title: Benzyl isothiocyanate induces protective autophagy in human prostate cancer cells via inhibition of mTOR signaling.
abstract: Benzyl isothiocyanate (BITC) is a dietary chemopreventive agent that inhibits the growth of various human cancer cells by causing apoptotic cell death. In this study, we demonstrate that BITC not only induces apoptosis but also induces autophagy in human hormone-sensitive (Rv1) and -refractory (PC3) prostate cancer cells. In BITC-treated cells, the induction of autophagy was detected by monitoring the processing of an autophagy marker protein, microtubule-associated protein 1 light chain 3 (LC3), the aggregation of LC3 into granular structures and the formation of acidic organelles. Inhibition of autophagy using 3-methyladenine increased BITC-induced apoptosis, whereas the administration of caspase inhibitor suppressed BITC-induced cell death. Our data also showed that BITC inhibits mammalian target of rapamycin (mTOR) kinase activity in a dose-dependent manner. The expression of phospho-mTOR (Ser2481), an indicator of mTOR intrinsic catalytic activity, and phospho-UNC-51-like kinase 1 (Ser757), a direct substrate of mTOR, were decreased in BITC-treated cells. However, the increased expression of phospho-mTOR (Ser2448), phospho-AKT (Ser473) and antiapoptotic Bcl-2 were detected only in PC3 cells at later stages of BITC treatment. Collectively, our results show that BITC induces a protective autophagy response in Rv1 and PC3 cells through inhibition of the mTOR signaling pathway. Activation of the AKT survival pathway was only observed in PC3 cells, representing a resistance mechanism of advanced prostate cancer upon BITC treatment. These findings could potentially contribute to the beneficial effect of BITC in prostate cancer treatments.
authors.affiliation: Central Laboratory, Shin-Kong Wu Ho-Su Memorial Hospital,   Taipei 111, Taiwan.
authors.forename: Ji-Fan
authors.initials: JF
authors.lastname: Lin
authors.forename: Te-Fu
authors.initials: TF
authors.lastname: Tsai
authors.forename: Po-Cheng
authors.initials: PC
authors.lastname: Liao
authors.forename: Yi-Hsuan
authors.initials: YH
authors.lastname: Lin
authors.forename: Yi-Chia
authors.initials: YC
authors.lastname: Lin
authors.forename: Hung-En
authors.initials: HE
authors.lastname: Chen
authors.forename: Kuang-Yu
authors.initials: KY
authors.lastname: Chou
authors.forename: Thomas I-Sheng
authors.initials: TI
authors.lastname: Hwang
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects; D005434:Flow Cytometry; D006801:Humans; D017879:Isothiocyanates / Q000494:pharmacology*; D008297:Male; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D017879:Isothiocyanates; C031403:benzyl isothiocyanate; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases