death upon activation of immune receptors, including TNFR11. Deficiency in the LUBAC components SHARPIN or HOIP in mice results in severe inflammation in adulthood or embryonic lethality, respectively, due to deregulation of TNFR1-mediated cell death2–8. In humans, deficiency in the third LUBAC component, HOIL-1, causes autoimmunity and inflammatory disease, similar to HOIP deficiency, whereas HOIL-1 deficiency in mice was reported to cause no overt phenotype9–11. By creating HOIL-1-deficient mice, we here show that HOIL-1 is, however, as essential for LUBAC function as HOIP, albeit for different reasons: whereas HOIP is LUBAC’s catalytically active component, HOIL-1 is required for LUBAC assembly, stability and optimal retention in the TNFR1-signalling complex (TNFR1-SC), thereby preventing aberrant cell death. Both, HOIL-1 and HOIP prevent embryonic lethality at mid-gestation by interfering with aberrant TNFR1-mediated endothelial cell death, which only partially depends on RIPK1 kinase activity. Co-deletion of Caspase-8 with RIPK3 or MLKL prevents cell death in Hoil-1^-/- embryos, yet only combined loss of Caspase-8 with MLKL results in viable HOIL-1-deficient mice. Interestingly, Ripk3^-/-Caspase-8^-/-Hoil-1^-/- embryos die at late-gestation due to haematopoietic defects that are rescued by co-deletion of RIPK1 but not MLKL. Collectively, these results demonstrate that both, HOIP and HOIL-1 are essential LUBAC components and are required for embryogenesis by preventing aberrant cell death. Furthermore, they unveil that, when LUBAC and Caspase-8 are absent, RIPK3 prevents RIPK1 from inducing embryonic lethality by causing defects in foetal haematopoiesis.

The linear ubiquitin chain assembly complex regulates TRAIL-induced gene activation and cell death

The linear ubiquitin chain assembly complex (LUBAC) is the only known E3 ubiquitin ligase which catalyses the generation of linear ubiquitin linkages de novo LUBAC is a crucial component of various immune receptor signalling pathways. Here, we show that LUBAC forms part of the TRAIL-R-associated complex I as well as of the cytoplasmic TRAIL-induced complex II In both of these complexes, HOIP limits caspase-8 activity and, consequently, apoptosis whilst being itself cleaved in a caspase-8-dependent manner. Yet, by limiting the formation of a RIPK1/RIPK3/MLKL-containing complex, LUBAC also restricts TRAIL-induced necroptosis. We identify RIPK1 and caspase-8 as linearly ubiquitinated targets of LUBAC following TRAIL stimulation. Contrary to its role in preventing TRAIL-induced RIPK1-independent apoptosis, HOIP presence, but not its activity, is required for preventing necroptosis. By promoting recruitment of the IKK complex to complex I, LUBAC also promotes TRAIL-induced activation of NF-κB and, consequently, the production of cytokines, downstream of FADD, caspase-8 and cIAP1/2. Hence, LUBAC controls the TRAIL signalling outcome from complex I and II, two platforms which both trigger cell death and gene activation.

The TRAIL-Induced Cancer Secretome Promotes a Tumor-Supportive Immune Microenvironment via CCR2

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is known for specifically killing cancer cells, whereas in resistant cancers, TRAIL/TRAIL-R can promote metastasis via Rac1 and PI3K. It remains unknown, however, whether and to what extent TRAIL/TRAIL-R signaling in cancer cells can affect the immune microenvironment. Here we show that TRAIL-triggered cytokine secretion from TRAIL-resistant cancer cells is FADD dependent and identify the TRAIL-induced secretome to drive monocyte polarization to myeloid-derived suppressor cells (MDSCs) and M2-like macrophages. TRAIL-R suppression in tumor cells impaired CCL2 production and diminished both lung MDSC presence and tumor growth. In accordance, the receptor of CCL2, CCR2, is required to facilitate increased MDSC presence and tumor growth. Finally, TRAIL and CCL2 are co-regulated with MDSC/M2 markers in lung adenocarcinoma patients. Collectively, endogenous TRAIL/TRAIL-R-mediated CCL2 secretion promotes accumulation of tumor-supportive immune cells in the cancer microenvironment, thereby revealing a tumor-supportive immune-modulatory role of the TRAIL/TRAIL-R system in cancer biology.

