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Lide Alaña et al., [Background] PTOV1 is an adaptor protein with functions in diverse processes, including gene transcription and protein translation, whose overexpression is associated with a higher proliferation index and tumor grade in prostate cancer (PC) and other neoplasms. Here we report its interaction with the Notch pathway and its involvement in PC progression. [Methods] Stable PTOV1 knockdown or overexpression were performed by lentiviral transduction. Protein interactions were analyzed by co-immunoprecipitation, pull-down and/or immunofluorescence. Endogenous gene expression was analyzed by real time RT-PCR and/or Western blotting. Exogenous promoter activities were studied by luciferase assays. Gene promoter interactions were analyzed by chromatin immunoprecipitation assays (ChIP). In vivo studies were performed in the Drosophila melanogaster wing, the SCID-Beige mouse model, and human prostate cancer tissues and metastasis. The Excel package was used for statistical analysis. [Results] Knockdown of PTOV1 in prostate epithelial cells and HaCaT skin keratinocytes caused the upregulation, and overexpression of PTOV1 the downregulation, of the Notch target genes HEY1 and HES1, suggesting that PTOV1 counteracts Notch signaling. Under conditions of inactive Notch signaling, endogenous PTOV1 associated with the HEY1 and HES1 promoters, together with components of the Notch repressor complex. Conversely, expression of active Notch1 provoked the dismissal of PTOV1 from these promoters. The antagonist role of PTOV1 on Notch activity was corroborated in the Drosophila melanogaster wing, where human PTOV1 exacerbated Notch deletion mutant phenotypes and suppressed the effects of constitutively active Notch. PTOV1 was required for optimal in vitro invasiveness and anchorage-independent growth of PC-3 cells, activities counteracted by Notch, and for their efficient growth and metastatic spread in vivo. In prostate tumors, the overexpression of PTOV1 was associated with decreased expression of HEY1 and HES1, and this correlation was significant in metastatic lesions. [Conclusions] High levels of the adaptor protein PTOV1 counteract the transcriptional activity of Notch. Our evidences link the pro-oncogenic and pro-metastatic effects of PTOV1 in prostate cancer to its inhibitory activity on Notch signaling and are supportive of a tumor suppressor role of Notch in prostate cancer progression. © 2014 Alaña et al.; licensee BioMed Central Ltd., This work was supported by: Instituto Carlos III RD06/0020/0058 RETICS, Ministry of Science and Innovation SAF2008-03936 and SAF2011-30496 (to R.P.), SAF2008-04136-C02-01 and SAF2011-24686 (to T.M.T.), AGAUR 2009SGR1482 (to R.P. and T.M.T.), Red Nacional de Biobancos, Instituto Carlos III (to R.B.), Fondo de Investigaciones de la Seguridad Social PI20231 (to P.L.F.) and Ministry of Science and Innovation BFU2009-09781 (to F.S.)