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Biomedical subjects

Y Luo

Publications and source records attributed to Y Luo.

At least 505 records · Page 28Linked to original sources
PubMed1991

Splice site skipping in polyomavirus late pre-mRNA processing.

Polyomavirus late nuclear primary transcripts contain tandem repeats of the late strand of the viral genome, as a result of inefficient transcription termination and polyadenylation. Pre-mRNA processing involves the splicing of short noncoding late leader exons to each other (removing genome-length introns) and the splicing of the last leader to a coding body exon (such as for the major virion structural protein, VP1). As a result, cytoplasmic mRNAs contain 1 to 12 tandem leader exons at their 5' ends that are followed by a single coding exon. To understand more about how polyomavirus exons are spliced together, we studied a double-genome construct consisting of two tandem but nonidentical polyomavirus late transcription units. The alternating leader exons are distinguishable from one another but retain identical flanking RNA-processing signals, as for the alternating VP1 exons. We transfected this construct and derivatives of it into mouse cells and determined which leader exons are spliced to which others and which VP1 exons are utilized. Results showed that leader exons are almost never skipped during splicing and are spliced sequentially to one another. On the other hand, VP1 exons were often skipped, with the VP1 exon closest to the polyadenylation site splicing to the nearest upstream leader exon. Splice site replacement experiments showed that VP1 exon skipping is not due to a relative weakness of its 3' splice site or to any sequence upstream of the VP1 3' splice site. Exon skipping is also not the result of sequences within the VP1 exon. Rather, VP1 3' splice site skipping can be eliminated by replacing the inefficient late polyadenylation signal with an efficient one, or by inserting a 5' splice site between the VP1 3' splice site and the late polyadenylation site. Thus, sequences that compose the distal border of the VP1 exon can influence usage of the upstream 3' splice site.

3T3 Cells↗
PubMed1991

Splice site choice in a complex transcription unit containing multiple inefficient polyadenylation signals.

The relationship between polyadenylation and splicing was investigated in a model system consisting of two tandem but nonidentical polyomavirus late transcription units. This model system exploits the polyomavirus late transcription termination and polyadenylation signals, which are sufficiently weak to allow the production of many multigenome-length primary transcripts with repeating introns, exons, and poly(A) sites. This double-genome construct contains exons of two types, those bordered by 3' and 5' splice sites (L1 and L2) and those bordered by a 3' splice site and a poly(A) site (V1 and V2). The L1 and L2 exons are distinguishable from one another but retain identical flanking RNA processing signals, as is the case for the V1 and V2 exons. Analysis of cytoplasmic RNAs obtained from mouse cells transfected with this construct and its derivatives revealed the following. (i) V1 and V2 exons are often skipped during pre-mRNA processing, while L1 and L2 exons are not skipped. (ii) No messages contain internal, unused polyadenylation signals. (iii) Poly(A) site choice is not required for the selection of an upstream 3' splice site. (iv) When two tandem poly(A) sites are placed downstream of a 3' splice site, the first poly(A) site is chosen almost exclusively, even though transcription can proceed past both sites. (v) Placing a 3' splice site between these two tandem poly(A) sites allows the more distal site to be chosen. These and other available data are most consistent with a model in which terminal exons are produced by the coordinate selection and use of a 3' splice site with the nearest available downstream poly(A) site.

Animals↗
PubMed1991

Ecdysterone receptor is a sequence-specific transcription factor involved in the developmental regulation of heat shock genes.

Purification of ecdysterone receptor from Drosophila melanogaster to apparent homogeneity is reported. Purified receptor binds specifically to several sequences in the promoters of the developmentally active hsp27 and hsp23 heat shock genes that were previously implied in ecdysterone regulation of the genes and that share limited homology among themselves and with mammalian steroid receptor binding sites. Some of these elements confer ecdysterone regulation on a basal promoter in transfected cells, acting in a synergistic fashion. Transcription in vitro of promoters containing such elements is stimulated up to 100-fold by added purified ecdysterone receptor, depending on receptor dosage and the number of elements present. Transcriptional enhancement requires sequence-specific binding of receptor to template promoters which facilitates the formation of a preinitiation complex. Ecdysterone stimulates DNA binding of the receptor in vitro.

Animals↗
PubMed1991

[Polarographic determination of sulfide in water].

Sulfide has a sensitive polarographic wave in the system of NaOH-EDTA-triethanolamine. The addition of triethanolamine to the system improved the shape of the wave and increased the sensitivity. The peak current was directly proportional to the concentration of sulfide in the range of 0.002-5.000 ppm. The detection limit for water sample was 2 ppb, and the relative standard deviation and recovery were 2.3-7.2% and 94.0-102.0%, respectively. The proposed method is simple, accurate, sensitive and reproducible.

Polarography↗
PubMed1991

[The species of titanium in natural water].

