The effects of electronic nicotine vapor on voluntary alcohol consumption in female and male C57BL/6 J mice

SIGNIFICANCE

Alcohol drinking and nicotine vaping often co-occur and dependence on both substances is common. However, the impact of nicotine vaping on alcohol consumption is not fully understood.

METHODS

We examined the effects of nicotine vaping on ethanol drinking in female and male C57BL/6 J mice using an electronic nicotine delivery system and intermittent access two-bottle choice (IA-2BC) drinking. Mice were exposed to electronic nicotine vapor (3%) or propylene glycol/vegetable glycerol (PG/VG) control for 3 h sessions daily for 4 weeks and voluntary alcohol consumption was monitored. Nicotine vapor exposure was stopped and voluntary alcohol drinking was measured for a 2 week abstinence period. We also examined the effects of alcohol and nicotine on locomotion, temperature, and nicotine metabolism.

RESULTS

Following acute nicotine vapor exposure, alcohol drinking was increased in males but not in females. Thermoregulation was disrupted following nicotine vapor exposure and voluntary drinking. Male and female mice displayed increased locomotor activity immediately following chronic nicotine vapor exposure, and an anxiolytic effect was seen in males. In nicotine vapor abstinence, female mice displayed increased alcohol consumption. Locomotor activity and anxiolytic effects remained elevated in male but not female mice. Female mice displayed higher levels of serum nicotine and hydroxycotinine, suggesting impaired metabolism following chronic drinking and nicotine vapor exposure.

CONCLUSION

Collectively, these results suggest that while both male and female ethanol-drinking mice experience the stimulatory effects of nicotine vapor, only in males is there a parallel increase in ethanol drinking and only females display impairments in nicotine metabolism after drinking.

Distinct roles of two eIF4E isoforms in the germline of Caenorhabditis elegans

Germ cells use both positive and negative mRNA translational control to regulate gene expression that drives their differentiation into gametes. mRNA translational control is mediated by RNA-binding proteins, miRNAs and translation initiation factors. We have uncovered the discrete roles of two translation initiation factor eIF4E isoforms (IFE-1, IFE-3) that bind 7-methylguanosine (m7G) mRNA caps during Caenorhabditiselegans germline development. IFE-3 plays important roles in germline sex determination (GSD), where it promotes oocyte cell fate and is dispensable for spermatogenesis. IFE-3 is expressed throughout the germline and localizes to germ granules, but is distinct from IFE-1 and PGL-1, and facilitates oocyte growth and viability. This contrasts with the robust expression in spermatocytes of IFE-1, the isoform that resides within P granules in spermatocytes and oocytes, and promotes late spermatogenesis. Each eIF4E is localized by its cognate eIF4E-binding protein (IFE-1:PGL-1 and IFE-3:IFET-1). IFE-3 and IFET-1 regulate translation of several GSD mRNAs, but not those under control of IFE-1. Distinct mutant phenotypes, in vivo localization and differential mRNA translation suggest independent dormant and active periods for each eIF4E isoform in the germline.

Spatial and temporal translational control of germ cell mRNAs mediated by the eIF4E isoform IFE-1

Regulated mRNA translation is vital for germ cells to produce new proteins in the spatial and temporal patterns that drive gamete development. Translational control involves the de-repression of stored mRNAs and their recruitment by eukaryotic initiation factors (eIFs) to ribosomes. C. elegans expresses five eIF4Es (IFE-1-IFE-5); several have been shown to selectively recruit unique pools of mRNA. Individual IFE knockouts yield unique phenotypes due to inefficient translation of certain mRNAs. Here, we identified mRNAs preferentially translated through the germline-specific eIF4E isoform IFE-1. Differential polysome microarray analysis identified 77 mRNAs recruited by IFE-1. Among the IFE-1-dependent mRNAs are several required for late germ cell differentiation and maturation. Polysome association of gld-1, vab-1, vpr-1, rab-7 and rnp-3 mRNAs relies on IFE-1. Live animal imaging showed IFE-1-dependent selectivity in spatial and temporal translation of germline mRNAs. Altered MAPK activation in oocytes suggests dual roles for IFE-1, both promoting and suppressing oocyte maturation at different stages. This single eIF4E isoform exerts positive, selective translational control during germ cell differentiation.

Southern-by-Sequencing: A Robust Screening Approach for Molecular Characterization of Genetically Modified Crops

Molecular characterization of events is an integral part of the advancement process during genetically modified (GM) crop product development. Assessment of these events is traditionally accomplished by polymerase chain reaction (PCR) and Southern blot analyses. Southern blot analysis can be time-consuming and comparatively expensive and does not provide sequence-level detail. We have developed a sequence-based application, Southern-by-Sequencing (SbS), utilizing sequence capture coupled with next-generation sequencing (NGS) technology to replace Southern blot analysis for event selection in a high-throughput molecular characterization environment. SbS is accomplished by hybridizing indexed and pooled whole-genome DNA libraries from GM plants to biotinylated probes designed to target the sequence of transformation plasmids used to generate events within the pool. This sequence capture process enriches the sequence data obtained for targeted regions of interest (transformation plasmid DNA). Taking advantage of the DNA adjacent to the targeted bases (referred to as next-to-target sequence) that accompanies the targeted transformation plasmid sequence, the data analysis detects plasmid-to-genome and plasmid-to-plasmid junctions introduced during insertion into the plant genome. Analysis of these junction sequences provides sequence-level information as to the following: the number of insertion loci including detection of unlinked, independently segregating, small DNA fragments; copy number; rearrangements, truncations, or deletions of the intended insertion DNA; and the presence of transformation plasmid backbone sequences. This molecular evidence from SbS analysis is used to characterize and select GM plants meeting optimal molecular characterization criteria. SbS technology has proven to be a robust event screening tool for use in a high-throughput molecular characterization environment.

