Preparation of polyclonal antibody specific for NOR1 and detection of its expression pattern in human tissues and nasopharyngeal carcinoma

Abberent expression of NOR1 protein in tumor associated macrophages contributes to the development of DEN-induced hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary tumor of the liver and the sixth most common lethal cancer worldwide. Recent evidences demonstrated that oxidored nitro domain containing protein 1 (NOR1), a putative tumor suppressor gene, is overexpressed in human HCC tissues. However, the role of NOR1 in HCC development remains unclear. Here, we described that NOR1 protein level is elevated in HCC and is associated with poorer clinical outcome. However, ecotopic overexpression of NOR1 protein in human HCC cell line HepG2 cells had no effect on cells proliferation, migration, and clonality. Immunofluoresence assay indicates NOR1 protein is mainly expressed at CD163 positive M2 tumor associated macrophages (TAMs). To explore the role of NOR1 in the development of HCC, we interrogated the susceptibility of mice lacking the NOR1 gene to DEN-induced hepatocarcinogenesis. NOR1 deficient mice displayed resistance to DEN-induced HCC. We also demonstrate that mNOR1 protein is enriched in F4/80 positive Kupffer cells (KCs) infiltrated in DEN induced murine HCC tissues. Loss of NOR1 led to increase of iNOS whereas decrease of Arg1, Ym1 expression in KCs. Overexpression of NOR1 in THP-1 macrophages led to decrease of iNOS but increase of Arg1. Mechanistic investigations showed that inflammatory cytokines IL-6, TNF-α production, and NF-κB activation were also decreased in NOR1 knockout mice exposed to DEN treatment. Our data suggested that NOR1 is overexpressed in HCC associated TAMs and promotes M2 alternative polarization. Genetic deletion of NOR1 in mice leads to impairment of IL-6 production and NF-κB activation, which in turn attenuates DEN-induced HCC development.

Significance of the NOR1-FOXA1/HDAC2-Slug regulatory network in epithelial-mesenchymal transition of tumor cells

The epithelial-mesenchymal transition (EMT) process is believed to play a crucial role in nasopharyngeal carcinoma (NPC) progression, a squamous cell carcinoma of the head and neck with the tendency to metastasize early. At present, much attention has been given to the inducer of EMT involved in NPC progression, while antagonists have been less intensively characterized. In this study, unbiased analysis of EMT-associated gene expression patterns was performed using data mining of global gene expression profiles derived from NPC samples, leading to the successful identification of NOR1, FOXA1, and Slug, all of which showed aberrant expression during NPC progression. The effect of tumor suppressor NOR1 on Slug-induced NPC cells during the EMT process was investigated by use of ectopic expression and RNA interference methods. The molecular mechanisms underlying the tumor-suppressing effect of NOR1 on Slug-induced EMT were thought to be dependent on the cooperation of NOR1 with the FOXA1-HDAC2 complex. We also showed that FOXA1 and HDAC2 bind the slug promoter and directly repress its transcription. Our data revealed a previously unrecognized role of the NOR1-FOXA1/HDAC2-Slug network in the regulation of the EMT process and aggressiveness of NPC.

NOR1 Suppresses Cancer Stem-Like Cells Properties of Tumor Cells via the Inhibition of the AKT-GSK-3β-Wnt/β-catenin-ALDH1A1 Signal Circuit

