The Role of NGX6 and Its Deletion Mutants in the Proliferation, Adhesion and Migration of Nasopharyngeal Carcinoma 5-8F Cells

EBV-positive glycoproteins associated with nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is closely related to Epstein-Barr virus (EBV) infection, and glycosylation of proteins is associated with precancerous lesions and carcinogenesis of NPC, and viral glycoproteins mediates the fusion of viruses with B cells or epithelial cells in the infection stage, promoting the conversion of normal epithelial cells into cancer cells. In the process of occurrence and development of NPC, various glycoproteins in the body promote or inhibit the proliferation, invasion, metastasis, and drug resistance of tumor cells, such as the tumor inhibitory effect of NGX6 and inhibin B (INHBB); the cancer-promoting effect of tenascin-C (TNC), fibronectin 1 (FN1), insulin-like growth factor binding protein-3 (IGFBP3), serglycin, and its core protein; and some effects of glycosylation of immune proteins on immunotherapy in NPC. This article provides an overview of the research progress on the interaction of glycoproteins associated with EBV infection with the occurrence and development of NPC.

miR-22 Regulates Invasion, Gene Expression and Predicts Overall Survival in Patients with Clear Cell Renal Cell Carcinoma

Background:

Clear cell renal cell carcinoma (ccRCC) is molecularly diverse and distinct molecular subtypes show different clinical outcomes. MicroRNAs (miRNAs) are essential components of gene regulatory networks and play a crucial role in progression of many cancer types including ccRCC.

Objective:

Identify prognostic miRNAs and determine the role of miR-22 in ccRCC.

Methods:

Hierarchical clustering was done in R using gene expression profiles of over 450 ccRCC cases in The Cancer Genome Atlas (TCGA). Kaplan-Meier analysis was performed to identify prognostic miRNAs in the TCGA dataset. RNA-Seq was performed to identify miR-22 target genes in primary ccRCC cells and Matrigel invasion assay was performed to assess the effects of miR-22 overexpression on cell invasion.

Results:

Hierarchical clustering analysis using 2,621 prognostic genes previously identified by our group demonstrated that ccRCC patients with longer overall survival expressed lower levels of genes promoting proliferation or immune responses, while better maintaining gene expression associated with cortical differentiation and cell adhesion. Targets of 26 miRNAs were significantly enriched in the 2,621 prognostic genes and these miRNAs were prognostic by themselves. MiR-22 was associated with poor overall survival in the TCGA dataset. Overexpression of miR-22 promoted invasion of primary ccRCC cells in vitro and modulated transcriptional programs implicated in cancer progression including DNA repair, cell proliferation and invasion.

Conclusions:

Our results suggest that ccRCCs with differential clinical outcomes have distinct transcriptomes for which miRNAs could serve as master regulators. MiR-22, as a master regulator, promotes ccRCC progression at least in part by enhancing cell invasion.

Expression and purification of a rapidly degraded protein, TMEM8B-a, in mammalian cell line

TMEM8B-a protein is the longer, predominant isoform of the TMEM8B gene product, which is a tumor metastasis suppressor in nasopharyngeal carcinoma (NPC) and lung cancer. TMEM8B-a is rapidly degraded via the proteasome pathway mediated by ezrin in many NPC and lung cancer cell lines, but TMEM8B-a is not ubiquitinated. In this study, we report the recombinant production of full-length modified TMEM8B-a in mammalian cells. We used the PiggyBac transposon system to efficiently generate normal and lung cancer cell lines with stable TMEM8B-a protein expression. 293FT cells were the best host cell line to express TMEM8B-a protein. Then, we treated the stable 293FT cell lines with various small-molecule inhibitors and demonstrated that treatment with MG-132 and bortezomib, which target the proteasome and disrupt its function, could prevent TMEM8B-a degradation and induce protein expression in 293FT cells. Finally, we utilized the combination of Twin-Strep-tag and Strep-Tactin XT resin to successfully purify the TMEM8B-a protein. The final yield was estimated to be approximately 10-20 μg of the purified TMEM8B-a per 3.0 × 10⁸ 293FT cells.

MiR-29c regulates the expression of miR-34c and miR-449a by targeting DNA methyltransferase 3a and 3b in nasopharyngeal carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) is prevalent in South East Asia and Southern China particularly, despite the reported 5-year survival ratio is relative higher than other deadly cancers such as liver, renal, pancreas cancer, the lethality is characterized by high metastatic potential in the early stage and high recurrence rate after radiation treatment. MicroRNA-29c was found to be down-regulated in the serum as well as in the tissue of nasopharyngeal carcinoma tissue.