The species of titanium in natural water was studied. Sample was filtered with a paper filter and a 0.45 micron membrane filter. The content of titanium in each case was determined by polarography proposed by Li, et al. It was found that the main species for all the tested samples was of the particle form. A supernatant of a river water sample was taken to study the effect of pH on the distribution of titanium species. It was found that pH was an important factor for species distribution. At pH1-2, the particle will change into the dissolved form in a short time; at pH 6-8, the dissolved form will change into the particle form in several days.

Hydrogen-Ion Concentration↗
PubMed1991

[Changes in atrial natriuretic peptide and vasopressin during the pressor response to central osmotic stimulation].

In order to study the mechanism of pressor response to central osmotic stimulation, rats were administered with hypertonic artificial cerebrospinal fluid (ACSF) intracerebroventricularly. Carotid arterial pressure and heart rate were recorded. Ten minutes after administration, blood samples, hypothalamus and hypophysis were taken for the determination of atrial natriuretic peptide (ANP) and vasopressin (AVP) by radioimmunoassay. The results showed that after central administration of hypertonic ACSF, the plasma level of AVP increased significantly with no apparent change in ANP. In hypothalamus and hypophysis, the content of ANP was increased while that of AVP decreased.

Animals↗
PubMed1991

Alterations of atrial natriuretic factor in mammillary bodies and median eminence from hypertensive and experimental brain hemorrhage rats.

The results of the present study demonstrate that atrial natriuretic factor (ANF) in the mammillary bodies has a dynamic change, while ANF in the median eminence is relatively constant in the course of the increase of blood pressure. It suggests that ANF in the mammillary bodies might take part in the regulation of blood pressure and ANF in the median eminence mainly participates in the functional regulation of the adenohypophysis.

Animals↗
PubMed1991

[Effects of microinjection of clonidine into nucleus tractus solitarii on atrial natriuretic factor in rats].

In order to study whether atrial natriuretic factor (ANF) is involved in the depressor effect of clonidine, microinjection of the latter into nucleus tractus solitarii (NTS) was carried out in anesthetized stroke-prone spontaneously hypertensive rats (SHRsp) and normotensive Wistar-Kyoto (WKY) rats. Each strain was randomly divided into three groups by injecting: (1) clonidine (1.0 microgram/0.2 microliter); (2) yohimbine (3.3 micrograms/0.2 microliter) followed by (1); (3) artificial cerebral spinal fluid (ACSF, 0.2 microliter) as control. A decrease of blood pressure and heart rate and a suppression of ANF release elicited by clonidine were significantly greater in SHRsp than in WKY rats. After blockade of alpha 2-receptor with yohimbine, the hypotensive effect of clonidine was blocked completely in WKY rats, but only partially in SHRsp, while the suppression effect on ANF release was eliminated in both strains. In addition, the decrease of plasma catecholamine produced by clonidine could also be blocked after yohimbine. The results suggest that ANF probably does not contribute to the depressor effect of centrally administered clonidine, while in SHRsp the decrease of plasma ANF might be a blood pressure-dependent compensatory response.

Animals↗
PubMed1991

Clinical relevance of antibodies to non-HLA antigens in organ transplantation.

This article summarizes work that focuses on alloantibodies that bind to endothelial cells and attempts to provide an evaluation of the apparent role that antigens distinct from classic HLA alleles, and not expressed in lymphocytes, may play in kidney transplant rejection. The most recent experience with the donor-skin crossmatch in prediction of early kidney allograft rejection also is described.

Endothelium, Vascular↗
PubMed1990

Marked difference in the in vivo antitumor efficacy between two immunotoxins targeted to different epitopes of common acute lymphoblastic leukemia antigen (CD10). Mechanisms involved in the differential activities of immunotoxins.

In the present study, two isotype-matching mAb, SN5d and SN5, which are directed toward two distinctively different epitopes of common acute lymphoblastic leukemia Ag (CD10) but show a very similar binding affinity to leukemia cells, were compared for their in vivo antitumor activity after conjugated to ricin A chain (RA). Our recently established nude mouse model carrying an ascitic tumor of NALM-6 human pre-B leukemia cells was used as the tumor model. A marked difference was observed in the in vivo antitumor efficacy between SN5d-RA and SN5-RA; SN5d-RA was much more effective than SN5-RA. Several experiments were carried out to gain information concerning the mechanisms involved in the different antitumor efficacy of the two immunotoxins. Although naked (unconjugated) mAb SN5d was much less effective than SN5d-RA conjugates in the in vivo tumor suppression, mAb SN5d was more effective than mAb SN5 in the in vivo tumor suppression. Additionally, marked differences were found between SN5d and SN5 in the induction of antigenic modulation and in the regulation of Ag biosynthesis and expression. Binding of SN5 to NALM-6 leukemia cells caused strong antigenic modulation (down-regulation of Ag expression) and strongly down-regulated Ag biosynthesis and cell surface expression of new Ag. In contrast, binding of SN5d to NALM-6 leukemia cells caused little modulation of overall cell surface expression of common acute lymphoblastic leukemia Ag; the decrease of old Ag by endocytosis after binding to mAb SN5d was compensated by newly exocytosed cell-surface expressed Ag. The present results appear to reveal a novel mechanism which regulates cytotoxic activities of antibodies and immunoconjugates.

