Construction of Epstein-Barr virus-based expression vector containing mini-oriP

Detection of SARS-CoV-2 antibodies in serum and dried blood spot samples of vaccinated individuals using a sensitive homogeneous proximity extension assay

A homogeneous PCR-based assay for sensitive and specific detection of antibodies in serum or dried blood spots (DBS) is presented and the method is used to monitor individuals infected with or vaccinated against SARS-CoV-2. Detection probes were prepared by conjugating the recombinant spike protein subunit 1 (S1), containing the receptor binding domain (RBD) of SARS-CoV-2, to each of a pair of specific oligonucleotides. The same was done for the nucleocapsid protein (NP). Upon incubation with serum or DBS samples, the bi- or multivalency of the antibodies (IgG, IgA or IgM) brings pairs of viral proteins with their conjugated oligonucleotides in proximity, allowing the antibodies to be detected by a modified proximity extension assay (PEA). Anti-S1 and anti-NP antibodies could be detected simultaneously from one incubation reaction. This Antibody PEA (AbPEA) test uses only 1 µl of neat or up to 100,000-fold diluted serum or one ø1.2 mm disc cut from a DBS. All 100 investigated sera and 21 DBS collected prior to the COVID-19 outbreak were negative, demonstrating a 100% specificity. The area under the curve, as evaluated by Receiver Operating Characteristic (ROC) analysis reached 0.998 (95%CI: 0.993-1) for samples taken from 11 days after symptoms onset. The kinetics of antibody responses were monitored after a first and second vaccination using serially collected DBS from 14 individuals. AbPEA offers highly specific and sensitive solution-phase antibody detection without requirement for secondary antibodies, no elution step when using DBS sample in a simple procedure that lends itself to multiplex survey of antibody responses.

MTCL2 promotes asymmetric microtubule organization by crosslinking microtubules on the Golgi membrane

The Golgi complex plays an active role in organizing asymmetric microtubule arrays essential for polarized vesicle transport. The coiled-coil protein MTCL1 stabilizes microtubules nucleated from the Golgi membrane. Here, we report an MTCL1 paralog, MTCL2, which preferentially acts on the perinuclear microtubules accumulated around the Golgi. MTCL2 associates with the Golgi membrane through the N-terminal coiled-coil region and directly binds microtubules through the conserved C-terminal domain without promoting microtubule stabilization. Knockdown of MTCL2 significantly impaired microtubule accumulation around the Golgi as well as the compactness of the Golgi ribbon assembly structure. Given that MTCL2 forms parallel oligomers through homo-interaction of the central coiled-coil motifs, our results indicate that MTCL2 promotes asymmetric microtubule organization by crosslinking microtubules on the Golgi membrane. Results of in vitro wound healing assays further suggest that this function of MTCL2 enables integration of the centrosomal and Golgi-associated microtubules on the Golgi membrane, supporting directional migration. Additionally, the results demonstrated the involvement of CLASPs and giantin in mediating the Golgi association of MTCL2.

Lipid flippase dysfunction as a therapeutic target for endosomal anomalies in Alzheimer’s disease

Endosomal anomalies because of vesicular traffic impairment have been indicated as an early pathology of Alzheimer’| disease (AD). However, the mechanisms and therapeutic targets remain unclear. We previously reported that βCTF, one of the pathogenic metabolites of APP, interacts with TMEM30A. TMEM30A constitutes a lipid flippase with P4-ATPase and regulates vesicular trafficking through the asymmetric distribution of phospholipids. Therefore, the alteration of lipid flippase activity in AD pathology has got attention. Herein, we showed that the interaction between βCTF and TMEM30A suppresses the physiological formation and activity of lipid flippase in AD model cells, A7, and App^{NL−G-F/NL−G-F} model mice. Furthermore, the T-RAP peptide derived from the βCTF binding site of TMEM30A improved endosomal anomalies, which could be a result of the restored lipid flippase activity. Our results provide insights into the mechanisms of vesicular traffic impairment and suggest a therapeutic target for AD.

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Interaction between βCTF and TMEM30A mediates endosomal anomalies

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Accumulated βCTF impairs lipid flippase function, a regulator of vesicle transport

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Age-dependent lipid flippase disorder can precede Aβ deposition in AD model mice

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βCTF interacting peptide, 'T-RAP′ can improve βCTF mediated endosomal anomalies

Epstein-Barr virus-based plasmid enables inheritable transgene expression in mouse cerebral cortex

Continuous development of the cerebral cortex from the prenatal to postnatal period depends on neurons and glial cells, both of which are generated from neural progenitor cells (NPCs). Owing to technical limitations regarding the transfer of genes into mouse brain, the mechanisms behind the long-term development of the cerebral cortex have not been well studied. Plasmid transfection into NPCs in embryonic mouse brains by in utero electroporation (IUE) is a widely used technique aimed at expressing transgenes in NPCs and their recent progeny neurons. Because the plasmids in NPCs are attenuated with each cell division, the transgene is not expressed in their descendants, including glial cells. The present study shows that an Epstein–Barr virus-based plasmid (EB-oriP plasmid) is helpful for studying long-term cerebral cortex development. The use of the EB-oriP plasmid for IUE allowed transgene expression even in the descendant progeny cells of adult mouse brains. Combining the EB-oriP plasmid with the shRNA expression cassette allowed examination of the genes of interest in the continuous development of the cerebral cortex. Furthermore, preferential transgene expression was achieved in combination with cell type-specific promoter-driven transgene expression. Meanwhile, introducing the EB-oriP plasmid twice into the same individual embryos during separate embryonic development stages suggested heterogeneity of NPCs. In summary, IUE using the EB-oriP plasmid is a novel option to study the long-term development of the cerebral cortex in mice.

Phosphorylation and dephosphorylation of Ser852 and Ser889 control the clustering, localization and function of PAR3

Cell polarity is essential for various asymmetric cellular events, and the partitioning defective (PAR) protein PAR3 (encoded by PARD3 in mammals) plays a unique role as a cellular landmark to establish polarity. In epithelial cells, PAR3 localizes at the subapical border, such as the tight junction in vertebrates, and functions as an apical determinant. Although we know a great deal about the regulators of PAR3 localization, how PAR3 is concentrated and localized to a specific membrane domain remains an important question to be clarified. In this study, we demonstrate that ASPP2 (also known as TP53BP2), which controls PAR3 localization, links PAR3 and protein phosphatase 1 (PP1). The ASPP2-PP1 complex dephosphorylates a novel phosphorylation site, Ser852, of PAR3. Furthermore, Ser852- or Ser889-unphosphorylatable PAR3 mutants form protein clusters, and ectopically localize to the lateral membrane. Concomitance of clustering and ectopic localization suggests that PAR3 localization is a consequence of local clustering. We also demonstrate that unphosphorylatable forms of PAR3 exhibited a low molecular turnover and failed to coordinate rapid reconstruction of the tight junction, supporting that both the phosphorylated and dephosphorylated states are essential for the functional integrity of PAR3.

Amplification of EBNA-1 through a single-plasmid vector-based gene amplification system in HEK293 cells as an efficient transient gene expression system

Our previous work showed that there is a limitation in the use of dihydrofolate reductase (dhfr)/methotrexate (MTX)-mediated gene amplification systems in dhfr-non-deficient HEK293 cells, as endogenous dhfr may interfere with the amplification process. In the present study, we successfully generated Epstein-Barr virus nuclear antigen-1 (EBNA-1)-amplified HEK293 cells in a dhfr-non-deficient HEK293 cell background using a single-plasmid vector-based gene amplification system with shRNA targeting the 3'-UTR of endogenous dhfr. The introduction of this shRNA efficiently downregulated the expression of endogenous dhfr in the HEK293 cells without affecting exogenous dhfr expression. The downregulation of endogenous dhfr improved the efficiency of EBNA-1 amplification, as evidenced by a comparison with the amplification extent in cells lacking shRNA expression at the same MTX concentration. The EBNA-1 expression levels from the EBNA-1-amplified clones selected in this study were higher than those obtained from EBNA-1-amplified clones that were generated using the conventional amplification in our previous study. Consistent with previous studies, EBNA-1 amplification improved the production of the Fc-fusion protein through a specific protein productivity (q_p)-enhancing effect, rather than by improving cell growth or transfection efficiency. In addition, the N-glycan profiles in the Fc-fusion protein produced using this transient gene expression (TGE) system were not affected by EBNA-1 amplification. These results indicate the potential utility of EBNA-1-amplified mammalian cells, developed using a single-plasmid vector-based gene amplification system, for efficient protein production. KEY POINTS: • EBNA-1-amplified HEK293 cells were established using gene amplification system. • EBNA-1 amplification in TGE system can increase the Fc-fusion protein productivity. • EBNA-1 amplification does not affect the N-glycan profile in the Fc-fusion protein.