Cancer stem cells (CSCs) play a key role in tumor radiotherapy and chemotherapy resistance, relapse, and metastasis, and are primarily maintained in a resting state in vivo. The failure of conventional therapies to target CSCs is the main cause of treatment failure. The discovery of CSCs in nasopharyngeal carcinoma (NPC) tumors is becoming more prevalent; however, the understanding of the mechanisms underlying the maintenance of tumor stemness is still limited. We previously cloned NOR1, a tumor suppressor gene downregulated in NPC cell lines and tissues. In this study, we demonstrate that Wnt/β-catenin and ALDH1A1 form a signal circuit and that NOR1 antagonizes the tumor stem cell-like phenotype in NPC cell lines: the ectopic overexpression of NOR1 reduced β-catenin and ALDH1A1 expression; β-catenin/TCF4 targeted the regulation of ALDH1A1 transcription in NPC cells; silencing ALDH1A1 reduced AKT (total and phosphorylated) and GSK-3β (phosphorylated) expression; and eventually feedback decreased β-catenin expression levels. We also found that NOR1 expression decreased cancer stem-like cell properties of NPC cells, reduced their ability to form tumor spheroids in vitro, reduced tumorigenicity in nude mice in vivo, and increased sensitivity to chemotherapy agents. Taken together, our findings illustrated a new function of NOR1 that suppresses cancer stem-like cell properties in tumor cells by inhibiting the AKT-GSK-3β-Wnt/β-catenin-ALDH1A1 signal circuit. The study suggests that NOR1 deletion expression in NPC cells may be a potential molecular target for cancer stem cell therapy. J. Cell. Physiol. 232: 2829-2840, 2017. © 2016 Wiley Periodicals, Inc.

The NOR1/OSCP1 proteins in cancer: from epigenetic silencing to functional characterization of a novel tumor suppressor

NOR1 (Oxidored-nitro domain-containing protein 1), also known as OSCP1, was first identified in nasopharyngeal carcinoma (NPC) cells in 2003. NOR1 is evolutionarily conserved among species with its expression is restricted to brain, testis and respiratory epithelial cells. NOR1 was downregulated in NPC and the downregulation associates with poor prognosis. Previous study demonstrated that hypermethylation of NOR1 promoter was observed in NPC and hematological malignancies, which has been believed to be the main epigenetic cause for NOR1 silencing in these cancers. Recently, the NOR1 tumor suppressor status has been fully established. NOR1 inhibited cancer cell growth by disturbing tumor cell energe metabolism. NOR1 also promote tumor cells apoptosis in oxidative stress and hypoxia by inhibition of stress induced autophagy. Moreover, NOR1 suppressed cancer cell epithelial-mesenchymal transition, invasion and metastasis via activation of FOXA1/HDAC2-slug regulatory network. Deciphering the molecular mechanisms underlying NOR1 mediated tumor suppressive role would be helpful to a deeper understanding of carcinogenesis and, furthermore, to the development of new therapeutic approaches. Here we summarize the current knowledge on NOR1 focusing on its expression pattern, epigenetic and genetic association with human cancers and its biological functions. This review will also elucidate the potential application of NOR1/OSCP1 for some human malignancies.

Oxidored-nitro domain-containing protein 1 expression is associated with the progression of hepatocellular carcinoma

Hepatocarcinogenesis is a stepwise process during which multiple genes are altered. Understanding the molecular mechanisms that induce hepatocarcinogenesis may improve the screening, prevention and treatment of patients with hepatocellular carcinoma (HCC). In recent years, the oxidored-nitro domain-containing protein 1 (NOR1) gene has been identified to have an important role in the development of HCC in vitro experiments. The current study aimed to examine the expression of NOR1 mRNA and protein expression in specimens of normal liver, hepatitis, cirrhosis and HCC, together representing the process of HCC development. Furthermore, the association between NOR1 expression and clinicopathological parameters of HCC patients was analyzed. Tissue microarrays containing the specimens of human normal liver, hepatitis, cirrhosis and HCC were purchased, and in situ hybridization and immunohistochemistry were used to detect the expression of NOR1 mRNA and protein expression, respectively. It was revealed that the positive rate of NOR1 protein and mRNA expression in the specimens of hepatitis and cirrhosis were not significantly different from that in the normal liver samples. However, the specimens of HCC exhibited an increased positive rate of NOR1 protein and mRNA expression in comparison with the normal liver samples. In addition, a higher positive rate of NOR1 protein expression was observed in HCC patients with a poor pathological differentiation grade and high tumor node metastasis (TNM) stage. In conclusion, the present study provides evidence, for the first time, of the increased expression of NOR1 in human HCC tissues, and its correlation with the pathological stage and TNM status. These findings indicate that NOR1 may be involved in the progression of HCC and it could be employed as a predictive biomarker in HCC development.

