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Biomedical subjects

M C Hung

Publications and source records attributed to M C Hung.

At least 19 recordsLinked to original sources
PubMed2000

Regulatable expression of p21-activated kinase-1 promotes anchorage-independent growth and abnormal organization of mitotic spindles in human epithelial breast cancer cells.

Stimulation of growth factor signaling has been implicated in the development of invasive phenotypes and the activation of p21-activated kinase (Pak1) in human breast cancer cells (Adam, L., Vadlamudi, R., Kondapaka, S. B., Chernoff, J., Mendelsohn, J., and Kumar, R. (1998) J. Biol. Chem. 273, 28238-28246; Adam, L., Vadlamudi, R., Mandal, M., Chernoff, J., and Kumar, R. (2000) J. Biol. Chem. 275, 12041-12050). To study the role of Pak1 in the regulation of motility and growth of breast epithelial cells, we developed human epithelial MCF-7 clones that overexpressed the kinase-active T423E Pak1 mutant under an inducible tetracycline promoter or that stably expressed the kinase-active H83L,H86L Pak1 mutant, which is deficient in small GTPase binding sites. The expression of both T423E and H83L,H86L Pak1 mutants in breast epithelial cells was accompanied by increased cell motility without any apparent effect on the growth rate of cells. The T423E Pak1 mutant was primarily localized to filopodia, and the H83L,H86L Pak1 mutant was primarily localized to ruffles. Cells expressing T423E Pak1 exhibited a regulatable stimulation of mitogen-activated protein kinase and Jun N-terminal kinase activities. The expression of kinase-active Pak1 mutants significantly stimulated anchorage-independent growth of cells in soft agar in a preferential mitogen-activated protein kinase-sensitive manner. In addition, regulatable expression of kinase-active Pak1 resulted in an abnormal organization of mitotic spindles characterized by appearance of multiple spindle orientations. We also provide evidence to suggest a close correlation between the status of Pak1 kinase activity and base-line invasiveness of human breast cancer cells and breast tumor grades. This study is the first demonstration of Pak1 regulation of anchorage-independent growth, potential Pak1 regulation of invasiveness, and abnormal organization of mitotic spindles of human epithelial breast cancer cells.

Breast Neoplasms↗
PubMed2000

Oncogenic signals of HER-2/neu in regulating the stability of the cyclin-dependent kinase inhibitor p27.

Overexpression and activation of HER-2/neu, a proto-oncogene, play a pivotal role in cancer formation. Strong expression of HER-2/neu in cancers has been associated with poor prognosis. Reduced expression of p27(Kip1), a cyclin-dependent kinase inhibitor, correlates with poor clinical outcome in many types of carcinomas. Because many cancers with the overexpression of HER-2/neu overlap with those affected by reduced p27 expression, we studied the link between HER-2/neu oncogenic signals and p27 regulation. We found that down-regulation of p27 correlates with HER-2/neu overexpression. To address the molecular mechanism of this inverse correlation, we found that reduction of p27 is caused by enhanced ubiquitin-mediated degradation, and the HER-2/Grb2/MAPK pathway is involved in the decrease of p27 stability. Also, HER-2/neu activity causes mislocation of p27 and Jun activation domain-binding protein 1 (JAB1), an exporter of p27, into the cytoplasm, thereby facilitating p27 degradation. These results reveal that HER-2/neu signals reduce p27 stability and thus present potential points for therapeutic intervention in HER-2/neu-associated cancers.

3T3 Cells↗
PubMed2000

Inhibition of angiogenesis and induction of apoptosis are involved in E1A-mediated bystander effect and tumor suppression.

Adenovirus type 5 E1A has been implicated in mediation of tumor suppression. Preclinical gene therapy studies have additionally shown that complete growth suppression can be achieved by incomplete transfer of E1A into tumors, suggesting that a bystander effect may also be associated with E1A. In this study, we investigated the E1A-mediated bystander effect and the mechanisms that may be associated with it. By s.c. inoculating nude mice with a mixture of E1A transfectants and parental cells, we found that the E1A transfectants exhibited a bystander effect on inhibition of tumor growth. We further showed that E1A mediated suppression of angiogenesis and induction of apoptosis in the tumors, likely contributing to the bystander effect. In addition, coculture of E1A transfectants and parental cells in a Transwell unit led to growth retardation and apoptosis mediated by the supernatant in the parental cells, indicating that a secreted factor may also contribute to the bystander effect. Taken together, our results suggested that E1A mediates a bystander effect on tumor suppression by inhibiting angiogenesis and inducing apoptosis.

