Biomedical subjects

Yi Sun

Publications and source records attributed to Yi Sun.

At least 91 records · Page 5Linked to original sources

PubMed2003

Formation and chemical reactivities of a new type of double-butterfly [[Fe2(mu-CO)(CO)6]2(mu-SZS-mu)]2-: synthetic and structural studies on novel linear and macrocyclic butterfly Fe/E (E=S, Se) cluster complexes.

A new type of double-butterfly [[Fe(2)(mu-CO)(CO)(6)](2)(mu-SZS-mu)](2-) (3), a dianion that has two mu-CO ligands, has been synthesized from dithiol HSZSH (Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2)), [Fe(3)(CO)(12)], and Et(3)N in a molar ratio of 1:2:2 at room temperature. Interestingly, the in situ reactions of dianions 3 with various electrophiles affords a series of novel linear and macrocyclic butterfly Fe/E (E=S, Se) cluster complexes. For instance, while reactions of 3 with PhC(O)Cl and Ph(2)PCl give linear clusters [[Fe(2)(mu-PhCO)(CO)(6)](2)(mu-SZS-mu)] (4 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2)) and [[Fe(2)(mu-Ph(2)P)(CO)(6)](2)(mu-SZS-mu)] (5 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2)), reactions with CS(2) followed by treatment with monohalides RX or dihalides X-Y-X give both linear clusters [[Fe(2)(mu-RCS(2))(CO)(6)](2)(mu-SZS-mu)] (6 a-e: Z=CH(2)(CH(2)OCH(2))(1,2)CH(2); R=Me, PhCH(2), FeCp(CO)(2)) and macrocyclic clusters [[Fe(2)(CO)(6)](2)(mu-SZS-mu)(mu-CS(2)YCS(2)-mu)] (7 a-e: Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2); Y=(CH(2))(2-4), 1,3,5-Me(CH(2))(2)C(6)H(3), 1,4-(CH(2))(2)C(6)H(4)). In addition, reactions of dianions 3 with [Fe(2)(mu-S(2))(CO)(6)] followed by treatment with RX or X-Y-X give linear clusters [[[Fe(2)(CO)(6)](2)(mu-RS)(mu(4)-S)](2)(mu-SZS-mu)] (8 a-c: Z=CH(2)(CH(2)OCH(2))(1,2)CH(2); R=Me, PhCH(2)) and macrocyclic clusters [[[Fe(2)(CO)(6)](2)(mu(4)-S)](2)(mu-SYS-mu)(mu-SZS-mu)] (9 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2); Y=(CH(2))(4)), and reactions with SeCl(2) afford macrocycles [[Fe(2)(CO)(6)](2)(mu(4)-Se)(mu-SZS-mu)] (10 d: Z=CH(2)(CH(2)OCH(2))(3)CH(2)) and [[[Fe(2)(CO)(6)](2)(mu(4)-Se)](2)(mu-SZS-mu)(2)] (11 a-d: Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2)). Production pathways have been suggested; these involve initial nucleophilic attacks by the Fe-centered dianions 3 at the corresponding electrophiles. All the products are new and have been characterized by combustion analysis and spectroscopy, and by X-ray diffraction techniques for 6 c, 7 d, 9 b, 10 d, and 11 c in particular. X-ray diffraction analyses revealed that the double-butterfly cluster core Fe(4)S(2)Se in 10 d is severely distorted in comparison to that in 11 c. In view of the Z chains in 10 a-c being shorter than the chain in 10 d, the double cluster core Fe(4)S(2)Se in 10 a-c would be expected to be even more severely distorted, a possible reason for why 10 a-c could not be formed.

Journal Article↗

PubMed2003

Ability of Ixodes persulcatus, Haemaphysalis concinna and Dermacentor silvarum ticks to acquire and transstadially transmit Borrelia garinii.

