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 STT gene on chromosome 18 fuses to either the SSX1 or the SSX2 gene on the X chromosome, In this study, we generated polyclonal antibodies against the SYT and SSX2 proteins, These antibodies specifically detected both these proteins and the SYT-SSX fusion proteins in transfected COS-1 cell extracts, Indirect immunofluorescence analysis of COS-1 cells expressing tagged or untagged STT, SSX2, STT-SSX1 or SYT-SSX2 indicated that all these proteins are localized in the nucleus, excluding the nucleoli, The SSX2 protein exhibited a diffuse staining pattern whereas both the SYT and SYT-SSX proteins appeared in several nuclear dots, Similar nuclear dots were also detected in primary synovial sarcoma cells growing in a short-term in vitro culture, Double immunofluorescence in conjunction with confocal laser-scanning microscopy revealed that the STT and STT-SSX nuclear dots do not co-localize with known nuclear structures as e.g. coiled bodies, SC35 interchromatin granules or PML bodies, The similar nuclear localization patterns of STT and SYT-SSX suggest that the STT-SSX fusion proteins are directed to SYT-associated nuclear domains where an abnormal function may be exerted.