METHODS

In this study, we found accidentally that the transfection of pre-miR-29c or miR-29c mimics significantly increases the expression level of miR-34c and miR-449a but doesn't affect that of miR-222 using real-time quantitative PCR in nasopharyngeal carcinoma cell lines. To explore the molecular mechanism of the regulatory role, the cells are treated with 5-Aza-2-deoxycytidine (5-Aza-CdR) treatment and the level of miR-34c and miR-449a but not miR-222 accumulated by the treatment. DNA methyltransferase 3a, 3b were down-regulated by the 5-Aza-CdR treatment with western blot and real-time quantitative PCR.

RESULTS

We found that pre-miR-29c or miR-29c mimics significantly increases the expression level of miR-34c and miR-449a. We further found DNA methyltransferase 3a and 3b are the target gene of miR-29c. Restoration of miR-29c in NPC cells down-regulated DNA methyltransferase 3a, 3b, but not DNA methyltransferase T1.

CONCLUSIONS

The regulation of miR-29c/DNMTs/miR-34c\449a is an important molecular axis of NPC development and targeting DNMTs or restoring of miR-29c might be a promising therapy strategy for the prevention of NPC.

Tumor suppressor NGX6 inhibits the growth and metastasis of multiple cancers

Nasopharyngeal carcinoma-associated gene 6 (NGX6) is a membrane protein primarily located in the nuclear membrane and cell membrane. Several groups reported that NGX6 gene was down-regulated in nasopharyngeal carcinoma (NPC), gastric cancer, lung cancer, liver cancer, and colorectal cancer and even less in the carcinomas with metastasis. Current studies have demonstrated that NGX6 possesses various biological functions, such as regulating protein expression of related genes, involving cell signal transduction pathways, negatively controlling cell cycle progression, inhibiting angiogenesis, and increasing the sensitivity of patients to anti-cancer drugs. Some factors regulating the expression level of NGX6 gene also have been studied. The methylation of promoter of NGX6 and histone H3K9 negatively regulates its expression, similar to the function of transcription factor special protein-1 (Sp1). However, the regulatory factor early growth response gene 1 (Egr-1) is provided with positive regulation function. This review will summarize the progress of those studies on NGX6 and elucidate the potential application of NGX6 for some malignant diseases.

NGX6a is degraded through a proteasome-dependent pathway without ubiquitination mediated by ezrin, a cytoskeleton-membrane linker

Our previous study demonstrated that the NGX6b gene acts as a suppressor in the invasion and migration of nasopharyngeal carcinoma (NPC). Recently, we identified the novel isoform NGX6a, which is longer than NGX6b. In this study, we first found that NGX6a was degraded in NPC cells and that this degradation was mediated by ezrin, a linker between membrane proteins and the cytoskeleton. Specific siRNAs against ezrin increase the protein level of NGX6a in these cells. During degradation, NGX6a is not ubiquitinated but is degraded through a proteasome-dependent pathway. The distribution pattern of ezrin was negatively associated with NGX6a in an immunochemistry analysis of a nasopharyngeal carcinoma tissue microarray and fetus multiple organ tissues and Western blot analysis in nasopharyngeal and NPC cell lines, suggesting that ezrin and NGX6a are associated and are involved in the progression and invasion of NPC. By mapping the interacting binding sites, the seven-transmembrane domain of NGX6a was found to be the critical region for the degradation of NGX6a, and the amino terminus of ezrin is required for the induction of NGX6a degradation. The knockdown of ezrin or transfection of the NGX6a mutant CO, which has an EGF-like domain and a transmembrane 1 domain, resulted in no degradation, significantly reducing the ability of invasion and migration of NPC cells. This study provides a novel molecular mechanism for the low expression of NGX6a in NPC cells and an important molecular event in the process of invasion and metastasis of nasopharyngeal carcinoma cells.

Egr-1 regulates the transcription of NGX6 gene through a Sp1/Egr-1 overlapping site in the promoter

Background

As a novel candidate metastasis suppressor gene, Nasopharyngeal carcinoma-associated gene 6 (NGX6) is involved in cellular growth, cell cycle progression and tumor angiogenesis. Previous studies have shown that NGX6 gene is down-regulated in colorectal cancer (CRC). However, little is known about its transcriptional regulation.

Results

We defined the minimal promoter of NGX6 gene in a 186-bp region (from-86 to +100) through mutation construct methods and luciferase assays. Results from Electrophoretic mobility shift assays (EMSA) and Chromatin immunoprecipitation (ChIP) revealed that Early growth response gene 1 (Egr-1) binds to the Sp1/Egr-1 overlapping site of NGX6 minimal promoter. Overexpression of Egr-1 increased the promoter activity and mRNA level of NGX6 gene; while knock-down of endogenous Egr-1 decreased mRNA expression of NGX6 gene.

