Biomedical subjects

Mark Lee

Publications and source records attributed to Mark Lee.

At least 19 recordsLinked to original sources

PubMed2006

The human TRIM5alpha restriction factor mediates accelerated uncoating of the N-tropic murine leukemia virus capsid.

The host cell factors TRIM5alpha(hu) and Fv-1 restrict N-tropic murine leukemia virus (N-MLV) infection at an early postentry step before or after reverse transcription, respectively. Interestingly, the identity of residue 110 of the MLV capsid determines susceptibility to both TRIM5alpha(hu) and Fv-1. In this study, we investigate the fate of the MLV capsid in cells expressing either the TRIM5alpha(hu) or Fv-1 restriction factor. The expression of TRIM5alpha(hu), but not Fv-1, specifically promoted the premature conversion of particulate N-MLV capsids within infected cells to soluble capsid proteins. The TRIM5alpha(hu)-mediated disassembly of particulate N-MLV capsids was dependent upon residue 110 of the viral capsid. Furthermore, the deletion or disruption of TRIM5alpha(hu) domains necessary for potent N-MLV restriction completely abrogated the disappearance of particulate N-MLV capsids observed with wild-type TRIM5alpha(hu). These results suggest that premature disassembly of the viral capsid contributes to the restriction of N-MLV infection by TRIM5alpha(hu), but not by Fv-1.

Amino Acid Substitution↗

PubMed2006

Specific recognition and accelerated uncoating of retroviral capsids by the TRIM5alpha restriction factor.

The host restriction factor TRIM5alpha mediates species-specific, early blocks to retrovirus infection; susceptibility to these blocks is determined by viral capsid sequences. Here we demonstrate that TRIM5alpha variants from Old World monkeys specifically associate with the HIV type 1 (HIV-1) capsid and that this interaction depends on the TRIM5alpha B30.2 domain. Human and New World monkey TRIM5alpha proteins associated less efficiently with the HIV-1 capsid, accounting for the lack of restriction in cells of these species. After infection, the expression of a restricting TRIM5alpha in the target cells correlated with a decrease in the amount of particulate capsid in the cytosol. In some cases, this loss of particulate capsid was accompanied by a detectable increase in soluble capsid protein. Inhibiting the proteasome did not abrogate restriction. Thus, TRIM5alpha restricts retroviral infection by specifically recognizing the capsid and promoting its rapid, premature disassembly.

Animals↗

PubMed2006

Dynamical electric and magnetic metamaterial response at terahertz frequencies.

Utilizing terahertz time domain spectroscopy, we have characterized the electromagnetic response of a planar array of split ring resonators (SRRs) fabricated upon a high resistivity GaAs substrate. The measured frequency dependent magnetic and electric resonances are in excellent agreement with theory and simulation. For two polarizations, the SRRs yield a negative electric response (epsilon < 0). We demonstrate, for the first time, dynamical control of the electrical response of the SRRs through photoexcitation of free carriers in the substrate. An excited carrier density of approximately 4 x 10(16) cm(-3) is sufficient to short the gap of the SRRs, thereby turning off the electric resonance, demonstrating the potential of such structures as terahertz switches. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum.

Journal Article↗

PubMed2006

Characteristics of the glmS ribozyme suggest only structural roles for divalent metal ions.

The glmS ribozyme is a riboswitch class that occurs in certain Gram-positive bacteria, where it resides within mRNAs encoding glucosamine 6-phosphate synthase. Members of this self-cleaving ribozyme class rapidly catalyze RNA transesterification upon binding GlcN6P, and genetic evidence suggests that this cleavage event is important for down-regulating GlmS protein expression. In this report, we present a refined secondary structure model of the glmS ribozyme and determine the importance of a conserved pseudoknot structure for optimal ribozyme function. Analyses of deletion constructs demonstrate that the pseudoknot, together with other structural elements, permits the ribozyme to achieve maximum rate constants for RNA cleavage at physiologically relevant Mg2+ concentrations. In addition, we show that substantial rate enhancements are supported by an exchange-inert cobalt (III) complex and by molar concentrations of monovalent ions. Our findings indicate that the glmS ribozyme forms a complex structure to employ catalytic strategies that do not require the direct participation of divalent metal ions.

