Phosphorylation status of Fas-associated death domain-containing protein (FADD) is associated with prostate cancer progression.

It has recently been demonstrated that phosphorylation of FADD at serine 194 plays an important role in the induction of apoptosis by anti-cancer drugs in human prostate cancer cells. The present study has assessed whether this phosphorylation status is valuable as a marker for human prostate cancer progression, and has investigated its biological role in cell growth. Immunohistochemical studies revealed much higher phosphorylation of FADD at serine 194 in normal epithelial cells than in cancer cells, although FADD was found to be highly expressed to the same extent in both cases. The positivity for phosphorylated FADD was significantly lower for patients with a Gleason score greater than or equal to 7, a positive surgical margin, extracapsular or seminal vesicle invasion. In addition, a relationship was also apparent in cancer cells refractory to neoadjuvant hormonal therapy. Interestingly, in Gleason score 3 + 4 tumours, the positivity for FADD phosphorylation was statistically increased by neoadjuvant hormonal therapy, resulting in a reduced percentage of cases with a positive surgical margin and extracapsular invasion. In vitro data showed different functions of phosphorylated and non-phosphorylated FADD: in normal epithelial cells, overexpression of a phosphorylation-mimicking mutant FADD (S194E) caused G2/M cell-cycle arrest, while a non-phosphorylation-mimicking mutant (S194A) had no effect, whereas S194A overexpression resulted in cell cycle progression and enhanced colony-forming activity in cancer cells, but S194E FADD was without influence. These results clearly demonstrate that transition from phosphorylated FADD to the non-phosphorylated form might be associated with carcinogenesis and that induction of FADD phosphorylation could therefore be a target for chemohormonal therapy of human prostate cancer. Moreover, assessment of FADD phosphorylation may be useful as a new biomarker to predict cancer progression.