Analysis of transforming activity of human synovial sarcoma-associated chimeric protein SYT-SSX1 bound to chromatin remodeling factor hBRM/hSNF2 alpha

Human synovial sarcoma has been shown to exclusively harbor the chromosomal translocation t(X;18) that produces the chimeric gene SYT-SSX. However, th e role of SYT-SSX in cellular transformation remains unclear. In this study , we have established 3Y1 rat fibroblast cell lines that constitutively exp ress SYT, SSX1, and SYT-SSX1 and found that SYT-SSX1 promoted growth rate i n culture, anchorage-independent growth in soft agar, and tumor formation i n nude mice. Deletion of the N-terminal 181 amino acids of SYT-SSX1 caused loss of its transforming activity. Furthermore, association of SYT-SSX1 wit h the chromatin remodeling factor hBRM/hSNF2 alpha, which regulates transcr iption, was demonstrated in both SYT-SSX1-expressing 3Y1 cells and in the h uman synovial sarcoma cell line HS-SY-II. The binding region between the tw o molecules was shown to reside within the N-terminal 181 amino acids stret ch (aa 1-181) of SYT-SSX1 and 50 amino acids (aa 156-205) of hBRM/hSNF2 alp ha and we found that the overexpression of this binding region of hBRM/hSNF 2 alpha significantly suppressed the anchorage-independent growth of SYT-SS X1-expressing 3Y1 cells. To analyze the transcriptional regulation by SYT-S SX1, we established conditional expression system of SYT-SSX1 and examined the gene expression profiles. The down-regulation of potential tumor suppre ssor DCC was observed among 1,176 genes analyzed by microarray analysis, an d semi-quantitative reverse transcription-PCR confirmed this finding. These data clearly demonstrate transforming activity of human oncogene SYT-SSX1 and also involvement of chromatin remodeling factor hBRM/hSNF2 alpha in hum an cancer.