We identify a novel alternative TrkA splice variant, TrkAIII, with deletion of exons 6, 7, and 9 and functional extracellular IG-C1 and N-glycosylation domains, that exhibits expression restricted to undifferentiated early neural progenitors, human neuroblastomas (NBs), and a subset of other neural crest-derived tumors. This NGF-unresponsive isoform is oncogenic in NIH3T3 cells and promotes tumorigenic NB cell behavior in vitro and in vivo (cell survival, xenograft growth, angiogenesis) resulting from spontaneous tyrosine kinase activity and IP3K/Akt/NF-kappaB but not Ras/MAPK signaling. TrkAIII antagonizes NGF/TrkAI signaling, which is responsible for NB growth arrest and differentiation through Ras/MAPK, and its expression is promoted by hypoxia at the expense of NGF-responsive receptors, providing a mechanism for converting NGF/TrkA/Ras/MAPK antioncogenic signals to TrkAIII/IP3K/Akt/NF-kappaB tumor-promoting signals during tumor progression.

Keywords:Breast cancer Thioredoxin Matrix metalloproteinase-9 MMP-9/TIMP-1 equilibrium NF-jB Invasion a b s t r a c t Increased expression of thioredoxin (Trx)-1 and matrix metalloproteinase (MMP)-9 associates with malignant breast cancer progression. Here, we describe a functional relationship between Trx-1 and MMP-9 in promoting MDA-MB-231 breast cancer cell invasive behaviour. Trx-1 overexpression stimulated MMP-9 expression, de-regulated the MMP-9/TIMP-1 equilibrium and augmented MMP-9 involvement in a more invasive phenotype. Trx-1 augmented MMP-9 transcription through NFjB, AP-1 and SP1 elements; stimulated p50/p65 NF-jB activity and recruitment to the MMP-9 promoter; and facilitated MMP-9 promoter-accessibility to NF-jB by preventing HDAC recruitment and maintaining MMP-9 promoter histone acetylation. Our data provide a functional basis for Trx-1 and MMP-9 association in malignant breast cancer and identify Trx-1 and NF-jB as potentially druggable targets for reducing MMP-9 involvement in malignant behaviour.

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