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H Yu

Publications and source records attributed to H Yu.

At least 757 records · Page 42Linked to original sources
PubMed1989

Role of the octamer motif in hybrid cell extinction of immunoglobulin gene expression: extinction is dominant in a two enhancer system.

We have shown previously that genes activated by the immunoglobulin heavy chain (IgH) enhancer or promoter in mouse myeloma cells are extinguished upon fusion of the myeloma with a mouse T cell lymphoma. Here we show that the conserved octamer sequence shared by the IgH enhancer and promoter, when multimerized to form a tissue-specific enhancer, can also render a gene extinguishable under the same experimental conditions. Extinction, however, is not correlated with either absence of the tissue-specific transcription factor OTF-2 or loss of its ability to bind the octamer sequence. It was also found that extinction mediated by the IgH enhancer is dominant to transcriptional activation by the SV40 enhancer. We propose, therefore, that the T cell-negative regulator responsible for IgH gene extinction does not simply prevent IgH enhancer activation but interferes with gene expression more directly, perhaps by disrupting the transcription complex established as a result of tissue-specific enhancer activation.

Animals↗
PubMed1989

Vanadate activation of bromoperoxidase from Corallina officinalis.

A nonheme bromoperoxidase has been purified to homogeneity from the red seaweed Corallina officinalis. Like the corresponding enzyme previously reported from C. pilulifera, this bromoperoxidase contains a significant amount of nonheme iron. However, it is vanadate ion and not iron that activates the enzyme, and maximal activity is achieved with stoichiometric vanadium incorporation. The absence of competition between vanadium and iron suggests that they occupy distinct binding sites in the protein. A correlation between vanadium content and catalytic activity indicates that less than 12 percent of the maximal activity of the enzyme can be derived from metals other than vanadium.

Binding Sites↗
PubMed1989

Adrenergic receptors mediate changes in c-fos mRNA levels in brain.

Recent evidence supports a role for transient c-fos expression as one step in signalling pathways by which membrane receptor-ligand interactions are transduced into appropriate intracellular responses. The activity of adrenergic receptors is mediated by second messenger systems which include ion fluxes, changes in cAMP concentration and enhanced phosphoinositide turnover. In order to determine if C-fos induction was also a step in adrenergic signal transduction in the brain, we performed in vivo studies with drugs specific for different adrenergic receptor types. Unexpectedly, we found that the stress associated with a single intraperitoneal (i.p.) injection of drug vehicle produced a transient increase (averaging 4.0-fold) in c-fos mRNA levels in rat brain. Injection of the alpha 2-adrenoreceptor antagonist, yohimbine, produced a transient increase which was larger in magnitude (averaging 9.6-fold) and longer in duration than that produced by injection of the drug vehicle alone. In experiments designed to ask whether either of these inductions was mediated by specific types of adrenergic receptors, we found that the alpha 2- and beta-adrenoreceptors were involved in both responses, while the alpha 1-receptor played a role in mediating the yohimbine induction, but no detectable role in the solvent induction. One hypothesis consistent with our results is that the norepinephrine (NE) released due to the stress associated with an i.p. injection interacts with postsynaptic beta-adrenergic receptors, resulting in the observed c-fos mRNA induction. When the negative feedback effect of NE, mediated by presynaptic alpha 2-receptors, is blocked by yohimbine, the postsynaptic response is enhanced and prolonged.

Adrenergic alpha-Antagonists↗
PubMed1988

Cigarette smoking, alcohol consumption and primary liver cancer: a case-control study in the USA.

Cigarette smoking and alcohol consumption were examined as potential risk factors in a case-control study of primary liver cancer (PLC). A total of 165 PLC cases and 465 matched controls from several US hospitals were studied. A weak but statistically significant (p less than 0.05) dose-response relationship was observed between alcohol consumption and PLC in elderly females independent of other major risk factors (adjusted OR = 1.87 and 3.48 for 1-2 and greater than 3 drinks per day, respectively) and a similar trend was evident in elderly males. The risk for PLC was also elevated in elderly females who were current cigarette smokers (adjusted OR = 3.30). Our results suggest that alcohol consumption and cigarette smoking may have minor age- and sex-specific effects on the development of PLC, and underscore the need for further investigations to elucidate major PLC risk factors in US populations.

