15">Western blot and real-time polymerase chain reaction were performed to study protein and mRNA expression. siRNA was used to knock down target genes. A total of 92 prostate biopsy specimens of patients who underwent androgen deprivation therapy were used for immunohistochemical analyses. Cox hazard proportional models and the Kaplan-Meier method were used for statistical analyses.
LAT1 was highly expressed in hormone resistant prostate cancer cell lines. Knockdown of LAT1 in LNCaP and C4-2 cells significantly suppressed cell proliferation, migration and invasion. Androgen receptor siRNA or androgen receptor blocking through bicalutamide (10 μM) or MDV3100 (10 μM) significantly increased LAT1 expression (p <0.01). Treatment with dihydrotestosterone (0.1 to 10 nM) reduced LAT1 expression in a dose dependent manner (p <0.01). Bicalutamide/MDV3100 plus siLAT1 synergistically suppressed prostate cancer cell proliferation compared to single inhibition by androgen receptor or LAT1 (p <0.01). High LAT1 expression correlated with significantly shorter prostate specific antigen recurrence-free survival in patients receiving androgen deprivation therapy (p <0.0001). LAT1 expression was an independent predictor of castration resistance on multivariate analysis (HR 3.56, p = 0.0133).
The current data may indicate a novel mechanism to acquire castration resistance through activation of the amino acid transporter LAT1.