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Biomedical subjects

M C Hung

Publications and source records attributed to M C Hung.

At least 109 records · Page 6Linked to original sources
PubMed1996

p66Shc isoform down-regulated and not required for HER-2/neu signaling pathway in human breast cancer cell lines with HER-2/neu overexpression.

The HER2/neu protooncogene encodes a transmembrane receptor tyrosine kinase of Mr185 kDa (called p185) which is structurally and functionally homologous to the epidermal growth factor receptor. Shc proteins are important downstream signal transducers of receptor tyrosine kinases. We reported here a novel finding that p66Sch was absent or nearly absent in p185-overexpressing breast cancer cells. This inverse correlation of p185 overexpression and p66Shc expression is probably specific to breast cancer cells because this phenomenon was not observed in p185-overexpressing human ovarian, lung, or oral cancer cells, or mouse fibroblast cells. In contrast, the p52Shc and p46Shc isoforms were expressed at similar levels in both p185-overexpressing and p185 basal level breast cancer cell lines. Furthermore, tyrosine phosphorylation of p52Shc and p46Shc and subsequent formation of Shc/Grb2 complex were detected in breast cancer cells in which the p185 tyrosine kinase is activated, indicating that p66Shc is not required for mediating the HER-2/neu signaling pathway in breast cancer cells.

3T3 Cells↗
PubMed1996

In vitro synthesis of an N-myristoylated fusion protein that binds to the liposomal surface.

To increase the efficiency of association of tumor necrosis factor (TNF), a hydrophilic model protein, with liposomes, an N-myristoylation signal sequence was linked to the N-terminus of TNF by gene fusion. A DNA sequence coding for the N-myristoylation signal of Rasheed leukemia virus-gag protein was fused to be 5'-end of the cDNA coding for the mature domain of TNF to give N-myristoylated fusion TNF cDNA. In vitro translation of the mRNA coding for this fusion cDNA using rabbit reticulocyte lysate gave rise to an N-myristoylated fusion TNF with a molecular mass of 18 kDa as determined by the incorporation of [3H]myristic acid and by immunoprecipitation with anti-TNF antibody. Replacement of Gly2 in the myristoylation signal with Ala entirely inhibited the incorporation of [3H]-myristic acid into the fusion protein. A liposome binding assay using Ficoll density gradient centrifugation revealed that incubating the N-myristoylated fusion TNF with dipalmitoyl phosphatidylcholine-liposomes caused the complete binding of the protein to the liposomes, whereas much less of the nonmyristoylated counterpart bound. Thus, N-myristoylated fusion TNF, with high affinity for liposomes, was synthesized by the in vitro translation/transcription system.

Amino Acid Sequence↗
PubMed1996

Sensitization of HER-2/neu-overexpressing non-small cell lung cancer cells to chemotherapeutic drugs by tyrosine kinase inhibitor emodin.

Overexpression of the HER-2/neu proto-oncogene which encodes tyrosine kinase receptor p185neu, has been observed frequently in many human cancers, including non-small cell lung cancer (NSCLC), and is correlated with poor patient survival in these cancers. In addition, HER-2/neu overexpression in NSCLC is known to induce chemoresistance. Recently, we demonstrated that emodin, a tyrosine kinase inhibitor, suppresses HER-2/neu tyrosine kinase activity in HER-2/neu-overexpressing breast cancer cells and preferentially represses proliferation of these cells. The work described here was carried out to examine (1) whether the tyrosine kinase activity of p185neu is required for resistance to chemotherapeutic drugs of HER-2/neu-overexpressing NSCLC cells and (2) whether the tyrosine kinase inhibitor emodin can sensitize these cells to chemotherapeutic drugs. We found that emodin decreased tyrosine phosphorylation of HER-2/neu and preferentially suppressed proliferation of HER-2/neu-overexpressing NSCLC cells. Furthermore, the combination of emodin with cisplatin, doxorubicin or etoposide (VP16) synergistically inhibited the proliferation of HER-2/neu-overexpressing lung cancer cells, whereas low doses of emodin, cisplatin, doxorubicin, or VP16 alone had only minimal antiproliferative effects on these cells. These results indicate that tyrosine kinase activity is required for the chemoresistant phenotype of HER-2/neu-overexpressing NSCLC cells and that tyrosine kinase inhibitors such as emodin can sensitize these cells to chemotherapeutic drugs. The results may have important implications in chemotherapy for HER-2/neu-overexpressing cancers.

