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Biomedical subjects

M Li

Publications and source records attributed to M Li.

At least 19 recordsLinked to original sources
PubMed2026

Longitudinal ctDNA tracking in early and recurrent breast cancer using an ultrasensitive structural variant-based assay: an extended analysis from the TRACER study.

BACKGROUND: Detection of circulating tumor DNA (ctDNA) following curative-intent therapy is prognostic of disease recurrence in early-stage breast cancer (EBC). An ultrasensitive structural variant (SV)-based ctDNA assay was evaluated previously in a 100-patient EBC cohort treated with neoadjuvant therapy, demonstrating high sensitivity, specificity, and a long lead-time to relapse. The stability of primary tumor-specific SVs at and after metastatic recurrence and their utility for longer-term ctDNA monitoring had not been established. PATIENTS AND METHODS: An updated retrospective analysis of ctDNA dynamics was conducted in an expanded cohort of 121 patients with EBC treated with neoadjuvant therapy. Plasma samples were collected at key clinical timepoints and serially in several patients who experienced metastatic recurrence. Clinical variables were abstracted from medical records. Associations between ctDNA detection, dynamics, and clinical outcomes were evaluated in the early-stage and metastatic settings. RESULTS: Thirty of 121 patients experienced clinical recurrence (28 distant, 2 local) over a median follow-up of 4.2 years (range 0.5-8.8; 25 ctDNA evaluable with adjuvant timepoints). All patients with detectable ctDNA in the adjuvant setting developed metastatic recurrence (22/22). Median lead time from ctDNA detection to metastatic recurrence was 346 days (range 0-1937). Among recurrent cases, 79% of primary tumor-specific SVs (n = 17 patients, tumor fraction ≥0.1%) remained detectable in plasma [range 7% (1/14 SV)-100% (15/15); median: 92%]. ctDNA dynamics in the recurrent metastatic setting demonstrated a strong relationship with radiographic outcomes in evaluable patients (n = 9). CONCLUSION: This SV-based digital PCR assay provided ultrasensitive ctDNA detection in an expanded EBC cohort, maintaining 100% positive predictive value for metastatic recurrence. In patients with recurrence, ctDNA dynamics were concordant with radiographic outcomes. Prospective studies evaluating the clinical utility of longitudinal ctDNA monitoring are warranted.

MRD↗
PubMed1992

Specification of subunit assembly by the hydrophilic amino-terminal domain of the Shaker potassium channel.

The functional heterogeneity of potassium channels in eukaryotic cells arises not only from the multiple potassium channel genes and splice variants but also from the combinatorial mixing of different potassium channel polypeptides to form heteromultimeric channels with distinct properties. One structural element that determines the compatibility of different potassium channel polypeptides in subunit assembly has now been localized to the hydrophilic amino-terminal domain. A Drosophila Shaker B (ShB) potassium channel truncated polypeptide that contains only the hydrophilic amino-terminal domain can form a homomultimer; the minimal requirement for the homophilic interaction has been localized to a fragment of 114 amino acids. Substitution of the amino-terminal domain of a distantly related mammalian potassium channel polypeptide (DRK1) with that of ShB permits the chimeric DRK1 polypeptide to coassemble with ShB.

Amino Acid Sequence↗
PubMed1992

Cloning and developmental expression of the alpha 3 chain of chicken type IX collagen.

Fibrous and nonfibrous collagens comprise two major groups within the collagen family and both groups are found in a diverse variety of tissue fabrics. Type IX collagen is in the nonfibrous group; three different subunits of type IX collagen have been identified and the alpha 1 and alpha 2 subunits have been cloned. Using molecular cloning methods we have isolated, from an embryonic chicken cartilage library, cDNA clones which code for the entire alpha 3 chain of chicken type IX collagen. The cDNA clones encompass 2416 base pairs which have a conceptual open reading frame for a protein containing 675 amino acids including 193 Gly-X-Y repeats. These collagen repeats are in three separate domains which are interspersed with four major noncollagen domains. The collagen repeats also have four minor interruptions. This chain organization directly aligns with both the alpha 1 and alpha 2 chains of chicken type IX collagen. Comparison of the deduced amino acid sequence with peptide sequences of type IX collagens shows identity with 95 of the 96 known residues of the chicken alpha 3 chain and 81 of the 98 known residues of the bovine alpha 3 chain. The identical residues match those in five peptide fragments, two from the bovine protein and three from the chicken protein. The chicken and bovine alpha 3 chains have conserved cross-linking sites, separated by 137 residues which span 40 nm, the length of the hole zone in a collagen fibril. The NC3 domain of the chicken alpha 3 chain contains a repeat Cys-Pro motif which is present in both vertebrate and invertebrate nonfibrillar collagens. Northern blot hybridization exhibits a major mRNA of about 3.3 kilobases; this transcript is found in cartilaginous tissues in the embryo, including the developing limb and is not detected in other tissues or in the precondensation stage of limb development. The composite data delineate the primary structure of the alpha 3 chain of chicken type IX collagen, show its close relationship to the alpha 1 and alpha 2 chains, demonstrate its mRNA transcript, and show the appearance of that transcript in tissues of the developing chick embryo.

