Poster abstracts
Poster number 68 submitted by Jack Kucinski
Initial rhabdomyosarcoma fusion-oncogene activity pioneers a distinct oncogenic signature in vivo
Jack Kucinski (Molecular, Cellular, and Developmental Biology Graduate Program), Cenny Taslim (Center for Childhood Cancer Research, The Abigail Wexner Research Institute, Nationwide Childrens Hospital), Alexi Tallan (Molecular, Cellular, and Developmental Biology Graduate Program), Katherine Silvius (Center for Childhood Cancer Research, The Abigail Wexner Research Institute, Nationwide Childrens Hospital), Benjamin Stanton (Center for Childhood Cancer Research, The Abigail Wexner Research Institute, Nationwide Childrens Hospital; Department of Pediatrics, The Ohio State University College of Medicine), Genevieve Kendall (Center for Childhood Cancer Research, The Abigail Wexner Research Institute, Nationwide Childrens Hospital; Department of Pediatrics, The Ohio State University College of Medicine)
Abstract:
Rhabdomyosarcoma is the most frequent childhood soft tissue sarcoma, with the fusion-positive subtype (FP-RMS) being more aggressive and resistant to current therapies. FP-RMS is driven by a chromosomal translocation mutation, with the fusion transcription factor PAX3::FOXO1 being the most common. PAX3::FOXO1 contains both paired and homeobox DNA binding domains from PAX3 and a transactivation domain from FOXO1. Previously, we generated multiple PAX3::FOXO1 zebrafish tumor models. In vitro, PAX3::FOXO1 has pioneer activity, meaning it can bind to inaccessible chromatin through degenerate motif recognition to alter the chromatin state; however, it had been technically challenging to investigate how PAX3::FOXO1 could initially generate a tumorigenic state in vivo. Therefore, we developed a zebrafish mRNA injection model to express PAX3::FOXO1 during gastrulation and reveal its earliest in vivo mechanisms. Through 2D chromatin sequencing and biochemical approaches, we showed that PAX3::FOXO1 invades inaccessible chromatin and first interacts with DNA by recognizing homeobox motifs, revealing an alternative mode of pioneering activity. PAX3::FOXO1 binding at its consensus motifs, containing both paired and homeodomain sequences, increases chromatin accessibility and repositions the active histone mark H3K27Ac to drive a neomorphic chromatin state. Even though improper skeletal muscle development classically describes rhabdomyosarcoma, these epigenetic changes correspond to direct activation of neural transcription factors and pathways by PAX3::FOXO1. These pathways included an FP-RMS chemotherapy-resistant neuronal signature identified from orthotopic mouse xenografts, suggesting tumor resistance and recurrence may be a recapitulation of initiation. Understanding how PAX3::FOXO1 cooperates with activated neural transcription factors across this injection model and our zebrafish tumor models could delineate mechanisms of disease aggressiveness.
References:
1. Kendall GC, Watson S, Xu L, LaVigne CA, Murchison W, Rakheja D, et al. PAX3-FOXO1 transgenic zebrafish models identify HES3 as a mediator of rhabdomyosarcoma tumorigenesis. Elife. 2018;7.
2. Sunkel BD, Wang M, LaHaye S, Kelly BJ, Fitch JR, Barr FG, et al. Evidence of pioneer factor activity of an oncogenic fusion transcription factor. iScience. 2021;24(8):102867.
3. Danielli SG, Wei Y, Dyer MA, Stewart E, Wachtel M, Schäfer BW, et al. Single cell transcriptomic profiling identifies tumor-acquired and therapy-resistant cell states in pediatric rhabdomyosarcoma. bioRxiv. 2023:2023.10.13.562224.
Keywords: pediatric cancer, cancer epigenetics, in vivo modeling