Overexpression of OsKTN80a,a katanin P80 ortholog,caused the repressed cell elongation and stalled cell division mediated by microtubule apparatus defects in primary root in Oryza sativa

Katanin, a microtubule-severing enzyme, consists of two subunits：the catalytic subunit P60, and the regulatory subunit P80. In several species, P80 functions in meiotic spindle organization, the flagella biogenesis, the neuronal development, and the male gamete production. However, the P80 function in higher plants remains elusive. In this study, we found that there are three katanin P80 orthologs （OsKTN80a, OsKTN80b, and OsKTN80c） in Oryza sativa L. Overexpression of OsKTN80a caused the retarded root growth of rice seedlings. Further investigation indicates that the retained root growth was caused by the repressed cell elongation in the elongation zone and the stalled cytokinesis in the division zone in the root tip. The in vivo examination suggests that OsKTN80a acts as a microtubule stabilizer. We＆amp;nbsp;prove that OsKTN80a, possibly associated with OsKTN60, is involved in root growth via regulating the cell elongation and division.     

Cortactin, an 80/85-kilodalton pp60src substrate, is a filamentous actin-binding protein enriched in the cell cortex

Two related cellular proteins, p80 and p85 (cortactin), become phosphorylated on tyrosine in pp60src-transformed cells and in cells stimulated with certain growth factors. The amino-terminal half of cortactin is comprised of multiple copies of an internal, tandem 37- amino acid repeat. The carboxyl-terminal half contains a distal SH3 domain. We report that cortactin is an F-actin-binding protein. The binding to F-actin is specific and saturable. The amino-terminal repeat region appears to be both necessary and sufficient to mediate actin binding, whereas the SH3 domain had no apparent effect on the actin- binding activity. Cortactin, present in several different cell types, is enriched in cortical structures such as membrane ruffles and lamellipodia. The properties of cortactin indicate that it may be important for microfilament-membrane interactions as well as transducing signals from the cell surface to the cytoskeleton. We suggest the name cortactin, reflecting the cortical subcellular localization and its actin-binding activity.     

Identification and characterization of a long isoform of human IFT80, IFT80-L

Intraflagellar transport (IFT) proteins are evolutionarily conserved throughout all ciliated organisms and are essential for the assembly and maintenance of cilia. IFT80, a component of the IFT complex, was linked recently to a human developmental disorder, Jeune asphyxiating thoracic dystrophy. We report here identification and characterization of a human IFT80 long isoform (namely IFT80-L), the carboxyl terminus of which shares the protein sequence of IFT80. Sequence analysis indicates that IFT80-L is likely an evolutionarily merged product of genes IFT80 and TRIM59, a RING finger gene we reported previously. Expression analysis of IFT80-L demonstrates that IFT80-L is ubiquitously expressed in humans. By using the nerve growth factor-induced cell differentiation assays, we reveal that IFT80-L is highly expressed in the rapidly proliferating cells but not in differentiated cells, which withdraw from the cell cycle. Our findings suggest that IFT80-L, like other IFT proteins, plays an important role in cell proliferation and differentiation.     

Mapping of a cell-binding domain in the cell adhesion molecule gp80 of Dictyostelium discoideum

At the aggregation stage of Dictyostelium discoideum development, a cell surface glycoprotein of Mr 80,000 (gp80) has been found to mediate the EDTA-resistant type of cell-cell adhesion via homophilic interaction (Siu, C.-H., A. Cho, and A. H. C. Choi. 1987. J. Cell Biol. 105:2523-2533). To investigate the structure-function relationships of gp80, we have isolated full length cDNA clones for gp80 and determined the DNA sequence. The deduced structure of gp80 showed three major domains. An amino-terminal globular domain composed of the bulk of the protein is supported by a short stalk region, which is followed by a membrane anchor at the carboxy terminus. Structural analysis suggested that the cell-binding domain of gp80 resides within the globular domain near the amino terminus. To investigate the relationship of the cell-binding activity to this region of the polypeptide, three protein A/gp80 (PA80) gene fusions were constructed using the expression vector pRIT2T. These PA80 fusion proteins were assayed for their ability to bind to aggregation stage cells. Binding of 125I-labeled fusion proteins PA80I (containing the Val123 to Ile514 fragment of gp80) and PA80II (Val123 to Ala258) was dosage dependent and could be inhibited by precoating cells with the cell cohesion-blocking mAb 80L5C4. On the other hand, there was no appreciable binding of PA80III (Ile174 to Ile514) to cells. Reassociation of cells was significantly inhibited in the presence of PA80I or PA80II. In addition, 125I-labeled PA80II exhibited homophilic interaction with immobilized PA80I, PA80II, or gp80. The results of these studies lead to the mapping of a cell-binding domain in the region between Val123 and Leu173 of gp80 and provide direct evidence that the cell-binding activity of gp80 resides in the protein moiety.     

Compound 48/80, a calmodulin antagonist, inhibits ion-porter function in plant roots

A rather specific inhibitor of calmodulin-regulated functions, compound 48/80. inhibited ³⁶Cl⁻, ⁸⁶Rb⁺ and ²²Na⁺ absorption by Hordeum vulgare, Phaseolus mungo and Zea mays roots. The compound did not inhibit plasmalemma or tonoplast Mg:²-ATPase activity; neither did it inhibit or uncouple respiration, or affect ATP content and seemed also not to cause depolarization of the membrane potential of roots cells. Compound 48/80 inhibited the ΔpH-mediated Cl⁻-H⁺ symport in ATP-depleted roots.     

CD80 expression on B cells regulates murine T follicular helper development, germinal center B cell survival, and plasma cell generation

Germinal center (GC) B cells and T follicular helper (T(FH)) cells interact in the production of high-affinity long-lived plasma cells (PCs) and memory B cells, although the mechanisms regulating the formation of these long-lived populations remain unclear. Because CD80 is one of the few markers shared by human and murine memory B cells, we investigated its role in the development of GCs, memory cells, and PCs. In CD80-deficient mice, fewer long-lived PCs were generated upon immunization compared with that in B6 controls. In concert, the absence of CD80 resulted in an increase in apoptotic GC B cells during the contraction phase of the GC. CD80(-/-) mice had fewer T(FH) cells compared with that of B6, and residual T(FH) cells failed to mature, with decreased ICOS and PD-1 expression and decreased synthesis of IL-21 mRNA. Mixed bone marrow chimeras demonstrated a B cell-intrinsic requirement for CD80 expression for normal T(FH) cell and PC development. Therefore, B cell expression of CD80 plays a critical role in regulating B-T interactions in both early and late GC responses. This, in turn, results in impaired ability to produce long-lived PCs. These data provide new insights into the development of GCs and Ab-forming cells and the functions of CD80 in humoral immunity.     

Mutations affecting a surface glycoprotein, gp80, of Dictyostelium discoideum.

We isolated two independent mutations in Dictyostelium discoideum that result in the absence of the antigenic determinant recognized by monoclonal antibody E28D8. This antibody reacts with a post-translational modification on the surface glycoprotein gp80 and several other proteins. Both of the mutations occur in the same locus, modB, which was mapped to linkage group VI. The modB mutations result in sufficient alteration of gp80 that it is absent or unrecognizable by two-dimensional gel electrophoresis. Strains carrying modB mutations exhibit "contact sites A"-mediated cell-cell adhesion although more weakly than do wild-type strains and develop to fruiting bodies carrying viable spores. Although gp80 has been implicated in the mechanism of cell-cell adhesion in D. discoideum, it is clear from the behavior of these mutant strains that the determinant on gp80 recognized by E28D8 is not necessary for either morphogenesis or reduced EDTA-resistant adhesion.     

Molecular cloning of F4/80-like-receptor, a seven-span membrane protein expressed differentially by dendritic cell and monocyte-macrophage subpopulations

A novel dendritic cell (DC) surface molecule termed F4/80-like-receptor (FIRE) has been selected based on its differential expression between DC subsets. The gene encoding FIRE has been cloned and sequenced, and mAbs specific for FIRE have been produced. FIRE is a seven-transmembrane-spanning molecule with two epidermal growth factor-like domains in the extracellular region. It is a novel member of the epidermal growth factor/transmembrane-7 protein subfamily and shows similarity to the macrophage marker F4/80. FIRE is expressed by CD8- DC, but not by CD8+ DC, and it is down-regulated on DC activation. It is expressed by blood monocytes and by some tissue macrophages, but not by most macrophage cell lines or by lymphoid cells. FIRE is a useful marker of myeloid cells with a DC developmental potential.     

Haemoglobin G-Szuhu, beta80 Asn-Lys, in the homozygous state in a patient with abetalipoproteinaemia.

An 11-year-old Jewish girl of Turkish extraction with abetalipoproteinaemia was found to be homozygous for haemoglobin Szuhu (beta80 Asn leads to Lys). Except for the abnormal haemoglobin, no other haematological or biochemical abnormalities were found in her consanguineous parents and one sister. In the propositus, erythrocyte morphology showed the acanthocytosis known to be in association with abetalipoproteinaemia. Increased autohaemolysis was also found, which reverted to normal after treatment with vitamin E. This case represents the first reported association of abetalipoproteinaemia with an abnormal haemoglobin, and the first homozygous Hb G-Szuhu.     

Helicoverpa armigera nucleopolyhedrovirus ORF80 encodes a late, nonstructural protein

The Helicoverpa armigera nucleopolyhedrovirus (HearNPV) ORF80 (ha80) has 765 bp encoding a protein with approximately 254 amino acids and a predicted molecular weight of 30.8 kDa. Homologues of ha80 are found in most baculovirus sequences, including those from lepidopteran NPVs, lepidopteran granuloviruses (GVs), hymenopteran baculoviruses, and one dipteran baculovirus, yet their functions remain unclear. In this study we characterized ha80, and showed that it was transcribed late in infected host cells (HzAM1). The product of ha80 was a 31 kDa protein that was not a structural protein of budded virus (BV) or occlusion-derived virus (ODV) particles. Ha80 was first detected in the cytoplasm of infected HzAM1 cells at 12 h p.i., and was observed in the nucleus at later stages of infection, suggesting that it may be involved in transporting viral proteins into the host cell nucleus or play its roles in the nucleus.     

Mast cell degranulation mediates compound 48/80-induced hyperalgesia in mice

Mast cells mediate allergies, hypersensitivities, host defense, and venom neutralization. An area of recent interest is the contribution of mast cells to inflammatory pain. Here we found that specific, local activation of mast cells produced plantar hyperalgesia in mice. Basic secretagogue compound 48/80 induced plantar mast cell degranulation accompanied by thermal hyperalgesia, tissue edema, and neutrophil influx in the hindpaws of ND4 Swiss mice. Blocking mast cell degranulation, neutrophil extravasation, and histamine signaling abrogated these responses. Compound 48/80 also produced edema, pain, and neutrophil influx in WT C57BL/6 but not in genetically mast cell-deficient C57BL/6-Kit(W-sh)(/)(W-sh) mice. These responses were restored following plantar reconstitution with bone marrow-derived cultured mast cells.