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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↗
PubMed2001

GPC3 mutation analysis in a spectrum of patients with overgrowth expands the phenotype of Simpson-Golabi-Behmel syndrome.

Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked overgrowth syndrome caused by deletions in glypican 3 (GPC3). SGBS is characterized by pre- and postnatal overgrowth, a characteristic facial appearance, and a spectrum of congenital malformations which overlaps that of other overgrowth syndromes. We performed GPC3 deletion screening on 80 male patients with somatic overgrowth in the following categories: SGBS (n = 19), possible SGBS (n = 26), including families in which individuals had previously been diagnosed with other overgrowth syndromes, and Wiedemann-Beckwith syndrome (WBS) (n = 35). Using exon-specific PCR and Southern blot analysis, we identified seven GPC3 deletions. In most cases a clear X-linked family history was not present. In two cases, GPC3 deletions were identified in patients belonging to pedigrees published previously as other overgrowth syndromes: one with a diagnosis of Sotos syndrome and the other Perlman syndrome with nephroblastomatosis. A third patient developed hepatoblastoma, a tumor type not previously described in SGBS. No GPC3 deletions were identified among the WBS patients. Direct sequencing of all GPC3 exons in the remaining 13 SGBS patients without GPC3 deletions did not identify any further mutations, raising the possibility of alternative silencing mechanisms and/or other genes in the pathogenesis of SGBS. Our results validate the clinical specificity of the facial appearance, skeletal/hand anomalies, and supernumerary nipples in patients with GPC3 deletions. Our data also suggest that nephroblastomatosis and hepatoblastoma are included in the phenotypic spectrum of GPC3 deletions and SGBS, underscoring the importance of tumor surveillance in these children.

Abnormalities, Multiple↗
PubMed2001

Caveolin-1 null mice are viable but show evidence of hyperproliferative and vascular abnormalities.

Caveolin-1 is the principal structural protein of caveolae membranes in fibroblasts and endothelia. Recently, we have shown that the human CAV-1 gene is localized to a suspected tumor suppressor locus, and mutations in Cav-1 have been implicated in human cancer. Here, we created a caveolin-1 null (CAV-1 -/-) mouse model, using standard homologous recombination techniques, to assess the role of caveolin-1 in caveolae biogenesis, endocytosis, cell proliferation, and endothelial nitric-oxide synthase (eNOS) signaling. Surprisingly, Cav-1 null mice are viable. We show that these mice lack caveolin-1 protein expression and plasmalemmal caveolae. In addition, analysis of cultured fibroblasts from Cav-1 null embryos reveals the following: (i) a loss of caveolin-2 protein expression; (ii) defects in the endocytosis of a known caveolar ligand, i.e. fluorescein isothiocyanate-albumin; and (iii) a hyperproliferative phenotype. Importantly, these phenotypic changes are reversed by recombinant expression of the caveolin-1 cDNA. Furthermore, examination of the lung parenchyma (an endothelial-rich tissue) shows hypercellularity with thickened alveolar septa and an increase in the number of vascular endothelial growth factor receptor (Flk-1)-positive endothelial cells. As predicted, endothelial cells from Cav-1 null mice lack caveolae membranes. Finally, we examined eNOS signaling by measuring the physiological response of aortic rings to various stimuli. Our results indicate that eNOS activity is up-regulated in Cav-1 null animals, and this activity can be blunted by using a specific NOS inhibitor, nitro-l-arginine methyl ester. These findings are in accordance with previous in vitro studies showing that caveolin-1 is an endogenous inhibitor of eNOS. Thus, caveolin-1 expression is required to stabilize the caveolin-2 protein product, to mediate the caveolar endocytosis of specific ligands, to negatively regulate the proliferation of certain cell types, and to provide tonic inhibition of eNOS activity in endothelial cells.

Albumins↗
PubMed2001

Induction of apoptosis by cyclo-oxygenase-2 inhibitor NS398 through a cytochrome C-dependent pathway in esophageal cancer cells.

