MMP9 and cancer: The recent studies on Slug knockdown in cancer cells identified the cancer-related target genes of slug; for example, Slug knockdown downregulated the expression of miR221, chemokine (C-X-C motif) receptor 4, and matrix metallopeptidase 9, and upregulated the expression of plakoglobin and ubiquitin-conjugating enzyme E2D3 34–37.