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Biomedical subjects

W Lu

Publications and source records attributed to W Lu.

At least 37 records · Page 2Linked to original sources
PubMed2001

Potentiation of simian immunodeficiency virus (SIV)-specific CD4(+) and CD8(+) T cell responses by a DNA-SIV and NYVAC-SIV prime/boost regimen.

T cell-mediated immune responses play an important role in the containment of HIV-1 replication. Therefore, an effective vaccine against HIV-1 should be able to elicit high frequencies of virus-specific CD8(+) and CD4(+) T cells. The highly attenuated poxvirus-based vaccine candidate, NYVAC-SIV-gag-pol-env (NYVAC-SIV-gpe), has been shown to induce and/or expand SIV-specific CD4(+) and CD8(+) T cell responses in both naive and infected macaques. In this study, the immunogenicity of NYVAC-SIV-gpe alone was compared with a combination regimen where priming with an optimized DNA-SIV-gag-env vaccine candidate was followed by a NYVAC-SIV-gpe boost. In macaques immunized with the prime-boost regimen, the extent and durability of CD8(+) T cell response to an immunodominant SIV gag epitope was increased and these animals recognized a broader array of subdominant SIV epitopes in the cytolytic assay. In addition, the prime-boost regimen significantly enhanced the proliferative responses to both SIV gag and env proteins. Thus, the combination of these vaccine modalities may represent a valuable strategy in the development of a vaccine for HIV.

Animals↗
PubMed2001

Structural basis for interaction of FGF-1, FGF-2, and FGF-7 with different heparan sulfate motifs.

Stromal cell-derived FGF-7 binds and activates only the resident FGFR2IIIb in epithelial cells while FGF-1 and FGF-2 exhibit a broader interaction with multiple isoforms of FGFR. Here we report the structure of FGF-7 that has been solved to 3.1 A resolution by molecular replacement with the structure of a dual function chimera of FGF-7 and FGF-1 (FGF-7/1) which was resolved to 2.3 A. Comparison of the FGF-7 structure to that of FGF-1 and FGF-2 revealed the strongly conserved Calpha backbone among the three FGF polypeptides and the surface hydrophobic patch that forms the primary receptor-binding domain. In contrast, a decrease and dispersion of the positive surface charge density characterized the heparin-binding domain of FGF-7 defined by homology to that of FGF-1 and FGF-2 in complexes with heparin. A simple heparin hexasaccharide that cocrystallized with FGF-1 and FGF-2 and protected both against protease in solution failed to exhibit the same properties with FGF-7. In contrast to FGF-1 and FGF-2, protection of FGF-7 was enhanced by heparin oligosaccharides of increased length with those exhibiting a 3-O-sulfate being the most effective. Protection of FGF-7 required interaction with specifically the fraction of crude heparin retained on antithrombin affinity columns. Conversely, heparin enriched by affinity for immobilized FGF-7 exhibited anti-factor Xa activity similar to that purified on an antithrombin affinity matrix. In contrast, an FGF-1 affinity matrix enriched the fraction of crude heparin with low anti-factor Xa activity. The results provide a structural basis to suggest that the unique FGF-7 heparin-binding (HB) domain underlies a specific restriction in respect to composition and length of the heparan sulfate motif that may impact specificity of localization, stability, and trafficking of FGF-7 in the microenvironment, and formation and activation of the FGFR2IIIb kinase signaling complex in epithelial cells.

Amino Acid Sequence↗
PubMed2001

Crystal structure of a cyclic form of bovine pancreatic trypsin inhibitor.

The crystal structure of a cyclic form of a mutant of bovine pancreatic trypsin inhibitor has been solved at 1.0 A resolution. The protein was synthesized by native chemical ligation and its structure is almost indistinguishable from the previously described recombinant form of the same mutant; however, the new loop containing the former termini became much better ordered.

Animals↗
PubMed2001

Characterization of cDNA encoding molt-inhibiting hormone of the crab, Cancer pagurus; expression of MIH in non-X-organ tissues.

