BackgroundThe high frequencies of recurrence and distant metastasis of adenoid cystic carcinoma (AdCC) emphasize the need to better understand the biological factors associated with these outcomes. To analyze the mechanisms of AdCC metastasis, we established the green fluorescence protein (GFP)-transfected subline ACCS-GFP from the AdCC parental cell line and the metastatic ACCS-M GFP line from an in vivo metastasis model.MethodsUsing these cell lines, we investigated the involvement of the epithelial–mesenchymal transition (EMT) and cancer stem cell (CSCs) in AdCC metastasis by real-time RT-PCR for EMT related genes and stem cell markers. Characteristics of CSCs were also analyzed by sphere-forming ability and tumorigenicity. Short hairpin RNA (shRNA) silencing of target gene was also performed.ResultsACCS-M GFP demonstrated characteristics of EMT and additionally displayed sphere-forming ability and high expression of EMT-related genes (Snail, Twist1, Twist2, Slug, zinc finger E-box binding homeobox 1 and 2 [Zeb1 and Zeb2], glycogen synthase kinase 3 beta [Gsk3β and transforming growth factor beta 2 [Tgf-β2]), stem cell markers (Nodal, Lefty, Oct-4, Pax6, Rex1, and Nanog), and differentiation markers (sex determining region Y [Sox2], Brachyury, and alpha fetoprotein [Afp]). These observations suggest that ACCS-M GFP shows the characteristics of CSCs and CSCs may be involved in the EMT of AdCC. Surprisingly, shRNA silencing of the T-box transcription factor Brachyury (also a differentiation marker) resulted in downregulation of the EMT and stem cell markers. In addition, sphere-forming ability, EMT characteristics, and tumorigenicity were simultaneously lost. Brachyury expression in clinical samples of AdCC was extremely high and closely related to EMT. This finding suggests that regulation of EMT by Brachyury in clinical AdCC may parallel that observed in vitro in this study.ConclusionsThe use of a single cell line is a limitation of this study. However, parallel data from in vitro and clinical samples suggest the possibility that EMT is directly linked to CSCs and that Brachyury is a regulator of EMT and CSCs.

Abstract. The prognosis of oral squamous cell carcinoma (OSCC) patients is affected by tumor recurrence and metastasis, and cancer stem cells are hypothesized to be involved in these processes. Thus, the aim of the present study was to determine whether the expression levels of five stem cell-related transcription factors, sex determining region Y-box 2 (SOX2), octamer-binding transcription factor 4 (Oct4), avian myelocytomatosis viral oncogene homolog (c-Myc), Krüppel-like factor 4 (KLF4) and brachyury, are associated with metastasis and survival in OSCC. Immunohistochemistry was performed to analyze the expression of these proteins in biopsy specimens obtained from 108 OSCC patients. The results revealed that the expression of SOX2, Oct4, KLF4 and brachyury were significantly associated with lymph node metastasis (P=0.002, P=0.031, P=0.003 and P=0.007, respectively). In addition, the expression of KLF4 and brachyury were significantly associated with distant metastasis (P=0.014 and P=0.012, respectively). Furthermore, multivariate analysis revealed that SOX2 and KLF4 are predictive factors for lymph node metastasis [odds ratios (ORs), 4.526 and 4.851, respectively], and KLF4 is also a predictive factor for distant metastasis (OR, 9.607). In addition, OSCC patients with low co-expression of SOX2, KLF4 and brachyury exhibited a significantly lower disease-specific survival rate (78.6 vs. 100%; P=0.025; χ 2 =5.033) and disease-free survival rate (60.7 vs. 90.9%; P=0.015; χ 2 =5.897) when compared with OSCC patients with high co-expression of these factors. The results indicate that SOX2, KLF4 and brachyury serve important roles in tumor progression, and these transcription factors may thus represent clinically useful prognostic markers for OSCC.

We have recently unravelled a novel function for CD82 in E-cadherin-mediated cellular adhesion. CD82 inhibits β-catenin tyrosine phosphorylation and stabilizes E-cadherin-β-catenin complexes at the cell membrane. This function inhibits cancer cell dissociation from the primary cancer nest and limits metastasis. In this study, we focused on the effect of CD82 on the Wnt/β-catenin (canonical) pathway, which controls the cellular distribution of β-catenin. CD82 had no effect on the expression of Wnt proteins but led to significant downregulation of Frizzled (Fzd) 2, 3, 5, 7 and 9, suggesting downregulation of the Wnt/β-catenin pathway. CD82 also inhibited phosphorylation of β-catenin at Ser45, Ser33, Ser37 and Thr41 by downregulation of glycogen synthase kinase-3β (GSK-3β) and kinase casein kinase 1α (CK1α). Downregulation of GSK-3β and CK1α also led to accumulation of β-catenin in the cytoplasm or at the cell membrane. CD82 translocated β-catenin to the cell membrane, suggesting that CD82 strengthens the interaction between E-cadherin and β-catenin. We concluded that CD82 attenuates Wnt signalling by controlling β-catenin cellular distribution at multiple levels: i) inhibition of β-catenin nuclear translocation by downregulation of Fzd receptor proteins; ii) accumulation of β-catenin at the cell membrane by downregulation of GSK-3β and CK1α; and iii) stabilization of the E-cadherin-β-catenin complex.

CD82/KAI1, a member of the tetraspanin superfamily, is a suppressor of metastasis and CD82 inhibits canonical Wnt signaling via downregulation of several Frizzled (FZD) isoforms, resulting in accumulation of β-catenin at the cell membrane. In this study, we investigated the mechanism through which CD82 inhibited FZD expression by examining the effects of microRNAs (miRNAs). The miRanda algorithm predicted 11 miRNAs from FZD sequences. Among these miRNAs, CD82 caused upregulation of miR-203 (by 2.095-fold) and downregulation of miR-338-3p (by 0.354-fold) as compared with control cells. Transfection with miR-203 and miR338-3p mimics or inhibitors revealed that miR-203 downregulated FZD2 mRNA (by 0.268-fold) and protein expression (by 0.701-fold). Moreover, transfection with the miR-203 mimic also inhibited cell migration. Therefore, these findings suggested that CD82 enhanced the expression of miR-203 and directly downregulate FZD2 expression, suppressing cancer metastasis by inhibition of the Wnt signaling pathway.

We have recently elucidated a novel function for CD82 in E-cadherin-mediated homocellular adhesion; due to this function, it can inhibit cancer cell dissociation from the primary cancer nest and limit metastasis. However, the effect of CD82 on selectin ligand-mediated heterocellular adhesion has not yet been elucidated. In this study, we focused on the effects of the metastasis suppressor CD82/KAI1 on heterocellular adhesion of cancer cells to the endothelium of blood vessels in order to further elucidate the function of tetraspanins. The over-expression of CD82 in cancer cells led to the inhibition of experimentally induced lung metastases in mice and significantly inhibited the adhesion of these cells to human umbilical vein epithelial cells (HUVECs) in vitro. Pre-treatment of the cells with function-perturbing antibodies against sLea/x significantly inhibited the adhesion of CD82-negative cells to HUVECs. In addition, cells over-expressing CD82 exhibited reduced expression of sLea/x compared to CD82-negative wild-type cells. Significant down-regulation of ST3 β-galactoside α-2, 3-sialyltransferase 4 (ST3GAL4) was detected by cDNA microarray, real-time PCR, and western blotting analyses. Knockdown of ST3GAL4 on CD82-negative wild-type cells inhibited expression of sLex and reduced cell adhesion to HUVECs. We concluded that CD82 decreases sLea/x expression via the down-regulation of ST3GAL4 expression and thereby reduces the adhesion of cancer cells to blood vessels, which results in inhibition of metastasis.