Nuclear localization of SYT, SSX and the synovial sarcoma-associated SYT-SSX fusion proteins

Synovial sarcoma is characterized by a prevalent chromosomal translocation,t(X;18)(p11;q11). As a result of this translocation the SYT gene onchromosome 18 fuses to either the SSX1 or the SSX2 gene on the Xchromosome. In this study, we generated polyclonal antibodies against theSYT and SSX2 proteins. These antibodies specifically detected both theseproteins and the SYT-SSX fusion proteins in transfected COS-1 cellextracts. Indirect immunofluorescence analysis of COS-1 cells expressingtagged or untagged SYT, SSX2, SYT-SSX1 or SYT- SSX2 indicated that allthese proteins are localized in the nucleus, excluding the nucleoli. TheSSX2 protein exhibited a diffuse staining pattern whereas both the SYT andSYT-SSX proteins appeared in several nuclear dots. Similar nuclear dotswere also detected in primary synovial sarcoma cells growing in ashort-term in vitro culture. Double immunofluorescence in conjunction withconfocal laser-scanning microscopy revealed that the SYT and SYT-SSXnuclear dots do not co- localize with known nuclear structures as e.g.coiled bodies, SC35 interchromatin granules or PML bodies. The similarnuclear localization patterns of SYT and SYT-SSX suggest that the SYT-SSXfusion proteins are directed to SYT-associated nuclear domains where anabnormal function may be exerted.