Adult↗
PubMed1988

T cell recognition of endogenous IgG2a expressed in B lymphoma cells.

We recently characterized a panel of C57BL/6J T cell clones specific for IgG2a of the a allotype in association with I-Ab. Several of the clones gave surprisingly strong responses in the presence of normal spleen cells from several H-2b strains, including C3H.SW, A.BY, D1.LP and BALB.B, without the addition of exogenous antigen. Experiments using Igh-congenic mouse strains demonstrated that this response was directed towards shared allotypic determinants expressed on endogenously synthesized IgG2a molecules in various strains. Here we present evidence that the cell(s) responsible for this stimulation are conventional low density splenic accessory cells. Presentation of endogenously synthesized IgG2a by this population of dendritic cells, macrophages, and/or activated B cells was chloroquine sensitive. Thus, we conclude that this response is probably directed towards secreted IgG2a molecules that are internalized, processed and re-expressed at the cell surface in association with class II molecules. We also tested the ability of T cell clone B61-34 to respond in the presence of the B lymphoma cell line M12.C3.A2. A strong response was again observed in the absence of exogenous antigen. Northern gel analysis of M12.C3.A2 messenger RNA provided evidence that these cells synthesize IgG2a in both a secreted and a membrane form. The response directed towards endogenous IgG2a expressed in M12.C3.A2 lymphoma cells is chloroquine resistant and considerably more efficient than that stimulated by IgG2a added as exogenous soluble antigen. These results demonstrate for the first time that B cells have the capacity to present antigenic determinants expressed on endogenously synthesized immunoglobulins to class II-restricted T cells. The implications of these findings with respect to network models of immune regulation are discussed.

Animals↗
PubMed1988

Case-control study of prostate cancer and socioeconomic factors.

A total of 1,162 prostate cancer cases and 3,124 age-matched hospital controls from several U.S. hospitals were studied to identify associations between prostate cancer and life-style variables. Among white males, college education, professional occupation, and non-Jewish ethnicity were weakly associated with the risk of prostate cancer (ORs = 1.5, 1.8, and 1.3, respectively, P less than 0.01). These relationships retained statistical significance after adjustment for age, marital status, body mass, cigarette smoking, alcohol consumption, and physical activity in multiple logistic regression models. Among black males, similar, though nonsignificant, risk elevations were observed for education and occupation. Weak positive effects of borderline statistical significance were observed for high body mass, low physical exercise, and high serum cholesterol (in elderly males only), and a significant reduction in risk was noted for never married black males. Cigarette smoking and alcohol consumption were not related to the risk of prostate cancer.

Adult↗
PubMed1988

Distribution of Clostridium botulinum in Japan and in Shinkiang district of China.

Soil specimens obtained from several areas of Japan, which are closely located to or facing the Continental land of China, were examined for the distribution of Clostridium botulinum, especially pertaining to types A and B. A total of 266 specimens of Japan, when cultured, showed no type A or B toxicity, although 30 (11.3%), 4 (1.5%), and 10 (3.8%) of the specimens showed C1, C2, and type E toxicities, respectively. On the contrary, types A and/or B toxicities were shown, by the same method, in 14 of 20 specimens of Shinkiang district, China. The highest number of C. botulinum cells found in one gram of soil specimen was 25 for type A and 10 for type B.

China↗
PubMed1988

Genes activated in the presence of an immunoglobulin enhancer or promoter are negatively regulated by a T-lymphoma cell line.

The tissue-specific expression of immunoglobulin genes can be partially explained by a requirement for activating factors found only in B lymphocytes and their derivatives. However, loss of immunoglobulin expression upon fusion of an immunoglobulin-producing myeloma cell with a T lymphoma cell (BW5147) or fibroblast (L cell) suggests that negatively acting factors also play a role in the tissue specificity of immunoglobulin genes. Expression of a cloned immunoglobulin heavy-chain gene introduced into myeloma cells was suppressed after fusion of the myeloma transformants with BW5147. The presence of either the immunoglobulin heavy-chain enhancer or promoter conferred suppression, under similar conditions, upon a heterologous gene that is normally expressed in both B and T lymphocytes. These immunoglobulin heavy-chain gene control regions, or gene modifications induced by them, are subject to negative control by T-lymphocyte-derived factors.