Conclusion

These results demonstrate that Egr-1 regulates NGX6 gene transcription through an overlapping Sp1/Egr-1 binding site as a positive regulator of NGX6 gene.

Increased expression of flotillin-2 protein as a novel biomarker for lymph node metastasis in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a head and neck malignant tumor rare throughout most of the world but common in Southeast Asia, especially in Southern China. Flotillin-2 (Flot-2) is not only an important component of cellular membrane, but also involves in various cellular processes such as membrane trafficking, T cell and B cell activation, regulation of several signaling pathways associated with cell growth and malignant transformation, keeping structure and junction of epidermal cells and formation of filopodia. Although such molecular effects of Flot-2 have been reported, whether the expression of Flot-2 protein is associated with clinicopathologic implication for NPC has not been reported. The purpose of this research is to investigate the expression of Flot-2 protein in NPC and control nasopharyngeal epithelial tissues by immunohistochemistry and elucidate the association between the expression of Flot-2 protein and clinicopathological characteristics of NPC. The results showed that the positive percentage of Flot-2 expression in the NPC, nasopharyngeal epithelia with atypical hyperplasia and in the control nasopharyngeal mucosa epithelia was 88.8% (119/134), 76.9% (10/13) and 5.7% (5/88), respectively. There was significantly higher expression of Flot-2 protein in NPC and nasopharyngeal epithelia with atypical hyperplasia compared to the control nasopharyngeal mucosa epithelia (P<0.001, respectively). The positive percentage of Flot-2 protein expression in NPC patients with lymph node metastasis was significantly higher than those without lymph node metastasis. Increasing of Flot-2 expression was obviously correlated with clinical stages of NPC patients. The expression of Flot-2 was proved to be the independent predicted factor for lymph node metastasis by multivariate analysis. The sensitivity of Flot-2 for predicting lymph node metastasis of NPC patients was 93%. Taken together, our results suggest that the increased expression of Flot-2 protein is a novel higher sensitivity biomarker that can predict lymph node metastases in NPC.

DNA promoter and histone H3 methylation downregulate NGX6 in gastric cancer cells

Nasopharyngeal carcinoma-associated gene 6 (NGX6) is a novel candidate tumor metastasis suppressor gene. Our study was to determine whether DNA hypermethylation and histone modification at the NGX6 gene promoter play important roles in silencing NGX6 expression in gastric cancer. NGX6 expression was downregulated in all gastric cancer cells and 76.19 % tissues. In three GC cell lines, hypermethylated NGX6 loci were characterized by histone H3-K9 hypoacetylation and hypermethylation. Trichostatin A treatment could moderately increase H3-K9 acetylation at the silenced loci; however, it had no effect on DNA and H3-K9 methylation and minimal effects on NGX6 expression. In contrast, 5'aza-2'-deoxycytidine treatment could rapidly decrease DNA and H3-K9 methylation at the silenced loci, leading to the reexpression of NGX6. Combined treatment with 5'aza-2'-deoxycytidine and trichostatin A had synergistic effects on the reexpression of NGX6 at the hypermethylation loci. Our current study shows that NGX6 expression is downregulated in GC cancer cells and tissues due to NGX6 promoter methylation and H3-K9 methylation, but not H3-K9 acetylation. Our findings indicate that the downregulation of NGX6 expression contributes to the development and progression of gastric cancer. More studies are needed to determine the precise mechanism of NGX6 in the progression of gastric cancer.

Over-expression of BCAT1, a c-Myc target gene, induces cell proliferation, migration and invasion in nasopharyngeal carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a common malignant tumor in southern China and Southeast Asia, but its molecular mechanisms of pathogenesis are poorly understood. Our previous work has demonstrated that BCAT1 mRNA is over expressed in NPC and knocking down its expression in 5-8F NPC cell line can potently inhibit cell cycle progression and cell proliferation. However, the mechanism of BCAT1 up-regulation and its functional role in NPC development remain to be elucidated yet.

METHODS

Immunohistochemistry (IHC) method was utilized to detect the expression of BCAT1 protein in NPC at different pathological stages. The roles of gene mutation, DNA amplification and transcription factor c-Myc in regulating BCAT1 expression were analyzed using PCR-sequencing, quantitative polymerase chain reaction (qPCR), IHC, ChIP and luciferase reporter system, respectively. The functions of BCAT1 in colony formation, cell migration and invasion properties were evaluated by RNA interference (RNAi).

