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Shao-Chun Wang

Publications and source records attributed to Shao-Chun Wang.

17 recordsLinked to original sources
PubMed2006

Tyrosine phosphorylation controls PCNA function through protein stability.

The proliferating cell nuclear antigen (PCNA) is an essential protein for DNA replication and damage repair. How its function is controlled remains an important question. Here, we show that the chromatin-bound PCNA protein is phosphorylated on Tyr 211, which is required for maintaining its function on chromatin and is dependent on the tyrosine kinase activity of EGF receptor (EGFR) in the nucleus. Phosphorylation on Tyr 211 by EGFR stabilizes chromatin-bound PCNA protein and associated functions. Consistently, increased PCNA Tyr 211 phosphorylation coincides with pronounced cell proliferation, and is better correlated with poor survival of breast cancer patients, as well as nuclear EGFR in tumours, than is the total PCNA level. These results identify a novel nuclear mechanism linking tyrosine kinase receptor function with the regulation of the PCNA sliding clamp.

Cell Nucleus↗
PubMed2006

Protein secondary structure controlled with light and photoresponsive surfactants.

The interaction of a light-responsive azobenzene surfactant with bovine serum albumin (BSA) has been investigated as a means to examine photoreversible changes in protein secondary structure. The cationic azobenzene surfactant undergoes a reversible photoisomeriztion upon exposure to the appropriate wavelength of light, with the visible-light (trans) form being more hydrophobic and, thus, inducing a greater degree of protein unfolding than the UV-light (cis) form. Fourier transform infrared (FT-IR) spectroscopy is used to provide quantitative information on the secondary structure elements in the protein (alpha-helices, beta-strands, beta-turns, and unordered domains). Comparing the secondary structure changes induced by light illumination in the presence of the photoresponsive surfactant with previous measurements of the tertiary structure of BSA obtained from small-angle neutron scattering (SANS) allows the three discrete conformation changes in BSA to be fully characterized. At low surfactant concentrations, an alpha-helix --> beta-structure rearrangement is observed as the tertiary structure of BSA changes from a heart-shaped to a distorted heart-shaped conformation. Intermediate surfactant concentrations lead to a dramatic decrease in the alpha-helix fraction in favor of unordered structures, which is accompanied by an unfolding of the C-terminal portion of the protein as evidenced from SANS. Further increases in photosurfactant concentration lead to a beta --> unordered transition with the protein adopting a highly elongated conformation in solution. Each of these protein conformational changes can be precisely and reversibly controlled with light illumination, as revealed through FT-IR spectra collected during repeated visible-light <--> UV-light cycles.

Animals↗
PubMed2006

Expression of PEA3 and lack of correlation between PEA3 and HER-2/neu expression in breast cancer.

The ETS protein PEA3 functions as a transcription factor to regulate gene expression. Although members of the ETS family have been reported to be involved in tumor progression, ectopic expression of PEA3 has been shown to suppress tumor formation. Despite several studies demonstrated frequent expression of PEA3 and its high association with HER-2/neu and have suggested a potential role of PEA3 in breast cancer, contradictory result has shown that the PEA3 was associated with better survival rate in breast cancer. In the current study, we address this discrepancy by examining the expression of PEA3 and HER-2/neu on 289 archived breast cancer tumor tissues and their correlation with clinicopathologic factors and prognosis. The staining of PEA3 was further validated by in situ hybridization for PEA3 mRNA. We found PEA3 was positive in 22.2% (64/289) of all cases and only 25.6% (21/82) of HER-2/neu-overexpressing cases showed co-expression of PEA3. In contrast to HER-2/neu, PEA3 expression was not correlated with prognosis or major clinicopathologic factors, except for a negative correlation with lymphovascular permeation ( p=0.007). This study demonstrates that PEA3 expression is not correlated with HER-2/neu expression in breast cancer tumor tissues, nor is it associated with adverse clinicopathologic factors or prognosis.

Adult↗
PubMed2006

Antitumor activity of an Ets protein, PEA3, in breast cancer cell lines MDA-MB-361DYT2 and BT474M1.