Synthesis of ecdysteroids (molting hormones) by crustacean Y-organs is regulated by a neuropeptide, molt-inhibiting hormone (MIH), produced in eyestalk neural ganglia. We report here the molecular cloning of a cDNA encoding MIH of the edible crab, Cancer pagurus. Full-length MIH cDNA was obtained by using reverse transcription-polymerase chain reaction (RT-PCR) with degenerate oligonucleotides based upon the amino acid sequence of MIH, in conjunction with 5'- and 3'-RACE. Full-length clones of MIH cDNA were obtained that encoded a 35 amino acid putative signal peptide and the mature 78 amino acid peptide. Of various tissues examined by Northern blot analysis, the X-organ was the sole major site of expression of the MIH gene. However, a nested-PCR approach using non-degenerate MIH-specific primers indicated the presence of MIH transcripts in other tissues. Southern blot analysis indicated a simple gene arrangement with at least two copies of the MIH gene in the genome of C. pagurus. Additional Southern blotting experiments detected MIH-hybridizing bands in another Cancer species, Cancer antennarius and another crab species, Carcinus maenas.

Amino Acid Sequence↗
PubMed2001

Post-translational modification of the hepatitis C virus core protein by tissue transglutaminase.

The hepatitis C virus (HCV) core protein is a structural protein that packages the viral genomic RNA. In this study, we demonstrate that a stable core protein dimer could be produced in liver cells. The production of this protein could be enhanced by calphostin C and serum deprivation. This protein was determined to be the core protein dimer because of its reactivity with the anti-core antibody, its similar electrophoretic mobility compared with that of the core protein dimer generated by cross-linking with glutaraldehyde, and its increase in size by a hemagglutinin tag fused to the core protein sequence. This core protein dimer was highly stable and resistant to SDS and beta-mercaptoethanol. The enzyme that mediated the formation of this stable core protein dimer was determined to be the tissue transglutaminase (tTG) because, first, tTG could be activated by calphostin C and serum deprivation; second, the formation of this dimer was suppressed by monodansylcadaverine, a tTG inhibitor; and third, the core protein could be cross-linked by tTG in vitro. Thus, the HCV core protein represents the first known viral structural protein substrate of tTG. The post-translational modification by tTG reduced the RNA binding activity of the core protein, raising the possibility that tTG may regulate the biological functions of the HCV core protein.

Cell Line↗
PubMed2001

Comparison of Pkd1-targeted mutants reveals that loss of polycystin-1 causes cystogenesis and bone defects.

A high level of polycystin-1 expression is detected in kidneys of all patients with autosomal dominant polycystic kidney disease (ADPKD). Mice that overexpress polycystin-1 also develop renal cysts. Whether overexpression of polycystin-1 is necessary for cyst formation is still unclear. Here, we report the generation of a targeted mouse mutant with a null mutation in Pkd1 and its phenotypic characterization in comparison with the del34 mutants that carry a 'truncation mutation' in Pkd1. We show that null homozygotes develop the same, but more aggressive, renal and pancreatic cystic disease as del34/del34. Moreover, we report that both homozygous mutants develop polyhydramnios, hydrops fetalis, spina bifida occulta and osteochondrodysplasia. Heterozygotes also develop adult-onset pancreatic disease. We show further that del34 homozygotes continue to produce mutant polycystin-1, thereby providing a possible explanation for increased immunoreactive polycystin-1 in ADPKD cyst epithelia in the context of the two-hit model. Our data demonstrate for the first time that loss of polycystin-1 leads to cyst formation and defective skeletogenesis, and indicate that polycystin-1 is critical in both epithelium and chondrocyte development.

Animals↗
PubMed2001

Enhanced dendritic cell-driven proliferation and anti-HIV activity of CD8(+) T cells by a new phenothiazine derivative, aminoperazine.

