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Biomedical subjects

F Fan

Publications and source records attributed to F Fan.

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

Overview of angiogenesis: Biologic implications for antiangiogenic therapy.

Tumor angiogenesis is essential for the growth of primary and metastatic tumors. This process requires the coordinated activities of multiple factors and cell types. For tumors to develop a neovascular blood supply, tumor cells and host cells must secrete proangiogenic factors that offset the activities of inhibitory angiogenic factors. In addition, the newly derived tumor endothelium must respond to signals in the microenvironment to survive under conditions such as hypoxia and acidity. Moreover, because the process of angiogenesis is regulated by redundant factors and pathways, inhibition of any single pathway is likely to select for cells whose angiogenesis is driven by other factors. Because antiangiogenic therapy is unlikely to induce tumor regression, the criteria for efficacy must be evaluated by means other than the standard criteria used to evaluate cytotoxic chemotherapy. Understanding the basic principles that drive tumor angiogenesis will lead to the development of therapies that will likely prolong survival without the toxicity associated with standard chemotherapy.

Angiogenesis Inducing Agents↗
PubMed2001

The effect of chemical carcinogenesis on rat glutathione S-transferase P1 gene transcriptional regulation.

To investigate mechanisms of rat glutathione S-transferase P1 gene (rGSTP1) expression regulation during chemical carcinogenesis. we studied enhancer elements located in the region between -2.5 kb to -2.2 kb. The region was upstream from the start site of transcription and was divided into two major fragments, GPEI and GPEII. The GPEII fragment was further divided into two smaller fragments, GPEII- I and GPEII-2. Using a luciferase reporter system, we identified a strong enhancer of GPEI and a weak enhancer of GPEII in HeLa and a rat hepatoma cell line CBRH79 19 cell. The enhancer of GPEII was located within the GPEII-I region. Chemical stimulation by glycidyl methatylate (GMA) and phorbol 12-o-tetradecanoate 13-acetate (TPA) analysis revealed that induction of rGSTP1 expression was mainly through GPEI. Although H2O2 could enhance GPEII enhancer activity, the enhancement is not mediated by the NF-kappaB factor that bound the NF-kappaB site in GPEII. Using electrophoretic mobility shift assays (EMSA) and the UV cross-linking assays, we found that HeLa and CBRH7919 cells had proteins that specifically bound GPEI core sequence and a 64 kDa protein that interacted with GPEII-1. The cells from normal rat liver did not express the binding proteins. Therefore, the trans-acting factors seem to be closely related to GPEI, GPEII enhancer activities and may play an important role in high expression of rGSTPI gene.

5' Flanking Region↗
PubMed2001

Vascular endothelial growth factor is upregulated by interleukin-1 beta in human vascular smooth muscle cells via the P38 mitogen-activated protein kinase pathway.

Small tumor vessels are composed of endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). These cells have been shown to communicate with each other via cytokine signaling during neovascularization. We previously demonstrated that interleukin-1 beta (IL-1 beta) leads to induction of vascular endothelial growth factor (VEGF) in human colon carcinoma cells. As pericytes play a role in regulating EC function, we hypothesized that IL-1 beta may mediate EC survival by induction of VEGF in a paracrine manner. We investigated the effects of IL-1 beta on VEGF expression in human VSMCs (hVSMCs) and the signal transduction pathways that may be involved. Treatment of hVSMCs with IL-1 beta induced VEGF expression in a time- and concentration-dependent manner and increased both the VEGF promoter activity and the mRNA half-life. Treatment with IL-1 beta induced the expression of P38 mitogen-activated protein kinase (MAPK) within 5 min but did not activate extracellular signal-regulated kinases (Erk)-1/2, c-jun amino terminal kinase (JNK), or Akt. SB203580, a specific P38 MAPK inhibitor, blocked the ability of IL-1 beta to induce VEGF mRNA and promoter activity. Conditioned media from hVSMCs pretreated with IL-1 beta prevented apoptosis of ECs, an effect that was partially abrogated by VEGF-neutralizing antibodies. These data demonstrate that IL-1 beta may induce VEGF in hVSMCs, and suggest that this paracrine signaling pathway, may prevent, in part, apoptosis of ECs.

Cell Survival↗
PubMed2001

Biochemical and genetic characterization of the action of triclosan on Staphylococcus aureus.

