Biomedical subjects

Wei-Min Tong

Publications and source records attributed to Wei-Min Tong.

15 recordsLinked to original sources

PubMed2006

PARP1 Val762Ala polymorphism reduces enzymatic activity.

Poly(ADP-ribose) polymerase 1 (PARP1) modifies a variety of nuclear proteins by poly(ADP-ribosyl)ation, and plays diverse roles in molecular and cellular processes. A common PARP1 single nucleotide polymorphism (SNP) at codon 762, resulting in the substitution of alanine (Ala) for valine (Val) in the catalytic domain has been implicated in susceptibility to cancer. To characterize the functional effect of this polymorphism on PARP1, we performed in vitro enzymatic analysis on PARP1-Ala762 and PARP1-Val762. We found that PARP1-Ala762 displayed 57.2% of the activity of PARP1-Val762 for auto-poly(ADP-ribosyl)ation and 61.9% of the activity of PARP1-Val762 for trans-poly(ADP-ribosyl)ation of histone H1. The kinetic characterization revealed that the K(m) of PARP1-Ala762 was increased to a 1.2-fold of the K(m) of PARP1-Val762 for trans-poly(ADP-ribosyl)ation. Thus, the PARP1 Val762Ala polymorphism reduces the enzymatic activity of PARP1 by increasing K(m). This finding suggests that different levels of poly(ADP-ribosyl)ation by PARP1 might aid in understanding the cancer risk of carriers of the PARP1 Val762Ala polymorphism.

Animals↗

PubMed2006

Aflatoxin-B exposure does not lead to p53 mutations but results in enhanced liver cancer of Hupki (human p53 knock-in) mice.

Hepatocellular carcinoma (HCC) is a common human malignancy that is often associated with risk factors such as aflatoxin-B1 (AFB1) exposure and Hepatitis-B virus infection in developing countries. There is a strong correlation between these risk factors and mutation of the tumor-suppressor gene p53 at codon 249. In vitro experiments have also shown that treatment of human liver cells with AFB1 results in p53 mutations. A tumor-promoting role for mutant p53 was demonstrated using transgenic mice models, in which HCC development was accelerated upon AFB1-exposure. However, wild-type mice in which AFB1 alone was used to induce liver cancers have failed to recapitulate p53 mutations, raising the possibility that mouse DNA context may not be appropriate for the generation of AFB1-induced p53 mutations. We have now tested this hypothesis using the Hupki mice (human p53 knock-in) in which the mouse DNA-binding domain has been replaced by the homologous human p53 segment. Mice were followed for 80 weeks after AFB1 injection for survival and HCC formation. Hupki mice were found to be more susceptible to AFB1 than wild-type mice. Moreover, only 19% of wild-type mice developed HCCs compared to 44% in Hupki mice. However, none of the liver tumors and normal tissues from Hupki mice contained any mutations in the DNA-binding domain of p53. These findings suggest that the human DNA context of the p53 gene alone may not be the sole determinant of AFB1-induced mutagenesis. Furthermore, humanized p53 appears not to be as effective as murine p53 in the mouse cellular environment in preventing malignant transformation.

Aflatoxin B1↗

PubMed2006

A novel function of DNA repair molecule Nbs1 in terminal differentiation of the lens fibre cells and cataractogenesis.

The Nbs1 protein, hypomorphic mutant in Nijmegen breakage syndrome (NBS), is a component of the Mre11/Rad50/Nbs1 (M/R/N) complex that acts as a DNA double-strand break sensor and functions in cell cycle checkpoint in response to DNA damage and DNA repair. Here we report that targeted disruption of murine NBS1 gene (Nbn) in the lens alters the M/R/N complex nuclear localization and results in microphthalmia in mice due to reduced proliferation of the lens epithelial cells. Unexpectedly, all Nbn-deficient lenses develop cataracts at an early age due to altered lens fibre cell differentiation, including disruption of normal lens epithelial and fibre cell architecture and incomplete denucleation of fibre cells, and these changes are independent of the p53 pathway. In addition, Nbn-deficient lenses show dysregulated transcription of various crystallins. Thus, this study implicates a novel function of Nbs1 in terminal differentiation of the lens fibre cells and in cataractogenesis.