In China, the ability of Ixodes persulcatus, Haemaphysalis concinna and Dermacentor silvarum to transmit Borrelia spirochetes was determined under laboratory conditions. Results showed that all three tick species can acquire spirochetes by feeding on infected mice. However, the capability of the three species to maintain spirochetes was different. Only I. persulcatus is able to maintain spirochetes alive during molting, and subsequent tick stages transmitted the infection to naive mice. In H. concinna and D. silvarum ticks, spirochetes could not survive after the digestion period of blood and after the molting process was finished, spirochetes were no longer detected. Contrary to H. concinna and D. silvarum, I. persulcatus should be considered the principal vector of Lyme disease in north China.

Animal Feed↗

PubMed2003

Ixodes sinensis: competence as a vector to transmit the Lyme disease spirochete Borrelia garinii.

In order to determine the principal vectors of Lyme disease in South China, the capability of Ixodes sinensis to transmit Lyme disease spirochetes transstadially was estimated in the laboratory. Results suggest that I. sinensis can acquire active Lyme disease spirochetes by feeding on infected mice of Kunming strains (KM), and the positive rates of larvae and nymph I. sinensis infected were 94.0% and 92.0%, respectively. I. sinensis maintained active spirochetes during blood digestion and molting periods; the subsequent questing tick stages were also found to be infected and infectious to naive KM mice, which resulted in more than 66.7% spirochete-positive KM mice. I. sinensis can transmit the Lyme disease spirochete Borrelia garinii from infected KM mice to naive KM mice during larvae-nymph and nymph-adult periods. Therefore, I. sinensis might be considered as a competent vector of Lyme disease in South China.

Animals↗

PubMed2003

AMPK-beta1 subunit is a p53-independent stress responsive protein that inhibits tumor cell growth upon forced expression.

In an effort to search for genes responsible for cell growth arrest and/or apoptosis associated with p53 signaling pathways, we profiled a human lung carcinoma line H1299, expressing a temperature-sensitive p53 (V138) against Affymetric human U95Av2 GeneChip A, consisting of 12 000 genes. 133 genes were identified that were either induced or repressed in response to p53-dependent cell growth arrest and apoptotic conditions. Among them, the beta1 subunit, but not other subunits of the AMP-activated protein kinase (AMPK) was strongly induced. The p53 consensus binding site search in the AMPK-beta1 promoter and the first intron identified four such putative sites. However, p53 failed to bind to any of these sites as assayed by in vitro gel retardation and in vivo chromatin immunoprecipitation. Furthermore, northern analysis showed that induction of this gene is independent of p53, as increased expression of the gene was observed in p53 null H1299/Neo control cells when the temperature was shifted to 32 degrees C. Moreover, a DNA damaging agent, etoposide, also induced beta1 subunit expression in multiple human tumor cells, regardless of p53 status. Thus, the beta1 subunit of AMPK is not a p53 downstream target gene, but can be induced by cold shock or the chemotherapeutic drug, etoposide in a p53-independent manner. To determine the biological significance of AMPK-beta1 induction, we over-expressed the gene in two tumor cell lines, H1299 and U2-OS. In both lines, forced AMPK-beta1 expression inhibits tumor cell growth, suggesting that AMPK-beta1 induction may facilitate stress-induced growth inhibition and cell killing.

AMP-Activated Protein Kinases↗

PubMed2003

Hepatocyte transformation and tumor development induced by hepatitis C virus NS3 c-terminal deleted protein.

