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L Park

Publications and source records attributed to L Park.

At least 37 records · Page 2Linked to original sources
PubMed1997

The salmon SmaI family of short interspersed repetitive elements (SINEs): interspecific and intraspecific variation of the insertion of SINEs in the genomes of chum and pink salmon.

The genomes of chum salmon and pink salmon contain a family of short interspersed repetitive elements (SINEs), designated the salmon SmaI family. It is restricted to these two species, a distribution that suggests that this SINE family might have been generated in their common ancestor. When insertions of the SmaI SINEs at 10 orthologous loci of these species were analyzed, however, it was found that there were no shared insertion sites between chum and pink salmon. Furthermore, at six loci where SmaI SINEs have been species-specifically inserted in chum salmon, insertions of SINEs were polymorphic among populations of chum salmon. By contrast, at four loci where SmaI SINEs had been species-specifically inserted in pink salmon, the SINEs were fixed among all populations of pink salmon. The interspecific and intraspecific variation of the SmaI SINEs cannot be explained by the assumption that the SmaI family was amplified in a common ancestor of these two species. To interpret these observations, we propose several possible models, including introgression and the horizontal transfer of SINEs from pink salmon to chum salmon during evolution.

Animals↗
PubMed1996

Modulation of sensitivity to transforming growth factor-beta 1 (TGF-beta 1) and the level of type II TGF-beta receptor in LNCaP cells by dihydrotestosterone.

Transforming growth factor-beta 1 (TGF-beta 1) and androgen are potential physiological regulators of prostate cancer cells. In the present study, we have used LNCaP cells as a model of androgen-responsive prostate cancer to investigate the effects of dihydrotestosterone (DHT) on the sensitivity to TGF-beta 1. The ability of LNCaP cells to respond to TGF-beta has been controversial. In some studies, LNCaP cells were insensitive to TGF-beta 1 while, in others, they were sensitive to the growth inhibitory effect of TGF-beta 1. The present study was carried out to establish androgenic conditions that rendered LNCaP cells sensitive to TGF-beta 1. Cells were cultured in phenol-red-free RPMI 1640 medium supplemented with 10% charcoal-stripped fetal bovine serum. DHT was added at the following concentrations: 0, 10(-12), 10(-10), and 10(-7) M. These concentrations were selected because they represent the zero DHT control, the low-proliferative dose, the high-proliferative dose, and the growth-arrest dose, respectively. The effects of TGF-beta 1 observed on LNCaP cells included inhibition of cell proliferation, decrease in cell viability, alteration in cell morphology, and enhancement of gene transcriptional activity through activation of a TGF-beta responsive promoter. Of the various DHT concentrations investigated in this study, these effects of TGF-beta 1 on LNCaP cells were consistently demonstrated only at 10(-10) M. At other concentrations, the effects of TGF-beta 1 were either minimal or undetectable. Accompanying these effects of TGF-beta 1, a low but statistically significant level of TGF-beta 1-specific binding and an increased protein level of TGF-beta receptor type II were detected by a competitive binding assay and Western blot analysis respectively. These results indicate that LNCaP cells can be induced by DHT to respond to TGF-beta 1 and that DHT modulates the sensitivity to TGF-beta 1 and the level of TGF-beta receptor type II in these cells.

Binding, Competitive↗
PubMed1996

Interleukin-15 up-regulates interleukin-2 receptor alpha chain but down-regulates its own high-affinity binding sites on human T and B cells.

The cytokines interleukin (IL)-2 and IL-15 share many biological activities as a consequence of their utilization of the beta and gamma chains of the IL-2 receptor. However, each cytokine binds to a specific receptor alpha chain; IL-2 with low affinity and IL-15 with high affinity. Here, we demonstrate that IL-15, like IL-2, up-regulates expression of IL-2R alpha on human T and B cells, but rapidly down-regulates IL-15 high-affinity binding sites, which represent IL-15R alpha. This leads to a decreased responsiveness to IL-15 as measured by induction of Jak3 tyrosine phosphorylation. These results suggest a mechanism by which IL-15, a product of activated macrophages, may cooperate with IL-2 at the initiation of an immune response and enhance subsequent IL-2 responsiveness during T cell expansion.