Triclosan, a widely used antibacterial agent, possesses potent activity against Staphylococcus aureus. This study reports on an investigation of the antibacterial target of triclosan in this pathogen. A strain of S. aureus overexpressing the enoyl-[acyl-carrier-protein] reductase (FabI), demonstrated by Western immunoblotting, gave rise to an increase in the MIC of triclosan, while susceptibilities to a range of unrelated antibacterials were unaffected. There are approximately 12 000 molecules of FabI per cell in mid-log phase growth. This number increased by approximately three- to four-fold in the S. aureus FabI overexpressor. Triclosan selectively inhibited the incorporation of [(14)C]acetate into TCA-precipitable product, an indicator of fatty acid biosynthesis. Furthermore, it inhibited de novo fatty acid biosynthesis in this organism. In vitro, triclosan inhibited recombinant, purified S. aureus FabI with an IC(50) of approximately 1 microM. The combination of these biochemical and genetic data provide further evidence that the mode of action of triclosan in S. aureus is via inhibition of FabI.

Anti-Infective Agents, Local↗
PubMed2001

CD44s expression is reduced in endometriotic lesions compared to eutopic endometrium in women with endometriosis.

Immunohistochemical expression of the standard form of CD44 (CD44s) was examined in archival formalin-fixed endometriotic and matching eutopic endometrial tissue obtained from 25 patients in proliferative (N = 16) and secretory (N = 9) stages of the cycle. CD44s was expressed in most eutopic endometria and endometriotic tissue. Its expression was significantly higher in secretory than in proliferative phase endometrium. It was low but detectable in 13 of 16 proliferative phase biopsies. The majority of these endometria exhibited both glandular and stromal staining (63%). In the secretory phase, glandular cells exhibited a significantly greater intensity of staining compared to stromal cells. In endometriotic tissue, stromal cell CD44s expression did not differ between tissue types in either stage of the cycle. In contrast, glandular expression in endometriotic tissue during the secretory phase was reduced (p < 0.05) compared to eutopic endometrium. It was absent in 66% of cases and reduced in the remaining cases. Our results indicate a correlation between CD44s expression and secretory differentiation of endometrial glands in the cycle, suggesting hormonal regulation of its expression. This cyclic pattern of CD44s expression was lost in corresponding endometriotic tissue. Reduced expression of CD44s in endometriotic tissue may provide insight into the pathophysiology of endometriosis.

Adult↗
PubMed2001

Scabies associated with radiation therapy for cutaneous T-cell lymphoma.

Scabies, infection with Sarcoptes scabiei, is known to be predisposed to by poor body hygiene, environmental exposure, and systemic immunodeficiency. We report the case of an 83-year-old man with Sezary's syndrome who developed scabies limited to the skin of the upper chest, the same location where he had previously received electron beam radiation treatments for cutaneous T-cell lymphoma. Histologic and immunohistochemical studies demonstrated that sections of the previously irradiated right and left chest skin, compared to non-irradiated chest, abdominal, and leg skin, had infestation by scabies, diminished involvement by T-cell lymphoma, and notably reduced numbers of Langerhans cells. These findings suggest that the development of scabies may be predisposed to by local cutaneous radiation therapy, and that it may be mediated by local cutaneous immunodeficiency secondary to reduced numbers of Langerhans cells.

Aged↗
PubMed2001

Role of angiogenesis inhibitors in cancer treatment.

Angiogenesis is essential for the growth of both primary and metastatic tumors. This process, more complex than was previously thought, requires the coordinated activities of multiple factors and cell types. For tumors to develop a neovascular blood supply, tumor and host cells must secrete pro-angiogenic factors that offset the activities of inhibitory angiogenic factors. In addition, the newly derived tumor endothelium must respond to survive in a relatively caustic microenvironment. Thus, endothelial-cell survival factors are essential in the maintenance of this neovasculature. Because redundant factors and pathways regulate angiogenesis, inhibition of any single pathway is unlikely to lead to prolonged response in most patients with solid malignancies. Since anti-angiogenic therapy is unlikely to induce tumor regression, the criteria for efficacy must be evaluated by means other than the standard criteria used to evaluate cytotoxic chemotherapy regimens. Understanding the basic principles that drive tumor angiogenesis will lead to the development of therapies that will likely prolong survival without the toxicity associated with standard chemotherapy.

Angiogenesis Inhibitors↗
PubMed2000

Activation of the transcription factor Oct-1 in response to DNA damage.