AIM: To study the effect of hepatitis C virus nonstructural protein 3 c-terminal deleted protein (HCV NS3-5') on hepatocyte transformation and tumor development. METHODS: QSG7701 cells were transfected with plasmid pRcHCNS3-5' (expressing HCV NS3 c-terminal deleted protein) by lipofectamine and selected in G418. The expression of HCV NS3 gene and protein was determined by PCR and immunohistochemistry respectively. Biological behavior of transfected cells was observed through cell proliferation assay, anchorage-independent growth and tumor development in nude mice. The expression of HCV NS3 and c-myc proteins in the induced tumor was evaluated by immunohistochemistry. RESULTS: HCV NS3 was strongly expressed in QSG7701 cells transfected with plasmid pRcHCNS3-5' and the positive signal was located in cytoplasm. Cell proliferation assay showed that the population doubling time in pRcHCNS3-5' transfected cells was much shorter than that in pRcCMV and non-transfected cells (24 h, 26 h, 28 h respectively). The cloning ratio of cells transfected with pRcHCNS3-5', pRcCMV and non-transfected cells was 33 %, 1.46 %, 1.11 %, respectively, the former one was higher than that in the rest two groups (P<0.01). Tumor development was seen in nude mice inoculated with pRcHCNS3-5' transfected cells after 15 days. HE staining showed its feature of hepatocarcinoma, and immunohistochemistry confirmed the expressions of HCV NS3 and c-myc proteins in tumor tissue. The positive control group inoculated with HepG2 also showed tumor development, while no tumor developed in the nude mice injected with pRcCMV and non-transfected cells after 40 days. CONCLUSION: 1.HCV NS3 c-terminal deleted protein has transforming and oncogenic potential. 2. Human liver cell line QSG7701 may be used as a good model to study HCV NS3 pathogenesis.

Animals↗

PubMed2003

[Role of matrix metalloproteinases in the pathogenesis and therapy of leukemia].

The invasion and metastasis of malignant tumor cells are important factors causing the death of cancer patients. The proteolytic activity of proteinases to most of the extracellular matrix macromolecules is closely correlated with the invasion and metastasis of malignant tumor cells. Matrix metalloproteinases (MMP) are key proteinases involved in these processes. MMP is a type of Zn(2+)-depended proteinases. MMP2 and MMP9 are the unique types of proteinase that hydrolyze the bone structure of excellulary matrix (type IV collagen). So they are particularly correlated with leukemia cells infiltration and metastasis. This review aims to introduce the function of MMP and the regulation of matrix gene expression, as well as their roles in leukemia cell invasion and metastasis. A new strategy that MMP may be a therapeutic target in the treatment of leukemia is particularly introduced.

Antineoplastic Agents↗

PubMed2003

Job titles and work areas as surrogate indicators of occupational exposure.

BACKGROUND: Job titles or work areas are often used as surrogate indicators of exposure in occupational epidemiological studies. In this article, we assess the validity and comparability of commonly used surrogate indicators. METHODS: We analyzed lung cancer mortality among a hypothetical and an actual cohort of rubber workers. Surrogate indicators of exposure were defined according to jobs in which workers were "only," "ever," "longest" or "last" employed, or in which they were employed at the "census" of the study. Occupational risks were estimated using standardized mortality ratios. Validity of surrogate indicators was assessed in the simulated data by comparison between estimated effects and the known underlying associations. Comparisons of surrogate indicators were conducted in both simulated and empirical data. RESULTS: Use of the definition "only" as the surrogate indicator gave valid but imprecise results. For all other definitions, we observed a moderate overestimation of risks in no-risk or low-risk jobs and attenuation of underlying dose-response relationships, without substantial differences among the applied definitions. CONCLUSIONS: Our results demonstrate a limitation of using surrogate indicators of exposure in occupational epidemiological studies. However, they suggest that the inconsistencies of published study findings in the rubber industry are unlikely to be attributable to the use of different surrogate indicators.

Cohort Studies↗

PubMed2003

[Hepatocyte transformation and tumor development induced by hepatitis C virus NS3 N-terminal protein].