B-Lymphocytes↗
PubMed1996

Characterization of species-specifically amplified SINEs in three salmonid species--chum salmon, pink salmon, and kokanee: the local environment of the genome may be important for the generation of a dominant source gene at a newly retroposed locus.

Short interspersed repetitive elements (SINEs), known as the HpaI family, are present in the genomes of all salmonid species (Kido et al., Proc. Natl. Acad. Sci. USA 1991, 88: 2326-2330). Recently, we showed that the retropositional efficiency of the SINE family in the lineage of chum salmon is extraordinarily high in comparison with that in other salmonid lineages. (Takasaki et al., Proc. Natl. Acad. Sci. USA 1994, 91: 10153-10157). To investigate the reason for this high efficiency, we searched for members of the HpaI SINE family that have been amplified species-specifically in pink salmon. Since the efficiency of the species-specific amplification in pink salmon is not high and since other members of the same subfamily of SINEs were also amplified species-specifically in pink salmon, the actual sequence of this subfamily might not be the cause of the high retropositional efficiency of SINEs in chum salmon. Rather, it appears that a highly dominant source gene for the subfamily may have been newly created by retroposition, and some aspect of the local environment around the site of retroposition may have been responsible for the creation of this dominant source gene in chum salmon. Furthermore, a total of 11 sequences of HpaI SINEs that have been amplified species-specifically in three salmon lineages was compiled and characterized. Judging from the distribution of members of the same-sequence subfamily of SINEs in different lineages and from the distribution of the different-sequence subfamilies in the same lineage, we have concluded that multiple dispersed loci are responsible for the amplification of SINEs. We also discuss the additional possibility of horizontal transmission of SINEs between species. The availability of the sets of primers used for the detection of the species-specific amplifications of the SINEs provides a convenient and reliable method for identification of these salmonid species.

Animals↗
PubMed1996

Influence of combinations of human major histocompatibility complex genes on the course of HIV-1 infection.

Major histocompatibility complex (MHC) genes (HLA in humans) regulate the immune response to foreign antigens. Molecular and serologic techniques were used to identify products of HLA class I, class II and transporter (TAP) genes (also part of the MHC) in homosexual seroconverters to human immunodeficiency virus type 1 (HIV-1). Comprehensive statistical analysis produced an HLA profile that predicted time from HIV-1 infection to the onset of AIDS. The profile was developed in a cohort of 139 men and evaluated in a second unrelated cohort of 102 men. In the evaluation cohort, the profile discriminated a sixfold difference between groups with the shortest and longest times to AIDS (P = 0.001). These findings support current theory about control of antigen processing by HLA genes and have implications for immunopathogenesis of HIV-1 and other infections.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Expression and localization of transforming growth factor-beta receptors type I and type II in the rat ventral prostate during regression.