S-phase modulation by irinotecan: pilot studies in advanced solid tumors

Two studies of irinotecan (CPT-11) followed 24 h later by an antimetabolite were conducted. The objectives of the studies were: (1) to determine whether the increase in S-phase in tumor cells seen 24 h after CPT-11 administration in animal studies is seen in advanced solid tumors in patients, (2) to determine the dose of CPT-11 required to produce this effect, (3) to compare two methods (immunohistochemistry, IHC, for cyclin A, and DNA flow cytometry, FC) for evaluating S-phase in tumor biopsies from patients, and (4) to establish the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of CPT-11, given 24 h before gemcitabine (GEM, 1000 mg/m(2)). In one study CPT-11 was followed 24 h later by 5-fluorouracil (5-FU), 400 mg/m(2) per week for 4 weeks every 6 weeks. Tumor biopsies were obtained before and 24 h after CPT-11 administration before administration of 5-FU and assayed for S-phase by IHC for cyclin A and by FC. The starting dose of CPT-11 was 80 mg/m(2) per week with subsequent exploration of 40 and 60 mg/m(2) per week to establish the dose-effect relationship of the increase in tumor cells in S-phase. In the second study, CPT-11 was given 24 h before GEM 1000 mg/m(2) per week for 2 weeks every 3 weeks. Doses of 20-80 mg/m(2) were explored to establish the MTD and DLT and to study tumor cell S-phase in selected patients. CPT-11 80 mg/m(2) produced a mean increase in S-phase by IHC for cyclin A of 137%. Lesser increases were seen with 40 and 60 mg/m(2). CPT-11 followed 24 h later by 5-FU 400 mg/m(2) per week for 4 weeks was well tolerated. In the study of CPT-11 followed by GEM 1000 mg/m(2), 60 mg/m(2) of CPT-11 was the MTD.

Differential impairment of triazolam and zolpidem clearance by ritonavir

BACKGROUND

The viral protease inhibitor ritonavir has the capacity to inhibit and induce the activity of cytochrome P450-3A (CYP3A) isoforms, leading to drug interactions that may influence the efficacy and toxicity of other antiretroviral therapies, as well as pharmacologic treatments of coincident or complicating diseases.

METHODS

The inhibitory effect of ritonavir on the biotransformation of the hypnotic agents triazolam and zolpidem was tested in vitro using human liver microsomes. In a double-blind clinical study, volunteer study subjects received 0.125 mg triazolam or 5.0 mg zolpidem concurrent with low-dose ritonavir (four doses of 200 mg), or with placebo.

RESULTS

Ritonavir was a potent in vitro inhibitor of triazolam hydroxylation but was less potent as an inhibitor of zolpidem hydroxylation. In the clinical study, ritonavir reduced triazolam clearance to < 4% of control values (p < .005), prolonged elimination half-life (41 versus 3 hours; p < .005), and magnified benzodiazepine agonist effects such as sedation and performance impairment. In contrast, ritonavir reduced zolpidem clearance to 78% of control values (p < .08), and slightly prolonged elimination half-life (2.4 versus 2.0 hours; NS). Benzodiazepine agonist effects of zolpidem were not altered by ritonavir.

CONCLUSION

Short-term low-dose administration of ritonavir produces a large and significant impairment of triazolam clearance and enhancement of clinical effects. In contrast, ritonavir produced small and clinically unimportant reductions in zolpidem clearance. The findings are consistent with the complete dependence of triazolam clearance on CYP3A activity, compared with the partial dependence of zolpidem clearance on CYP3A.

Alprazolam-ritonavir interaction: implications for product labeling

BACKGROUND

Pharmacokinetic interactions involving antiretroviral therapies may critically influence the efficacy and toxicity of these drugs, as well as pharmacologic treatments of coincident or complicating diseases. The viral protease inhibitor ritonavir is of particular concern since it both inhibits and induces the activity of cytochrome P450 3A (CYP3A) isoforms.

METHODS

The inhibitory effect of ritonavir on the metabolism of alprazolam, a CYP3A-mediated reaction in humans, was tested in vitro using human liver microsomes. In a double-blind clinical study, volunteer subjects received 1.0 mg of alprazolam concurrent with low-dose ritonavir (four doses of 200 mg) or with placebo.

RESULTS

Ritonavir was a potent in vitro inhibitor of alprazolam hydroxylation. The 50% inhibitory concentration was 0.11 micromol/L (0.08 microg/mL); this is below the usual therapeutic plasma concentration range (generally exceeding 2 microg/mL). In the clinical study, ritonavir reduced alprazolam clearance to 41% of control values (P < .001), prolonged elimination half-life (mean values, 30 versus 13 hours; P < .005), and magnified benzodiazepine agonist effects such as sedation and performance impairment.

CONCLUSION

Consistent with in vitro results, administration of low doses of ritonavir for a short duration of time resulted in large impairment of alprazolam clearance and enhancement of clinical effects. Removal from product labeling of a warning against coadministration of ritonavir and alprazolam was based on a previous study only of extended exposure to ritonavir, in which CYP3A induction offset inhibition. Kinetic interactions involving antiretroviral therapies may be complex and time dependent. Product labeling should reflect this complexity.