T cell anergy, apoptosis, and chronic activation of T lymphocytes are prevailing features of HIV infection. The inability to develop an efficient natural antiviral activity in infected patients might be the consequence of a failure of the Ag presentation by dendritic cells (DCs) in chronically activated lymphoid tissues. We have identified a new phenothiazine derivative aminoperazine (APR; 2-amino-10-[3'-(1-methyl-4-piperazinyl)propyl]phenothiazine, C(20)H(26)N(4)S; m.w. 354.51) able to increase (effective dose from 0.1 to 100 nM) the Ag-specific DC-driven proliferation and differentiation of in vitro HIV-infected and uninfected normal donor T cells and of T cells from HIV-1-infected patients. The immunomodulatory effect of APR-sensitized DCs were ascribed to soluble factors derived from DCs. APR was also capable of increasing HIV gag-p24-specific proliferation and anti-HIV cytotoxic activity of patients' CD8(+) T cells against autologous B-lymphoblastoid cell lines expressing a HIV gag gene, resulting in the suppression of both proviral DNA and supernatant viral RNA in the HIV-1-infected patients' T cell culture. This new phenothiazine derivative (APR) might be used for boosting the immune response of vaccinated individuals and for restoring the immunity of immunocompromised patients.

Adjuvants, Immunologic↗
PubMed2001

Inhibition of MDM2 by hsp90 contributes to mutant p53 stabilization.

Stabilization and overexpression are hallmarks of mutant p53 found in nearly 50% of human tumors. Mutations in the conformation-sensitive core domain of p53 often lead to association with molecular chaperones such as hsp70 and hsp90. Inhibition of hsp90 function accelerates mutant p53 degradation. We recently found that expression of p53 core domain mutants inhibits MDM2 degradation, suggesting that mutant p53 can modulate MDM2 functions. In this report, we show that mutant p53 mediates formation of MDM2-p53-hsp90 complexes. Release of MDM2 from the p53-hsp90 complex after DNA damage restores MDM2 but not p53 turnover, whereas dissociation of hsp90 by geldanamycin increases the degradation of both MDM2 and mutant p53. Mutant p53 degradation after hsp90 inhibition requires MDM2 expression. The interaction between MDM2 and hsp90 is disrupted by the 2A10 antibody, which recognizes a site on MDM2 important for binding to alternative reading frame (ARF). Expression of mutant p53 prevents MDM2 from binding ARF and accumulating in the nucleolus in an hsp90-dependent fashion. These results suggest that hsp90 recruited by mutant p53 conceals the ARF-binding site on MDM2 and inhibits its ubiquitin-protein isopeptide ligase function, resulting in the stabilization of both mutant p53 and MDM2.

Benzoquinones↗
PubMed2001

Domain coexistence in nonlinear optical pattern formation.

We report on domain coexistence of a variety of different modes in a two-dimensional nonlinear optoelectronic model. The changes of stabilities of these modes are shown to give rise to new forms of spatial and spatiotemporal structures. The existence of these domain patterns explains some of the patterns recently observed in an optical system with a large array optoelectronic feedback circuit.

Journal Article↗
PubMed2001

Synthesis of a novel hepatitis C virus protein by ribosomal frameshift.

Hepatitis C virus (HCV) is an important human pathogen that affects approximately 100 million people worldwide. Its RNA genome codes for a polyprotein, which is cleaved by viral and cellular proteases to produce at least 10 mature viral protein products. We report here the discovery of a novel HCV protein synthesized by ribosomal frameshift. This protein, which we named the F protein, is synthesized from the initiation codon of the polyprotein sequence followed by ribosomal frameshift into the -2/+1 reading frame. This ribosomal frameshift requires only codons 8-14 of the core protein-coding sequence, and the shift junction is located at or near codon 11. An F protein analog synthesized in vitro reacted with the sera of HCV patients but not with the sera of hepatitis B patients, indicating the expression of the F protein during natural HCV infection. This unexpected finding may open new avenues for the development of anti-HCV drugs.

Amino Acid Sequence↗
PubMed2001

Amphetamine administration does not alter protein levels of the GLT-1 and EAAC1 glutamate transporter subtypes in rat midbrain, nucleus accumbens, striatum, or prefrontal cortex.