Polyomavirus enhancer activator 3 (PEA3) is a member of the Ets family of transcription factors. We demonstrated in a previous study that, by downregulating the HER-2/neu oncogene at the transcriptional level, PEA3 can inhibit the growth and development into tumors of HER-2/neu-overexpressing ovarian cancer cells. Here, we establish stable clones of the human breast cancer cell line MDA-MB-361DYT2 that express PEA3 under the control of a tetracycline-inducible promoter. Ectopic expression of PEA3 in this cell line inhibited cell growth and resulted in cell cycle accumulation in the G1 phase. We demonstrate that expression of PEA3 in an orthotopic breast cancer model inhibited tumor growth and prolonged the survival of tumor-bearing mice. In a parallel experiment with another breast cancer cell line, BT474M1, we were unable to obtain stable PEA3-inducible transfectants, suggesting that PEA3 may exert a strong growth inhibition effect in this cell line. Indeed, PEA3 coupled with the liposome SN2 demonstrated therapeutic effects in mice bearing tumors induced by BT474M1. These results provide evidence for the antitumor activity of PEA3 in human breast cancers.

Animals↗
PubMed2006

AIM2 suppresses human breast cancer cell proliferation in vitro and mammary tumor growth in a mouse model.

IFN-inducible proteins are known to mediate IFN-directed antitumor effects. The human IFN-inducible protein absent in melanoma 2 (AIM2) gene encodes a 39-kDa protein, which contains a 200-amino-acid repeat as a signature of HIN-200 family (hematopoietic IFN-inducible nuclear proteins). Although AIM2 is known to inhibit fibroblast cell growth in vitro, its antitumor activity has not been shown. Here, we showed that AIM2 expression suppressed the proliferation and tumorigenicity of human breast cancer cells, and that AIM2 gene therapy inhibited mammary tumor growth in an orthotopic tumor model. We further showed that AIM2 significantly increased sub-G(1) phase cell population, indicating that AIM2 could induce tumor cell apoptosis. Moreover, AIM2 expression greatly suppressed nuclear factor-kappaB transcriptional activity and desensitized tumor necrosis factor-alpha-mediated nuclear factor-kappaB activation. Together, these results suggest that AIM2 associates with tumor suppression activity and may serve as a potential therapeutic gene for future development of AIM2-based gene therapy for human breast cancer.

Animals↗
PubMed2005

Probing lysozyme conformation with light reveals a new folding intermediate.

A means to control lysozyme conformation with light illumination has been developed using the interaction of the protein with a photoresponsive surfactant. Upon exposure to the appropriate wavelength of light, the azobenzene surfactant undergoes a reversible photoisomerization, with the visible-light (trans) form being more hydrophobic than the UV-light (cis) form. As a result, surfactant binding to the protein and, thus, protein unfolding, can be tuned with light. Small-angle neutron scattering (SANS) measurements were used to provide detailed information of the protein conformation in solution. Shape-reconstruction methods applied to the SANS data indicate that under visible light the protein exhibits a native-like form at low surfactant concentrations, a partially swollen form at intermediate concentrations, and a swollen/unfolded form at higher surfactant concentrations. Furthermore, the SANS data combined with FT-IR spectroscopic analysis of the protein secondary structure reveal that unfolding occurs primarily in the alpha domain of lysozyme, while the beta domain remains relatively intact. Thus, the surfactant-unfolded intermediate of lysozyme appears to be a separate structure than the well-known alpha-domain intermediate of lysozyme that contains a folded alpha domain and unfolded beta domain. Because the interactions between the photosurfactant and protein can be tuned with light, illumination with UV light returns the protein to a native-like conformation. Fluorescence emission data of the nonpolar probe Nile red indicate that hydrophobic domains become available for probe partitioning in surfactant-protein solutions under visible light, while the availability of these hydrophobic domains to the probe decrease under UV light. Dynamic light scattering and UV-vis spectroscopic measurements further confirm the shape-reconstruction findings and reveal three discrete conformations of lysozyme. The results clearly demonstrate that visible light causes a greater degree of lysozyme swelling than UV light, thus allowing for the protein conformation to be controlled with light.