Role of tyrosine kinase, ODC, and p34cdc2 kinase and cyclin B-associated cdc2 in jejunal enterocyte proliferation, maturation, and exfoliation in diabetic and DFMO-treated rats

BACKGROUND

Several signal transduction pathways involved in rapidly proliferating cells of the intestine are currently not well understood. In the jejunum, crypt enterocytes are constantly replicating, lower villi are maturing, and upper villi are constantly shed. Type I diabetes is associated with jejunal mucosal hyperplasia, and administration of diflouromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), causes hypoplasia. Phosphorylation of proteins controls cellular proliferation and/or exfoliation. Cell division cycle kinase (p34cdc2) and cyclin B-associated p34cdc2 kinase regulate the cell cycle during the transition from G2-M phase. Our aims were to: 1) investigate the activities of tyrosine kinase, ODC, total p34cdc2 kinase, and cyclin B-associated p34cdc2 kinase and 2) phosphorylate proteins at tyrosine residues in jejunal upper villi, lower villi, and crypt enterocytes of DFMO-treated control and diabetic rats.

METHODS

Diabetes was induced by streptozotocin. DFMO was administered in drinking water in both control and diabetic groups for 10 days after the induction of diabetes. Jejunal enterocytes were isolated and kept frozen at -70 degrees C until ready to process.

RESULTS

Diabetic rats showed jejunal mucosal hyperplasia as indicated by increases in the jejunal mucosal weight/cm and DNA content compared to control rats. Diabetic crypt enterocytes showed significant increases in activities of tyrosine kinase, ODC, total p34cdc2 kinase, and cyclin B-associated cdc2 as well as increased phosphorylation of proteins at tyrosine residues compared to control rats. DFMO prevented diabetes-induced jejunal hyperplasia, and decreased the activities of these enzymes and phosphorylation of proteins at tyrosine residues in both diabetic and control rats. Phosphorylation of a 14 kd protein became prominent in crypt, upper villi, and lower villi enterocytes of DFMO-treated diabetic and control groups.

CONCLUSION

Diabetic jejunal mucosal hyperplasia appears to involve activation of complex signal transduction pathways such as tyrosine kinase, ODC, p34cdc2 kinase, and cyclin B. These enzymes are involved in proliferation and/or exfoliation of jejunal enterocytes. Our results also suggest that tyrosine phosphorylation of a 14 kd protein may be involved in cell exfoliation and that jejunal mucosal hypoplasia may be a synergistic effect caused by down regulation of the above enzymes.

Effect of gamma subunit carboxyl methylation on the interaction of G protein alpha subunits with beta gamma subunits of defined composition

A baculovirus expression system was used to determine the contribution of carboxyl methylation of specific G protein gamma subunits to the interaction between alpha and beta gamma subunits. beta gamma subunits were carboxyl methylated by a membrane bound methyltransferase in Sf9 cells, and periodate-oxidized adenosine inhibited this methylation by 90%. Carboxyl methylation of beta(1) gamma(2), beta(2) gamma(3), and beta(2) gamma(7) enhanced pertussis toxin-catalyzed ADP-ribosylation of alpha(i2) and alpha(i3) by about 2-fold. On the other hand, methylation did not enhance membrane attachment of beta gamma subunits. These results suggest that methylation of isoprenylated gamma subunits is required for optimal G protein-mediated signal transduction, but not membrane attachment.

Effects of diabetes and difluoromethylornithine treatment on hyperplasia, activity of MAP-kinase, and activity and association with cyclin B of p34cdc2 kinase in rat jejunal mucosa

BACKGROUND

The different signal transduction pathways of rapidly proliferating cells of the intestine are not clearly understood. We report here a possible signaling pathway that involves regulation of activity of two closely related kinases, MAP-K (mitogen-activated protein kinase) and p34cdc2 kinase, during hyperplasia of diabetic jejunal mucosa. Our aim was to investigate the activity and phosphorylation of MAP-K and activity and association of p34cdc2 kinase with cyclin B during diabetes-induced jejunal mucosal hyperplasia in vivo.

METHODS

We studied untreated and difluoromethylornithine (DFMO) treated control rats and rats with streptozotocin-induced type I diabetes. Assays were done 10 days after the induction of diabetes. In diabetic rats there was jejunal hyperplasia as indicated by increases in the jejunal mucosal weight/cm and DNA content as well as increased activities of MAP-K and p34cdc2 kinase and association of the latter with cyclin B as compared to corresponding values in control rats. Administration of DFMO, an irreversible inhibitor of the proliferation-associated enzyme ornithine decarboxylase (ODC), prevented diabetes-I induced jejunal hyperplasia and decreased all of the above enzymic parameters in both diabetic and control rats. In our previous in vivo study, DFMO administration also blocked diabetic jejunal hyperplasia and in addition decreased ornithine decarboxylase and tyrosine kinase activities jejunal and tyrosine phosphorylation of proteins.

CONCLUSION

Thus the jejunal mucosal hyperplasia found in diabetes appears to involve activation of signal transduction pathways involving tyrosine kinases, MAP-K, p34cdc2 kinase, and cyclin B.

