Molecular events associated with epithelial to mesenchymal transition of nasopharyngeal carcinoma cells in the absence of Epstein-Barr virus genome.

Epithelial-mesenchymal transition (EMT) is an important process in tumor metastasis. The EMT-related events associated with metastasis of NPC in the absence of EBV have not been elucidated. We established an EBV-negative NPC cell line from a bone marrow biopsy of an NPC patient. Using a Matrigel system we isolated an invasive and non-invasive sublines, designated NPC-BM29 and NPC-BM00. NPC-BM29 acquired an invasive-like phenotype characterized by EMT, marked by down-regulation of E-cadherin and beta-catenin with concomitant increased expression of Ets1. NPC-BM29 cells expressed >or= 10-fold higher of MMP-9 than NPC-BM00 cells. NPC-BM29 cells grew better in 2% serum than NPC-BM00 cells, with a population doubling-time of 26.8 h and 30.7 h, respectively. A marked reduction in colony-formation ability of NPC-BM00 cells compared to NPC-BM29 was observed. Wound-healing assay revealed that NPC-BM29 cells displayed higher motility than NPC-BM00 and the motility was further enhanced by cell treatment with TPA, a PKC activator. Cell surface markers and tumor-associated molecules, AE3, MAK6 and sialyl-Tn, were up-regulated in NPC-BM29 cells, whereas the expression of HLA-DR and CD54 was significantly increased in NPC-BM00 cells. NPC-BM29 consistently released higher levels of IL-8 and IL-10 than NPC-BM00, with low levels of IL-1alpha expression in both cell lines. Higher level of VEGF production was detected in NPC-BM00 than NPC-BM29 cells. These data show that EBV is not required for exhibiting multiple metastatic phenotypes associated with EMT. More studies that target right molecules/signalings associated with the EMT may offer new therapeutic intervention options for NPC invasion and metastasis.

Inhibitory effects of some derivatives of glycyrrhizic acid against Epstein-Barr virus infection: structure-activity relationships.

Glycyrrhizic acid (18beta-GL or GL) is a herbal drug with a broad spectrum of antiviral activities and pharmacological effects and multiple sites of action. Previously we showed that GL inhibits Epstein-Barr virus (EBV) infection in vitro by interfering with an early step of the EBV replication cycle (possibly attachment/penetration). Here we tested the effects of 15 GL derivatives against EBV infection by scoring the numbers of cell expressing viral antigens and quantifying EBV DNA copy numbers in superinfected Raji cells. The derivatives were made either by transformation of GL on carboxyl and hydroxyl groups or by conjugation of amino acid residues into the carbohydrate part. We identified seven compounds active against EBV and all showed dose-dependent inhibition as determined by both assays. Among these active compounds, the introduction of amino acid residues into the GL carbohydrate part enhanced the antiviral activity in three of the seven active compounds. However, when Glu(OH)-OMe was substituted by Glu(OMe)-OMe, its antiviral activity was completely abolished. Introduction of potassium or ammonium salt to GL reduced the antiviral activity with no significant effect on cytotoxicity. The alpha-isomer (18alpha-GL) of 18beta-GL was as potent as the beta-form, but its sodium salt lost antiviral activity. The metabolic product of GL, 18beta-glycyrrhetinic acid (18beta-GA or GA), was 7.5-fold more active against EBV than its parental compound GL but, concomitantly, exhibited increased cytotoxicity resulting in a decreased therapeutic index.

Inhibition of nuclear factor kappaB is associated with neuroprotective effects of glycyrrhizic acid on glutamate-induced excitotoxicity in primary neurons.

Glycyrrhizic acid is an herbal drug with a broad spectrum of antiviral activities and pharmacological effects and multiple sites of action. We investigated whether glycyrrhizic acid protects against glutamate-induced excitotoxicity and the underlying mechanisms. We found that glycyrrhizic acid protected against neurotoxicity in rat primary neuronal cultures and hippocampal slices by suppression of the glutamate-induced apoptosis. Glycyrrhizic acid conferred neuroprotective properties in a concentration-dependent manner, as determined by cell survival, apoptosis, and Ca(2+) influx. Glycyrrhizic acid selectively inhibited the Ca(2+) influx activated through N-methyl-D-aspartate (NMDA) receptor by glutamate, but not through membrane depolarization elicited by high K(+) induction. Glycyrrhizic acid treatment also diminished glutamate-induced DNA fragmentation and cleavage of poly (ADP-ribose) polymerase (PARP). Electrophoretic mobility shift assay (EMSA) indicated that glycyrrhizic acid inhibited the binding activity of nuclear factor kappaB (NF-kappaB) to its target elements. Western blot analysis of NF-kappaB inhibitor (IkappaBalpha) protein revealed that the inhibitory effect of glycyrrhizic acid on glutamate-induced activation of NF-kappaB activity was attributable to the inhibition of IkappaB kinase activity. Thus, the site of action of glycyrrhizic acid could be a downstream consequence of Ca(2+)entry through NMDA receptors and that NF-kappaB may be one downstream target in this process. These observations suggest that glycyrrhizic acid may be of therapeutic value for the prevention of cerebral damage elicited by the glutamate.

Functional assays of HLA A2-restricted epitope variant of latent membrane protein 1 (LMP-1) of Epstein-Barr virus in nasopharyngeal carcinoma of Southern China and Taiwan.

Human leukocyte antigen (HLA) A2 was consistently associated with increased risk for nasopharyngeal carcinoma (NPC) in Chinese populations. Previously we have reported that an Epstein-Barr virus (EBV) strain carrying an HLA A2-restricted epitope variant of LMP-1 is prevalent in NPC in southern China and Taiwan (Lin et al., J. Gen. Virol. 85: 2023-2034, 2004). The variant has mutation selectively involved one of the two anchor residues in position 2 (125 L-->F) and an additional mutation in position 5 (129 M-->I). Functional assays of the epitope variant were carried out in the present work. The stabilization assay on T2 cells indicated that the variant peptide YFL (YFLEILWRL) prevalent in NPC binds to HLA A2 molecules less efficiently than the prototype peptide YLL (YLLEMLWRL). A dose-dependent binding of the HLA A2 molecules with added peptides was observed. In ex vivo cytotoxic T lymphocyte (CTL) assays with CD8-enriched effectors from A2-positive donors revealed that the YLL-specific CTL was able to lyse EBV-infected B cells expressing HLA A2, whereas the CTL recognition was abrogated with the peptide YFL. Cytokine (IFN-gamma) responses, measured both by intracytoplasmic staining and ELISPOT assays after peptide stimulation, also indicated that the variant epitope peptide failed to give an IFN-gamma response. The IFN-gamma response was almost entirely restricted to those tetramer-positive cells. These results show that EBV isolates from NPC of southern China and Taiwan is dominated by an HLA A2-restricted 'epitope-loss variants' of LMP-1, which would allow the virus to resist immune recognition and may in part contribute to the prevalence of NPC in these populations.

A quantitative bioassay for HIV-1 gene expression based on UV activation: effect of glycyrrhizic acid.

Previous reports have shown that HIV-LTRcat constructs stably transfected in HeLa cells are inducible after exposure to UV light. We have optimized this system for studying the effect of drugs on HIV-1 gene expression. The maximum UV response was observed in quiescent stationary cells stimulated with fresh medium for 3h. Glycyrrhizic acid suppressed UV-induced HIV gene expression in a concentration-dependent manner. The inhibitory effect was strongest when GL was added immediately after UV exposure; it was still evident when GL was added at 5 h, it was completely lost at 10 h, after UV exposure. The inhibitory effect was even more pronounced if the cells were pretreated with sub-effective dose (0.0012 mM) of GL prior to UV exposure. The IC50 values with and without pretreatment were 0.04 and 0.38 mM, respectively. Cell proliferation and viability were not affected by GL at doses as high as 2.4 mM. The inhibitory effect of GL on UV-induced CAT activity correlated with the complete inhibition of binding activities of NF-kappaB p65, NF-kappaB p50, c-Fos, and c-Rel. Thus, the UV-based bioassay as proposed here can be exploited for the routine screening of the compounds that interfere with HIV-1 gene expression.