Identification of CAD as an androgen receptor interactant and an early marker of prostate tumor recurrence

Markers of prostate tumor recurrence after radical prostatectomy are lacking and highly demanded. The androgen receptor (AR) is a nuclear receptor that plays a pivotal role in normal and cancerous prostate tissue. AR interacts with a number of proteins modulating its stability, localization, and activity. To test the hypothesis that an increased expression of AR partners might foster tumor development, we immunopurified AR partners in human tumors xenografted into mice. One of the identified AR partners was the multifunctional enzyme carbamoyl-phosphate synthetase II, aspartate transcarbamylase, and dihydroorotase (CAD), which catalyzes the 3 initial steps of pyrimidine biosynthesis. We combined experiments in C4-2, LNCaP, 22RV1, and PC3 human prostate cell lines and analysis of frozen radical prostatectomy samples to study the CAD-AR interaction. We show here that in prostate tumor cells, CAD fosters AR translocation into the nucleus and stimulates its transcriptional activity. Notably, in radical prostatectomy specimens, CAD expression was not correlated with proliferation markers, but a higher CAD mRNA level was associated with local tumor extension (P=0.049) and cancer relapse (P=0.017). These results demonstrate an unsuspected function for a key metabolic enzyme and identify CAD as a potential predictive marker of cancer relapse.