Search PubMed⌕ Search

Biomedical subjects

J Gu

Publications and source records attributed to J Gu.

At least 127 records · Page 7Linked to original sources
PubMed1999

Cytochrome P450 and steroid hydroxylase activity in mouse olfactory and vomeronasal mucosa.

The aims of this study are to identify the sex steroid-metabolizing cytochrome P450 enzymes of the vomeronasal organ (VNO) and to determine the activities of VNO microsomes to metabolize estradiol, progesterone, and testosterone. Several P450 isoforms, including CYP1A2, CYP2A, CYP2B, CYP2C, CYP2G1, and CYP3A, NADPH P450-reductase, and microsomal epoxide hydrolase were detected in mouse VNO, although their expression levels were much lower than those in the main olfactory epithelium. VNO microsomes were active toward the three steroid hormones, producing metabolite profiles similar to those seen with olfactory mucosal microsomes. Thus, the mammalian VNO, a steroid hormone target tissue, contains multiple steroid-metabolizing P450 isoforms and is capable of metabolic disposition of the three major sex steroid hormones. These findings support the proposed roles of olfactory mucosal and VNO microsomal P450 enzymes in maintaining cellular hormonal homeostasis and other perireceptor processes associated with olfactory chemosensory function.

Animals↗
PubMed1999

PTEN gene and integrin signaling in cancer.

Integrins are major adhesion- and signaling-receptor proteins that mediate cell migration and invasion. They also trigger a variety of signal transduction pathways and regulate cytoskeletal organization, specific gene expression, growth control, and apoptosis (programmed cell death). Consequently, integrins are thought to play important roles in embryonic development and in the biology of cancers. The functions of integrins can be negatively regulated by the recently discovered tumor suppressor PTEN, a protein with homology to protein tyrosine phosphatases and tensin. The PTEN gene is mutated in a wide range of human cancers. PTEN inhibits cell migration and invasion by directly dephosphorylating two key tyrosine-phosphorylated proteins, thereby antagonizing interactions of integrins with the extracellular matrix and integrin-triggered signaling pathways. Other studies demonstrate important roles for PTEN in dephosphorylating a key signal transduction lipid. In the absence of PTEN, this lipid signal transduction pathway can protect tumor cells from apoptosis. Thus, PTEN appears to be a unique tumor suppressor-with both lipid phosphatase and protein tyrosine phosphatase activities-that negatively regulates cell interactions with the extracellular matrix and that maintains cell sensitivity to apoptosis, e.g., after loss of cell contact with the extracellular matrix. The complex signal transduction pathways regulated by PTEN are described in this review. PTEN and the signaling pathways it regulates may provide novel targets for potential therapy.

Cell Adhesion Molecules↗
PubMed1999

Emerging HIV infections with distinct subtypes of HIV-1 infection among injection drug users from geographically separate locations in Guangxi Province, China.

Heroin users from Guangxi province, a southern province of China that borders Vietnam in the south and Yunnan province in China in the west, were studied for prevalence and risk factors for HIV-1 infection. Viral env sequences from HIV-1-positive individuals were also determined for subtypes of HIV-1. The overall HIV prevalence among 227 heroin users was 40%. Most had used drugs for < or = 3 years. Sharing of injection equipment and unprotected sex were significantly associated with HIV-1 infection. Subtypes C and E HIV-1 were detected in infected heroin users and were sharply segregated in two geographic locations: only subtype C was found in a border city with Yunnan province, whereas only subtype E was found in a city bordering northern Vietnam. HIV-1 strains within each subtype were remarkably homogenous, with a mean intersubject DNA distance of 2.32% for subtype E and 1.13% for subtype C, respectively. Phylogenetic analysis of C2-V5 region of Guangxi subtype E env sequences revealed significant clustering with subtype E sequences from southern Vietnam and Cambodia. These results suggest that HIV-1 infection among heroin users in Guangxi represents two emerging epidemics initiated from distinct sources: one from Vietnam and another from Yunnan province. Factors associated with HIV-1 infection were not restricted to injection practices. Unprotected sexual behaviors are likely to increase the probability of HIV transmission beyond this high-risk population. Designing and implementing effective intervention strategies targeted toward both injection drug use and high risk sexual behavior are urgently needed to further reduce HIV-1 spread in China.

