Activation of the ras-mitogen-activated protein kinase pathway and phosphorylation of ets-2 at position threonine 72 in human ovarian cancer cell lines.

The activation status of the ras pathway was studied in eight ovarian tumor cell lines. Three biochemical parameters indicative of ras activation were tested: (a) the ratio of the ras-GTP:ras-GDP complex; (b) the activity of mitogen-activated protein kinases p42/p44; and (c) ets-2 phosphorylation at position threonine 72, a mitogen-activated protein kinase phosphorylation site in vivo. Four of the ovarian tumor cell lines had an activated ras pathway by these three parameters, whereas only one of these contained a mutated ras gene. In addition, ras/ets-2 responsive genes such as the urokinase plasminogen activator (uPA) were activated in these four cell lines. Transient transfection assays indicated that the compound ets-AP1 oncogene responsive enhancer present in the uPA gene was the target of ras signaling in ovarian tumor cells and that the combination of activated ras and ets-2 could superactivate the uPA enhancer element. Coexpression of the dominant-negative ras-Asn17 cDNA gene abrogated activity of this uPA element in ovarian tumor cells. These data indicate that ets-2 is a nuclear target of ras action in ovarian tumor cell lines and that ras signaling pathways may be activated in ovarian cancer by mechanisms independent of direct genetic damage to ras genes.

Ultrastructural immunohistochemical localization of Clara cell secretory protein in pulmonary epithelium of rabbits.

Highly purified Clara cells (93 +/- 3%) isolated from the lungs of rabbits were used to produce an antiserum against Clara cell secretory proteins. This antiserum was used to identify and study the biosynthesis and secretion of [35S]methionine-labeled proteins from isolated Clara cells. The antiserum recognized one major secretory protein with apparent molecular weight of 6 kDa and reacted weakly with a higher molecular weight protein of about 180 kDa. Biosynthesis and secretion of these proteins was not detected in preparations of isolated alveolar type II cells or alveolar macrophages. Immunocytochemical localization of the antigen with colloidal gold indicated a dual localization in bronchiolar Clara cells. Gold labeling was found over the osmiophilic secretory granules of Clara cells and smooth endoplasmic reticulum. In tracheal Clara cells, labeling was found mostly in association with secretory granules and relatively little in association with the smooth endoplasmic reticulum. Labeling was also found over the lamellar bodies of type II cells, although the reaction was weak. Labeling of ciliated cells, alveolar type I cells, capillary endothelial cells, and alveolar macrophages was not distinguishable from background. These data indicate that Clara cells of both the bronchioles and trachea of rabbits synthesize and secrete the low molecular weight protein previously called Clara cell secretory protein (CCSP). This antigen does not belong to that group of surfactant proteins whose molecular weights range from 26 to 40 kDa.

Purification, characterization and proteinase-inhibitory activity of a Clara-cell secretory protein from the pulmonary extracellular lining of rabbits.

A low-Mr Clara-cell secretory protein, CCSP, previously shown to be a major secretory product of Clara cells, was isolated from rabbit lung lavage effluents. CCSP accounted for 4.4 +/- 0.5% of the protein in the soluble phase of cell- and surfactant-free pulmonary lavage effluents (LE). Purification of this protein from LE was achieved in two steps. First, the LE was acidified with HCIO4 and, secondly, CCSP was isolated by gel-exclusion chromatography on Sephadex G-50. Purified CCSP was homogeneous by SDS/polyacrylamide-gel electrophoresis (PAGE), consisting of a single major isoform with a pI of 6.0. The Mr of CCSP was 5800 according to SDS/PAGE under reducing conditions and 12,600 under non-reducing conditions. However, by gel chromatography the Mr of the protein under non-reducing conditions was 12,400 and under reducing conditions it increased to 15,000. The discrepancy obtained by using these two techniques was attributed to anomalous electrophoretic mobilities of the protein in its reduced state. The molecule contained three half-cystine residues, but no free thiol groups, and tryptophan was not detectable. The first seven N-terminal amino acid residues were Gly-Ile-Xaa-Pro-Arg-Phe-Ala-. The third residue was not identified. CCSP showed inhibitory activity against the thiol proteinase papain (50% inhibition at 4 microM-CCSP), but only weak activities against human polymorphonuclear-leucocyte elastase, and bovine trypsin. The molecule was not digested by, and did not complex with, trypsin. CCSP was immunochemically different from surfactant apoprotein B (Mr 10,000) present in rabbit lung surfactant. This study is the first partial characterization of the major secretory protein of rabbit lung Clara cells.

Relationship of tri-O-cresyl phosphate-induced delayed neurotoxicity to enhancement of in vitro phosphorylation of hen brain and spinal cord proteins.

