Acetazolamide inhibits the recovery from triethyl tin intoxication: Putative role of carbonic anhydrase in dehydration of central myelin

The vacuolar degeneration of central myelin was produced in Sprague-Dawley rats by oral administration of triethyl tin. The wet weight of brain stems which seems to reflect the degree of accumulation of water increased during the administration of the toxin, whereas the activity of 2, 3-cyclic nucleotide 3-phosphodiesterase altered less remarkably. When TET was withdrawn from the drinking water, the rats showed a dramatic clinical improvement along with reduction in wet weight of brain stems. Treatment with acetazolamide following TET inhibited the clinical improvement and reduction in wet weight of brain stems. The present results indicates that central myelin has plasticity in recovering from the vacuolar degeneration by removing the accumulated fluid and carbonic anhydrase is possibly involved in the dehydration, of myelin in such a recovery phase.     

Brassinosteroid-Induced Bending of the Leaf Lamina of Dwarf Rice Seedlings: An Auxin-Mediated Phenomenon

A synthetic brassinosteroid (BR), 2,3,22ß,23ß-tetrahydroxy-24ß-methyl-B-homo7-oxa-5-cholestan-6-one, an isomer of the growth promoter brassinolide,when applied to seedlings of dwarf rice Oryza sativa var. Tan-ginbozuand Waito-C, induced a significant bending of the second leaflamina at 100 ng/plant and higher dosages. Promotion of thesecond leaf sheath elongation, the characteristic response ofdwarf rice varieties to gibberellins, was significantly butmodestly enhanced by BR at a dosage of 10,000 ng/plant, fiveorders of magnitude higher than the minimal dosage responseto GA₃. Gibberellin A₃ had no significant effect on the bendingof the second leaf lamina, nor did any synergism exist betweenBR and GA₃ in leaf lamina bending or leaf sheath elongation.Neither ethylene nor (2-chloroethyl)phosphonic acid (ethephon)caused the bending of the second leaf lamina, and neither synergizedthe BR effect. However, IAA and -naphthaleneacetic acid causedsignificant bending at 5,000 ng/plant, and both auxins significantlysynergized the effect of BR on the bending, IAA being effectiveat 500 ng/ plant in this regard. The antiauxins, 2,3,5-triiodobenzoicacid (TIBA) and -(p-chlorophenoxy)isobutyric acid (PCIB) completelynullified both the BR-induced bending and the BR$IAA-synergizedbending. The BR-induced bending response may thus be mediatedthrough endogenous auxin. (Received May 11, 1982; Accepted August 25, 1982)     

Redistribution of intramembrane particles of human erythrocytes induced by HVJ (Sendai virus): A prerequisite for the virus-induced cell fusion

Aggregation of intramembrane particles of human erythrocytes was found to be induced by HVJ (Sendai virus) under conditions which lead to cell fusion. Degree of polyerythrocyte formation was compared under a variety of conditions with extent of cluster formation observed with the same preparations. Both structural changes of the membranes, ie, fusion and clustering of the particles, behaved very similarly under widely different virus-to-cell ratios and over the time course of cell fusion. Furthermore, by inclusion of high concentrations of antispectrin antibodies within the ghosts, inhibition of clustering of intramembrane particles and hindrance of virus-induced cell fusion were found to occur simultaneously. Antibodies by themselves did not induce aggregation of particles under isotonic conditions, whereas particle clustering could be induced under hypotonic conditions at antibody concentrations causing partial cross-linking of spectrin molecules. In conclusion, clustering of intramembrane particles seems to be required for virus-induced fusion of human erythrocytes.     

Cutting edge: a novel Toll/IL-1 receptor domain-containing adapter that preferentially activates the IFN-beta promoter in the Toll-like receptor signaling

MyD88 is a Toll/IL-1 receptor (TIR) domain-containing adapter common to signaling pathways via Toll-like receptor (TLR) family. However, accumulating evidence demonstrates the existence of a MyD88-independent pathway, which may explain unique biological responses of individual TLRs, particularly TLR3 and TLR4. TIR domain-containing adapter protein (TIRAP)/MyD88 adapter-like, a second adapter harboring the TIR domain, is essential for MyD88-dependent TLR2 and TLR4 signaling pathways, but not for MyD88-independent pathways. Here, we identified a novel TIR domain-containing molecule, named TIR domain-containing adapter inducing IFN-beta (TRIF). As is the case in MyD88 and TIRAP, overexpression of TRIF activated the NF-kappaB-dependent promoter. A dominant-negative form of TRIF inhibited TLR2-, TLR4-, and TLR7-dependent NF-kappaB activation. Furthermore, TRIF, but neither MyD88 nor TIRAP, activated the IFN-beta promoter. Dominant-negative TRIF inhibited TLR3-dependent activation of both the NF-kappaB-dependent and IFN-beta promoters. TRIF associated with TLR3 and IFN regulatory factor 3. These findings suggest that TRIF is involved in the TLR signaling, particularly in the MyD88-independent pathway.     

