No abstract

We have previously reported that the LRRC4 gene, which contains a conserved leucine-rich repeat (LRR) cassette and an immunoglobulin (Ig) IgC2 domain, is associated with glioma suppression both in vitro and in vivo. The present study provides evidence that the conspicuous absence of LRRC4 in high-grade gliomas directly contributes to the increasing tumor grade. The loss of LRRC4 in U251 cells is caused by the loss of homozygosity at chromosome 7q32-ter. It was also found that LRRC4 requires a functional LRR cassette domain to suppress U251 cell proliferation. In the LRR cassette domain, the third LRR motif of the core LRR is found to be indispensable for the function of LRRC4. The inhibitory effect of LRRC4 is accompanied by a decrease in the expression of pERK, pAkt, pNF-Bp65, signal transducer and activator of transcription protein-3 (STAT3), and mutant p53, and an increase in the expression of c-Jun NH 2 -terminal kinase (JNK)2 and p-c-Jun, suggesting that LRRC4 plays a major role in suppressing U251 cell proliferation by regulating the extracellular signal-regulated kinase (ERK)/Akt/NF-Bp65, STAT3, and JNK2/c-Jun pathways. In conclusion, LRRC4 may act as a novel candidate of tumor suppressor gene. Therefore, the loss of LRRC4 function may be an important event in the progression of gliomas.

Many natural compounds derived from plants or microbes show promising potential for anticancer treatment, but few have been found to target energy-relevant regulators. In this study, we report that neoalbaconol (NA), a novel small-molecular compound isolated from the fungus, Albatrellus confluens, could target 3-phosphoinositide-dependent protein kinase 1 (PDK1) and inhibit its downstream phosphoinositide-3 kinase (PI3-K)/Akt-hexokinase 2 (HK2) pathway, which eventually resulted in energy depletion. By targeting PDK1, NA reduced the consumption of glucose and ATP generation, activated autophagy and caused apoptotic and necroptotic death of cancer cells through independent pathway. Necroptosis was remarkably induced, which was confirmed by several necroptosis-specific markers: the activation of autophagy, presence of necrotic morphology, increase of receptor-interacting protein 1 (RIP1)/RIP3 colocalization and interaction and rescued by necroptosis inhibitor necrostatin-1. The possibility that Akt overexpression reversed the NA-induced energy crisis confirmed the importance of the PDK1-Akt-energy pathway in NA-mediated cell death. Moreover, NA shows the capability to inhibit PI3-K/Akt signaling and suppress tumor growth in the nasopharyngeal carcinoma (NPC) nude mouse model. These results supported the feasibility of NA in anticancer treatments.

Epstein-Barr virus (EBV) is closely associated with several malignancies, including nasopharyngeal carcinoma. To investigate the EBV activity in tumor development, we tried to establish a malignant model of EBV-infected cells in nude mice. On the basis of the Maxi-EBV system, a human embryonic kidney epithelial cell line (293) with a low malignant potential was used for a stable EBV genome infection. The derived cell line, termed 293-EBV, exhibited obvious morphological transformation and significantly increased growth ability, with the cell cycle redistributed. The clonability and tumorigenicity were also substantially accelerated. In 293-EBV cells, the expression level of the transcription factor NF-kB and JNK2 were upregulated. The result suggested that latent membrane protein 1 (LMP1) was an important viral protein responsible for the enhanced malignant potential. Matured and budding virus particles were observed in tumor tissues, confirming the spontaneous reactivation of EBV from latent genome to lytic cycle at the site of tumor development. Primary culture of tumor tissues showed two patterns about the EBV maintenance or not in newly grown cells, and this was dependent on the thickness of the planted tissues. Moreover, the tumor cells lost EBV genome easily when subcultured at low density. Our findings revealed the cell-to-cell contact mechanism, which was required for the EBV maintenance in the tumor cells during the expansion of EBV-infected cells. This mechanism might give an explanation to the phenomenon that EBV genome in epithelial tumor cells becomes easily lost during subculture in vitro. Our results provided further evidence of a function for EBV in the etiology of tumor development.