OBJECTIVE: To study the effect of hepatitis C virus nonstructural protein 3 N-terminal protein (HCV NS3-5') on hepatocyte transformation and tumor development. METHODS: QSG7701 cells were transfected with plasmid pRcHCNS3-5' (expressing HCV NS3 N-terminal protein) by lipofectamine and selected in G418. The expression of HCV NS3 gene and protein was determined by PCR and immunohistochemistry respectively. Biological effect of transfected cells was observed through cell proliferation assay, anchor independent growth, and tumor development in nude mice. The expression of HCV NS3 and c-myc protein in the induced tumor was evaluated by immunohistochemistry. RESULTS: HCV NS3 was strongly expressed in QSG7701 cells transfected with plasmid pRcHCNS3-5' and the positive signal was located in cytoplasm. The HCV NS3 expression and c-myc protein in the induced cytoplasm. Cell proliferation assay showed that the population doubling time in the pRcHCNS3-5' transfected cells was much shorter than that in the pRcCMV and non-transfected cells (24 h, 26 h, 28 h respectively). The cloning efficiencies of transfected cells with pRcHCNS3-5', pRcCMV and non-transfected cells were 33.0%, 1.5%, 1.1% respectively (P < 0.01). Tumor developed in nude mice inoculated with pRcHCNS3-5'transfected cells 15 days after the inoculation. HE staining showed hepatocarcinoma character and immunohistochemistry confirmed HCV NS3 and c-myc expression in the tumor tissue. The positive control group also showed tumor development, while no tumor mass obtained in the nude mice inoculated with pRcCMV and non-transfected cells even 40 days after the injection. CONCLUSION: HCV NS3 N-terminal protein showed cell transformation and tumorigenic features.

Animals↗

PubMed2003

[Determination of adenosine, rutin and quercetin in Carthamus tinctorius by HPCE].

AIM: To develop a method for determination of adenosine, rutin and quercetin in Carthamus tinctorius L. by high performance capillary electrophoresis(HPCE). METHODS: A fused silica capillary (66.5 cm x 50 microns ID, an effective length of 58 cm) was used. The running buffer composed of 50 mmol.L-1 borax (pH 9.7) containing 18% methanol. The applied voltage was 24 kV and the capillary temperature was 20 degrees C. The detection wavelength was 210 nm. Rifampicin was used as internal standard. RESULTS: A good linearity between peak area ratio of the common peak to the internal standard and the concentration was found in the range of 10-160 mg.L-1 for adenosine, 100-2,000 mg.L-1 for rutin and 100-1,600 mg.L-1 for quercetin (r > 0.998). The average recoveries were 98.5%-100.5%, 96.9%-99.5% and 99.1%-99.5% for adenosine, rutin and quercetin, respectively. The relative standard deviation was less than 6.5% (n = 5). CONCLUSION: The method is simple, rapid and with satisfactory recoveries and good reproducibilities. It can be used to control the quality of Carthamus tinctorius.

Adenosine↗

PubMed2003

Certainties and uncertainties of land cover statistics in China.

Vegetation or land cover maps have been made directly or indirectly available for the entire territory of China. The certainties and uncertainties of land cover statistics were analyzed by comparing three data sources: China's Vegetation Map, IGPB DISCover, and University of Maryland Product. Great similarities in the statistics of 7 aggregated land cover types were found among the three data sources,particularly between the two global land cover maps. The per-pixel agreement between any 2 of 3 maps was between 38.0%-51.4%; the per-pixel agreement among all three maps was only 27.1%. Certainties were found in regions where vegetation types are typical and human land use practice is relatively homogenous; the uncertainties occurred to either vegetation transition zones or regions where land cover types and land use practice are relatively diversified. Systematic and multidisciplinary efforts are necessary to promote accurate mapping of nationwide land cover types in China. Intensive efforts should be made in regions where uncertainties of land cover information are found.

China↗

PubMed2002

Mutations in Rab3a alter circadian period and homeostatic response to sleep loss in the mouse.

Rab3a is the most abundant Rab (ras-associated binding) protein in the brain and has a regulatory role in synaptic vesicle trafficking. Mice with a targeted loss-of-function mutation in Rab3a have defects in Ca(2+)-dependent synaptic transmission: the number of vesicles released in response to an action potential is greater than in wildtype mice, resulting in greater synaptic depression and the abolishment of CA3 mossy-fiber long term potentiation. The effect of these changes on behavior is unknown. In a screen for mouse mutants with abnormal rest-activity and sleep patterns, we identified a semidominant mutation, called earlybird, that shortens the circadian period of locomotor activity. Sequence analysis of Rab3a identified a point mutation in the conserved amino acid (Asp77Gly) within the GTP-binding domain of this protein in earlybird mutants, resulting in significantly reduced levels of Rab3a protein. Phenotypic assessment of earlybird mice and a null allele of Rab3a revealed anomalies in circadian period and sleep homeostasis, providing evidence that Rab3a-mediated synaptic transmission is involved in these behaviors.