Non-steroidal anti-inflammatory drugs (NSAIDs) can induce tumor cells to undergo apoptosis in vitro. They have also shown cancer-preventive activity in vivo. The mechanism of their effects is, however, not well defined. We investigated the mechanism by which a new NSAID, NS398, induces apoptosis in esophageal cancer cell lines. NS398 decreased cell viability in 2 cyclo-oxygenase-2-positive (COX-2(+)) esophageal cancer cell lines but not in a COX-2(-) cell line. DNA fragmentation and TUNEL assays demonstrated that NS398 induced the 2 COX-2(+) cancer cell lines to undergo apoptosis. The percentage of apoptosis induced by NS398 was associated with the level of COX-2 expression. Further investigation showed that the cytochrome c pathway was responsible for NS398-induced apoptosis; i.e., cytochrome c was released from mitochondria, caspase-9 and caspase-3 were activated and finally poly(ADP-ribose)polymerase (PARP) was cleaved. Furthermore, the effect of NS398 was inhibited by the caspase inhibitor Z-DEVD-FMK and prostaglandin E(2). In contrast, bcl-2, bax, c-myc, Fas and Fas-ligand showed minor changes. Altogether, our data suggest that induction of apoptosis by NS398 is associated with COX-2 expression and occurs through the cytochrome c-dependent pathway, which sequentially activates caspase-9 and caspase-3 and cleaves PARP.

Apoptosis↗
PubMed2001

Crystal structure of human epidermal growth factor and its dimerization.

Epidermal growth factor (EGF) is a typical growth-stimulating peptide and functions by binding to specific cell-surface receptors and inducing dimerization of the receptors. Little is known about the molecular mechanism of EGF-induced dimerization of EGF receptors. The crystal structure of human EGF has been determined at pH 8.1. There are two human EGF molecules A and B in the asymmetric unit of the crystals, which form a potential dimer. Importantly, a number of residues known to be indispensable for EGF binding to its receptor are involved in the interface between the two EGF molecules, suggesting a crucial role of EGF dimerization in the EGF-induced dimerization of receptors. In addition, the crystal structure of EGF shares the main features of the NMR structure of mouse EGF determined at pH 2.0, but structural comparisons between different models have revealed new detailed features and properties of the EGF structure.

Crystallization↗
PubMed2001

Coupled capillary wave fluctuations in thin aqueous films on an aqueous subphase.

X-ray scattering and interfacial tension measurements are used to demonstrate the formation of nanometer-thick aqueous films on aqueous bulk subphases from polymer-salt biphase mixtures. X-ray scattering determines a coupling constant that characterizes the coupled capillary wave fluctuations of the liquid-vapor and liquid-liquid interfaces of this thin film. These data also determine an effective Hamakar constant that characterizes the long-range interaction between the interfaces and parameters that characterize the short-range part of the interfacial interaction.

Journal Article↗
PubMed2001

Closing the pseudogap by Zeeman splitting in Bi2Sr2CaCu2O8+y at high magnetic fields.

Interlayer tunneling resistivity is used to probe the low-energy density-of-states (DOS) depletion due to the pseudogap in the normal state of Bi2Sr2CaCu2O8+y. Measurements up to 60 T reveal that a field that restores DOS to its ungapped state shows strikingly different temperature and doping dependencies from the characteristic fields of the superconducting state. The pseudogap closing field and the pseudogap temperature T small star, filled evaluated independently are related through a simple Zeeman energy scaling. These findings indicate a predominant role of spins over the orbital effects in the formation of the pseudogap.

Journal Article↗
PubMed2001

Imprinting status of 11p15 genes in Beckwith-Wiedemann syndrome patients with CDKN1C mutations.