Azo Compounds↗
PubMed2005

Endosomal transport of ErbB-2: mechanism for nuclear entry of the cell surface receptor.

The cell membrane receptor ErbB-2 migrates to the nucleus. However, the mechanism of its nuclear translocation is unclear. Here, we report a novel mechanism of its nuclear localization that involves interaction with the transport receptor importin beta1, nuclear pore protein Nup358, and a host of players in endocytic internalization. Knocking down importin beta1 using small interfering RNA oligonucleotides or inactivation of small GTPase Ran by RanQ69L, a dominant-negative mutant of Ran, causes a nuclear transport defect of ErbB-2. Mutation of a putative nuclear localization signal in ErbB-2 destroys its interaction with importin beta1 and arrests nuclear translocation, while inactivation of nuclear export receptor piles up ErbB-2 within the nucleus. Additionally, blocking of internalization by a dominant-negative mutant of dynamin halts its nuclear localization. Thus, the cell membrane-embedded ErbB-2, through endocytosis using the endocytic vesicle as a vehicle, importin beta1 as a driver and Nup358 as a traffic light, migrates from the cell surface to the nucleus. This novel mechanism explains how a receptor tyrosine kinase on the cell surface can be translocated into the nucleus. This pathway may serve as a general mechanism to allow direct communication between cell surface receptors and the nucleus, and our findings thus open a new era in understanding direct trafficking between the cell membrane and nucleus.

Active Transport, Cell Nucleus↗
PubMed2005

Cytoplasmic/nuclear shuttling and tumor progression.

Protein localization is a highly dynamic biological process. To ensure a proper cellular function, the spatial distribution of different proteins needs to be delicately regulated and coordinated. In cancer, this process is tightly correlated with the outcome of cell proliferation and the response to apoptotic stress. Here we summarize our recent studies regarding the role of subcellular trafficking on cancer cell growth through an AKT-independent regulation of the forkhead transcription factor and, on cancer metastasis, through the regulated localization and subsequent protein degradation of the Snail protein, a key transcription factor involved in epithelial-mesenchymal transition (EMT). In both cases, cellular signaling pathways mediated by distinct protein kinases modulate the appropriate protein localization and functioning. Finally, we address a novel translocation pathway for tyrosine kinase receptors between the cell membrane and the nucleus. We demonstrate that the ErbB family proteins are also expressed in the nucleus and can function as transcriptional regulators. Using a genomic approach, we have identified a number of the target genes regulated by this pathway that are closely related to cancer cell proliferation and metastasis. Our findings, together with the seminal discoveries by other groups, highlight the importance of protein localization in cancer biology and its potential to be a therapeutic target for cancer.

Active Transport, Cell Nucleus↗
PubMed2004

Upregulation of IKKalpha/IKKbeta by integrin-linked kinase is required for HER2/neu-induced NF-kappaB antiapoptotic pathway.

Constitutively active HER2/neu activates nuclear factor kappa-B (NF-kappaB) in cells and induces their resistance to apoptotic stimuli such as tumor necrosis factor-alpha (TNF-alpha). Here, we show that integrin-linked kinase (ILK), the crucial signal transducer in the integrin pathway, is involved in HER2/neu-mediated activation of NF-kappaB. Expression of HER2/neu increases ILK activity. Blocking ILK activity with a kinase-deficient mutant ILK (ILK-KD) inhibits NF-kappaB activation and sensitizes HER2/neu-transformed cells to TNF-alpha-induced apoptosis. Stable expression of ILK-KD in HER2/neu-transformed cells suppressed Akt phosphorylation and the expression of IkappaB kinase alpha and beta (IKKalpha and beta) at both the protein and mRNA levels, preventing IkappaB-alpha degradation and NF-kappaB activation. Furthermore, HER2/neu stimulated the transcriptional activity of the putative IKKbeta promoter through ILK and Akt. Our results demonstrate that upregulation of IKKalpha and IKKbeta by the ILK/Akt pathway is required for the HER2/neu-mediated NF-kappaB antiapoptotic pathway.

Animals↗
PubMed2004

A delayed chemically induced tumorigenesis in Brca2 mutant mice.