Adenovirus E1A Proteins↗
PubMed2000

High tumoral maspin expression is associated with improved survival of patients with oral squamous cell carcinoma.

Maspin, a member of the serpin family of protease inhibitors, is known to have tumor-suppressor functions. However, the association between its expression level and survival has not been demonstrated in human cancer. Using the immunohistochemical technique to examine the expression levels of maspin in 44 cases of oral squamous cell carcinoma (SCC), we found that 66% of the cases expressed low to intermediate levels of maspin and 34% of the cases expressed high levels of maspin. We further examined maspin protein expression in a series of six SCC cell lines from the head and neck, and found that all but one expressed low or no maspin protein. We also compared the clinicopathological features of the oral SCC cases with the maspin expression level, and found that high maspin expression was associated with the absence of lymph node metastasis. More importantly, we showed that higher maspin expression was significantly associated with better rates of overall survival, suggesting that high maspin expression may be a favorable prognostic marker for oral SCC.

Adult↗
PubMed2000

Beta-catenin, a novel prognostic marker for breast cancer: its roles in cyclin D1 expression and cancer progression.

Beta-catenin can function as an oncogene when it is translocated to the nucleus, binds to T cell factor or lymphoid enhancer factor family members, and transactivates its target genes. In this study, we demonstrate that cyclin D1 is one of the targets of beta-catenin in breast cancer cells. Transactivation of beta-catenin correlated significantly with cyclin D1 expression both in eight breast cell lines in vitro and in 123 patient samples. More importantly, we found that high beta-catenin activity significantly correlated with poor prognosis of the patients and was a strong and independent prognostic factor in breast cancer. Our studies, therefore, indicated that beta-catenin can be involved in breast cancer formation and/or progression and may serve as a target for breast cancer therapy.

Adult↗
PubMed2000

HER-2/neu blocks tumor necrosis factor-induced apoptosis via the Akt/NF-kappaB pathway.

Overexpression of HER-2/neu correlates with poor survival of breast and ovarian cancer patients and induces resistance to tumor necrosis factor (TNF), which causes cancer cells to escape from host immune defenses. The mechanism of HER-2/neu-induced TNF resistance is unknown. Here we report that HER-2/neu activates Akt and NF-kappaB without extracellular stimulation. Blocking of the Akt pathway by a dominant-negative Akt sensitizes the HER-2/neu-overexpressing cells to TNF-induced apoptosis and inhibits IkappaB kinases, IkappaB phosphorylation, and NF-kappaB activation. Our results suggested that HER-2/neu constitutively activates the Akt/NF-kappaB anti-apoptotic cascade to confer resistance to TNF on cancer cells and reduce host defenses against neoplasia.

3T3 Cells↗
PubMed2000

Tumor suppression and sensitization to tumor necrosis factor alpha-induced apoptosis by an interferon-inducible protein, p202, in breast cancer cells.

p202, an IFN-inducible protein, interacts with several important regulatory proteins, leading to growth arrest or differentiation. In this report, we demonstrate that, in addition to inhibiting in vitro cell growth, p202 can also suppress the tumorigenicity of breast cancer cells in vivo. Furthermore, we found that p202 expression could sensitize breast cancer cells to apoptosis induced by tumor necrosis factor alpha treatment. One possible mechanism contributing to this sensitization is the inactivation of nuclear factor-kappaB by its interaction with p202. These results provide a scientific basis for a novel therapeutic strategy that combines p202 and tumor necrosis factor alpha treatment against breast cancer.

Apoptosis↗
PubMed2000

Role of erbB2 in breast cancer chemosensitivity.