Of the three ubiquitously expressed transforming growth factor-beta (TGF beta) receptors, only type I and type II receptors contain serine/threonine kinase activity and have a direct role in TGF beta signal transduction. In the prostate, it has been reported that the level of type III receptor expression increases transiently after castration. However, the relationship between the TGF beta signaling receptors, type I and type II, and androgen is currently unclear. Thus, in the present study, we made an initial attempt to elucidate the effect of androgen on type I and type II receptor expression in the rat ventral prostate by measuring the levels of messenger RNA (mRNA) and protein at specific time points after castration up to 10 days. Within 3 days after castration, an increase in type II receptor mRNA was observed in the prostate, and the level continued to rise until 7 days postcastration (approximately 8-fold increase). Between days 7-10 postcastration, no significant change in the level of type II receptor mRNA was observed. Testosterone administration immediately after castration abolished the induction of type II receptor mRNA during the same 10-day period. Western blot analysis performed for type II receptor showed a similar result, in that the level of type II receptor protein increased approximately 5-fold by day 10 postcastration. In a similar manner to the expression of type II receptor mRNA, the level of type I receptor mRNA increased steadily until day 7 postcastration (approximately 6-fold increase). Between days 7-10 postcastration, the level of type I receptor mRNA did not change significantly. As with type II receptor mRNA, the induction of type I receptor mRNA was suppressed when testosterone was administered immediately after castration. To localize the expression of TGF beta receptor type II, immunohistochemical studies were performed. The results of these studies demonstrated a preferential localization of type II receptor in the prostatic epithelial cells and an increased staining intensity for the receptor after castration. Taken together, these data indicate that TGF beta signaling receptors, type I and type II, are under negative androgenic regulation at the transcriptional level and that TGF beta may be an important regulator of a stromal-epithelial interaction in the rat ventral prostate.

Animals↗
PubMed1996

BMS181321 accumulation in rodent and human cells: the role of P-glycoprotein.

A 2-nitroimidazole with a side chain that contains technetium-99m as a chelate, BMS181321, is undergoing evaluation as an imaging agent for myocardial and cerebral ischaemia, as well as a diagnostic probe for hypoxic cells in solid tumours. Its accumulation in hypoxic and aerobic populations of three lines of Chinese hamster ovary cells of differing P-glycoprotein status, as well as one rat and two human cell lines has been determined. There was selective accumulation of BMS181321 in hypoxic vs aerobic cells. P-glycoprotein level was not a factor in this accumulation and hypoxic human cells accumulated BMS181321 more rapidly than the rodent cells. These results indicate P-glycoprotein levels in tumour cells will not confound the use of BMS181321 as a hypoxic cell marker.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Species-specific amplification of tRNA-derived short interspersed repetitive elements (SINEs) by retroposition: a process of parasitization of entire genomes during the evolution of salmonids.

Fourteen members of the Hpa I subfamilies of tRNA-derived SINEs in particular salmonid species were isolated from genomic libraries of chum salmon, kokanee, coho salmon, masu salmon, and steelhead. Alignment of the sequences of these 14 members, together with those of 4 members already published, 3 of which were previously demonstrated to have been amplified specifically in certain lineages, revealed the presence of five subfamilies with particular diagnostic nucleotides. The amplification of members of the same subfamily in different salmonid lineages and the amplification of members of different subfamilies in the same salmonid lineage suggest that multiple dispersed loci were responsible for amplification or, alternatively, that SINEs were transmitted horizontally between species. These two possibilities are not mutually exclusive. Our results also indicate that the Hpa I SINEs in salmonids behave like parasites. The amplification of these SINEs is ongoing and continues to shape the evolution of salmonid genomes.

Animals↗
PubMed1994

Hck expression correlates with granulocyte-macrophage colony-stimulating factor-induced proliferation in HL-60 cells.

The human myeloid cell line HL-60 expresses approximately 300 high-affinity granulocyte-macrophage colony-stimulating factor receptors (GM-CSFRs), yet treatment of these cells with GM-CSF does not result in enhanced cellular proliferation or increases in protein tyrosine phosphorylation. In contrast, GM-CSF induces rapid increases in protein tyrosine phosphorylation and proliferative responses in HL-60 cells pretreated for 3 days in dimethyl sulfoxide (DMSO). Similarly, HL-60 cells pretreated with retinoic acid or 1,25 dihydroxyvitamin D3 were also capable of responding to GM-CSF. Interestingly, each of these treatments resulted in increased expression of the src-like tyrosine kinase hck. Stimulation with GM-CSF increased hck autophosphorylation in DMSO-treated HL-60 cells, suggesting that hck is a component of the GM-CSF signal transduction pathway. To determine if hck has a role in the DMSO-induced recoupling of the GM-CSFR, we overexpressed hck in HL-60 cells. The resulting cell line (HL-60/hck) expresses hck mRNA and protein at levels comparable with DMSO-treated HL-60 cells. Stimulation of HL-60/hck cells with GM-CSF results in activation of hck, increases in protein tyrosine phosphorylation, and increased proliferation. These results show that cytokine receptors can exist in an uncoupled form and suggest that in HL-60 cells, appropriate levels of the src-like tyrosine kinase hck are critical for functional coupling of the GM-CSFR to biologic responses.

