Human antigen R knockdown attenuates the invasive activity of oral cancer cells through inactivation of matrix metalloproteinase-1 gene expression

Background/purpose: The RNA-binding protein human antigen R (HuR) recognizes AU-rich elements in the 3′-untranslated regions of mRNA. The expression of cytoplasmic HuR is related to the malignancy of many carcinomas. The aim of this study is investigation of effect of HuR knockdown for invasive activity of oral carcinoma. Materials and methods: Proliferation, invasion, real-time PCR, and reporter gene assays were performed to confirm that the knockdown of HuR downregulates the invasive activity of cancer cells. Immunohistochemical staining was performed for high invasive carcinoma, squamous cell carcinoma (SCC) and low invasive carcinoma, verrucous carcinoma (VC), to determine if the localization of cytoplasmic HuR is related to matrix metalloproteinase-1 (MMP-1) expression. Results: Invasive activity was significantly lower in HuR knockdown cancer cells than in control cells. A luciferase assay revealed that HuR knockdown inactivated the promoter activity of the MMP-1 gene. The mRNA levels of the transcription factors required for MMP-1 expression, including c-fos and c-jun, were decreased in HuR knockdown cancer cells. Immunohistochemical analysis revealed the level of cytoplasmic HuR and MMP-1 in invasive carcinoma to be higher than in low invasive cancer. HuR induced MMP-1 expression in the invasive front of most SCC cases. Conclusion: HuR knockdown attenuated the invasive activity of cancer cells by decreasing the expression of the MMP-1, at least partially. HuR localization may help determine the invasive phenotype of cancer cells and inhibit cancer cell invasion. Furthermore, in oral SCC, HuR may be related to invasive activity through the expression of MMP-1.