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder characterized by somatic overgrowth, congenital malformations, and predisposition to childhood tumors. Aberrant expression of multiple imprinted genes, including H19, IGF2, KCNQ1OT1, and CDKN1C, has been observed in BWS patients. It has been estimated that mutations in CDKN1C occur in 12-17% of BWS patients. We have screened 10 autosomal dominant pedigrees and 65 sporadic BWS cases by PCR/heteroduplex analysis and DNA sequencing and have identified four mutations, two of which were associated with biallelic IGF2 expression and normal H19 and KCNQ1OT1 imprinting. One patient demonstrated phenotypic expression of paternally transmitted mutation in this maternally expressed gene, a second proband is the child of one of a pair of monozygotic twin females who carry the mutation de novo, and a third patient exhibited unusual skeletal changes more commonly found in other overgrowth syndromes. When considered with other studies published to date, this work reveals the frequency of CDKN1C mutations in BWS to be only 4.9%. This is the first report of an analysis of the imprinting status of genes in the 11p15 region where CDKN1C mutations were associated with loss of IGF2 imprinting and maintenance of H19 and KCNQ1OT1 imprinting.

Amino Acid Sequence↗
PubMed2001

An essential role of the NF-kappa B/Toll-like receptor pathway in induction of inflammatory and tissue-repair gene expression by necrotic cells.

Tissue damage induced by infection or injury can result in necrosis, a mode of cell death characterized by induction of an inflammatory response. In contrast, cells dying by apoptosis do not induce inflammation. However, the reasons for underlying differences between these two modes of cell death in inducing inflammation are not known. Here we show that necrotic cells, but not apoptotic cells, activate NF-kappaB and induce expression of genes involved in inflammatory and tissue-repair responses, including neutrophil-specific chemokine genes KC and macrophage-inflammatory protein-2, in viable fibroblasts and macrophages. Intriguingly, NF-kappaB activation by necrotic cells was dependent on Toll-like receptor 2, a signaling pathway that induces inflammation in response to microbial agents. These results have identified a novel mechanism by which cell necrosis, but not apoptosis, can induce expression of genes involved in inflammation and tissue-repair responses. Furthermore, these results also demonstrate that the NF-kappaB/Toll-like receptor 2 pathway can be activated both by exogenous microbial agents and endogenous inflammatory stimuli.

Animals↗
PubMed2001

'Inverse' melting of a vortex lattice.

Inverse melting is the process in which a crystal reversibly transforms into a liquid or amorphous phase when its temperature is decreased. Such a process is considered to be very rare, and the search for it is often hampered by the formation of non-equilibrium states or intermediate phases. Here we report the discovery of first-order inverse melting of the lattice formed by magnetic flux lines in a high-temperature superconductor. At low temperatures, disorder in the material pins the vortices, preventing the observation of their equilibrium properties and therefore the determination of whether a phase transition occurs. But by using a technique to 'dither' the vortices, we were able to equilibrate the lattice, which enabled us to obtain direct thermodynamic evidence of inverse melting of the ordered lattice into a disordered vortex phase as the temperature is decreased. The ordered lattice has larger entropy than the low-temperature disordered phase. The mechanism of the first-order phase transition changes gradually from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures.

Journal Article↗
PubMed2001

Protein disulfide isomerase and sulfhydryl-dependent pathways in platelet activation.

The inhibition of blood platelet aggregation and secretion was studied using covalent thiol reagents, maleimides, or mercuribenzoates, or using inhibitors of protein disulfide isomerase (PDI), bacitracin or antibodies to PDI. As expected, both types of inhibitors were effective against stimulation by normal physiologic stimuli. On the other hand, when stimulation was initiated with the peptide LSARLAF, that specifically activates the integrin alphaIIbbeta3 (the fibrinogen receptor), the PDI inhibitors were without effect. LSARLAF-induced aggregation was, however, inhibited by the sulfhydryl reagents. To further investigate the role of sulfhydryl-containing proteins and alphaIIbbeta3, platelets were labeled with membrane-impermeant sulfhydryl reagents. Nine bands were found labeled on gel electrophoresis. Two of the labeled bands were identified as alphaIIb and beta3. The conclusions are that while PDI is required for platelet aggregation and secretion, an additional sulfhydryl-dependent step or protein is also required. This latter reaction occurs at the level of alphaIIbbeta3. In distinction to most literature reports, at least a subpopulation of alphaIIbbeta3 contains free sulfhydryl groups, consistent with the possibility that it is a substrate for PDI or part of the sulfhydryl-dependent response.

