Increased susceptibility of the c-Myc overexpressing cell line, SNU-16, to TNF-alpha

Isoforms of the p53 Family and Gastric Cancer: A Ménage à Trois for an Unfinished Affair

Simple Summary

The p53 family is a complex family of transcription factors with different cellular functions that are involved in several physiological processes. A massive amount of data has been accumulated on their critical role in the tumorigenesis and the aggressiveness of cancers of different origins. If common features are observed, there are numerous specificities that may reflect particularities of the tissues from which the cancers originated. In this regard, gastric cancer tumorigenesis is rather remarkable, as it is induced by bacterial and viral infections, various chemical carcinogens, and familial genetic alterations, which provide an example of the variety of molecular mechanisms responsible for cell transformation and how they impact the p53 family. This review summarizes the knowledge gathered from over 40 years of research on the role of the p53 family in gastric cancer, which still displays one of the most elevated mortality rates amongst all types of cancers.

Abstract

Gastric cancer is one of the most aggressive cancers, with a median survival of 12 months. This illustrates its complexity and the lack of therapeutic options, such as personalized therapy, because predictive markers do not exist. Thus, gastric cancer remains mostly treated with cytotoxic chemotherapies. In addition, less than 20% of patients respond to immunotherapy. TP53 mutations are particularly frequent in gastric cancer (±50% and up to 70% in metastatic) and are considered an early event in the tumorigenic process. Alterations in the expression of other members of the p53 family, i.e., p63 and p73, have also been described. In this context, the role of the members of the p53 family and their isoforms have been investigated over the years, resulting in conflicting data. For instance, whether mutations of TP53 or the dysregulation of its homologs may represent biomarkers for aggressivity or response to therapy still remains a matter of debate. This uncertainty illustrates the lack of information on the molecular pathways involving the p53 family in gastric cancer. In this review, we summarize and discuss the most relevant molecular and clinical data on the role of the p53 family in gastric cancer and enumerate potential therapeutic innovative strategies.

BET inhibition as a new strategy for the treatment of gastric cancer

Gastric cancer is one of the most common malignancies and a leading cause of cancer death worldwide. The prognosis of stomach cancer is generally poor as this cancer is not very sensitive to commonly used chemotherapies. Epigenetic modifications play a key role in gastric cancer and contribute to the development and progression of this malignancy. In order to explore new treatment options in this target area we have screened a library of epigenetic inhibitors against gastric cancer cell lines and identified inhibitors for the BET family of bromodomains as potent inhibitors of gastric cancer cell proliferations. Here we show that both the pan-BET inhibitor (+)-JQ1 as well as a newly developed specific isoxazole inhibitor, PNZ5, showed potent inhibition of gastric cancer cell growth. Intriguingly, we found differences in the antiproliferative response between gastric cancer cells tested derived from Brazilian patients as compared to those from Asian patients, the latter being largely resistant to BET inhibition. As BET inhibitors are entering clinical trials these findings provide the first starting point for future therapies targeting gastric cancer.

Expression of Fibroblast Growth Factor 10 Is Correlated with Poor Prognosis in Gastric Adenocarcinoma

Fibroblast growth factor receptor 2 (FGFR2) has been proved to be a significant prognostic factor and a potential therapeutic target in several types of cancer, including gastric cancer. FGFR2 consists two isoforms: FGFR2-IIIb and FGFR2-IIIc, which can be stimulated by different ligands and trigger different downstream signaling pathways. As a specific ligand to FGFR2-IIIb, fibroblast growth factor 10 (FGF10) is expressed in the gastric mesenchyme cell and is involved in stomach development and morphogenesis, but its expression and clinical significance is not well elucidated in gastric cancer. We analyzed FGF10 expression by immunohistochemistry in 178 samples of gastric adenocarcinoma (134 male and 44 female patients, with the average age of 63.2 years old and the average follow-up of 21.6 months). Using the arbitrarily scoring method based on positive cell percentage and staining intensity, we sub-divided the patients into FGF10 high-expression group (58 patients) and low-expression group (120 patients). We thus found that FGF10 expression is significantly associated with lymph node invasion (P = 0.004) and distant metastasis (P = 0.032). Importantly, FGF10 expression is an independent unfavorable prognostic factor (P = 0.042). Moreover, FGF10 knockdown significantly decreased the migration of cultured gastric adenocarcinoma cells, suggesting that FGF10 could promote the invasion of gastric adenocarcinoma. In conclusion, FGF10 expression was identified as a poor prognostic biomarker in gastric adenocarcinoma, and FGF10 could promote the invasion of gastric cancer cells. We suggest that FGF10 could be a potential and promising drug target in gastric adenocarcinoma.

Reparixin attenuates neuronal injury in experimental Klebsiella pneumoniae meningoencephalitis through dual effects on neuroprotection and neuroinflammation

AIMS

Bacterial meningitis causes high mortality and brain damage. The host immune response is associated with brain injury. Chemokine (C-X-C motif) (CXC) chemokines are neutrophil chemoattractants. This study focused on the beneficial effects of intracerebroventricular administration of reparixin, an inhibitor of chemokine (C-X-C motif) receptor (CXCR)1/2, to rats at 2 h following experimental Klebsiella pneumoniae meningoencephalitis.

METHODS

We used a previously established meningoencephalitis animal model in which Sprague-Dawley rats were infected by K. pneumoniae. Sham and infected animals were treated with vehicle or reparixin and sacrificed at various time points. Leukocyte infiltration into cerebrospinal fluid (CSF) and brain as well as gene and protein expression of chemokines and receptors, and neuronal apoptosis were examined. Primary cultures of neuron/glia were infected with K. pneumoniae as an in vitro model of meningoencephalitis.

RESULTS

Levels of chemokine (C-X-C motif) ligand (CXCL)2 in CSF time-dependently increased markedly as early as 2 h, and peaked at 8 h following infection and were much higher than those in serum collected simultaneously. Reparixin significantly reduced leukocyte infiltration into CSF and brain tissues, clinical illness, and brain cell apoptosis at 24 h. Reparixin reduced the elevated CSF concentrations of chemokines [CXCL1, CXCL2, chemokine (C-C motif) ligand (CCL)2 and CCL5] and proinflammatory cytokines. Reparixin also reduced the expression of mRNA of various chemokines, chemokine receptors and proinflammatory cytokines in infected brain tissues. Using primary cultures that are devoid of leukocytes, we further observed that reparixin attenuated the neuronal, but not microglial cell death after infection.

CONCLUSIONS

Reparixin not only reduces amplified inflammation, but also provides direct neuroprotective effects in K. pneumoniae meningoencephalitis.

GAGE12 mediates human gastric carcinoma growth and metastasis

The spontaneous metastasis from human gastric carcinoma (GC) remains poorly reproduced in animal models. Here, we established an experimental mouse model in which GC progressively developed in the orthotopic stomach wall and metastasized to multiple organs; the tumors colonized in the ovary exhibited typical characteristics of Krukenberg tumor. The expression of mesenchymal markers was low in primary tumors and high in those in intravasating and extravasating veins. However, the expression of epithelial markers did not differ, indicating that the acquisition of mesenchymal markers without a concordant loss of typical epithelial markers was associated with metastasis. We identified 35 differentially expressed genes (DEGs) in GC cells metastasized to ovary, among which overexpression of GAGE12 family genes, the top-ranked DEGs, were validated. In addition, knockdown of the GAGE12 gene family affected transcription of many of the aforementioned 35 DEGs and inhibited trans-well migration, tumor sphere formation in vitro and tumor growth in vivo. In accordance, GAGE12 overexpression augmented migration, tumor sphere formation and sustained in vivo tumor growth. Taken together, the GAGE12 gene family promotes GC growth and metastasis by modulating the expression of GC metastasis-related genes.

Biology of SNU cell lines

SNU (Seoul National University) cell lines have been established from Korean cancer patients since 1982. Of these 109 cell lines have been characterized and reported, i.e., 17 colorectal carcinoma, 12 hepatocellular carcinoma, 11 gastric carcinoma, 12 uterine cervical carcinoma, 17 B-lymphoblastoid cell lines derived from cancer patients, 5 ovarian carcinoma, 3 malignant mixed Mllerian tumor, 6 laryngeal squamous cell carcinoma, 7 renal cell carcinoma, 9 brain tumor, 6 biliary tract, and 4 pancreatic carcinoma cell lines. These SNU cell lines have been distributed to biomedical researchers domestic and worldwide through the KCLB (Korean Cell Line Bank), and have proven to be of value in various scientific research fields. The characteristics of these cell lines have been reported in over 180 international journals by our laboratory and by many other researchers from 1987. In this paper, the cellular and molecular characteristics of SNU human cancer cell lines are summarized according to their genetic and epigenetic alterations and functional analysis.

ZnCl(2) prevents c-myc repression and apoptosis in serum-deprived Syrian hamster embryo cells

In order to understand the c-myc implication in the apoptotic process better, we investigated the influence of ZnCl(2) on its expression in normal and transformed Syrian hamster embryo (SHE) cells in relation to apoptosis induced by serum withdrawal. Normal primary SHE cells exposed to a serum-free medium undergo rapid apoptosis characterised by a dramatic down-regulation of c-myc transcription. In these normal cells treated with ZnCl(2), c-myc expression is maintained in serum-starved conditions while apoptosis is inhibited. The results shed light on the involvement of c-myc expression in the survival of normal cells in the absence of growth factors. The regulation of c-myc expression appears to be influenced by zinc treatment as an inhibitor of apoptosis, but mechanisms sustaining the level of c-myc transcription remain to be demonstrated. The hypothesis that maintenance of c-myc expression allows cells to escape apoptosis is in accordance with results in transformed SHE cells that underwent low apoptosis and poor down-regulation of c-myc in serum-deprived conditions.

Regulation of c-myc stability by selective stress conditions and by MEKK1 requires aa 127-189 of c-myc

C-myc availability is central for its ability to serve as a regulator of cell growth and death. Here we study the regulation of c-myc protein stability and identify domains of c-myc that are important for its stabilization in response to stress kinases activated following selective stress conditions. UV-irradiation elicited an increase in c-myc protein levels, which could be attenuated by inhibitors of stress kinases but also by actinomycin D-inhibitor of transcription. Inhibition of protein synthesis results in a noticeable decrease in c-myc levels, further pointing to the short half-life of the protein. However, in combination with tumor necrosis factor-alpha (TNF-alpha), cycloheximide efficiently increases steady-state levels of c-myc, suggesting that selective stress conditions are required to increase c-myc protein stability. Expression of MEKK1, an upstream regulator of protein kinases that has been implicated in mediating the response to diverse stress conditions, also results in an efficient increase in the half-life of c-myc protein. To map c-myc domains that are responsive to stress kinases, we monitored changes in the level of c-myc deletion mutants following MEKK1 expression. Of the seven c-myc deletion mutants analysed, the domain spanning amino acids 127-189 was found to be required for MEKK1-dependent increase in c-myc stability. In all, the present study identifies a novel domain that is important for the regulation of c-myc stability by stress kinases in response to selective stress conditions.

Cell death induced by chemical homobifunctional cross-linkers. Cross-linker induced apoptosis

Physical association of proteins that underlies cytotoxic signal induction and transduction suggests a possibility of regulating cell response by modifying protein-protein interactions. For protein complexing, chemical cross-linking agents have been traditionally used. However, the ability of various cross-linkers to induce and modify cell responses, cell death in particular, is still obscure. We have undertaken the investigation to test the apoptosis-inducing and modifying properties of the homobifunctional cross-linkers-dimethyl suberimidate (DMS) and 1,5-bis(succinimido-oxycarbonyloxy)pentane (BSOCOP). The functional groups of these cross-linkers are different but both are able to interact with available amino groups. It was shown that bifunctional cross-linkers, unlike their monofunctional analogues, are capable of inducing cell death in transformed cells, thus indicating the crucial role of cross-linking in cell killing. DMS- and BSOCOP-treated cells were shown to undergo cell death by apoptosis, though the signaling pathways were distinct. DMS inhibited bcl-X(L) and bak but not bax gene expression, while BSOCOP potentiated bax mRNA synthesis immediately after application. Cell pre-incubation with DMS, but not with BSOCOP, resulted in an increasing sensitivity to TNF, although activities of anti-Fas cytotoxic antibodies were then inhibited. Thus, this study has demonstrated for the first time that chemical cross-linkers are capable of inducing apoptosis by themselves and modifying the TNF-dependent and Fas-mediated cell death that may have potential therapeutic significance.

Protooncogenes as mediators of apoptosis

Apoptosis has been well established as a vital biological phenomenon that is important in the maintenance of cellular homeostasis. Three major protooncogene families and their encoded proteins function as mediators of apoptosis in various cell types and are the subject of this chapter. Protooncogenic proteins such as c-Myc/Max, c-Fos/c-Jun, and Bcl-2/Bax utilize a synergetic effect to enhance their roles in the pro- or antiapoptotic action. These family members activate and repress the expression of their target genes, control cell cycle progression, and execute programmed cell death. Repression or overproduction of these protooncogenic proteins induces apoptosis, which may vary as a result of either cell type specificity or the nature of the apoptotic stimuli. The proapoptotic and antiapoptotic proteins exert their effects in the membrane of cellular organelles. Here they generate cell-type-specific signals that activate the caspase family of proteases and their regulators for the execution of apoptosis.

The relationship between angiogenesis and the immune response in carcinogenesis and the progression of malignant disease

Recent studies have demonstrated that angiogenesis and suppressed cell-mediated immunity (CMI) play a central role in the pathogenesis of malignant disease facilitating tumour growth, invasion and metastasis. In the majority of tumours, the malignant process is preceded by a pathological condition or exposure to an irritant which itself is associated with the induction of angiogenesis and/or suppressed CMI. These include: cigarette smoking, chronic bronchitis and lung cancer; chronic oesophagitis and oesophageal cancer; chronic viral infections such as human papilloma virus and ano-genital cancers, chronic hepatitis B and C and hepatocellular carcinoma, and Epstein-Barr virus (EBV) and lymphomas; chronic inflammatory conditions such as Crohn's disease and ulcerative colitis and colorectal cancer; asbestos exposure and mesothelioma and excessive sunlight exposure/sunburn and malignant melanoma. Chronic exposure to growth factors (insulin-like growth factor-I in acromegaly), mutations in tumour suppressor genes (TP53 in Li Fraumeni syndrome) and long-term exposure to immunosuppressive agents (cyclosporin A) may also give rise to similar environments and are associated with the development of a range of solid tumours. The increased blood supply would facilitate the development and proliferation of an abnormal clone or clones of cells arising as the result of: (a) an inherited genetic abnormality; and/or (b) acquired somatic mutations, the latter due to local production and/or enhanced delivery of carcinogens and mutagenic growth factors. With progressive detrimental mutations and growth-induced tumour hypoxia, the transformed cell, to a lesser or greater extent, may amplify the angiogenic process and CMI suppression, thereby facilitating further tumour growth and metastasis. There is accumulating evidence that long-term treatment with cyclo-oxygenase inhibitors (aspirin and indomethacin), cytokines such as interferon-alpha, anti-oestrogens (tamoxifen and raloxifene) and captopril significantly reduces the incidence of solid tumours such as breast and colorectal cancer. These agents are anti-angiogenic and, in the case of aspirin, indomethacin and interferon-alpha have proven immunomodulatory effects. Collectively these observations indicate that angiogenesis and suppressed CMI play a central role in the development and progression of malignant disease.

HPV 16 E6 blocks TNF-mediated apoptosis in mouse fibroblast LM cells

The interaction between hosts and the viruses that infect them is a dynamic one, and a growing literature documents the fact that many viruses have developed mechanisms designed to avoid elimination by the host immune system. One of the immune strategies used by the host and targeted by virus proteins is apoptosis triggered by the cytokine tumor necrosis factor (TNF). Mouse fibroblast LM cells are spontaneously sensitive to TNF. When the wild-type E6 protein from the human papillomavirus type 16 (HPV 16) was expressed in LM cells, the cells became resistant to TNF. This resistance was examined by several means, including cell morphology, the dose- and time-independent response to TNF in a cell death ELISA, trypan blue exclusion, and cell proliferation. The level of p53 did not rise in TNF-treated cells prior to apoptosis, suggesting a p53-independent mechanism. Significant, though not complete, resistance to TNF was also observed following transfection of a plasmid expressing a mutant E6 protein, which is unable to mediate rapid degradation of the p53 tumor suppressor. These results indicate that the HPV 16 E6 protein can protect LM cells from TNF-triggered apoptosis and likely does so by a mechanism other than mediation of p53 degradation.