Bacillus cereus↗

PubMed2006

Removal of arginine 332 allows human TRIM5alpha to bind human immunodeficiency virus capsids and to restrict infection.

Human TRIM5alpha (TRIM5alpha(hu)) only modestly inhibits human immunodeficiency virus type 1 (HIV-1) and does not inhibit simian immunodeficiency virus (SIV(mac)). Alteration of arginine 332 in the TRIM5alpha(hu) B30.2 domain to proline, the residue found in rhesus monkey TRIM5alpha, has been shown to create a potent restricting factor for both HIV-1 and SIV(mac.) Here we demonstrate that the potentiation of HIV-1 inhibition results from the removal of a positively charged residue at position 332 of TRIM5alpha(hu.) The increase in restricting activity correlated with an increase in the ability of TRIM5alpha(hu) mutants lacking arginine 332 to bind HIV-1 capsid complexes. A change in the cyclophilin A-binding loop of the HIV-1 capsid decreased TRIM5alpha(hu) R332P binding and allowed escape from restriction. The ability of TRIM5alpha(hu) to restrict SIV(mac) could be disrupted by the presence of any charged residue at position 332. Thus, charged residues in the v1 region of the TRIM5alpha(hu) B30.2 domain can modulate capsid binding and restriction potency. Therapeutic strategies designed to neutralize arginine 332 of TRIM5alpha(hu) might potentiate the innate resistance of human cells to HIV-1 infection.

Anti-HIV Agents↗

PubMed2005

History of infection control and its contributions to the development and success of brain tumor operations.

Before advancements in infection control, only conditions that brought patients near death warranted the risk of surgical intervention. If patients survived the operation, infection was nearly inevitable and death by overwhelming sepsis was knocking at their door. In the late 19th century, with the development of germ theory by Louis Pasteur and its subsequent application to surgical sterility by Joseph Lister, surgeons were able to operate with a substantially reduced risk of infection. Consequently, surgeons became more confident and began to explore more extravagant procedures, including elective operations within the cranial vault. As scientific knowledge expanded in the 20th century, so did the advancement of infection control with the use of prophylactic antibiotic drugs, heat sterilization of instruments, and microbial barriers. Recent reports have placed the rate of complications due to infection between 0.75 and 2.32% for intracranial operations.

Anti-Bacterial Agents↗

PubMed2005

Knee fusion using dual platings with the locking compression plate.

Knee arthrodesis is often used as a salvage procedure for infected, nonreconstructable total knee arthroplasties. We report 3 cases of infected total knee arthroplasties treated with knee fusion using locking compression plates. After at least 2 years of follow-up, these patients have healed with improvement in both symptoms and mobility.

Aged↗

PubMed2004

Phase diagram of coulomb interactions across the metal-insulator transition in Si:B.

Measurements of the single-particle density of states (DOS) near T=0 K in Si:B are used to construct an energy-density phase diagram of Coulomb interactions across the critical density n(c) of the metal-insulator transition. Insulators and metals are found to be distinguishable only below a phase boundary epsilon*(|n/n(c)-1|) determined by the Coulomb energy. Above epsilon* is a mixed state where metals and insulators equidistant from n(c) cannot be distinguished from their DOS structure. The data imply a diverging screening radius at n(c), which may signal an interaction-driven thermodynamic state change.

Journal Article↗

PubMed2004

The axonal attractant Netrin-1 is an angiogenic factor.

Blood vessels and nerves often follow parallel trajectories, suggesting that distal targets use common cues that induce vascularization and innervation. Netrins are secreted by the floor plate and attract commissural axons toward the midline of the neural tube. Here, we show that Netrin-1 is also a potent vascular mitogen. Netrin-1 stimulates proliferation, induces migration, and promotes adhesion of endothelial cells and vascular smooth muscle cells with a specific activity comparable to vascular endothelial growth factor and platelet-derived growth factor. Our evidence indicates that the netrin receptor, Neogenin, mediates netrin signaling in vascular smooth muscle cells, but suggests that an unidentified receptor mediates the proangiogenic effects of Netrin-1 on endothelial cells. Netrin-1 also stimulates angiogenesis in vivo and augments the response to vascular endothelial growth factor. Thus, we demonstrate that Netrin-1 is a secreted neural guidance cue with the unique ability to attract both blood vessels and axons, and suggest that other cues may also function as vascular endothelial growth factors.