Mammalian cells exhibit complex cellular responses to genotoxic stress, including cell cycle checkpoint, DNA repair, and apoptosis. Inactivation of these important biological events will result in genomic instability and cell transformation. It has been demonstrated that gene activation is a critical initial step during the cellular response to DNA damage. A number of investigations have shown that transcription factors are involved in the regulation of stress-inducible genes. These transcription factors include p53, c-Myc, and AP-1 (c-fos and c-jun). However, the role for the octamer-binding transcription factor Oct-1 in the DNA damage-activated response is unknown. In this report, we have presented the novel observation that the transcription factor Oct-1 is induced after cells are exposed to multiple DNA-damaging agents and therapeutic agents, including UV radiation, methylmethane sulfonate, ionizing radiation, etoposide, cisplatin, and camptothecin. The induction of the Oct-1 protein is mediated through a posttranscriptional mechanism and does not require the normal cellular function of the tumor suppressor p53, indicating that the Oct-1 protein, as a transcription factor, may play a role in p53-independent gene activation. In addition to increased protein level, the activity of Oct-1 DNA binding to its specific consensus sequence is also enhanced by DNA damage. Therefore, these results have implicated that the transcription factor Oct-1 might participate in cellular response to DNA damage, particularly in p53-independent gene activation.

DNA Damage↗
PubMed2000

Regulated gene expression in Staphylococcus aureus for identifying conditional lethal phenotypes and antibiotic mode of action.

Selectively regulating gene expression in bacteria has provided an important tool for studying gene function. However, well-regulated gene control systems have been restricted primarily for use in laboratory non-pathogenic strains of bacteria (e.g. Escherichia coli, Bacillus subtilis). The development of analogous systems for use in bacterial pathogens such as Staphylococcus aureus would significantly enhance our ability to examine the contribution of any given gene product to pathogen growth and viability. In this report, we adapt, examine and compare three regulated gene expression systems in S. aureus, which had previously been used in B. subtilis. We demonstrate that all three systems function and exhibit titratable induction, together covering a dynamic range of gene expression of approximately 3000-fold. This dynamic range correlates well with the physiological expression levels of cellular proteins. Importantly, we show that one of these systems, the Spac system, is particularly useful for examining gene essentiality and creating specific conditional lethal phenotypes. Moreover, we find that titration of selective target gene products using this system allows direct demonstration of antibiotic mode of action.

Anti-Bacterial Agents↗
PubMed2000

BRCA1 activation of the GADD45 promoter.

Breast cancer susceptibility gene BRCA1 has been implicated in the control of gene regulation and such regulated genes are thought to mediate the biological role of BRCA1. Overexpression of BRCA1 induces GADD45, a p53-regulated and stress-inducible gene. However, the molecular mechanism by which BRCA1 induces the expression GADD45 remains unclear. In this report, we have shown that the GADD45 promoter is strongly activated following expression of wild-type BRCA1. In contrast, both the tumor-derived BRCA1 mutants (p1749R and Y1853insA) and truncated BRCA1 mutant protein (Delta500 - 1863 BRCA1), which lack transactivation activity, were unable to activate the GADD45 promoter, indicating that the BRCA1-mediated activation of the GADD45 promoter requires normal transcriptional properties of BRCA1. BRCA1 did not induce the c-Jun and c-fos promoters, which rules out a general effect of BRCA1 on other immediate-responsive genes. Expression of the human papillomavirus E6 and the dominant-negative mutant p53 proteins had no effect on the induction of the GADD45 promoter by BRCA1, suggesting that activation of the GADD45 promoter by BRCA1 is independent of cellular p53 function. With the 5'-deletion analysis, the BRCA1-responsive element of the GADD45 promoter was mapped at the region from -121 to -75. Disruption of this region resulted in the abrogation of BRCA1 activation of the GADD45 promoter. Taken together, these results demonstrate that the mechanism by which BRCA1 induces GADD45 is mainly through the transactivation of the GADD45 promoter, further demonstrating the evidence that GADD45 acts as one of the BRCA1-regulated genes. Oncogene (2000) 19, 4050 - 4057.

Adenocarcinoma↗
PubMed2000

The central region of Gadd45 is required for its interaction with p21/WAF1.