Blood Platelets↗
PubMed2001

O-ethyl and o-methyl n-(2,3,4,6-tetra-o-acetyl-beta-d-glucopyranosyl)thiocarbamate.

In both the title structures, O-ethyl N-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)thiocarbamate, C(17)H(25)NO(10)S, and O-methyl N-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)thiocarbamate, C(16)H(23)NO(10)S, the hexopyranosyl ring adopts the (4)C(1) conformation. All the ring substituents are in equatorial positions. The acetoxymethyl group is in a gauche-gauche conformation. The S atom is in a synperiplanar conformation, while the C-N-C-O linkage is antiperiplanar. N-H.O intermolecular hydrogen bonds link the molecules into infinite chains and these are connected by C-H.O interactions.

Carbohydrate Conformation↗
PubMed2001

Cell-associated ovalbumin is cross-presented much more efficiently than soluble ovalbumin in vivo.

To better understand the antigenic requirements for cross-presentation, we compared the in vivo efficiency of presentation of cell-associated vs soluble OVA with the OT-I (CD8) and OT-II (CD4) TCR transgenic lines. Cross-presentation of cell-associated OVA was very efficient, requiring as little as 21 ng of OVA to activate OT-II cells and 100-fold less to activate OT-I cells. In contrast, soluble OVA was presented inefficiently, requiring at least 10,000 ng OVA for activation of either T cell subset. Thus, cell-associated OVA was presented 500-fold more efficiently than soluble OVA to CD4 T cells and 50,000-fold more efficiently to CD8 T cells. These data, which represent the first quantitative in vivo analysis of cross-presentation, show that cell-associated OVA is very efficiently presented via the class I pathway.

Animals↗
PubMed2001

Transgenic mice with an expanded CAG repeat controlled by the human AR promoter show polyglutamine nuclear inclusions and neuronal dysfunction without neuronal cell death.

We generated transgenic mice that expressed a highly expanded 239 polyglutamine (polyQ) repeat under the control of the human androgen receptor promoter. These transgenic mice developed progressive neurological phenotypes of muscular weakness and ataxia, small body size and short life-span. PolyQ nuclear inclusions (NIs) were remarkable and widespread but found in selective regions of the central nervous system (CNS) such as the spinal cord, cerebrum and cerebellum as well as in selective peripheral visceral organs. This distribution pattern resembled that of spinal and bulbar muscular atrophy somewhat, but was more widespread. In neuronal tissues, NIs were present in astrocytes as well as neurons. Cytoplasmic and axonal inclusions were not observed. In the CNS regions with abundant NIs, neuronal populations were well-preserved, and neither neuronal cell death, reactive astrogliosis nor microglial invasions were detected. These findings suggest that polyQ alone can induce the neuronal dysfunction that precedes gross neuronal degeneration and provides a clue for investigating molecular mechanisms that underly the pathway to neuronal dysfunction from polyQ expansion.

Animals↗
PubMed2001

Caveolin-3 null mice show a loss of caveolae, changes in the microdomain distribution of the dystrophin-glycoprotein complex, and t-tubule abnormalities.

