UCLA

Background: Cancer of the head and neck, including oral, laryngeal, and pharyngeal sites, is the sixth most common malignancy in the world. Every year, nearly 650,000 patients worldwide receive the diagnosis of head and neck cancer, and around 350,000 die from this disease [1]. More than 95% of these cancers are head and neck squamous cell carcinoma (HNSCC) in histology [1]. Early detection of the cancer and discovery of new targeted therapies are a few of the main approaches that may be able to increase patient survival rates.

SOX5, or the SRY box 5 protein, is a member of the SOX family of transcription factors and has yet to be fully characterized in oral cancer. In cancer biology, SOX5 has been shown to be involved in epithelial to mesenchymal transition (EMT) in breast cancer, hepatocellular cancer, prostate cancer, lung adenocarcinoma, and osteosarcoma [2-6]. SOX5 has also recently

been linked to nasopharyngeal cancer, but no study to date has described the role of SOX5 in oral cancer [7].

Equally significant in the pathogenesis of HNSCC, overexpression of epithelial growth factor (EGF) and its receptor(EGFR) has been found in roughly 90% of HNSCC tumors [8]. The downstream target effectors of EGFR, including the JAK/STAT pathway, have also been shown to be activated in HNSCC [8, 9]. In particular, STAT3 is known to be constitutively activated in many types of cancers, including HNSCC [8, 10].

Objectives: This study aims to identify the role and regulating mechanisms of SOX5 in oral cancer. Considering the prominence of EGFR and STAT3 in HNSCC, a link between STAT3 and SOX5 could help to elucidate a pathway of activation and regulation. SOX5 has been shown to be a downstream target of STAT3 in murine Th17 cells, but no relationship has yet been defined in cancer.

Methods: Phenotypic studies were conducted in highly invasive oral cancer cell lines (UM1 and UM5) with knockdown of SOX5 and in a low-invasive oral cancer cell line (UM2) with SOX5 upregulation. MTT, migration, and invasion assays were utilized to assess phenotype, and Western blotting and qPCR were used to quantify protein and gene expression levels. Chromatin immunoprecipitation (ChIP) followed by qPCR was used to examine if STAT3 binds to the promoter of SOX5.

Results: Endogenous SOX5 is up-regulated in UM1 and UM5 cells, when compared to UM2and UM6 cells, respectively (p<0.05). Knockdown of SOX5 in UM1 and UM5 cells shows decreased proliferation, migration, and invasion potential. When treated with EGF, expression of SOX5 increased in all cell lines, and UM2 showed an increased ability to migrate and invade. ChIP

assay results indicate that STAT3 binds to the promoter region of SOX5 in both UM1 and UM5 cells.

Conclusions: This study has demonstrated that SOX5 may play an important role in head and neck cancer progression by promoting cancer cell growth, migration, and invasion. EGF induces the expression of SOX5 in head and neck cancer cells via the regulation of STAT3 and enhances cancer cell migration and invasion. These findings suggest that EGF-STAT3-SOX5 axis is an important regulatory pathway in head and neck cancer progression.