RESULTS

The positive rates of BCAT1 protein expression in normal epithelia, low-to-moderate grade atypical hyperplasia tissues, high-grade atypical hyperplasia tissues and NPC tissues were 23.6% (17/72), 75% (18/24), 88.9% (8/9) and 88.8% (71/80), respectively. Only one SNP site in exon1 was detected, and 42.4% (12/28) of the NPC tissues displayed the amplification of microsatellite loci in BCAT1. C-Myc could directly bind to the c-Myc binding site in promoter region of BCAT1 and up-regulate its expression. The mRNA and protein of c-Myc and BCAT1 were co-expressed in 53.6% (15/28) and 59.1% (13/22) of NPC tissues, respectively, and BCAT1 mRNA expression was also down-regulated in c-Myc knockdown cell lines. In addition, BCAT1 knockdown cells demonstrated reduced proliferation and decreased cell migration and invasion abilities.

CONCLUSIONS

Our study indicates that gene amplification and c-Myc up-regulation are responsible for BCAT1 overexpression in primary NPC, and overexpression of BCAT1 induces cell proliferation, migration and invasion. The results suggest that BCAT1 may be a novel molecular target for the diagnosis and treatment of NPC.

LPLUNC1 inhibits nasopharyngeal carcinoma cell growth via down-regulation of the MAP kinase and cyclin D1/E2F pathways

Long-palate, lung and nasal epithelium clone 1 (LPLUNC1) gene expression is relatively tissue specific. It is highly expressed in nontumor nasopharyngeal epithelial tissues, but its expression is reduced in nasopharyngeal carcinoma (NPC), indicating that LPLUNC1 may be associated with the tumorigenesis of NPC. To study the effects of LPLUNC1 on NPC tumorigenesis, a full-length LPLUNC1 expression plasmid was stably transfected into the NPC cell line, 5-8F. Our data indicated that LPLUNC1 inhibited NPC cell proliferation in vitro and tumor formation in vivo. LPLUNC1 also delayed cell cycle progression from G1 to S phase and inhibited the expression of cyclin D1, cyclin-dependent kinase 4 (CDK4) and phosphorylated Rb. To further investigate the molecular mechanisms underlying the suppressive effects of LPLUNC1 on NPC tumorigenesis, cDNA microarray was performed. These studies revealed that LPLUNC1 inhibited the expression of certain mitogen-activated protein (MAP) kinases (MAPK) kinases and cell cycle-related molecules. Western blotting confirmed that the expression of MEK1, phosphorylated ERK1/2, phosphorylated JNK1/2, c-Myc and c-Jun were inhibited by LPLUNC1. Furthermore, the transcriptional activity of AP-1 was down-regulated by LPLUNC1, suggesting that the MAPK signaling pathway is regulated by LPLUNC1. Taken together, the present study indicates that LPLUNC1 delays NPC cell growth by inhibiting the MAPK and cyclin D1/E2F pathways and suggests that LPLUNC1 may represent a promising candidate tumor suppressor gene associated with NPC.

Signaling Transduction Network Mediated by Tumor Suppressor/Susceptibility Genes in NPC

Nasopharyngeal carcinoma (NPC) is a polygenetic disease. SPLUNC1, UBAP1, BRD7, NAG7, NOR1, NGX6 and LTF genes were found to be tumor suppressor/susceptibility genes in different stages of NPC. SPLUNC1, an early warning molecular diagnosis marker, inhibits the bacteria clone formation, and is an innated immune molecule. SPLUNC1 can negatively regulate the ERK/MAPK signaling transduction pathway to inhibit NPC cell proliferation and induce apoptosis. BRD7, a transcript regulation factor, interacts with BRD2, and promotes apoptosis induced by BRD2. Its promoter is regulated by c-Myc and SP1. BRD7 inhibits NPC cell cycle progression, preventing passage through G0/G1 by suppressing ras/MEK/ERK, Rb/E2F and Wnt signaling pathways. Abnormal activation of BRD7 is crucial to cell cycle turbulence in NPC. NGX6, a metastasis-associated protein, can negative-regulate the EGF/Ras/MAPK signaling transduction pathway, and interacts with ezrin protein to inhibit NPC cell invasion and metastasis. LTF, also a metastasis-associated protein, can negatively regulate MAPK signal transduction pathways, such as JNK2 and ERK, to inhibit NPC cell proliferation and growth. Taken together, it was found that these tumor suppressor/susceptibility genes can regulate key molecules involved in cell signal pathways such as ras/MEK/ERK, Rb/E2F and EGFR ras/MEK/MAPK, and can regulate the expression of some adhesion molecules such as ezrin, nm23 and α-catenin. According to functional genomics and signaling transduction pathways, we have described a signaling cross-talk network between the tumor suppressor/susceptibility genes involved in NPC. These tumor suppressor/susceptibility genes may be potential treatment targets for NPC in the future.

