S100A4 and cancer: In the case of MMP9, several studies in different types of cancer report either an increase in MMP9 activity with elevated S100A4 expression levels or a decrease of MMP9 expression with a knock-down of S100A4 [15],[41-44] One possible mechanism, which is discussed for the S100A4 dependent MMP9 regulation, is the direct or indirect activation of p53 or JNK, since S100A4 is a binding partner of p53 and can modulate its activity [45],[46].