China↗
PubMed1999

Shc and FAK differentially regulate cell motility and directionality modulated by PTEN.

Cell migration is modulated by regulatory molecules such as growth factors, oncogenes, and the tumor suppressor PTEN. We previously described inhibition of cell migration by PTEN and restoration of motility by focal adhesion kinase (FAK) and p130 Crk-associated substrate (p130(Cas)). We now report a novel pathway regulating random cell motility involving Shc and mitogen-activated protein (MAP) kinase, which is downmodulated by PTEN and additive to a FAK pathway regulating directional migration. Overexpression of Shc or constitutively activated MEK1 in PTEN- reconstituted U87-MG cells stimulated integrin- mediated MAP kinase activation and cell migration. Conversely, overexpression of dominant negative Shc inhibited cell migration; Akt appeared uninvolved. PTEN directly dephosphorylated Shc. The migration induced by FAK or p130(Cas) was directionally persistent and involved extensive organization of actin microfilaments and focal adhesions. In contrast, Shc or MEK1 induced a random type of motility associated with less actin cytoskeletal and focal adhesion organization. These results identify two distinct, additive pathways regulating cell migration that are downregulated by tumor suppressor PTEN: one involves Shc, a MAP kinase pathway, and random migration, whereas the other involves FAK, p130(Cas), more extensive actin cytoskeletal organization, focal contacts, and directionally persistent cell motility. Integration of these pathways provides an intracellular mechanism for regulating the speed and the directionality of cell migration.

Actins↗
PubMed1999

Functional interaction of DFF35 and DFF45 with caspase-activated DNA fragmentation nuclease DFF40.

DNA fragmentation factor (DFF) functions downstream of caspase-3 and directly triggers DNA fragmentation during apoptosis. Here we described the identification and characterization of DFF35, an isoform of DFF45 comprised of 268 amino acids. Functional assays have shown that only DFF45, not DFF35, can assist in the synthesis of highly active DFF40. Using the deletion mutants, we mapped the function domains of DFF35/45 and demonstrated that the intact structure/conformation of DFF45 is essential for it to function as a chaperone and assist in the synthesis of active DFF40. Whereas the amino acid residues 101-180 of DFF35/45 mediate its binding to DFF40, the amino acid residues 23-100, which is homologous between DFF35/45 and DFF40, may function to inhibit the activity of DFF40. In contrast to DFF45, DFF35 cannot work as a chaperone, but it can bind to DFF40 more strongly than DFF45 and can inhibit its nuclease activity. These findings suggest that DFF35 may function in vivo as an important alternative mechanism to inhibit the activity of DFF40 and further, that the inhibitory effects of both DFF35 and DFF45 on DFF40 can put the death machinery under strict control.

Amino Acid Sequence↗
PubMed1999

PTEN interactions with focal adhesion kinase and suppression of the extracellular matrix-dependent phosphatidylinositol 3-kinase/Akt cell survival pathway.

The tumor suppressor PTEN is a phosphatase with sequence homology to tensin. PTEN dephosphorylates phosphatidylinositol 3,4, 5-trisphosphate (PIP3) and focal adhesion kinase (FAK), and it can inhibit cell growth, invasion, migration, and focal adhesions. We investigated molecular interactions of PTEN and FAK in glioblastoma and breast cancer cells lacking PTEN. The PTEN trapping mutant D92A bound wild-type FAK, requiring FAK autophosphorylation site Tyr397. In PTEN-mutated cancer cells, FAK phosphorylation was retained even in suspension after detachment from extracellular matrix, accompanied by enhanced PI 3-K association with FAK and sustained PI 3-K activity, PIP3 levels, and Akt phosphorylation; expression of exogenous PTEN suppressed all five properties. PTEN-mutated cells were resistant to apoptosis in suspension, but most of the cells entered apoptosis after expression of exogenous PTEN or wortmannin treatment. Moreover, overexpression of FAK in PTEN-transfected cells reversed the decreased FAK phosphorylation and PI 3-K activity, and it partially rescued PIP3 levels, Akt phosphorylation, and PTEN-induced apoptosis. Our results show that FAK Tyr397 is important in PTEN interactions with FAK, that PTEN regulates FAK phosphorylation and molecular associations after detachment from matrix, and that PTEN negatively regulates the extracellular matrix-dependent PI 3-K/Akt cell survival pathway in a process that can include FAK.

