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Expression of Trk receptors is an important prognostic factor in neuroblastoma (NB) and other cancers. TrkB and its ligand brain-derived neurotrophic factor (BDNF) are preferentially expressed in NB with poor prognosis, conferring invasive and metastatic potential to the tumor cells as well as enhancing therapy resistance. Galectin-1 (Gal-1) has emerged as an interesting cancer target, as it is involved in modulating cell proliferation, cell death and cell migration, all of which are linked to cancer initiation and progression. We previously identified Gal-1 mRNA to be upregulated in patients with aggressive, relapsing NB and found that Gal-1 protein was upregulated in human SY5Y NB cells on activation of ectopically expressed TrkB (SY5Y-TrkB), but not TrkA (SY5Y-TrkA). Here, we report that Gal-1 mRNA levels positively correlated with TrkB expression and anticorrelated with TrkA expression in a cohort of 102 primary NB. Immunohistochemical analyses of 92 primary NB specimens revealed high Gal-1 expression in stromal septae and in neuroblasts. BDNF-mediated activation of TrkB enhanced invasiveness and migration in vitro, which could be impaired by transient transfection using Gal-1-specific siRNA or a neutralizing antibody directed against Gal-1. The addition of recombinant Gal-1 (rGal-1) in the absence of BDNF partially restored migration and invasive capacity. Using the Trk inhibitor K252a, we could show that the upregulation of Gal-1 protein strictly depended on activated TrkB. Our data suggest that targeting Gal-1 might be a promising strategy for the treatment of aggressive NB.Oncogene (2009) 28, 2015–2023; doi:10.1038/onc.2009.70; published online 13 April 2009 [ABSTRACT FROM AUTHOR]