Abundant but inactive-state gp140proto-trk is expressed in neuroblastomas of patients with good prognosis.

Steady-state levels of gp140proto-trk in cell lines and tumor tissues of neuroblastoma were examined by immunoblotting with anti-gp140proto-trk. The level of gp140proto-trk varied but showed good correlations with the stage of the tumor and the age of the patients at the time of diagnosis. Moreover, patients with higher expression of gp140proto-trk clearly had a far better survival rate than those with lower expression, suggesting that suppression of gp140proto-trk strongly correlates with the malignant conversion of the tumor. However, we found that neither autophosphorylation of gp140proto-trk nor tyrosine phosphorylation of cellular proteins was elevated in tumors of the higher expression group. These results suggest that gp140proto-trk does not actively participate in the process of transformation or the suppression of malignant conversion. Rather, the higher level of gp140proto-trk may reflect the greater level of differentiation of tumor cells.