Mechanism of benzo(a)pyrene induction of alpha-human chorionic gonadotropin gene expression in human lung tumor cells

Human lung cells (ChaGo) derived from a bronchogenic carcinoma synthesize and secrete in the culture medium the alpha subunit of the glycoprotein hormone, human chorionic gonadotropin (alpha-hCG). The synthesis of alpha-hCG by ChaGo cells could be further stimulated by treatment with sublethal concentrations of the polycyclic aromatic hydrocarbons (PAHs), benzo(a)pyrene (BaP), or dimethylbenzanthracene. The production of alpha-hCG could be correlated to the levels of alpha-hCG-specific mRNA sequences in control and PAH-treated cells. Further analysis of the RNA species (Northern blot) revealed that the level of the mature (approximately 1.0 kb) and the high molecular weight alpha-hCG specific nuclear RNA sequences (approximately 2.2 and 5 kb) were all greater in PAH-treated cells. Addition of [3H]BaP (0.25 microgram/ml) in the culture medium of ChaGo cells led to immediate uptake of the radioactive compound apparently by simple diffusion. SDS PAGE and subsequent fluorography revealed that the radioactive compound interacted and formed covalent complexes with cytoplasmic and nuclear proteins. This covalent interaction of the [3H]BaP molecule with cellular proteins could be significantly inhibited by either inhibiting the activity of the enzyme aryl hydrocarbon hydroxylase with 7,8-benzoflavone or by reducing the cellular concentration of the enzyme by simultaneous incubation with cycloheximide. These results suggested that in ChaGo cells, the observed covalent complexes were formed by the interaction of the BaP metabolites with cellular proteins. The concentrations at which 7,8-benzoflavone or cycloheximide inhibited formation of metabolites from [3H]BaP and their covalent interaction with cell protein did not affect the BaP-induced stimulation of alpha-hCG gene expression. However, the cytotoxic effects of BaP in ChaGo cells seemed to be exerted by the metabolism of the compounds. Results presented in this report suggest that BaP metabolism and the interaction of the metabolites with cell proteins were not essential for the BaP-induced modulation of alpha-hCG gene expression.     

Effects of p,p''-DDT on the Rat Brain Concentrations of Biogenic Amine and Amino Acid Neurotransmitters and Their Association with p,p''-DDT-Induced Tremor and Hyperthermia

Male, Fischer strain 344 adult rats were given various doses (25-100 mg/kg) of p,p'-DDT by oral gavage, and levels of biogenic amines, their metabolites, and amino acid neurotransmitters, tremor activity, and rectal temperature were measured at several intervals (2, 5, 12, and 24 h) after dosing. Dose-related increases in rectal temperature and in tremor activity were observed at 50-100 mg/kg 12 h after dosing. Tremorigenic doses of DDT increased the 5-hydroxyindoleacetic acid (5-HIAA) level in hypothalamus, brainstem, and striatum, whereas doses of 75 and 100 mg/kg increased the 3-methoxy-4-hydroxyphenylglycol (MHPG) level in hypothalamus and brainstem and the 3,4-dihydroxyphenylacetic acid level in striatum. Six amino acids were assayed in the brainstem, hypothalamus, and striatum; aspartate and glutamate levels were increased only in brainstem at 25-100 mg/kg. No consistent changes in concentrations of taurine, glutamine, glycine, or gamma-aminobutyric acid were observed in any of the regions assayed. Time-related increases in rectal temperature were seen 2-12 h after dosing, and the presence of tremor was observed 5-12 h after dosing; for both the time of peak effect was at 12 h. The DDT-induced hyperthermia and tremor were associated with dose- and time-related increases in levels of 5-HIAA, MHPG, aspartate, and glutamate. It is suggested that an increase in the turnover rate of 5-hydroxytryptamine (5-HT) may be responsible for the DDT-induced hyperthermia, whereas increases in the metabolism of 5-HT and norepinephrine may be involved in the tremor.     

Identification of hepatitis B virus polypeptides encoded by the entire pre-s open reading frame.

The open reading frame (ORF) that encodes the 226-amino-acid coat protein (hepatitis B virus surface antigen [HBsAg]) of hepatitis B virus has the potential to encode a 400-amino-acid polypeptide. The entire ORF would direct the synthesis of a polypeptide whose C-terminal amino acids represent HBsAg with an additional 174 amino acids at the N terminus (pre-s). Recently, virus particles have been shown to contain a polypeptide that corresponds to HBsAg with an additional 55 amino acids at the N terminus encoded by the DNA sequence immediately upstream of the HBsAg gene. A novel ORF expression vector containing the TAC promoter, the first eight codons of the gene for beta-galactosidase, and the entire coding sequence for chloramphenicol acetyltransferase was used in bacteria to express determinants of the 174 amino acids predicted from the pre-s portion of the ORF. The resulting tribrid protein containing 108 amino acids encoded by pre-s was expressed as one of the major proteins of bacteria harboring the recombinant plasmid. Single-step purification of the tribrid fusion protein was achieved by fractionation on a chloramphenicol affinity resin. Polyclonal antiserum generated to the fusion protein was capable of detecting 42- and 46-kilodalton polypeptides from virus particles; both polypeptides were also shown to contain HBsAg determinants. The ability of the polyclonal antiserum to identify polypeptides with these characteristics from virus particles presents compelling evidence that the DNA sequence of the entire ORF is expressed as a contiguous polypeptide containing HBsAg. The presence of multiple promoters and primary translation products from this single ORF argues that the function and potential interaction of the encoded polypeptides play a crucial role in the life cycle of the virus. Furthermore, the procedure and vector described in this report can be applied to other systems to facilitate the generation of antibodies to defined determinants and should allow the characterization of the epitope specificity of existing antibodies.     

