Carboxyl terminal activating region 3 of latent membrane protein 1 encoded by the Epstein­Barr virus regulates cell proliferation and protein expression in NP69 cells.

In the present study, the mechanism by which carboxyl terminal activating region 3 (CTAR3) of latent membrane protein 1 (LMP1), encoded by the Epstein­Barr virus, regulated cell proliferation and protein expression was investigated in the nasopharyngeal epithelial cell line NP69. The deletion mutant LMP1 (LMP1Δ232­351; amino acid residues including 232­351 codons in CTAR3 deleted) was generated by polymerase chain reaction. An NP69­LMP1Δ232­351 cell line was established by retroviral infection. Finally, cell proliferation and protein expression of NP69 cells expressing LMP1Δ232­351 were examined using a cell growth curve and western blot analysis. The results demonstrated: i) The proliferation of NP69­LMP1Δ232­351 cells was significantly decreased compared with cells expressing wild type LMP1 (LMP1WT; n=3; P<0.05); ii) 17 proteins exhibited differential protein expression (>2­fold change) in NP69­LMP1Δ232­351 cells compared with NP69­LMP1WT cells; and iii) LMP1WT was involved in activating the Janus kinase 3 (JAK3) promoter and regulating the expression of JAK3 protein, while LMP1Δ232­351 was almost defective in ability to activate the JAK promoter. These results suggested that LMP1­CTAR3 may be an important functional domain for regulating cell proliferation and protein expression in nasopharyngeal epithelial cells.

Up-regulation of breast cancer resistance protein plays a role in HER2-mediated chemoresistance through PI3K/Akt and nuclear factor-kappa B signaling pathways in MCF7 breast cancer cells.

Human epidermal growth factor receptor 2 (HER2/neu, also known as ErbB2) overexpression is correlated with the poor prognosis and chemoresistance in cancer. Breast cancer resistance protein (BCRP and ABCG2) is a drug efflux pump responsible for multidrug resistance (MDR) in a variety of cancer cells. HER2 and BCRP are associated with poor treatment response in breast cancer patients, although the relationship between HER2 and BCRP expression is not clear. Here, we showed that transfection of HER2 into MCF7 breast cancer cells (MCF7/HER2) resulted in an up-regulation of BCRP via the phosphatidylinositol 3-kinase (PI3K)/Akt and nuclear factor-kappa B (NF-κB) signaling. Treatment of MCF/HER2 cells with the PI3K inhibitor LY294002, the IκB phosphorylation inhibitor Bay11-7082, and the dominant negative mutant of IκBα inhibited HER2-induced BCRP promoter activity. Furthermore, we found that HER2 overexpression led to an increased resistance of MCF7 cells to multiple antitumor drugs such as paclitaxel (Taxol), cisplatin (DDP), etoposide (VP-16), adriamycin (ADM), mitoxantrone (MX), and 5-fluorouracil (5-FU). Moreover, silencing the expression of BCRP or selectively inhibiting the activity of Akt or NF-κB sensitized the MCF7/HER2 cells to these chemotherapy agents at least in part. Taken together, up-regulation of BCRP through PI3K/AKT/NF-κB signaling pathway played an important role in HER2-mediated chemoresistance of MCF7 cells, and AKT, NF-κB, and BCRP pathways might serve as potential targets for therapeutic intervention.

TCRP1 promotes radioresistance of oral squamous cell carcinoma cells via Akt signal pathway.

Tongue cancer resistance-associated protein 1 (TCRP1) is a novel gene located on human chromosome 11q13.4 which has been reported as a candidate related to chemotherapeutic resistance to cisplatin. Results suggest that TCRP also contribute to radioresistance in oral squamous cell carcinoma (OSCC) cells. We previously established exogenous overexpression of TCRP1 cell line Tca8113/TCRP1 and TCRP1 knockdown cell line Tca8113/PYM-siRNA and paired control cell lines, which provides a cell model system to investigate the roles and mechanisms of TCRP1-mediated radioresponse in OSCC. In this study, we first compared the radiosensitivity of up/down-regulating expression of TCRP1 cell lines and paired control cell lines by a clonogenic survival assay, Hoechst 33258 staining, cell growth assay, and comet assay. The results indicated that TCRP1 played a significant role in mediating OSCC radioresistance through decreased cells apoptosis and increased cellular proliferation and long-term survival. The further study found that TCRP1 function by up-regulating Akt activity and levels and then elevating the level of NF-κB. In summary, these results provided strong evidence for the linkage between TCRP1 and radiation sensitivity and may provide theoretical base of TCRP1 as a potential molecular mark of estimating the response for irradiation in OSCC.

