Minhui Xu1, Shinichi Sakamoto2, Jun Matsushima3, Toru Kimura4, Takeshi Ueda5, Atsushi Mizokami6, Yoshikatsu Kanai7, Tomohiko Ichikawa1. 1. Department of Urology, Chiba University Graduate School of Medicine, Chiba, Japan. 2. Department of Urology, Chiba University Graduate School of Medicine, Chiba, Japan. Electronic address: rbatbat1@yahoo.co.jp. 3. Department of Diagnostic Pathology, Chiba University Graduate School of Medicine, Chiba, Japan. 4. Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Tokyo, Japan. 5. Prostate Center and Division of Urology, Chiba Cancer Center, Chiba, Japan. 6. Department of Integrative Cancer Therapy and Urology, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan. 7. Division of Bio-system Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan.
Abstract
PURPOSE: Cancer cells require massive amounts of amino acids for survival. LAT1 (L-type amino acid transporter 1) transports essential amino acids, including leucine, which trigger the downstream mTOR (mammalian target of rapamycin) pathway. We examined the association between androgen receptor and LAT1, and the association between LAT1 expression and the acquisition of castration resistance. MATERIALS AND METHODS: 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. RESULTS: 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). CONCLUSIONS: The current data may indicate a novel mechanism to acquire castration resistance through activation of the amino acid transporter LAT1.
PURPOSE: Cancer cells require massive amounts of amino acids for survival. LAT1 (L-type amino acid transporter 1) transports essential amino acids, including leucine, which trigger the downstream mTOR (mammalian target of rapamycin) pathway. We examined the association between androgen receptor and LAT1, and the association between LAT1 expression and the acquisition of castration resistance. MATERIALS AND METHODS: 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. RESULTS: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). CONCLUSIONS: The current data may indicate a novel mechanism to acquire castration resistance through activation of the amino acid transporter LAT1.
Authors: Alicia-Marie K Beier; Martin Puhr; Matthias B Stope; Christian Thomas; Holger H H Erb Journal: J Cancer Res Clin Oncol Date: 2022-09-23 Impact factor: 4.322