Biomedical subjects

D Yuan

Publications and source records attributed to D Yuan.

At least 55 records · Page 3Linked to original sources

PubMed1994

Role of differential mRNA stability in the regulated expression of IgM and IgD.

The expression of IgM and IgD heavy chain mRNA in resting vs activated B cells offers a unique tool for the assessment of the effect of translation on mRNA stability because mu and delta mRNA have identical VDJ sequences but differ substantially in the rest of the molecule. We have shown that despite the 5' UTR identity that allows equal access to the translation machinery, mu mRNA has a significantly higher turnover rate than delta mRNA. However, the short t1/2 of mu mRNA increases significantly after B cell activation. Furthermore, the induction of microS mRNA after B cell activation provides yet another related molecule for comparison. Thus, despite the fact that microS and microM mRNA differ at their 3' ends, they have identical turnover rates in activated B cells. In addition, because the turnover rates of delta mRNA and beta 2 and GAPDH mRNA remain unchanged, these experiments suggest that B cell activation results in the induction of regulatory factor(s) that target specific sequences within mRNA-mu to confer greater stability. They also argue against a more passive regulation of mRNA stability that is a consequence of alterations in the secretory machinery.

Animals↗

PubMed1994

Interactions between B lymphocytes and NK cells.

The ability of natural killer (NK) cells to secrete lymphokines confers upon them the potential to regulate cell types via mechanisms other than direct cytotoxicity. During the past few years increasing evidence has been accumulating to show that NK and B cells can interact productively. First, NK cells cocultured with B cells can induce them to initiate polyclonal Ig secretion. This help is mediated by a soluble factor (or factors) that appears to be different from any known cytokine. Second, preactivated B lymphocytes can induce NK cells to produce greater amounts of IFN-gamma via an interaction that requires direct cell contact. Third, in contrast to previous suggestions, NK cells do not have the ability to kill primary B lymphocytes regardless of their stage of differentiation. Evaluation of the in vivo relevance of these interactions revealed that activated NK cells can increase the IgG2a response to a specific protein antigen. Without activation, NK cells neither enhance nor inhibit B cell responses to antigens. The deviation of the isotype distribution may allow increased NK cell specificity for certain pathogens by enhancing antibody-dependent cytotoxicity.

Animals↗

PubMed1993

Transcriptional analysis of inhibition of lipopolysaccharide response by anti-IgM.

Murine splenic B cells, when stimulated with LPS, show a generalized enhancement of gene transcription. In addition to this general increase, there is a specific increase in microseconds mRNA production and differentiation to high rate IgM secretion. Anti-mu added concomitantly with LPS at the start of culture has been demonstrated to inhibit the LPS-induced increase in microseconds mRNA production without affecting the proliferative capacity of the cells. By "run-on" analysis of nascent transcription, we have shown that the effect of anti-mu is mediated by the abrogation of the up-regulation of transcription of the mu-gene induced by LPS. Furthermore, by assessing the site of transcription termination, it is possible to infer that alterations in 3'-end processing induced by LPS are also inhibited. We have also found that CAT3 gene activity driven by a number of promoter/enhancers with diverse regulatory motifs are inhibited by anti-mu. These results suggest that the effect of anti-mu cannot be restricted to interactions with a single regulatory element. Therefore, cross-linking of surface IgM may affect a number of genes involved in differentiation to Ig secretion.

Animals↗

PubMed1993

Regulatory elements necessary for termination of transcription within the Ig heavy chain gene locus.

Previous experiments have shown that the extent of delta gene transcription during B cell development is regulated primarily at the transcriptional level. We have shown that deletion of a sequence located between the mu and delta coding regions in the Ig heavy chain locus where transcriptional termination has been previously mapped abrogates the termination. Restoration of termination requires reintroduction of this segment as well as sequence elements within the microM poly (A) site which cannot be substituted by the microS poly (A) site. Recognition of the termination site by non-lymphoid cells suggests that initiation of delta transcription in mature B lymphocytes requires the activation of an anti-termination mechanism not yet developed in early B cells.

