title: RalBP1 is necessary for metastasis of human cancer cell lines.
abstract: RalA expression in human prostate cancer is associated with cell migration and is necessary for bone metastasis. However, the downstream effectors of RalA that mediate these functions remain unclear. Here we examined cell migration after small interfering RNA-mediated depletion of Ral effectors Ral binding protein 1 (RalBP1/RLIP), exocyst complex component 2 (Sec5), and phospholipase D1 (PLD1) and found that RalBP1 and RalA depletion inhibited cell migration to a similar extent. Stable lentivirus short hairpin interfering RNA-mediated depletion of RalA and RalBP1 in PC3 human prostate cancer cells inhibited bone metastasis after intracardiac inoculation. Depletion of RalBP1 diminished orthotopic tumor growth of PC3 cells and inhibited spontaneous metastasis from this site. Interestingly, the expression of wild-type or RalA mutants deficient in RalBP1 binding was effective at rescuing the reduced metastatic capacity of RalA-depleted PC3 cells, suggesting that RalA depletion does not reduce this solely by diminished interaction with RalBP1. To determine whether the role of RalBP1 in metastasis is relevant beyond prostate cancer, we studied the requirement of RalBP1 expression in an experimental metastasis model of human bladder cancer, a tumor type with high RalBP1 expression. Depletion of RalBP1 in UMUC3 cells resulted in decreased lung colonization while having a minimal effect on subcutaneous tumor growth. Our studies are the first to suggest that the expression of RalBP1 is necessary for human cancer cell metastasis. Furthermore, we show that the requirement for RalA expression for manifestation of this phenotype is not entirely dependent on a RalA-RalBP1 interaction.
authors.affiliation: Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Wu
authors.forename: Charles
authors.initials: C
authors.lastname: Owens
authors.forename: Nidhi
authors.initials: N
authors.lastname: Chandra
authors.forename: Kay
authors.initials: K
authors.lastname: Popovic
authors.forename: Mark
authors.initials: M
authors.lastname: Conaway
authors.forename: Dan
authors.initials: D
authors.lastname: Theodorescu
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D001859:Bone Neoplasms / Q000556:secondary; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects / Q000235:genetics; D049109:Cell Proliferation; D020690:GTPase-Activating Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D055029:Inverted Repeat Sequences; D008175:Lung Neoplasms / Q000556:secondary; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009362:Neoplasm Metastasis / Q000235:genetics*; D009368:Neoplasm Transplantation; D010739:Phospholipase D / Q000172:deficiency / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014183:Transplantation, Heterologous; D001749:Urinary Bladder Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D033921:Vesicular Transport Proteins / Q000172:deficiency / Q000378:metabolism; D020725:ral GTP-Binding Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; C470182:EXOC2 protein, human; D020690:GTPase-Activating Proteins; C095637:RALBP1 protein, human; D034741:RNA, Small Interfering; D033921:Vesicular Transport Proteins; D010739:Phospholipase D; C106801:phospholipase D1; C492198:RALA protein, human; D020725:ral GTP-Binding Proteins