Inhibition of eukaryotic translation by nucleoside 5'-monophosphate analogues of mRNA 5'-cap: changes in N7 substituent affect analogue activity

Nucleotide cap analogues of 7-methylguanosine 5'-monophosphate (m7GMP) were synthesized in which the 7-methyl moiety was replaced with 7-ethyl (e7), 7-propyl (p7), 7-isopropyl (ip7), 7-butyl (b7), 7-isobutyl (ib7), 7-cyclopentyl (cp7), 7-(carboxymethyl) (cm7), 7-benzyl (bn7), 7-(2-phenylethyl) [7-(2-PhEt)], and 7-(1-phenylethyl) [7-(1-PhEt)]. These derivatives were assayed as competitive inhibitors of capped mRNA translation in reticulocyte lysate. We observed that N7 alkyl and alicyclic substituents larger than ethyl significantly decreased the inhibitory activity of these cap analogues presumably by decreasing their affinity for cap binding proteins, which participate in the initiation of translation. This result defined a maximum size for this class of N7 substituents in the nucleotide binding domain of cap binding proteins. Like m7GMP, the N7-substituted GMP derivatives synthesized in this study were found to be predominantly in the anti conformation as determined by proton NMR analyses. However, bn7GMP and 7-(2-PhEt)GMP, which have aromatic N7 substituents, were more effective than m7GMP as competitive inhibitors of translation. The increased affinity of bn7GMP for cap binding proteins was further examined by synthesis of beta-globin mRNA containing 5'-bn7G, 5'-m7G, or 5'-e7G cap structures. These modified mRNAs were tested as translation templates. Messenger RNA capped with bn7G was observed to increase the translation activity of the template 1.8-fold relative to that of its m7G-capped mRNA counterpart. By contrast, e7G-capped mRNA was 25% less active than m7G-capped mRNA.2+V photo-cross-linking of m7G-capped mRNA to cap binding proteins

Trisomy 7 and sex chromosome loss in human brain tissue

Short-term cultures of nonneoplastic brain tissue from 11 patients, seven of whom had a malignant brain tumor, were cytogenetically examined. In only a single case was a wholly normal chromosome complement detected; the remaining ten cases exhibited mosaicism with clonal numerical aberrations found alongside cells carrying a normal karyotype. The abnormal clones were characterized by trisomy 7, the loss of the Y chromosome in men and an X chromosome in women, or by combinations thereof. No structural aberrations were present. Our findings demonstrate that although -Y, -X, and +7 have in the past repeatedly been associated with brain tumors, these changes presumably reflect normal in vivo organ mosaicism and, thus, should not be accepted as neoplasia-specific in this context.

Inhibition of adenylate cyclase in bovine ciliary process and rabbit iris ciliary body to alpha 2-adrenergic agonists

Alpha 2-adrenergic inhibition of adenylate cyclase in bovine ciliary processes and rabbit iris ciliary body (ICB) was studied. With bovine ciliary process membrane, it was found that cAMP production in the presence of 1 microM isoproterenol was increased with increasing NaCl concentrations from 0 to 200 mM. Clonidine, an alpha 2-adrenergic agonist, produced a NaCl concentration-dependent inhibition of cAMP production in the presence of isoproterenol with a maximum inhibition at 200 mM NaCl (P less than 0.05). NaCl concentrations had no effect on basal adenylate cyclase activities and activity in the presence of clonidine alone. The alpha 2-adrenergic agonists, lofexidine, clonidine and p-amino-clonidine were tested for their ability to inhibit isoproterenol-stimulated adenylate cyclase in bovine ciliary process membrane in the presence of 200 mM NaCl. Their dose-response curves showed that they had similar IC50's but the maximum inhibition differed among these agonists. Clonidine was found to be a partial agonists producing 55% of the inhibition obtained with lofexidine. The specificity of inhibition of isoproterenol-stimulated adenylate cyclase by alpha 2-agonists and blockade by pertussis toxin was examined by adenine labelling in rabbit ICB. The results demonstrate that alpha 2-adrenergic receptors exert specific inhibitory effects on adenylate cyclase activity in rabbit ICB, which are mediated by an inhibition guanine nucleotide regulatory protein, Gi.

Genetic convergence during serial in vitro passage of a polyclonal squamous cell carcinoma

A cell line was established from an in situ squamous cell carcinoma of the skin (Bowen's disease), and its in vitro karyotypic evolution was cytogenetically analyzed. Initially, considerable genetic heterogeneity was evident. Nine cytogenetically abnormal clones, eight of which were apparently unrelated, were found among the 83 metaphases analyzed from the primary culture and the first passage. With increasing time in culture this complexity was reduced, so that a single clone dominated passages 7-11. The clone that emerged from this genetic convergence had a t(12;17)(p13;q21) as the sole abnormality. Our findings indicate that the cytogenetic multiclonality that has been repeatedly detected in short-term cultures of squamous cell carcinomas is not caused by the in vitro conditions. Instead, the principles of Darwinian selection apply: the altered, but stable, selection pressure facing a newly established and initially multiclonal cell line will lead to a reduction of genetic heterogeneity until the one clone that now has the proliferative advantage outgrows the other subpopulations.

3-Hydroxyumbilicaric Acid and 3-Methoxyumbilicaric Acid, New Tridepsides From the Lichen Parmelinopsis bonariensis

The new tridepsides 3-hydroxyumbilicaric acid (4) and 3-methoxyumbilicaric acid (5) have been detected in the lichen Parmelinopsis bonariensis and the structures established by unambiguous synthesis.

