Abundant but Inactive‐state gpl40^prototrk Is Expressed in Neuroblastomas of Patients with Good Prognosis

Steady‐state levels of gp140^proto‐trk in cell lines and tumor tissues of neurohlastoma were examined by immunoblotting with anti‐gpl40^proto‐trk The level of gpl40^proto‐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 gpl40^proto‐trk clearly had a far better survival rate than those with lower expression, suggesting that suppression of gp140^proto‐trkstrongly correlates with the malignant conversion of the tumor. However, we found that neither autophosphorylation of gpl40^proto‐trknor tyrosine phosphoryla‐tion of cellular proteins was elevated in tumors of the higher expression group. These results suggest that gpl40^proto‐trk does not actively participate in the process of transformation or the suppression of malignant conversion. Rather, the higher level of gpl40^proto‐trkmay reflect the greater level of differentiation of tumor cells.