Negative regulation of Par-4 by oncogenic Ras is essential for cellular transformation

Oncogenic variants of the cellular Ras protein are often associated with di fferent types of human cancers. However, the mechanisms by which oncogenic Ras induces transformation are not fully established. Expression of the tra nscriptional repressor Par-4 was downregulated by oncogenic Ras via the Raf -MEK-ERK pathway. Restoration of Par-4 levels by abrogation of the Raf-MEK- ERK pathway with the MEK-inhibitor PD98059 or by ectopic Par-4, that acted to inhibit ERK expression and activation, was sufficient to suppress oncoge nic Ras-induced transformation. These findings identify Par-4 as a novel ta rget that has to be downmodulated by oncogenic Ras for successful transform ation.