The erbB2 gene, which encodes a transmembrane growth factor receptor, is overexpressed in approximately 30% of breast cancers. Overexpressing this gene makes breast cancers resistant to certain chemotherapeutic agents. In this article, we review what is known about ErbB2-mediated chemoresistance and the controversies surrounding it. We also examine the antiapoptotic function of erbB2 as one of the molecular mechanisms of ErbB2-mediated Taxol resistance and describe several emerging strategies for overcoming intrinsic ErbB2-mediated chemoresistance. Finally, we discuss future avenues for studies of chemosensitivity in ErbB2-overexpressing breast cancers that may lead to the development of effective biology-based treatment strategies.

Antibodies, Monoclonal↗
PubMed2000

Ibotenic acid-induced lesions of the medial septum increase hippocampal membrane associated protein kinase c activity and reduce acetylcholine synthesis: prevention by a phosphatidylcholine/vitamin B12 diet.

Ibotenic acid infusion into the medial septum (MS) results in biochemical alterations in the hippocampus. The biochemical events involved in this neuronal lesion are poorly understood. We investigated the effect of a purified diet supplemented with egg phosphatidylcholine (PC) and vitamin B(12) on ibotenic acid-medicated biochemical changes in the rat hippocampus and crude synaptosomal membranes. Male Wistar rats with this MS lesion were fed a purified diet (control diet) or a purified diet supplemented with 5.7 g PC and 125 microg vitamin B(12) per 100 g (experimental diet) for 18 days. Sham-operated rats were fed the control diet. Compared with the sham-operated rats, MS-lesioned rats fed the control diet showed increased activity of membrane-bound protein kinase C (PKC), decreased activity of choline acetyltransferase, and decreased concentrations of acetylcholine in the hippocampus. The ratio of cholesterol to phospholipid in the crude synaptic membrane was lower in the lesioned rats than in the sham-operated rats, but this was not accompanied by any alteration in membrane lipid fluidity. MS-lesioned rats fed the experimental diet showed lowered PKC activity and elevated acetylcholine concentrations than did rats fed the control diet, but there were no significant effects on choline acetyltransferase activity and the lipid ratio. The ibotenic acid-mediated elevation of PKC activity was observed as early as 2 days postinjury in the control diet-fed rats but not in the experimental diet-fed rats. We propose that ibotenic acid mediates pathophysiologic actions through the activation of PKC and that PC combined with vitamin B(12) ameliorates the second messenger-mediated injury.

Journal Article↗
PubMed2000

New taxanes with an opened oxetane ring from the roots of Taxus mairei.

Two novel taxoids, taxumairols N (1) and O (2), have been isolated from extracts of the roots of Taxus mairei. The structures of 1 and 2 were identified as 7beta,9alpha,10beta,13alpha-tetraacetoxy-2alp ha, 4alpha,5alpha,20-tetrahydroxytax-11-ene and 7beta,9alpha,10beta, 13alpha-tetraacetoxy-1beta,2alpha,4alpha,5alp ha, 20-pentahydroxytax-11-ene on the basis of 1D and 2D NMR techniques including COSY, HMQC, HMBC, and NOESY experiments.

Magnetic Resonance Spectroscopy↗
PubMed2000

The ets protein PEA3 suppresses HER-2/neu overexpression and inhibits tumorigenesis.

Because HER-2/neu overexpression is important in cancer development, we looked for a method of suppressing the cell transformation mediated by HER-2/neu overexpression. We have identified that the DNA-binding protein PEA3, which is encoded by a previously isolated gene of the ets family, specifically targeted a DNA sequence on the HER-2/neu promoter and downregulated the promoter activity. Expression of PEA3 resulted in preferential inhibition of cell growth and tumor development of HER-2/neu-overexpressing cancer cells. This is a new approach to targeting HER-2/neu overexpression and also provides a rationale to the design for repressors of diseases caused by overexpression of pathogenic genes.

3T3 Cells↗
PubMed2000

Adenovirus-mediated N5 gene transfer inhibits tumor cell proliferation by induction of apoptosis.