Cell cycle arrest represents an important response to genotoxic stress and the tumor suppressor p53 has been described to act as a critical effector in this biological event. Upon stress, p53 becomes transcriptionally active and up-regulates the transcription of downstream effector genes, which contain p53 recognition sites in their regulatory regions. Among the genes activated are p21 and GADD45, each of which independently exhibits growth-suppressive activity. The Gadd45 protein has been described to form a complex with p21, and thus, work was undertaken to map the regions of Gadd45 involved in this interaction and to examine the roles of those two proteins in growth suppression. In this report, a Gadd45 overlapping peptide library and a series of Gadd45 deletion mutants were used to define the domains of Gadd45 involved in the association with p21. Results using both in vitro and in vivo methods have shown that the interaction of Gadd45 with p21 involves a central region of Gadd45. Interestingly, the p21-binding domain of Gadd45 also encodes the Cdc2-binding activity, indicating that the central region of Gadd45 may serve as an important "core," through which Gadd45 protein is able to present cross-talk with other cell cycle regulators. In addition, GADD45 inhibition of Cdc2 kinase activity was compared with Myd118 and CR6, two other members of the GADD45 family. GADD45 was shown to generate the strongest inhibitory effect on Cdc2 activity. Finally, results from short-term survival assays further demonstrated that p21 and GADD45 act upon different cellular pathways to exert their growth-suppressive function.

Binding Sites↗
PubMed2000

The GADD45 inhibition of Cdc2 kinase correlates with GADD45-mediated growth suppression.

Cell cycle growth arrest is an important cellular response to genotoxic stress. Gadd45, a p53-regulated stress protein, plays an important role in the cell cycle G(2)-M checkpoint following exposure to certain types of DNA-damaging agents such as UV radiation and methylmethane sulfonate. Recent findings indicate that Gadd45 interacts with Cdc2 protein and inhibits Cdc2 kinase activity. In the present study, a series of Myc-tagged Gadd45 deletion mutants and a Gadd45 overlapping peptide library were used to define the Gadd45 domains that are involved in the interaction of Gadd45 with Cdc2. Both in vitro and in vivo studies indicate that the interaction of Gadd45 with Cdc2 involves a central region of the Gadd45 protein (amino acids 65-84). The Cdc2-binding domain of Gadd45 is also required for Gadd45 inhibition of Cdc2 kinase activity. Sequence analysis of the central Gadd45 region reveals no homology to inhibitory motifs of known cyclin-dependent kinase inhibitors, indicating that the Cdc2-binding and -inhibitory domains on Gadd45 are a novel motif. The peptide containing the Cdc2-binding domain (amino acids 65-84) disrupted the Cdc2-cyclin B1 protein complex, suggesting that dissociation of this complex results from a direct interaction between the Gadd45 and Cdc2 proteins. GADD45-induced cell cycle G(2)-M arrest was abolished when its Cdc2 binding motif was disrupted. Importantly, a short term survival assay demonstrated that GADD45-induced cell cycle G(2)-M arrest correlates with GADD45-mediated growth suppression. These findings indicate that the cell cycle G(2)-M growth arrest mediated by GADD45 is one of the major mechanisms by which GADD45 suppresses cell growth.

Amino Acid Sequence↗
PubMed2000

Endothelial cell survival and apoptosis in the tumor vasculature.

Angiogenesis is essential for the growth and metastasis of solid tumors. The balance of endothelial cell (EC) proliferation and apoptosis is a major determinant in tumor angiogenesis. Recently, several studies demonstrated that numerous angiogenic factors not only induce angiogenesis but also function as EC survival factors. Vascular endothelial growth factor (VEGF), a potent angiogenic factor, is also an EC survival factor in embryonic vasculogenesis and tumor angiogenesis. VEGF activates specific intracellular survival pathways in ECs including Bcl-2, A1, IAP, Akt, and Erk. Integrins may function as EC survival factors by preventing anoikis by enhancing binding to the extracellular matrix. In addition, integrins may function in concert with VEGF to promote EC survival. Angiopoietin-1 (Ang-1) has recently been shown to stabilize EC networks by binding to the EC-specific tyrosine kinase receptor Tie-2. Pericytes also function as EC survival factors, by cell-cell contact, secretion of survival factors, or both. Targeting any of the above mechanisms for EC survival may provide novel antineoplastic strategies.

Angiopoietin-1↗
PubMed2000

Role of the tumor microenvironment in mediating response to anti-angiogenic therapy.

Despite the development of innovative anti-angiogenic strategies, early clinical trials have not replicated the results observed from preclinical models. One reason for this apparent discrepancy is the fact that tumor endothelium is phenotypically distinct from normal tissue endothelium. Moreover, it has recently become apparent that each individual tumor may display a different angiogenic phenotype. The expression of angiogenic factors in tumors is controlled by both intrinsic factors in the tumor cell and the influence of the host microenvironment. The diversity of angiogenic factor expression in tumors growing at different sites, combined with the fact that endothelial cells in different organs and tumors are phenotypically distinct, constitutes a formidable challenge for the development of effective anti-angiogenic regimens. This review provides an overview of how the microenvironment regulates tumor angiogenesis and affects the efficacy of anti-angiogenic therapy.