Antineoplastic Agents↗
PubMed1996

Identification of a specific DNA region required for enhanced transcription of HER2/neu in the MDA-MB453 breast cancer cell line.

Overexpression and/or amplification of the HER2/neu gene has been shown in roughly 30% of breast cancer patients. Increased levels of HER2/neu mRNA in some breast cancer cell lines is partially caused by increased gene transcription. In MDA-MB453 human breast cancer cells, an activated trans-acting factor is involved in the increased transcription of HER2/neu by mediating its effects through a specific DNA region in the HER2/neu promoter. A methylation interference experiment showed a novel sequence for protein-DNA interactions. Three polypeptides of approximately 110, 70, and 35 kD interact with this DNA element. This region of the human HER2/neu promoter is highly conserved in the rat and mouse promoters and was shown to be capable of mediating transcriptional trans-activation in HER2/neu-overexpressing MDA-MB453 cells while having little effect in a control cell line that expresses basal levels of HER2/neu. Knowledge on interactions between this DNA element and nuclear protein factors may help us better understand the molecular mechanisms regulating HER2/neu overexpression in breast cancer cells.

Animals↗
PubMed1995

Dominant-negative mutants of Grb2 induced reversal of the transformed phenotypes caused by the point mutation-activated rat HER-2/Neu.

To clarify the role of the Shc-Grb2-Sos trimer in the oncogenic signaling of the point mutation-activated HER-2/neu receptor tyrosine kinase (named p185), we interfered with the protein-protein interactions in the Shc.Grb2.Sos complex by introducing Grb2 mutants with deletions in either amino- (delta N-Grb2) or carboxyl-(delta C-Grb2) terminal SH3 domains into B104-1-1 cells derived from NIH3T3 cells expressing the point mutation-activated HER-2/neu. We found that the transformed phenotypes of the B104-1-1 cells were largely reversed by the delta N-Grb2. The effect of the delta C-Grb2 was much weaker. Biochemical analysis showed that the delta N-Grb2 was able to associate Shc but not p185 or Sos, while the delta C-Grb2 bound to Shc, p185, and Sos. The p185-mediated Ras activation was severely inhibited by the delta N-Grb2 but not the delta C-Grb2. Taken together, these data demonstrate that interruption of the interaction between Shc and the endogenous Grb2 by the delta N-Grb2 impairs the oncogenic signaling of the activated p185, indicating that (i) the delta N-Grb2 functions as a strong dominant-negative mutant, and (ii) Shc/Grb2/Sos pathway plays a major role in mediating the oncogenic signal of the activated p185. Unlike the delta N-Grb2, delta C-Grb2 appears to be a relatively weak dominant-negative mutant, probably due to its ability to largely fulfill the biological functions of the wild-type Grb2.

3T3 Cells↗
PubMed1995

Requirement for neuregulin receptor erbB2 in neural and cardiac development.

The receptor erbB2/neu is a member of the epidermal growth factor receptor (EGFR or erbB) family that also includes erbB3 and erbB4. Amplification of the erbB2/neu gene is found in many cancer types and its overexpression is correlated with a poor prognosis for breast and ovarian cancer patients. Investigation of the biology of erbB2 led to the identification of a family of ligands termed neuregulins which included the neu-differentiation factors, the heregulins, a ligand with acetylcholine-receptor-inducing activity and glial growth factor. Several lines of evidence suggest that heterodimerization of erbB2 with other erbB receptors is required for neuregulin signalling. Here we investigate the developmental role of erbB2 in mammalian development in mice carrying an erbB2 null allele. We find that mutant embryos die before E11, probably as a result of dysfunctions associated with a lack of cardiac trabeculae. Development of cranial neural-crest-derived sensory ganglia was markedly affected. DiI retrograde tracing revealed that the development of motor nerves was also compromised. Our results demonstrate the importance of erbB2 in neural and cardiac development.

