Chimeric TLS/FUS-CHOP gene expression and the heterogeneity of its junction in human myxoid and round cell liposarcoma.

Myxoid liposarcomas have a unique and specific t(12;16)q13;p11) chromosomal translocation. The breakpoint has recently been identified and shown to involve the TLS/FUS gene on chromosome 16 and the CHOP gene on chromosome 12. This translocation causes fusion of these genes resulting in the expression of a novel chimeric TLS/FUS-CHOP message. Using the polymerase chain reaction with primer sets derived from sequences of TLS/FUS and CHOP cDNAs, we could amplify three types of the fusion transcripts from seven of seven samples of myxoid and round cell liposarcomas. In six of the seven positive samples, two kinds of chimeric messenger RNAs were found that have been reported previously. However, the last sample had a novel chimeric message that had an extra sequence of 33 bp derived from the TLS/FUS gene. Thus, it was shown that these fusion transcripts had a varying extent of the sequence of TLS/FUS gene incorporated at the site of the fusion. However, the TLS/FUS-CHOP fusion transcripts were not detected in two pleomorphic liposarcomas or in three myxoid variants of malignant fibrous histiocytomas. Our findings indicate that in liposarcomas TLS/FUS-CHOP fusion transcripts have variations at the junction of chimeric messages, which was the case for Ewing's sarcoma. Detection of the chimeric message by reverse transcription polymerase chain reaction was also suggested to be a useful approach for the diagnosis of myxoid and round cell liposarcomas that have (12;16) translocation, and for distinguishing them from pleomorphic liposarcoma and myxoid variant of malignant fibrous histiocytomas.