Caveolin-3, a muscle-specific caveolin-related protein, is the principal structural protein of caveolae membrane domains in striated muscle cells. Recently, we identified a novel autosomal dominant form of limb-girdle muscular dystrophy (LGMD-1C) in humans that is due to mutations within the coding sequence of the human caveolin-3 gene (3p25). These LGMD-1C mutations lead to an approximately 95% reduction in caveolin-3 protein expression, i.e. a caveolin-3 deficiency. Here, we created a caveolin-3 null (CAV3 -/-) mouse model, using standard homologous recombination techniques, to mimic a caveolin-3 deficiency. We show that these mice lack caveolin-3 protein expression and sarcolemmal caveolae membranes. In addition, analysis of skeletal muscle tissue from these caveolin-3 null mice reveals: (i) mild myopathic changes; (ii) an exclusion of the dystrophin-glycoprotein complex from lipid raft domains; and (iii) abnormalities in the organization of the T-tubule system, with dilated and longitudinally oriented T-tubules. These results have clear mechanistic implications for understanding the pathogenesis of LGMD-1C at a molecular level.

Animals↗
PubMed2001

Parvalbumin expression is downregulated in rat fast-twitch skeletal muscles during aging.

In this study, the protein expression profile of extensor digitorum longous (EDL) and Soleus (SOL) muscles, representing fast- and slow-twitch skeletal muscles, respectively, was established using high resolution two-dimensional electrophoresis (2-DE). One protein spot was found uniquely expressed in EDL muscle. N-terminal sequence analysis identified the protein as parvalbumin. Parvalbumin is a high affinity calcium binding protein that regulates muscle contraction and relaxation. Our experiments revealed that parvalbumin expression in EDL muscle was down-regulated during aging. In addition, high-intensity exercise could reverse this age-related change. Soleus muscles do not normally express parvalbumin, but high-intensity exercise could ectopically induce its expression in both young and old SOL muscles. We have also confirmed our 2-DE findings by immunohistochemistry on muscle sections. Our results suggest that high-intensity training could be used to improve muscle functions during aging because parvalbumin play an important role in regulating skeletal muscle contraction and relaxation.

Aging↗
PubMed2001

Natural-resistance-associated macrophage protein 1 is an H+/bivalent cation antiporter.

In mammals, natural-resistance-associated macrophage protein 1 (Nramp1) regulates macrophage activation and is associated with infectious and autoimmune diseases. Nramp2 is associated with anaemia. Both belong to a highly conserved eukaryote/prokaryote protein family. We used Xenopus oocytes to demonstrate that, like Nramp2, Nramp1 is a bivalent cation (Fe2+, Zn2+ and Mn2+) transporter. Strikingly, however, where Nramp2 is a symporter of H+ and metal ions, Nramp1 is a highly pH-dependent antiporter that fluxes metal ions in either direction against a proton gradient. At pH 9.0, oocytes injected with cRNA from wild-type murine Nramp1 with a glycine residue at position 169 (Nramp1(G169); P=3.22x10(-6)) and human NRAMP1 (P=3.87x10(-5)) showed significantly enhanced uptake of radiolabelled Zn2+ compared with water-injected controls. At pH 5.5, Nramp1(G169) (P=1.34x10(-13)) and NRAMP1 (P=1.09x10(-6)) oocytes showed significant efflux of Zn2+. Zn2+ transport was abolished when the proton gradient was dissipated using carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Using pre-acidified oocytes, currents of 130+/-57 nA were evoked by 100 microM Zn2+ at pH 7.5, and 139+/-47 nA by 100 microM Fe2+ at pH 7.0, in Nramp1(G169) oocytes; currents of 254+/-49 nA and 242+/-26 nA were evoked, respectively, in NRAMP1 oocytes. Steady-state currents evoked by increasing concentrations of Zn2+ were saturable, with apparent affinity constants of approx. 614 nM for Nramp1(G169) and approx. 562 nM for NRAMP1 oocytes, and a curvilinear voltage dependence of transporter activity (i.e. the data points approximate to a curve that approaches a linear asymptote). In the present study we propose a new model for metal ion homoeostasis in macrophages. Under normal physiological conditions, Nramp2, localized to early endosomal membranes, delivers extracellularly acquired bivalent cations into the cytosol. Nramp1, localized to late endosomal/lysosomal membranes, delivers bivalent cations from the cytosol into this acidic compartment where they may directly affect antimicrobial activity.

Animals↗