Inactivating mutations in the EGF-like ligand binding domain of NOTCH1 are a prominent feature of the mutational landscape of oral squamous cell carcinoma (OSCC). In this study, we investigated NOTCH1 mutations in keratinocyte lines derived from OSCC biopsies that had been subjected to whole exome sequencing. One line, SJG6, was found to have truncating mutations in both NOTCH1 alleles, resulting in loss of NOTCH1 expression. Overexpression of the NOTCH1 intracellular domain (NICD) in SJG6 cells promoted cell adhesion and differentiation, while suppressing proliferation, migration and clonal growth, consistent with the previously reported tumour suppressive function of NOTCH1 in OSCC. Comparative gene expression profiling identified SERPINE1 as being downregulated on NICD overexpression and predicted an interaction between SERPINE1 and genes involved in cell proliferation and migration. Mechanistically, overexpression of NICD resulted in upregulation of ETV7/TEL2, which negatively regulates SERPINE1 expression. Knockdown of SERPINE1 phenocopied the effects of NICD overexpression in culture. Consistent with previous studies and our in vitro findings, there were inverse correlations between ETV7 and SERPINE1 expression and survival in OSCC primary tumours. Our results suggest that the tumour suppressive role of NOTCH1 in OSCC is mediated, at least in part, by inhibition of SERPINE1 via ETV7.
Keywords: ETV7/TEL2; NOTCH1; SERPINE1; cell adhesion; oral squamous cell carcinoma (OSCC).