Abstract 5282: New insights into the roles of transcriptional regulation and differentiation state in rhabdomyosarcoma cell migration

The differentiation state of a tumor cell has been known to impact the cell’s pro-tumor and pro-metastatic abilities; for example, in epithelial tumors like lung cancer, epithelial-mesenchymal transitions (EMT) involve a conversion from a differentiated phenotype to a stem-like state, allowing for increased tumor cell motility and successful metastasis. In rhabdomyosarcoma (RMS), a pediatric soft tissue sarcoma, tumors are heterogeneous for cells at different stages of myogenesis or muscle cell differentiation, but it is not fully clear whether certain myogenic cell types have a propensity towards metastatic migration than others. In both development and RMS, master regulatory factors (MRFs) are essential for transcriptional regulation of genes involved in myogenesis. One of these MRFs is myogenin, a transcription factor expressed during mid-differentiation that leads to a more committed myocyte state. Myogenin-positive RMS cells in a zebrafish model have been shown to exhibit many metastasis-promoting abilities, such as increased migratory velocity compared to stem-like RMS cells, the ability to enter the bloodstream, and the capacity to seed tumor-free areas surrounding the tumor. This indicates that metastasis in RMS may rely heavily on transcriptional regulation and likely involves cells of a myocyte-like state. Knowing this, our lab carried out a human cell line knockdown (KD) scratch assay screen of multiple epigenetic factors to investigate if any may also be involved in RMS cell movement. From this screen, BRD1, a bromodomain-containing transcriptional regulator, emerged as a driver of RMS cell migration, and subsequent quantitative PCR (qPCR) analysis of BRD1 KD cells additionally indicated a significant role in MRF and stem cell marker expression. Immunofluorescent staining of untreated RMS cells 24 hours post-scratch revealed that migratory cells exhibit increased BRD1 and myogenin expression as well as decreased MyoD expression (an earlier MRF), suggesting that migratory RMS cells are at a later differentiation state. These results and future experiments would significantly impact the field, as the metastatic functions of BRD1 and myogenin were previously unknown and understudied, respectively. Citation Format: Andrea Largent, Yadong Wang, Abraham Hengyucius, Eleanor Chen. New insights into the roles of transcriptional regulation and differentiation state in rhabdomyosarcoma cell migration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5282.