RET receptor expression and interaction with TRK receptors in neuroblastomas.

Neuroblastomas (NBs) have heterogeneous clinical behavior, from spontaneous regression or differentiation to relentless progression. Evidence from our laboratory and others suggests that neurotrophin receptors contribute to these disparate behaviors. Previously, the role of TRK receptors in NB pathogenesis was investigated. In the present study, the expression of RET and its coreceptors in a panel of NB cell lines was investigated and responses to cognate ligands GDNF, NRTN, and ARTN with GFRalpha13 coreceptor expression, respectively were found to be correlated. RET expression was high in NBLS, moderate in SY5Y, low/absent in NBEBc1 and NLF cells. All cell lines expressed at least one of GFRalpha coreceptors. In addition, NBLS, SY5Y, NBEBc1 and NLF cells showed different morphological changes in response to ligands. As expected, activation of RET/GFRalpha3 by ARTN resulted in RET phosphorylation. Interestingly, activation of TrkA by its cognate ligand NGF resulted in RET phosphorylation at Y905, Y1015, and Y1062, and this was inhibited in a dosedependent manner by the TRK inhibitor (CEP701). Conversely, RET activation by ARTN in NBLS cells led to phosphorylation of TrkA. This suggests a physical association between RET and TRK proteins, and crosstalk between these two receptor pathways. Finally, RET, GFR and TRK expression in primary tumors was investigated and a significant association between RET, its coreceptors and TRK expression was demonstrated. Thus, the present data support a complex model of interacting neurotrophin receptor pathways in the regulation of cell growth and differentiation in NBs.