Animals↗

PubMed1992

Mechanism of lipopolysaccharide-mediated transcriptional enhancement of the mu gene.

LPS induces both B cell proliferation and differentiation to Ig secretion. By treating stimulated cells for a brief period with staurosporine, and inhibitor of protein kinase C, it is possible to allow continued proliferation but partially inhibit differentiation. Analysis of the molecular basis for the decrease in IgM production shows that the increased transcription of the Ig-H chain gene induced by LPS is abrogated by staurosporine treatment whereas alteration of 3' end processing is not affected. These experiments indicate that LPS continues to mediate its effect on some of the more distal differentiative events through protein kinase C even after initial cell activation.

Alkaloids↗

PubMed1992

Activation of B lymphocytes by NK cells.

The ability of NK cells to induce differentiation of B lymphocytes to IgM secretion in vitro has been investigated. Homogeneous preparations of NK cells obtained from IL-2 propagated splenocytes from SCID mice were found to have the ability to induce resting B lymphocytes to proliferate and secrete significant amounts of IgM. The induction is greatly enhanced by the presence of both IL-2 and IL-5 and does not require T lymphocytes or adherent cells in the responding population. Cell contact between the two populations is not necessary suggesting that the effect is mediated by soluble factor(s) which can be produced even by irradiated NK cells. Because the activity cannot be replaced by either r-tau-IFN or tumor necrosis factor-alpha or inhibited by antibodies to these lymphokines, a novel NK cell-derived factor(s) may be involved. The implications of this interaction between NK cells and B lymphocytes are discussed.

Animals↗

PubMed1992

[Effect of He-Ne laser acupuncture on lymph-nodes in rats].

The lymphocytes and antigen presenting cells in lymph node of rats stimulated by He-Ne laser acupuncture were observed by using TEM and SEM to investigate the ultrastructural changes of them. There were numerous activated T-cells which showed deeply indented nucleus, abundant small void mitochondria and free ribosomes in the paracortex area. The B-cells were gradually differentiated into large lymphocytes, immature and mature plasmatic cells which with a lot of rough endoplasmic reticulum. They were prominently increased in the pulp area. The macrophages had short processes with numerous folds and microvilli and tended to neighboring lymphocytes. The nucleus pores were increased. There were a lot of pinocytosomes, phagosomes, lysosomes in various size of macrophages. The bundles (5-6 nm in diameter) of microfilaments of the macrophages were extended from the cytoplasm to the processes. The interdigitating cells which contained the characterized single layer of rER, numerous polysomes, mitochondria and well-developed Golgi-complex were closed to macrophages and lymphocytes. In conclusion the activities of the cellular immunity and humoral immunity were enhanced by laser.

Acupuncture Points↗

PubMed1991

Analysis of immunoglobulin heavy chain delta transcription termination in the production of delta S or delta M mRNA.

mRNA encoding secreted immunoglobulin is synthesized either by termination of transcription 3' to secreted terminus sequences and 5' to the membrane terminus sequences or by cleavage of a pre-mRNA transcript containing both secreted and membrane sequences at the appropriate polyadenylation site 5' to the membrane sequences. In vitro "run-on" transcription analysis was used to examine the delta transcription termination patterns in resting membrane IgD expressing B lymphocytes, in KWD2, an IgD-secreting hybridoma, and in TEPC 1017, an IgD-secreting plasmacytoma. In resting B cells, transcription terminated in a region 4 to 7 kilobases 3' to the delta M exons. Transcription in the secreting cells continued through the delta M exons, but terminated at more upstream sites. Additionally, an increased loading of polymerases in the region of the delta S exon and its 5' flanking sequence was detected in the secreting cells and was particularly pronounced in TEPC 1017. It is hypothesized that this peak correlates with high delta S mRNA production.

