Tyrosine phosphorylation in activated human neutrophils. Comparison of the effects of different classes of agonists and identification of the signaling pathways involved

The tyrosine phosphorylation responses initiated in human neutrophils by soluble and particulate agonists were characterized. Chemotactic factors, hematopoietic growth factors, and inflammatory microcrystals stimulated in a time- and concentration-dependent manner the tyrosine phosphorylation of distinct patterns of substrates: pp120, pp85, pp70, and pp60 in the case of chemotactic factors; pp155, pp130, pp120, pp85, pp60, and pp40 in the case of granulocyte macrophage-CSF; and pp130, pp120, pp70, and pp60 in the case of monosodium urate (MSU) crystals. Several of the single bands on one-dimensional blots (including pp40, pp70, and pp120) could be resolved into multiple spots on two-dimensional gels. The responses of several other chemotactic factors resembled those of FMLP. Cytokineplasts retained the capacity to respond to FMLP, granulocyte-macrophage-CSF, or MSU crystals with a stimulation of tyrosine phosphorylation, and contained the major substrates detected in intact neutrophils. Several unrelated tyrosine kinase inhibitors (herbimycin A, genistein, and erbstatin) strongly diminished the tyrosine phosphorylation response to chemotactic factors. Pertussis toxin abrogated the tyrosine phosphorylation response to FMLP, whereas protein kinase C (Ro 21-8220, chelerithryn) inhibitors were without effect. Chelation of intracellular calcium attenuated the tyrosine phosphorylation response to FMLP. These results indicate that G proteins play a crucial role in the coupling of chemotactic factor receptors to tyrosine phosphorylation and that this coupling occurs in parallel to that of phospholipase C. These results also underline the complexity of the transduction pathways implicated in the initiation of tyrosine phosphorylation.

Tyrosine phosphorylation in activated human neutrophils. Comparison of the effects of different classes of agonists and identification of the signaling pathways involved

The tyrosine phosphorylation responses initiated in human neutrophils by soluble and particulate agonists were characterized. Chemotactic factors, hematopoietic growth factors, and inflammatory microcrystals stimulated in a time- and concentration-dependent manner the tyrosine phosphorylation of distinct patterns of substrates: pp120, pp85, pp70, and pp60 in the case of chemotactic factors; pp155, pp130, pp120, pp85, pp60, and pp40 in the case of granulocyte macrophage-CSF; and pp130, pp120, pp70, and pp60 in the case of monosodium urate (MSU) crystals. Several of the single bands on one-dimensional blots (including pp40, pp70, and pp120) could be resolved into multiple spots on two-dimensional gels. The responses of several other chemotactic factors resembled those of FMLP. Cytokineplasts retained the capacity to respond to FMLP, granulocyte-macrophage-CSF, or MSU crystals with a stimulation of tyrosine phosphorylation, and contained the major substrates detected in intact neutrophils. Several unrelated tyrosine kinase inhibitors (herbimycin A, genistein, and erbstatin) strongly diminished the tyrosine phosphorylation response to chemotactic factors. Pertussis toxin abrogated the tyrosine phosphorylation response to FMLP, whereas protein kinase C (Ro 21-8220, chelerithryn) inhibitors were without effect. Chelation of intracellular calcium attenuated the tyrosine phosphorylation response to FMLP. These results indicate that G proteins play a crucial role in the coupling of chemotactic factor receptors to tyrosine phosphorylation and that this coupling occurs in parallel to that of phospholipase C. These results also underline the complexity of the transduction pathways implicated in the initiation of tyrosine phosphorylation.

Effect of hydrogen peroxide on cytoskeletal proteins of Drosophila cells: comparison with heat shock and other stresses

Hydrogen peroxide, which was shown to trigger the heat-shock response by activating the immediate binding of the heat-shock factor to DNA heat shock regulatory elements in the promoter of heat-shock genes of Drosophila cells, has also been reported to enhance the synthesis of actin. We show here that very short and transient H2O2 treatments, from 1 s to 2 min, are sufficient to induce an increase of actin synthesis. This increase becomes apparent 2 to 3 h after the short H2O2 treatment. It is inhibited if actinomycin D is present during the short H2O2 treatment. An increase of actin synthesis was also observed during the recovery period after two other stresses: reoxygenation after anoxia and ethanol treatment. The synthesis of two cytoskeletal proteins, tubulin and a 46-kDa insoluble protein of the intermediate filament fraction, was also slightly increased by H2O2 in Drosophila cells, but this increase was not actinomycin D-dependent. H2O2 does not provoke the translocation of the 46-kDa protein to the nuclear fraction as does heat shock. The very rapid stimulation of actin synthesis by H2O2 and the involvement of cytoskeletal elements in many stress situations suggest that actin may play a key role in the response to external stimuli.

Expression of Drosophila's 27 kDa heat shock protein into rodent cells confers thermal resistance

The role of hsp27, one of Drosophila melanogaster's small heat shock proteins, in the process of thermotolerance was investigated. The coding sequence of hsp27 was subcloned downstream of the human hsp27 promoter which has been shown to be constitutively expressed in Chinese hamster O23 cells. Cellular resistance to a thermal stress was measured two days after transfection by a survival assay following a 3.5 h heat treatment at 44 degrees C. Expression of Drosophila hsp27 was shown to confer thermal resistance to O23 cells in a manner which was dependent on the level of expression of this hsp. Immunoblot analysis confirmed that the thermal resistance was related to the expression of Drosophila hsp27 as none of the endogeneous hsps showed an increased level under these conditions.

