ACTIVATION OF TRK GENES IN EWINGS-SARCOMA - TRK A RECEPTOR EXPRESSIONLINKED TO NEURAL DIFFERENTIATION

Trk receptors have been identified by immunohistochemical methods in p rimitive neuroectodermal tumor (PNET)/Ewing's sarcoma (ES). However, t he presence of different members of the Trk family of receptors in PNE T/ES has not been specified. We have examined whether Trk A, B, and C receptors are specifically expressed in ES both with and without featu res of neural differentiation. Ten ES tumors (five primary tumors of b one and five extraosseous tumors transplanted into nude mice) were inv estigated for expression of Trk receptors by immunohistochemistry and reverse transcription-polymerase chain reaction. One primary ES and th e five grafted ES tumors exhibited signs of neural differentiation; th e remaining four primaries were undifferentiated ES. Other tumor types were analyzed as controls; they included three neuroblastomas (NB), t wo Lymphomas, and single cases of pheochromocytoma (PHEO), schwannoma (SCHW), osteosarcoma, and carcinoma of breast, colon, and kidney. Trk receptors were detected in paraffin-embedded tumor tissue sections by means of a pan-Trk polyclonal antibody raised against the 14 carboxyte rminal residues of gp140(trk), and trk A, B, and C transcripts were sp ecifically detected by polymerase chain reaction-based amplification o n cDNAs derived from tumor RNA with MuLV reverse transcriptase. Reacti vity to the pan-Trk antibody was exhibited by six ES tumors, the three NBs, and the single PHEO and SCHW cases; immunoreactivity was restric ted to differentiated tumors, in the case of ES. Tumor types positive for immunostaining were also distinguished by containing transcripts o f TRK genes. However, the trk A, B, and C expression pattern of ES dif fered from that of NBs, PHEO, and SCHW. Transcripts of trk A, B, and C were detected in seven, four, and one case of ES, respectively, and i n five, two, and five cases of NE, PHEO, and SCHW, respectively. Inter estingly, all differentiated ES tumors contained trk A transcripts. Tu mors of neuroectodermal phenotype and/or derivation were thus characte rized by a distinct consensus expression pattern: trk A(+)/B-/C- for d ifferentiated ES and trk A(+)/B-/C+ for NB-PHEO-SCHW. These results in dicate that the TRK gene family is frequently activated in ES; they al so suggest that Trk A receptor is a feature of ES with neural differen tiation, whereas Trk B and C receptors seem to be present in undiffere ntiated ES.