Our laboratory and others have previously shown that glutamate transmission is required for chronic amphetamine-induced neuroadaptations, and that glutamate transmission itself is altered by chronic amphetamine administration. For example, N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor subunit expression are altered in a region- and withdrawal-specific manner. The goal of this study was to determine whether repeated amphetamine administration influences the expression of two glutamate transporter subtypes, GLT-1 and EAAC1. Rats were treated with saline or 5 mg/kg amphetamine for 5 days (chronic saline and amphetamine groups, respectively), or saline for 4 days and 5 mg/kg amphetamine on day 5 (acute amphetamine group), and decapitated 24 h after the last injection. Tissue was dissected from brain regions involved in the psychomotor effects of amphetamine (nucleus accumbens, striatum, prefrontal cortex, ventral tegmental area, and substantia nigra). Levels of GLT-1 and EAAC1 were quantified by Western blotting and normalized to actin levels. We found no significant change in levels of GLT-1 or EAAC1 in response to either acute or chronic amphetamine treatment. These findings suggest that the transporter component of the glutamate system might not play a significant role in the alterations in glutamate transmission observed following repeated amphetamine administration.

ATP-Binding Cassette Transporters↗
PubMed2001

Nonredundant roles of the mPer1 and mPer2 genes in the mammalian circadian clock.

Mice carrying a null mutation in the Period 1 (mPer1) gene were generated using embryonic stem cell technology. Homozygous mPer1 mutants display a shorter circadian period with reduced precision and stability. Mice deficient in both mPer1 and mPer2 do not express circadian rhythms. While mPER2 regulates clock gene expression at the transcriptional level, mPER1 is dispensable for the rhythmic RNA expression of mPer1 and mPer2 and may instead regulate mPER2 at a posttranscriptional level. Studies of clock-controlled genes (CCGs) reveal a complex pattern of regulation by mPER1 and mPER2, suggesting independent controls by the two proteins over some output pathways. Genes encoding key enzymes in heme biosynthesis are under circadian control and are regulated by mPER1 and mPER2. Together, our studies show that mPER1 and mPER2 have distinct and complementary roles in the mouse clock mechanism.

Animals↗
PubMed2001

Activation of p53 by roscovitine-mediated suppression of MDM2 expression.

The p53 tumor suppressor is regulated by the MDM2 oncoprotein. Overexpression of MDM2 maintains p53 at low levels and contributes to the functional inactivation of p53 in a subset of tumors. We found that treatment with roscovitine and olomoucin, which were originally developed as cyclin-dependent kinase (CDK) inhibitors, can efficiently stabilize and activate nuclear p53 in tumor cells with MDM2 amplification or cytoplasmic p53. These inhibitors block the degradation of p53 without affecting p53-MDM2 binding and the nuclear shuttling function of p53 and MDM2. Roscovitine also induces stabilization of the p53 Ala-315 mutant, indicating that it does not act by regulating the CDK phosphorylation of serine 315. Roscovitine induces down-regulation of MDM2 expression at both protein and mRNA levels. Ectopic expression of MDM2 can abrogate the ability of roscovitine to induce p53 stabilization. Low concentrations of roscovitine cooperate with the DNA-damaging agent camptothecin to activate p53 in a synergistic fashion. These results show that the small molecule CDK inhibitors can be used to activate p53 through their potent inhibitory effect on MDM2 expression and may be useful as sensitizing agents for other DNA-damaging drugs.

Cell Compartmentation↗
PubMed2001

Differential functions of members of the low density lipoprotein receptor family suggested by their distinct endocytosis rates.

The low density lipoprotein receptor (LDLR) family is composed of a class of cell surface endocytic receptors that recognize extracellular ligands and internalize them for degradation by lysosomes. In addition to LDLR, mammalian members of this family include the LDLR-related protein (LRP), the very low density lipoprotein receptor (VLDLR), the apolipoprotein E receptor-2 (apoER2), and megalin. Herein we have analyzed the endocytic functions of the cytoplasmic tails of these receptors using LRP minireceptors, its chimeric receptor constructs, and full-length VLDLR and apoER2 stably expressed in LRP-null Chinese hamster ovary cells. We find that the initial endocytosis rates mediated by different cytoplasmic tails are significantly different, with half-times of ligand internalization ranging from less than 30 s to more than 8 min. The tail of LRP mediates the highest rate of endocytosis, whereas those of the VLDLR and apoER2 exhibit least endocytosis function. Compared with the tail of LRP, the tails of the LDLR and megalin display significantly lower levels of endocytosis rates. Ligand degradation analyses strongly support differential endocytosis rates initiated by these receptors. Interestingly apoER2, which has recently been shown to mediate intracellular signal transduction, exhibited the lowest level of ligand degradation efficiency. These results thus suggest that the endocytic functions of members of the LDLR family are distinct and that certain receptors in this family may play their main roles in areas other than receptor-mediated endocytosis.