CNS sites involved in sympathetic and parasympathetic control of the pancreas: a viral tracing study

The viral transneuronal tracing method was used to identify the CNS cell groups that regulate the parasympathetic and sympathetic outflow systems of the pancreas. Pseudorabies virus (PRV) was injected into the pancreas of vagotomized rats and after 6 days survival, the pattern of transneuronal labeling in the CNS sympathetic regulatory regions was determined. The converse experiment was performed in order to elucidate the central parasympathetic cell groups that regulate the pancreas. Immunohistochemical methods were used to identify putative neuropeptide- and catecholamine-containing CNS neurons involved in these regulatory circuits. The major finding of this study indicates that five brain regions, viz., paraventricular hypothalamic nucleus, perifornical hypothalamic region, A5 catecholamine cell group, rostral ventrolateral medulla, and lateral paragigantocellular reticular nucleus, contain a considerable amount of overlap in cell body labeling. In addition, the ventrolateral part of the periaqueductal gray matter and gigantocellular reticular nucleus, ventral part also showed a similar overlap, but the numbers of neurons found in these areas were considerably lower than the five major regions. These data suggest that these brain regions may provide parallel and possibly redundant, autonomic pathways affecting glucagon and adrenaline release.

Suicide inactivation of thioether S-methyltransferase by ethyl sulfide

Thioether S-methyltransferase is an important enzyme in the metabolism of sulfur and selenium-containing compounds in animals. Ethyl vinyl sulfide was previously shown to be a substrate for this enzyme yielding methyl ethyl vinyl sulfonium ion (MEVS+) upon reaction with S-adenosylmethionine. Since vinyl sulfonium ions are reactive toward nucleophiles, the inactivation of thioether S-methyltransferase as a result of its methylation of ethyl vinyl sulfide was investigated. Ethyl vinyl sulfide was found to inactivate thioether S-methyltransferase in a time-dependent, pseudo-first-order process with k(inact) and KI values of 0.05 min(-1) and 0.275 mM, respectively. Calculation of the partition ratio revealed one inactivation event for every 100 turnovers. Dimethyl sulfide, an alternate substrate for thioether S-methyltransferase which yields the nonreactive product trimethyl sulfonium ion, protected the enzyme from inactivation by ethyl vinyl sulfide. The inactivation is a result of covalent reaction of methyl ethyl vinyl sulfonium ion with the enzyme as shown by comigration of radioactivity with the enzyme during denaturing gel filtration of reaction mixtures containing thioether S-methyltransferase, ethyl vinyl sulfide, and S-adenosyl[methyl-3H]methionine. Using this method the stoichiometry of inactivation was determined to be 1 mol of [3H]-methyl group/mol of thioether S-methyltransferase inactivated. Both the alternate substrate, dimethyl sulfide, and the competitive product inhibitor, S-adenosylhomocysteine, inhibited such covalent labeling of the enzyme by ethyl vinyl sulfide and S-adenosyl[methyl-3H]methionine. Chemically synthesized MEVS+ inactivated thioether S-methyltransferase, and [methyl-14C]MEVS+ covalently labeled the enzyme with 14C. These results reveal a previously unrecognized mechanism for biochemical activation of vinyl thioethers by methylation to form reactive vinyl sulfonium ions.

Relation of ornithine decarboxylase and tyrosine kinase activity in the jejunal mucosa in vivo

Our aim was to study the relationship between jejunal mucosal activity of ornithine decarboxylase and tyrosine kinase during proliferation in adolescent rats in vivo. Their relationship in the proliferating intestinal mucosa under in vivo conditions has not been reported before. From the results of in vitro studies, it was speculated that tyrosine kinase activity modulated ornithine decarboxylase activity during colonic mucosal proliferation (Majumdar AP. Am J Physiol 259:G626-G630, 1990). Jejunal mucosal hyperplasia was induced by Type 1 diabetes and suppressed in both control and diabetic rats by administration of difluoromethylornithine. Jejunal mucosal weight and enzyme activity were determined after 3, 6, and 10 days, and tyrosine-specific phosphorylated proteins after 10 days of induction of diabetes. Difluoromethylornithine suppressed jejunal mucosal proliferation and tyrosine kinase activity after the 6- and 10- day study periods. After the 3-day study period although jejunal mucosal growth was suppressed, tyrosine kinase activity was not. Activity of tyrosine kinase and ornithine decarboxylase were highly significantly correlated at all time periods in both control and diabetic rats. Tyrosine-specific phosphorylated proteins of 34, 54, 80, and 200 kDa proteins were observed in jejunal mucosa of both control and diabetic rats. In the difluoromethylornithine-treated rats, phosphorylation of the above proteins was negligible while the phosphorylation of a 14-kDa protein was prominent. We speculate that in vivo ornithine decarboxylase activity may be modulating tyrosine kinase activity and that phosphorylation of a 14-kDa protein was associated with suppressed mucosal growth in difluoromethylornithine-treated rats.

Cloning and base sequence analysis of a cDNA encoding mouse lung thioether S-methyltransferase

Thioether S-methyltransferase catalyzes transfer of the methyl group from S-adenosylmethionine to X in compounds of the structure R-X-R', where X may be sulfur, selenium, or tellurium, and R and R' may be various organic groups. To obtain a cDNA clone of thioether S-methyltransferase, a mouse lung cDNA library in lambda gt11 was screened with a 99 base-pair probe obtained by performing the polymerase chain reaction on oligo(dT) primed, reverse transcribed, mouse lung RNA using two degenerate primers designed from partial amino-acid sequences of the enzyme. The entire coding and 3'-untranslated regions were obtained and sequenced. The predicted protein contains 264 amino-acid residues and has a calculated M(r) of 29,460. The amino-acid sequence of thioether S-methyltransferase contains three motifs characteristic of many methyltransferases and has a high level of identity with the amino-acid sequences of nicotinamide N-methyltransferase and phenylethanolamine N-methyltransferase. However, in spite of the fact that they are both mammalian cytosolic sulfur methyltransferases, the sequences of thioether S-methyltransferase and thiopurine S-methyltransferase share little identity.