Epstein-Barr virus-derived vector suitable for long-term expression in neurons

Exogenous gene expression is a fundamental and indispensable technique for testing gene function in neurons. Several ways to express exogenous genes in neurons are available, but each method has pros and cons. The lentivirus vector is useful for high efficiency gene transfer to neurons and stabilizes gene expression via genome integration, but this integration may destroy the host genome. The Epstein-Barr virus (EBV)-derived vector (EB vector) is an accessible and useful vector in human cell lines because the vector is not integrated into the host genome but stays in the nucleus as an episome. However, there has been no report on this process in rodent neurons.

We examined the usefulness of the EB vector for testing gene function in neurons. We found that EB vector-derived exogenous proteins such as green fluorescent protein (GFP) and GFP-tagged actin were easily detectable even after three weeks of transfection. Second, a tetracycline-induced gene expression system in the EB vector was active after three weeks of transfection, indicating that plasmids were retained in neurons for up to three weeks. Third, we determined that only Family of repeat element of the plasmid vector is essential for its long-term presence in neurons. These results show that the modified EB vector is a useful tool for examining gene function in neurons.

Structural insights into modulation and selectivity of transsynaptic neurexin-LRRTM interaction

Leucine-rich repeat transmembrane neuronal proteins (LRRTMs) function as postsynaptic organizers that induce excitatory synapses. Neurexins (Nrxns) and heparan sulfate proteoglycans have been identified as presynaptic ligands for LRRTMs. Specifically, LRRTM1 and LRRTM2 bind to the Nrxn splice variant lacking an insert at the splice site 4 (S4). Here, we report the crystal structure of the Nrxn1β–LRRTM2 complex at 3.4 Å resolution. The Nrxn1β–LRRTM2 interface involves Ca²⁺-mediated interactions and overlaps with the Nrxn–neuroligin interface. Together with structure-based mutational analyses at the molecular and cellular levels, the present structural analysis unveils the mechanism of selective binding between Nrxn and LRRTM1/2 and its modulation by the S4 insertion of Nrxn.

Leucine-rich repeat transmembrane neuronal proteins (LRRTMs) function as postsynaptic organizers that induce excitatory synapses. Here authors solve the crystal structure of LRRTM2 in complex with its ligand Nrxn1β and shed light on how selective binding of ligands to LRRTM1/2 is achieved.

Transcription Factors and Medium Suitable for Initiating the Differentiation of Human-Induced Pluripotent Stem Cells to the Hepatocyte Lineage

Transcription factors and culture media were investigated to determine the condition to initiate the differentiation of human-induced pluripotent stem (iPS) cells most efficiently. The expression of genes in human adult liver was compared with that in 201B7 cells (iPS cells) using cDNA microarray analysis. Episomal plasmids expressing transcription factors were constructed. 201B7 cells were transfected with the episomal plasmids and cultured in ReproFF (feeder-free media maintaining pluripotency), Leibovitz-15 (L15), William's E (WE), or Dulbecco's modified Eagle medium/Nutrient F-12 Ham (DF12) for 7 days. RNA was isolated and subjected to real-time quantitative PCR to analyze the expression of alpha-feto protein (AFP) and albumin. cDNA microarray analysis revealed 16 transcription factors that were upregulated in human adult liver relative to that in 201B7 cells. Episomal plasmids expressing these 16 genes were transfected into 201B7 cells. CCAAT/enhancer-binding protein alpha (CEBPA), CCAAT/enhancer-binding protein beta (CEBPB), forkhead box A1 (FOXA1), and forkhead box A3 (FOXA3) up-regulated AFP and down-regulated Nanog. These four genes were further analyzed. The expression of AFP and albumin was the highest in 201B7 cells transfected with the combination of CEBPA, CEBPB, FOXA1, and FOXA3 and cultured in WE. The combination of CEBPA, CEBPB, FOXA1, and FOXA3 was suitable for 201B7 cells to initiate differentiation to the hepatocyte lineage and WE was the most suitable medium for culture after transfection. J. Cell. Biochem. 117: 2001-2009, 2016. © 2016 Wiley Periodicals, Inc.

Dual gene expression in embryoid bodies derived from human induced pluripotent stem cells using episomal vectors

Transcription factors are essential for the differentiation of human induced pluripotent stem cells (iPS) into specialized cell types. Embryoid body (EB) formation promotes the differentiation of iPS cells. We sought to establish an efficient method of transfection and rotary culture to generate EBs that stably express two genes. The pMetLuc2-Reporter vector was transfected using FuGENE HD (FuGENE), Lipofectamine LTX (LTX), X-tremeGENE, or TransIT-2020 transfection reagents. The media was analyzed using a Metridia luciferase (MetLuc) assay. Transfections were performed on cells adherent to plates/dishes (adherent method) or suspended in the media (suspension method). The 201B7 cells transfected with episomal vectors were selected using G418 (200 μg/mL) or hygromycin B (300 μg/mL). Rotary culture was performed at 2.5 or 9.9 rpm. Efficiency of EB formation was compared among plates and dishes. Cell density was compared at 1.6×10(3),×10(4), and×10(5) cells/mL. The suspended method of transfection using the FuGENE HD reagent was the most efficient. The expression of pEBMulti/Met-Hyg was detected 11 days posttransfection. Double transformants were selected 6 days posttransfection with pEBNK/EGFP-Neo and pEBNK/Cherry-Hyg. Both EGFP and CherryPicker were expressed in all of the surviving cells. EBs were formed most efficiently from cells cultured at a density of 1.6×10(5) cells/mL in six-well plates or 6 cm dishes. The selected cells formed EBs. FuGENE-mediated transfection of plasmids using the suspension method was effective in transforming iPS cells. Furthermore, the episomal vectors enabled us to perform a stable double transfection of EB-forming iPS cells.

Tumor suppressor protein Lgl mediates G1 cell cycle arrest at high cell density by forming an Lgl-VprBP-DDB1 complex

Lgl is a conserved tumor suppressor suggested to be involved in cell polarity regulation and suppression of cell proliferation. Lgl inhibits formation of the VprBP-DDB1-Cul4A-Roc1 ubiquitin E3 ligase complex, which is implicated in cell cycle progression, by promoting formation of the Lgl-VprBP-DDB1 complex to prevent overproliferation.

Lethal giant larvae (Lgl) is an evolutionarily conserved tumor suppressor whose loss of function causes disrupted epithelial architecture with enhanced cell proliferation and defects in cell polarity. A role for Lgl in the establishment and maintenance of cell polarity via suppression of the PAR-aPKC polarity complex is established; however, the mechanism by which Lgl regulates cell proliferation is not fully understood. Here we show that depletion of Lgl1 and Lgl2 in MDCK epithelial cells results in overproliferation and overproduction of Lgl2 causes G1 arrest. We also show that Lgl associates with the VprBP-DDB1 complex independently of the PAR-aPKC complex and prevents the VprBP-DDB1 subunits from binding to Cul4A, a central component of the CRL4 [VprBP] ubiquitin E3 ligase complex implicated in G1- to S-phase progression. Consistently, depletion of VprBP or Cul4 rescues the overproliferation of Lgl-depleted cells. In addition, the affinity between Lgl2 and the VprBP-DDB1 complex increases at high cell density. Further, aPKC-mediated phosphorylation of Lgl2 negatively regulates the interaction between Lgl2 and VprBP-DDB1 complex. These results suggest a mechanism protecting overproliferation of epithelial cells in which Lgl plays a critical role by inhibiting formation of the CRL4 [VprBP] complex, resulting in G1 arrest.

Novel mitochondria-targeted heat-soluble proteins identified in the anhydrobiotic Tardigrade improve osmotic tolerance of human cells

Tardigrades are able to tolerate almost complete dehydration through transition to a metabolically inactive state, called “anhydrobiosis”. Late Embryogenesis Abundant (LEA) proteins are heat-soluble proteins involved in the desiccation tolerance of many anhydrobiotic organisms. Tardigrades, Ramazzottius varieornatus, however, express predominantly tardigrade-unique heat-soluble proteins: CAHS (Cytoplasmic Abundant Heat Soluble) and SAHS (Secretory Abundant Heat Soluble) proteins, which are secreted or localized in most intracellular compartments, except the mitochondria. Although mitochondrial integrity is crucial to ensure cellular survival, protective molecules for mitochondria have remained elusive. Here, we identified two novel mitochondrial heat-soluble proteins, RvLEAM and MAHS (Mitochondrial Abundant Heat Soluble), as potent mitochondrial protectants from Ramazzottius varieornatus. RvLEAM is a group3 LEA protein and immunohistochemistry confirmed its mitochondrial localization in tardigrade cells. MAHS-green fluorescent protein fusion protein localized in human mitochondria and was heat-soluble in vitro, though no sequence similarity with other known proteins was found, and one region was conserved among tardigrades. Furthermore, we demonstrated that RvLEAM protein as well as MAHS protein improved the hyperosmotic tolerance of human cells. The findings of the present study revealed that tardigrade mitochondria contain at least two types of heat-soluble proteins that might have protective roles in water-deficient environments.

In vivo image analysis using iRFP transgenic mice

Fluorescent proteins with light wavelengths within the optical window are one of the improvements in in vivo imaging techniques. Near-infrared (NIR) fluorescent protein (iRFP) is a stable, nontoxic protein that emits fluorescence within the NIR optical window without the addition of exogenous substrate. However, studies utilizing an in vivo iRFP model have not yet been published. Here, we report the generation of transgenic iRFP mice with ubiquitous NIR fluorescence expression. iRFP expression was observed in approximately 50% of the offspring from a matings between iRFP transgenic and WT mice. The serum and blood cell indices and body weights of iRFP mice were similar to those of WT mice. Red fluorescence with an excitation wavelength of 690 nm and an emission wavelength of 713 nm was detected in both newborn and adult iRFP mice. We also detected fluorescence emission in whole organs of the iRFP mice, including the brain, heart, liver, kidney, spleen, lung, pancreas, bone, testis, thymus, and adipose tissue. Therefore, iRFP transgenic mice may therefore be a useful tool for various types of in vivo imaging.

MTCL1 crosslinks and stabilizes non-centrosomal microtubules on the Golgi membrane

Recent studies have revealed the presence of a microtubule subpopulation called Golgi-derived microtubules that support Golgi ribbon formation, which is required for maintaining polarized cell migration. CLASPs and AKAP450/CG-NAP are involved in their formation, but the underlying molecular mechanisms remain unclear. Here, we find that the microtubule-crosslinking protein, MTCL1, is recruited to the Golgi membranes through interactions with CLASPs and AKAP450/CG-NAP, and promotes microtubule growth from the Golgi membrane. Correspondingly, MTCL1 knockdown specifically impairs the formation of the stable perinuclear microtubule network to which the Golgi ribbon tethers and extends. Rescue experiments demonstrate that besides its crosslinking activity mediated by the N-terminal microtubule-binding region, the C-terminal microtubule-binding region plays essential roles in these MTCL1 functions through a novel microtubule-stabilizing activity. These results suggest that MTCL1 cooperates with CLASPs and AKAP450/CG-NAP in the formation of the Golgi-derived microtubules, and mediates their development into a stable microtubule network.

Fluorescence-based co-culture of normal and cancerous cells as an indicator of therapeutic effects in cancer

Comprehensive evaluation of the effects of cancer therapies in vitro is difficult because of the need to distinguish the main effects from the side effects within the data. This problem cannot be overcome by methods involving monoculture, because the effects of anti-cancer drugs in a monoculture can only be measured on either normal or cancerous cells in isolation. In order to promote therapeutic development, therefore, we need a novel drug evaluation method which can simultaneously determine both therapeutic activity and toxicity under a co-culture of normal and cancerous cells. Co-culture creates a more biomimetic condition in comparison to monoculture. The novel method proposed in this study uses an easy experiment for estimating the effects of treatments with various kinds of drugs as a solution to the abovementioned problems. We have previously established two cell lines: a rat gastric mucosal cell line (RGM) and its corresponding cancerous mutant cell line (RGK). In this study, we have developed a new evaluation procedure using a co-culture of green fluorescent protein-expressing RGM cells (RGM-GFP) and kusabira orange-expressing RGK cells (RGK-KO). These cell lines emit green and red fluorescence, respectively. We demonstrated the capability of the method in evaluations of the cancer-selective effects of anti-cancer drugs and X-ray treatment. These results clearly distinguished the cancer-selective toxicity of the applied therapies.

Establishment of monoclonal anti-human CD26 antibodies suitable for immunostaining of formalin-fixed tissue

Background

A T cell costimulatory molecule with dipeptidyl peptidase IV (DPPIV) activity in its extracellular region, CD26 is a multifunctional molecule associated with various proteins such as adenosine deaminase, caveolin-1, CXCR4, collagen, and fibronectin, while playing an important role in the regulation of inflammatory responses and tumor biology. We have focused on CD26 as a novel therapeutic target for various tumors and immune disorders, and have developed a humanized anti-CD26 monoclonal antibody (mAb), YS110, which is currently being evaluated in a phase I clinical trial for patients with CD26-expressing tumors, including malignant mesothelioma. Since detection of tumor CD26 expression is required for determining potential eligibility for YS110 therapy, the development of anti-human CD26 mAb that can clearly and reliably detect the denatured CD26 molecule in the formalin-fixed paraffin-embedded tissues is critical.

Methods

To develop novel anti-CD26 mAbs capable of binding to the denatured CD26, we immunized mice with CD26 protein denatured in urea buffer. After the fusion of splenocytes and myeloma cells, the mAbs were screened for specific reactivity with human CD26 by flow cytometry, enzyme-linked immunosorbent assay, and immunohistochemistry. The binding competitiveness of novel anti-CD26 mAbs with the humanized anti-CD26 mAb YS110 was also examined.

Results

We have succeeded in developing novel anti-human CD26 mAbs suitable for immunohistochemical staining of CD26 in formalin-fixed tissue sections with reliable clarity and intensity. Importantly, some of these mAbs exhibit no cross-reactivity with the humanized anti-CD26 mAb.

Conclusions

These novel mAbs are potentially useful as companion diagnostic agents to analyze CD26 expression in the clinical setting while advancing future CD26-related research.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/5987140221097729

Improved detection of electrical activity with a voltage probe based on a voltage-sensing phosphatase

  One of the most awaited techniques in modern physiology is the sensitive detection of spatiotemporal electrical activity in a complex network of excitable cells. The use of genetically encoded voltage probes has been expected to enable such analysis. However, in spite of recent progress, existing probes still suffer from low signal amplitude and/or kinetics too slow to detect fast electrical activity. Here, we have developed an improved voltage probe named Mermaid2, which is based on the voltage-sensor domain of the voltage-sensing phosphatase from Ciona intestinalis and Förster energy transfer between a pair of fluorescent proteins. In mammalian cells, Mermaid2 permits ratiometric readouts of fractional changes of more than 50% over a physiologically relevant voltage range with fast kinetics, and it was used to follow a train of action potentials at frequencies of up to 150 Hz. Mermaid2 was also able to detect single action potentials and subthreshold voltage responses in hippocampal neurons in vitro, in addition to cortical electrical activity evoked by sound stimuli in single trials in living mice.

Cancer cells uptake porphyrinsviaheme carrier protein 1

Although exogenous porphyrin accumulation in cancer cells is important for the success of photodynamic therapies, the mechanism is not clear. We hypothesized that a newly reported transporter, heme carrier protein 1 (HCP1), is highly expressed in cancer cells, and transports porphyrins into the cells. We investigated the following three unknowns: whether cancer cells take up hematoporphyrin derivative via HCP1, whether HCP1 is involved in photodynamic therapies, and whether cancer cells highly express HCP1. First, when HCP1-overexpressed cells were treated with hematoporphyrin derivative and then exposed to an eximer laser beam, they emitted a significantly higher intensity of hematoporphyrin derivative fluorescence and became more susceptible to the laser beam than control. Second, when three other types of cancer cells with silenced HCP1 were treated with hematoporphyrin derivative and then exposed to the laser beam, they emitted a significantly lower intensity of hematoporphyrin derivative fluorescence. Third, non-cancer cells slightly expressed HCP1; on the other hand, the three other types of cancer cells clearly expressed HCP1. These results indicated that cancer cells uptake hematoporphyrin derivative via HCP1 and over-expression of HCP1 increases the efficacy of photodynamic therapies by increasing porphyrin accumulation in the cells. This is the first report about a transporter of porphyrin in cancer cells.

A novel PAR-1-binding protein, MTCL1, plays critical roles in organizing microtubules in polarizing epithelial cells

The establishment of epithelial polarity is tightly linked to the dramatic reorganization of microtubules (MTs) from a radial array to a vertical alignment of non-centrosomal MT bundles along the lateral membrane and a meshwork under the apical and basal membranes. However, little is known about the underlying molecular mechanism of this polarity-dependent MT remodeling. The evolutionarily conserved cell polarity-regulating kinase PAR-1, whose activity is essential for maintaining the dynamic state of MTs, plays indispensable roles to promote this process. Here, we identify a novel PAR-1-binding protein, named MTCL1 (Microtubule crosslinking factor 1), which crosslinks MTs through its N-terminal MT-binding region and subsequent coiled-coil motifs. MTCL1 colocalized with the apicobasal MT bundles in epithelial cells, and its knockdown impaired the development of these MT bundles and the epithelial cell specific columnar shape. Rescue experiments revealed that the N-terminal MT-binding region was indispensable for restoring these defects of the knockdown cells. MT regrowth assays indicated that MTCL1 was not required for the initial radial growth of MTs from the apical centrosome, but was essential for the accumulation of non-centrosomal MTs to the sublateral regions. Interestingly, MTCL1 recruited a subpopulation of PAR-1b to the apicobasal MT bundles, and its interaction with PAR-1b was required for MTCL1-dependent development of the apicobasal MT bundles. These results suggest that MTCL1 mediates the epithelial cell-specific reorganization of non-centrosomal MTs through its MT-crosslinking activity, and cooperates with PAR-1b to maintain the correct temporal balance between dynamic and stable MTs within the apicobasal MT bundles.

Trans-synaptic interaction of GluRdelta2 and Neurexin through Cbln1 mediates synapse formation in the cerebellum

Elucidation of molecular mechanisms that regulate synapse formation is required for the understanding of neural wiring, higher brain functions, and mental disorders. Despite the wealth of in vitro information, fundamental questions about how glutamatergic synapses are formed in the mammalian brain remain unanswered. Glutamate receptor (GluR) delta2 is essential for cerebellar synapse formation in vivo. Here, we show that the N-terminal domain (NTD) of GluRdelta2 interacts with presynaptic neurexins (NRXNs) through cerebellin 1 precursor protein (Cbln1). The synaptogenic activity of GluRdelta2 is abolished in cerebellar primary cultures from Cbln1 knockout mice and is restored by recombinant Cbln1. Knockdown of NRXNs in cerebellar granule cells also hinders the synaptogenic activity of GluRdelta2. Both the NTD of GluRdelta2 and the extracellular domain of NRXN1beta suppressed the synaptogenic activity of Cbln1 in cerebellar primary cultures and in vivo. These results suggest that GluRdelta2 mediates cerebellar synapse formation by interacting with presynaptic NRXNs through Cbln1.

Possible involvement of arylhydrocarbon receptor variants in TCDD-induced thymic atrophy and XRE-dependent transcriptional activity in Wistar Hannover GALAS rats

Wistar Hannover Global Alliance for Laboratory Animal Standardization (WH GALAS) rats have been distributed for international standardization of preclinical and toxicological research. Han/Wistar (Kuopio) rats are exceptionally resistant to acute toxicities caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and mediated by the aryl hydrocarbon receptor (AhR), and they have a mutated AhR, named AhR(hw/hw). We found that the WH GALAS rat has either of the three AhR allele, AhR(wt/wt), AhRwt/hw and AhRhw/hw. We administered TCDD (0, 5 and 10 microg/kg) to Long-Evans (L-E) rats having AhR(wt/wt) and two WH GALAS rat strains having either AhR(wt/wt) or AhR(hw/hw), and examined the weights of their body, liver and thymus 168 hr post-administration. WH GALAS AhR(hw/hw) strain was more resistant to TCDD-induced effects on thymus weight than L-E and WH GALAS AhR(wt/wt) strains. In order to study differences in susceptibility of thymic atrophy among the strains, we examined CYP1A1 mRNA and AhR protein levels between L-E and WH GALAS strains. However, no significant difference was observed in the amount of AhR protein or CYP1A1 mRNA in the thymus. Next, we carried out in vitro assays to examine the transactivation activities of AhR variants and found that the AhR deletion variant (AhRdv) transcribed from AhR(hw/hw) significantly enhanced transactivation activity of the synthesized xenobiotic response element. All AhR variants similarly suppressed the growth of Jurkat T cells upon TCDD exposure. This study suggests that WH GALAS rat having different AhR alleles is an interesting experimental animal model but should be utilized with caution for preclinical research on chemicals having AhR agonistic activities.

The amino-terminal domain of glutamate receptor delta2 triggers presynaptic differentiation

Glutamate receptor (GluR) delta2 selectively expressed in cerebellar Purkinje cells plays key roles in synapse formation, long-term depression and motor learning. We propose that GluRdelta2 regulates synapse formation by making a physical linkage between the active zone and postsynaptic density. To examine the issue, GluRdelta2-transfected 293T cells were cultured with cerebellar neurons. We found numerous punctate signals for presynaptic markers on the surface of 293T cells expressing GluRdelta2. The presynaptic specializations induced by GluRdelta2 were capable of exo- and endocytosis as indicated by FM1-43 dye labeling. Replacement of the extracellular N-terminal domain (NTD) of GluRdelta2 with that of the AMPA receptor GluRalpha1 abolished the inducing activity. The NTD of GluRdelta2 fused to the immunoglobulin constant region successfully induced the accumulation of presynaptic specializations on the surface of beads bearing the fusion protein. These results suggest that GluRdelta2 triggers presynaptic differentiation by direct interaction with presynaptic components through the NTD.

Ser515 phosphorylation-independent regulation of cytosolic phospholipase A2alpha (cPLA2alpha) by calmodulin-dependent protein kinase: possible interaction with catalytic domain A of cPLA2alpha

Calmodulin (CaM)-dependent protein kinase (CaM kinase) is proposed to regulate the type alpha of cytosolic phospholipase A(2) (cPLA(2)alpha), which has a dominant role in the release of arachidonic acid (AA), via phosphorylation of Ser515 of the enzyme. However, the exact role of CaM kinase in the activation of cPLA(2)alpha has not been well established. We investigated the effects induced by transfection with mutant cPLA(2)alpha and inhibitors for CaM and CaM kinase on the Ca(2+)-stimulated release of AA and translocation of cPLA(2)alpha. The mutation of Ser515 to Ala (S515A) did not change cPLA(2)alpha activity, although S228A and S505A completely and partially decreased the activity, respectively. Stimulation with hydrogen peroxide (H(2)O(2), 1 mM) and A23187 (10 microM) markedly released AA in C12 cells expressing S515A and wild-type cPLA(2)alpha, but the responses in C12-S505A, C12-S727A, and C12-S505A/S515A/S727A (AAA) cells were reduced. In HEK293T cells expressing cPLA(2)alpha, A23187 caused the translocation of the wild-type, the every mutants, cPLA(2)alpha-C2 domain, and cPLA(2)alpha-Delta397-749 lacking proposed phosphorylation sites such as Ser505 and Ser515. Treatment with inhibitors of CaM (W-7) and CaM kinase (KN-93) at 10 microM significantly decreased the release of AA in C12-cPLA(2)alpha cells and C12-S515A cells. KN-93 inhibited the A23187-induced translocation of the wild-type, S515A, AAA and cPLA(2)alpha-Delta397-749, but not cPLA(2)alpha-C2 domain. Our findings show a possible effect of CaM kinase on cPLA(2)alpha in a catalytic domain A-dependent and Ser515-independent manner.

TheC. elegansCBFβ homologue BRO-1 interacts with the Runx factor, RNT-1, to promote stem cell proliferation and self-renewal

In this report, we investigate the C. elegans CBFβ homologue,BRO-1. bro-1 mutants have a similar male-specific sensory ray loss phenotype to rnt-1 (the C. elegans homologue of the mammalian CBFβ-interacting Runx factors), caused by failed cell divisions in the seam lineages. Our studies indicate that BRO-1 and RNT-1 form a cell proliferation-promoting complex, and that BRO-1 increases both the affinity and specificity of RNT-1-DNA interactions. Overexpression of bro-1,like rnt-1, leads to an expansion of seam cell number and co-overexpression of bro-1 and rnt-1 results in massive seam cell hyperplasia. Finally, we find that BRO-1 appears to act independently of RNT-1 in certain situations. These studies provide new insights into the function and regulation of this important cancer-associated DNA-binding complex in stem cells and support the view that Runx/CBFβ factors have oncogenic potential.

Humanized anti-CD26 monoclonal antibody as a treatment for malignant mesothelioma tumors

PURPOSE

CD26 is a 110-kDa cell surface antigen with a role in tumor development. In this report, we show that CD26 is highly expressed on the cell surface of malignant mesothelioma and that a newly developed humanized anti-CD26 monoclonal antibody (mAb) has an inhibitory effect on malignant mesothelioma cells in both in vitro and in vivo experiments.

EXPERIMENTAL DESIGN

Using immunohistochemistry, 12 patients' surgical specimens consisting of seven malignant mesothelioma, three reactive mesothelial cells, and two adenomatoid tumors were evaluated for expression of CD26. The effects of CD26 on malignant mesothelioma cells were assessed in the presence of transfection of CD26-expressing plasmid, humanized anti-CD26 mAb, or small interfering RNA against CD26. The in vivo growth inhibitory effect of humanized anti-CD26 mAb was assessed in human malignant mesothelioma cell mouse xenograft models.

RESULTS

In surgical specimens, CD26 is highly expressed in malignant mesothelioma but not in benign mesothelial tissues. Depletion of CD26 by small interfering RNA results in the loss of adhesive property, suggesting that CD26 is a binding protein to the extracellular matrix. Moreover, our in vitro data indicate that humanized anti-CD26 mAb induces cell lysis of malignant mesothelioma cells via antibody-dependent cell-mediated cytotoxicity in addition to its direct anti-tumor effect via p27(kip1) accumulation. In vivo experiments with mouse xenograft models involving human malignant mesothelioma cells show that humanized anti-CD26 mAb treatment drastically inhibits tumor growth in tumor-bearing mice, resulting in enhanced survival.

CONCLUSIONS

Our data strongly suggest that humanized anti-CD26 mAb treatment may have potential clinical use as a novel cancer therapeutic agent in CD26-positive malignant mesothelioma.

Involvement of an Autocrine Stromal Cell–Derived Factor-1/CXCR4 System on the Distant Metastasis of Human Oral Squamous Cell Carcinoma

We have previously shown that a stromal cell-derived factor-1 (SDF-1; CXCL12)/CXCR4 system is involved in the establishment of lymph node metastasis, but not in that of distant metastasis, in oral squamous cell carcinoma (SCC). In this study, we investigated the role of the autocrine SDF-1/CXCR4 system, with a focus on distant metastasis in oral SCC cells. The immunohistochemical staining of SDF-1 and CXCR4 using primary oral SCCs and metastatic lymph nodes showed a significantly higher number of SDF-1-positive cases among the metastatic lymph nodes than among the primary oral SCCs, which was associated with a poor survival rate among those of the former group. The forced expression of SDF-1 in B88 cells, which exhibit functional CXCR4 and lymph node metastatic potential (i.e., the autocrine SDF-1/CXCR4 system), conferred enhanced cell motility and anchorage-independent growth potential onto the cells. Orthotopic inoculation of the transfectant into nude mice was associated with an increase in the number of metastatic lymph nodes and more aggressive metastatic foci in the lymph nodes. Furthermore, the SDF-1 transfectant (i.e., the autocrine SDF-1/CXCR4 system) exhibited dramatic metastasis to the lung after i.v. inoculation, whereas the mock transfectant (i.e., the paracrine SDF-1/CXCR4 system) did not. Under the present conditions, AMD3100, a CXCR4 antagonist, significantly inhibited the lung metastasis of the SDF-1 transfectant, ameliorated body weight loss, and improved the survival rate of tumor-bearing nude mice. These results suggested that, in cases of oral SCC, the paracrine SDF-1/CXCR4 system potentiates lymph node metastasis, but distant metastasis might require the autocrine SDF-1/CXCR4 system.

Easy stable transfection of a human cancer cell line by electrogene transfer with an Epstein–Barr virus-based plasmid vector

We report an easy and stable transfection technique using electrogene transfer with a nonviral Epstein-Barr (EB) virus-based vector. To achieve stable transfection of human breast cancer cells, we conducted electrogene transfer of an EB virus-based plasmid vector (reduced size of oriP) containing the enhanced green fluorescence protein (eGFP) gene. Because the EB virus-based vector exhibits high transfer efficiency and strong persistent transgene expression as a result of autonomous replication in human cells, and as Nucleofector electrogene transfer can achieve highly efficient gene transfection, this method is particularly suitable for generation of stably transfected cell lines.

Caveolin-1 triggers T-cell activation via CD26 in association with CARMA1

CD26 is a widely distributed 110-kDa cell surface glycoprotein with an important role in T-cell costimulation. We demonstrated previously that CD26 binds to caveolin-1 in antigen-presenting cells, and following exogenous CD26 stimulation, Tollip and IRAK-1 disengage from caveolin-1 in antigen-presenting cells. IRAK-1 is then subsequently phosphorylated to up-regulate CD86 expression, resulting in subsequent T-cell proliferation. However, it is unclear whether caveolin-1 is a costimulatory ligand for CD26 in T-cells. Using soluble caveolin-1-Fc fusion protein, we now show that caveolin-1 is the costimulatory ligand for CD26, and that ligation of CD26 by caveolin-1 induces T-cell proliferation and NF-kappaB activation in a T-cell receptor/CD3-dependent manner. We also demonstrated that the cytoplasmic tail of CD26 interacts with CARMA1 in T-cells, resulting in signaling events that lead to NF-kappaB activation. Ligation of CD26 by caveolin-1 recruits a complex consisting of CD26, CARMA1, Bcl10, and IkappaB kinase to lipid rafts. Taken together, our findings provide novel insights into the regulation of T-cell costimulation via the CD26 molecule.

A designed curved DNA segment that is a remarkable activator of eukaryotic transcription

To identify artificial DNA segments that can stably express transgenes in the genome of host cells, we built a series of curved DNA segments that mimic a left-handed superhelical structure. Curved DNA segments of 288 bp (T32) and 180 bp (T20) were able to activate transcription from the herpes simplex virus thymidine kinase (tk) promoter by approximately 150-fold and 70-fold, respectively, compared to a control in a transient transfection assay in COS-7 cells. The T20 segment was also able to activate transcription from the human adenovirus type 2 E1A promoter with an 18-fold increase in the same assay system, and also activated transcription from the tk promoter on episomes in COS-7 cells. We also established five HeLa cell lines with genomes containing T20 upstream of the transgene promoter and control cell lines with T20 deleted from the transgene locus. Interestingly, T20 was found to activate transcription in all the stable transformants, irrespective of the locus. This suggests that the T20 segment may allow stable expression of transgenes, which is of importance in many fields, and may also be useful for the construction of nonviral vectors for gene therapy.

