Reversible desensitization of fibroblasts to cadmium receptor stimuli: evidence that growth in high zinc represses a xenobiotic receptor

The xenobiotic Cd2+ triggers the production of inositol trisphosphate and releases stored Ca2+ in certain cell types, apparently by binding to a zinc site in the external domain of an "orphan" receptor (no known endogenous stimulus). Cd2+ and bradykinin evoke similar spikes in cytosolic free Ca2+. Growth in high Zn2+ (100-200 microM) abolished the free Ca2+ spike evoked by Cd2+ without affecting the spike produced by bradykinin. Growth in high Zn2+ almost abolished Cd(2+)-evoked production of [3H]inositol mono-, bis-, and trisphosphate. Bradykinin-evoked [3H]inositol phosphate production was not affected by growth in high Zn2+. Growth in high Zn2+ nearly prevented the stimulation of 45Ca2+ efflux by Cd2+ without affecting the stimulation of 45Ca2+ efflux by bradykinin or histamine. Removing Zn2+ from the culture medium and incubating the cells for several hours fully restored responsiveness to Cd2+. Cycloheximide, actinomycin D, or tunicamycin prevented the restoration of Cd2+ responsiveness, indicating that resensitization requires macromolecular synthesis. Growth in high Zn2+ reversibly abolished Ca2+ mobilization evoked by two additional stimuli: a decrease in extracellular pH or Na+ concentration. These findings support the hypothesis that the three stimuli (Cd2+ or a decrease in external pH or Na+ concentration) activate the same orphan receptor. Growth in high Zn2+ apparently desensitizes the cells to the Cd2+ receptor stimuli by repressing receptor synthesis.

[Determination and clinical significance of lipoprotein(a) in cardio-cerebrovascular diseases]

We determined the level of lipoprotein (a) [Lp(a)] in 1,266 healthy persons and established the reference value of Lp(a) in various groups of age and sex. The analysis of lipids in myocardial infarction survivors and stroke survivors suggest that increased Lp(a) is an independent risk factor in cardio-cerebrovascular diseases. The characteristics of abnormal lipids in cardio-cerebrovascular diseases are discussed.

[Identification of twenty-eight species mycobacteria with their cellular fatty acids by capillary gas chromatography]

Cellular fatty acid (FA) of 28 species of mycobacteria were analysed by capillary gas chromatography (GC). There were more than sixty volatile FA before C12:0 have no any difference between species both in quality and quantity. The identification scheme of Mycobacterium based on cellular FA was presented here. According to this scheme, all the tested species could be divided into 8 groups by the FA peak height order of C18:1, C18:0 and TBSA which were quite stable; after that, 17 species (60%) might be identified to species level with help of some distinctive FA such as C19:0, C21:0. Most pathogenic bacteria could be separated by the scheme (M. tuberculosis, M. bovis and some complexes). This scheme was also demonstrated to be objective rationality by computer cluster analysis with cellular FA components.

The conserved dinucleotide AG of the 3' splice site may be recognized twice during in vitro splicing of mammalian mRNA precursors

We have previously used site-directed mutagenesis to introduce an additional branch site into the first intron of the human beta-globin gene at nt -24 between the natural branch site (nt -37) and the normal 3' splice site (nt -1). We found that either the upstream or downstream branch site could be used during in vitro splicing, depending on which site best matched the mammalian branch site consensus YURAC (R = purine; Y = pyrimidine). Here we show that introduction of an additional AG dinucleotide at nt -20 between the downstream branch site and the normal 3' splice site results in alternative 3' splicing. Splicing to the new AG uses the upstream branch site exclusively, presumably because the downstream branch site is only 4 nt from this 3' splice site. We were surprised, however, to find that the presence of the new AG also prevents the use of the upstream branch site for splicing to the normal 3' splice site. Analysis of additional mutants confirmed earlier work [Krainer et al.: Mechanisms of human beta-globin pre-mRNA splicing. In Berg, P. (Ed.), The Robert A. Welch Foundation Conferences on Chemical Research XXIX. Genetic Chemistry: The Molecular Basis of Heredity. Welch Foundation, Houston, TX, 1985, pp. 353-382] that the new AG cannot function by itself as a complete 3' splice site; rather, it appears that alternative 3' splicing initiates at the normal 3' splice site but then searches, once the reaction is underway, for the first AG downstream from the chosen branch site. Taken together, our data suggest that the conserved AG dinucleotide at the 3' splice site may be recognized twice during mammalian mRNA splicing in vitro.