Sequential methylation of 2-mercaptoethanol to the dimethyl sulfonium ion, 2-(dimethylthio)ethanol, in vivo and in vitro

Thioether methyltransferase (S-adenosyl-L-methionine: thioether S-methyltransferase; EC 2.1.1.96) catalyzes the methylation of X in compounds of the type R-X-R'(X = S, Se, Te), yielding a methyl onium ion. Previous results using mice have demonstrated a role for thioether methyltransferase in the conversion and clearance of thioethers by methylation to more water-soluble methyl sulfonium ions suitable for excretion in the urine. A potential major physiological source of thiethers is reactions catalyzed by microsomal thiol methyltransferase (S-adenosyl-L-methionine: thiol S-methyltransferase; EC 2.1.1.9), which has been shown to methylate a diverse range of aliphatic sulfhydryl compounds. This study provides evidence for the sequential methylation of the aliphatic thiol, 2-mercaptoethanol, first to the methyl thioether, 2-(methylthio)ethanol, by thiol methyltransferase followed by methylation of this methyl thioeter to the dimethyl sulfonium ion, 2-(-dimethylthio)ethanol, by thioether methyltransferase. This sequence of reactions was demonstrated in vivo by injecting mice i.p. with radioactive 2-mercaptoethanol and analyzing the labeled methylated products, 2-(methylthio)ethanol and 2(dimethylthio)ethanol, in the urine by HPLC. In addition, the system converting 2-mercaptoethanol to 2-(dimethylthio)ethanol was reconstituted in vitro using solubilized mouse liver microsomes as a source of thiol methyltransferase and purified thioether methyltransferase from mouse lung. The results of these in vivo and in vitro studies established the sequential methylation of 2-mercaptoethanol by these two enzymes.

Effect of prenylcysteine analogues on chemoattractant receptor-mediated G protein activation

The hypothesis that carboxylmethylation of gamma subunits plays a role in G protein activation was tested by examining the ability of N-acetyl-S-farnesyl-L-cysteine (AFC) and its methyl ester (AFC-ME) to inhibit G protein-mediated signalling in intact HL-60 granulocytes and isolated HL-60 plasma membranes. Incubation of HL-60 granulocytes with AFC or AFC-ME inhibited superoxide release stimulated by fMet-Leu-Phe, but not by opsonized bacteria. AFC-ME, but not AFC, inhibited NaF- and PMA-stimulated superoxide release. Addition of AFC to HL-60 membranes inhibited fMet-Leu-Phe-, leukotriene B4- (LTB4) and C5a-stimulated GTP gamma S binding and GTP hydrolysis more potently than it inhibited basal guanine nucleotide exchange. AFC-ME inhibited basal- and ligand-stimulated G protein activation with equal potency, but less potently than AFC. AFC also inhibited mastoparan-stimulated GTP gamma S binding. Binding of fMet-Leu-Phe and LTB4 to HL-60 membranes was completely inhibited by AFC, while AFC-ME inhibited ligand binding by less than 50%. Neither AFC nor AFC-ME inhibited pertussis toxin or cholera toxin-catalysed ADP-ribosylation of alpha i. It was concluded that AFC interrupts signal propagation in G protein-dependent pathways by multiple mechanisms, including inhibition of ligand-receptor interactions, of receptor-G protein coupling and of guanine nucleotide binding to G proteins. Carboxylmethylation alters the specificity of AFC interruption of signal propagation in intact cells and isolated membranes.

Role of carboxylmethylation in chemoattractant receptor-stimulated G protein activation and functional responses

The role of G protein gamma subunit carboxylmethylation was examined in HL-60 granulocytes using an inhibitor of S-adenosylmethionine-dependent methylation, periodate-oxidized adenosine (Adox). A 40-60% reduction in gamma subunit carboxyl-methylation was associated with attenuation of fMet-Leu-Phe-stimulated GTP gamma S binding and GTP hydrolysis, while plasma membrane density of formyl peptide receptors, alpha i2, alpha i3, beta, gamma 5, and gamma 7 were not reduced. Reduced pertussis toxin-catalyzed ADP-ribosylation was re-established by in vitro methylation or addition of transducin beta gamma subunits. Superoxide release and inositol phosphate generation stimulated by fMet-Leu-Phe were significantly inhibited by Adox treatment. Carboxylmethylation contributes to transmembrane signalling and functional responses by enhancing association of alpha and beta gamma subunits.

Polyamines and intestinal epithelial hyperplasia in streptozotocin-diabetic rats

We measured specific activity of ornithine decarboxylase (ODC) and contents of putrescine and of the polyamines (spermidine and spermine) in isolated villus and crypt enterocytes from the jejunum of adolescent streptozotocin-diabetic and weight-matched control rats and diabetic and control rats treated with difluoromethyl ornithine (DFMO) 10 days after induction of diabetes. Consistent with previous observations by others of elevated ODC activity and contents of putrescine and of the polyamines in the intestinal epithelium undergoing hyperplasia, our studies showed elevated ODC activity and contents of putrescine and spermidine, but not of spermine, in the hyperplastic intestinal epithelium of diabetic rats. As in previous studies, suppression of ODC activity by DFMO prevented not only the jejunal epithelial hyperplasia in the diabetic rats, but also retarded jejunal epithelial growth in the control rats. DFMO administration lowered ODC activity by over 80% in both diabetic and control rat enterocytes and prevented the rise in enterocyte contents of putrescine and spermidine in the diabetic rat. The observation that, in both diabetic and control rats, treatment with DFMO lowered spermidine content in the crypt enterocytes but had no similar consistent effect on contents of putrescine or spermine suggested that spermidine could have been responsible for the intestinal epithelial hyperplasia in the diabetic rats and for the normal growth of the intestinal epithelium in control rats.

