Introduction Biomarkers that predict disease progression might assist the development of better therapeutic strategies for aggressive cancers, such as ovarian cancer. Here, we investigated the role of collagen type IV alpha 6 (COL4A6) in cell invasiveness and tumor formation and the prognostic impact of COL4A6 expression in ovarian cancer.

Methods A2780CP70 and OVCAR8 cells transfected with a small interference RNA of COL4A6 (shCOL4A6) and A2780 and OVCAR4 cells transfected with a COL4A6 expression plasmid. Site-directed mutagenesis assay, luciferase assay, chromatin immunoprecipitation assay, invasion assay and xenograft animal study were performed in this study. COL4A6 mRNA expression levels of 160 ovarian tumors were determined by real-time RT-PCR.

Results Small interference RNA-mediated specific reduction in COL4A6 protein levels suppressed the invasive ability and oncogenic potential of ovarian cancer cells and decreased tumor formation. A combination of experimental approaches, including real-time RT-PCR, casein zymography and chromatin immunoprecipitation assays, showed that COL4A6 knockdown attenuated discoidin domain receptors/p-DDR1 expression and suppressed binding of E2F to its putative DDR1 promoter binding site, suggesting that the E2F-DDR1 axis is upregulated by COL4A6. Pharmacological inhibition of DDR1 abrogated the COL4A6-dependent cell invasiveness. Analysis of 160 ovarian cancer patients indicated that high COL4A6 mRNA levels are associated with advanced disease stage. The 5-year recurrence-free and overall survival rates were significantly lower (p=0.001 and p=0.001, respectively) among patients with high expression levels of tissue COL4A6 mRNA compared to those with low expression.

Conclusion/Implications COL4A6 may promote tumor aggressiveness via the E2F/DDR1 axis and that COL4A6 expression can predict clinical outcome in ovarian cancer patients.