Animals↗
PubMed1995

Liposome-mediated in vivo E1A gene transfer suppressed dissemination of ovarian cancer cells that overexpress HER-2/neu.

The HER-2/neu proto-oncogene is frequently amplified or overexpressed in many different types of human cancers, a phenomenon that has been shown to correlate with shorter survival time and lower survival rate in ovarian cancer patients. We previously reported that increased HER-2/neu expression led to more severe malignancy and increased metastatic potential in animal models and that the adenovirus 5 E1A gene repressed HER-2/neu gene expression at transcriptional level and was able to suppress tumor growth when stably transfected into human ovarian cancer SKOV-3 cells which overexpress HER-2/neu. To investigate whether the E1A gene may be used as a therapeutic agent for HER-2/neu-overexpressing human cancers in living hosts, we first developed tumor-bearing mice by injecting SKOV-3 cells that overexpress HER-2/neu intraperitonealy into female nu/nu mice. Five days later, we used cationic liposomes to directly deliver the E1A gene into adenocarcinomas that developed in the peritoneal cavity and on the mesentery of the mice that received the SKOV-3 cell injection. We found that liposome-mediated E1A gene transfer significantly inhibited growth and dissemination of ovarian cancer cells that overexpress HER-2/neu in the treated mice; about 70% of these mice survived at least 365 days, whereas all the control mice that did not receive the gene therapy developed severe tumor symptoms and died within 160 days. The results suggest that liposome-mediated E1A gene transfer may serve as an effective therapy for human ovarian cancers that overexpress HER-2/neu by directly targeting the HER-2/neu oncogene.

Adenovirus E1A Proteins↗
PubMed1995

Suppressed transformation and induced differentiation of HER-2/neu-overexpressing breast cancer cells by emodin.

The amplification and overexpression of the HER-2/neu proto-oncogene, which encodes the tyrosine kinase receptor p185neu, have been observed frequently in tumors from human breast cancer patients and are correlated with poor prognosis. To explore the potential of chemotherapy directed at the tyrosine kinase of p185neu, we have found that emodin (3-methyl-1,6,8-trihydroxyanthraquinone), a tyrosine kinase inhibitor, suppresses autophosphorylation and transphosphorylation activities of HER-2/neu tyrosine kinase, resulting in tyrosine hypophosphorylation of p185neu in HER-2/neu-overexpressing breast cancer cells. Emodin, at a 40-microM concentration, which repressed tyrosine kinase of p185neu, efficiently inhibited both anchorage-dependent and anchorage-independent growth of HER-2/neu-overexpressing breast cancer cells. However, the inhibition was much less effective for those cells expressing basal levels of p185neu under the same conditions. Emodin also induced differentiation of HER-2/neu-overexpressing breast cancer cells by exhibiting a morphological maturation property of large lacy nuclei surrounded by sizable flat cytoplasm and by showing a measurable production of large lipid droplets, which is a marker of mature breast cells. Therefore, our results indicate that emodin inhibits HER-2/neu tyrosine kinase activity and preferentially suppresses growth and induces differentiation of HER-2/neu-overexpressing cancer cells. These results may have chemotherapeutic implications for using emodin to target HER-2/neu-overexpressing cancer cells.

Breast Neoplasms↗
PubMed1995

Tyrosine phosphorylation of Shc proteins and formation of Shc/Grb2 complex correlate to the transformation of NIH3T3 cells mediated by the point-mutation activated neu.

PLC-gamma, ras-GAP and Shc have been proposed to be in vivo substrates for the neu-encoded p185neu receptor tyrosine kinases. We compared the tyrosine phosphorylation levels of PLC-gamma, ras-GAP and Shc in two NIH3T3 derived cell lines, transformed B104-1-1 and non-transformed DHFR/G8 cells in which point-mutation activated and normal rat neu genes were transfected and expressed, respectively. We found that tyrosine phosphorylation of Shc and formation of Shc/Grb2 complex were more significant in B104-1-1 cells than in DHFR/G8 cells, while no obvious difference could be detected for the tyrosine phosphorylation levels of ras-GAP and PLC-gamma between these two cell lines. Furthermore, we observed that association with Shc was severely impaired by deletion of most of the major autophosphorylation sites of the point-mutated neu. The truncated neu product, however, fully retained its ability to transform NIH3T3 cells, induce Shc tyrosine phosphorylation and Shc/Grb2 complex formation. Our results suggest that tyrosine phosphorylation of Shc which allows formation of Shc/Grb2 complex may play an important role for cell transformation induced by the point mutation-activated neu, and that stable binding to mutant p185neu may not be necessary for Shc to mediate this signaling pathway.

3T3 Cells↗
PubMed1995

HER-2/neu-targeting gene therapy--a review.

The HER-2/neu (also named c-erbB-2) oncogene is known to be overexpressed in many human cancers, including breast, ovarian, lung, gastric and oral cancers. In animal models, HER-2/neu overexpression was shown to enhance malignancy and metastasis phenotypes. Repression of HER-2/neu overexpression suppresses the malignant phenotypes of HER-2/neu-overexpressing cancer cells, suggesting that HER-2/neu may serve as an excellent target for developing anti-cancer agents. We have previously shown that the adenovirus-5 (Ad5) E1a gene products and the SV40 large T antigen (large T) inhibit transcription of the HER-2/neu promoter and accordingly suppresses transformation induced by HER-2/neu. In this review, we summarize our recent findings on using cationic liposomes or an Ad vector to deliver E1a or large T into tumor-bearing mice. Our results indicate that both cationic liposomes or an Ad vector can efficiently deliver E1a or large T into tumor cells in mice, and this results in suppression of tumor growth and longer survival of the mice.

Adenoviridae↗
PubMed1995

HER-2/neu-targeting cancer therapy via adenovirus-mediated E1A delivery in an animal model.

Overexpression of HER-2/neu has been demonstrated in human ovarian cancer and correlated with poor prognosis. We previously found that the adenovirus type 5 early region 1A (E1A) gene product can repress overexpression and suppress the tumorigenic potential of the HER-2/neu-overexpressing cancer cells. To develop an efficient HER-2/neu-targeting gene therapy with E1A, a replication-deficient adenovirus containing the E1A gene, Ad.E1A(+), was used to transduce the HER-2/neu-overexpressing human ovarian cancer cell line SK-OV3.ip1. Tumor cell growth in vitro and colony formation in soft agarose were greatly inhibited by Ad.E1A(+) transduction. To test therapeutic efficacy in vivo, tumor-bearing mice were established by i.p. injection with ovarian cancer cells and treated by i.p. injection of 10(8) PFU viral solution containing either replication-deficient Ad.E1A(+); control virus Ad.E1A(-) which is the same adenovirus as Ad.E1A(+) except for E1A deletion, or just PBS. Ad.E1A(+) significantly prolonged survival in treated mice for 1 year (80%) whereas in control groups, all mice died of cancer within 4.5 months. Immunohistochemistry analysis indicated that Ad.E1A protein was expressed in tumor tissue and expression of HER-2/neu p185 protein was suppressed in vivo. As a control, another ovarian cancer cell line 2774, in which HER-2/neu is expressed at a basal level, was also inoculated i.p. following the same therapeutic procedure. Ad.E1A(+) could not prolong survival of 2774 cells, indicating that Ad.E1A(+) specifically targeted HER-2/neu-overexpressing tumor cells and functioned as an antitumor agent.

Adenoviridae↗
PubMed1995

Cell cycle-dependent regulation of p185neu: a relationship between disruption of this regulation and transformation.

