BMI-1 promotes Ewing sarcoma tumorigenicity independent of CDKN2a-repression

Over-expression of the polycomb group gene BMI-1 is implicated in the pathogenesis of many human cancers. In this study, we investigate the role of BMI-1 as a functional oncogene in the Ewing’s Sarcoma Family of Tumors (ESFT), a highly aggressive group of bone and soft tissue tumors. Our data show that BMI-1 is highly expressed by the majority of primary ESFT and ESFT cell lines. However, in contrast to previous reports in other human cancer cell types, knockdown of BMI-1 in ESFT cell lines has no effect on cell survival. Instead, gain and loss of function studies in vitro and in vivo demonstrate that BMI-1 promotes the anchorage independent growth and tumorigenicity of ESFT. Importantly, we also find that modulation of BMI-1 alters the tumorigenicity of both p16-wild type and p16-null cell lines and that BMI-1-mediated effects on growth promotion are independent of CDKN2a repression. Gene expression profiling of ESFT cells following BMI-1 modulation reveals novel downstream effectors of BMI-1 function including key developmental, cell:cell and cell:matrix adhesion pathways. These data support a central role for BMI-1 in the pathogenesis of ESFT and reveal that p16-independent functions of BMI-1 are largely responsible for its oncogenic function in this tumor family. Keywords: Modification of BMI-1 expression in ESFT cell lines 6 samples, 2 conditions, 3 replicates per condition