Cell Division↗
PubMed1994

Proliferative responses and binding properties of hematopoietic cells transfected with low-affinity receptors for leukemia inhibitory factor, oncostatin M, and ciliary neurotrophic factor.

Specific low-affinity receptors for leukemia inhibitory factor (LIF), oncostatin M (OSM; gp130), and ciliary neurotrophic factor (CNTF; receptor alpha, CNTFR alpha) may be utilized in various combinations to generate high-affinity binding sites and signal transduction. We have tested the ability of combinations of these receptors to transduce a proliferative signal in BAF-B03 cells. Coexpression of the LIF receptor and gp130 in these cells conferred high-affinity LIF and OSM binding and responsiveness to LIF and OSM. These cells also responded to CNTF in the absence of detectable binding. The further addition of CNTFR alpha conferred high-affinity CNTF binding and enhanced responsiveness to CNTF but did not modify responses to LIF or OSM. Coexpression of LIF receptor and CNTFR alpha resulted in a nonfunctional high-affinity binding site. These data are consistent with a role for the CNTFR alpha in enhancing CNTF action but the CNTFR alpha is not absolutely required for CNTF action and suggest a wider range of targets for CNTF.

Animals↗
PubMed1994

CD8+ lymphocyte activation at human immunodeficiency virus type 1 seroconversion: development of HLA-DR+ CD38- CD8+ cells is associated with subsequent stable CD4+ cell levels. The Multicenter AIDS Cohort Study Group.

Subsets of activated CD8+ lymphocytes defined by membrane expression of the activation antigens HLA-DR and CD38 were counted by three-color flow cytometry in homosexual men who subsequently became seropositive for human immunodeficiency virus type 1 (HIV). Profound CD8+ cell activation was seen in all subjects at seroconversion and 6 and 12 months later. The HLA-DR+ CD38+ CD8+ cell population, which has potent direct HIV cytotoxic T cell activity, was markedly elevated at seroconversion in all subjects. In some men, these levels remained elevated throughout the first year of infection. During the next 5 years, these men had stable CD4+ cell levels, whereas the others did not. Long-term survivors (seropositive for 9 years, > 800 CD4+ cells/mm3) also had elevated levels of this subset, despite few other activated CD8+ cells. Thus, selective elevation of HLA-DR+ CD38- CD8+ cells was a marker of subsequent stable HIV disease.

ADP-ribosyl Cyclase↗
PubMed1993

Amyloid beta-protein as a substrate interacts with extracellular matrix to promote neurite outgrowth.

Progressive deposition of amyloid beta-protein (A beta) in brain parenchyma and blood vessels is a characteristic feature of Alzheimer disease. Recent evidence suggests that addition of solubilized synthetic A beta to medium may produce toxic or trophic effects on cultured hippocampal neurons. Because soluble A beta may not accumulate in significant quantities in brain, we asked whether immobilized A beta peptide as a substrate alters neurite outgrowth from cultured rat peripheral sensory neurons. This paradigm may closely mimic the conditions in Alzheimer disease brain tissue, in which neurites contact insoluble, extracellular aggregates of beta-amyloid. We detected no detrimental effects of A beta substrate on neurite outgrowth. Rather, A beta in combination with low doses of laminin or fibronectin enhanced neurite out-growth from these neuronal explants. Our results suggest that insoluble A beta in the cerebral neuropil may serve as a neurite-promoting matrix, perhaps explaining the apparent regenerative response of neurites observed around amyloid plaques in Alzheimer disease. Moreover, in concert with the recent discovery of A beta production by cultured neurons, our data suggest that A beta plays a normal physiological role in brain by complexing with the extracellular matrix.