Amanitins↗

PubMed1991

Productive interactions between B and natural killer cells.

In this report, we have established that natural killer (NK) cells can increase IgG2a secretion by B lymphocytes as well as alter the distribution of the remaining immunoglobulin isotypes. The effect of NK cells on B cell differentiation is similar to that obtained by the direct addition of recombinant interferon-gamma (IFN-gamma) and, therefore, most likely results from the elaboration of IFN-gamma by NK cells, this is a clear demonstration that NK cells can regulate cell function(s) via a mechanism other than cytotoxicity. In addition, we have shown that the induction of NK cells by B lymphocytes requires close interactions between the two cell types. Further, while only low-density B lymphocytes activated in vivo are effective inducers of NK cells, high-density, resting B cells can be rendered effective by preactivation with either interleukin-4 or anti-mu.

Animals↗

PubMed1990

Regulation of Ig H chain gene transcription by IL-5.

Stimulation of B lymphocytes to high rate Ig secretion is accompanied by increased RNA polymerase initiation on the mu-delta gene complex as well as alterations in the sites of polymerase termination. Stimulation of Ig secretion by in vivo preactivated B lymphocytes with IL-5 seems to operate via a mechanism that only affects polymerase termination so that newly synthesized transcripts are preferentially processed to microS mRNA. The absence of increased polymerase initiation may account for previous observations indicating that IL-5 acts primarily as a terminal differentiation factor.

Animals↗

PubMed1989

Cognate interactions between helper T cells and B cells. II. Dissection of cognate help by using a class II-restricted, antigen-specific, IL-2-dependent helper T cell clone.

In order to determine the involvement of T-B cell contact vs lymphokine production in mediating B cell cycle entry and progression, Th cell clones "defective" in lymphokine production were cloned. Th-3.1 is one such clone that required IL-2 to produce significant levels of IL-4 and IFN-gamma. Unlike conventional Th clones, Th-3.1 induced B cell proliferation only in the presence of Ag and IL-2. In contrast to the absolute requirement of IL-2 for Th-3.1-induced B cell proliferation, IL-2 was not required for the formation of stable Th-3.1-B cell conjugates or Th-3.1-induced B cell entry into the G1 phase of the cell cycle. In the absence of IL-2 and under conditions that promoted Th-B cell interactions, Th-3.1 induced 10 to 20% of resting B cells to enter G1. B cell entry into the cell cycle was not inhibited by anti-lymphokine mAb or promoted by exogenous lymphokines, suggesting that endogenous lymphokine activity was not required for Th-3.1-induced G0 to G1 transition. The data suggested that the IL-2-independent induction of B cells into G1 by Th-3.1 was a cell contact-dependent event. Direct proof that Th-3.1-B cell contact was necessary for B cell cycle entry was provided by comparative in situ analysis of the RNA synthetic activity and the RNA content of B cells that were in physical contact with Th-3.1 or not in contact with Th-3.1. In situ autoradiography of RNA synthesis illustrated that a high frequency of B cells in contact with Th-3.1 expressed heightened RNA synthetic activity, whereas "bystander" B cells were less frequently induced into cycle. In situ laser cytometry of B cell size and total RNA content showed that B cells in physical contact with Th-3.1 had a higher RNA content and were larger than "bystander" B cells present in the same microcultures. This model system has allowed the dissection of T cell help into IL-2-dependent and IL-2-independent phases. Early cell contact-dependent events and B cell cycle progression into G1 were IL-2 independent, whereas the production of lymphokines (IL-4, IFN-gamma) by Th-3.1 and Th-3.1-induced B cell proliferation was IL-2 dependent.

Animals↗

PubMed1989

Role of transcriptional termination in the regulation of mu mRNA expression in B lymphocytes.