Ion chromatographic analysis of the purity and synthesis of sulfonium and selenonium ions

The use of single-column ion chromatography with conductometric detection was shown to be useful for the analysis of sulfonium and selenonium ions. A Hamilton PRP X-200 cation column was eluted with either solvent A (5 mM nitric acid in 30% methanol) or solvent B (4 mM nitric acid). With solvent B, trimethylsulfonium ion was separated from trimethylselenonium ion. With solvent A, amounts of trimethylsulfonium ion from 2 to 250 nmol were detected with a linear response. The retention times and response factors for a series of sulfonium ions with various organic groups were determined. In general the ions with more hydrophobic groups eluted later, but all had similar response factors. The method was shown to be useful for optimizing conditions for the synthesis of methylsulfonium ions, specifically the reaction of methyl iodide with diallyl sulfide.

Se-(8-azidoadenosyl)[75Se]selenomethionine as a photoaffinity label for S-adenosylmethionine binding proteins

A method is described for the synthesis and purification of the photoaffinity label Se-(8-azidoadenosyl)[75Se]selenomethionine. This photoaffinity label can be used to specifically and covalently label the S-adenosylmethionine binding site of proteins that use this cofactor, as exemplified by labeling of thioether methyltransferase. By utilizing the gamma-emitting isotope of selenium, Se-(8-azidoadenosyl)[75Se]selenomethionine eliminates the need for the impregnation of acrylamide gels with fluorographic enhancers and dilution of liquid samples into scintillation cocktails, as is required with the commonly used methyl-3H-labeled and 35S-labeled S-(8-azidoadenosyl)methionine.

Biosynthesis and urinary excretion of methyl sulfonium derivatives of the sulfur mustard analog, 2-chloroethyl ethyl sulfide, and other thioethers

Thioether methyltransferase was previously shown to catalyze the S-adenosylmethionine-dependent methylation of dimethyl selenide, dimethyl telluride, and various thioethers to produce the corresponding methyl onium ions. In this paper we show that the following thioethers are also substrates for this enzyme in vitro: 2-hydroxyethyl ethyl sulfide, 2-chloroethyl ethyl sulfide, thiodiglycol, t-butyl sulfide, and isopropyl sulfide. To demonstrate thioether methylation in vivo, mice were injected with [methyl-3H]methionine plus different thioethers, and extracts of lungs, livers, kidneys, and urine were analyzed by high-performance liquid chromatography for the presence of [3H]methyl sulfonium ions. The following thioethers were tested, and all were found to be methylated in vivo: dimethyl sulfide, diethyl sulfide, methyl n-propyl sulfide, tetrahydrothiophene, 2-(methylthio)ethylamine, 2-hydroxyethyl ethyl sulfide, and 2-chloroethyl ethyl sulfide. This supports our hypothesis that the physiological role of thioether methyltransferase is to methylate seleno-, telluro-, and thioethers to more water-soluble onium ions suitable for urinary excretion. Conversion of the mustard gas analog, 2-chloroethyl ethyl sulfide, to the methyl sulfonium derivative represents a newly discovered mechanism for biochemical detoxification of sulfur mustards, as this conversion blocks formation of the reactive episulfonium ion that is the ultimate alkylating agent for this class of compounds.

S-adenosyl-L-methionine:thioether S-methyltransferase, a new enzyme in sulfur and selenium metabolism

The final urinary excretion product of selenium detoxification is trimethylselenonium ion. An assay has been developed for the enzyme, S-adenosylmethionine:thioether S-methyltransferase, responsible for this final methylation reaction. This assay employed high pressure liquid chromatography separation and quantitation of the trimethylselenonium ion produced by thioether methyltransferase acting on S-adenosylmethionine and dimethyl selenide. The enzyme was shown to reside primarily in the cytosol of mouse lung (30 pmol/mg protein/min) and liver (7 pmol/mg protein/min). Purification from mouse lung to a preparation that exhibited a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was achieved by DEAE, gel filtration, and chromatofocusing chromatographies. Thioether methyltransferase is monomeric with a molecular weight of 28,000 and has a pI of 5.3. The pH optimum was 6.3, and Km values for dimethyl selenide and S-adenosylmethionine were 0.4 and 1.0 microM, respectively. The enzyme was inhibited 50% by 25 microM sinefungin, an analog of S-adenosylmethionine, or 40 microM S-adenosylhomocysteine, the reaction product. Pure thioether methyltransferase methylated selenium in dimethyl selenide, tellurium in dimethyl telluride, and S in dimethyl sulfide and many other thioethers. These data suggest a general role for this novel enzyme in the synthesis of onium compounds with increased aqueous solubility helpful in their excretion.