Alleles↗

PubMed2002

MADM, a novel adaptor protein that mediates phosphorylation of the 14-3-3 binding site of myeloid leukemia factor 1.

A yeast two-hybrid screen was conducted to identify binding partners of Mlf1, an oncoprotein recently identified in a translocation with nucleophosmin that causes acute myeloid leukemia. Two proteins isolated in this screen were 14-3-3zeta and a novel adaptor, Madm. Mlf1 contains a classic RSXSXP sequence for 14-3-3 binding and is associated with 14-3-3zeta via this phosphorylated motif. Madm co-immunoprecipitated with Mlf1 and co-localized in the cytoplasm. In addition, Madm recruited a serine kinase, which phosphorylated both Madm and Mlf1 including the RSXSXP motif. In contrast to wild-type Mlf1, the oncogenic fusion protein nucleophosmin (NPM)-MLF1 did not bind 14-3-3zeta, had altered Madm binding, and localized exclusively in the nucleus. Ectopic expression of Madm in M1 myeloid cells suppressed cytokine-induced differentiation unlike Mlf1, which promotes maturation. Because the Mlf1 binding region of Madm and its own dimerization domain overlapped, the levels of Madm and Mlf1 may affect complex formation and regulate differentiation. In summary, this study has identified two partner proteins of Mlf1 that may influence its subcellular localization and biological function.

14-3-3 Proteins↗

PubMed2002

The effect of gp130 stimulation on glutamate-induced excitotoxicity in primary hippocampal neurons.

Primary hippocampal neurons from newborn rats treated with glutamate showed clear excitotoxicity. This excitotoxicity could be reversed by treatment of the cells with cytokines of the interleukin-6 family. Stimulation of gp130 on hippocampal neurons resulted in tyrosine phosphorylation of STAT3 and activation of p42 and p44 MAP kinases. Receptors for the interleukin-6 type cytokines are active in membrane bound and soluble form. To address the question whether the neurotrophic effect of interleukin-6 type cytokines requires soluble cytokine receptors we used fusion proteins of interleukin-6 coupled to the soluble interleukin-6 receptor and ciliary neurotrophic factor coupled to the soluble ciliary neurotrophic factor receptor. Ciliary neurotrophic factor was as active as the cytokine-receptor fusion protein, indicating that hippocampal neurons express ciliary neurotrophic factor receptor on the cell surface. In contrast, interleukin-6 was only active at very high concentrations whereas the fusion protein of interleukin-6 coupled to the soluble interleukin-6 receptor (Hyper-IL-6) exhibited high neurotrophic activity at the same concentrations as ciliary neurotrophic factor. These data indicate that interleukin-6 receptor expression is very low on hippocampal neurons and that gp130 stimulation can be used to rescue hippocampal neurons from excitotoxicity.

Animals↗

PubMed2002

Histone deacetylase 5 is not a p53 target gene, but its overexpression inhibits tumor cell growth and induces apoptosis.