Multiple unrelated clonal chromosome abnormalities in an in situ squamous cell carcinoma of the skin

We have cytogenetically analyzed short-term cultures from an in situ squamous cell carcinoma of the skin (Bowen's disease). The following mosaic tumor karyotype was found: 46,XX, -1, +der(1)(pter----p22::q11----cen----p22:), -9, +der(9)t(1;9)(q11; p24)/46,XX,t(3;6) (q21;p21)/46,XX,t(5;14)(q13;q24),t(7;18)(q32;q11)/46,XX,t(8;11)(p22;q13) /46, XX,t(8;11) (p22;q13),t(15;17) (q13;q24)/46,XX,t(12;15)(q12;p11). None of the rearrangements correspond to previously known cancer-associated abnormalities. Two of the clones are obviously related, and it is reasonable to assume that the t(15;17) developed as an evolutionary change in a cell that already contained t(8;11)(p22;q13). Since five clones without cytogenetic similarities were found in this in situ skin carcinoma, we suggest that the tumor was of polyclonal origin. It is impossible to decide whether all, or indeed any, of the visible abnormalities constitute pathogenetically essential primary changes, or merely represent chromosomal markers of secondary importance in tumorigenesis.

Beta-globin mRNAs capped with m7G, m2.7(2)G or m2.2.7(3)G differ in intrinsic translation efficiency

We examined the intramolecular effect of altered cap structures on translation efficiency of artificial beta-globin mRNAs. For these studies, synthetic dinucleotides of the form X(5')ppp(5')G [X = 7-methyl guanosine (m7G), 2,7-dimethyl guanosine (m2(2,7)G) or 2,2,7-trimethyl guanosine (m3(2,2,7)G)], were transcriptionally incorporated into mRNAs, containing rabbit beta-globin coding sequences, using T7 RNA polymerase and a beta-globin cDNA template. These synthetic mRNAs were assayed in reticulocyte lysate for activity relative to m7G-capped mRNA. m2(2,7)G-Capped mRNA was found to be 1.5-fold more active than m7G-capped mRNA. Messenger RNA capped with m3(2,2,7)G was less active with activity of 0.24 relative to its m7G-capped counterpart (activity = 1.0). These data suggest that m7G-capped mRNAs become more active as translation templates after addition of a single N2 methyl moiety, which is especially pertinent to gene expression in togaviridae. The latter are observed to synthesize m2(2,7)G and m3(2,2,7)G-capped mRNAs in addition to m7G-capped templates during the course of infection in animal cells.

Disposition and metabolism of [14C]-amezinium metilsulfate in rats

Disposition and metabolism of [14C]-amezinium metilsulfate (4-amino-6-methoxy-1-phenylpyridazinium methylsulfate, Risumic) were systematically studied in rats after intravenous (5 mg/kg) or oral (20, 100 mg/kg) administration. After oral administration at 20 mg/kg, blood level reached the maximum (Cmax) of 0.65 microgram eq/ml at 3 h (tmax) and decreased with t1/2 of 8.1 h. Levels in plasma and most tissues elevated to the Cmax at 3 h. The liver level was the highest (61 times as high as plasma level) of all examined tissues. Most tissue levels decreased thereafter essentially in parallel with plasma levels. The findings by whole-body autoradiography essentially agreed with those by radiometry. In lactating rats, milk levels were virtually similar to plasma levels. [14C]-Amezinium metilsulfate radioactivity in fetus and fetal blood was around 0.3 microgram eq/g, being about 1/10 level of maternal plasma level. About 24, 72 and 42% were excreted in urine, feces and bile, respectively. Re-absorption of biliary metabolites accounted for about 31%, being about 13% of orally given [14C]-amezinium metilsulfate. Plasma and aorta contained unchanged amezinium and glucuronide of hydroxyl amezinium MIII. In the brain, the major metabolite was O-demethyl amezinium MV and unchanged drug was not detected. Urinary metabolites were largely MIII glucuronide and the unchanged drug. Biliary metabolite was found composed mostly from MIII glucuronide. In feces, MIII and the unchanged amezinium were found. MIII and its glucuronide were novel metabolites which were identified by thin-layer chromatography and mass spectrometry.

Human T cell response to the surface antigen of hepatitis B virus (HBsAg). Endosomal and nonendosomal processing pathways are accessible to both endogenous and exogenous antigen

We have studied the antigen specificity and processing requirements of three vaccine-induced cloned human T cell lines specific for HBsAg, the envelope protein of hepatitis B virus. Each T cell line recognized endogenously expressed antigen as well as exogenous antigen. Two clones required endosomal processing, both for exogenous and endogenous antigen; while the other T cell line depended on nonendosomal processing to generate antigenic peptides from both endogenous and exogenous antigen. Thus, the two processing pathways are accessible to exogenous and endogenous antigen. These results suggest that vaccine-induced T cells can participate actively in the immune response to live virus.

Iron transfer from ferritin to transferrin. Effect of serum factors

The transfer of iron from 59Fe-labelled human spleen ferritin to human apotransferrin occurs in the absence of either reducing or chelating agents. The reaction is first order with respect to ferritin and zero order to apotransferrin. The transfer is enhanced by low-Mr substances from human serum such as ascorbate, citrate, bicarbonate and lactate. A mixture of the four molecules at their normal physiological concentrations can increase the iron exchange to the same extent as that observed with an ultrafiltrate of serum. A pathway of intracellular iron mobilization is considered.