Tumor suppressor gene OSCP1/NOR1 regulates apoptosis, proliferation, differentiation, and ROS generation during eye development of Drosophila melanogaster

OSCP1/NOR1 (organic solute carrier partner 1/oxidored nitrodomain-containing protein 1) is a known tumor suppressor protein. OSCP1 has been reported to mediate transport of various organic solutes into cells; however, its role during development has not yet been addressed. Here we report the results of studies on dOSCP1 (the Drosophila ortholog of hOSCP1) to elucidate the role of OSCP1/NOR1 during development. Knockdown of dOSCP1 in the eye imaginal discs induced a rough-eye phenotype in adult flies. This phenotype resulted from induction of caspase-dependent apoptosis followed by a compensatory cell proliferation and generation of reactive oxygen species in eye imaginal discs. The induction of apoptosis appears to be associated with down-regulation of the anti-apoptotic Buffy gene and up-regulation of the pro-apoptotic Debcl gene. These effects of knockdown of dOSCP1 lead to mitochondrial fragmentation, degradation, and a shortfall in ATP production. We also found that knockdown of dOSCP1 causes a defect in cone cell and pigment cell differentiation in pupal retinae. Moreover, mutations in epidermal growth factor receptor pathway-related genes, such as Spitz and Drk, enhanced the rough-eye phenotype induced by dOSCP1 knockdown. These results suggest that dOSCP1 positively regulates the epidermal growth factor receptor signaling pathway. Overall, our findings indicate that dOSCP1 plays multiple roles during eye development in Drosophila.

Structural characterization and subcellular localization of Drosophila organic solute carrier partner 1

Background

Organic solute carrier partner 1 (OSCP1) is known to facilitate the transport of various organic solutes into cells and reported to play a role in cell growth and cell differentiation. Moreover, OSCP1 is known as a tumor suppressor gene that is frequently down-expressed in nasopharyngeal carcinomas and acute myeloid leukemia. However, the underlying mechanisms of action remain unclear and the subcellular localization of OSCP1 has yet to be determined in detail.

Results

Drosophila contains a single orthologue of OSCP1 (dOSCP1) that shares 58% homology with its human counterpart. To study the expression pattern and subcellular localization of dOSCP1, we prepared a specific antibody. Subcellular localization analyses of dOSCP1 with these revealed localization in the plasma membrane, endoplasmic reticulum, Golgi apparatus and mitochondria, but no detection in cytosol. dOSCP1 signals were also detected in the nucleus, although at weaker intensity than in plasma membranes and subcellular organelles. In addition, native polyacrylamide gel electrophoresis analysis with and without β-mercaptoethanol treatment revealed that recombinant dOSCP1 forms dimers and trimers in solution. The dimer form of dOSCP1 could also be detected by Western immunoblot analyses in third instar larval extracts.

Conclusions

The data revealed that dOSCP1 localizes not only in the plasma membrane but also in the nucleus, ER, Golgi apparatus and mitochondria. It is therefore conceivable that this protein may interact with various partners or form multimeric complexes with other proteins to play multiple roles in cells, providing clues to understanding the functions of dOSCP1 during Drosophila development.

Expression of oxidored nitro domain-containing protein 1(NOR1) impairs nasopharyngeal carcinoma cells adaptation to hypoxia and inhibits PDK1 expression

Hypoxia is a characteristic pathophysiological property of locally advanced solid tumors and a relevant factor of the tumor (patho-)physiome since it can promote tumor progression and resistance to therapy. Tumors alter their metabolic pathways to survive in nutrient and oxygen poor microenvironments by a process known as the "Warburg Effect." The current studies identify a novel tumor suppressor gene, termed oxidored nitro domain-containing protein 1 (NOR1) which alters hypoxia cellular response in nasopharyngeal carcinoma. NOR1 expression causes apoptosis of tumor cells in hypoxia by altering the expression of PDK1 expression and mitochondrial Bax-Bcl2 balance thus suppress tumor cell adaptation to hypoxia. Although the importance of hypoxia cellular response is well documented in tumor progression, this is the first demonstration of a human tumor suppressor which functions by regulating mitochondrial apoptotic pathways to suppress tumor survival in oxygen poor microenvironments.

