PAX3-FOXO1 dictates myogenic reprogramming and rhabdomyosarcoma identity in endothelial progenitors

Abstract

Fusion-positive rhabdomyosarcoma (FP-RMS) driven by the expression of the PAX3-FOXO1 (P3F) fusion oncoprotein is an aggressive subtype of pediatric rhabdomyosarcoma. FP-RMS histologically resembles developing muscle yet occurs throughout the body in areas devoid of skeletal muscle highlighting that FP-RMS is not derived from an exclusively myogenic cell of origin. Here we demonstrate that P3F reprograms mouse and human endothelial progenitors to FP-RMS. We show that P3F expression in aP2-Cre expressing cells reprograms endothelial progenitors to functional myogenic stem cells capable of regenerating injured muscle fibers. Further, we describe a FP-RMS mouse model driven by P3F expression and Cdkn2a loss in endothelial cells. Additionally, we show that P3F expression in TP53-null human iPSCs blocks endothelial-directed differentiation and guides cells to become myogenic cells that form FP-RMS tumors in immunocompromised mice. Together these findings demonstrate that FP-RMS can originate from aberrant development of non-myogenic cells driven by P3F.

APax3lineage gives rise to transient haematopoietic progenitors

“…In this context, we note that a t(2;13)(q35;q14) genetic translocation produces a tumorigenic PAX3-FOXO1 fusion protein in patients with paediatric alveolar rhabdomyosarcoma (aRMS) 16,17 . This mutation increases the proliferation of Pax3 -expressing cells whilst inhibiting their terminal differentiation 18 and also promotes the trans-differentiation of endothelial cells towards a myogenic fate 19 . Thus, it should be examined whether PAX3-FOXO1 could also induce myogenic trans-differentiation in haematopoietic cells, or whether it might alter haematopoietic development via an endothelial-derived Pax3 lineage haematopoietic progenitor.…”

Rhabdomyosarcoma fusion oncoprotein initially pioneers a neural signature in vivo

“…Since pioneer factors regulate transcriptional signatures and dependencies, we hypothesized that understanding these mechanisms in vivo would reveal targetable vulnerabilities critical for tumor initiation. In FP-RMS, PAX3::FOXO1 is a core dependency and is transforming in genetic mice and zebrafish models 12,[29][30][31] . We previously developed the zebrafish PAX3::FOXO1-driven tumor model, which we utilized to elucidate disease biology.…”

Epigenetic determinants of fusion-driven sarcomas: paradigms and challenges

“…In agreement, ARF6 has been described as an actionable vulnerability for VGLL2-NCOA2 driven RMS ( Watson et al, 2023 ) and HES3 as prognostic marker and a mediator of PAX3-FOXO1 tumorigenesis ( Kendall et al, 2018 ). Exciting translational animal models have been developed over the course of several decades, allowing for mechanistic studies of sarcomagenesis, including diverse mouse syngeneic models ( Keller et al, 2004a ; Keller et al, 2004b ; Searcy et al, 2023 ) and mouse xenograft models ( Patel et al, 2022 ; Wei et al, 2022 ). We anticipate continued advances in the area of translational animal modeling for fusion-driven sarcomas to give insight into cell of origin, and the fundamental requirements for transformation and drug resistance.…”