Kit signaling through PI 3-kinase and Src kinase pathways: an essential role for Rac1 and JNK activation in mast cell proliferation

The receptor tyrosine kinase Kit plays critical roles in hematopoiesis, gametogenesis and melanogenesis. In mast cells, Kit receptor activation mediates several cellular responses including cell proliferation and suppression of apoptosis induced by growth factor deprivation and gamma-irradiation. Kit receptor functions are mediated by kinase activation, receptor autophosphorylation and association with various signaling molecules. We have investigated the role of phosphatidylinositol 3'-kinase (PI 3-kinase) and Src kinases in Kit-mediated cell proliferation and suppression of apoptosis induced both by factor deprivation and irradiation in bone marrow-derived mast cells (BMMC). Analysis of Kit-/- BMMC expressing mutant Kit receptors and the use of pharmacological inhibitors revealed that both signaling pathways contribute to these Kit-mediated responses and that elimination of both pathways abolishes them. We demonstrate that the PI 3-kinase and Src kinase signaling pathways converge to activate Rac1 and JNK. Analysis of BMMC expressing wild-type and dominant-negative mutant forms of Rac1 and JNK revealed that the Rac1/JNK pathway is critical for Kit ligand (KL)-induced proliferation of mast cells but not for suppression of apoptosis. In addition, KL was shown to inhibit sustained activation of JNK induced by gamma-irradiation and concomitant irradiation-induced apoptosis.     

An essential role for gamma interferon in innate resistance to Shigella flexneri infection

The purpose of this experiment was to study endurance performance and substrate storage and utilization in fat- or carbohydrate-fed rats. Ninety-nine rats were randomly divided into three groups and over 4 wk were fed either a carbohydrate-rich [CHO; 10% total energy content in the diet (E%) fat, 20 E% protein, 70 E% carbohydrate] diet or one of two fat-rich diets (65 E% fat, 20 E% protein, 15 E% carbohydrate) containing either saturated (Sat) or monounsaturated fatty acids (Mono). Each dietary group was randomly assigned to a trained (6 days/wk, progressive to 60 min, 28 m/min at a 10% incline) or a sedentary group. Rats were killed either before or after a treadmill endurance run to exhaustion. Training increased endurance (206%), but diet composition did not affect endurance in either trained or sedentary rats. beta-Hydroxyacyl-CoA dehydrogenase activity was increased in fat-fed but not carbohydrate-fed rats (P < 0.05). Respiratory exchange ratio during the initial phase of exercise was lower after the Mono compared with the Sat diet (P < 0. 05) and higher after the CHO than the Sat diet (P < 0.05). Thus adaptation to a high-fat diet containing a moderate amount of carbohydrates did not induce enhanced endurance in either trained or untrained rats; however, substrate utilization was modulated by both amount and type of dietary fat during the initial stage of exercise in trained and sedentary rats.     

Identification of the SH3 domain of GAP as an essential sequence for Ras-GAP-mediated signaling

Guanosine triphosphatase activating protein (GAP) is an essential component of Ras signaling pathways. GAP functions in different cell types as a deactivator and a transmitter of cellular Ras signals. A domain (amino acids 275 to 351) encompassing the Src homology region 3 (SH3) of GAP was found to be essential for GAP signaling. A monoclonal antibody was used to block germinal vesicle breakdown (GVBD) induced by the oncogenic protein Ha-ras Lys12 in Xenopus oocytes. The monoclonal antibody, which was found to recognize the peptide containing amino acids 275 to 351 within the amino-terminal domain of GAP, did not modify the stimulation of the Ha-Ras-GTPase by GAP. Injection of peptides corresponding to amino acids 275 to 351 and 317 to 326 blocked GVBD induced by insulin or by Ha-Ras Lys12 but not that induced by progesterone. These findings confirm that GAP is an effector for Ras in Xenopus oocytes and that the SH3 domain is essential for signal transduction.     