p53 tumor suppressor is activated by phosphorylation and acetylation on DNA damage. One of unknown p53 early transcripts was identified to be histone deacetylase-5 (HDAC5). We tested a hypothesis that HDAC5 is a p53 down-stream target gene that on induction by p53 inactivates p53 by removal of acetyl group in p53 molecule, thus functioning as an auto-regulatory negative feedback loop in analogue to p53-murine double minute 2 interaction. Six p53 binding consensus sites were identified in the promoter of HDAC5. p53 binds to one of the sites weakly. However, luciferase constructs driven by the HDAC5 promoter containing three to six potential binding sites were not activated by p53, nor was the expression of HDAC5 mRNA induced by p53-activating agents. Furthermore, HDAC5 does not bind to p53 nor reduces etoposide-induced p53 acetylation. Thus, HDAC5 is not a p53 target gene and may act in a p53-independent manner. We next studied the effect of HDAC5 on tumor cell growth and apoptosis. Transfection of HDAC5 inhibited growth of multiple tumor cell lines including U2OS osteogenic sarcoma cells, SY5Y neuroblastoma cells, and MCF breast carcinoma cells. The growth suppression seen in HDAC5-overexpressing cells appears to be attributable partly to a reduced growth rate as revealed by cell growth assay using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and mainly to spontaneous apoptosis as shown by DNA fragmentation ELISA and morphological appearance. Mechanistically, repression of three cell proliferation genes in mitogen-activated protein kinase pathway and induction of seven apoptosis-related genes were identified by microarray profiling in HDAC5-overexpressed cells. Among induced genes, four (TNFR1, TNFSF7, caspase-8, and DAPK1) were associated with the tumor necrosis factor ligand-receptor death pathway. Induction of TNFR1, TNFSF7, and caspase-8 were confirmed by Northern and Western analyses. Thus, activation of tumor necrosis factor death receptor pathway appears to be associated with HDAC5-induced spontaneous apoptosis.

Apoptosis↗

PubMed2002

Autocrine human growth hormone inhibits placental transforming growth factor-beta gene transcription to prevent apoptosis and allow cell cycle progression of human mammary carcinoma cells.

Multiple cellular effects of human growth hormone (hGH) are mediated by an indirect mechanism requiring transcriptional activation of genes encoding protein effector molecules such as insulin-like growth factor-1. Such protein effector molecules then act directly to mediate the cellular functions of hGH. We report here that autocrine hGH production by mammary carcinoma cells specifically results in the transcriptional repression of the p53-regulated placental transforming growth factor-beta (PTGF-beta) gene. Transcriptional repression of the PTGF-beta gene does not require the p53-binding sites in the PTGF-beta promoter, and autocrine hGH also desensitized the response of the PTGF-beta promoter to p53 overexpression. Transcriptional repression of the PTGF-beta gene is accompanied by consequent decreases in its protein product, Smad-mediated transcription, and its cellular effects that include cell cycle arrest and apoptosis. PTGF-beta specifically inhibited the autocrine hGH-stimulated expression of cyclin D1 required for autocrine hGH-stimulated mammary carcinoma cell cycle progression. Thus, one mechanism by which autocrine hGH promotes an increase in mammary carcinoma cell number is by transcriptional repression of protein effector molecules that promote cell cycle arrest and apoptosis. Such transcriptional repression of negative regulatory factors, such as PTGF-beta, may also be requisite for direct stimulation of mammary carcinoma cell mitogenesis by hGH.

Apoptosis↗

PubMed2002

Combinatorial interactions of p53, activating protein-2, and YB-1 with a single enhancer element regulate gelatinase A expression in neoplastic cells.

Gelatinase A, also denoted matrix metalloproteinase 2, plays multiple critical roles in the neoplastic process, including facilitation of neoangiogenesis and formation of distal metastases. The transcriptional regulation of the gelatinase A gene is under the control of strong, evolutionarily conserved cis-acting enhancer elements, designated the r2 (human) or RE-1 (rat), that harbor contiguous binding motifs for the transcription factors activating protein-2 (AP2), p53, and YB-1. Using recombinant transcription factors, complex patterns of RE-1 binding were observed by electrophoretic mobility shift assay. Increased complex formation was detected with the AP2/YB-1 and AP2/p53 combinations, while YB-1 competed with p53 for binding. The combination of AP2, p53, and YB-1 yielded novel ternary complexes, particularly when binding to single-stranded RE-1 probes. Transient transfection of hepatocellular carcinoma cell lines with a series of gelatinase A luciferase reporter constructs were in accordance with the binding patterns determined by electrophoretic mobility shift assay. Combined AP2 and p53 increased gelatinase A luciferase reporter activity significantly, and the inclusion of YB-1 yielded further increase in both reporter activity and secreted levels of gelatinase A protein. YB-1 and p53 expression are increased following multiple genotoxic stresses, including irradiation, and the synergistic interactions of these induced transcription factors with the widely expressed AP2 protein provide a probable pathophysiologic mechanism for the enhanced tumor cell synthesis of gelatinase A induced by radiation.