Microarray analysis of differentially expressed genes between nasopharyngeal carcinoma cell lines 5-8F and 6-10B

Nasopharyngeal carcinoma (NPC) cell lines 5-8F (high tumorigenic and metastatic) and 6-10B (low tumorigenic and metastatic) are subclones of SUNE1. To address their biological differences, three biologic repeats of expression microarray analysis were performed. Only 60 differently expressed genes were identified between the two cell lines. These genes were randomly distributed on all the chromosomes. Gene ontology analysis showed that most of these genes participated in cellular and metabolic processes, and the primary molecular functions of each were catalytic activity, ion binding, and protein binding. Literature mining revealed that these genes were specifically related to apoptosis, cell cycle, metastasis, chemokines, and immunoediting, but not cancer, NPC, stem cells, lymphangiogenesis, angiogenesis, inflammation, nor proliferation. In particular, 42/60 genes have established metastatic functions (P < 0.00001), while 11 out of those 42 genes formed gene networks related to metastasis (P = 0.013). Thus, the 60 genes identified by this microarray experiment most likely represent a core set of genes that comprise shared metastatic gene networks between the two cell lines and mediate their differential metastatic characteristics. Among the gene networks identified, the PTHLH gene was of particular interest. Predicted to regulate the WNT pathway through the DKK1 gene, the PTHLH gene may affect metastasis and apoptosis of NPC and merits further study.

Identification of a new seven-span transmembrane protein: NGX6a is downregulated in nasopharyngeal carcinoma and is associated with tumor metastasis

Nasopharyngeal carcinoma (NPC)-associated gene 6 (NGX6) is a novel candidate metastasis suppressor gene that can significantly decrease the growth, motility, and invasion of NPC cells. In this study, we generated a highly specific NGX6 polyclonal antibody and analyzed its distribution in the human fetus by Western blot and immunohistochemistry. The result of the Western blot showed the protein of NGX6 had two types of isoforms, isoform a (NGX6a) and isoform b (NGX6b). Isoform a is composed of 472 amino acids with a calculated molecular mass of 52 kDa, whereas isoform b is composed of 338 amino acids with a calculated molecular mass of 37 kDa. It is predicated that there is an epidermal growth factor domain in the N terminal of both a and b isoforms, and seven transmembrane domains in NGX6a, but only two transmembrane domains in NGX6b. The expression level of NGX6a was higher than that of NGX6b in human fetal tissue. Obvious high expression of NGX6a protein presents in the nervous system and epithelial tissues of the human fetus, but the NGX6b protein (37 kDa) is mainly expressed in the nervous system. We further analyzed the tissue microarray, which contained 154 NPC biopsies and 70 non-NPC biopsies, and found that NGX6a was significantly downregulated in NPC and associated with tumor metastasis.

NGX6 inhibits AP-1 and Ets-1 expression and down-regulates cyclin D1 in human colorectal cancer

Colorectal cancer (CRC) is a common malignant tumor that is associated with an increased incidence of morbidity and mortality. Nasopharyngeal carcinoma-associated gene 6 (NGX6) is a novel candidate suppressor gene of tumor metastasis, which is down-regulated in CRC. In the present study, we constructed a colorectal tissue microarray to examine the expression profiles of NGX6, phospho-c-Jun N-terminal kinase (p-JNK), and phospho-extracellular signal-regulated kinase (p-ERK ) in CRC tissues. We found that the NGX6 expression was lower in CRC tissues and metastatic lymph nodes, whereas the expressions of p-JNK and p-ERK were higher in CRC tissues, than in normal intestinal mucosa. The expressions of NGX6, p-JNK, and p-ERK were associated with the clinical pathological features of colorectal tissues. NGX6 overexpression inhibited the activation and nuclear translocation of JNK1, which led to an accumulation of p-JNK in the cytoplasm, but did not inhibit the activation and nuclear translocation of ERK1/2. NGX6 also inhibited the expression of the transcription factors AP-1 (c-jun and c-fos) and Ets-1. In addition, NGX6 overexpression decreased the expression of cyclin D1 and dramatically suppressed the transcriptional efficiency of the cyclin D1 promoter. We propose that NGX6 expression is lost in the multistep process of human colorectal carcinogenesis. Its overexpression can inhibit the expression of transcription factors AP-1 and Ets-1, and down-regulate the transcriptional activity of the cyclin D1 promoter in human CRC.