title: Up-Regulation of LAT1 during Antiandrogen Therapy Contributes to Progression in Prostate Cancer Cells.
abstract: OBJECTIVE
  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.
  
  
  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.affiliation: Department of Urology, Chiba University Graduate School of Medicine, Chiba, Japan.
authors.forename: Minhui
authors.initials: M
authors.lastname: Xu
authors.affiliation: Department of Urology, Chiba University Graduate School of Medicine, Chiba, Japan. Electronic address: rbatbat1@yahoo.co.jp.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Sakamoto
authors.affiliation: Department of Diagnostic Pathology, Chiba University Graduate School of Medicine, Chiba, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Matsushima
authors.affiliation: Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Kimura
authors.affiliation: Prostate Center and Division of Urology, Chiba Cancer Center, Chiba, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ueda
authors.affiliation: Department of Integrative Cancer Therapy and Urology, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Mizokami
authors.affiliation: Division of Bio-system Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Kanai
authors.affiliation: Department of Urology, Chiba University Graduate School of Medicine, Chiba, Japan.
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ichikawa
mesh_terms: D000368:Aged; D000726:Androgen Antagonists / Q000627:therapeutic use; D000813:Anilides / Q000627:therapeutic use*; D001706:Biopsy; D015153:Blotting, Western; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D018450:Disease Progression; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D027283:Large Neutral Amino Acid-Transporter 1 / Q000096:biosynthesis / Q000235:genetics*; D008297:Male; D009570:Nitriles / Q000627:therapeutic use*; D011467:Prostate / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D014105:Tosyl Compounds / Q000627:therapeutic use*; D015854:Up-Regulation / Q000187:drug effects*
chemical_list: D000726:Androgen Antagonists; D000813:Anilides; D027283:Large Neutral Amino Acid-Transporter 1; D009570:Nitriles; D012334:RNA, Neoplasm; D014105:Tosyl Compounds; C053541:bicalutamide
keywords: androgen antagonists; castration; large neutral amino acid-transporter 1; prostatic neoplasms; treatment failure