Cell Adhesion Molecules↗
PubMed1999

p73 is regulated by tyrosine kinase c-Abl in the apoptotic response to DNA damage.

The protein p73 is a structural and functional homologue of the p53 tumour-suppressor protein but, unlike p53, it is not induced in response to DNA damage. The tyrosine kinase c-Abl is activated by certain DNA-damaging agents and contributes to the induction of programmed cell death (apoptosis) by p53-dependent and p53-independent mechanisms. Here we show that c-Abl binds to p73 in cells, interacting through its SH3 domain with the carboxy-terminal homo-oligomerization domain of p73. c-Abl phosphorylates p73 on a tyrosine residue at position 99 both in vitro and in cells that have been exposed to ionizing radiation. Our results show that c-Abl stimulates p73-mediated transactivation and apoptosis. This regulation of p73 by c-Abl in response to DNA damage is also demonstrated by a failure of ionizing-radiation-induced apoptosis after disruption of the c-Abl-p73 interaction. These findings show that p73 is regulated by a c-Abl-dependent mechanism and that p73 participates in the apoptotic response to DNA damage.

Animals↗
PubMed1999

Inhibition of hypoxia-inducible factor 1 activation by carbon monoxide and nitric oxide. Implications for oxygen sensing and signaling.

It has been proposed that cells sense hypoxia by a heme protein, which transmits a signal that activates the heterodimeric transcription factor hypoxia-inducible factor 1 (HIF-1), thereby inducing a number of physiologically relevant genes such as erythropoietin (Epo). We have investigated the mechanism by which two heme-binding ligands, carbon monoxide and nitric oxide, affect oxygen sensing and signaling. Two concentrations of CO (10 and 80%) suppressed the activation of HIF-1 and induction of Epo mRNA by hypoxia in a dose-dependent manner. In contrast, CO had no effect on the induction of HIF-1 activity and Epo expression by either cobalt chloride or the iron chelator desferrioxamine. The affinity of CO for the putative sensor was much lower than that of oxygen (Haldane coefficient, approximately 0.5). Parallel experiments were done with 100 microM sodium nitroprusside, a nitric oxide donor. Both NO and CO inhibited HIF-1 DNA binding by abrogating hypoxia-induced accumulation of HIF-1alpha protein. Moreover, both NO and CO specifically targeted the internal oxygen-dependent degradation domain of HIF-1alpha, and also repressed the C-terminal transactivation domain of HIF-1alpha. Thus, NO and CO act proximally, presumably as heme ligands binding to the oxygen sensor, whereas desferrioxamine and perhaps cobalt appear to act at a site downstream.

Aryl Hydrocarbon Receptor Nuclear Translocator↗
PubMed1999

Mutation of Pten/Mmac1 in mice causes neoplasia in multiple organ systems.

Pten/Mmac1+/- heterozygous mice exhibited neoplasms in multiple organs including the endometrium, liver, prostate, gastrointestinal tract, thyroid, and thymus. Loss of the wild-type allele was detected in neoplasms of the thymus and liver. Surprisingly, tumors of the gastrointestinal epithelium developed in association with gut lymphoid tissue. Tumors of the endometrium, thyroid, prostate, and liver were not associated with lymphoid tissue and appeared to be highly mitotic. In addition, these mice have nonneoplastic hyperplasia of lymph nodes that was caused by an inherited defect in apoptosis detected in B cells and macrophages. Examination of peripheral lymphoid tissue including lymphoid aggregates associated with polyps revealed that the normal organization of B and T cells was disrupted in heterozygous animals. Taken together, these data suggest that PTEN is a regulator of apoptosis and proliferation that behaves as a "landscaper" tumor suppressor in the gut and a "gatekeeper" tumor suppressor in other organs.

Animals↗
PubMed1999

Plasma levels of insulin-like growth factor-I and lung cancer risk: a case-control analysis.