The respiratory burst of human neutrophils treated with various stimulators in vitro is dampened by exogenous unsaturated fatty acids

Cis-unsaturated free fatty acids (FFA) at concentrations between 10 and 30 microM suppressed the superoxide respiratory burst induced in human neutrophils by the chemotactic peptide, N-formylmethionyl-leucyl-phenylalanine (FMLP). Corresponding trans-isomers had a reduced efficacy while saturated FFA were inert. The effects of unsaturated FFA were maximally achieved after several min of preincubation with cells and reversed upon washing. Increased concentrations of Ca2+ in the medium also relieved the inhibition. Unsaturated FFA were equally effective in dampening the respiratory burst induced by fluoride ions but less so with bursts elicited by 9 nM phorbol myristate acetate (PMA). Moreover reactions triggered by higher concentrations (e.g., 100 nM) of PMA were resistant to the effects of FFA. Radioimmunoassays showed that unsaturated FFA directly elevated intracellular cyclic adenosine monophosphate (cAMP) by severalfold above basal levels. It is suggested that inhibition is brought about by unsaturated FFA perturbation of the neutrophil membrane structure, perhaps with an independent contribution from a cAMP-dependent mechanism.     

Estrogen-binding properties of rat serum alpha 1-fetoprotein and its isoforms. Investigation of the apparent non-integrality of sites on the unfractionated protein.

Rat fetal serum alpha 1-fetoprotein (AFP), a heterogeneous glycoprotein, binds estrogens with high affinity but at a fractional number of sites even after treatment with charcoal (n = 0.6), which may mean 60% of the protein has 1 site and the remainder none. To investigate the origin of this fractional number of sites the "native" protein (purified by negative affinity chromatography) was further purified (step 1) and fractionated (step 2) into its two main charge variants (electrophoretically "slow" and "fast") by a two-step fast-protein liquid chromatography method. The binding parameters for estrone and estradiol-17 beta of the "native" and "repurified" proteins and of each charge variant were determined by equilibrium microdialysis. The molar extinction coefficient at 278 nm of each sample was also determined. (1) The "repurified" AFP and each charge variant had a number of binding sites for estrogens close to unity. This increase in the number of sites could neither be explained by the loss of a non-binding isoform (corresponding to 40% of the protein) during chromatography, nor by the existence of complex negative modulatory interactions between isoforms. (2) The affinities for estrogens of the "repurified" protein and the two charge variants were slightly decreased compared to that of "native" AFP, except that the "fast" form had the "native" protein's high affinity for estrone--but not for estradiol-17 beta. (3) The molar extinction coefficients at 278 nm of the "repurified" AFP and the isoforms were much lower than that of the "native" protein. These results suggest that the presence of (an) inhibitor(s) of estrogen binding on the "native" protein which is/are removed by the ion-exchange fast protein liquid chromatography (FPLC) column. A ligand absorbing at 278 nm, which may or may not be the inhibitor, is also removed. The isoform heterogeneity with respect to estrone binding is discussed.     

Cellular source of soluble interleukin 2 receptors in serum of mice after recombinant interleukin 2 administration.

Previous studies have shown that peripheral blood mononuclear cells activated in vitro not only express cell-associated interleukin 2 receptors (IL2R) but also release a soluble form of this receptor. In this study, we demonstrate that administration of human recombinant IL 2 (rIL 2) to mice results in increased spleen weights, splenic natural killer (NK) cell cytolytic activity, and serum levels of soluble IL2R. However, compared with rIL 2-treated heterozygote controls, beige mice treated with rIL 2 displayed similar elevations in serum soluble IL2R but significantly less splenic NK activity. Likewise, administration of anti-asialo GM1 antiserum to rIL 2-treated mice resulted in a dramatic reduction in splenic NK cytolytic activity, but no reduction in serum soluble IL2R. Conversely, while rIL 2 treatment of BALB/c mice produced increased splenic NK activity and serum soluble IL2R, similar treatment of BALB/c nude mice resulted in elevation of only splenic NK activity. These studies demonstrate that administration of rIL 2 to normal mice can elevate both serum IL2R levels and splenic NK cytolytic activity. However, the results suggest that T cells are likely to be the source of elevated serum IL2R after rIL 2 administration.