An essential role for phosphatidylinositol transfer protein in phospholipase C-mediated inositol lipid signaling

Transmembrane signaling by the phospholipase C-beta (PLC-beta) pathway is known to require at least three components: the receptor, the G protein, and the PLC. Recent studies have indicated that if the cytosol is allowed to leak out of HL60 cells, then G protein-stimulated PLC activity is greatly diminished, indicating an essential role for a cytosolic component(s). We now report the complete purification of one component based on its ability to reconstitute GTP gamma S-mediated PLC activity and identify it as the phosphatidylinositol transfer protein (PI-TP). Based on the in vitro effects of PI-TP, we surmise that it is involved in transporting PI from intracellular compartments for conversion to PI bisphosphate (PIP2) prior to hydrolysis by PLC-beta 2/PLC-beta 3, the endogenous PLC isoforms present in these cells.     

Urokinase and the intestinal mucosa: evidence for a role in epithelial cell turnover

The enzyme nitric oxide synthase catalyzes the oxidation of the amino acid L-arginine to L-citrulline and nitric oxide in an NADPH-dependent reaction. Nitric oxide plays a critical role in signal transduction pathways in the cardiovascular and nervous systems and is a key component of the cytostatic/cytotoxic function of the immune system. Characterization of nitric oxide synthase substrates and cofactors has outlined the broad details of the overall reaction and suggested possibilities for chemical steps in the reaction; however, the molecular details of the reaction mechanism are still poorly understood. Recent evidence suggests a role for the reduced bound pterin in the first step of the reaction--the hydroxylation of L-arginine.     

Development of essential thrombocythemia in a patient treated with interferon alfa and pentostatin for hairy cell leukemia

A patient is reported who developed essential thrombocythemia after successful treatment for hairy cell leukemia. He was initially treated with interferon alfa and subsequently relapsed within one year of treatment. His diagnosis was reconfirmed and then treated with Pentostatin. Six years after treatment he had a progressive increase in the platelet count and was diagnosed as essential thrombocythemia. Second cancers including various types of hematological malignancy have been reported in patients with hairy cell leukemia treated with chemotherapy or interferon alfa. These malignancies may represent either a new clonal disorder or a complication of drug treatment. This is the first report of a chronic myeloproliferative disorder following successful treatment of hairy cell leukemia.     

Dominant negative mutants of TRAF3 reveal an important role for the coiled coil domains in cell death signaling by the lymphotoxin-beta receptor

Ligation of the lymphotoxin-beta receptor (LTbetaR) recruits tumor necrosis factor receptor-associated factor-3 (TRAF3) and initiates cell death in HT29 adenocarcinoma cells. The minimal receptor binding domain (TRAF-C) defined by two hybrid analyses is not sufficient for direct recruitment to the ligated receptor. A series of TRAF3 deletion mutants reveal that a subregion of the coiled coil motif is required for efficient recruitment to the LTbetaR. Furthermore, the ability of TRAF3 to self-associate maps to an adjacent subregion. A TRAF3 deletion mutant that lacks the N-terminal zinc RING and zinc finger motifs, but retains the coiled coil and TRAF-C motifs, competitively displaces endogenous TRAF3 from the LTbetaR. A second TRAF3 mutant that lacks the receptor binding domain, yet contains the TRAF3 self-association domain, prevents TRAF3 homodimers from being recruited to the LTbetaR. Both of these mutants have a dominant negative effect on cell death and demonstrate that the recruitment of TRAF3 oligomers is necessary to initiate signal transduction that activates the cell death pathway.     