BACKGROUND: Insulin-like growth factors (IGFs), in particular IGF-I and IGF-II, strongly stimulate the proliferation of a variety of cancer cells, including those from lung cancer. To examine the possible causal role of IGFs in lung cancer development, we compared plasma levels of IGF-I, IGF-II, and an IGF-binding protein (IGFBP-3) in patients with newly diagnosed lung cancer and in control subjects. METHODS: From an ongoing hospital-based, case-control study, we selected 204 consecutive patients with histologically confirmed, primary lung cancer and 218 control subjects who were matched to the case patients by age, sex, race, and smoking status. IGF-I, IGF-II, and IGFBP-3 plasma levels were measured by enzyme-linked immunosorbent assay and then divided into quartiles, based on their distribution in the control subjects. Associations between the IGF variables and lung cancer risk were estimated by use of odds ratios (ORs). Reported P values are two-sided. RESULTS: IGF and IGFBP-3 levels were positively correlated (all r>.27; all P<.001). High plasma levels of IGF-I were associated with an increased risk of lung cancer (OR = 2.06; 95% confidence interval [CI] = 1.19-3.56; P = .01), and this association was dose dependent in both univariate and multivariate analyses. Plasma IGFBP-3 showed no association with lung cancer risk unless adjusted for IGF-I level; when both of these variables were analyzed together, high plasma levels of IGFBP-3 were associated with reduced risk of lung cancer (OR = 0.48; 95% CI = 0.25-0.92; P = .03). IGF-II was not associated with lung cancer risk. CONCLUSIONS: Plasma levels of IGF-I are higher and plasma levels of IGFBP-3 are lower in patients with lung cancer than in control subjects. If these findings can be confirmed in prospective studies, measuring levels of IGF-I and IGFBP-3 in blood may prove useful in assessing lung cancer risk.

Analysis of Variance↗
PubMed1999

Tumor suppressor PTEN inhibition of cell invasion, migration, and growth: differential involvement of focal adhesion kinase and p130Cas.

PTEN/MMAC1 is a major new tumor suppressor gene that encodes a dual-specificity phosphatase with sequence similarity to the cytoskeletal protein tensin. Recently, we reported that PTEN dephosphorylates focal adhesion kinase (FAK) and inhibits cell migration, spreading, and focal adhesion formation. Here, the effects of PTEN on cell invasion, migration, and growth as well as the involvement of FAK and p130 Crk-associated substrate (p130Cas) were investigated in U87MG glioblastoma cells missing PTEN. Cell invasion, migration, and growth were down-regulated by expression of phosphatase-active forms of PTEN but not by PTEN with an inactive phosphatase domain; these effects were correlated with decreased tyrosine phosphorylation levels of FAK and p130Cas. Overexpression of FAK concomitant with PTEN resulted in increased total tyrosine phosphorylation levels of FAK and p130Cas and effectively antagonized the effects of PTEN on cell invasion and migration and partially on cell growth. Overexpression of p130Cas increased total tyrosine phosphorylation levels of p130Cas without affecting those of FAK; however, although p130Cas could reverse PTEN inhibition of cell invasion and migration, it did not rescue cell growth in U87MG cells. In contrast to FAK, p130Cas could not be shown to interact with PTEN in cells, and it was not dephosphorylated directly by PTEN in vitro. These results suggest important roles of PTEN in the phenotype of tumor progression, and that the effects of PTEN on cell invasion, migration, and growth are mediated by distinct downstream pathways that diverge at the level of FAK.

Cell Adhesion Molecules↗
PubMed1999

Capillary electrophoresis enantioseparation of drugs using beta-cyclodextrin polymer: intramolecular synergistic effect.

Enantiomers of eight basic compounds of pharmaceutical interest were studied by capillary electrophoresis (CE) using a soluble cyclodextrin (CD) polymer and native CD as chiral selectors. The effects of the polymer concentration and the pH of the buffer solution on resolution were examined. It was found that the beta-CD polymer shows higher stereoselectivity than its parent cyclodextrin. Such improvement is due to the structural difference between beta-CD and beta-CD polymer. These results suggested the existence of an intramolecular synergistic effect in CE.

Buffers↗
PubMed1999

The M.ADP.Pi state is required for helical order in the thick filaments of skeletal muscle.