Animals↗

PubMed2005

An essential function for NBS1 in the prevention of ataxia and cerebellar defects.

Nijmegen breakage syndrome (NBS), ataxia telangiectasia and ataxia telangiectasia-like disorder (ATLD) show overlapping phenotypes such as growth retardation, microcephaly, cerebellar developmental defects and ataxia. However, the molecular pathogenesis of these neurological defects remains elusive. Here we show that inactivation of the Nbn gene (also known as Nbs1) in mouse neural tissues results in a combination of the neurological anomalies characteristic of NBS, ataxia telangiectasia and ATLD, including microcephaly, growth retardation, cerebellar defects and ataxia. Loss of Nbn causes proliferation arrest of granule cell progenitors and apoptosis of postmitotic neurons in the cerebellum. Furthermore, Nbn-deficient neuroprogenitors show proliferation defects (but not increased apoptosis) and contain more chromosomal breaks, which are accompanied by ataxia telangiectasia mutated protein (ATM)-mediated p53 activation. Notably, depletion of p53 substantially rescues the neurological defects of Nbn mutant mice. This study gives insight into the physiological function of NBS1 (the Nbn gene product) and the function of the DNA damage response in the neurological anomalies of NBS, ataxia telangiectasia and ATLD.

ATP-Binding Cassette Transporters↗

PubMed2005

Skin hyperproliferation and susceptibility to chemical carcinogenesis in transgenic mice expressing E6 and E7 of human papillomavirus type 38.

The oncoproteins E6 and E7 of human papillomavirus type 38 (HPV38) display several transforming activities in vitro, including immortalization of primary human keratinocytes. To evaluate the oncogenic activities of the viral proteins in an in vivo model, we generated transgenic mice expressing HPV38 E6 and E7 under the control of the bovine homologue of the human keratin 10 (K10) promoter. Two distinct lines of HPV38 E6/E7-expressing transgenic mice that express the viral genes at different levels were obtained. In both lines, HPV38 E6 and E7 induced cellular proliferation, hyperplasia, and dysplasia in the epidermis. The rate of occurrence of these events was proportional to the levels of HPV38 E6 and E7 expression in the two transgenic lines. Exposure of the epidermis of nontransgenic mice to UV led to p21WAF1 accumulation and cell cycle arrest. In contrast, keratinocytes from transgenic mice continued to proliferate and were not positive for p21WAF1, indicating that cell cycle checkpoints are altered in keratinocytes expressing the viral genes. Although the HPV38 E6/E7-expressing transgenic mice did not develop spontaneous tumors during their life span, two-stage carcinogen treatment led to a high incidence of papillomas, keratoacanthomas, and squamous-cell carcinomas in HPV38 mice compared with nontransgenic animals. Together, these data show that HPV38 E6 and E7 display transforming properties in vivo, providing further support for the role of HPV38 in carcinogenesis.

Animals↗

PubMed2004

Poly(ADP-ribose) polymerase-1, a novel partner of progesterone receptors in endometrial cancer and its precursors.

Endometrial carcinomas are the most common malignancy of the female genital tract. Although the downregulation of the progesterone receptor (PR) in the progression of endometrioid carcinomas (ECs) has been well documented, the mechanism of PR alteration in endometrioid carcinogenesis is poorly understood. Recently, biochemical studies have shown that the DNA strand break-sensing molecule poly(ADP-ribose) polymerase (PARP-1) was associated with the DNA binding domain of PR. In our present study, we show that in normal endometrial epithelium, the expression level of PARP-1 protein is high in the proliferative phase but markedly decreases during the secretory phase. Interestingly, PARP-1 expression gradually increases in nonatypical and atypical endometrial hyperplasia, reaching its highest level in grade I, and decreases significantly toward grade III ECs. Notably, PARP-1 and PR expressions, in each stage, are positively correlated (p < 0.0001), with the exception of nonendometrioid carcinomas. Thus, these data suggest that PARP-1 is substantially involved in the regulation of progesterone action in the development of ECs.

Adenocarcinoma, Clear Cell↗

PubMed2004

Depletion of the 110-kilodalton isoform of poly(ADP-ribose) glycohydrolase increases sensitivity to genotoxic and endotoxic stress in mice.

