[When p19ARF finds a partner or new "dangerous liaisons"].

In man, the MTS1 (multiple tumor suppressor 1) locus has been located on chromosome band 9p21 and encodes two unrelated genes, p16INK4a and p19ARF that both act, through different mechanisms, as cell proliferation inhibitors. The inhibitory mechanism of p19ARF has begun to be elucidated by the finding that the protein has the ability to bind the mdm2 oncoprotein. mdm2 is implicated in the degradation of p53 and its functional inactivation. While this result provides an opportunity for understanding the tumor suppression role of p19ARF, it allows to define a new cell cycle regulatory pathway, the p19ARF-p53 pathway. In this respect, MTS1 is unique in its ability to control two crucial pathways that regulate the cell cycle. For this reason, it will be crucial to investigate the status of p19ARF in a variety human tumors.