Gene therapy designed to initiate apoptotic cell death provides a potentially effective method to treat cancer. A prerequisite for this approach is the identification of genes that function in distinct apoptotic pathways. Although apoptotic pathways initiated by receptors such as tumor necrosis factor receptor-1 are well characterized, little is known about apoptotic pathways initiated within the nucleus in response to genotoxic stress. We have demonstrated previously that the nuclear, death domain-containing protein p84N5 can induce apoptosis upon transfection into cells, suggesting that it may play a role in an apoptotic pathway initiated within the nucleus. To test the possibility that N5 could be used in the gene therapy of cancer, we have generated a recombinant adenovirus engineered to express N5 and tested the effects of viral infection on the growth and tumorigenicity of tumor cells. N5 adenovirus infection significantly reduced the proliferation and tumorigenicity of breast, ovarian, and osteosarcoma tumor cell lines. Reduced proliferation and tumorigenicity were mediated by an induction of apoptosis as indicated by DNA fragmentation in infected cells. The results suggest that the N5 cDNA is a candidate for the gene therapy of cancer.

Adenoviridae↗
PubMed2000

Use of binomial group testing in tests of hypotheses for classification or quantitative covariables.

In group testing, the test unit consists of a group of individuals. If the group test is positive, then one or more individuals in the group are assumed to be positive. A group observation in binomial group testing can be, say, the test result (positive or negative) for a pool of blood samples that come from several different individuals. It has been shown that, when the proportion (p) of infected individuals is low, group testing is often preferable to individual testing for identifying infected individuals and for estimating proportions of those infected. We extend the potential applications of group testing to hypothesis-testing problems wherein one wants to test for a relationship between p and a classification or quantitative covariable. Asymptotic relative efficiencies (AREs) of tests based on group testing versus the usual individual testing are obtained. The Pitman ARE strongly favors group testing in many cases. Small-sample results from simulation studies are given and are consistent with the large-sample (asymptotic) findings. We illustrate the potential advantages of group testing in hypothesis testing using HIV-1 seroprevalence data.

Adolescent↗
PubMed2000

Cyclin D1 is required for transformation by activated Neu and is induced through an E2F-dependent signaling pathway.

The neu (c-erbB-2) proto-oncogene encodes a tyrosine kinase receptor that is overexpressed in 20 to 30% of human breast tumors. Herein, cyclin D1 protein levels were increased in mammary tumors induced by overexpression of wild-type Neu or activating mutants of Neu in transgenic mice and in MCF7 cells overexpressing transforming Neu. Analyses of 12 Neu mutants in MCF7 cells indicated important roles for specific C-terminal autophosphorylation sites and the extracellular domain in cyclin D1 promoter activation. Induction of cyclin D1 by NeuT involved Ras, Rac, Rho, extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38, but not phosphatidylinositol 3-kinase. NeuT induction of the cyclin D1 promoter required the E2F and Sp1 DNA binding sites and was inhibited by dominant negative E2F-1 or DP-1. Neu-induced transformation was inhibited by a cyclin D1 antisense or dominant negative E2F-1 construct in Rat-1 cells. Growth of NeuT-transformed mammary adenocarcinoma cells in nude mice was blocked by the cyclin D1 antisense construct. These results demonstrate that E2F-1 mediates a Neu-signaling cascade to cyclin D1 and identify cyclin D1 as a critical downstream target of neu-induced transformation.

Animals↗
PubMed2000

Application of the random arbitrary primed polymerase chain reaction differential display method to isolate genes of cholesterol metabolism-related proteins from rat liver.

The random arbitrary primed (RAP) polymerase chain reaction (PCR) differential display (DD) method was applied to isolate genes related to cholesterol metabolism from exogenously hypercholesterolemic (ExHC) rats and the progenitor, SD rats. Forty-seven trials of RAP-PCR DD resulted in the isolation of 37 clones differing in strain, cholesterol supplementation or their interaction. Among their fingerprints, five clones gave reproducible patterns by a Northern blotting analysis. The sequence of two clones with lower mRNA abundance in ExHC rats than in SD rats was homologous to that of fatty acid synthase and oxalyl-CoA decarboxylase. Two other clones with higher mRNA on the n-cholesterol diet were matrin F/G protein and the NMDA receptor glutamate-binding subunit. The other clone with higher mRNA abundance in ExHC rats on the cholesterol diet was myelodysplasia/myeloid leukemia factor 2. Fifteen trials of reverse transcriptase (RT)-PCR DD yielded 10 clones, but none of the fingerprints were reproduced by the Northern blotting analysis. These results indicate that RAP-PCR DD is an appropriate alternative to RT-PCR DD for isolating the genes involved in hypercholesterolemia.