Poly(ADP-ribosylation) is rapidly stimulated in cells following DNA damage. This posttranslational modification is regulated by the synthesizing enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the degrading enzyme poly(ADP-ribose) glycohydrolase (PARG). Although the role of PARP-1 in response to DNA damage has been studied extensively, the function of PARG and the impact of poly(ADP-ribose) homeostasis in various cellular processes are largely unknown. Here we show that by gene targeting in embryonic stem cells and mice, we specifically deleted the 110-kDa PARG protein (PARG(110)) normally found in the nucleus and that depletion of PARG(110) severely compromised the automodification of PARP-1 in vivo. PARG(110)-deficient mice were viable and fertile, but these mice were hypersensitive to alkylating agents and ionizing radiation. In addition, these mice were susceptible to streptozotocin-induced diabetes and endotoxic shock. These data indicate that PARG(110) plays an important role in DNA damage responses and in pathological processes.

Alkylating Agents↗

PubMed2003

Nbn heterozygosity renders mice susceptible to tumor formation and ionizing radiation-induced tumorigenesis.

Nijmegen Breakage Syndrome (NBS) is a rare autosomal recessive disease characterized by microcephaly, growth retardation, immunodeficiency, chromosomal instability, and predisposition to cancer. Heterozygous NBS patients show increased chromosomal instability and are suspected to be at a high risk for cancer. To study the impact of NBS1 heterozygosity on malignancy susceptibility, we disrupted the murine homologue (Nbn) of NBS1 in mice using gene targeting techniques. While null mutation in the Nbn gene resulted in embryonic lethality at the blastocyst stage because of growth retardation and increased apoptosis, heterozygous knockout (Nbn(+/-)) mice developed a wide array of tumors affecting the liver, mammary gland, prostate, and lung, in addition to lymphomas. Moreover, gamma-irradiation enhanced tumor development in Nbn(+/-) mice, giving rise to a high frequency of epithelial tumors, mostly in the thyroid and lung, as well as lymphomas. These mice also developed numerous tumors in the ovary and testis. Southern and Western blot analyses showed a remaining wild-type allele and nibrin expression in Nbn(+/-) tumors. Sequencing analysis confirmed no mutation in the Nbn cDNA derived from these tumors. Cytogenetic analysis revealed that primary Nbn(+/-) embryonic fibroblasts and tumor cells exhibit increased chromosomal aberrations. These data suggest that haploinsufficiency, not loss of heterozygosity, of Nbn could be the mechanism underlying the tumor development. Taken together, our heterozygous Nbn-knockout mice represent a novel model to study the consequences of NBS1 heterozygosity on tumor development.

Animals↗

PubMed2003

Pancreatic beta-cell-specific ablation of the multiple endocrine neoplasia type 1 (MEN1) gene causes full penetrance of insulinoma development in mice.

The function of the predisposition gene to multiple endocrine neoplasia type 1 (MEN1) syndrome remains largely unknown. Previous studies demonstrated that null mutation of the Men1 gene caused mid-gestation lethality in mice, whereas heterozygous Men1 knockout mice developed multiple endocrine tumors late in life. To seek direct evidence on the causal role of menin in suppressing tumor development, we generated mice in which the Men1 gene was disrupted specifically in pancreatic beta cells. These mice began to develop hyperplastic islets at as early as 2 months of age and insulinomas at 6 months of age. The islet lesions exhibited features of multistage tumor progression, including beta-cell dedifferentiation, angiogenesis, and altered expression of both E-cadherin and beta-catenin. Additionally, disturbance of blood insulin and glucose levels correlated with tumor development, mimicking human MEN1 symptoms. Our data indicate that this strain of mice provides a powerful tool for the study of the mechanisms of tumorigenesis related to MEN1 disease.

Animals↗

PubMed2003

Heterozygous Men1 mutant mice develop a range of endocrine tumors mimicking multiple endocrine neoplasia type 1.