Amino Acid Sequence↗
PubMed1992

Secondary structures of a new class of lipid body proteins from oilseeds.

The three main isoforms of the 19-kDa lipid body proteins (oleosin) have been purified to homogeneity from embryos of rapeseed. The secondary structures of these proteins as derived from circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy were compared with the secondary structures predicted from the primary sequences. The salient feature of the primary sequence of all oleosins is its division into three defined structural domains: a central hydrophobic domain flanked on either side by relatively hydrophilic domains, respectively. Using a variety of predictive methods based on primary amino acid sequence data, the oleosins exhibited a high probability of beta-strand structure in the 70-residue central hydrophobic domain, with relatively little alpha-helical content. Secondary structure data derived from CD and FTIR were consistent with the predictions from primary sequence, showing that the oleosins contained about 45% beta-strand and 13% alpha-helical structure. Under high salt conditions, a 40-kDa polypeptide was obtained from purified preparations of the 19-kDa oleosins. The 40-kDa polypeptide has a very similar secondary structure, as analyzed by CD and FTIR, to that of the 19-kDa oleosins. This polypeptide is therefore probably a dimer of the 19-kDa oleosins that is formed in high salt environments. A model of the general structure of oleosins is proposed whereby the central hydrophobic domain of the protein with a predominantly beta-strand structure is embedded into the non-aqueous phase of lipid-bodies. This hydrophobic region is flanked by putative alpha-helical structures in the polar N- and C-terminal domains which are probably oriented at the lipid-water interface.

Amino Acid Sequence↗
PubMed1992

The ontogeny of m1-m5 muscarinic receptor subtypes in rat forebrain.

The ontogeny of muscarinic receptor subtypes in rat forebrain has been determined utilizing a panel of antisera recognizing unique epitopes of the m1-m5 receptor proteins. Total receptor density in forebrain, as measured by the non-selective antagonist, [3H]quinuclidinyl benzilate (QNB), was found to increase from 507 fmol/mg in neonates (3.5 days) to 1727 fmol/mg in mature animals (45 days). Adult levels were reached two weeks post-partum. A recently developed precipitation protocol was then used to further characterize receptor ontogeny. Cumulatively, 90% of [3H]QNB labelled muscarinic receptors from adult forebrain were immunoprecipitated with subtype selective antibodies (m1-m5). In 3- to 4-day-old neonates, m1 receptors are expressed at 31% of adult levels, m2 receptors at 32% of adult levels, m3 receptors at 36% of adult levels, and m4 receptors at 20% of adult levels. In mature animals, m1 receptors were equal to 35%, m2 equal to 18%, m3 equal to 11%, and m4 equal to 26%, of total receptors, respectively. Levels of m5 receptors are consistently very low at all ages tested (less than or equal to 1% of total receptor density). Although there were subtle differences in the time courses of development between muscarinic receptor subtypes, in general, they developed with similar ontogenic profiles. Subtypes coupled preferentially to inhibition of adenylate cyclase (m2 and m4) comprised 35% of total receptors expressed in neonates. The combined m2/m4 receptor density increased at a uniform rate during development from 173 to 757 fmol/mg. Receptors preferentially coupled to phosphoinositide turnover (m1, m3, and m5) were found in newborns at approximately 270 fmol/mg.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

FDC-P1 myeloid cells engineered to express fibroblast growth factor receptor 1 proliferate and differentiate in the presence of fibroblast growth factor and heparin.