Animals↗

PubMed2002

Wild-type TP53 inhibits G(2)-phase checkpoint abrogation and radiosensitization induced by PD0166285, a WEE1 kinase inhibitor.

The WEE1 protein kinase carries out the inhibitory phosphorylation of CDC2 on tyrosine 15 (Tyr15), which is required for activation of the G(2)-phase checkpoint in response to DNA damage. PD0166285 is a newly identified WEE1 inhibitor and is a potential selective G(2)-phase checkpoint abrogator. To determine the role of TP53 in PD0166285-induced G(2)-phase checkpoint abrogation, human H1299 lung carcinoma cells expressing a temperature-sensitive TP53 were used. Upon exposure to gamma radiation, cells cultured under nonpermissive conditions (TP53 mutant conformation) underwent G(2)-phase arrest. However, under permissive conditions (TP53 wild-type conformation), PD0166285 greatly inhibited the accumulation of cells in G(2) phase. This abrogation was accompanied by a nearly complete blockage of Tyr15 phosphorylation of CDC2, an increased activity of CDC2 kinase, and an enhanced sensitivity to radiation. However, under permissive conditions (TP53 wild-type conformation), PD0166285 neither disrupted the G(2)-phase arrest nor increased cell death. The compound inhibited Tyr15 phosphorylation only partially and did not activate CDC2 kinase activity. To understand the potential mechanism(s) by which TP53 inhibits PD0166285-induced G(2)-phase checkpoint abrogation, two TP53 target proteins, 14-3-3rho and CDKN1A (also known as p21), that are known to be involved in G(2)-phase checkpoint control in other cell models were examined. It was found that 14-3-3rho was not expressed in H1299 cells, and that although CDKN1A did associate with CDC2 to form a complex, the level of CDKN1A associated with CDC2 was not increased in response to radiation or to PD0166285. The level of cyclin B1, required for CDC2 activity, was decreased in the presence of functional TP53. Thus inhibition of PD0166285-induced G(2)-phase checkpoint abrogation by TP53 was achieved at least in part through partial blockage of CDC2 dephosphorylation of Tyr15 and inhibition of cyclin B1 expression.

Cell Cycle Proteins↗

PubMed2002

Insulin-like growth factor receptor-1 as an anti-cancer target: blocking transformation and inducing apoptosis.

IGF-IR (Insulin-like growth factor receptor 1) is a tetrameric glycoprotein composed of two alpha and two beta subunits. The alpha subunit localizes extra-cellularly for ligand binding, whereas the beta subunit consists of transmembrane chains and a cytoplasmic tyrosine kinase domain for enzymatic activity. IGF-IR ligands, IGF-I and IGF-II, are mitogens and survival factors for many cancer cells. Binding of ligands to the IGF-IR initiates a cascade of events leading to activation of signal transduction pathways, mainly MAPK and PI-3K pathways, to stimulate proliferation/mitogenesis, to induce neoplastic transformation, to inhibit apoptosis, and to promote angiogenesis and metastasis. It has been shown that the presence of IGF-IR was required for transformation induced by many oncogenes and over-expression or constitutive activation of IGF-IR gave rise to transformed phenotypes. Significantly, over-expression of IGF-IR was observed in multiple human cancers including carcinomas of breast, lung, colon, and prostate. Patients with IGF-IR positive cancers had a worse prognosis in some cases. Furthermore, down-regulation or functional inactivation of IGF-IR sensitized tumor cells to apoptosis and reversed tumor cell phenotype. Thus, IGF-IR appears to be a promising cancer target. Indeed, a variety of approaches aimed at targeting IGF-IR have been utilized to prove the concept, or are being developed for potential anticancer therapies. These include targeting functional IGF-IR on cell surface, targeting ligand/receptor interaction, targeting receptor expression and functions, and targeting receptor kinase activity. Cancer patients could eventually benefit from the development of these specific IGF-IR antagonists.

Animals↗