Understanding SS18-SSX chromatin binding that facilitates synovial sarcomagenesis

Background

Synovial sarcoma (SS) remains a deadly soft-tissue malignancy with a predilection for younger patients. The tumor is associated in most cases with the SS18-SSX fusion oncogene. Our mouse models of synovial sarcomagenesis, driven by conditional expression of the human SS18-SSX cDNA, faithfully recapitulate characteristics of human SSs. They imply a causative role for SS18-SSX expression in SS.

Despite the lack of a DNA-binding motif, the putative function of SS18-SSX fusion proteins is to epigenetically regulate the expression of genes that facilitate synovial sarcomagenesis.

The mechanisms for action identified thus far have implicated epigenetic machinery. This is important in two ways.  First, SS becomes an ideal model disease by which we may unravel fundamental biology of epigenetic drivers of oncogenesis.  Second, epigenetic mechanisms in cells are intrinsically more targetable by pharmacologic means. The major impediment in the understanding of the SS18-SSX fusions is difficulty in immunoprecipitation. No adequate antibodies are available that specifically pull down the fusion without also pulling down the counteracting native protein, SS18. While tagged versions of the protein can be transiently expressed in cells, these never match the precise cellular context and expression levels that truly drive synovial sarcomagenesis.

Project Goal

Our objective is to determine the epigenetic regulatory function of SS18-SSX in synovial sarcomagenesis by performing chromatin immunoprecipitation (ChIP) with V5-tagged SS18-SSX in the mouse tumors that the fusion explicitly generates. By doing so, we can identify the DNA binding sites that correlate with transcriptome expression data that we have already generated.