Full-length murine fibroblast growth factor (FGF) receptor 1 (FGFR-1L) cDNA was introduced into the FDC-P1 mouse myeloid progenitor cell line, which lacks FGF receptors and depends on interleukin 3 (IL-3) or granulocyte/macrophage colony-stimulating factor (GM-CSF) for its proliferation and survival. The expression of the FGFR-1L gene in FDC-P1 cells allowed these cells to grow in the presence of FGF and heparin. The resulting cell line, designated FD FGFR-1L.A, exhibited a more mature myeloid phenotype than did the parental FD FGFR-1L cells or uninfected FDC-P1 cells. They formed mainly dispersed colonies in soft-agar cultures when grown in the presence of FGF and heparin, suggestive of myeloid differentiation. The cells can be switched between growth on FGF/heparin and IL-3. Northern blot analysis and cytochemical staining demonstrated that FD FGFR-1L.A cells expressed myeloperoxidase mRNA and protein, biochemical markers specifically expressed during differentiation from the promyelocytic to the granulocytic stages, whereas the parental FD FGFR-1L cells and FDC-P1 cells failed to express this marker. These results indicate that the expression of FGFR-1L by FDC-P1 cells transmitted signals for growth in the presence of FGF and heparin and generated an additional signal for early myeloid differentiation but failed to commit FD FGFR-1L.A cells to terminal differentiation. This in vitro culture system can be used for molecular analysis of the regulation of cellular growth and differentiation mediated by the FGFs and their receptors.

Animals↗
PubMed1992

Synergistic suppression: anomalous inhibition of the proliferation of factor-dependent hemopoietic cells by combination of two colony-stimulating factors.

Cells of the continuous murine hemopoietic cell line FDC-P1 expressing macrophage-colony-stimulating factor (M-CSF) receptors following retroviral insertion of murine c-fms cDNA proliferated clonally when stimulated by granulocyte/macrophage (GM)-CSF, multipotential CSF, or M-CSF. However, M-CSF combined with either GM-CSF or multi-CSF, even at low CSF concentrations, strongly inhibited colony formation, with loss of clonogenicity in affected cells accompanied by increased macrophage differentiation. Stimulation by these CSF combinations did not induce short-term changes in CSF receptor expression or internalization. FDC-P1 cells expressing another inserted tyrosine kinase receptor, basic fibroblast growth factor receptor, did not exhibit suppression when GM-CSF was combined with fibroblast growth factor. This phenomenon of synergistic suppression may have relevance for the future clinical use of combinations of CSFs, because a potentially similar suppression is also observable with some normal macrophage progenitor cells.

Animals↗
PubMed1992

Regulation of ribosomal protein S25 in HL60 cells isolated for resistance to adriamycin.

The ribosomal protein S25 gene is highly overexpressed in HL60 cells isolated for resistance to adriamycin. In contrast there is no overexpression of 3 other ribosomal genes which code for proteins S14, S17 and S24. Studies with an antibody against a synthetic peptide of the S25 protein show that although the S25 gene is overexpressed in resistant cells there is no corresponding increase in the levels of S25 protein. These results suggest that the r-protein levels are highly regulated by translational controls or protein turnover.

Amino Acid Sequence↗
PubMed1992

Viscosity measurements of barium sulfate mixtures for use in motility studies of the pharynx and esophagus.

Detailed viscosity measurements have been made of barium sulfate mixtures over a wide range of viscosities for use in radiography of the esophagus, stomach, and duodenum. A new methodology was developed for more accurate estimation of viscosity in non-Newtonian fluids in conventional cylinder-type viscometers. As base cases, the variation of viscosity with shear rate was measured for standard commercial mixes of e.z.hd (250% w/v) and a diluted mixture of liquid e.z.paque (40% w/v). These suspensions are strongly shear thinning at low shear rates. Above about 3s-1 the viscosity is nearly constant, but relatively low. To increase the viscosity of the barium sulfate mixture, Knott's strawberry syrup was mixed to different proportions with e.z.hd powder. In this way viscosity was systematically increased to values 130,000 times that of water. For these mixtures the variation of viscosity with temperature, and the change in mixture density with powder-syrup ratio are documented. From least-square fits through the data, simple mathematical formulas are derived for approximate calculation of viscosity as a function of mixture ratio and temperature. These empirical formulas should be useful in the design of "test kits" for systematic study for pharyngeal and esophageal motility, and clinical analysis of motility disorders as they relate to bolus consistency.

Barium Sulfate↗
PubMed1992

Inhibitory effect of cyclosporin A on T lymphocyte DNA synthesis.

