p53, apoptosis and axon-guidance molecules.

The p53 tumor-suppressor gene regulates apoptosis through the transcriptional activation of its target genes. The expression of the axon-guidance molecule UNC5B (also designated p53RDL1), which is a receptor for netrin-1, is directly regulated by p53. In the absence of netrin-1, UNC5B mediates p53-dependent apoptosis. Conversely, in the presence of netrin-1, p53-induced apoptosis is inhibited through the signaling pathway activated by the interaction between netrin-1 and UNC5B. A number of other molecules that are involved in axon guidance are inactivated in human cancers and are also regulated by p53. These findings suggest a close link between axon-guidance molecules and tumorigenesis.