A severe de novo methylation of episomal vectors by human ES cells

Episomal vectors can allow efficient genetic modification of cells and have the potential advantage of avoiding chromosomal position of integration effects. Here we explore the use of an Epstein-Barr virus-based episomal vector with human embryonic stem (ES) cells, and find high initial transfection rates, but a rapid loss of reporter gene expression. Similar to mouse ES cells, human ES cells express high levels of the de novo DNA methyltransferases, and we detected dramatic CpG methylation and minor non-CpG methylation on the episomes recovered from the human ES cells 7 days after the transfection, which was not present on the same episome recovered from 293 cells. Interestingly, the oriP region of the episomes was relatively excluded from this methylation. These findings define some of the limitations of using episomal vectors with human ES cells and offer a unique platform for analyzing epigenetic gene silencing in human ES cells.

Crk-associated substrate lymphocyte type regulates transforming growth factor-beta signaling by inhibiting Smad6 and Smad7

Crk-associated substrate lymphocyte type (Cas-L) is a 105 kDa docking protein with diverse functional properties, including regulation of cell division, proliferation, migration and adhesion. Cas-L is also involved in beta1 integrin- or antigen receptor-mediated signaling in B and T cells. In the present study, we demonstrate that Cas-L potentiates transforming growth factor-beta (TGF-beta) signaling pathway by interacting with Smad6 and Smad7. Immunoprecipitation experiments reveal that single domain deletion of full-length Cas-L completely abolishes its docking function with Smad6 and Smad7, suggesting that the natural structure of Cas-L is necessary for its association with Smad6 and Smad7. On the other hand, both N-terminal and C-terminal deletion mutants of Smad6 and Smad7 still retain their docking ability to Cas-L, suggesting that Smad6 and Smad7 possess several binding motifs to Cas-L. Moreover, Cas-L interaction with Mad-homology (MH)2 domain, but not with MH1 domain of Smad6 or Smad7, ameliorates TGF-beta-induced signaling pathway. Finally, depletion of Cas-L by small-interfering RNA oligo attenuates TGF-beta-induced growth inhibition of Huh-7 cells, with a concomitant reduction in phosphorylation of Smad2 and Smad3. These results strongly suggest that Cas-L is a potential regulator of TGF-beta signaling pathway.

Lgl mediates apical domain disassembly by suppressing the PAR-3-aPKC-PAR-6 complex to orient apical membrane polarity

The basolateral tumor suppressor protein Lgl is important for the regulation of epithelial cell polarity and tissue morphology. Recent studies have shown a physical and functional interaction of Lgl with another polarity-regulating protein machinery, the apical PAR-3-aPKC-PAR-6 complex, in epithelial cells. However, the mechanism of Lgl-mediated regulation of epithelial cell polarity remains obscure. By an siRNA method, we here show that endogenous Lgl is required for the disassembly of apical membrane domains in depolarizing MDCK cells induced by Ca2+ depletion. Importantly, this Lgl function is mediated by the suppression of the apical PAR-3-aPKC-PAR-6 complex activity. Analysis using 2D- or 3D-cultured cells in collagen gel suggests the importance of this suppressive regulation of Lgl on the collagen-mediated re-establishment of apical membrane domains and lumen formation. These results indicate that basolateral Lgl plays a crucial role in the disassembly of apical membrane domains to induce the orientation of apical membrane polarity, which is mediated by the suppression of apical PAR-3-aPKC-PAR-6 complex activity.

CD26 mediates dissociation of Tollip and IRAK-1 from caveolin-1 and induces upregulation of CD86 on antigen-presenting cells

CD26 is a T-cell costimulatory molecule with dipeptidyl peptidase IV enzyme activity in its extracellular region. We have previously reported that the addition of recombinant soluble CD26 resulted in enhanced proliferation of human T lymphocytes induced by the recall antigen tetanus toxoid (TT) via upregulation of CD86 on monocytes and that caveolin-1 was a binding protein of CD26, and the CD26-caveolin-1 interaction resulted in caveolin-1 phosphorylation (p-cav-1) as well as TT-mediated T-cell proliferation. However, the mechanism involved in this immune enhancement has not yet been elucidated. In the present work, we perform experiments to identify the molecular mechanisms by which p-cav-1 leads directly to the upregulation of CD86. Through proteomic analysis, we identify Tollip (Toll-interacting protein) and IRAK-1 (interleukin-1 receptor-associated serine/threonine kinase 1) as caveolin-1-interacting proteins in monocytes. We also demonstrate that following stimulation by exogenous CD26, Tollip and IRAK-1 dissociate from caveolin-1, and IRAK-1 is then phosphorylated in the cytosol, leading to the upregulation of CD86 via activation of NF-kappaB. Binding of CD26 to caveolin-1 therefore regulates signaling pathways in antigen-presenting cells to induce antigen-specific T-cell proliferation.

Electrogene transfer of an Epstein-Barr virus-based plasmid replicon vector containing the diphtheria toxin A gene suppresses mammary carcinoma growth in SCID mice

Experimental mammary cancer therapy in mice was conducted using electrogene transfer of a non-viral EBV-based plasmid vector (reduced size of the oriP gene), containing the DT-A gene. Because the EBV-based plasmid vector exhibits high transfer efficiency and strong persistent transgene expression due to autonomous replication in human cells, it is particularly suitable as a tool for cancer gene therapy. In vitro, 79% of MDA-MB231 human mammary carcinoma cells died as a result of the EBV-based vector containing DT-A (pEB-DTA) by 48 h after transfection. DNA synthesis was also significantly decreased as compared to levels with a control vector. In vivo, mammary tumors induced by inoculation of SCID mice with MDA-MB231 cells were subsequently treated by direct injection of pEB-DTA vector or pEB-GFP vector as a control once a week for 5 weeks. After each injection, the tumors were subjected to in vivo electrogene transfer. Significantly reduced tumor volumes were observed for the pEB-DTA group in experimental week 1 and thereafter throughout the study. At necropsy, strong and extent expression of GFP was still observed in tumors receiving pEB-GFP 6 days after the last electrogene transfer. The ratio of histological necrotic area to viable area was significantly increased in the pEB-DTA-treated tumors, where levels of apoptosis were significantly higher than those observed in the pEB-GFP group. DNA synthesis showed a tendency to decrease in the pEB-DTA group but this was not significant. The incidence and multiplicity of lung metastasis were similar between the groups. There was also no difference in the density of microvessels between groups. We therefore conclude that the EBV-based plasmid vector system combined with in vivo electrogene transfer can result in efficient gene transfection and that the non-viral replicon vector containing DT-A suppresses tumor growth due to apoptotic cell death in this model.

Identification of the Hepatic Efflux Transporters of Organic Anions Using Double-Transfected Madin-Darby Canine Kidney II Cells Expressing Human Organic Anion-Transporting Polypeptide 1B1 (OATP1B1)/Multidrug Resistance-Associated Protein 2, OATP1B1/Multidrug Resistance 1, and OATP1B1/Breast Cancer Resistance Protein

Until recently, it was generally believed that the transport of various organic anions across the bile canalicular membrane was mainly mediated by multidrug resistance-associated protein 2 (MRP2/ABCC2). However, a number of new reports have shown that some organic anions are also substrates of multidrug resistance 1 (MDR1/ABCB1) and/or breast cancer resistance protein (BCRP/ABCG2), implying MDR1 and BCRP could also be involved in the biliary excretion of organic anions in humans. In the present study, we constructed new double-transfected Madin-Darby canine kidney II (MDCKII) cells expressing organic anion-transporting polypeptide 1B1 (OATP1B1)/MDR1 and OATP1B1/BCRP, and we investigated the transcellular transport of four kinds of organic anions, estradiol-17beta-d-glucuronide (EG), estrone-3-sulfate (ES), pravastatin (PRA), and cerivastatin (CER), to identify which efflux transporters mediate the biliary excretion of compounds using double-transfected cells. We observed the vectorial transport of EG and ES in all the double transfectants. MRP2 showed the highest efflux clearance of EG among these efflux transporters, whereas BCRP-mediated clearance of ES was the highest in these double transfectants. In addition, two kinds of 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors, CER and PRA, were also substrates of all these efflux transporters. The rank order of the efflux clearance of PRA mediated by each transporter was the same as that of EG, whereas the contribution of MDR1 to the efflux of CER was relatively greater than for PRA. This experimental system is very useful for identifying which transporters are involved in the biliary excretion of organic anions that cannot easily penetrate the plasma membrane.