Angiogenesis Inhibitors↗
PubMed2000

Nup50, a nucleoplasmically oriented nucleoporin with a role in nuclear protein export.

We present here a detailed analysis of a rat polypeptide termed Nup50 (formerly NPAP60) that was previously found to be associated with the nuclear pore complex (F. Fan et al., Genomics 40:444-453, 1997). We have found that Nup50 (and/or a related 70-kDa polypeptide) is present in numerous rat cells and tissues. By immunofluorescence microscopy, Nup50 was found to be highly concentrated at the nuclear envelope of rat liver nuclei, whereas in cultured NRK cells it also is abundant in intranuclear regions. On the basis of immunogold electron microscopy of both rat liver nuclear envelopes and NRK cells, we determined that Nup50 is specifically localized in the nucleoplasmic fibrils of the pore complex. Microinjection of anti-Nup50 antibodies into the nucleus of NRK cells resulted in strong inhibition of nuclear export of a protein containing a leucine-rich nuclear export sequence, whereas nuclear import of a protein containing a classical nuclear localization sequence was unaffected. Correspondingly, CRM1, the export receptor for leucine-rich export sequences, directly bound to a fragment of Nup50 in vitro, whereas several other import and export receptors did not significantly interact with this fragment. Taken together, our data indicate that Nup50 has a direct role in nuclear protein export and probably serves as a binding site on the nuclear side of the pore complex for export receptor-cargo complexes.

Animals↗
PubMed1999

Probing the affinity and specificity of yeast alcohol dehydrogenase I for coenzymes.

Yeast (Saccharomyces cerevisiae) alcohol dehydrogenase I (SceADH) binds NAD+ and NADH less tightly and turns over substrates more rapidly than does horse (Equus caballus) liver alcohol dehydrogenase E isoenzyme (EcaADH), and neither enzyme uses NADP efficiently. Amino acid residues in the proposed adenylate binding pocket of SceADH were substituted in attempts to improve affinity for coenzymes or reactivity with NADP. Substitutions in SceADH (Gly202Ile or Ser246Ile) with the corresponding residues in the adenine binding site of the homologous EcaADH have modest effects on coenzyme binding and other kinetic constants, but the Ser246Ile substitution decreases turnover numbers by 350-fold. The Ser176Phe substitution (also near adenine site) significantly decreases affinity for coenzymes and turnover numbers. In the consensus nucleotide-binding betaalphabeta fold sequence, SceADH has two alanine residues (177-GAAGGLG-183) instead of the Leu200 in EcaADH (199-GLGGVG-204); the Ala178-Ala179 to Leu substitution significantly decreases affinity for coenzymes and turnover numbers. Some NADP-dependent enzymes have an Ala corresponding to Gly183 in SceADH; the Gly183Ala substitution significantly decreases affinity for coenzymes and turnover numbers. NADP-dependent enzymes usually have a neutral residue instead of the Asp (Asp201 in SceADH) that interacts with the hydroxyl groups of the adenosine ribose, along with a basic residue (at position 202 or 203) to stabilize the 2'-phosphate of NADP. The Gly203Arg change in SceADH does not significantly affect the kinetics. The Gly183Ala or Gly203Arg substitutions do not enable SceADH to use NADP+ as coenzyme. SceADH with the single Asp201Gly or double Asp201Gly:Gly203Arg substitutions have similar, low activity with NADP+. The results suggest that several of the amino acid residues participate in coenzyme binding and that conversion of specificity for coenzyme requires multiple substitutions.

Alcohol Dehydrogenase↗
PubMed1999

Polymorphisms in the human DNA repair gene XPF.

DNA sequence polymorphisms were sought in the coding region and at the exon-intron boundaries of the human XPF gene, which plays a role in nucleotide excision repair. Based on a survey of 38 individuals, we found six single nucleotide polymorphisms, one in the 5' non-coding region of the XPF gene, and five in the 2751 bp coding region. At each site, the frequency of the rarer allele varies from about 0.01 to over 0.38. Except for the 5' non-coding and one coding sequence polymorphism, the rarer alleles for the remaining four polymorphisms were found only in heterozygotes. Of the five polymorphisms in the coding region, one is silent, one results in a conserved amino acid difference, and the remaining three result in non-conserved amino acid differences. Because of its biological function in nucleotide excision repair, functionally significant XPF gene polymorphisms are candidates for influencing cancer susceptibility and overall genetic stability. Nucleotide sequence diversity estimates for XPF are similar to the lipoprotein lipase and beta-globin genes.

Alleles↗