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‐trk)strongly correlates with the malignant conversion of the tumor. However, we found that neither autophosphorylation of gpl40(proto‐trk)nor 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‐trk)may reflect the greater level of differentiation of tumor cells.