BRCA2 is a breast cancer susceptibility gene. Germline mutations of BRCA2 account for about 10-30% of familial breast cancer cases. Consistent with its tumor-suppressor activity, BRCA2 plays an important role in DNA repair. To assess the susceptibility of carriers of mutant BRCA2 to tumorigenesis induced by DNA-damaging carcinogens, we generated a Brca2 knockout mouse strain and studied its susceptibility to chemically induced tumorigenesis. Similar to previously reported Brca2 knockout mice, our Brca2-/- embryos die at E8.5-9.5, while the Brca2+/- mice are tumor-free and fertile. Unexpectedly, Brca2+/- mice developed tumors slower than did their wild-type littermates when treated with a potent carcinogen 7,12-dimethylbenz[a]anthracene (DMBA). In vitro experiments showed that Brca2+/- mouse cells and Capan-1 cells, a human pancreatic cancer cell line deficient of BRCA2, were more sensitive to DMBA-induced apoptosis, than were Brca2+/+ mouse cells and a derivative of Capan-1 cells that expressed exogenous wild-type BRCA2, respectively. Our results suggest that enhanced sensitivity of Brca2 mutant cells to DMBA-induced apoptosis at the dose of DMBA we used contributes to the delayed tumorigenesis of Brca2+/- animals. This suggestion may also provide a rational explanation for a previous unexpected finding that cigarette smoking appears to reduce the breast cancer risk of BRCA2 mutation carriers.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2004

Selective activation of ceruloplasmin promoter in ovarian tumors: potential use for gene therapy.

Gene therapy provides a novel treatment approach to cancer patients. Ideally, expression of therapeutic genes driven by cancer-specific promoters would only target tumors resulting in minimal toxicity to normal tissues. While there is a need of more effective and tolerable treatments for ovarian cancer patients, we aimed to identify gene promoters with high activity in ovarian tumors that can be potentially used in gene therapy to drive the expression of a therapeutic gene in tumors. To identify such promoters, a literature search was performed to reveal genes that are preferentially expressed in ovarian cancer compared with normal ovarian tissue. We found that the ceruloplasmin promoter drove up to 30-fold higher luciferase expression in ovarian cancer cells compared with immortalized normal cells. Furthermore, deletion studies revealed an activator protein-1 (AP-1) site in the ceruloplasmin promoter to be critical for optimal ceruloplasmin promoter activity. Ceruloplasmin promoter activity was significantly activated by 1-O-tetradecanoyl phorbol-13-acetate, a c-jun activator, and conversely suppressed by SP600125, a c-jun inhibitor. Consistently, the ceruloplasmin AP-1 site was specifically recognized by c-jun both in vitro and in vivo. Immunohistochemical analyses of human ovarian cancer specimens showed a direct correlation (r = 0.7, P = 0.007) between expression levels of c-jun and ceruloplasmin. In nude mice carrying SKOV3.ip1 xenografts, the ceruloplasmin promoter demonstrated significantly higher activities in tumors compared with normal organs. Together, these results suggest that the ceruloplasmin promoter activity is significantly enhanced in ovarian cancer and therefore may be exploited as a promising cancer-specific promoter in developing new gene therapy strategies for ovarian cancer.

Cell Line, Tumor↗
PubMed2004

Binding at and transactivation of the COX-2 promoter by nuclear tyrosine kinase receptor ErbB-2.

Pathological expression of human ErbB-2 protein, also known as HER-2, is common in many types of cancer. ErbB-2 is a member of the EGF receptor tyrosine kinase family and has been rigorously studied as a signaling molecule on the cell membrane. Here, we report that ErbB-2 is also expressed in the nucleus in cultured cells as well as primary tumor tissues. Nuclear ErbB-2 was found to associate with multiple genomic targets in vivo, including the cyclooxygenase enzyme COX-2 gene promoter. ErbB-2 forms a complex at a specific nucleotide sequence of the COX-2 promoter and is able to stimulate its transcription. This study demonstrates the presence of ErbB-2 in the nucleus and identifies the function of ErbB-2 as a transcriptional regulator.