--LUBAC deficiency perturbs TLR3 signaling to cause immunodeficiency and autoinflammation

LUBAC components interact with the TLR3 signaling cascade at different levels, thereby tightly controlling TLR3-mediated innate immunity.

The linear ubiquitin chain assembly complex (LUBAC), consisting of SHANK-associated RH-domain–interacting protein (SHARPIN), heme-oxidized IRP2 ubiquitin ligase-1 (HOIL-1), and HOIL-1–interacting protein (HOIP), is a critical regulator of inflammation and immunity. This is highlighted by the fact that patients with perturbed linear ubiquitination caused by mutations in the Hoip or Hoil-1 genes, resulting in knockouts of these proteins, may simultaneously suffer from immunodeficiency and autoinflammation. TLR3 plays a crucial, albeit controversial, role in viral infection and tissue damage. We identify a pivotal role of LUBAC in TLR3 signaling and discover a functional interaction between LUBAC components and TLR3 as crucial for immunity to influenza A virus infection. On the biochemical level, we identify LUBAC components as interacting with the TLR3-signaling complex (SC), thereby enabling TLR3-mediated gene activation. Absence of LUBAC components increases formation of a previously unrecognized TLR3-induced death-inducing SC, leading to enhanced cell death. Intriguingly, excessive TLR3-mediated cell death, induced by double-stranded RNA present in the skin of SHARPIN-deficient chronic proliferative dermatitis mice (cpdm), is a major contributor to their autoinflammatory skin phenotype, as genetic coablation of Tlr3 substantially ameliorated cpdm dermatitis. Thus, LUBAC components control TLR3-mediated innate immunity, thereby preventing development of immunodeficiency and autoinflammation.

SPATA2-Mediated Binding of CYLD to HOIP Enables CYLD Recruitment to Signaling Complexes

Recruitment of the deubiquitinase CYLD to signaling complexes is mediated by its interaction with HOIP, the catalytically active component of the linear ubiquitin chain assembly complex (LUBAC). Here, we identify SPATA2 as a constitutive direct binding partner of HOIP that bridges the interaction between CYLD and HOIP. SPATA2 recruitment to TNFR1- and NOD2-signaling complexes is dependent on HOIP, and loss of SPATA2 abolishes CYLD recruitment. Deficiency in SPATA2 exerts limited effects on gene activation pathways but diminishes necroptosis induced by tumor necrosis factor (TNF), resembling loss of CYLD. In summary, we describe SPATA2 as a previously unrecognized factor in LUBAC-dependent signaling pathways that serves as an adaptor between HOIP and CYLD, thereby enabling recruitment of CYLD to signaling complexes.

The role of ORMDL proteins, guardians of cellular sphingolipids, in asthma

A family of widely expressed ORM-like (ORMDL) proteins has been recently linked to asthma in genomewide association studies in humans and extensively explored in in vivo studies in mice. ORMDL proteins are key regulators of serine palmitoyltransferase, an enzyme catalyzing the initial step of sphingolipid biosynthesis. Sphingolipids play prominent roles in cell signaling and response to stress, and they affect the mechanistic properties of cellular membranes. Deregulation of sphingolipid biosynthesis and their recycling has been proven to support and even cause several diseases including allergy, inflammation, and asthma. ORMDL3, the most extensively studied member of the ORMDL family, has been shown to be important for endoplasmic reticulum homeostasis by regulating the unfolded protein response and calcium response. In immune cells, ORMDL3 is involved in migration and in the production of proinflammatory cytokines. Furthermore, changes in the expression level of ORMDL3 are important in allergen-induced asthma pathologies. This review focuses on functional aspects of the ORMDL family proteins, which may serve as new therapeutic targets for the treatment of asthma and some other life-threatening diseases.

Formation and removal of poly-ubiquitin chains in the regulation of tumor necrosis factor-induced gene activation and cell death

Tumor necrosis factor (TNF) is a potent cytokine known for its involvement in inflammation, repression of tumorigenesis and activation of immune cells. Consequently, accurate regulation of the TNF signaling pathway is crucial for preventing the potent noxious effects of TNF. These pathological conditions include chronic inflammation, septic shock, cachexia and cancer. The TNF signaling cascade utilizes a complex network of post-translational modifications to control the cellular response following its activation. Next to phosphorylation, the ubiquitination of signaling complex components is probably the most important modification. This process is mediated by a specialist class of enzymes, the ubiquitin ligases. Equally important is the class of dedicated ubiquitin-specific proteases, the deubiquitinases. Together with ubiquitin binding proteins, this ubiquitination-deubiquitination system enables the dynamics of signaling complexes. In TNF signaling, these dynamics translate into the precise regulation of the induction of gene activation or cell death. Here, we review and discuss current knowledge of TNF signaling regulation by the ubiquitin system.

LUBAC-Recruited CYLD and A20 Regulate Gene Activation and Cell Death by Exerting Opposing Effects on Linear Ubiquitin in Signaling Complexes

Ubiquitination and deubiquitination are crucial for assembly and disassembly of signaling complexes. LUBAC-generated linear (M1) ubiquitin is important for signaling via various immune receptors. We show here that the deubiquitinases CYLD and A20, but not OTULIN, are recruited to the TNFR1- and NOD2-associated signaling complexes (TNF-RSC and NOD2-SC), at which they cooperate to limit gene activation. Whereas CYLD recruitment depends on its interaction with LUBAC, but not on LUBAC’s M1-chain-forming capacity, A20 recruitment requires this activity. Intriguingly, CYLD and A20 exert opposing effects on M1 chain stability in the TNF-RSC and NOD2-SC. While CYLD cleaves M1 chains, and thereby sensitizes cells to TNF-induced death, A20 binding to them prevents their removal and, consequently, inhibits cell death. Thus, CYLD and A20 cooperatively restrict gene activation and regulate cell death via their respective activities on M1 chains. Hence, the interplay between LUBAC, M1-ubiquitin, CYLD, and A20 is central for physiological signaling through innate immune receptors.

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LUBAC directly recruits CYLD to the TNFR1 complex where it antagonizes M1 linkages

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M1-ubiquitin chains recruit A20, which, in turn, protects them from degradation

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CYLD and A20 inhibit gene activation but oppose each other in regulating cell death

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OTULIN controls LUBAC activity prior to stimulation but not in signaling complexes

HOIP deficiency causes embryonic lethality by aberrant TNFR1-mediated endothelial cell death

Linear ubiquitination is crucial for innate and adaptive immunity. The linear ubiquitin chain assembly complex (LUBAC), consisting of HOIL-1, HOIP, and SHARPIN, is the only known ubiquitin ligase that generates linear ubiquitin linkages. HOIP is the catalytically active LUBAC component. Here, we show that both constitutive and Tie2-Cre-driven HOIP deletion lead to aberrant endothelial cell death, resulting in defective vascularization and embryonic lethality at midgestation. Ablation of tumor necrosis factor receptor 1 (TNFR1) prevents cell death, vascularization defects, and death at midgestation. HOIP-deficient cells are more sensitive to death induction by both tumor necrosis factor (TNF) and lymphotoxin-α (LT-α), and aberrant complex-II formation is responsible for sensitization to TNFR1-mediated cell death in the absence of HOIP. Finally, we show that HOIP's catalytic activity is necessary for preventing TNF-induced cell death. Hence, LUBAC and its linear-ubiquitin-forming activity are required for maintaining vascular integrity during embryogenesis by preventing TNFR1-mediated endothelial cell death.

Nonredundant roles of Src-family kinases and Syk in the initiation of B-cell antigen receptor signaling

When a BCR on a mature B cell is engaged by its ligand, the cell becomes activated, and the Ab-mediated immune response can be triggered. The initiation of BCR signaling is orchestrated by kinases of the Src and Syk families. However, the proximal BCR-induced phosphorylation remains incompletely understood. According to a model of sequential activation of kinases, Syk acts downstream of Src family kinases (SFKs). In addition, signaling independent of SFKs and initiated by Syk has been proposed. Both hypotheses lack sufficient evidence from relevant B cell models, mainly because of the redundancy of Src family members and the importance of BCR signaling for B cell development. We addressed this issue by analyzing controlled BCR triggering ex vivo on primary murine B cells and on murine and chicken B cell lines. Chemical and Csk-based genetic inhibitor treatments revealed that SFKs are required for signal initiation and Syk activation. In addition, ligand and anti-BCR Ab-induced signaling differ in their sensitivity to the inhibition of SFKs.

LST1/A is a myeloid leukocyte-specific transmembrane adaptor protein recruiting protein tyrosine phosphatases SHP-1 and SHP-2 to the plasma membrane

Transmembrane adaptor proteins are membrane-anchored proteins consisting of a short extracellular part, a transmembrane domain, and a cytoplasmic part with various protein-protein interaction motifs but lacking any enzymatic activity. They participate in the regulation of various signaling pathways by recruiting other proteins to the proximity of cellular membranes where the signaling is often initiated and propagated. In this work, we show that LST1/A, an incompletely characterized protein encoded by MHCIII locus, is a palmitoylated transmembrane adaptor protein. It is expressed specifically in leukocytes of the myeloid lineage, where it localizes to the tetraspanin-enriched microdomains. In addition, it binds SHP-1 and SHP-2 phosphatases in a phosphotyrosine-dependent manner, facilitating their recruitment to the plasma membrane. These data suggest a role for LST1/A in negative regulation of signal propagation.

Regulation of Src family kinases involved in T cell receptor signaling by protein-tyrosine phosphatase CD148

CD148 is a receptor-like protein-tyrosine phosphatase known to inhibit transduction of mitogenic signals in non-hematopoietic cells. Similarly, in the hematopoietic lineage, CD148 inhibited signal transduction downstream of T cell receptor. However, it also augmented immunoreceptor signaling in B cells and macrophages via dephosphorylating C-terminal tyrosine of Src family kinases (SFK). Accordingly, endogenous CD148 compensated for the loss of the main SFK activator CD45 in murine B cells and macrophages but not in T cells. Hypothetical explanations for the difference between T cells and other leukocyte lineages include the inability of CD148 to dephosphorylate a specific set of SFKs involved in T cell activation or the lack of CD148 expression during critical stages of T cell development. Here we describe striking differences in CD148 expression between human and murine thymocyte subsets, the only unifying feature being the absence of CD148 during the positive selection when the major developmental block occurs under CD45 deficiency. Moreover, we demonstrate that similar to CD45, CD148 has both activating and inhibitory effects on the SFKs involved in TCR signaling. However, in the absence of CD45, activating effects prevail, resulting in functional complementation of CD45 deficiency in human T cell lines. Importantly, this is independent of the tyrosines in the CD148 C-terminal tail, contradicting the recently proposed phosphotyrosine displacement model as a mechanism of SFK activation by CD148. Collectively, our data suggest that differential effects of CD148 in T cells and other leukocyte subsets cannot be explained by the CD148 inability to activate T cell SFKs but rather by its dual inhibitory/activatory function and specific expression pattern.

Gamma-tubulins and their functions

gamma-Tubulin is a ubiquitous phylogenetically conserved member of tubulin superfamily. In comparison with alpha beta-tubulin dimers, it is a low abundance protein present within the cells in both various types of microtubule-organizing centers and cytoplasmic protein complexes. gamma-Tubulin small complexes are subunits of the gamma-tubulin ring complex, which is involved in microtubule nucleation and capping of the minus ends of microtubules. In the past years important findings have advanced the understanding of the structure and function of gamma-tubulin ring complexes. Recent evidences suggest that the functions of gamma-tubulin extend beyond microtubule nucleation.

Comparison of the expression of specific cell surface epitopes on in vitro fertilized and parthenogenetic bovine embryos

Parthenogenetic embryos, which are produced by the spontaneous or artificial stimulation of the oocyte, partially develop in the complete absence of the male gamete but fail to produce live young in many mammalian species. The identification of developmentally regulated molecules on the cell surface of embryos has implicated their possible role in cell interactions during embryogenesis and differentiation. In this study the expression patterns of four stage-specific cell surface antigenic determinants (TEC-1, -2, -3, and -4) were investigated in both parthenogenetic and in vitro fertilized bovine embryos. When compared to embryos produced using in vitro fertilization methods the parthenogenotes, although appearing morphologically normal, differed markedly in their TEC epitope pattern of presentation. TEC-1, -2, -3, and -4 epitope presentation on in vitro fertilized embryos occurred during specific stages of preimplantation development. TEC-1 and -2 presentation was detected on oocytes and blastocysts only, TEC-3 on morulae and blastocysts, and TEC-4 on oocytes through to 8-cell embryos, with all subsequent stages negative. Parthenogenetic embryos did not show TEC-1, -2, or -3 epitope presentation whereas the TEC-4 epitope was present throughout the developmental period examined. Enzymatic cleavage of sialic acid residues on in vitro fertilized and parthenogenetic embryos resulted in presentation of the TEC epitopes during all the embryonic stages. Western blot analysis of the embryos showed the TEC epitopes to be present on all the embryonic stages examined. This study suggests the mechanisms responsible for control and presentation of each of the TEC epitopes may not be functioning the same in parthenogenetic embryos that undergo changed glycosylation or deglycosylation resulting in altered patterns of sialylation. The study also shows TEC epitope presentation may prove to be a useful indicator of parthenogenetically activated bovine embryos. J. Exp. Zool. 284:392-400, 1999.

Requirement for a negative charge at threonine 60 of the FcRgamma for complete activation of Syk

Aggregation of FcepsilonRI on mast cells results in the phosphorylation of the FcepsilonRIgamma chain on tyrosine and threonine residues within the immunoreceptor tyrosine-based activation motif. In the present study we sought to identify the site of threonine phosphorylation in FcepsilonRIgamma and investigate its functional importance. We found that threonine 60 was phosphorylated in vitro and in vivo. Expression of a mutated FcepsilonRIgamma (T60A), in either FcepsilonRIgamma-deficient or gamma-null mast cells, resulted in a delay of FcepsilonRI endocytosis, inhibition of TNF-alpha mRNA production, and inhibition of degranulation but did not affect FcepsilonRI-induced cell adhesion. Tyrosine phosphorylation of the T60A mutant gamma chain was normal, but Syk phosphorylation was dramatically reduced in these transfectants. This correlated with reduced co-immunoprecipitation of FcepsilonRIgamma with Syk. Substitution of an aspartic residue for threonine 60 of the FcepsilonRIgamma reconstituted complete activation of Syk and co-immunoprecipitation of FcepsilonRIgamma with Syk. We conclude that the negative charge provided by phosphorylation of threonine 60 of the FcepsilonRIgamma is required for the appropriate interaction and activation of Syk. This is a likely requirement for immunoreceptor tyrosine-based activation motifs involved in Syk activation.

Treatment of Vicia faba root tip cells with specific inhibitors to cyclin-dependent kinases leads to abnormal spindle formation

Many events during cell division are triggered by an evolutionary conserved regulator, the cyclin-dependent kinase (Cdk). Here we used two novel drugs, the purine analogues bohemine and roscovitine, to study the role of Cdks in cell cycle progression and microtubule organisation in Vicia faba root tip cells. Both drugs inhibited the activity of immunopurified Vicia faba and alfalfa Cdc2-kinase. The transcript levels of an A- and B-type cyclin, as well as of the cdc2 genes, declined in treated root tips, while the mRNA level of a D-type cyclin gene was not affected. An observed transient arrest at the G1/S and G2/M regulatory points indicated that inhibition of the Cdc2-kinase had an effect on both transitions. In contrast to the regular bipolar spindle in untreated cell, in drug-treated metaphase cells abnormally short and dense kinetochore microtubule fibres were observed. These microtubules were randomly arranged in the vicinity of the kinetochores and connected the chromosomes. Thus, the chromosomes were not aligned on the metaphase plate but were arranged in a circle, with kinetochores pointing inwards and chromosome arms pointing outwards. gamma-Tubulin, which plays a role in microtubule nucleation, also localised to the centre of the monopolar spindle. The observed abnormalities in mitosis, after inhibition of Cdc2-kinase by specific drugs, suggest a role for this enzyme in regulating some of the steps leading to a bipolar spindle structure.

The stage-specific expression of TEC-1, -2, -3, and -4 antigens on bovine preimplantation embryos

The preimplantation developmental period is associated with constant changes within the embryo, and some of these changes are apparent on the embryo cell surface. For example, during transition from maternal to embryonic genome control and the compaction and differentiation of embryonic cells, the cell surface undergoes morphologic alterations that reflect changes in gene control. In order to gain insight into the events occurring during embryonic development and cellular differentiation, monoclonal antibodies specific for cell surface antigens (TEC antigens) of embryonic cells have been generated previously and shown to recognise either the carbohydrate moiety of embryoglycan or a developmentally regulated protein epitope. The TEC antigens have been identified on mouse preimplantation embryos, and their expression is specific to particular developmental stages. To determine whether these antigens are conserved in higher mammals, we examined the expression of four TEC antigens (TEC-1 to TEC-4) on in vitro-derived bovine and murine embryos during the preimplantation stage of development. It was found that bovine oocytes and embryos derived from in vitro maturation (IVM) and in vitro fertilisation (IVF) showed stage-specific expression of each of the TEC antigens investigated, with the pattern of expression overlapping but not identical to that seen in the mouse. Immunoprecipitation together with Western blot analysis showed that the TEC monoclonal antibodies recognised a single glycoprotein band with an apparent molecular weight of 70 kDa. Confocal microscopy of immunofluorescence staining of the bovine cells showed this protein to be located on the cell surface. The apparent negative expression of these TEC antigens by immunohistochemistry and immunoprecipitation at particular stages of development appears to be due to the epitopes being inaccessible to the TEC antibodies, since Western blotting revealed the TEC antigens to be present at all stages of development examined. Antibodies identifying stage-specific antigens will provide useful markers to characterise early embryonic cells, monitor normal embryonic development in vitro, and identify cell surface structures having a function in cell-cell interactions during embryogenesis and differentiation.

Cell-surface levels of human carcinoembryonic antigen are inversely correlated with colonocyte differentiation in colon carcinogenesis

Human carcinoembryonic antigen (CEA) is overexpressed in a wide variety of epithelial malignancies including colon cancer. CEA can function in vitro as a homotypic intercellular adhesion molecule and can block the terminal differentiation of rodent myoblasts, thus raising the possibility that deregulated expression of CEA might directly contribute to malignant progression. To address this question, the expression pattern and cell-surface levels of CEA were studied during malignant transformation of the colonic epithelium in sporadic and familial adenomatous polyposis-related neoplasms. The level of immunohistochemically detected CEA was higher in 30% to 62% of microadenomas and small adenomas from familial adenomatous polyposis patients compared with adjacent normal mucosa, and this proportion was positively correlated with lesion size and degree of dysplasia. Cytofluorometric analysis of highly purified single epithelial cell suspensions from freshly excised carcinomas versus adjacent normal tissue demonstrated up to a 20-fold increase of mean cell-surface CEA in a group of colon carcinomas representative of the overall majority of such tumors--from Dukes' stages A to D and ranging mainly from well to moderately differentiated, the degree of overproduction was inversely correlated with tumor differentiation and directly correlated with stage. A marked tendency toward nonpolarized versus apical cell-surface expression with progression was also noted. Nonspecific cross-reacting antigen (NCA), a CEA family member, is also a homotypic adhesion molecule and blocks terminal myogenic differentiation, whereas biliary glycoprotein is a CEA family adhesion molecule that does not. Cell-surface NCA showed even greater overexpression (up to 70-told) in dedifferentiated tumors, whereas total-cell biliary glycoprotein showed approximately 2-fold lower levels than was normal in more differentiated tumors and approximately 2-fold higher levels than in further progressed tumors. These results therefore support the suggestion that CEA and NCA can directly contribute to colon carcinogenesis by inhibiting colonocyte differentiation.

Changes of MAP2 phosphorylation during brain development

The microtubule-associated protein MAP2 is essential for development of early neuronal morphology and maintenance of adult neuronal morphology. Several splice variants exist, MAP2a-d, with a lack of MAP2a in cat brain. MAP2 is widely used as a neuronal marker. In this study we compared five monoclonal antibodies (MAbs) against MAP2. They show differences in the immunocytochemical distribution of MAP2 isoforms during development of the visual cortex and cerebellum of the cat. Local and temporal differences were seen with MAb AP18, an antibody directed against a phosphorylation-dependent epitope near the N-terminal end. In large pyramidal dendrites in visual cortex, the AP18 epitope remained in parts immunoreactive after treatment with alkaline phosphatase. Three MAbs, AP14, MT-01, and MT-02, recognized the central region of the MAP2b molecule, which is not present in MAP2c and 2d, and reacted with phosphorylation-independent epitopes. During the first postnatal week the immunostaining in cerebellum differed between antibodies in that some cellular elements in external and internal granular layers and Purkinje cells were stained to various degrees, whereas at later stages staining patterns were similar. At early stages, antibody MT-02 stained cell bodies and dendrites in cerebral cortex and cerebellum. With progressing maturation, immunoreactivity became restricted to distal parts of apical dendrites of pyramidal cells and was absent from perikarya and finer proximal dendrites in cortex. MT-02 did not stain MAP2 in cerebellum of adult animals. This study demonstrates that the immunocytochemical detection of MAP2 depends on modifications such as phosphorylation and conformational changes of the molecule, and that MAP2 staining patterns differ between MAbs. Phosphorylation and specific conformations in the molecule may be essential for modulating function and molecular stability of MAP2, and monoclonal antibodies against such sites may provide tools for studying the functional role of modifications.

Autoimmune damage to spermatogenesis in rodents immunized with mouse F9 embryonic carcinoma cells

Significant inhibition of spermatogenesis and appearance of antibodies against spermatogenic cells identified by cytotoxicity and immunofluorescence reactions were observed in mice of inbred strains 129/Sv and BALB/c and in albino guinea pigs after syngeneic, allogeneic, and xenogeneic immunization with mouse F9 embryonic carcinoma cells and Freund's complete adjuvant. A similar syngeneic immunization with PYS-2 cells was ineffective. Appropriate absorption experiments confirmed the similarity between the antigens of F9 and spermatogenic cells and the absence of such a similarity with antigens of PYS-2 cells. These results support the hypothesis that the oncofetal F9 antigens represent spermatogenic differentiation antigens and thus play an essential role in spermatogenic cell differentiation.