The synthesis of mRNA for mu-chain of membrane vs secretory IgM in normal resting B lymphocytes is stringently regulated. Very minimal amounts of microseconds mRNA are produced until the cells are stimulated. We have found a strong correlation between the initiation of mu S mRNA production and an alteration in the site of termination of polymerases transcribing the mu-gene. Furthermore, since the abundance of mu S mRNA is dependent on the differentiation stage of the B lymphocyte, we examined subpopulations of cells at various stages of activation and found that along with increased initiation of polymerases at the mu-locus, termination is moved further upstream in more highly differentiated cells. Therefore regulation of mu S mRNA may require factor(s) that induce transcriptional termination and these may be related to the factor(s) that augment transcriptional initiation.

Animals↗

PubMed1989

Regulation of B lymphocytes by natural killer cells. Role of IFN-gamma.

Using a co-culture system of fractionated B cells and highly purified NK cells, we have demonstrated direct interactions between B lymphocytes and NK cells. B cells are able to stimulate the production of IFN-gamma by NK cells. This stimulatory ability is restricted to a subpopulation of large, presumably in vivo activated B lymphocytes. The secreted IFN-gamma in turn inhibits polyclonally induced B cell proliferation. Small resting B cells neither stimulate IFN-gamma production nor are they measurably affected by NK cells.

Animals↗

PubMed1989

Regulation of microM vs microS mRNA expression in an inducible B cell line.

During the course of B lymphocyte differentiation into immunoglobulin secreting cells the abundance of mRNA for the heavy chain of secreted IgM (microS) increases dramatically. In order to understand the regulatory events responsible for the selective increase in micS mRNA we have looked for transcriptional alterations of VDJC mu gene segments as well as changes in the relative stability of microM and microS mRNA in BCL1 lymphoma cells which can be stimulated to increase the expression of microS mRNA. These experiments showed that although the transcriptional level of the mu gene locus is not preferentially augmented after stimulation, an alteration in the sites of polymerase termination is a significant factor contributing to the higher microS to microM ratio. This switch is dependent on new RNA synthesis. In addition, although the half-life of microS mRNA is not selectively increased, stimulation of the cells does result in a specific enhancement of the half-lives of both species of mu mRNA, which accounts for the higher steady state levels of total mu message.

Amanitins↗

PubMed1989

The human immunoglobulin C mu-C delta locus: regulation of mu and delta RNA expression during B cell development.

Whether the immunoglobulin (Ig) heavy chain genes C mu and C delta are expressed singly or in combination, their transcripts undergo differentiation-specific alterations in membrane (M) versus secreted (S) forms as well as in abundance. To better understand this regulation, we have cloned cDNAs for human delta m and delta s to establish the 3' end of the C mu-C delta transcription unit. Steady state mRNA levels and transcription rates were then analyzed in normal and transformed human B cells representing different maturation and activation states. The ratio of micron/microsecond RNA and of delta m/delta s RNA correlated with developmental stage, with a higher ratio at earlier stages. Steady state ratios of total mu/delta RNA paralleled ratios of C mu/C delta nascent transcription, suggesting no major posttranscriptional control for differential expression. However, at all developmental stages, transcription termination occurred downstream of the micron exons, suggesting a strong posttranscriptional regulatory component for production of secreted versus membrane forms of mu RNA. The relative abundance of mature delta S RNA was considerably higher in the human than in the mouse, correlating with the increased levels of circulating IgD in the former species. Stimulation of human splenocytes with mitogens did not increase delta RNA; in fact, splenocytes activated with pokeweed mitogen were nearly devoid of delta RNA, and Staphylococcus aureus Cowan I caused only a minor change.

Amino Acid Sequence↗

PubMed1988

Alternative expression of secreted and membrane forms of immunoglobulin mu-chain is regulated by transcriptional termination in stable plasmacytoma transfectants.