Base Sequence↗
PubMed2003

beta-catenin nuclear localization is associated with grade in ovarian serous carcinoma.

OBJECTIVE: beta-Catenin has been previously associated with oncogenic activity in human cancers. We evaluated whether beta-catenin also plays a role in papillary serous ovarian neoplasms. METHODS: Immunohistochemistry for beta-catenin was performed on the primary ovarian serous neoplasms of 105 women. Of these, 10 were low malignant potential (LMP) serous tumors, and 95 were serous cancers. Nuclear beta-catenin staining was correlated with grade of tumor and median survival. OVCAR-3, OVCA-420, OVCA-432, and MDAH-277-10c were evaluated for beta-catenin localization and transfected with a T-cell factor (TCF) responsive reporter to evaluate beta-catenin transcriptional activity. RESULTS: Of 105 serous tumors, 13 (12.3%) demonstrated beta-catenin nuclear staining. Eleven of 48 high-grade serous carcinomas (23.0%) demonstrated nuclear staining compared with 1 low-grade serous carcinoma (2.1%) (P = 0.006). One LMP tumor had nuclear staining. beta-Catenin nuclear localization was undetectable in the cell lines tested. Furthermore, transient transfection of the cell lines with a TCF-responsive reporter did not demonstrate significant constitutive transcriptional activation. CONCLUSIONS: We found a statistically significant correlation between beta-catenin nuclear localization and ovarian high-grade serous carcinomas. Thus, deregulation of beta-catenin may play a role in the pathogenesis of ovarian high-grade serous carcinomas in contrast to ovarian low-grade serous carcinomas and LMP serous tumors.

Adult↗
PubMed2002

External control of Her2 expression and cancer cell growth by targeting a Ras-linked coactivator.

Overproduction of the Her2 oncoprotein has been found in approximately 30% of breast tumors, and patients who have Her2 excesses typically have more aggressive disease. Here we show that the expression of the Her2 gene can be decreased by inhibiting the interaction of the two cancer-linked proteins, DRIP130/CRSP130/Sur-2 (a Ras-linked subunit of human mediator complexes) and ESX (an epithelial-restricted transcription factor). Disruption of the interaction by a short cell-permeable peptide reduced the expression of the Her2 gene and specifically impaired the growth and viability of Her2-overexpressing breast cancer cells. The association of ESX with DRIP130 is mediated by a small hydrophobic face of an 8-aa helix in ESX, suggesting a therapeutic approach to incapacitating the Her2 gene by small organic molecules.

Amino Acid Sequence↗
PubMed2002

Inhibition of cancer cell growth by BRCA2.

The breast cancer susceptibility gene BRCA2 has been suggested to function as a "caretaker" of the genome. Cells without wild-type BRCA2 are deficient in repairing DNA damage. However, whether BRCA2 can also suppress oncogenesis by regulating cell proliferation remains to be determined. To address this question, the expression of wild-type BRCA2 protein was reconstituted, in an either constitutive or regulated manner, in the pancreatic cancer cell line Capan-1, which expresses only a mutant BRCA2. Expression of wild-type BRCA2 inhibited cell proliferation in culture and suppressed tumor growth in animals. Our results showed that, in addition to the DNA repair function, BRCA2 also suppresses tumor development by inhibiting cancer cell growth.

Animals↗
PubMed2002

Systemic tumor suppression by the proapoptotic gene bik.

Metastatic breast cancer requires systemic treatment. We have developed a systemic gene therapy approach for breast cancer, consisting of a nonviral gene delivery system (SN) and a proapoptotic gene, bik. The transfection efficiency of SN carrying a reporter gene was 5-10 times higher than the common nonviral agents Fugene-6 and Lipofectamine in the presence of serum. The SN-bik gene complex induced significant apoptosis in four breast cancer cell lines in vitro as well as in orthotopic tumor tissues in nude mice. Systemically administrated SN-bik significantly inhibited the growth and metastasis of human breast cancer cells implanted in nude mice and prolonged the life span of the treated animals. This study demonstrates that SN-bik is a promising approach for further development as a potential therapeutic agent of cancer.

Animals↗