Oxidored-nitro domain containing protein 1 (NOR1) expression suppresses slug/vimentin but not snail in nasopharyngeal carcinoma: Inhibition of EMT in vitro and in vivo in mice

Oxidored-nitro domain containing protein 1 (NOR1) is a putative tumor suppressor gene. In this study, NOR1 expression was detected in NPC tissues and non-cancerous nasopharyngeal epithelium. The data showed that NOR1 protein was decreased in NPC tissues. Lost expression NOR1 protein was associated with poor overall and event-free survival of NPC patients. Overexpression of NOR1 in NPC cells resulted in a significant morphological change and decreased expression of epithelial-to-mesenchymal transition (EMT) mediators (e.g., slug and vimentin), but induced cytokeratin 13 expression. A nude mouse metastasis assay revealed that overexpression of NOR1 decreased NPC tumor cells metastasis capacity in vivo. Knockdown of NOR1 expression in HeLa cells was sufficient to abrogate epithelial traits and to enhance cell migration and invasion. Concomitant inhibition of slug or vimentin alleviated induction of EMT, migration or invasion by NOR1 siRNA in HeLa cells in vitro. In conclusion, the data from the current study suggest, for the first time, that NOR1 plays an important role in NPC in ex vivo, in vitro, and in vivo.

Tumor suppressor gene Oxidored-nitro domain-containing protein 1 regulates nasopharyngeal cancer cell autophagy, metabolism, and apoptosis in vitro

Autophagy is a cellular survival mechanism that involves the catabolic degradation of damaged proteins and organelles during stress. It is particularly required for tumor cell survival during starvation and tumorigenesis. NOR1 is a putative tumor suppressor gene. This study investigated in vitro the effects of NOR1 on the regulation of nasopharyngeal carcinoma autophagy, metabolism, and apoptosis. The data showed that acute oxidative stress induced the expression of NOR1 in normal human cells and tumor cells. Restoration of NOR1 expression downregulated basal autophagy, assessed by autophagy marker LC3 conversion and transmission electron microscopy. In NOR1-expressing tumor cells, reduced autophagy inhibited mitochondrial respiration and energy metabolism. Restoration of NOR1 expression in nasopharyngeal carcinoma cells enhanced apoptosis after induction of oxidative stress. NOR1 expression upregulated Bax expression, Bax translocation to the mitochondria, Smac/DIABLO release from the mitochondria, and activation of caspase-9, and -3, and PARP. In contrast, knockdown of NOR1 expression using NOR1 RNAi resulted in an increase in autophagy and attenuated hydrogen peroxide-induced cell death in HeLa cells. In addition, expression of NOR1 significantly inhibited cisplatin-induced autophagy, resulting in increased cisplatin cytotoxicity and apoptosis. These data revealed novel aspects of the interplay between autophagy and apoptosis in nasopharyngeal carcinoma cells, which underlies the tumor suppression function of NOR1. This work may provide novel insights to contribute to the development of a combinatorial therapy for nasopharyngeal carcinoma.

Overexpression of oxidored-nitro domain containing protein 1 inhibits human nasopharyngeal carcinoma and cervical cancer cell proliferation and induces apoptosis: Involvement of mitochondrial apoptotic pathways

Oxidored-nitro domain containing protein 1 (NOR1) is a novel member of the nitroreductase family that was first isolated as a tumor suppressor gene from human nasopharyngeal carcinoma (NPC). However, the role of NOR1 gene dysfunction in human cancers has not been addressed. We analyzed the expression of NOR1 in various human cancer and benign tissue specimens and found significant downregulation in nine types of cancer compared with corresponding non-tumor tissues. The recombinant expression vector pCDNA3.1-myc-his-NOR1 was constructed and transfected into human NPC 6-10B nasopharyngeal cancer and HeLa cervical cancer (CCA) cells. We found that stable NOR1 overexpression resulted in suppression of 6-10B and HeLa cell proliferation and led to S phase cell cycle arrest. In addition, NOR1 upregulation enhanced apoptosis in pCDNA3.1-myc-his-NOR1 stably transfected cells, and it also altered the expression of proteins involved in the mitochondria-dependent apoptotic pathway. Furthermore, we also found that the NOR1 protein is a cytoplasmic protein that is partially localized in the mitochondria and endoplasmic reticulum. Therefore, NOR1 is an important tumor suppressor gene associated with NPC and CCA and may play antitumor roles by inhibiting proliferation, preventing colony formation, and promoting the apoptosis of tumor cells via the mitochondrial-dependent apoptotic pathway. However, the precise mechanism behind the NOR1 antitumor effects needs to be investigated further.