Alzheimer Disease↗
PubMed1993

Fasciclin I and II have distinct roles in the development of grasshopper pioneer neurons.

We have used a new technique, micro-CALI (chromophore-assisted laser inactivation), to investigate the function of the neural cell adhesion molecules fasciclin I and II in the development of the grasshopper Ti1 neurons. Micro-CALI of fasciclin I results in defasciculation of the Ti1 axons similar to that achieved using large scale CALI (Jay and Keshishian, 1990). The initial point of axon separation corresponds to the site of laser irradiation, and defasciculation always continues distal to this point. Micro-CALI of fasciclin II prevents the initiation of Ti1 axon outgrowth but has no effect on fasciculation. This effect is restricted to a 3 hr interval between cytokinesis and growth cone emergence.

Animals↗
PubMed1992

Decreased G-CSF and IL-3 production and gene expression from mononuclear cells of newborn infants.

Newborns are predisposed to neutropenia and thrombocytopenia during bacterial sepsis. The presence of peripheral cytopenias during overwhelming infection may be secondary to decreased hematopoietic growth factor production during states of increased demand. We therefore examined circulating levels of granulocyte-colony stimulating factor (G-CSF) and IL-3, production of G-CSF and IL-3 from unstimulated and stimulated mononuclear cells (MNC), expression of G-CSF and IL-3 genes during unstimulated and stimulated conditions, and equilibrium and binding of G-CSF receptors on mature effector peripheral blood cells of adults and neonates. Serum from cord and adult peripheral blood contained negligible amounts of both G-CSF (less than or equal to 50 pg/mL) and IL-3 (less than or equal to 5 pg/mL). Constitutive supernatant levels of G-CSF and IL-3 from cord and adult unstimulated MNC were also undetectable. However, there was a significant difference in G-CSF and IL-3 production from stimulated cord and adult MNC. Supernatants from stimulated adult MNC had significantly more G-CSF (p less than 0.007) and IL-3 (p less than 0.02). Additionally, Northern blot hybridization and densitometry of autoradiographs demonstrated significantly more G-CSF and IL-3 mRNA transcripts from adult than from cord MNC. Lastly, affinity, binding, and number of G-CSF receptors on cord and adult peripheral effector cells were equal. These data suggest that, during states of increased demand, cord MNC produce less G-CSF and IL-3 than do adult MNC and have an associated reduction in their respective mRNA transcripts. These findings may have implications in the pathogenesis of neonatal cytopenias during states of increased demand, such as sepsis.

Adult↗
PubMed1990

Expression cloning of a human granulocyte colony-stimulating factor receptor: a structural mosaic of hematopoietin receptor, immunoglobulin, and fibronectin domains.

We report the isolation from a placental library, of two cDNAs that can encode high affinity receptors for granulocyte colony-stimulating factor (G-CSF) when expressed in COS-7 cells. The cDNAs are predicted to encode integral membrane proteins of 759 and 812 amino acids in length. The predicted extracellular and membrane spanning sequences of the two clones are identical, as are the first 96 amino acids of their respective cytoplasmic regions. Different COOH termini of 34 or 87 residues are predicted for the two cDNAs, due apparently to alternate splicing. The receptor with the longer cytoplasmic domain is the closest human homologue of the murine G-CSF receptor recently described by Fukunaga et al. (Fukunaga, R., E. Ishizaka-Ikeda, Y. Seto, and S. Nagata. 1990. Cell. 61:341). A hybridization probe derived from the placental G-CSF receptor cDNA detects a approximately 3-kb transcript in RNAs isolated from placenta and a number of lymphoid and myeloid cells. The extracellular region of the G-CSF receptors is composed of four distinct types of structural domains, previously recognized in other cell surface proteins. In addition to the two domains of the HP receptor family-defining region (Patthy, L. 1990. Cell. 61:13) it incorporates one NH2-terminal Ig-like domain, and three additional repeats of fibronectin type III-like domains. The presence of both an NH2-terminal Ig-like domain and multiple membrane-proximal FN3-like domains suggests that the G-CSF receptor may be derived from an ancestral NCAM-like molecule and that the G-CSF receptor may function in some adhesion or recognition events at the cell surface in addition to the binding of G-CSF.