The thick filaments of mammalian and avian skeletal muscle fibers are disordered at low temperature, but become increasingly ordered into an helical structure as the temperature is raised. Wray and colleagues (Schlichting, I., and J. Wray. 1986. J. Muscle Res. Cell Motil. 7:79; Wray, J., R. S. Goody, and K. Holmes. 1986. Adv. Exp. Med. Biol. 226:49-59) interpreted the transition as reflecting a coupling between nucleotide state and global conformation with M.ATP (disordered) being favored at 0 degrees C and M.ADP.P(i) (ordered) at 20 degrees C. However, hitherto this has been limited to a qualitative correlation and the biochemical state of the myosin heads required to obtain the helical array has not been unequivocally identified. In the present study we have critically tested whether the helical arrangement of the myosin heads requires the M.ADP.P(i) state. X-ray diffraction patterns were recorded from skinned rabbit psoas muscle fiber bundles stretched to non-overlap to avoid complications due to interaction with actin. The effect of temperature on the intensities of the myosin-based layer lines and on the phosphate burst of myosin hydrolyzing ATP in solution were examined under closely matched conditions. The results showed that the fraction of myosin mass in the helix closely followed that of the fraction of myosin in the M.ADP.P(i) state. Similar results were found by using a series of nucleoside triphosphates, including CTP and GTP. In addition, fibers treated by N-phenylmaleimide (Barnett, V. A., A. Ehrlich, and M. Schoenberg. 1992. Biophys. J. 61:358-367) so that the myosin was exclusively in the M.ATP state revealed no helical order. Diffraction patterns from muscle fibers in nucleotide-free and in ADP-containing solutions did not show helical structure. All these confirmed that in the presence of nucleotides, the M.NDP.P(i) state is required for helical order. We also found that the spacing of the third meridional reflection of the thick filament is linked to the helical order. The spacing in the ordered M.NDP.P(i) state is 143.4 A, but in the disordered state, it is 144. 2 A. This may be explained by the different interference functions for the myosin heads and the thick filament backbone.

Adenosine Diphosphate↗
PubMed1999

Expression of RET proto-oncogene and GDNF deficit in Hirschsprung's disease.

PURPOSE: The aim of this study was to investigate GDNF (glial cell line-derived neurotrophic factor) protein expression and RNA expression level of the RET proto-oncogene in human aganglionic (AG) bowel in Hirschsprung's disease (HD) and to further understand the pathophysiology of HD. METHODS: To evaluate the possible implication of the RET gene and GDNF for the development of HD, mRNA expression level of the RETgene was examined by using the reverse transcription-polymerase chain reaction (RT-PCR) technique and protein expression level of the GDNF using an immunohistochemical technique in the bowel specimens of 15 HD patients. RESULTS: A significantly less intense signal for RETmRNA was found in the AG bowel compared with the ganglionic bowel. In different age groups of patients, the intensities of RET level had similar results. In the same patients, there was strong GDNF immunoreactivity in the myenteric plexuse in ganglionic bowel. In the myenteron in AG bowel, the number of GDNF immunoreactive neuron cells was reduced significantly compared with normal ganglionic bowel. CONCLUSIONS: From these preliminary data we conclude that the decreased RET expression in the AG bowel may suggest mal development of neural crest-derived cells in HD. The reduced level of GDNF in AG bowel may suggest a GDNF expression deficit interrupting the faithful signaling via RET, and both are implicated in the pathogenesis of HD.

Base Sequence↗
PubMed1999

Three measures of mutagen sensitivity in a cancer-free population.

Different individuals appear to respond differently to the same carcinogen, and different mutagens act differently on cells. We conducted mutagen sensitivity assays by using three mutagens (bleomycin, a radiomimetic agent; 4-nitroquinoline-1-oxide [4-NQO], an ultraviolet light mimetic agent; and benzo[a]pyrene diol epoxide [BPDE], a tobacco mutagen) in parallel in healthy human subjects to determine the relationships among these assays. Our results showed that the mean breaks per cell values (b/c) (+/- SD) for bleomycin, 4-NQO, and BPDE sensitivity were 0.49 (+/- 0.26), 0.53 (+/- 0.30), and 0.66 (+/- 0.41), respectively. Age, sex, smoking status, and family history of cancer were not correlated with any of these mutagen sensitivities. Also, there was no correlation between bleomycin and 4-NQO or 4-NQO and BPDE sensitivity, but a weak correlation between bleomycin and BPDE was observed (correlation coefficient = 0.289; P = 0.001). When the 75th percentile of b/c was used as a cutoff point in each assay, only one individual (1.8%) was sensitive to all three mutagens. Ten individuals (17.9%) were sensitive to two mutagens, 20 (35.7%) to one mutagen, and 25 (44.6%) to none of three mutagens. Our study suggests that these three mutagens may involve different DNA damage and repair pathways. The lack of correlation between the assay results may indicate the necessity of using a battery of mutagen sensitivity tests to refine our ability to identify a subpopulation at high cancer risk.