Differential expression of oxidored nitro domain containing protein 1 (NOR1), in mouse tissues and in normal and cancerous human tissues

Oxidored nitro domain containing protein 1 (NOR1) is usually restrictively expressed in the brain and testis. Detection of altered NOR1 expression could help us to identify its functions in cell growth, differentiation, metabolism, or even carcinogenesis. In this study, NOR1 homologues were identified in multiple species through GenBank search. NOR1 is a novel protein conserved in multiple species. Mouse NOR1 shared high homology with human NOR1. Furthermore, NOR1 expression was analyzed in mouse tissues by using RT-PCR, Western blot, and immunohistochemistry. The data showed that NOR1 is broadly expressed in neurons of mouse brain and the expression profile changes during postnatal development of the mouse brain. Moreover, in non-nervous tissues, strong immunostaining for NOR1 protein was observed in the testis, epididymis and trachea. In addition, expression of human NOR1 protein in different normal and cancerous human tissues was analyzed via search of the human RNA and protein databases; the data showed that although most malignant cells weakly stained or were negative for NOR1 expression, the liver cancer cells displayed moderate to strong expression of NOR1. These data suggested that NOR1 might serve as a cancer/testis/brain antigen in cells, and that altered NOR1 expression in liver cancer may help us to elucidate the functions of NOR1 protein in liver carcinogenesis.

NOR1 is an HSF1- and NRF1-regulated putative tumor suppressor inactivated by promoter hypermethylation in nasopharyngeal carcinoma

Promoter hypermethylation-mediated silencing of tumor suppressor genes (TSGs) is a hallmark of oncogenesis. Oxidored-nitro domain-containing protein 1 (NOR1) is a candidate TSG that is downregulated in nasopharyngeal carcinoma (NPC). In the present study, we identified a functional NOR1 promoter that is regulated by heat shock factor 1 and nuclear respiratory factor 1. The promoter is located within a CpG island. Hypermethylation of this CpG island was found in NPC tissue samples and cancer cell lines, whereas no aberrant promoter methylation was detected in non-cancerous nasopharyngeal tissue samples or normal nasopharyngeal epithelial cells. Treatment of NPC 6-10B cells and leukemia HL60 cells with 5'-aza-2'-deoxycytidine increased endogenous levels of NOR1 messenger RNA. Ectopic expression of NOR1 in NPC HNE1 cells inhibited tumor cell colony formation and viability. These findings suggest that promoter hypermethylation may participate in transcriptional inactivation of the NOR1 gene in NPC. Frequent epigenetic inactivation of the NOR1 gene in NPC suggests that it may be a critical tumor suppressor involved in the development of NPC.

A novel strategy for rapid construction of libraries of full-length antibodies highly expressed on mammalian cell surfaces

Development of a versatile mammalian display system is essential for the selection of functional human antibodies with high affinities. Here we described a novel strategy for rapid construction of full-length antibody libraries that could be efficiently expressed on mammalian cell surfaces. The universal vector pDGB-HC-TM was constructed by inserting multiple cloning site unique sequences recognized by restriction endonucleases BsmBI, SfiI, and BstXI for the pop-in and pop-out of genes of interest. Cytomegalovirus promoter, a commonly used promoter for high expression of proteins in a variety of mammalian cells, was used to drive expression of the inserted antibody genes and a transmembrane domain from platelet-derived growth factor receptor was fused in frame to the C-terminus of heavy chain consistent region to anchor the antibody expressed on the mammalian cell surface. Using this strategy, we constructed a full-length human antibody display library. DNA sequence analysis and expression analysis indicated that the library constructed had a combinatory expressible, detectable diversity of 6.58 x 10(10).