Differential roles of SS18–SSX fusion gene and insulin-like growth factor-1 receptor in synovial sarcoma cell growth

Recently we demonstrated that the synovial sarcoma specific fusion gene SS18–SSX is crucial for cyclin D1 expression and is linked to cell proliferation. In this report we explore the role of SS18–SSX and IGF-1R for their potential functions in cellular proliferation and survival in cultured synovial sarcoma cells. We found that targeting of SS18–SSX mRNA by antisense oligonucleotide treatment drastically and rapidly decreased cell proliferation but caused only a slight increase of apoptosis. The synovial sarcoma cells were confirmed to express IGF-1R, and treatment with an IGF-1R inhibitor resulted in substantially reduced cell viability by inducing apoptosis in these cells. Conversely, inhibition of the IGF-1R resulted only in a slight to moderate decrease in DNA synthesis. In conclusion, SS18–SSX and IGF-1R seem to play important but different roles in maintaining malignant growth of synovial sarcoma cells. Whereas SS18–SSX maintains cyclin D1 and cell proliferation, IGF-1R protects from apoptosis.