Laminin-10/11 and fibronectin differentially prevent apoptosis induced by serum removal via phosphatidylinositol 3-kinase/Akt- and MEK1/ERK-dependent pathways

Cell adhesion to the extracellular matrix inhibits apoptosis, but the molecular mechanisms underlying the signals transduced by different matrix components are not well understood. Here, we examined integrin-mediated antiapoptotic signals from laminin-10/11 in comparison with those from fibronectin, the best characterized extracellular adhesive ligand. We found that the activation of protein kinase B/Akt in cells adhering to laminin-10/11 can rescue cell apoptosis induced by serum removal. Consistent with this, wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase, or ectopic expression of a dominant-negative mutant of Akt selectively accelerated cell death upon serum removal. In contrast to laminin-10/11, fibronectin rescued cells from serum depletion-induced apoptosis mainly through the extracellular signal-regulated kinase pathway. Cell survival on fibronectin but not laminin was significantly reduced by treatment with PD98059, a specific inhibitor of mitogen- or extracellular signal-regulated kinase kinase-1 (MEK1) and by expression of a dominant-negative mutant of MEK1. Laminin-10/11 was more potent than fibronectin in preventing apoptosis induced by serum depletion. These results, taken together, demonstrate laminin-10/11 potency as a survival factor and demonstrate that different extracellular matrix components can transduce distinct survival signals through preferential activation of subsets of multiple integrin-mediated signaling pathways.     

Cross-talk between integrin α6β4 and insulin-like growth factor-1 receptor (IGF1R) through direct α6β4 binding to IGF1 and subsequent α6β4-IGF1-IGF1R ternary complex formation in anchorage-independent conditions

Integrin αvβ3 plays a role in insulin-like growth factor-1 (IGF1) signaling (integrin-IGF1 receptor (IGF1R) cross-talk). The specifics of the cross-talk are, however, unclear. In a current model, "ligand occupancy" of αvβ3 (i.e. the binding of extracellular matrix proteins) enhances signaling induced by IGF1 binding to IGF1R. We recently reported that IGF1 directly binds to αvβ3 and induces αvβ3-IGF1-IGF1R ternary complex formation. Consistently, the integrin binding-defective IGF1 mutant (R36E/R37E) is defective in inducing ternary complex formation and IGF signaling, but it still binds to IGF1R. Like αvβ3, integrin α6β4 is overexpressed in many cancers and is implicated in cancer progression. Here, we discovered that α6β4 directly bound to IGF1, but not to R36E/R37E. Grafting the β4 sequence WPNSDP (residues 167-172), which corresponds to the specificity loop of β3, to integrin β1 markedly enhanced IGF1 binding to β1, suggesting that the WPNSDP sequence is involved in IGF1 recognition. WT IGF1 induced α6β4-IGF1-IGF1R ternary complex formation, whereas R36E/R37E did not. When cells were attached to matrix, exogenous IGF1 or α6β4 expression had little or no effect on intracellular signaling. When cell-matrix adhesion was reduced (in poly(2-hydroxyethyl methacrylate-coated plates), IGF1 induced intracellular signaling and enhanced cell survival in an α6β4-dependent manner. Also IGF1 enhanced colony formation in soft agar in an α6β4-dependent manner. These results suggest that IGF binding to α6β4 plays a major role in IGF signaling in anchorage-independent conditions, which mimic the in vivo environment, and is a novel therapeutic target.     

Basement membrane assembly of the integrin α8β1 ligand nephronectin requires Fraser syndrome-associated proteins

Dysfunction of the basement membrane protein QBRICK provokes Fraser syndrome, which results in renal dysmorphogenesis, cryptophthalmos, syndactyly, and dystrophic epidermolysis bullosa through unknown mechanisms. Here, we show that integrin α8β1 binding to basement membranes was significantly impaired in Qbrick-null mice. This impaired integrin α8β1 binding was not a direct consequence of the loss of QBRICK, which itself is a ligand of integrin α8β1, because knock-in mice with a mutation in the integrin-binding site of QBRICK developed normally and do not exhibit any defects in integrin α8β1 binding. Instead, the loss of QBRICK significantly diminished the expression of nephronectin, an integrin α8β1 ligand necessary for renal development. In vivo, nephronectin associated with QBRICK and localized at the sublamina densa region, where QBRICK was also located. Collectively, these findings indicate that QBRICK facilitates the integrin α8β1-dependent interactions of cells with basement membranes by regulating the basement membrane assembly of nephronectin and explain why renal defects occur in Fraser syndrome.     

siRNA-mediated inhibition of endogenous Huntington disease gene expression induces an aberrant configuration of the ER network in vitro

Huntingtin is a ubiquitously expressed cytoplasmic protein encoded by the Huntington disease (HD) gene, in which a CAG expansion induces an autosomal dominant progressive neurodegenerative disorder; however, its biological function has not been completely elucidated. Here, we report for the first time that short interfering RNA (siRNA)-mediated inhibition of endogenous Hdh (a mouse homologue of huntingtin) gene expression induced an aberrant configuration of the endoplasmic reticulum (ER) network in vitro. Studies using immunofluorescence microscopy with several ER markers revealed that the ER network appeared to be congregated in various types of cell lines transfected with siRNA directed against Hdh, but not with other siRNAs so far tested. Other subcellular organelles and structures, including the nucleus, Golgi apparatus, mitochondria, lysosomes, microtubules, actin cytoskeletons, cytoplasm, lipid rafts, and plasma membrane, exhibited normal configurations. Western blot analysis of cellular prion protein (PrP(C)) revealed normal glycosylation, which is a simple marker of post-translational modification in the ER and Golgi compartments, and immunofluorescence microscopy detected no altered subcellular distribution of PrP(C) in the post-ER compartments. Further investigation is required to determine whether the distorted ER network, i.e., loss of the huntingtin function, participates in the development of HD.