Cloning and functional characterization of TCRP1, a novel gene mediating resistance to cisplatin in an oral squamous cell carcinoma cell line.

To explore the mechanisms of chemotherapy resistance, we previously established a multi-drug resistant cell line, Tca8113/Pingyangmycin (Tca8113/PYM) and identified differential expression in known genes and ESTs using microarray analysis. From among those ESTs we have now identified a novel gene producing an mRNA of 1834 nucleotides translated into a protein having 235 amino acids. This gene was denominated as tongue cancer resistance-associated protein 1 gene (TCRP1, accession number: EF363480). We further determined its functional characteristics. The results demonstrate that TCRP1 mediates a specific resistance to cisplatin in Tca8113 cells by reducing the cisplatin-induced apoptosis. This suggests that TCRP1 might be a novel molecular target to develop agents to reverse cisplatin-induced chemoresistance.

Cloning and characterization of the NPCEDRG gene promoter.

NPCEDRG is a novel tumor suppressive gene that localizes to 3p21.3, a chromosomal region frequently associated with loss of heterozygosity (LOH) in a number of malignancies including nasopharyngeal carcinoma (NPC). Its transcriptional down-expression has been shown in the cell lines and primary tumor tissues of NPC. Reintroduction of NPCEDRG into CNE2, a cell line derived from NPC, was effective to induce cell differentiation, control cell growth, and regulate the cell cycle. Little is known about the transcriptional mechanisms controlling NPCEDRG gene expression. In this article, we describe the NPCEDRG gene structure and the transcriptional expression of NPCEDRG; we found that NPCEDRG was expressed weakly in most of NPC cell lines. Using 5' rapid amplification of complementary DNA ends (5'-RACEs), we found that the NPCEDRG gene has several transcription start sites (TSSs) due to the existence of alternatively spliced variants, and the specific TSS of NPCEDRG was located -25 nucleotides upstream of the translation start site. We amend that Human NPCEDRG CDS containing 516 bp but not the 510 bp reported previously. To characterize the NPCEDRG promoter, transient luciferase and/or EGFP reporter assay were carried out with the constructs including various lengths of the 5' flanking region of the NPCEDRG gene. The results demonstrated that the basal promoter is located at the region from -215 to -8 nucleotides, and the optimal promoter is located at the region from -625 to -8 nucleotides upstream of the translation start site. In silico analysis suggested that the promoter region contained potential binding sites for SP1, c-Myb, AREB6, Nkx2-5, and so on. These results provide important clues to elucidate the regulation of NPCEDRG gene expression and function. Further studies are apparently required for the identification of the transcription factors, essential for NPCEDRG expression, which would lead to better understanding of the molecular mechanism of NPCEDRG expression in nasopharyngeal epithelial cells.

Identification of carbonic anhydrase 9 as a contributor to pingyangmycin-induced drug resistance in human tongue cancer cells.

Drug resistance is the major obstacle to successful cancer treatment. To understand the mechanisms responsible for drug resistance in tongue cancer, Tca8113 cells derived from moderately differentiated human tongue squamous cell carcinoma were exposed to stepwise escalated concentrations of pingyangmycin (PYM) to develop the resistant cell line called Tca8113/PYM, which showed over 18.78-fold increased resistance to PYM as compared with Tca8113 cells, and cross-resistance to cisplatin, pirarubicin, paclitaxel, adriamycin, and mitomycin. We found that the resistance was not associated with multidrug resistance transporter 1 (p170, p-gp), multidrug resistance-associated protein 1 and breast cancer resistance protein overexpression, so we hypothesized that Tca8113/PYM cells must have some other resistance mechanism selected by PYM. To test this hypothesis, the global gene expression profiles between Tca8113 and Tca8113/PYM cells were compared by cDNA microarray. Eighty-nine genes and thirteen expressed sequence tags with differential expression levels between the two cell lines were identified. Some differential expression levels were validated with real-time PCR and western blot. Furthermore, the functional validation showed that both carbonic anhydrase (CA) inhibitor acetazolamide application and CA9 silencing with CA9 antisense oligonucleotides contribute to the medium pH increase of Tca8113/PYM cells and enhanced PYM chemosensitivity. Moreover, both acetazolamide and CA9 antisense oligonucleotides significantly increased PYM-induced caspase 3 activation in Tca8113/PYM cells. Thus, our study suggests that the resistance of Tca8113/PYM cells is probably associated with CA9 and other differential expression molecules, and that CA9 may be an important marker for prediction of PYM responsiveness in tongue cancer chemotherapy.