Structure and function of p185neu receptor tyrosine kinase were found to be regulated in a cell cycle-dependent manner. In M phase, p185neu is hyperphosphorylated at serine and/or threonine residues. The phosphotyrosine [Tyr(P)] content of p185neu is at its highest level in G0/G1 phase, decreases through S and G2 phases, and reaches its lowest level in M phase. Phospholipase C-gamma (PLC-gamma) and GTPase-activating protein (GAP), substrates of p185neu, also have a similar profile of Tyr(P) content during the cell cycle. These results, along with in vitro immune complex kinase assays, suggest that the tyrosine kinase activity of p185neu is least active in M phase. Interestingly, the mutation-activated neu oncogene (neu*)-encoded protein product, p185neu* escaped from cell cycle regulation. Taken together, we demonstrate in this report that the structure and function of p185neu are regulated in a cell cycle-dependent manner, yet p185neu* escapes from this regulation and remains active through the cell cycle. Disruption of this cell cycle regulation may define a mechanism for p185neu*-mediated cellular transformation.

3T3 Cells↗
PubMed1995

HER-2/neu oncogene characterization in head and neck squamous cell carcinoma.

OBJECTIVE: To characterize the HER-2/neu oncogene in head and neck squamous cell carcinoma (HNSCC) cell lines and tumor tissue specimens. DESIGN: Molecular analysis of HER-2/neu oncogene amplification and expression in HNSCC cell lines by Southern, Northern, and Western blot techniques, and HER-2/neu oncoprotein expression in HNSCC tumor tissue sections by immunohistochemical analysis. SPECIMENS: Eleven HNSCC cell lines, eight paired samples of frozen HNSCC tumor tissue specimens and adjacent nonmalignant mucosa, and 38 paraffin-embedded slides derived from HNSCC tumor specimens (including those from which the cell lines were derived) were analyzed. RESULTS: Southern blot analysis showed twofold HER-2/neu gene amplification in two (18%) of the 11 HNSCC cell lines, MDA-1386 and Tu-167. Northern blot analysis showed messenger RNA overexpression in the same two cell lines, and to a lesser degree in MDA-1483. Western blot analysis showed high levels of HER-2/neu oncoprotein expression in two (18%) of the 11 cell lines (MDA-1386 and Tu-167), a moderate level of protein expression in one cell line (9%) (MDA-1483), and low levels of protein expression in eight cell lines (73%). Some HER-2/neu protein expression was seen in all of the HNSCC cell lines. Immunohistochemical analysis of the tumor tissue sections from which the cell lines were derived corroborated the Western blot results. Western blot analysis of frozen primary tumor specimens showed HER-2/neu oncoprotein overexpression in two (25%) of eight specimens. Immunohistochemical analysis showed high levels of protein expression in six (16%) of the 38 tumor tissue slides, moderate levels in 12 (31%), and low levels in 20 (53%). CONCLUSIONS: The HER-2/neu oncogene is overexpressed in a subset of HNSCC tumors and cell lines. The results from Western blot and immunohistochemical analyses underscore a variable HER2/neu oncoprotein expression in HNSCC. Gene amplification was observed in a few of the cell lines, suggesting a potential mechanism of oncoprotein overexpression. Messenger RNA overexpression, however, can be seen in the absence of gene amplification, indicating that transcriptional or posttranscriptional control mechanisms must be involved. Further studies are indicated to determine the biologic role of HER-2/neu expression in the clinical progression of these lesions and to further define the molecular basis regulating its expression.

Aged↗
PubMed1995

ADP-ribosylation inhibitors inhibit cellular RNA synthesis but do not affect expression of manganous superoxide dismutase or heat shock protein 70 in tumor necrosis factor alpha-sensitive and -resistant tumor cells.

We have shown that the cytotoxic response of TNF-sensitive L929 cells and TNF-resistant EMT-6 cells to TNF-alpha can be modulated by ADP-ribosylation inhibitors independently of ADP-ribosylation rates. To explore the possibility that these inhibitors modulate TNF cytotoxicity by interfering with cellular protective mechanisms, we evaluated their effects on general RNA synthesis and on mRNA expression of two proposed protective genes, manganous superoxide dismutase (MnSOD) and heat shock protein 70 (hsp70). We found that ADP-ribosylation inhibitors could inhibit general RNA synthesis in a dose-dependent fashion to a similar extent in both EMT-6 and L929 cells, although these inhibitors increased or decreased the sensitivity of the cells to TNF, respectively. In EMT-6 cells, combination of actinomycin D with these inhibitors further inhibited the RNA synthesis rate, and it actually decreased the TNF sensitivity of the EMT-6 cells. Furthermore, the expression of MnSOD or hsp70 was not regulated by these inhibitors. Thus, TNF resistance must depend on other mechanisms in addition to the expression of these protective genes.

