α-Catulin marks the invasion front of squamous cell carcinoma and is important for tumor cell metastasis

Squamous cell carcinomas (SCC) comprise the most common types of human epithelial cancers. One subtype, head and neck squamous cell carcinoma (HNSCC), is a particularly aggressive cancer with poor prognosis due to late diagnosis and lymph node metastasis. Of all the processes involved in carcinogenesis, local invasion and distant metastasis are clinically the most relevant, but are the least well understood on a molecular level. Here, we find that in vivo, the α-catenin homologue-α-catulin, a protein originally reported to interact with Lbc Rho guanine nucleotide exchange factor, is highly expressed at the tumor invasion front and in the metastatic streams of cells in both malignant hHNSCCs and a mouse model of oral SCC. Knockdown of α-catulin in hHNSCC cell lines dramatically decrease the migratory and invasive potential of those cells in vitro and metastatic potential in xenotransplants in vivo. Analysis of tumors deficient in α-catulin showed that the tumor cells are unable to invade the surrounding stroma. Accordingly, transcriptional profiling of those tumors revealed that α-catulin ablation is accompanied by changes in genes involved in cell migration and invasion. Interestingly enough, in vitro experiments show that an upregulation of α-catulin expression correlates with the transition of tumor cells from an epithelial to a mesenchymal morphology, as well as an upregulation of epithelial-to-mesenchymal transition (EMT) markers vimentin and snail. Overall, these results strongly indicate that α-catulin contributes to the invasive behavior of metastatic cells and may be used as a prognostic marker and future therapeutic target for patients with cancer.