The p75 and its carboxyl-terminal fragment exert opposing effects on melanoma cell proliferation and apoptosis via modulation of the NF-κB pathway.

The p75 neurotrophin receptor (p75 ), a member of the tumor necrosis factor superfamily of receptors, is sensitive to proteolysis and has been observed to be expressed in various cancers. However, the roles of p75 and its proteolytic fragments in tumorigenesis remain incompletely understood. Here, we report that the proportion of the p75 carboxyl-terminal fragment (p75 -CTF) is much higher than that of the full-length p75 (p75 -FL) in melanoma cells. Whereas p75 -FL positively regulates apoptosis, p75 -CTF promotes cell proliferation and survival, as well as increasing sorafenib resistance in vivo and in vitro. Moreover, p75 -CTF activates the nuclear factor kappa B pathway and enhances the mRNA and protein levels of its downstream genes c-IAP1/2, FLIP, bFGF, IL8 and VEGF. On the contrary, p75 -FL inhibits these processes. Taken together, these findings demonstrate that p75 -CTF and p75 -FL have opposing functions in melanoma cells, suggesting that the ratio of the two proteins affects the balance between cell death and survival. The presence of distinct p75 proteolytic fragments may affect biological outcomes in tumor cells.