Chromatin immunoprecipitation (ChIP) assay confirmed a higher binding affinity of FOXK1 for the consensus motif within the MMP9 promoter in melanoma cells compared with IgG control, whereas it did not bind to another DNA fragment without the motif (Fig. 5e and Supplementary Fig. 7e), indicating the specificity of the binding. Here, MMP9 is linked to melanoma.