Periodate-oxidized adenosine inhibits the formation of dimethylselenide and trimethylselenonium ion in mice treated with selenite

The metabolic detoxification of selenite and many other selenium compounds involves a series of S-adenosylmethionine-dependent methylations yielding dimethylselenide (DMSe), which is exhaled, and trimethylselenonium ion (TMSe), which is excreted in the urine. This paper shows that periodate-oxidized adenosine (Adox) inhibits these methylation reactions in vivo and increases the toxicity of selenite. When Adox was injected in mice at 100 mumol/kg 30 min before injection of [75Se]selenite at 0.4 mg Se/kg the appearances of [75Se]DMSe in the breath and [75Se]TMSe in the liver were completely inhibited for 90 min. This was mediated by accumulation of S-adenosylhomocysteine, the methyltransferase inhibitor, in the livers of Adox-treated mice due to inhibition of its hydrolase enzyme. During 24 h, Adox-treated mice excreted no detectable urinary [75Se]TMSe and exhaled only 20% as much [75Se]DMSe as controls. The urine of Adox-treated mice also contained S-adenosylhomocysteine at a level (ca. 4 mM), 200 times that of untreated mice, which provided a convenient index of methylation potential in the intact animal. When three groups of three mice each were injected with 100 mumol Adox/kg, selenite at 4 mg Se/kg, or a combination of the two, the mice receiving the combination were dead within 2 days, while the mice in the other two groups all survived at least 4 days. These results verify the enzymatic nature of selenium methylation in vivo, support its importance in detoxification, and indicate the value of Adox in further studies of selenium metabolism.

Chromatographic analysis of the chiral and covalent instability of S-adenosyl-L-methionine

The chirality of biologically active S-adenosyl-L-methionine (AdoMet) is S,S, where the designations refer to the sulfur and the alpha-carbon, respectively. This paper describes a cation-exchange high-performance liquid chromatographic (HPLC) method for separating (S,S)-AdoMet from the biologically inactive (R,S)-AdoMet that results from racemization at the sulfur. This method was used to measure the rates of the degradation reactions of (S,S)-AdoMet as a function of pH. These reactions and the first-order rate constants, which were found at 37 degrees C and pH 7.5, are racemization, 1.8 X 10(-6) s-1; cleavage to homoserine lactone and 5'-(methylthio)adenosine, 4.6 X 10(-6) s-1; and hydrolysis to adenine and S-pentosylmethionine, 3 X 10(-6) s-1. Racemization showed no change in rate over the pH range from 7.5 to 1.5. The cleavage reaction persisted until the pH was lowered to 1.5, but hydrolysis ceased at pH 6. Commercial samples of nonradioactive AdoMet contained 20-30% (R,S)-AdoMet, while a sample of [methyl-3H]AdoMet had less than 1% (R,S)-AdoMet. Preparing enzyme substrates by mixing such samples will cause an underestimate of specific activity and an overestimate of the amount of product. The (R,S)-AdoMet/(S,S)-AdoMet ratio in mouse liver was 0.03, much less than the value of 0.19 calculated from the above rate constants. An enzyme extract from mouse liver did not degrade (R,S)-AdoMet, but a more thorough search may find such an activity. In any event, the cleavage and hydrolysis reactions partially balance the racemization of (S,S)-AdoMet in vivo and prevent excessive accumulation of (R,S)-AdoMet.

Effect of methotrexate with 5-methyltetrahydrofolate rescue and dietary homocystine on survival of leukemic mice and on concentrations of liver adenosylamino acids

We have increased significantly the survival time of DBA/2 mice bearing methionine-dependent L1210 or L5178Y leukemia cells by i.p. administration of lethal doses of methotrexate (five daily doses of 25 mg/kg body weight) followed by rescue with 5-methyl tetrahydrofolate (five daily doses of 20 mg/kg body weight). The mice were maintained on a semipurified choline- and cyst(e)ine-free diet containing 0.32% L-methionine. We further increased significantly the survival time of the treated animals bearing L5178Y cells, but not those bearing L1210 cells, by substitution of 0.86% DL-homocystine for the methionine in the diet. We have examined the effects of both diets in mice treated with methotrexate and 5-methyl tetrahydrofolate, singly and in combination, on the concentrations of S-adenosylmethionine and S-adenosylhomocysteine in the liver, a tissue highly active in the metabolism of these amino acids. The substitution of homocystine for methionine in the diet of untreated animals led to a significant increase in S-adenosylhomocysteine and decrease in S-adenosylmethionine in the liver, with a resultant profound decrease in the ratio of S-adenosylmethionine to S-adenosylhomocysteine which was not further altered significantly by administration of methotrexate.

Fractionation and kinetic properties of rat liver and kidney methionine adenosyltransferase isozymes

Three isozymes of methionine adenosyltransferase (EC 2.5.1.6; MAT-I, -II, and -III) exist in normal rat liver and are conveniently purified (MAT-III to homogeneity) by a three-step column chromatography procedure. MAT-I shows Michaelis-Menten kinetics with a Km (L-methionine) of 41 microM and a molecular weight of 208 000 and is slightly inhibited by S-adenosyl-L-methionine (Adomet). MAT-II, which is also the only isozyme found in normal rat kidney, shows negative cooperativity with a Hill coefficient of 0.7. It has a L-methionine concentration required for half-maximal velocity [S0.5(Met)] of 8 microM and a molecular weight of 120 000 and is strongly inhibited by Adomet. MAT-I and -II comprise 15% and 5%, respectively, of total MAT activity in rat liver. The predominant isozyme in rat liver, MAT-III, demonstrates positive cooperativity with a Hill coefficient of 1.8. It has a molecular weight of 97 000 and apparently consists of two subunits of identical molecular weight (47 000). This liver-specific isozyme is strongly activated by both dimethyl sulfoxide and Adomet and has a S0.5(Met) of 215 microM.

