Sprouty4 is required for Mdm2 regulation of invasion, focal adhesion formation and metastasis in cells lacking p53.

Although the E3 ligase Mdm2 and its homologue and binding partner MdmX are the major regulators of the p53 tumor suppressor protein, it is now evident that Mdm2 and MdmX have multiple functions that are independent of p53. For example, Mdm2 can regulate cell migration, although mechanistic insight into this function is still lacking. Here we show in cells lacking p53 expression that knockdown of Mdm2 or MdmX, as well as pharmacological inhibition of the Mdm2/MdmX complex, not only reduces cell migration and invasion, but also impairs cell spreading and focal adhesion formation. In addition, Mdm2 knockdown decreases metastasis in vivo. Remarkably, Mdm2 modulates the expression of Sprouty4, which is required for the Mdm2 mediated effects on cell migration, focal adhesion formation and metastasis. Our findings describe a molecular mechanism by which the Mdm2-X complex, through Sprouty4, regulates cellular processes leading to decreased metastatic capability independent of p53.