T cells of atopic asthmatics preferentially infiltrate into human bronchial xenografts in SCID mice

T cells play an important role in the pathogenesis of bronchial asthma. However, it is not completely known how circulating lymphocytes infiltrate into the airways of asthmatic patients. Because SCID mice are unable to reject xenogenic transplants, many xenotransplant models using various human tissues have been developed. Therefore, to examine the interaction between bronchi and T lymphocytes of asthma, it may be possible to use the human bronchial xenograft and PBMC xenograft in SCID mice. We transplanted human bronchi into the subcutaneum of SCID mice and i.p. injected PBMCs that were obtained from patients with atopic asthma, atopic dermatitis and rheumatoid arthritis, and normal subjects (asthmatic, dermatitis, rheumatic, and normal huPBMC-SCID mice). There was no difference in the percentage of CD3-, CD4-, CD8-, CD25-, CD45RO-, CD103-, and cutaneous lymphocyte Ag-positive cells in PBMCs among the patients with asthma, dermatitis, rheumatoid arthritis, and normal subjects, and CD3-positive cells in peripheral blood of asthmatic, dermatitis, rheumatic, and normal huPBMC-SCID mice. The number of CD3-, CD4-, and CD8-positive cells in the xenografts of asthmatic huPBMC-SCID mice was higher than those of dermatitis, rheumatic, and normal huPBMC-SCID mice. IL-4 mRNA and IL-5 mRNA were significantly higher in the xenografts of asthmatic huPBMC-SCID mice than those in the xenografts of normal huPBMC-SCID mice, but there were no significant differences in the expressions of IL-2 mRNA or IFN-gamma mRNA between them. These findings suggest that T cells, especially Th2-type T cells, of asthmatics preferentially infiltrate into the human bronchi.     

Mammalian copper chaperone Cox17p has an essential role in activation of cytochrome C oxidase and embryonic development

Cox17p is essential for the assembly of functional cytochrome c oxidase (CCO) and for delivery of copper ions to the mitochondrion for insertion into the enzyme in yeast. Although this small protein has already been cloned or purified from humans, mice, and pigs, the function of Cox17p in the mammalian system has not yet been elucidated. In vitro biochemical data for mammalian Cox17p indicate that the copper binds to the sequence -KPCCAC-. Although mouse embryos homozygous for COX17 disruption die between embryonic days E8.5 and E10, they develop normally until E6.5. This phenotype is strikingly similar to embryos of Ctr1(-/-), a cell surface copper transporter, in its lethality around the time of gastrulation. COX17-deficient embryos exhibit severe reductions in CCO activity at E6.5. Succinate dehydrogenase activity and immunoreactivities for anti-COX subunit antibodies were normal in the COX17(-/-) embryos, indicating that this defect was not caused by the deficiency of other complexes and/or subunits but was caused by impaired CCO activation by Cox17p. Since other copper chaperone (Atox1 and CCS)-deficient mice show a more moderate defect, the disruption of the COX17 locus causes the expression of only the phenotype of Ctr1(-/-). We found that the activity of lactate dehydrogenase was also normal in E6.5 embryos, implying that the activation of CCO by Cox17p may not be essential to the progress of embryogenesis before gastrulation.     

Ligand-independent dimer formation of epidermal growth factor receptor (EGFR) is a step separable from ligand-induced EGFR signaling

Dimerization and phosphorylation of the epidermal growth factor (EGF) receptor (EGFR) are the initial and essential events of EGF-induced signal transduction. However, the mechanism by which EGFR ligands induce dimerization and phosphorylation is not fully understood. Here, we demonstrate that EGFRs can form dimers on the cell surface independent of ligand binding. However, a chimeric receptor, comprising the extracellular and transmembrane domains of EGFR and the cytoplasmic domain of the erythropoietin receptor (EpoR), did not form a dimer in the absence of ligands, suggesting that the cytoplasmic domain of EGFR is important for predimer formation. Analysis of deletion mutants of EGFR showed that the region between (835)Ala and (918)Asp of the EGFR cytoplasmic domain is required for EGFR predimer formation. In contrast to wild-type EGFR ligands, a mutant form of heparin-binding EGF-like growth factor (HB2) did not induce dimerization of the EGFR-EpoR chimeric receptor and therefore failed to activate the chimeric receptor. However, when the dimerization was induced by a monoclonal antibody to EGFR, HB2 could activate the chimeric receptor. These results indicate that EGFR can form a ligand-independent inactive dimer and that receptor dimerization and activation are mechanistically distinct and separable events.     

Sprouty1 and Sprouty2 provide a control mechanism for the Ras/MAPK signalling pathway

Sprouty (Spry) inhibits signalling by receptor tyrosine kinases; however, the molecular mechanism underlying this function has not been defined. Here we show that after stimulation by growth factors Spry1 and Spry2 translocate to the plasma membrane and become phosphorylated on a conserved tyrosine. Next, they bind to the adaptor protein Grb2 and inhibit the recruitment of the Grb2-Sos complex either to the fibroblast growth factor receptor (FGFR) docking adaptor protein FRS2 or to Shp2. Membrane translocation of Spry is necessary for its phosphorylation, which is essential for its inhibitor activity. A tyrosine-phosphorylated octapeptide derived from mouse Spry2 inhibits Grb2 from binding FRS2, Shp2 or mouse Spry2 in vitro and blocks activation of the extracellular-signal-regulated kinase (ERK) in cells stimulated by growth factor. A non-phosphorylated Spry mutant cannot bind Grb2 and acts as a dominant negative, inducing prolonged activation of ERK in response to FGF and promoting the FGF-induced outgrowth of neurites in PC12 cells. Our findings suggest that Spry functions in a negative feedback mechanism in which its inhibitor activity is controlled rapidly and reversibly by post-translational mechanisms.     