Prosomes and heat shock complexes in Drosophila melanogaster cells

Prosomes and heat shock protein (HSP) complexes isolated from the cytoplasm of Drosophila cells in culture were biochemically and immunologically characterized. The two complexes were found to separate on sucrose gradients, allowing the analysis of their protein constituents by two-dimensional polyacrylamide gel electrophoresis and by reaction with anti-HSP sera and prosome-specific monoclonal antibodies. All of the prosomal proteins were found to be clearly distinct from the HSP; none of the prosomal proteins was synthesized de novo in heat shock. However, an antiprosome (anti-p27K) monoclonal antibody (mouse anti-duck) recognizing the Drosophila p29K prosomal protein allowed immunoprecipitation from a heat-shocked postmitochondrial supernatant of the crude HSP complex, including the low- and the high-molecular-weight components, in particular the 70 x 10(3)-molecular weight HSP. The highly purified small 16S HSP complex still contained this preexistent p29K prosomal protein, which thus also seems to be a metabolically stable constituent of the HSP complex. The significance of this structural and possibly functional relationship between prosomes and HSP, involving the highly ubiquitous and evolutionarily conserved prosomal protein p27/29K, remains to be elucidated.

Hydrogen peroxide (H2O2) induces actin and some heat-shock proteins in Drosophila cells

Drosophila cells of a clone derived from line Kc were treated with various concentrations of hydrogen peroxide (H2O2). The concentration of 10 mM was lethal, whereas concentrations of 1-100 microM did not affect cell viability, rate of multiplication or protein synthesis. The intermediate concentration of 1 mM H2O2 was used to study the response of the cells to an oxidative stress. We observed a transitory decrease of the global protein synthesis, which was accompanied by changes in the polypeptide pattern. There was a 2.5-fold increase of the synthesis of the heat-shock proteins 70-68 and 23. The most prominent response was a 6.5-fold increase of actin synthesis 3 h after a 1 mM H2O2 treatment. When aminotriazole (an inhibitor of catalase) was added in association with H2O2, the increase of actin synthesis became 8.5-fold. Experiments in which catalase was added at various times after H2O2 showed that a 10-min treatment with H2O2 was sufficient to induce actin and heat-shock protein synthesis 3 h later. H2O2 was shown to induce the transcriptional activation of an actin gene and of the heat-shock protein genes 70 and 23 within minutes. These results are coherent with the hypothesis that the byproducts of O2 reduction (the superoxide ion and hydrogen peroxide) could be inducers of the heat-shock response. Whether the increase of actin synthesis is a stress-related response, and the mode of action of H2O2 are discussed.

HSP 26 and 27 are phosphorylated in response to heat shock and ecdysterone in Drosophila melanogaster cells

Protein phosphorylation has been studied in Drosophila melanogaster 8.9 K cells following heat shock. By in vivo double labelling with [35S]-methionine and [32P]-orthophosphate, we observed that two proteins are newly phosphorylated among the 26,000-27,000 dalton heat-shock proteins group. These two proteins are also phosphorylated after ecdysterone treatment, albeit at a lower level. That this phosphorylation event is induced by two different treatments, i.e. ecdysterone, a key steroid hormone of development, and heat-shock, a cellular stress suggests a possible common pathway for those two events and an important function for the phosphorylated heat-shock proteins.

Characterization of the epidermal-growth-factor-dependent phosphorylation system from normal mouse-liver sinusoidal plasma membranes

Blood sinusoidal plasma membrane subfractions were isolated from normal mouse liver in the presence of the proteinase inhibitors PhMeSO2F and iodoacetamide. They were purified from smooth microsomal and Golgi vesicle contaminants. The phosphorylation reaction was studied at 33 degrees C, in the presence of 2 mM MnCl2. Addition of epidermal growth factor (EGF) to the preparations stimulated 32P incorporation from [gamma-32P]ATP or [gamma-32P]GTP essentially into one 170 000 Mr protein. Some incorporation was observed in a minor 120 000-Mr component which appears to be a degradation product of the 170 000-Mr component. No EGF-dependent phosphorylation of other membrane proteins or various exogenous proteins could be detected in vitro. The dephosphorylation of the 170 000-Mr component was observed after 4 min of incubation at 33 degrees C. This dephosphorylation reaction was inhibited by addition of 5 mM p-nitrophenyl phosphate but not by addition of micromolar Zn2+, Be2+ or orthovanadate. The 170 000-Mr protein specifically bound 125I-labeled EGF and thus appeared to be the hepatic EGF receptor. The EGF stimulatable kinase activity considerably enhances incorporation of 32P into tyrosine residues of the 170 000-Mr EGF receptor at 33 degrees C. Tryptic peptide maps of the 32P-labeled 170 000-Mr protein revealed a multiplicity of phosphorylated sites. Seven 32P-labeled phosphopeptides were observed after EGF stimulation, three of them being largely prominent. Tryptic peptide maps of the 170 000-Mr protein after it was covalently linked to 125I-labeled EGF showed only one 125I-labeled peptide, the migration of which appeared different from that of 32P-labeled phosphopeptides. These findings were confirmed by V8 protease unidimensional peptide mapping of the 170 000-Mr protein, labeled with 32P or 125I-EGF.