title: Targeting the Vav3 oncogene enhances docetaxel-induced apoptosis through the inhibition of androgen receptor phosphorylation in LNCaP prostate cancer cells under chronic hypoxia.
abstract: BACKGROUND
  The Vav family of Rho/Rac guanosine nucleotide exchange factors comprises three members in mammalian cells. Vav3 enhances androgen receptor (AR) activity during progression to androgen independence in prostate cancer. We examined Vav3 small interfering RNA (siRNA) effects on cell proliferation and apoptosis in docetaxel-treated LNCaP cells under chronic hypoxia (LNCaPH).
  
  
  METHODS
  We examined individual and combined effects of Vav3 siRNA (si-Vav3) and docetaxel on cell growth and apoptosis under chronic hypoxia by cell proliferation, flow cytometric, DNA fragmentation, and immunoblot analyses. To clarify the molecular basis of si-Vav3- and docetaxel-induced apoptosis, we analyzed alterations in phosphatidylinositol 3-kinase (PI3K)/Akt, extracellular signal-regulate kinase (ERK), c-jun N-terminal kinase (JNK), and AR pathways using kinase inhibitors in LNCaPH cells. The effects of si-Vav3/atelocollagen complex alone or in combination with docetaxel were assessed on xenografts in nude mice by tumor growth delay.
  
  
  RESULTS
  Vav3 overexpression was observed in LNCaPH compared with the expression under normoxia. Interrupting Vav3 signaling using siRNA enhanced docetaxel-induced cell growth suppression compared with that induced by docetaxel alone by inhibition of Akt and ERK phosphorylation, resulting in AR phosphorylation inhibition. In addition to increased B-cell lymphoma 2 (Bcl-2) phosphorylation through JNK signaling in response to docetaxel, si-Vav3 enhanced docetaxel-induced apoptosis, as characterized by the accumulation of sub-G1 phase cells and DNA fragmentation, through Bcl-xL/Bcl-2-associated death promoter (Bad) dephosphorylation, resulting in increased caspase-9, caspase-3, and cleaved poly(ADP-ribose) polymerase activation. Xenograft tumor growth was slightly inhibited by si-Vav3/atelocollagen complex injection and combined use of si-Vav3/atelocollagen complex and docetaxel produced a greater effect than docetaxel alone.
  
  
  CONCLUSIONS
  Interrupting Vav3 signaling enhances docetaxel-induced apoptosis in LNCaP cells under chronic hypoxia by inhibiting the PI3K/Akt, ERK, and AR signaling pathways. Therapy targeting Vav3 in combination with docetaxel may have practical implications for managing castration-resistant prostate cancer.
authors.affiliation: Department of Urology, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama-machi, Yufu, Oita 879-5593, Japan. TAKE@oita-u.ac.jp
authors.forename: Takeo
authors.initials: T
authors.lastname: Nomura
authors.forename: Mutsushi
authors.initials: M
authors.lastname: Yamasaki
authors.forename: Kenichi
authors.initials: K
authors.lastname: Hirai
authors.forename: Toru
authors.initials: T
authors.lastname: Inoue
authors.forename: Ryuta
authors.initials: R
authors.lastname: Sato
authors.forename: Keiko
authors.initials: K
authors.lastname: Matsuura
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Moriyama
authors.forename: Fuminori
authors.initials: F
authors.lastname: Sato
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Mimata
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D000077143:Docetaxel; D015870:Gene Expression; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051567:Proto-Oncogene Proteins c-vav / Q000235:genetics*; D034622:RNA Interference; D011944:Receptors, Androgen / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D043823:Taxoids / Q000494:pharmacology*; D047368:Tumor Burden / Q000187:drug effects / Q000235:genetics
chemical_list: D000970:Antineoplastic Agents; D051567:Proto-Oncogene Proteins c-vav; D011944:Receptors, Androgen; D043823:Taxoids; C496621:VAV3 protein, human; D000077143:Docetaxel; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt