Background: Oral cancer has been estimated as the sixth most frequent solid cancer all over the world, in which tongue squamous cell carcinoma (TSCC) is the most common type of oral cancers. However, the mechanism of TSCC metastasizing to lymph node and distant sites has not been completely understood.
Methods: In this study, RT-qPCR method was used to detect the mRNA level of Numb, PTEN and Notch1 genes, as well as EMT-associated genes. Western blot assay was utilized to detect protein level of these genes. In addition, we determined cell proliferation by MTT assay and employed transwell invasion assay and wound healing assay to probe the abilities of invasion and migration, respectively. To investigate the role of PTEN, its inhibitor VO-Ohpic trihydrate was used to treat SCC-4 and CAL27 cells.
Results: We found that Numb expression was downregulated in SCC-9 and CAL-27 cells compared to NHOK cells. Instead, Notch1 level in SCC-9 and CAL-27 cells were higher than that in NHOK cells. Furthermore, the results showed that Numb overexpression significantly suppressed proliferation, migration and invasion of SCC-9 and CAL-27 cells via regulating Notch1 signaling and EMT-related genes expression. By contrast, we observed that RBP-Jκ knockdown had an inhibitory role in proliferation, migration and invasion of SCC-9 and CAL-27 cells. In cells with Numb overexpression or RBP-Jκ knockdown, p-FAK and EMT-related genes were remarkably regulated.
Conclusions: Our findings provide new mechanism of understanding the metastasis of TSCC and help develop therapeutic strategies for treating tongue cancer.
Keywords: Epithelial-mesenchymal transition (EMT); Notch1 signaling; Numb; PTEN; Tongue squamous cell carcinoma (TSCC).