The zeta isoform of protein kinase C controls interleukin-2-mediated proliferation in a murine T cell line: evidence for an additional role of protein kinase C epsilon and beta

In order to address a role of protein kinase C in signal transduction through interleukin-2, interleukin-4, and interleukin-9 receptors, we took advantage of the availability of a selective protein kinase C inhibitor, GF109203X, and the availability of TS1 beta and TS1 alpha beta cell lines which can be maintained in interleukin-2, interleukin-4, or interleukin-9 independently. In this report we report that inhibition of protein kinase C activity by GF109203X does not block interleukin-4- or interleukin-9-dependent proliferation and, on the contrary, does block interleukin-2-dependent proliferation, suggesting that interleukin-4 and interleukin-9 do not use signal transduction pathways mediated by protein kinase C and that the common gamma chain of interleukin-2, interleukin-4, and interleukin-9 receptors is not responsible per se for the activation of protein kinase C through interleukin-2 receptor. Moreover, GF109203X induces apoptosis in cells cultured in interleukin-2 but not in interleukin-4 or interleukin-9. Using antisense oligonucleotides, we report that the zeta and epsilon protein kinase C isoforms are involved in signaling through high-affinity interleukin-2 receptor and beta and zeta are involved in signaling through intermediate-affinity interleukin-2 receptor. Taken together, our data indicate that activation of the zeta, beta, and epsilon protein kinase C isoforms is an important step in interleukin-2-mediated proliferation.     

Bezafibrate-induced myopathy: no evidence for defects in muscle metabolism

The authors report 8 cases of coverage of the inguinal and perineal areas with the inferiorly based rectus abdominis myocutaneous flap. This flap seems to be the technique of choice for coverage of such defects. The design of the flap can be explained by the low venous pressure zone concept.     

The role of ErbB receptor signaling in cell fate decisions by cortical progenitors: evidence for a biased, lineage-based responsiveness to different ligands

We recently identified the required collaborative signaling of TGFalpha and collagen type IV to regulate cell fate choice in the cerebral cortex, measured by the expression of the limbic system associated membrane protein (LAMP) by nonlimbic, sensorimotor progenitors. We show that activation of different members of the erbB receptor family can similarly modulate the specification of cortical area fate. The region of the cerebral wall from which progenitor cells arise does not influence the response to the neuregulin-1 or TGFalpha, but a subpopulation of progenitors is not competent to express LAMP in response to neuregulin-1. The heterogeneity in the responsiveness by progenitors to the two growth factors is reflected in the expression of different repertoires of erbB receptors. Using clonal analysis, we demonstrate that there may be a lineage-dependent mechanism regulating the ability of neuronal progenitors to respond to specific inductive cues that control cell fate.     

Identification of the region of alpha-catenin that plays an essential role in cadherin-mediated cell adhesion

alpha-Catenin is an intrinsic component of the cadherin adhesion complex and is a 102-kDa protein with multiple interaction sites, including homodimerization sites, and binding sites for beta- and gamma-catenin (plakoglobin), alpha-actinin, and actin. Besides the binding to beta- or gamma-catenin, it is unknown, however, which interaction is critical for the function of cadherins. By expressing a series of E-cadherin-alpha-catenin chimeric molecules on leukemia cells (K562), we have identified the region of alpha-catenin that confers aggregation inducing activity to nonfunctional tail-less E-cadherin. The region has been mapped to the carboxyl-terminal 295 amino acids of alpha-catenin. Consistent with this result, expression in alpha-catenin-deficient cells (DLD-1/Delta alpha) of a mutant alpha-catenin molecule consisting of the amino-terminal beta-/gamma-catenin-binding site and the carboxyl-terminal cell adhesion region identified in the above experiments induced E-cadherin-mediated cell aggregation and compaction. Cells expressing E-cadherin chimeric molecules with the homologous carboxyl-terminal region of vinculin, which contains the actin-binding site of vinculin, did not, however, aggregate as strongly as ones expressing E-cadherin-alpha-catenin chimeric molecules.     