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary syndrome characterized by the occurrence of multiple endocrine tumors of the parathyroid, pancreas, and anterior pituitary in patients. To study tumorigenesis related to the MEN1 syndrome, we have generated Men1 knockout mice using the gene targeting approach. Heterozygous Men1 mutant mice developed the same range of major endocrine tumors as is seen in MEN1 patients, affecting the parathyroid, pancreatic islets, pituitary and adrenal glands, as well as the thyroid, and exhibiting multistage tumor progression with metastatic potential. In particular, extrapancreatic gastrinoma, pancreatic glucagonoma, and mixed hormone-producing tumors in islets were observed. In addition, there was a high incidence of gonadal tumors of endocrine origin, i.e. Leydig cell tumors, and ovary sex-cord stromal cell tumors in heterozygous Men1 mutant mice. Hormonal disturbance, such as abnormal PTH and insulin levels, was also observed in these mice. These tumors were associated with loss of heterozygosity of the wild-type Men1 allele, suggesting that menin is involved in suppressing the development of these endocrine tumors. All of these features are reminiscent of MEN1 symptoms in humans and establish heterozygous Men1 mutant mice as a suitable model for this disease.

Animals↗

PubMed2003

Mice deficient in the X-linked lymphoproliferative disease gene sap exhibit increased susceptibility to murine gammaherpesvirus-68 and hypo-gammaglobulinemia.

X-linked lymphoproliferative disease is characterized by immune dysregulation and uncontrolled lymphoproliferation on exposure to Epstein-Barr virus (EBV). This disease has been attributed to mutations in the SAP gene (also denominated as SH2D1A or DSHP). To delineate the role of SAP in the pathophysiology of X-linked lymphoproliferative disease, a strain of sap-deficient mice has been generated by deleting exon 2 of the gene. After infection with murine gammaherpesvirus-68, which is homologous to EBV, the mutant mice exhibit more vigorous CD8+ T cell proliferation and more disseminated lymphocyte infiltration compared to their wild-type littermates. Chronic tissue damage and hemophagocytosis were evident in sap-deficient mice but not in their wild-type littermates. Concordantly, murine gammaherpesvirus-68 reactivation was observed in sap-deficient mice, indicating an impaired control of the virus. Notably, IgE deficiency and decreased serum IgG level were observed in mutant mice prior to and after murine gammaherpesvirus-68 infection, which reproduces hypo-gammaglobulinemia in X-linked lymphoproliferative disease patients. This mouse model will therefore be a useful tool for dissecting the various phenotypes of X-linked lymphoproliferative disease.

Agammaglobulinemia↗

PubMed2003

Null mutation of DNA strand break-binding molecule poly(ADP-ribose) polymerase causes medulloblastomas in p53(-/-) mice.

Medulloblastoma is an invasive embryonal tumor of the cerebellum with predominant neuronal differentiation. Although several genes have been implicated in medulloblasoma formation, such as Patched (Ptc1) and the adenomatous polyposis coli gene (Apc), the majority of these tumors cannot be explained by mutations in these genes. The cellular origin as well as the genetic and molecular changes involved in the genesis and progression of human medulloblastomas remain largely unknown. Here we show that disruption of poly(ADP-ribose) polymerase (PARP-1) causes a high incidence (49%) of aggressive brain tumors in p53 null mice, with typical features of human cerebellar medulloblastomas. At as early as 8 weeks of age, lesions started on the outer surface of the cerebellum from remnant granule cell precursors of the developmental external germinal layer. Progression of these tumors is associated with the re-activation of the neuronal specific transcription factor Math1, dysregulation of Shh/Ptc1 signaling pathway, and chromosomal aberrations, including triradial and quadriradial chromosomes. The present study indicates that the loss of function of DNA double-strand break-sensing and repair molecules is an etiological factor in the evolution of the cerebellar medulloblastomas. These PARP-1/p53 double null mice represent a novel model for the pathogenesis of human medulloblastomas.

Animals↗

PubMed2003

Involvement of poly(ADP-Ribose) polymerase 1 and poly(ADP-Ribosyl)ation in regulation of centrosome function.

