MMP9 and cancer: K8/18 depletion leads to hyperactivation of the PI3K/AKT/ nuclear factor kappa B (NF-κB) pathway and increased expression of matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9), which prompts the tight junction protein claudin-1 to assume an active role in cancer progression [84].