Animals↗
PubMed2001

Predicting the reactivity of proteins from their sequence alone: Kazal family of protein inhibitors of serine proteinases.

An additivity-based sequence to reactivity algorithm for the interaction of members of the Kazal family of protein inhibitors with six selected serine proteinases is described. Ten consensus variable contact positions in the inhibitor were identified, and the 19 possible variants at each of these positions were expressed. The free energies of interaction of these variants and the wild type were measured. For an additive system, this data set allows for the calculation of all possible sequences, subject to some restrictions. The algorithm was extensively tested. It is exceptionally fast so that all possible sequences can be predicted. The strongest, the most specific possible, and the least specific inhibitors were designed, and an evolutionary problem was solved.

Algorithms↗
PubMed2001

Contribution of peptide bonds to inhibitor-protease binding: crystal structures of the turkey ovomucoid third domain backbone variants OMTKY3-Pro18I and OMTKY3-psi[COO]-Leu18I in complex with Streptomyces griseus proteinase B (SGPB) and the structure of the free inhibitor, OMTKY-3-psi[CH2NH2+]-Asp19I.

X-ray crystallography has been used to determine the 3D structures of two complexes between Streptomyces griseus proteinase B (SGPB), a bacterial serine proteinase, and backbone variants of turkey ovomucoid third domain (OMTKY3). The natural P1 residue (Leu18I) has been substituted by a proline residue (OMTKY3-Pro18I) and in the second variant, the peptide bond between Thr17I and Leu18I was replaced by an ester bond (OMTKY3-psi[COO]-Leu18I). Both variants lack the P1 NH group that donates a bifurcated hydrogen bond to the carbonyl O of Ser214 and O(gamma) of the catalytic Ser195, one of the common interactions between serine proteinases and their canonical inhibitors. The SGPB:OMTKY3-Pro18I complex has many structural differences in the vicinity of the S1 pocket when compared with the previously determined structure of SGPB:OMTKY3-Leu18I. The result is a huge difference in the DeltaG degrees of binding (8.3 kcal/mol), only part of which can be attributed to the missing hydrogen bond. In contrast, very little structural difference exists between the complexes of SGPB:OMTKY3-psi[COO]-Leu18I and SGPB:OMTKY3-Leu18I, aside from an ester O replacing the P1 NH group. Therefore, the difference in DeltaG degrees, 1.5 kcal/mol as calculated from the measured equilibrium association constants, can be attributed to the contribution of the P1 NH hydrogen bond toward binding. A crystal structure of OMTKY3 having a reduced peptide bond between P1 Leu18I and P'1 Asp19I, (OMTKY3-psi[CH2NH2+]-Asp19I) has also been determined by X-ray crystallography. This variant has very weak association equilibrium constants with SGPB and with chymotrypsin. The structure of the free inhibitor suggests that the reduced peptide bond has not introduced any major structural changes in the inhibitor. Therefore, its poor ability to inhibit serine proteinases is likely due to the disruptions of the canonical interactions at the oxyanion hole.

Animals↗
PubMed2001

Stabilization of the MDM2 oncoprotein by mutant p53.

MDM2 is a short-lived protein that regulates p53 degradation. We report here that transient coexpression of MDM2 and several p53 hotspot mutants resulted in stabilization and increased expression of MDM2. Ectopic expression of the mutant p53(175H) allele by recombinant adenovirus infection or stable transfection also stabilized endogenous MDM2 in p53-null cells. A panel of human tumor cell lines expressing different endogenous mutant p53 alleles also contained stabilized nuclear MDM2 at elevated levels when compared with p53-null cells. MDM2 was present in complexes with mutant p53 in tumor cells, and stabilization of MDM2 required direct binding to mutant p53. These results reveal a novel property of mutant p53 and a unique feature of tumors with p53 missense mutations. Accumulation of stable MDM2 may contribute to tumorigenesis through its p53-independent transforming functions.

Humans↗