Animals↗
PubMed1990

Detection of subclinical nasopharyngeal carcinoma by fibreoptic endoscopy and multiple biopsy.

Of 6054 people who had high titres of antibodies against the viral capsid antigen of Epstein-Barr virus but no symptoms or signs of nasopharyngeal carcinoma as assessed by conventional methods, 130 were randomly recruited and examined by fibreoptic endoscopy and biopsy of several sites of the nasopharynx. 7 cases of nasopharyngeal carcinoma were detected. The tumours were largely confined to the pharyngeal recess, which suggests that it is the area of the nasopharynx most prone to the development of the tumour. Tumour was found in both recesses in 1 subject, who also had evidence of transition from severe epithelial dysplasia to carcinoma in a sample from the left roof, which suggests that the disease was multifocal in origin. This study showed that endoscopy and biopsy of several sites of the nasopharynx are more effective than the conventional approach in the detection of subclinical nasopharyngeal carcinoma among seropositive individuals at high risk of the disorder.

Adult↗
PubMed1990

Synergistic potentiation of in vivo antitumor activity of anti-human T-leukemia immunotoxins by recombinant alpha-interferon and daunorubicin.

In the present study, immunotoxins (ITs) containing ricin A chain (RA) and anti-human T leukemia monoclonal antibodies SN1 and SN2 were used with or without alpha-interferon (IFN) and/or daunorubicin (DNR) for in vivo tumor suppression. SN1 and SN2 are directed toward two unique human T-leukemia-associated cell surface antigens, TALLA and GP37, respectively. As the tumor model, we used nude mice bearing ascitic tumors of Ichikawa, a human T acute lymphoblastic leukemia cell line. In initial studies, we investigated the effect of the IT injection schedule on the efficacy of ITs in the in vivo suppression of the ascitic tumors. Four doses of 20 micrograms each of SN1-RA and SN2-RA completely suppress the tumor growth in 100% of the treated mice when the IT treatment is initiated either 1 or 2 days after tumor inoculation of 1.6 x 10(7) Ichikawa cells into the mice. Subsequently, we investigated the potentiating effects of IFN and DNR on the in vivo antitumor activity of ITs. To this end, we chose to initiate the treatment 4 days after the tumor inoculation when IT treatment alone is only partially effective. ITs (10 micrograms each of SN1-RA and SN2-RA) plus IFN (2 x 10(5) IU) or ITs plus IFN plus DNR (5 micrograms) completely suppress tumor growth in 100% of the treated mice while similar treatment with any one of the three agents is only partially effective. Similar treatment with ITs plus DNR or IFN plus DNR results in complete suppression of tumor growth in 80% of the treated mice. These results were reproducible in a repeated experiment. To gain information about the mechanisms involving the IFN potentiation of IT activity, we carried out several experiments. The cell surface expression of TALLA and GP37 was slightly augmented by the in vitro incubation of Ichikawa cells with IFN as measured by fluorescence-activated cell sorter analysis. The degree of the increase in either TALLA or GP37 was significantly smaller than that of HLA class I antigens in the same experiment. In in vitro experiments, IFN did not show any significant cytotoxic activity against Ichikawa cells or augment the cytotoxic activity of ITs against Ichikawa cells. On the other hand, injections of IFN into nude mice augmented activity of macrophages and NK cells; however, Ichikawa leukemia cells were rather resistant to the NK cell lysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Effect of tumor-derived immunosuppressive factor(s) on interleukin 2 and on expression of interleukin 2 receptor.

In this paper, we have described the effects of tumor-derived immunosuppressive factor(s) (TDSF) on interleukin 2 (IL-2) production, on IL-2 responsiveness and on the expression of IL-2 receptors. The results showed that TDSF was able to markedly inhibit the production of IL-2 from PHA-stimulated lymphocytes and IL-2-dependent proliferation of activated lymphocytes, and to partially inhibit the expression of IL-2 receptor. These results suggest that inhibiting IL-2 production and responsiveness may be a major mechanism by which TDSF inhibit T lymphocyte proliferation and other immune responses. That TDSF exerted a very potent inhibiting action on IL-2 responsiveness is especially noticeable if we consider using IL-2 as an immunotherapeutic agent. This may be an important reason why treatment of tumor with IL-2 did not yield satisfactory results so far.

Glycoproteins↗