The first CH domain of affixin activates Cdc42 and Rac1 through alphaPIX, a Cdc42/Rac1-specific guanine nucleotide exchanging factor

Rho GTPases, Cdc42 and Rac1, play pivotal roles in cell migration by efficiently integrating cell-substrate adhesion and actin polymerization. Although it has been suggested that integrins stimulate these Rho GTPases via some of integrin binding proteins such as focal adhesion kinase (FAK) and paxillin, the precise molecular mechanism is largely unknown. In this study, we showed that the over-expression of RP1 corresponding to the first CH domain (CH1) of affixin, an integrin-linked kinase (ILK)-binding protein, induced a significant actin reorganization in MDCK cells by activating Cdc42/Rac1. Affixin full length and RP1 co-immunoprecipitated with alphaPIX, a Cdc42/Rac1-specific guanine nucleotide exchanging factor (GEF), and they co-localized at the tips of lamellipodia in motile cells. The involvement of alphaPIX in the RP1-induced Cdc42 activation was demonstrated by the significant dominant negative effect of a point mutant of alphaPIX, alphaPIX (L383R, L384S), lacking GEF activity. Our data strongly support that ILK and affixin provide a novel signalling pathway that links integrin signalling to Cdc42/Rac1 activation.

CD26 up-regulates expression of CD86 on antigen-presenting cells by means of caveolin-1

CD26 is a T cell costimulatory molecule with dipeptidyl peptidase IV activity in its extracellular region. We previously reported that recombinant soluble CD26 enhanced T cell proliferation induced by the recall antigen tetanus toxoid (TT). However, the mechanism involved in this enhancement is not yet elucidated. We now demonstrate that CD26 binds Caveolin-1 on antigen-presenting cells, and that residues 201-211 of CD26 along with the serine catalytic site at residue 630 contribute to binding to caveolin-1 scaffolding domain. In addition, after CD26-caveolin-1 interaction on TT-loaded monocytes, caveolin-1 is phosphorylated, which links to activate NF-kappaB, followed by up-regulation of CD86. Finally, reduced caveolin-1 expression on monocytes inhibits CD26-mediated CD86 up-regulation and abrogates CD26 effect on TT-induced T cell proliferation. Taken together, these results strongly suggest that CD26-caveolin-1 interaction plays a role in the up-regulation of CD86 on TT-loaded monocytes and subsequent engagement with CD28 on T cells, leading to antigen-specific T cell activation.

aPKC Acts Upstream of PAR-1b in Both the Establishment and Maintenance of Mammalian Epithelial Polarity

BACKGROUND

aPKC and PAR-1 are required for cell polarity in various contexts. In mammalian epithelial cells, aPKC localizes at tight junctions (TJs) and plays an indispensable role in the development of asymmetric intercellular junctions essential for the establishment and maintenance of apicobasal polarity. On the other hand, one of the mammalian PAR-1 kinases, PAR-1b/EMK1/MARK2, localizes to the lateral membrane in a complimentary manner with aPKC, but little is known about its role in apicobasal polarity of epithelial cells as well as its functional relationship with aPKC.

RESULTS

We demonstrate that PAR-1b is essential for the asymmetric development of membrane domains of polarized MDCK cells. Nonetheless, it is not required for the junctional localization of aPKC nor the formation of TJs, suggesting that PAR-1b works downstream of aPKC during epithelial cell polarization. On the other hand, aPKC phosphorylates threonine 595 of PAR-1b and enhances its binding with 14-3-3/PAR-5. In polarized MDCK cells, T595 phosphorylation and 14-3-3 binding are observed only in the soluble form of PAR-1b, and okadaic acid treatment induces T595-dependent dissociation of PAR-1b from the lateral membrane. Furthermore, T595A mutation induces not only PAR-1b leakage into the apical membrane, but also abnormal development of membrane domains. These results suggest that in polarized epithelial cells, aPKC phosphorylates PAR-1b at TJs, and in cooperation with 14-3-3, promotes the dissociation of PAR-1b from the lateral membrane to regulate PAR-1b activity for the membrane domain development.

CONCLUSIONS

These results suggest that mammalian aPKC functions upstream of PAR-1b in both the establishment and maintenance of epithelial cell polarity.

Negative feedback loop in T-cell activation through MAPK-catalyzed threonine phosphorylation of LAT

Mitogen-activated protein kinase (MAPK) cascades are involved in a variety of cellular responses including proliferation, differentiation, and apoptosis. We have developed an expression screening method to detect in vivo substrates of MAPKs in mammalian cells, and identified a membrane protein, linker for activation of T cells (LAT), as an MAPK target. LAT, an adapter protein essential for T-cell signaling, is phosphorylated at its Thr 155 by ERK in response to T-cell receptor stimulation. Thr 155 phosphorylation reduces the ability of LAT to recruit PLCgamma1 and SLP76, leading to attenuation of subsequent downstream events such as [Ca2+]i mobilization and activation of the ERK pathway. Our data reveal a new role for MAPKs in a negative feedback loop in T-cell activation via threonine phosphorylation of LAT.

A Constitutively Active Arylhydrocarbon Receptor Induces Growth Inhibition of Jurkat T Cells through Changes in the Expression of Genes Related to Apoptosis and Cell Cycle Arrest

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to suppress T cell-dependent immune reactions through the activation of the arylhydrocarbon receptor (AhR). Our previous findings suggest that TCDD inhibits the activation and subsequent expansion of T cells following antigen stimulation in mice, leading to a decreased level of T cell-derived cytokines involved in antibody production. In the present study, we investigated the effects of activated AhR on T cells by transiently expressing a constitutively active AhR (CA-AhR) mutant in AhR-null Jurkat T cells. In agreement with our previous findings, CA-AhR markedly inhibited the growth of Jurkat T cells. The inhibited cell growth was found to be concomitant with both an increase in the annexin V-positive apoptotic cells and the accumulation of cells in the G(1) phase. The growth inhibition was also shown to be mediated by both xenobiotic response element (XRE)-dependent and -independent mechanisms, because an A78D mutant of the CA-AhR, which lacks the ability of XRE-dependent transcription, partially inhibited the growth of Jurkat T cells. Furthermore, we demonstrated that CA-AhR induces expression changes in genes related to apoptosis and cell cycle arrest. These expression changes were shown to be solely mediated in an XRE-dependent manner, because the A78D mutant of the CA-AhR did not induce them. To summarize, these results suggest that AhR activation causes apoptosis and cell cycle arrest, especially through expression changes in genes related to apoptosis and cell cycle arrest by the XRE-dependent mechanism, leading to the inhibition of T cell growth.

An RNA-dependent protein kinase is involved in tunicamycin-induced apoptosis and Alzheimer's disease

Various types of stress, such as disruption of calcium homeostasis, inhibition of protein glycosylation and reduction of disulfide bonds, result in accumulation of misfolded proteins in the endoplasmic reticulum (ER). The initial cellular response involves removal of such proteins by the ER, but excessive and/or long-term stress results in apoptosis. In this study, we used a randomized ribozyme library and ER stress-mediated apoptosis (tunicamycin-induced apoptosis) in SK-N-SH human neuroblastoma cells as a selective phenotype to identify factors involved in this process. We identified a double-stranded RNA-dependent protein kinase (PKR) as one of the participants in this process. The level of nuclear PKR was elevated, but the level of cytoplasmic PKR barely changed in tunicamycin-treated SK-N-SH cells. Furthermore, tunicamycin also raised levels of phosphorylated PKR in the nucleus. We also detected the accumulation of phosphorylated PKR in the nuclei of autopsied brain tissues in Alzheimer's disease. Thus, PKR might play a role in ER stress-induced apoptosis and in Alzheimer's disease.

