MMP9 and cancer: Intriguingly, we have reported that SKIP is necessary for the expression of the urokinase type plasminogen activator, uPA, a key proteinase involved in cancer cell invasion and metastasis [24], but conversely to MMP-9, SKIP depletion decreased the induction of uPA by TGF-β1, which suggested a differential involvement of SKIP in TGF-β-induced cancer proteinases.