4-Nitroquinoline-1-oxide↗
PubMed1999

Activation of mitogen-activated protein kinases (Erk1 and Erk2) cascade results in phosphorylation of NF-M tail domains in transfected NIH 3T3 cells.

Neurofilaments (NFs) are neuron-specific intermediate filaments, and are the major cytoskeletal component in large myelinated axons. Lysine-serine-proline (KSP) repeats in the tail domains of high molecular weight NF proteins (NF-M and NF-H) are extensively phosphorylated in vivo in the axon. This phosphorylation in the tail domain has been postulated to play an important role in mediating neuron-specific properties, including axonal caliber and conduction velocity. Recent studies have shown that the mitogen-activated protein kinases (extracellular signal-regulated kinases, Erk1 and Erk2) phosphorylate KSP motifs in peptide substrates derived from the NF-M and NF-H tail domains in vitro. However, it is not clear whether activation of the mitogen activated protein (MAP) kinase pathway is able to phosphorylate these domains in vivo. To answer this question, a constitutively active form of mitogen-activated Erk activating kinase (MEK1) was cotransfected with an NF-M expression construct into NIH 3T3 cells. The activated mutant, but not the dominant negative mutant, induced phosphorylation of NF-M. In addition, it was shown that epidermal growth factor, which induces the MAP kinase cascade in NIH 3T3 cells, also activated endogenous Erk1 and Erk2 and NF-M tail domain phosphorylation in the transfected cells. These results present direct evidence that in-vivo activation of Erk1 and Erk 2 is sufficient for NF-M tail domain phosphorylation in transfected cells.

3T3 Cells↗
PubMed1999

Ethnic differences in poly(ADP-ribose) polymerase pseudogene genotype distribution and association with lung cancer risk.

Poly(ADP-ribose) polymerase (PADPRP) is a nuclear DNA-binding enzyme that can modulate chromatin structure close to DNA replication, recombination and repair regions. Two-allele polymorphism on the PADPRP chromosome 13 pseudogene has been studied in several ethnic subpopulations, and the association of each allele with different types of cancer has been investigated. To study the frequency of the allele in the context of lung cancer, we performed a PCR assay for the PADPRP polymorphism in 288 lung cancer patients and 292 matched controls and examined the frequency of the alleles in different ethnic groups. Our results showed that the allele distribution was significantly different among members of different ethnic groups. Specifically, the A allele was dominant in Mexican-American and Caucasian groups but not in the African-American group. The frequencies of the B allele in Mexican-American, Caucasian and African-American controls were 0.184, 0.218 and 0.606, respectively, with the Caucasian cases and controls showing an almost identical lower B allele frequency (0.199 in cases versus 0.218 in controls), and the African-American cases and controls showing an almost identical but considerably higher frequency (0.578 in cases versus 0. 606 in controls). In contrast, the Mexican-American cases and controls exhibited a considerable difference in the B allele frequency (0.306 in cases versus 0.184 in controls). When we combined subjects with the AB or BB genotype into a susceptible genotype group and compared them with the AA group using univariate analysis, the susceptible genotype was not shown to be associated with a risk of lung cancer in either the Caucasian or African-American subpopulation but was significantly associated with an increased risk (2.29-fold) of lung cancer in the Mexican-American group. When lung cancer was categorized by histologic type, no elevated risk was noted for squamous cell carcinoma in any ethnicity. However, in Mexican-Americans, susceptible genotypes were associated with significantly increased risks of adenocarcinoma (3. 21-fold) and large cell carcinoma (10.79). Our study and others have demonstrated that the PADPRP polymorphism may modify an individual's susceptibility to certain cancers. Assessment of the interaction between genetic constitution and environmental exposure might expand our understanding of carcinogenesis and enhance our ability to evaluate the populational cancer risk.

Adenocarcinoma↗