Fusion of the NH₂-terminal domain of the bHLH protein TCF12 to TEC in extraskeletal myxoid chondrosarcoma with translocation t(9; 15)(q22; q21)

Extraskeletal myxoid chondrosarcomas (EMC) are characterized by recurrent t(9; 22) or t(9; 17) translocations resulting in fusions of the NH₂-terminal transactivation domains of EWS or TAF2N to the entire TEC protein. We report an EMC with a new translocation, t(9; 15)(q22; q21), and a third type of TEC-containing fusion gene. The chimeric transcript encodes a protein in which the first 108 amino acids of the NH₂ terminus of the basic helix-loop-helix (bHLH) protein TCF12 is linked to the entire TEC protein. The translocation separates the NH₂-terminal domain of TCF12 from the bHLH domain as well as from a potential leucine zipper domain located immediately downstream of the breakpoint. These results demonstrate that the NH₂-terminal transactivation domains of EWS or TAF2N are not essential for the oncogenic properties of fusion proteins in EMC, and that EWS or TAF2N may be replaced by a similar domain from a bHLH protein that presumably endows the fusion protein with similar functions.