During B cell differentiation the mu H chain of IgM is produced initially as a cell surface (m) and later as a secreted (s) form. Production of either the secreted (microseconds) or the membrane (micron) mRNA results from selection of either the promoter proximal (microseconds) or distal (micron) poly(A)/cleavage site. We have transfected lymphoid cell lines of disparate developmental stages with productively rearranged Ig mu-chain constructs to determine the mechanism by which alternative 3' end selection is achieved. Stable transfectants of lymphomas (early stage, microseconds less than or equal to micron) and a plasmacytoma (late stage, microsecond much greater than micron) produce the anticipated levels of microsecond and micron mRNA. Transcription termination between the microsecond and micron poly(A) sites occurs only in the plasmacytoma transfectants, and appears to be the rate-limiting step in the production of the final steady state microsecond/micron mRNA ratio. We propose that as the B cell becomes terminally committed to secretion, the mechanism responsible for the regulation of the steady state microsecond/micron mRNA ratio shifts from exclusively post-transcriptional to predominantly transcriptional termination.

Animals↗

PubMed1988

Alpha 1-adrenergic stimulation of cardiac gene transcription in neonatal rat myocardial cells. Effects on myosin light chain-2 gene expression.

Previous studies have demonstrated that alpha-adrenergic stimulation of cultured, neonatal rat myocardial cells results in an increase in intracellular volume and protein content of cultured neonatal rat myocardial cells. Utilizing this model of cardiac hypertrophy, we have examined the effects of alpha-adrenergic stimulation on the accumulation of sarcomeres and the expression of a rat cardiac myofibrillar gene, myosin light chain-2 (MLC-2). Following alpha-adrenergic stimulation, cultured myocardial cells displayed a severalfold increase in the number of sarcomeric units, as assessed by electron microscopy, an increase in cellular MLC-2 content, and a 2-3 fold increase in the steady state levels of MLC-2 mRNA. This effect of alpha-adrenergic stimulation was accompanied by a 2-3-fold increase in total transcriptional activity, which was dependent on the concentration and duration of exposure to the agonist, and displayed alpha 1-adrenergic receptor specificity. The transcriptional response was not immediate, with a lag period of at least 1 h, and a maximal effect required continuous occupancy of the receptor. The increase in steady state levels of MLC-2 mRNA is regulated, in part, at the level of transcription of the cardiac MLC-2 gene. These results suggest that alpha 1-adrenergic stimulation may be important in the growth of the neonatal heart through the activation of total transcriptional activity. In addition, increases in the levels of myofibrillar proteins during myocardial cell growth and hypertrophy, may be mediated in part by the stimulation of transcription of myofibrillar genes.

Animals↗

PubMed1988

Transcriptional regulation of mu and delta gene expression in bone marrow pre-B and B lymphocytes.

Newly formed B cells first express IgM and subsequently display IgD on the cell surface. This is an ontologically, as well as developmentally, regulated process because IgD is virtually absent on neonatal splenic B cells. In the present studies we have examined, by means of nascent RNA chain labeling, the relative levels of mu to delta gene transcription in bone marrow B cells, pre-B cells, and earlier progenitors of B cells. Pre-B cells were obtained from Whitlock-type long term cultures of bone marrow cells from normal and C.B17 scid mice. Both populations were found to transcribe the delta gene at very low but detectable levels. A similarly low level of delta transcription was found to occur in surface IgM-positive cells from both cultured and freshly isolated bone marrow B cells. In all populations analyzed, termination of the majority of polymerases occurred within a discrete 1-kb region located between the microM and C delta I exons. Analysis of steady state RNA indicated that long term cultured bone marrow cells from normal mice produced both 2.7-kb normal sized microM mRNA as well as 2.9-kb aberrantly spliced I mu-mRNA, whereas those from C.B17 scid mice contained only aberrant sized mu-mRNA. In contrast to these results, our previous findings with spleen cells obtained from both neonatal and adult animals showed that delta gene transcription occurs at a relatively high level. Therefore, it is possible that activation of regulatory signals that allow polymerases to progress beyond the termination site 3' of the microM exons may occur when newly formed B cells migrate from the bone marrow to the splenic environment.

Animals↗