Expression of Cytosolic Phospholipase A2α in Murine C12 Cells, a Variant of L929 Cells, Induces Arachidonic Acid Release in Response to Phorbol Myristate Acetate and Ca2+ Ionophores, but Not to Tumor Necrosis Factor-α

Tumor necrosis factor-alpha (TNFalpha)-induced cell death is regulated through the release of arachidonic acid (AA) by group IVA cytosolic phospholipase A2 (cPLA2alpha) in the murine fibroblast cell line L929. However, the signaling pathway by which TNFalpha activates cPLA2alpha remained to be solved. We examined AA release in L929 cells, in a variant of L929 (C12 cells) lacking cPLA2alpha, and in C12 cells transfected with cPLA2alpha expression vectors. In transient and stable clones of C12 cells expressing cPLA2alpha, Ca2+ ionophore A23187 and phorbol myristate acetate (PMA) stimulated AA release within 90 min, although no response to TNFalpha was observed within 6 h. These results suggest that C12 cells may lack the components necessary for TNFalpha-induced AA release, in addition to cPLA2alpha. PMA is known to stimulate AA release via phosphorylation of Ser505 in cPLA2alpha by activating extracellular signal-regulated kinases (ERK1/2). However, PMA-induced AA release from C12 cells expressing mutant cPLA2alpha S505A (mutation of Ser505 to Ala), which is not phosphorylated by ERK1/2, was similar to that from L929 cells and C12 cells expressing wild-type cPLA2alpha. The role of Ser505 phosphorylation in AA release induced by PMA is also discussed.

Orexin receptor type-1 couples exclusively to pertussis toxin-insensitive G-proteins, while orexin receptor type-2 couples to both pertussis toxin-sensitive and -insensitive G-proteins

Signal transduction pathways of orexin receptors were examined using a nerve-like cell line transfected with orexin receptor type-1 (OX1R) and orexin receptor type-2 (OX2R). Forskolin-stimulated cyclic adenosine 3,5-monophosphate (cAMP) accumulation in OX2R-expressing cells was inhibited by orexin in a dose-dependent manner, and the effect was abolished by pretreatment with pertussis toxin (PTX). The inhibitory effect of orexin on forskolin-stimulated cAMP accumulation was not observed in OX1R-expressing cells. Administration of orexin to these cells resulted in a transient increase of intracellular calcium concentration ([Ca(2+)](i)). Orexin-stimulated increases in [Ca(2+)](i) in OX1R- or OX2R-expressing cells were not affected by the PTX pretreatment. These observations suggest that OX1R couples exclusively to PTX-insensitive G-proteins, while OX2R couples to both PTX-sensitive and -insensitive G-proteins. To examine the relative contributions of these G-proteins in OX2R-mediated activation of neurons, we used histaminergic tuberomammillary nucleus neurons, in which OX2R is abundantly expressed. We found that a phospholipase C (PLC)-inhibitor, U73122, inhibits orexin-mediated neuronal activation, but PTX showed no effect on it. This suggests that although OX2R couples to multiple G-proteins, activation of neurons by orexins through OX2R is mediated via a PTX-insensitive, PLC dependent pathway.

Current and future strategies for the treatment of malignant brain tumors

Glioblastoma (GB) is the most common subtype of primary brain tumor in adults. These tumors are highly invasive, very aggressive, and often infiltrate critical neurological areas within the brain. The mean survival time after diagnosis of GB has remained unchanged during the last few decades, in spite of advances in surgical techniques, radiotherapy, and also chemotherapy; patients' survival ranges from 9 to 12 months after initial diagnosis. In the same time frame, with our increasing understanding and knowledge of the physiopathology of several cancers, meaningful advances have been made in the treatment and control of several cancers, such as breast, prostate, and hematopoietic malignancies. Although a number of the genetic lesions present in GB have been elucidated and our understanding of the progressions of this cancer has increased dramatically over the last few years, it has not yet been possible to harness this information towards developing effective cures. In this review, we will focus on the classical ways in which GB is currently being treated, and will introduce a novel therapeutic modality, i.e., gene therapy, which we believe will be used in combination with classical treatment strategies to prolong the life-span of patients and to ultimately be able to control and/or cure these brain tumors. We will discuss the use of several vector systems that are needed to introduce the therapeutic genes within either the tumor mass, if these are not resectable, or the tumor bed, after successful tumor resection. We also discuss different therapeutic modalities that could be exploited using gene therapy, i.e., conditional cytotoxic approach, direct cytotoxicity, immunotherapy, inhibition of angiogenesis, and the use of pro-apoptotic genes. The advantages and disadvantages of each of the current vector systems available to transfer genes into the CNS are also discussed. With the advances in molecular techniques, both towards the elucidation of the physiopathology of GB and the development of novel, more efficient and less toxic vectors to deliver putative therapeutic genes into the CNS, it should be possible to develop new rationale and effective therapeutic approaches to treat this devastating cancer.

Long-term expression of a transferred gene in Epstein-Barr virus transformed human B cells

Delivering a gene into the Epstein-Barr virus (EBV)-transformed B cells is useful in studying effects of the gene on B-cell functions. However, although people have been able to efficiently transfer genes into and get them expressed in B-lympho blastoid cells for a time probably long enough to kill the cells using vectors harbouring oriP, the expression time of the delivered gene is not long enough in order to study the gene function in B cells. To solve this problem, we constructed an adeno-associated virus (AAV) plasmid pAGX(+) based on plasmids pSub201 and pRc/CMV. We developed and packaged recombinant AAV (rAAV) expression vectors containing an antisense or a sense DNA fragment of 6A8 cDNA encoding a human alpha-mannosidase, or an antisense fragment of 5D4 cDNA encoding a human cell membrane protein, or EYFP DNA. EBV-transformed B cell SKW6 and 3D5 were transduced with those rAAV or the mock. Transduction with the rAAV-EYFP showed an infection frequency of 64 +/- 3.5% and 58 +/- 6.2% for SKW6 and 3D5 cell, respectively. Genomic polymerase chain reaction (PCR) for neoR gene indicated an integration of the transferred gene into the host DNA. After being cultured and propagated for over 12 months, the cells were detected for the expression of the transferred gene. The RT-PCR, enzymatic assay and Con A binding test demonstrated an inhibition of 6A8 alpha-mannosidase in both SKW6 and 3D5 cells transduced with the antisense 6A8 DNA. Immunofluorescence staining with monoclonal antibodies (MoAb) 5D4 showed a reduction of the 5D4 protein expression on both the cells transduced with the antisense 5D4 DNA. The DNA fragmentation assay showed a resistance of the cells with 6A8 alpha-mannosidase inhibition to apoptosis induction by anti-Fas antibody. The data indicate that the AAV vector pAGX(+) can efficiently introduce genes into EBV-transformed B cells and the delivered gene can be expressed in the cells for more than 12 months which may be long enough for the study of gene functions in B cells.

Two distinct action mechanisms of immunophilin-ligand complexes for the blockade of T-cell activation

The immunosuppressive effects of cyclosporin A (CsA) and FK506 are mediated through binding to immunophilins. Here we show that FK506-FKBP complex suppresses the activation of JNK and p38 pathways at a level upstream of mitogen-activated protein kinase (MAPK) kinase kinase (MAPKK-K) besides the calcineurin-NFAT pathway. A238L, a viral gene product that binds to immunophilin, also blocks activation of both pathways. In contrast, direct inhibitors of calcineurin, Cabin 1 and FR901725, suppress the activation of NFAT but not the JNK or p38 pathway. We further demonstrate that co-expression of a constitutively active NFAT and a constitutively active MEKK1 renders the interleukin-2 promoter in Jurkat T lymphocytes resistant to CsA and FK506, whereas Jurkat cells expressing a constitutively active NFAT alone are still sensitive to CsA or FK506. Therefore, CsA and FK506 exert their immunosuppressive effects through targeting both the calcineurin-dependent NFAT pathway and calcineurin-independent activation pathway for JNK and p38.