Angiogenic Proteins↗

PubMed2004

A glycine-dependent riboswitch that uses cooperative binding to control gene expression.

We identified a previously unknown riboswitch class in bacteria that is selectively triggered by glycine. A representative of these glycine-sensing RNAs from Bacillus subtilis operates as a rare genetic on switch for the gcvT operon, which codes for proteins that form the glycine cleavage system. Most glycine riboswitches integrate two ligand-binding domains that function cooperatively to more closely approximate a two-state genetic switch. This advanced form of riboswitch may have evolved to ensure that excess glycine is efficiently used to provide carbon flux through the citric acid cycle and maintain adequate amounts of the amino acid for protein synthesis. Thus, riboswitches perform key regulatory roles and exhibit complex performance characteristics that previously had been observed only with protein factors.

5' Untranslated Regions↗

PubMed2004

Prevention of type I diabetes transfer by glutamic acid decarboxylase 65 peptide 206-220-specific T cells.

Glutamic acid decarboxylase (GAD) 65 is one of the major pancreatic antigens targeted by self-reactive T cells in type I diabetes mellitus. T cells specific for GAD65 are among the first to enter inflamed islets and may be important for the initiation of autoimmune diabetes. However, we previously reported that nonobese diabetic (NOD) mice transgenic for a T cell antigen receptor (TCR) specific for one of the immunodominant epitopes of GAD65, peptide 286-300 (G286), are protected from insulitis and diabetes. To examine whether other GAD65-reactive T cells share this phenotype, we have generated TCR transgenic NOD mice for a second immunodominant epitope of GAD65, peptide 206-220 (G206). As in G286 mice, G206 mice do not develop islet inflammation or diabetes. When adoptively transferred along with diabetogenic T cells, activated G206 T cells significantly delayed the onset of diabetes in NOD.scid recipients. Both G206 and G286 T cells produce immunoregulatory cytokines IFN-gamma and IL-10 at low levels when activated by cognate antigens. These data suggest that GAD65-specific T cells may play a protective role in diabetes pathogenesis by regulating pathogenic T cell responses. A better understanding of the functions of autoreactive T cells in type I diabetes will be necessary for choosing desirable targets for immunotherapy.

Amino Acid Sequence↗

PubMed2004

New RNA motifs suggest an expanded scope for riboswitches in bacterial genetic control.

The expression of certain genes involved in fundamental metabolism is regulated by metabolite-binding "riboswitch" elements embedded within their corresponding mRNAs. We have identified at least six additional elements within the Bacillus subtilis genome that exhibit characteristics of riboswitch function (glmS, gcvT, ydaO/yuaA, ykkC/yxkD, ykoK, and yybP/ykoY). These motifs exhibit extensive sequence and secondary-structure conservation among many bacterial species and occur upstream of related genes. The element located upstream of the glmS gene in Gram-positive organisms functions as a metabolite-dependent ribozyme that responds to glucosamine-6-phosphate. Other motifs form complex folded structures when transcribed as RNA molecules and carry intrinsic terminator structures. These findings indicate that riboswitches serve as a major genetic regulatory mechanism for the control of metabolic genes in many microbial species.

Bacillus subtilis↗

PubMed2004

Preliminary stabilization of the less invasive stabilization system.

We describe the use of a universal T-handle chuck to provide preliminary stabilization of the Less Invasive Stabilization System supracondylar femur implant and aiming device. This technique is helpful to maintain the position of the plate against the bone during intraoperative radiographs and initial screw insertion. Use of this simple technique may help avoid the problems that occur when the plate is positioned too far away from the lateral femoral cortex.

Bone Plates↗

PubMed2004

Evolving spinal analgesia practice in palliative care.

Intraspinal analgesia can be helpful in some patients with intractable pain. Over 15 years palliative care professionals evolved their spinals policy through a repeated series of evaluations, discussions and literature reviews. One hundred intraspinal lines were then reviewed. Notable changes in policy were the switch from epidurals to intrathecals, and the insertion of lines during working hours rather than as emergencies. Our efficacy, and frequency of adverse effects, is equal or better to published studies. Key issues in reducing adverse effects were the improved care of the spinal line exit site, a change from bolus administration to continuous infusions, and modifying line insertion techniques. Current policy is to use continuous infusions of diamorphine and bupivacaine in a 1:5 ratio through externalized intrathecal lines. The lines are effective in approximately two thirds of patients and can be kept in place for up to 18 months. The policy continues to be updated and common documentation is now in place.

