Characterization of an embryonal rhabdomyosarcoma cell line showing amplification and over-expression of the N-myc oncogene.

A parent rhabdomyosarcoma cell line designated SCMC-RM2 was established from bone-marrow tumor cells taken from an 11-year-old girl with an embryonal rhabdomyosarcoma. Subsequently a cloned SCMC-RM2-1 cell line was isolated from a parent line. These cell lines grew as adherent monolayers in liquid culture with a doubling time of 50 and 52 hr, respectively. In addition, colonies were established in soft agar, which grew in a dose-dependent fashion with a cloning efficiency of 0.7 and 0.8%, respectively. Chromosomal analysis showed these cell lines had neither double minutes nor homogeneously staining regions. Chromosome number ranged from 61 to 93, translocation; t(9;13)(p22;q14) was identified, and no alteration of chromosome 2 was observed. Surface membrane antigen profile of parent and cloned lines by using a panel of 24 monoclonal antibodies (MAbs) excluded the possibility of these being neuroblastoma cell lines. In addition, MAbs to the cytoplasmic protein desmin, myoglobin, muscle actin (alpha and gamma) and alpha-sarcomeric actin reacted with these cell lines, SCMC-RM2 and SCMC-RM2-1 being thus identified as rhabdomyosarcoma. Southern blot analyses revealed 8- and 7-fold amplification of the N-myc gene in SCMC-RM2 and SCMC-RM2-1 as compared with the promyelocytic cell line HL60. Over-expression of the N-myc mRNA was noted over control cell lines.