Animals↗
PubMed1986

DNA rearrangement causes a high rate of spontaneous mutation at the immunoglobulin heavy-chain locus of a mouse myeloma cell line.

The spontaneous mutation rate of immunoglobulin genes expressed in myeloma cells is well above that of other genes expressed in these or in other cell types. The nature of such mutations in one myeloma cell line, MPC11, was explored at the molecular level. Included in this study were MPC11 variants representing 24 independent and spontaneous mutations affecting immunoglobulin secretion. Of the mutants studied, 19 had ceased immunoglobulin heavy chain (IgH) production (nonproducers), and 5 produced from as little as 1/1,000 to as much as 1/10 the amount of immunoglobulin produced by MPC11 (low producers). Only one of the MPC11 mutants (a nonproducer) showed no evidence of DNA rearrangement in or near the expressed IgH gene. The formerly expressed gamma 2b gene had been deleted in 18 of the 19 nonproducers. All of the low producers had undergone DNA rearrangement in or near the expressed IgH gene, and three of them produced immunoglobulin of a new heavy chain class. The cause for reduced heavy-chain synthesis in the low producers is not yet known. However, in several of these mutants, the defect appeared to be posttranscriptional. In these cell lines, steady-state IgH mRNA levels were much lower than in the parent cell line, while the heavy-chain gene transcription rate remained unchanged.

Animals↗
PubMed1985

Black thyroid: clinical manifestations, ultrastructural findings, and possible mechanisms.

Ultrastructural examination of three black thyroid glands showed lysosomal accumulations of lipofuscin-like pigment and granular electron-dense material in association with 1) a minocycline-associated black thyroid with normal thyroid function; 2) a minocycline-associated black thyroid with a significant inflammatory component, fibrosis, and primary hypothyroidism; and 3) a black thyroid gland with no exposure to minocycline. The deposition of the pigments in the three cases resulted in macroscopically recognizable black thyroid glands. It is speculated that an imbalance in lysosomal function accounts for this abnormality. The glandular hypofunction documented in case 2 is unique and confirms the need to monitor function carefully in patients who are receiving minocycline. In one case electrondense deposits were identified in the thyroid gland interstitium.

Adult↗
PubMed1985

RNA sequence containing hexanucleotide AAUAAA directs efficient mRNA polyadenylation in vitro.

To determine whether a specific nucleotide sequence is required to direct polyadenylation of a simian virus 40 early pre-mRNA in a soluble HeLa whole-cell lysate, we constructed a series of rearranged and deleted DNA templates, transcribed them in vitro, and determined whether the resultant RNAs could be polyadenylated when incubated in whole-cell lysate. When a 237-base-pair DNA fragment encoding the 3' end of the simian virus 40 early pre-mRNA was transferred to recombinant plasmids encoding RNAs that were not substrates for polyadenylation, the resultant RNAs could now be polyadenylated efficiently. In one case, the chimeric RNA was polyadenylated even more efficiently than was the original simian virus 40 early transcript. Analysis of the RNAs produced from the deletion mutant templates revealed that only RNAs containing at least one copy of the AAUAAA sequence situated near the 3' end and implicated in 3'-end formation and polyadenylation in vivo could be polyadenylated in vitro. Surprisingly, this sequence directed polyadenylation of pre-mRNAs not only when near the RNA 3' end, i.e., 50 nucleotides or less away, but also when the 3' end was situated over 400 nucleotides downstream. Thus, our results show that a polyadenylic acid polymerase activity in HeLa lysates can recognize a specific nucleotide sequence in pre-mRNA and then, in the absence of the nucleolytic cleavage that presumably occurs in vivo, locate the RNA 3' end and use it as a primer for polyadenylic acid synthesis.

Base Sequence↗