Identification of proteins responsible for the multiple drug resistance in 5-fluorouracil-induced breast cancer cell using proteomics analysis.

PURPOSE: This study aimed to explore the mechanism of multi-drug resistance (MDR) in 5-fluorouracil (5-FU)-induced breast cancer cell MCF-7. METHODS: MCF-7 cells were exposed in stepwise escalating concentration of 5-FU to develop the resistant cell line, MCF-7/5-FU. Biological and molecular characteristics of the cells were studied through MTT, flow cytometry, real-time PCR, western-blot, and the global protein profiles between MCF-7/5-FU and parental MCF-7 were compared using proteomic approach. Then some of the differentially expressed proteins were validated by western-blot. In addition, the role of 14-3-3sigma was validated using gene transfection. RESULTS: Drug resistance of MCF-7/5-FU cells to 5-FU, MX, cDDP, ADM, TAXOL all increased significantly compared with MCF-7 cells and that maybe related to BCRP, but not MDR1 and MRP1. Differentially expressed proteins between MCF-7/5-FU and MCF-7 cells were identified; 12 proteins were up-regulated and 18 proteins were down-regulated in MCF-7/5-FU cells. Expressive levels of some proteins in western-blot validation were consistent with the results in proteomic analysis. Enforced 14-3-3sigma expression can increase the sensitivity of MCF-7/5-FU cells to 5-FU and cDDP. CONCLUSION: MDR of MCF-7/5-FU likely associated with differentially expressed proteins and 14-3-3sigma may play a positive role in chemotherapy. These findings may provide theoretical support for the prediction of chemotherapeutic response and reverse of MDR.

Transcriptional suppression of breast cancer resistance protein (BCRP) by wild-type p53 through the NF-kappaB pathway in MCF-7 cells.

Breast cancer resistance protein (BCRP) has been shown to confer multidrug resistance, but the mechanisms of its regulation are poorly understood. Here, we investigate the effects of wild-type and mutant p53, and nuclear factor kappa-B (NF-kappaB) (p50) on BCRP promoter activity in MCF-7 cells. Our results demonstrated that wild-type p53 markedly suppressed BCRP activity and enhanced the chemosensitivity of cells to mitoxantrone, whereas mutant p53 had little inhibitory effect. After inhibition of NF-kappaB, similar results were obtained. Following knockdown of endogenous p53, BCRP and p50 expressions were increased, and the chemosensitivity of the cells to mitoxantrone was decreased. We conclude that wild-type p53 acts as a negative regulator of BCRP gene transcription.

Quantitative proteomic analysis of formalin-fixed and paraffin-embedded nasopharyngeal carcinoma using iTRAQ labeling, two-dimensional liquid chromatography, and tandem mass spectrometry.

Formalin-fixed, paraffin-embedded (FFPE) tissue specimens represent a potentially valuable resource for protein biomarker investigations. In this study, proteins were extracted by a heat-induced antigen retrieval technique combined with a retrieval solution containing 2% SDS from FFPE tissues of normal nasopharyngeal epithelial tissues (NNET) and three histological types of nasopharyngeal carcinoma (NPC) with diverse differentiation degrees. Then two-dimensional liquid chromatography-tandem mass spectrometry coupled with isobaric tags for relative and absolute quantification (iTRAQ) labeling was employed to quantitatively identify the differentially expressed proteins among the types of NPC FFPE tissues. Our study resulted in the identification of 730 unique proteins, the distributions of subcellular localizations and molecular functions of which were similar to those of the proteomic database of human NPC and NNET that we had set up based on the frozen tissues. Additionally, the relative expression levels of cathepsin D, keratin8, SFN, and stathmin1 identified and quantified in this report were consistent with the immunohistochemistry results acquired in our previous study. In conclusion, we have developed an effective approach to identifying protein changes in FFPE NPC tissues utilizing iTRAQ technology in conjunction with an economical and easily accessible sample preparation method.

Functional characterization of p53 in nasopharyngeal carcinoma by stable shRNA expression.