The interference of Cyclosporin A (CyA) with peripheral lymphocytes DNA synthesis was investigated. The results showed that the drug could strongly inhibit T cell proliferation in response to PHA stimulation if added at the start or at the early phase of the process, and it failed to do so if added 48 h later when most cells had already started to proliferate. Without PHA, no obvious differences were detected between normal control and CyA-treated cells. A comparison was made between T cell DNA synthesis of peripheral blood lymphocytes of healthy volunteers and renal transplant patients. It was found that T-cell DNA synthesis of patients was significantly lower than that of the healthy controls. From the above it may be suggested that CyA activity on T cell proliferation is similar in vivo and in vitro.

Cell Cycle↗
PubMed1992

Enhancement of B cell responses by the interaction of CD2 with LFA-3.

Potential effect of the interaction of CD2 with its ligand LFA-3 on B cell responses in vitro was studied to evaluate the action of CD2-LFA-3 in immune responses. It was found that: 1) addition of autologous erythrocytes to unfractional mononuclear cells resulted in enhancement of PWM-induced lymphocyte proliferation, and had no significant influence on non-mitogen stimulation; 2) autologous erythrocytes potentiated the synthesis of immunoglobulins; and 3) costimulating effects of autologous RBC can be depressed by preincubation of PBMNC with anti-CD2 monoclonal antibody (WuTll). The results suggest that preincubation of mononuclear cells with anti-CD2 McAb has a down-regulating effects on B cell responses and the interaction of CD2 with its ligand LFA-3 expressed by RBC is closely related to immune responses.

Adult↗
PubMed1992

An in vitro reversible interconversion of rat liver fatty acid binding protein having different isoelectric points by virtue of the fatty acid content.

Rat liver fatty acid binding protein (FABP) was purified to homogeneity by procedures including Sephadex G-100 and DEAE-cellulose column chromatographies. FABP was resolved into two major peaks, A and B, by the first DEAE-cellulose column chromatography. Each of these two fractions exhibited apparent homogeneity upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate with a molecular weight of 14,000 Da and amino acid analysis of these fractions has revealed that they are virtually identical or closely resemble each other. However, their fatty acid content was significantly different and heterogeneity was clearly demonstrated in the patterns of isoelectric focusing. In this communication, a single isoform (pI 5.0) from peak B FABP was further purified by successive DEAE-cellulose column chromatography and used as the final preparation. When the final FABP was partly freed of fatty acids by a mild delipidation technique using Lipidex 1,000, the pI shifted upward from 5.0 to 7.0. However, the pI of the delipidated FABP returned to its original pI of 5.0 after recombining fatty acids. These in vitro manipulations of bound fatty acid content made clear its possible cause of the microheterogeneity of FABP.

Amino Acids↗
PubMed1992

NMDA-, but not kainate- or quisqualate-dependent increases in cerebellar cGMP are dependent upon monoaminergic innervation.

As previously reported, intracerebellar injections of D-serine, quisqualate and kainate elevated mouse cerebellar cGMP levels. Similarly, activation of endogenous excitatory amino acid utilizing neurons with harmaline or pentylenetetrazole also increased cerebellar cGMP. We previously have demonstrated that the harmaline- and pentylenetetrazol-dependent cGMP increases are NMDA receptor mediated. In this report we further demonstrate that NMDA-dependent increases in cGMP are dependent upon monoaminergic innervation of the cerebellum, while kainate- and quisqualate-dependent cGMP increases are independent of such innervation.

Animals↗
PubMed1992

Excitatory amino acid signal transduction in the hippocampus: role of noradrenergic afferents and nitric oxide in cGMP increases in vivo.

Previous studies have demonstrated that excitatory amino acid (EAA)-dependent increases in cerebellar cGMP are dependent upon the prior activation of nitric oxide (NO) synthase. Additionally, the actions of NMDA, but not kainate or quisqualate, in elevating cerebellar cGMP have been shown to be dependent upon intact noradrenergic innervation of the cerebellum. In the current study we extended these observations to the hippocampus and again found that EAA-dependent increases in hippocampal cGMP also involve prior formation of NO. And as in the case of the cerebellum, NMDA-dependent increases in hippocampal cGMP involve prior release of norepinephrine which in turn apparently activates an alpha 1-adrenergic receptor to elicit cGMP increases. In toto, these data suggest that a key role of NMDA receptors in these brain regions is to presynaptically regulate the release of norepinephrine, thereby modulating the tone of this monoaminergic system. This may be a general principle which needs experimentation in other terminal fields of noradrenergic pathways.

Analysis of Variance↗
PubMed1992

Prostaglandin E2 prevents ovariectomy-induced cancellous bone loss in rats.