Enhancement of endogenous kinase-dependent in vitro protein phosphorylation of subcellular fractions from brains and spinal cords of hens paralyzed 3 weeks after intoxication with tri-o-cresyl phosphate was correlated with the development of organophosphorus compound-induced delayed neurotoxicity (OPIDN). This was documented by showing: parallel dose-dependence curves for both responses, phosphorylation enhancement in proteins from hens treated with OPIDN-producing O-4-bromo-2,5-dichlorophenyl-O-methyl phenylphosphonothioates, but not in those treated with non-OPIDN-producing O,O-diethyl-O-4-nitrophenyl phosphorothioate or tri-p-cresyl phosphate, and shared age and species selectivities for both effects. These results strengthen our earlier observation of a close temporal relationship between protein phosphorylation enhancement and OPIDN. Further studies suggest that the proximate cause of the enhanced phosphorylation is not related to an alteration in protein phosphatase activity or to the preservation of a rate-limiting pool of [gamma-32P]ATP by adenosine triphosphatase inhibition. Therefore, it is most likely related either to altered protein kinase activity or amount (due to chemically originated physical disruption of the neuron). These data support the hypothesis that increased protein phosphorylation may be involved in the development of OPIDN.

Biosynthesis and release of proteins by isolated pulmonary Clara cells.

The major proteins synthesized and released by Clara cells were identified and compared with those synthesized and released by mixed lung cells. Highly purified Clara cells (85.9 +/- 2.4%) and mixed lung cells (Clara cells 4%, Type II cells 33%, granulocytes 18%, macrophages 2.7%, ciliated cells 1.2%) were isolated from rabbit lungs, incubated with Ham's F12 medium in collagen/fibronectin-coated plastic culture dishes in the presence of 35S-methionine for periods of 4 and 18 hrs. Radiolabelled proteins were isolated from the cells and from the culture medium, electrophoresed on polyacrylamide gels in the presence of SDS under reducing conditions, and then autoradiographed. After 4 and 18 hr of incubation of the Clara cells the major radiolabelled cell-associated proteins were those with molecular weights of 6, 48, and 180 Kd. The major radiolabelled proteins released by Clara cells into the medium after 4 hrs of incubation had molecular weights of 6, 48, and 180 Kd, accounting for 42, 16, and 10%, respectively, of the total extracellular protein-associated radioactivity. After 18 hr of incubation the 6 and 48 Kd proteins represented 30 and 18% of the total released radioactivity, and the relative amount of the 180 Kd protein had decreased to 3%. With the mixed lung cells, the major proteins released into the medium had molecular weights of 6 and 48 Kd. Under nonreducing conditions the 6 Kd protein released by Clara cells had an apparent molecular weight of 12 Kd. Labelling isolated Clara cells with a mixture of 14C-amino acids also identified this low molecular weight protein as the major secretory product of the Clara cell. The 6 Kd protein did not label when the cells were incubated with 14C-glucosamine indicating that it was not a glycoprotein. These data demonstrate the release of several proteins from isolated Clara cells but the major protein had a molecular weight of 6 Kd.

Changes in in vitro brain and spinal cord protein phosphorylation after a single oral administration of tri-o-cresyl phosphate to hens.

The effect of a single oral 750 mg/kg dose of tri-o-cresyl phosphate (TOCP) on the endogenous phosphorylation of brain and spinal cord proteins was assessed in hens during the development of and recovery from delayed neurotoxicity. Crude membrane and cytosolic fractions were prepared from the brains and spinal cords of control and TOCP-treated hens at 1, 7, 14, 21, 35, and 55 days after treatment. Brain and spinal cord protein phosphorylation with [gamma-32P]ATP was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), autoradiography, and microdensitometry. TOCP administration conferred calcium and calmodulin dependence on the phosphorylation of a few brain cytosolic proteins and caused an increase in the phosphorylation of a number of other cytosolic and membrane proteins. This effect of TOCP was large in magnitude, and its time course reflected the onset of and recovery from the signs of ataxia and paralysis associated with delayed neurotoxicity in the hen. The molecular weights (Mr) and maximal phosphorylation (percent of control) for the most prominently affected bands were as follows: brain cytosol--50K (183%), 55K (575%), 60K (529%), 65K (273%), and 70K (548%); brain membranes--50K (622%) and 60K (697%); and spinal cord cytosol--20K (182%). The role of endogenous phosphorylation reactions in and their potential usefulness as biochemical indicators of delayed neurotoxicity are being explored further.

Characterization of delayed neurotoxicity in the mouse following chronic oral administration of tri-o-cresyl phosphate.