Nasopharyngeal carcinoma (NPC) is a high-incidence malignancy in Southern China and Southeast Asia. Although mutation of p53 tumor-suppressor gene is a rare event in NPC, NPC has a high frequency of overexpressed/accumulated p53 protein, which was reported to be dysfunction or inactivation in most of NPC. We report here a functional characterization of p53 in an undifferentiated NPC cell line CNE2. To elucidate the biological function of p53, we employed the RNA interference (RNAi) approach to knockdown the endogenously expressed p53 in CNE2 cells. Interestingly, suppression of p53 expression in CNE2 cells was associated with significant down-regulation of p21WAF1/CIP1 expression and decreased HDM2 protein level in both steady state and genotoxic stress induced by ionizing radiation (IR). Consistent with these biochemical data were the accelerated cell cycle progression and the increased proliferation rate, suggesting that p53 retained growth inhibitory activity in CNE2 cells. Indeed, down-regulation of p53 in CNE2 enhanced the ability of CNE2 cells to grow anchorage-independently in vitro and to develop tumors in vivo. Together with the radioresistance acquired by CNE2sip53 cells, our data indicate that in contrast to a previous study, p53 in this NPC cell line remains functional, which may have an important therapeutical implication.

[Construction and function analysis of the Epstein-Barr virus-encoded latent membrane protein-1 of CTAR3 region].

OBJECTIVE: The role of carboxyl terminal activating region of latent membrane protein1 (LMP1) in Epstein-Barr virus infection and oncogenesis is unclear. In this study, we investigated the activating sites and functionary mechanism of LMP1. METHODS: We recombined a deletion mutant type LMP1 (LMP1Delta232-351), deleted the amino acid residues including 232-351 codons in carboxyl terminal activating region-3 by PCR. Then we compared mutant type LMP1Delta232-351 with wild type LMP1 (LMP1WT) to alter biological effect in Nasopharyngeal Epithelial Cell line NP69. Moreover, we constructed a Janus Kinase 3 (JKA3) promoter luciferase reporter system (pGL-2/JAK3-LUC). We respectively cotransfected the LMP1Delta232-351 and LMP1WT with promoter including NF-kappaB binding sequence or JAK3 promoter luciferase reporter into 293 cells (controlled with pLNSX vector), and compared their actions to activating promoters by results of luciferase activity assay. RESULTS: (1) The colony forming number (CFN) of NP69-LMP1Delta232-351 cells significantly decreased to compare with CFN of NP69-LMP1WT (n=3, p<0.01). (2) LMP1WT was able to up-regulate the transcription activity of JAK3 promoter and the level of up-regulation was correlated with its concentration in Human embryonic kidney 293 cell line; while LMP1Delta232-351 was almost defective ability to activate the promoter. CONCLUSION: The carboxyl terminal activating region-3 may be one of the most important function sites of LMP1, which involved in activating the JAK3 promoter and regulating the expression of JAK3 protein.

[Analysis of differential proteins in laryngeal carcinoma cell line Hep-2 with transfection of LCRG1].

BACKGROUND & OBJECTIVE: Laryngeal carcinoma-related gene 1 (LCRG1), a novel laryngeal carcinoma-related tumor suppressor gene, was cloned with mRNA differential display method. Previous researches showed LCRG1 might inhibit cell growth, proliferation, colony formation in soft agar, and tumorigenesis of laryngeal carcinoma cell line Hep-2. This study was to screen the proteins associated with the tumor suppressive function of LCRG1 by comparative proteomics method. METHODS: The whole cellular proteins of Hep-2/LCRG1 and Hep-2/pcDNA3.1(+) cells were extracted and separated by two-dimensional gel electrophoresis (2-DE) technology. After electrophoresis, the gels were stained by Coomassie Brilliant Blue G-250, and analyzed using PDQuest software. The differentially expressed proteins were cut from the gels, analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), or electrospray ionization-quadrupole time-of-flight MS/MS (ESI-Q-TOF MS/MS), and identified through searching database with Mascot software. RESULTS: The well-resolved, reproducible 2-DE patterns of Hep-2/LCRG1 and Hep-2/pcDNA3.1(+) cells were established. The total protein spots were 1,075+/-43 in Hep-2/LCRG1 cells and 1,027+/-23 in Hep-2/pcDNA3.1(+) cells, with an average matching rate of 91%. Using mass spectrometry technology, 20 differential protein spots between the 2 cell lines were identified. Among them, 16 were identified by MALDI-TOF-MS, and 4 were identified by ESI-Q-TOF MS/MS. Some of the identified proteins were characterized as members of cellular transcription and metabolism enzymes. CONCLUSIONS: In this study, 2-DE gels of Hep-2/LCRG1 cell line with high expression of LCRG1 mRNA and vector control Hep-2/pcDNA3.1(+) cell line were established; some differential proteins related to LCRG1 were identified by mass spectrometry. These data will help to illustrate the molecular mechanism of LCRG1.