The object of this study was to determine whether prostaglandin E2 (PGE2) can prevent ovariectomy-induced cancellous bone loss. Thirty-five 3-month-old female Sprague-Dawley rats were divided into two groups. The rats in the first group were ovariectomized (OVX) while the others received sham operation (sham-OVX). The OVX group was further divided into three treatment groups. The daily doses for the three groups were 0, 1 and 6 mg PGE2/kg for 90 days. Bone histomorphometric analyses were performed on double-fluorescent-labeled undecalcified proximal tibial metaphysis (PTM). We confirmed that OVX induces massive cancellous bone loss (-80%) and a higher bone turnover (+143%). The new findings from the present study demonstrate that bone loss due to ovarian hormone deficiency can be prevented by a low-dose (1 mg) daily administration of PGE2. Furthermore, a higher-dose (6 mg) daily administration of PGE2 not only prevents bone loss but also adds extra bone to the proximal tibial metaphyses. PGE2 at the 1-mg dose level significantly increased trabecular bone area, trabecular width, trabecular node density, density of node to node, ratio of node to free end, and thus significantly decreased trabecular separation from OVX controls. At this dose level, these same parameters did not differ significantly from sham-OVX controls. However, at the 6-mg dose level PGE2, there were significant increases in trabecular bone area, trabecular width, trabecular node density, density of node to node, and ratio of node to free end, while there was significant decrease in trabecular separation from both OVX and sham-operated controls. The changes in indices of trabecular bone microanatomical structure indicated that PGE2 prevented bone loss as well as the disconnection of existing trabeculae. In summary, PGE2 administration to OVX rats decreased bone turnover and increased bone formation parameters resulting in a positive bone balance that prevented bone loss (in both lower and higher doses) and added extra bone to metaphyses of OVX rats (in higher dose). These findings support the strategy of the use of bone stimulation agents in the prevention of estrogen depletion bone loss (postmenopausal osteoporosis).

Aging↗
PubMed1992

Functional modulation of brain sodium channels by cAMP-dependent phosphorylation.

Voltage-gated Na+ channels, which are responsible for the generation of action potentials in brain, are phosphorylated by cAMP-dependent protein kinase in vitro and in intact neurons. Phosphorylation by cAMP-dependent protein kinase reduces peak Na+ currents 40%--50% in membrane patches excised from rat brain neurons or from CHO cells expressing type IIA Na+ channels. Inhibition of basal cAMP-dependent protein kinase activity by transfection with a plasmid encoding a dominant negative mutant regulatory subunit increases Na+ channel number and activity, indicating that even the basal level of kinase activity is sufficient to reduce Na+ channel activity significantly. Na+ currents in membrane patches from kinase-deficient cells were reduced up to 80% by phosphorylation by cAMP-dependent protein kinase. These effects could be blocked by a specific peptide inhibitor of cAMP-dependent protein kinase and reversed by phosphoprotein phosphatases. Convergent modulation of brain Na+ channels by neurotransmitters acting through the cAMP and protein kinase C signaling pathways may result in associative regulation of electrical activity by different synaptic inputs.

Animals↗
PubMed1992

Comparison of the expression of a mutant dihydrofolate reductase under control of different internal promoters in retroviral vectors.

To determine the effect of different promoters on the expression of an altered dihydrofolate reductase (DHFR) gene conferring methotrexate (MTX) resistance in different cell types, double-copy retroviral vectors were constructed carrying a murine mutant DHFR under the control of five different promoters, i.e., human adenosine deaminase (ADA), simian virus 40 (SV40), thymidine kinase (TK), human beta-actin, and cytomegalovirus (CMV). Their expression was compared in NIH-3T3 cells, three human leukemia cell lines, and mouse bone marrow. The variant DHFR is readily expressed from these various promoters in retroviral vectors at a selectable level. In 3T3 cells, the DHFR constructs containing the SV40 promoter conferred the highest levels of resistance to MTX. In K562 and Raji cells, the construct with the TK promoter produced the highest level of resistance. However granulocyte-macrophage colony-forming unit (CFU-GM) colonies from mouse marrow were more resistant to MTX when infected with vectors containing the SV40 promoter and ADA promoter as compared to the other promoter constructs. These studies show that mouse fibroblast cell lines such as NIH-3T3 do not predict the effectiveness of retroviral-mediated gene transfer for marrow progenitor cells, and that the activity of retroviral vector-encoded promoters vary in an unpredictable manner from cell type to cell type. Possible implications for basic gene transfer studies and clinical applications are discussed.

3T3 Cells↗