Animals↗
PubMed1995

Human pro-tumor necrosis factor: molecular determinants of membrane translocation, sorting, and maturation.

Human pro-tumor necrosis factor (pro-TNF) is a type II transmembrane protein with a highly conserved 76-residue leader sequence. We have analyzed the behavior, both in a microsomal translocational system and by transfection, of a series of mutants with deletions from the cytoplasmic, transmembrane, and linking domains. Cytoplasmic deletions included the Arg doublet at -49 and -48 and/or the Lys doublet at -58 and -57; additional mutants included deletion of residues -73 to -55 and -73 to -55, -49, and -48. The transmembrane and linking domain mutants included deletions in the -42 to -35 region, combined with the deletion of residues -32 to -1. Two hybrid mutants combined the cytoplasmic deletions with the deletion of residues -32 to -1. All of the cytoplasmic deletion mutants were properly translocated, as were the transmembrane deletion mutants with deletions up to residues -36, -35, -32 to -1, although the last one exhibited reduced efficiency; further incremental deletions, including deletions of residues -38 to -35 and -32 to -1, completely blocked translocation. Both hybrid mutants were effectively translocated; furthermore, transfection analysis revealed competent expression and maturation of both the cytoplasmic and hybrid mutants. Thus, proper expression and maturation of human pro-TNF can be accomplished with as few as approximately 12 of the 26 residues of the native transmembrane domain and with a net negative charge in the cytoplasmic domain flanking the transmembrane region.

Amino Acid Sequence↗
PubMed1994

Triplex formation at the rat neu oncogene promoter.

Current cancer chemotherapy treatments generally act by affecting rapidly growing malignant cells. Unfortunately, they are relatively nonspecific and thus have a tendency to affect other rapidly growing normal cells in a deleterious manner. Triplex-forming oligodeoxyribonucleotides (TFOs) promise to be a new class of sequence-specific DNA-binding drugs which will target malignancies at the transcriptional level. The formation of an intermolecular triplex (triple helix) has been shown to block the binding of transcription factors and repress transcription in genes such as c-myc and that encoding the epidermal growth factor receptor. The rat neu oncogene promoter contain promoter-enhancer elements which are purine/pyrimidine rich. These enhancer elements are amenable to targeting by TFOs. the human counterpart of rat neu, HER2, is often found to be amplified or overexpressed in a variety of malignancies, such as those of the breast, lungs, ovary, colon and stomach. TFOs may proved to be the basis of effective chemotherapy drugs for these cancers. TFO binding at the "GTG" element (5'GGTGGGGGGG) and at the 'GA' element (5'GGAGGAGGAGGG) has been characterized by gel mobility shift analysis and DNase 1 footprinting. Binding has been shown to occur at a Kd as low as 10(-8) M and has been shown to be sequence specific.

Animals↗
PubMed1994

Nuclear localization of p185neu tyrosine kinase and its association with transcriptional transactivation.

The rat neu protooncogene encodes a 185 kD transmembrane protein (p185neu), which is a member of the epidermal growth factor receptor (EGFr) family. In searching for the signaling transducer of p185neu by using a two-hybrid selection system, we found, surprisingly, that the cytoplasmic domain of p185neu, when fused to the DNA-binding domain of GAL4 (amino acids 1-147), functioned as a transcriptional activator. We subsequently observed nuclear localization of p185neu. Interestingly, nuclear p185neu has a much higher extent of tyrosine phosphorylation than its nonnuclear counterpart. Our results suggest that a transmembrane receptor tyrosine kinase may enter the nucleus and be involved in transcriptional activation. This novel finding unveils a clue in the understanding of the mechanism of receptor tyrosine kinase-mediated signal transduction.

Animals↗