Identification of a New Transcriptional Co-Regulator of STEAP1 in Ewing’s Sarcoma

Abstract

Ewing’s sarcoma (ES) is caused by a chromosomal translocation leading to the formation of the fused EWSFLI1 gene, which codes for an aberrant transcription factor EWSFLI1. The transcriptional targets of EWSFLI1 have been viewed as promising and novel drug targets in the treatment of ES. One such target is six transmembrane epithelial antigen of the prostate 1 (STEAP1), a transmembrane protein that is upregulated by EWSFLI1 in ES. STEAP1 is a hallmark of tumor invasiveness and an indicator of tumor responsiveness to therapy. EWSFLI1 binds to the STEAP1 promoter region, but the mechanism of action by which it upregulates STEAP1 expression in ES is not entirely understood. Upon analysis of the STEAP1 promoter, we predicted two binding sites for NKX2.2, another crucial transcription factor involved in ES pathogenesis. We confirmed the interaction of NKX2.2 with the STEAP1 promoter using chromatin immunoprecipitation (ChIP) analysis. We used single-molecule RNA imaging, biochemical, and genetic studies to identify the novel role of NKX2.2 in regulating STEAP1 expression in ES. Our results show that NKX2.2 is a co-regulator of STEAP1 expression and functions by interacting with the STEAP1 promoter at sites proximal to the reported EWSFLI1 sites. The co-operative interaction of NKX2.2 with EWSFLI1 in regulating STEAP1 holds potential as a new target for therapeutic interventions for ES.

Comparative Evaluation of STEAP1 Targeting Chimeric Antigen Receptors with Different Costimulatory Domains and Spacers

“…STEAP1 is expressed in ~90% of prostate cancers and in sizeable subpopulations of other cancer types such as pancreatic cancer, glioblastoma, lung cancer, bladder cancer, breast cancer, ovarian cancer, leukemia, lymphoma, and head and neck cancer [ 14 , 15 , 20 , 21 ]. Furthermore, a key oncogenic driver in pediatric Ewing’s sarcoma is a chromosomal translocation giving the fused EWSFLI1 gene, which leads to the upregulation of STEAP1 [ 14 , 15 , 16 , 22 , 23 , 24 ].…”

Targeting STEAP1 as an anticancer strategy

“…In addition to EWS::FLI1, NKX2.2 is a positive regulator of STEAP1 expression ( 35 ). Initially, the transcriptional repressive roles of NKX2.2 were recognized as being necessary and sufficient for the oncogenic properties of EWS ( 36 ).…”

Epigenetic and Transcriptional Signaling in Ewing Sarcoma—Disease Etiology and Therapeutic Opportunities

“…Follow-up studies found that NKX2.2-repressed genes are enriched in the EWSR1-FLI1-repressed dataset that contributes to mesenchymal differentiation and terminal differentiation [ 63 , 92 ]. More recently, studies found that NKX2.2 binds to the promoter region of STEAP1 (six transmembrane epithelial antigen of the prostate 1), a gene which is essential for EwS survival [ 94 ], together with EWSR1-FLI1 to regulate expression of STEAP1 [ 95 ]. Although this study did not highlight the direct interaction between NKX2.2 and EWSR1-FLI1 on the chromatin in the genome-wide level, it provided some understanding of how NKX2.2 coordinates the effects of EWSR1-FLI1.…”