Establishment and characterization of a cell line (S-RMS1) derived from a congenital spindle rhabdomyosarcoma with SRF4-NCOA2 fusion transcript.. S-RMS1

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcomas in children and is classified into two major subgroups: embryonal and alveolar (ERMS and ARMS). Spindle cell RMS was previously described as an uncommon variant of ERMS and it is currently considered as a distinct RMS subtype characterized by recurrent fusion genes such as VGLL2-CITED2, VGLL2-NCOA2, TEAD1-NCOA2 and SRF-NCOA2. No spindle cell RMS cell line has been reported in the literature so far. Here, we describe the establishment and characterization of the first human cell line derived from a primary congenital spindle cell RMS harboring the SRF4-NCOA2 gene fusion. The cell line was established from a surgical sample obtained after neoadjuvant chemotherapy, from a 4 months old boy diagnosed at birth. Morphological and molecular characteristics were analyzed and compared with two rhabdomyosarcoma cell lines, RH30 and RD18. The established cell line showed cells small in size, with a fibroblast-like morphology and positivity for MyoD-1, desmin and smooth muscle actin (SMA). The population doubling time was 3.7 days and the cell line expresses the fusion transcript SRF4-NCOA2. Whole genome sequencing demonstrated that S-RMS1 cell lines retained the same genetic profile of the tumor at diagnosis: variant prioritization using a new phenotype-based approach with the term “Rhabdomyosarcoma” identified 88 and 86 genes bearing disease-associated variants in the tumor at diagnosis surgical sample and in the S-RMS1 cell line respectively; among these 84 were common between the two samples. Western blot analysis identified down regulation of AKT-p and YAP-p. RT-qPCR showed a significant deregulation in Endoglin, MYCN, TGFbR1, GATA6, Myogenin and Mef2C transcripts. This is the first report of the establishment of a cell line derived from a primary congenital sclerosing/spindle rhabdomyosarcoma with SRF4-NCOA2 gene fusion. This new cell line should represent a useful tool for the molecular characterization of this rare and little unknown rhabdomyosarcoma subtype