A TFG–TEC nuclear localization mutant forms complexes with the wild-type TFG–TEC oncoprotein and suppresses its activity

Human EMCs (extraskeletal myxoid chondrosarcomas) are soft tissue tumours characterized by specific chromosomal abnormalities. Recently, a proportion of EMCs were found to harbour a characteristic translocation, t(3;9)(q11-12;q22), involving the TFG (TRK-fused gene) at 3q11-12 and the TEC (translocated in extraskeletal chondrosarcoma) gene at 9q22. The present study used both in vitro and in vivo systems to show that the TFG–TEC protein self-associates, and that this is dependent upon the CC (coiled-coil) domain (amino acids 97–124), the AF1 (activation function 1) domain (amino acids 275–562) and the DBD (DNA-binding domain) (amino acids 563–655). The TFG–TEC protein also associated with a mutant NLS-TFG–TEC (AAAA) protein, which harbours mutations in the NLS (nuclear localization signal). Subcellular localization assays showed that the NLS mutant TFG–TEC (AAAA) protein interfered with the nuclear localization of wild-type TFG–TEC. Most importantly, the mutant protein inhibited TFG–TEC-mediated transcriptional activation in vivo. Thus mutations in the TFG–TEC NLS yield a dominant-negative protein. These results show that the biological functions of the TFG-TEC oncogene can be modulated by a dominant-negative mutant.