Animals↗
PubMed2000

E1A-mediated paclitaxel sensitization in HER-2/neu-overexpressing ovarian cancer SKOV3.ip1 through apoptosis involving the caspase-3 pathway.

HER-2/neu-overexpressing breast cancer cells are more resistant to the chemotherapeutic agent paclitaxel (Taxol) than low-HER-2/neu-expressing breast cancer cells, and the adenoviral type 5 EIA can down-regulate HER-2/neu overexpression. Therefore, in this study, we asked (a) whether EIA might sensitize response to paclitaxel in human HER-2/neu-overexpressing ovarian cancer cells, and, if so, what is the mechanism responsible; and (b) whether this enhanced chemosensitivity would translate into a therapeutic effect in an ovarian cancer xenograft model. Consequently, we demonstrated that: (a) adenovirus type 5 E1A could enhance the sensitivity of paclitaxel in paclitaxel-resistant HER-2/neu-overexpressing human ovarian cancer cells in vitro by inducing apoptosis, (b) this induction was heavily dependent on activation of the caspase-3 pathway, and (c) nude mice bearing i.p. HER-2/neu-overexpressing human ovarian cancer cells and treated with both paclitaxel and E1A gene therapy survived significantly longer than did mice treated only with paclitaxel or E1A gene therapy. Thus, we concluded that the E1A gene enhanced both the in vitro and in vivo sensitivity of paclitaxel in paclitaxel-resistant HER-2/ neu-overexpressing ovarian cancer SKOV3.ipl cells. Because a Phase I clinical trial using E1A gene targeted to HER-2/neu down-regulation has recently been completed, the current study also provided a scientific basis to further develop a novel therapy that combines paclitaxel and E1A gene therapy and its testing in a Phase II trial.

Adenovirus E1A Proteins↗
PubMed1999

The PTEN/MMAC1/TEP tumor suppressor gene decreases cell growth and induces apoptosis and anoikis in breast cancer cells.

The PTEN/MMAC1/TEP (PTEN) tumor suppressor gene at 10q23.3 is mutated in multiple types of sporadic tumors including breast cancers and also in the germline of patients with the Cowden's breast cancer predisposition syndrome. The PTEN gene encodes a multifunctional phosphatase capable of dephosphorylating the same sites in membrane phosphatidylinositols phosphorylated by phosphatidylinositol 3'-kinase (PI3K). We demonstrate herein that loss of PTEN function in breast cancer cells results in an increase in basal levels of phosphorylation of multiple components of the P13K signaling cascade as well as an increase in duration of ligand-induced signaling through the P13K cascade. These alterations are reversed by wild-type but not phosphatase inactive PTEN. In the presence of high concentrations of serum, enforced expression of PTEN induces a predominant G1 arrest consistent with the capacity of PTEN to evoke increases in the expression of the p27Kip1 cyclin dependent kinase inhibitor. In the presence of low concentrations of serum, enforced PTEN expression results in a marked increase in cellular apoptosis, a finding which is consistent with the capacity of PTEN to alter the phosphorylation, and presumably function, of the AKT, BAD, p70S6 kinase and GSK3 alpha apoptosis regulators. Under anchorage-independent conditions, PTEN also induces anoikis, a form of apoptosis that occurs when cells are dissociated from the extracellular matrix, which is enhanced in conjunction with low serum culture conditions. Together, these data suggest that PTEN effects on the PI3K signaling cascade are influenced by the cell stimulatory context, and that depending on the exposure to growth factors and other exogenous stimuli such as integrin ligation, PTEN can induce cell cycle arrest, apoptosis or anoikis in breast cancer cells.

Apoptosis↗