[Rapid identification of Mycobacterium tuberculosis and other mycobacteria with Mycobacterium tuberculosis whole chromosomal DNA probe]

The dot-blots containing DNA isolated from nonmycobacterial and mycobacterial microorganisms were hybridized with 32P-labeled M. tuberculosis whole chromosomal DNA at the various temperatures. The probe did not cross-hybridize to DNA of nonmycobacterial microorganisms (E. coli, Plasmid pUC19, Nocardia asteriodes), nor with DNA from all mycobacteria tested except M. bovis BCG under the higher temperature conditions. Microorganisms could also be directly spotted and lysed on nitrocellulose filters and used for hybridization thus making this technique suitable for clinical diagnosis.

A compensatory base change in human U2 snRNA can suppress a branch site mutation

We have developed an assay to test whether U2 snRNA can base-pair with the branch site during mammalian mRNA splicing. The beta 110 point mutation (GG----AG) within the first intron of human beta-globin generates a new 3' splice site that is preferentially used. We show here that use of the normal 3' splice site can be restored either by improving the match of a cryptic branch site to the branch site consensus or by introducing mutant U2 snRNAs with greater complementarity to the cryptic branch site. These data indicate that human U2 snRNA can form base pairs with the mRNA precursor; however, base pairing appears to be optional because some mammalian branch sites do not match the consensus.

The natural 5' splice site of simian virus 40 large T antigen can be improved by increasing the base complementarity to U1 RNA

The use of alternative 5' splice sites in the simian virus 40 early-transcription unit controls the ratio of large T to small t antigen during viral infection. To study the regulation of these alternative 5' splice sites, we made two mutants which improve the match of the large-T-antigen 5' splice site to the 5' splice site consensus sequence. Whether these mutants were assayed in vitro or in vivo, we found that the efficiency of large-T splicing is increased by improving the match of the large-T-antigen 5' splice site to the consensus. We conclude that the match of a 5' splice site is an important determinant of 5' splice site utilization and that the simian virus 40 large-T-antigen 5' splice site is almost certainly recognized by the U1 small nuclear RNA component of the U1 small nuclear ribonucleoprotein particle.

A compensatory base change in U1 snRNA suppresses a 5' splice site mutation

Indirect evidence suggests that the 5' end of U1 snRNA recognizes the 5' splice site in mRNA precursors by complementary base pairing. To test this hypothesis, we asked whether point mutations in the alternative 12S and 13S 5' splice sites of the adenovirus E1A gene can be suppressed by compensatory base changes in human U1 snRNA. When the mutant E1A and U1 genes are contransfected into HeLa cells, we observe efficient suppression of one mutation at position +5 in the 12S splice site, but exceedingly weak suppression of another mutation at position +3 in the 13S splice site. These and other results suggest that base pairing between U1 and the 5' splice site is necessary but not sufficient for the splicing of mRNA precursors.

Characterization of potent Na+/H+ exchange inhibitors from the amiloride series in A431 cells

Na+/H+ exchange is stimulated in a variety of cell types by addition of mitogenic polypeptides such as epidermal growth factor or platelet-derived growth factor. In order to assess the importance of Na+/H+ exchange in the mitogenic response, it is desirable to have available inhibitors of this process which exhibit high affinity and good specificity. We characterize in this report a number of 5-alkylamino-substituted derivatives of amiloride [3,5-diamino-6-chloro-N-(diaminomethylene)pyrazinecarboxamide++ +] which show much higher affinity than the parent compound for the Na+/H+ antiporter in A431 cells. High affinity is conferred by substitution with two alkyl groups and is increased by introducing a branched alkyl chain. An analogue bearing a 5-anilino group is also very potent. These analogues effectively inhibit the elevation of intracellular pH upon stimulation of Na+/H+ exchange by growth factors. We have assessed other potential inhibitory effects of these compounds on cellular metabolism. In agreement with previous reports, we find that amiloride inhibits protein synthesis both in cells and in cell-free translation systems. While amiloride and its analogues show similar inhibition of protein synthesis in a cell-free system, most analogues inhibit cellular protein synthesis at much lower concentrations than does amiloride. These analogues are also potent inhibitors of purified Na,K-ATPase and cause a profound decrease in intracellular K+ as well as ATP content. These latter effects, however, require analogue concentrations which are 5-7 times higher than those inhibiting cellular protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)