Hardness controlled enzymes and electronegativity controlled enzymes: role of an absolute hardness-electronegativity (eta-chi) activity diagram as a coordinate for biological activities

We found that absolute hardness-absolute electronegativity (eta-chi) activity diagrams play an important role as a new coordinate of bioactivity in structure-activity relationships. In this paper, the eta-chi activity diagram, focusing on the molecular mechanism of bioactive compounds is used to discuss two major problems. First, the potency of bioactivities for xenobiotics such as polychlorinated dibenzo-p-dioxins (PCDDs) 3 and polychlorinated biphenyls (PCBs) 4, were found to be strongly related to their absolute hardness (eta). Second, the antibacterial activity of new quinolones such as norfloxacin 1 and enoxacin 2, was found to be strongly related to their absolute electronegativity (chi). These findings predict at least two chemical properties for a hardness-controlled or electronegativity-controlled enzyme.     

Chemical modification of bacterial luciferase with ethoxyformic anhydride: evidence for an essential histidyl residue

Bacterial luciferase is a heteropolymeric protein (alphabeta) that catalyses the conversion of chemical energy to light by oxidation of a reduced flavin mononucleotide and a long chain aliphatic aldehyde. Elucidation of the specific amino acid residues involved in the enzymatic reaction is essential for understanding the mechanisms of the bioluminescent reaction. Luciferase has been found to be inactivated by ethoxyformic anhydride with a second-order rate constant of 146 M-1 min-1 at pH 6.1 and 0 degrees C with a concomitant increase in absorbance at 240 nm due to formation of ethoxyformylhistidyl derivatives. Activity could be restored by hydroxylamine and the pH curve of inactivation indicated the involvement of a residue having a pKa of 6.8. Both substrates, FMNH2 and aldehyde, protected the enzyme against inactivation, suggesting that the modification occurred at or near the active site. Incorporation of [14C]ethoxyformyl groups in luciferase indicated that inactivation resulted from the modification of about three histidyl residues, one histidine being found on the alpha subunit and two on the beta subunit. Hybridization experiments, in which ethoxyformylluciferase, alphambetam, was complemented with native subunits, alpha or beta, showed that the hybrid alphambetam, has the same activity as alphambetam whereas the activity of the hybrid alphabetam, was close to that of the reconstituted luciferase alphabeta. The results indicate that modification of only one histidyl residue on the alpha subunit inactivates luciferase and suggest that this histidyl residue plays an essential role in the mechanism of the bacterial bioluminescent reaction.     

Differential activities of secreted lymphotoxin-alpha3 and membrane lymphotoxin-alpha1beta2 in lymphotoxin-induced inflammation: critical role of TNF receptor 1 signaling

Lymphotoxin (LT, LT alpha, TNF beta) is a member of the immediate TNF family that also includes TNF-alpha and lymphotoxin-beta (LT beta). LT is produced by activated lymphocytes and functions as either a secreted homotrimer or a membrane-associated heterotrimer that includes the transmembrane protein LT beta. Secreted LT alpha3 can bind to two cell surface receptors, TNFR1 and TNFR2, while the membrane-bound heterotrimer LT alpha1beta2 has been shown to interact with a distinct receptor, LT betaR. LT alpha induces inflammation at the sites of expression of a rat insulin promoter-driven lymphotoxin (RIPLT) transgene in the pancreas and kidney. To determine the role of the various ligands and their receptors in LT-induced inflammation, mice deficient in either TNFR1, TNFR2, or LT beta were crossed to RIPLT-transgenic mice. Our results indicate that LT alpha-induced inflammation is dependent on the interaction of LT alpha3 with TNFR1, and there is no obvious role for TNFR2, since in its absence, LT alpha-induced inflammation is quantitatively and qualitatively similar to that seen in the wild type. However, the absence of LT beta results in accentuated infiltration of the kidney with an increase in the proportion of memory cells in the infiltrate. These data show a crucial role for the secreted LT alpha3 signaling via TNFR1 in LT alpha-induced inflammation, and a separate and distinct role for the membrane LT alpha1beta2 form in this inflammatory process.     

mraY is an essential gene for cell growth in Escherichia coli

The synthesis of the murein precursor lipid I is performed by MraY. We have shown that mraY is an essential gene for cell growth. Cells depleted of MraY first swell and then lyse. The expression of mraY DNA in vitro produces a 40-kDa polypeptide detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.