The regulatory mechanism of centrosome function is crucial to the accurate transmission of chromosomes to the daughter cells in mitosis. Recent findings on the posttranslational modifications of many centrosomal proteins led us to speculate that these modifications might be involved in centrosome behavior. Poly(ADP-ribose) polymerase 1 (PARP-1) catalyzes poly(ADP-ribosyl)ation to various proteins. We show here that PARP-1 localizes to centrosomes and catalyzes poly(ADP-ribosyl)ation of centrosomal proteins. Moreover, centrosome hyperamplification is frequently observed with PARP inhibitor, as well as in PARP-1-null cells. Thus, it is possible that chromosomal instability known in PARP-1-null cells can be attributed to the centrosomal dysfunction. P53 tumor suppressor protein has been also shown to be localized at centrosomes and to be involved in the regulation of centrosome duplication and monitoring of the chromosomal stability. We found that centrosomal p53 is poly(ADP-ribosyl)ated in vivo and centrosomal PARP-1 directly catalyzes poly(ADP-ribosyl)ation of p53 in vitro. These results indicate that PARP-1 and PARP-1-mediated poly(ADP-ribosyl)ation of centrosomal proteins are involved in the regulation of centrosome function.

Aneuploidy↗

PubMed2002

Synergistic role of Ku80 and poly(ADP-ribose) polymerase in suppressing chromosomal aberrations and liver cancer formation.

Liver cancer is one of the major human tumors in the world. Basic and epidemiological studies have proposed that the major risk factors for liver cancer include alcohol and diet as well as infection with hepatitis B and C viruses. However, the mechanistic clues for the development of this type of cancer is largely unknown. Poly(ADP-ribose) polymerase (PARP-1) and a component of nonhomologous end-joining (NHEJ) machinery, Ku80, are two major DNA end-binding molecules that play a multifunctional role in DNA damage signaling and repair, recombination as well as the maintenance of genomic stability. Here we show that the interaction of PARP-1 and Ku80 is essential for development because PARP-1/Ku80 double null mice died at embryonic day (E) 9.5. Interestingly, haplo-insufficiency of Ku80 in PARP-1-/- mice promotes the development of hepatocellular adenoma and hepatocellular carcinoma (HCC). These tumors exhibited a multistage tumor progression associated with the loss of E-cadherin expression and the mutation of beta-catenin. Cytogenetic analysis revealed that Ku80 heterozygosity elevated chromosomal instability in PARP-1-/- cells and that these liver tumors harbored a high degree of chromosomal aberrations including fragmentations, end-to-end fusions, and recurrent nonreciprocal translocations (NRT). These features are reminiscent of human HCC. Taken together, these data implicate a synergistic function of Ku80 and PARP-1 in minimized chromosome aberrations and cancer development and suggest that defects in DNA end-processing molecules may be etiological factors in human HCC formation.

Animals↗

PubMed2002

Association between high initial tissue levels of cyclin d1 and recurrence of nasopharyngeal carcinoma.

OBJECTIVES/HYPOTHESIS: Cyclin D1 expression and the rate of apoptosis have been reported to serve as important prognostic indicators in human cancers. The purpose of the present study was to determine the prognostic significance of both initial cyclin D1 expression and the apoptotic index in nasopharyngeal carcinoma. STUDY DESIGN: Cohort study. METHODS: Cyclin D1 protein levels and apoptosis in tumors and their corresponding adjacent, histologically normal tissues were determined at the time of initial diagnosis using immunohistochemical staining, Western blot analysis, and in situ end labeling, respectively, in 64 patients with T1-T4/N0-N2, poorly differentiated squamous cell carcinoma of the nasopharynx. All cases were treated by routine radiation therapy with a total median dose of 70 Gy and followed up for 10 years. RESULTS: High levels of cyclin D1 were found in 35 of 64 tumor specimens (54.7%); no cyclin D1--positive cells were determinable in normal epithelium of the nasopharynx. Rates of early local recurrence (within 5 y) were significantly higher (P <.01) for patients with high levels of cyclin D1 before radiation therapy (24 of 35 patients [68.6%]) as compared with patients with low or no expression (3 of 29 [10.3%]). Furthermore, patients bearing high levels of cyclin D1 had a poorer prognosis concerning 10-year survival than the others (P <.001), whereas overexpression of cyclin D1 did not correlate with the initial TMN classification (P >.05). According to the rate of spontaneous apoptosis in tumors below or above the median, patients were divided into two groups. There was no statistically significant difference for the overall survival between the two groups (P >.05). CONCLUSIONS: The present study demonstrates that cyclin D1 can be used as an indicator of recurrence and subsequent prognosis in nasopharyngeal carcinoma after radiation therapy. At the same time, the apoptotic state before radiation therapy is of no value in predicting the prognosis of patients with nasopharyngeal carcinoma.

Adult↗