The sensitivity of the mouse to organophosphorus-induced delayed neurotoxicity (OPIDN) has been investigated. One group of five mice received two single 1000-mg/kg po doses of tri-o-cresyl phosphate (TOCP) at a 21-day interval (on Days 1 and 21 of the study); a second group of five mice was given 225 mg/kg of TOCP daily for 270 days. A third group of five animals served as an untreated control. All animals were killed 270 days after the start of the experiment. Daily po dosing of 225 mg/kg TOCP caused a decrease in body weight gain, muscle wasting, weakness, and ataxia which progressed to severe hindlimb paralysis at termination. On the other hand, po administration of two single 1000-mg/kg doses of TOCP at a 21-day interval produced no observable adverse effects. Brain acetylcholinesterase (AChE) and neurotoxic esterase (NTE) activity were 35 and 10% of the control, respectively, in daily dosed animals while AChE and NTE in mice receiving two single 1000-mg/kg doses of TOCP were not significantly altered from the control group. Plasma butyrylcholinesterase activity was 12% of the control group in daily dosed animals. Hepatic microsomal enzyme activities of aniline hydroxylase and p-chloro-N-methylaniline demethylase and NADPH-cytochrome P-450 content in daily dosed animals were increased (141 to 161% of the control group) when compared to controls and mice receiving two single 1000-mg/kg doses of TOCP; the latter being not significantly different from each other. Degeneration of the axon and myelin of the spinal cord and sciatic fascicle were observed and were consistent with OPIDN. This study demonstrates that chronic dosing of TOCP produces OPIDN and induces hepatic microsomal enzyme activity in mice. It is concluded that while the mouse is susceptible to OPIDN, it is a less sensitive and a less appropriate test animal for studying this effect when compared to the adult hen.

Partial characterization of endogenous phosphorylation conditions for hen brain cytosolic and membrane proteins.

The optimal conditions for endogenous protein phosphorylation with 5 microM [gamma-32P]ATP, 10 mM MgCl2 in preparations containing synaptosomal cytosol or membranes (shocked crude mitochondrial fraction P2) from adult hen brains were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, autoradiography and microdensitometry. Phosphate incorporation increased linearly with protein concentration from 75-125 micrograms/200 microliters in brain cytosol and was maximal at 75 micrograms/200 microliters in brain membranes. Optimal incubation times were 60-90 s for brain cytosol and 10-15 s for brain membranes. With the exception of the 20 kilodalton myelin basic protein in the membrane fraction, pH 6.5 is generally optimal. While temperature optima varied considerably with different bands, most of them were found between 35 and 45 degrees C. When identical preparations from hen and rat brain were co-electrophoresed, one of the most striking differences was that the enhancement of phosphorylation of a 55 kilodalton doublet, which may be tubulin, by addition of 50 microM Ca2+ was at least 3 times greater in rat than in hen brain cytosol. Another species difference was apparent in the membrane fractions in which the 20 kilodalton hen brain presumptive myelin basic protein (MBP) was phosphorylated to approximately the same extent as that of the 16 and 20 kilodalton rat brain MBPs combined.

Comparison of endogenous phosphorylation of hen and rat spinal cord proteins and partial characterization of optimal phosphorylation conditions for hen spinal cord.

The optimal conditions for the endogenous phosphorylation of hen spinal cord cytosolic and membrane proteins with 5 ?M [?-(32)P]ATP, 10 mM MgCl(2), were determined by 10% SDS-polyacrylamide gel electrophoresis, autoradiography, and microdensitometry. Phosphate incorporation increased linearly with concentrations ranging from 35-75 ?g/100 ?l for cytosolic proteins and 21-125 ?g/200 ?l for membrane proteins. Optimal incubation times, temperatures, and pH values were 60 s, 30 degrees C, and 6.0, respectively, for spinal cord cytosolic proteins and 15 s, 45 degrees C, and 8.0, respectively, for spinal cord membranes. Prominent species differences in protein phosphorylation between these fractions in hens and similarly prepared fractions in rats, co-electrophoresed, include 80K and 30K protein phosphate acceptors unique to rat spinal cord cytosol, 60K and 16K protein phosphate acceptors characteristic of rat spinal cord membranes, a 50K protein phosphate acceptor present only in hen spinal cord membranes, and greater phosphorylation of a more abundant 20K protein in both hen spinal cord fractions. The functional significance of these differences is presently unclear. However, their characterization provides a basis from which to launch future investigations of the biochemistry, pharmacology, and toxicology of spinal cord protein phosphorylation and indicates that caution should be exercised in the choice of an animal model with characteristics appropriate to those of the system it is representing.

Effect of oral administration of tri-o-cresyl phosphate on in vitro phosphorylation of membrane and cytosolic proteins from chicken brain.

The effects of a single oral dose of 750 mg/kg tri-o-cresyl phosphate (TOCP) on the endogenous phosphorylation of specific brain proteins were assessed in male adult chickens following the development of delayed neurotoxicity. Phosphorylation of crude synaptosomal (P2) membrane and synaptosomal cytosolic proteins was assayed in vitro by using [gamma-32P]ATP as phosphate donor. Following resolution of brain proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis, specific protein phosphorylation was detected by autoradiography and quantified by microdensitometry. TOCP administration enhanced the phosphorylation of both cytosolic (Mr 65,000 and 55,000) and membrane (20,000) proteins by as much as 146% and 200%, respectively.