Experimental dissection of flagellar surface motility in Chlamydomonas

Experiments have explored the possible relationships between the flagellar surface motility of chlamydomonas, visualized as translocation of polystyrene beads by paralyzed (pf) mutants (Bloodgood, 1977, J. Cell Biol. 15:983-989), and the capacity of gametic flagella to participate in the mating reaction. While vegetative and gametic flagella bind beads with equal efficiencies and are capable of transporting them along entire flagellar lengths, beads on vegetative flagella are primarily associated with the proximal half of the flagella whereas those of gametic flagella exhibit no such preference. This difference may relate to the "tipping" response of gametes during sexual flagellar agglutination (Goodenough and Jurivich, 1978, J. Cell Biol. 79:680-693). Colchicine, vinblastine, chymotrypsin, cytochalasins B and D, and anti-beta-tubulin antiserum are all able to inhibit the binding of beads to the flagellar suface. Trysin digestion and an antiserum directed against whole chlamydomonas flagella have no effect on the ability of flagella to bind beads, but the beads remain immobile. These results suggest that at least two flagellar activities participate in surface motility: (a) bead binding, which may involve a tubulin-like component at the flagellar surface; and (b) bead translocation, which may depend on a second component (e.g. an ATPase) of the flagellar surface. Surface motility is shown to be distinct from gametic adhesiveness per se, but it may participate in concentrating dispersed agglutinins, in driving them toward the flagellar tips, and/or in generating a signal-to-fuse from the flagellar tips to the cell body. Directly supporting these concepts is the observation that bound beads remain immobilized at the flagellar tips during the "tip-locking" stage of pf x pf matings, and the observation that bound ligands such as antibody fail to be tipped by trypsinized flagella.

Decarboxylated S-adenosylmethionine in mammalian cells

The content of decarboxylated S-adenosylmethionine in rat tissues was found to be of the order of 0.9 to 2.5 nmol/g wet weight, about 2 to 4% of the content of S-adenosylmethionine. Three methods were used for determinations: separation by high pressure liquid chromatography followed by quantitation using UV absorbance, separation by paper electrophoresis after labeling with radioactive methionine to get the ratio of S-adenosylmethionine to decarboxylated S-adenosylmethionine, and separation by electrophoresis followed by elution and assay by an isotope dilution technique using spermidine synthase. The three methods gave comparable results, although the labeling with methionine appeared to slightly overestimate levels in the liver. Hepatic decarboxylated S-adenosylmethionine content was reduced by more than 90% for at least 8 h by treatment with methylglyoxal bis(guanylhydrazone), a potent reversible inhibitor of S-adenosylmethionine decarboxylase, but had returned to control levels by 24 h. The related irreversible inhibitor, 1,1'-[(methylethanediylidene)-dinitrilo]bis(3-aminoguanidine), reduced levels slightly less to about 20% of control, but maintained them at this value for 2 days.

Flagellar tip activation stimulated by membrane adhesions in Chlamydomonas gametes

Membrane adhesions between the flagella of mating-type "plus" and "minus" gametes of Chlamydomonas reinhardi are shown to stimulate a rapid change in the ultrastructure of the flagellar tips, designated as flagellar tip activation (FTA). A dense substance, termed fibrous tip material (FTM), accumulates between the flagellar membrane and the nine single A microtubules of the tip. The A microtubules then elongate, growing into the distal region of the tip, increasing tip length by 30%. This study describes FTA kinetics during normal and mutant matings, presents experiments designed to probe its role in the mating reaction, and offers the following conclusions: (a) FTA is elicited by agents that cross-link flagellar membrane components (including natural sexual agglutinins, antiflagellar antisera, and concanavalin A) but not by flagellar adherence to polylysine-coated films. (b) FTA is reversed by flagellar disadhesion. (c) Gametes can undergo repeated cycles of FTA during successive rounds of adhesion/disadhesion. (d) FTA, flagellar tipping, and sexual signaling are simultaneously blocked by colchicine and by vinblastine, suggesting that tubulinlike molecules, perhaps exposed at the membrane surface, are involved in all three responses. (e) FTA is not blocked by short exposure to chymotrypsin, by cytochalasins B and D, nor by concanavalin A, even though all block cell fusion; the response is therefore autonomous and experimentally dissociable from later stages in the mating reaction. (f) Under no experimental conditions is mating-structure activation observed to occur unless FTA also occurs. This study concludes that FTA is a necessary event in the sexual signaling sequence, and presents a testable working model for its mechanism.

Biosynthesis of S-N6-methyladenosylhomocysteine, an inhibitor of RNA methyltransferases

This paper demonstrates that N6-methyladenosine (6-methylaminopurine ribonucleoside) will condense in vitro with homocysteine to form S-N6-methyladenosylhomocysteine in a reaction catalyzed by mouse liver S-adenosylhomocysteine hydrolase. Injection of mice with N6-methyladenosine is followed by accumulation of S-N6-methyladenosylhomocysteine in the liver. Studies from other laboratories have shown that S-N6-methyladenosylhomocysteine is nearly as potent an RNA methyltransferase inhibitor as S-adenosylhomocysteine. This indicates that administration of N6-methyladenosine may be a general method for blocking in vivo RNA methylation in studies to determine the role of methylation in RNA processing and translational function.