Amino Acid Sequence↗
PubMed1990

Quality control in the flow cytometric measurement of T-lymphocyte subsets: the multicenter AIDS cohort study experience. The Multicenter AIDS Cohort Study Group.

Since 1984, the Multicenter AIDS Cohort Study (MACS) has utilized four flow cytometry laboratories to measure T-lymphocyte subset levels semiannually in a large cohort of homosexual men. This report summarizes the steps taken in the MACS laboratories to attain comparability of lymphocyte subset determinations across the centers and over time. Identical flow cytometers, monoclonal antibodies, and analytic procedures have been used, and over a period of time, the procedure for sample preparation was also standardized. Interlaboratory proficiency testing utilizing identical specimens analyzed in the four laboratories was performed to evaluate the comparability of the data among the laboratories. Our results verify that such testing can identify technical bias in flow cytometric evaluations performed at different laboratories. Temporal laboratory consistency in flow cytometric measurements was evaluated using data from each site's HIV-seronegative homosexual reference group. Both sequential 95% confidence intervals (mean +/- 2 x SEM) and the within-person standard deviations of the immune measurements were considered. Significant variation in CD3, CD4, and CD8 lymphocyte subset percentages over time in the seronegative reference population was observed. Our observations indicate that the lymphocyte subset values of this seronegative group should be used to adjust those obtained on the seropositive study participants during a particular time period, thereby allowing improved discrimination of the effects of HIV on T cells in infected individuals. The data presented are of use for designing epidemiologic and intervention studies in HIV-1-infected individuals, especially for calculating sample sizes. The methods we have used to assess the quality of data in the MACS have general application to quality control programs in flow cytometry laboratories. In particular, comparison of sequential confidence intervals and within-person standard deviations for lymphocyte subset determinations on control populations are essential to a comprehensive proficiency testing program because they permit assessment of consistency within a laboratory over time.

Acquired Immunodeficiency Syndrome↗
PubMed1990

IL-3 inhibits the binding of GM-CSF to AML blasts, but the two cytokines act synergistically in supporting blast proliferation.

Equilibrium binding of 125I-labeled recombinant granulocyte macrophage colony-stimulating factor (GM-CSF) to the blast cells of acute myeloblastic leukemia (AML) revealed the presence of two classes of binding components of high and low affinity, with dissociation constants (Kd) in the range of 5-10 pM and 1-10 nM, respectively. Specificity studies revealed that interleukin-3 (IL-3) could partially inhibit the binding of GM-CSF to AML blasts and to the cells of the leukemic lines M07-E, KG-1, and HL-60. The inhibition of GM-CSF binding by IL-3 was directly dependent on the presence of IL-3 receptors. Analysis of competition curves indicated that the Kd and the number of binding sites per cell of unlabeled and iodinated GM-CSF were identical. In contrast, the inhibition of GM-CSF binding by IL-3 was mediated by IL-3 occupancy of a high affinity receptor only, with the same number of sites as the high affinity GM-CSF receptor but a slightly higher Kd. Despite this competitive binding, IL-3 augmented AML blast proliferation in the presence of GM-CSF, indicating that the two growth factors have converging pathways in supporting blast proliferation. In striking contrast to AML blasts, GM-CSF binding to neutrophils was compatible with the presence of only one class of binding site of intermediate affinity (Kd approximately 100-160 pM). Furthermore, IL-3 does not compete for the binding of GM-CSF to neutrophils.

Binding Sites↗