Analysis of transforming mechanism of human synovial sarcoma oncogene SYT-SSX

人类滑膜肉瘤主要发生在四肢关节周围，超过90%的病例具有染色体易位t（X;18），导致形成嵌合基因SYT-SSX（滑膜肉瘤易位-滑膜肉瘤X断点）。由于SYT和SSX没有已知功能蛋白的同源区域，SYT-SSX的转化机制尚未阐明。本研究建立了表达SYT、SSX和SYT-SSX的大鼠成纤维细胞系3 Y1，发现SYT-SSX可诱导裸鼠非贴壁生长和肿瘤形成。在该SYT-SSX表达细胞系中，已显示SWI/SNF型染色质重塑因子hBRM之一与SYT-SSX结合，并且这种结合对于3 Y1细胞的转化是必需的。特别是hBRM 155 -206的50个氨基酸组成的特异性肽段阻断SYT-SSX与hBRM的结合，抑制SYT-SSX-3 Y1细胞的生长，为建立滑膜肉瘤基因治疗的基础技术之一。我们还发现，与3 Y1细胞相反，SYT-SSX诱导人腺癌细胞系SW 13的生长抑制。在该细胞系中，SYT-SSX诱导p21 WAF 1/CIP 1表达，通过免疫印迹证实。p21启动子调控的荧光素酶检测发现SYT-SSX通过转录因子Sp1依赖和p53非依赖的机制激活p21启动子。因此，SYT-SSX在不同的细胞系中对细胞生长具有不同的作用，例如生长正性和生长负性机制。我们目前认为SYT-SSX的生长抑制功能的增强可能诱导肿瘤细胞抑制作为滑膜肉瘤的特异性治疗。

Human synovial sarcoma occurs primarily around the joint of extremities and more than 90% of cases have chromosomal translocation t(X;18) resulting the formation of chimeric gene SYT-SSX (synovial sarcoma translocation-synovial sarcoma X break point). As both of SYT and SSX did not share any homology region of known functional proteins, the transforming mechanism of SYT-SSX has not yet been elucidated. In this project, we established rat fibroblast cell line 3Y1 expressing SYT, SSX, and SYT-SSX, and found that SYT-SSX induced anchorage-independent growth and tumor formation in nude mice. In this SYT-SSX expressing cell lines, one of the SWI/SNF type of chromatin remodeling factor hBRM has been shown to bind to SYT-SSX and this association was essential for the transformation of 3Y1 cells. Especially, as the disruption of the binding of SYT-SSX and hBRM by specific peptides composed of 50 amino acids corresponding to hBRM155-206, suppressed the growth of SYT-SSX-3Y1 cells, these peptides could be one of the basic technique for the establishment of gene therapy for synovial sarcoma. We also found that in contrast to 3Y1 cells, SYT-SSX induced growth suppression of human adenocarcinoma cell line SW13. In this cell line, SYT-SSX induced p21WAF1/CIP1 expression confirmed by immunoblotting. The luciferase assay using p21 promoter-regulated construction, SYT-SSX was found to activate p21 promoter by transcription factor Sp1-dependent and p53-independent mechanism. Thus, SYT-SSX has differential effect for cell growth such as growth positive and growth negative mechanism, in different cell lines. We are currently considering the augmentation of growth negative function of SYT-SSX may induce the tumor cell suppression as a specific therapy of synovial sarcoma.