Adult↗

PubMed2003

Essential requirement for Wnt signaling in proliferation of adult small intestine and colon revealed by adenoviral expression of Dickkopf-1.

Whereas the adult gastrointestinal epithelium undergoes tremendous self-renewal through active proliferation in crypt stem cell compartments, the responsible growth factors regulating this continuous proliferation have not been defined. The exploration of physiologic functions of Wnt proteins in adult organisms has been hampered by functional redundancy and the necessity for conditional inactivation strategies. Dickkopf-1 (Dkk1) is a potent secreted Wnt antagonist that interacts with Wnt coreceptors of the LRP family. To address the contribution of Wnt signaling to gastrointestinal epithelial proliferation, adenoviral expression of Dkk1 was used to achieve stringent, conditional, and reversible Wnt inhibition in adult animals. Adenovirus Dkk1 (Ad Dkk1) treatment of adult mice repressed expression of the Wnt target genes CD44 and EphB2 within 2 days in both small intestine and colon, indicating an extremely broad role for Wnt signaling in the maintenance of adult gastrointestinal gene expression. In parallel, Ad Dkk1 markedly inhibited proliferation in small intestine and colon, accompanied by progressive architectural degeneration with the loss of crypts, villi, and glandular structure by 7 days. Whereas decreased Dkk1 expression at later time points (>10 days) was followed by crypt and villus regeneration, which was consistent with a reversible process, substantial mortality ensued from colitis and systemic infection. These results indicate the efficacy of systemic expression of secreted Wnt antagonists as a general strategy for conditional inactivation of Wnt signaling in adult organisms and illustrate a striking reliance on a single growth factor pathway for the maintenance of the architecture of the adult small intestine and colon.

Adenoviridae↗

PubMed2003

Adequacy of representation of the National Drug File Reference Terminology Physiologic Effects reference hierarchy for commonly prescribed medications.

The National Drug File Reference Terminology contains a novel reference hierarchy to describe physiologic effects (PE) of drugs. The PE reference hierarchy contains 1697 concepts arranged into two broad categories; organ specific and generalized systemic effects. This investigation evaluated the appropriateness of the PE concepts for classifying a random selection of commonly prescribed medications. Ten physician reviewers classified the physiologic effects of ten drugs and rated the accuracy of the selected term. Inter reviewer agreement, overall confidence, and concept frequencies were assessed and were correlated with the complexity of the drug's known physiologic effects. In general, agreement between reviewers was fair to moderate (kappa 0.08-0.49). The physiologic effects modeled became more disperse with drugs having and inducing multiple physiologic processes. Complete modeling of all physiologic effects was limited by reviewers focusing on different physiologic processes. The reviewers were generally comfortable with the accuracy of the concepts selected. Overall, the PE reference hierarchy was useful for physician reviewers classifying the physiologic effects of drugs. Ongoing evolution of the PE reference hierarchy as it evolves should take into account the experiences of our reviewers.

Drug Therapy↗

PubMed2002

Broadband modulation of light by using an electro-optic polymer.

A major challenge to increasing bandwidth in optical telecommunications is to encode electronic signals onto a lightwave carrier by modulating the light up to very fast rates. Polymer electro-optic materials have the necessary properties to function in photonic devices beyond the 40-GHz bandwidth currently available. An appropriate choice of polymers is shown to effectively eliminate the factors contributing to an optical modulator's decay in the high-frequency response. The resulting device modulates light with a bandwidth of 150 to 200 GHz and produces detectable modulation signal at 1.6 THz. These rates are faster than anticipated bandwidth requirements for the foreseeable future.

Journal Article↗

PubMed2002

Terahertz near-field imaging.

A near-field probe is described that enables high spatial resolution imaging with terahertz (THz) pulses. The spatial resolution capabilities of the system lie in the range of few microns and we demonstrate a resolution of 7 microm using broad-banded THz pulses with an intensity maximum near 0.5 THz. We present a study of the performance of the near-field probes in the collection mode configuration and discuss some image properties.

Diagnostic Imaging↗