A synergistic effect of 2-ethyl-l-isopropoxycarbonyl-3-(4-tolylcarbamoyl) isourea with gibberellic acid on growth of rice seedlings

2-Ethyl-1-isopropoxycarbonyl-3-(4-tolylcarbamoyl)isourea [EITIU]stimulated both shoot and root growth of rice seedlings. Gibberellicacid [GA]-induced shoot elongation was further stimulated byEITIU, and the combined application of both compounds was shownto be distinctly synergistic. A similar synergistic action wasobserved in the growth of rice mesocotyls in the dark. The inhibitionof root growth caused by GA was overcome by combination withEITIU. The growth-stimulating activity of EITIU was not observedin lettuce hypocotyls. ¹ This paper is Part I in the series "Plant growth-regulatingactivities of isourea derivatives and related compounds." (Received February 7, 1976; )     

Labeling and measuring stressed mitochondria using a PINK1-based ratiometric fluorescent sensor

Mitochondria are essential organelles that carry out a number of pivotal metabolic processes and maintain cellular homeostasis. Mitochondrial dysfunction caused by various stresses is associated with many diseases such as type 2 diabetes, obesity, cancer, heart failure, neurodegenerative disorders, and aging. Therefore, it is important to understand the stimuli that induce mitochondrial stress. However, broad analysis of mitochondrial stress has not been carried out to date. Here, we present a set of fluorescent tools, called mito-Pain (mitochondrial PINK1 accumulation index), which enable the labeling of stressed mitochondria. Mito-Pain uses PTEN-induced putative kinase 1 (PINK1) stabilization on mitochondria and quantifies mitochondrial stress levels by comparison with PINK1-GFP, which is stabilized under mitochondrial stress, and RFP-Omp25, which is constitutively localized on mitochondria. To identify compounds that induce mitochondrial stress, we screened a library of 3374 compounds using mito-Pain and identified 57 compounds as mitochondrial stress inducers. Furthermore, we classified each compound into several categories based on mitochondrial response: depolarization, mitochondrial morphology, or Parkin recruitment. Parkin recruitment to mitochondria was often associated with mitochondrial depolarization and aggregation, suggesting that Parkin is recruited to heavily damaged mitochondria. In addition, many of the compounds led to various mitochondrial morphological changes, including fragmentation, aggregation, elongation, and swelling, with or without Parkin recruitment or mitochondrial depolarization. We also found that several compounds induced an ectopic response of Parkin, leading to the formation of cytosolic puncta dependent on PINK1. Thus, mito-Pain enables the detection of stressed mitochondria under a wide variety of conditions and provides insights into mitochondrial quality control systems.     

The polarity-inducing kinase Par-1 controls Xenopus gastrulation in cooperation with 14-3-3 and aPKC

Par (partitioning-defective) genes were originally identified in Caenorhabditis elegans as determinants of anterior/posterior polarity. However, neither their function in vertebrate development nor their action mechanism has been fully addressed. Here we show that two members of Par proteins, 14-3-3 (Par-5) and atypical PKC (aPKC), regulate the serine/threonine kinase Par-1 to control Xenopus gastrulation. We find first that Xenopus Par-1 (xPar-1) is essential for gastrulation but not for cell fate specification during early embryonic development. We then find that xPar-1 binds to 14-3-3 in an aPKC-dependent manner. Our analyses identify two aPKC phosphorylation sites in xPar-1, which are essential for 14-3-3 binding and for proper gastrulation movements. The aPKC phosphorylation-dependent binding of xPar-1 to 14-3-3 does not markedly affect the kinase activity of xPar-1, but induces relocation of xPar-1 from the plasma membranes to the cytoplasm. Finally, we show that Xenopus aPKC and its binding partner Xenopus Par-6 are also essential for gastrulation. Thus, our results identify a requirement of Par proteins for Xenopus gastrulation and reveal a novel interrelationship within Par proteins that may provide a general mechanism for spatial control of Par-1.     

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.     

CK2 controls multiple protein kinases by phosphorylating a kinase-targeting molecular chaperone, Cdc37

Cdc37 is a kinase-associated molecular chaperone whose function in concert with Hsp90 is essential for many signaling protein kinases. Here, we report that mammalian Cdc37 is a pivotal substrate of CK2 (casein kinase II). Purified Cdc37 was phosphorylated in vitro on a conserved serine residue, Ser13, by CK2. Moreover, Ser13 was the unique phosphorylation site of Cdc37 in vivo. Crucially, the CK2 phosphorylation of Cdc37 on Ser13 was essential for the optimal binding activity of Cdc37 toward various kinases examined, including Raf1, Akt, Aurora-B, Cdk4, Src, MOK, MAK, and MRK. In addition, nonphosphorylatable mutants of Cdc37 significantly suppressed the association of Hsp90 with protein kinases, while the Hsp90-binding activity of the mutants was unchanged. The treatment of cells with a specific CK2 inhibitor suppressed the phosphorylation of Cdc37 in vivo and reduced the levels of Cdc37 target kinases. These results unveil a regulatory mechanism of Cdc37, identify a novel molecular link between CK2 and many crucial protein kinases via Cdc37, and reveal the molecular basis for the ability of CK2 to regulate pleiotropic cellular functions.