FGF18, a prominent player in FGF signaling, promotes gastric tumorigenesis through autocrine manner and is negatively regulated by miR-590-5p

Fibroblast growth factors (FGFs) and their receptors are significant components during fundamental cellular processes. FGF18 plays a distinctive role in modulating the activity of both tumor cells and tumor microenvironment. This study aims to comprehensively investigate the expression and functional role of FGF18 in gastric cancer (GC) and elucidate its regulatory mechanisms. The upregulation of FGF18 was detected in seven out of eleven (63.6%) GC cell lines. In primary GC samples, FGF18 was overexpressed in genomically stable and chromosomal instability subtypes of GC and its overexpression was associated with poor survival. Knocking down FGF18 inhibited tumor formation abilities, induced G1 phase cell cycle arrest and enhanced anti-cancer drug sensitivity. Expression microarray profiling revealed that silencing of FGF18 activated ATM pathway but quenched TGF-β pathway. The key factors that altered in the related signaling were validated by western blot and immunofluorescence. Meanwhile, treating GC cells with human recombinant FGF18 or FGF18-conditioned medium accelerated tumor growth through activation of ERK-MAPK signaling. FGF18 was further confirmed to be a direct target of tumor suppressor, miR-590-5p. Their expressions showed a negative correlation in primary GC samples and more importantly, re-overexpression of FGF18 partly abolished the tumor-suppressive effect of miR-590-5p. Our study not only identified that FGF18 serves as a novel prognostic marker and a therapeutic target in GC but also enriched the knowledge of FGF-FGFR signaling during gastric tumorigenesis.

Upregulation of Id1 by Epstein-Barr virus-encoded LMP1 confers resistance to TGFbeta-mediated growth inhibition

Background

Epstein-Barr virus (EBV)-encoded LMP1 protein is commonly expressed in nasopharyngeal carcinoma (NPC). LMP1 is a prime candidate for driving tumourigenesis given its ability to activate multiple signalling pathways and to alter the expression and activity of variety of downstream targets. Resistance to TGFβ-mediated cytostasis is one of the growth transforming effects of LMP1. Of the downstream targets manipulated by LMP1, the induction of Id1 and inactivation of Foxo3a appear particularly relevant to LMP1-mediated effects. Id1, a HLH protein is implicated in cell transformation and plays a role in cell proliferation, whilst Foxo3a, a transcription factor controls cell integrity and homeostasis by regulating apoptosis. The mechanism(s) by which LMP1 induces these effects have not been fully characterised.

Results

In this study, we demonstrate that the ability of LMP1 to induce the phosphorylation and inactivation of Foxo3a is linked to the upregulation of Id1. Furthermore, we show that the induction of Id1 is essential for the transforming function of LMP1 as over-expression of Id1 increases cell proliferation, attenuates TGFβ-SMAD-mediated transcription and renders cells refractory to TGFβ-mediated cytostasis. Id1 silencing in LMP1-expressing epithelial cells abolishes the inhibitory effect of LMP1 on TGFβ-mediated cell growth arrest and reduces the ability of LMP1 to attenuate SMAD transcriptional activity. In response to TGFβ stimulation, LMP1 does not abolish SMAD phosphorylation but inhibits p21 protein expression. In addition, we found the induction of Id1 in LMP1-expressing cells upon stimulation by TGFβ. We provide evidence that LMP1 suppresses the transcriptional repressor ATF3, possibly leading to the TGFβ-induced Id1 upregulation.

Conclusion

The current data provide novel information regarding the mechanisms by which LMP1 suppresses TGFβ-induced cytostasis, highlighting the importance of Id1 in LMP1 mediated cell transformation

The significance of LMP1 expression in nasopharyngeal carcinoma

The Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) is a key effector of EBV-mediated B cell transformation. LMP1 displays potent oncogenic properties in rodent fibroblasts, and induces a wide range of effects in B cells and epithelial cells. LMP1 functions as a constitutively active tumor necrosis factor receptor (TNFR) engaging a multitude of signaling pathways that include NF-kappaB, the mitogen-activated protein kinases (MAPKs), JNK, p38, the JAK/STAT pathway and, more recently, the small Rho GTPases. The constitutive activation of these signaling cascades explains LMP1's ability to induce such a diverse array of morphological and phenotypic effects in cells and provides an insight into how LMP1 may induce cell transformation. The frequent expression of LMP1 in undifferentiated nasopharyngeal carcinoma (NPC) points to a role for this viral oncoprotein as a key effector molecule in NPC pathogenesis.

Establishment of two immortalized nasopharyngeal epithelial cell lines using SV40 large T and HPV16E6/E7 viral oncogenes

Nasopharyngeal carcinoma (NPC) is a common cancer in Southeast Asia, especially in southern China. One of the most striking features of this disease is its close relationship with Epstein-Barr Virus (EBV). However, to date there is no direct study on the mechanisms involved in the role of EBV in the tumorigenesis of NPC, largely due to lack of an experimental model. Available hypotheses on the association between EBV and NPC are generated from non-nasopharyngeal epithelial cell systems such as human keratinocytes or mouse epithelial cells, which may not truly represent the biological properties of nasopharyngeal epithelial (NP) cells. In this study, we report the establishment of two immortalized NP cell lines, NP69SV40T and NP39E6/E7, using SV40T and HPV16E6/E7 oncogenes. We found that NP60SV40T and NP39E6/E7 cell lines not only maintained many characteristics of normal NP cells (i.e. keratin profile and responsive to TGFbeta inhibition) but also highly responsive to one of the EBV encoded genes, LMP1. Comparative genome hybridization (CGH) analysis showed that these two cell lines contained multiple genetic alterations, some of which have been described in NPC. The immortalized NP cell lines are non-tumorigenic and exhibit anchorage-dependent growth. These cell lines may provide a possible cell model system for studying the mechanisms involved in the tumorigenesis of NPC.

Latent membrane protein-1 of Epstein-Barr virus inhibits cell growth and induces sensitivity to cisplatin in nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma is closely associated with Epstein-Barr virus (EBV) and the EBV encoded latent membrane protein-1 expression (LMP1) is commonly found in the tumour cells. LMP1 has been shown to be involved in modulation of cell growth in B cells but the biological properties of LMP1 expression in nasopharyngeal carcinoma cells are less defined. In this study, a full length LMP1 gene was introduced into an EBV negative nasopharyngeal carcinoma cell line, CNE2, and five LMP1-expressing clones were isolated. Expression of LMP1 did not confer cell growth advantage in CNE2 cells; instead, it induced growth inhibition both in vitro and in vivo. In addition, the LMP1 transfected cells were more susceptible to cisplatin-induced cell death and showed 1.4-4.0-fold increased sensitivity to cisplatin compared to the vector infected control clones. The effect of LMP1 on the balance of Bcl-2 and Bax ratio may play a role in inducing susceptibility to cisplatin-induced cell death. These results demonstrated that LMP1 did not confer growth advantage in CNE2 cells, suggesting that expression of LMP1 may not be crucial in sustaining cell growth in established cell lines. Alternatively, LMP1 alone may not be sufficient to facilitate nasopharyngeal carcinoma cell growth and additional oncogenic factors may be needed along with LMP1 in modulating the malignant property of nasopharyngeal carcinoma.