In vitro differentiation of rhabdomyosarcomas induced by nickel or by Moloney murine sarcoma virus.

In vitro cultures and clonal derivatives have been established from rat rhabdomyosarcomas induced by Moloney-Murine Sarcoma Virus (MSV) or by nickel sulfide; differentiation ability has been studied as expression of desmin, embryonic and adult myosin isoforms, alpha-actin isoforms and cellular fusion. The two rhabdomyosarcoma models showed different levels of myogenic differentiation. Multinucleated myotube-like structures were frequently observed in cultures derived from nickel-induced tumours. Desmin was present in 50-80% of cells and embryonic myosin in up to 10%. In MSV-tumour-derived cultures and in their metastases or clonal derivatives two cell types are present in different ratios: spindle-shaped cells, adherent to plastic surfaces, and rounded cells, loosely attached or floating free in the medium. These cultures showed features of myogenic differentiation (10-80% desmin-positive cells), but embryonic myosin expression and production of multinucleated myotube-like structures were very rare events. Cultures from autochthonous lymph node and lung metastatic cells showed similar patterns of differentiation. Retinoic acid increased differentiated features (myotube formation and embryonic myosin expression) only in nickel-induced rhabdomyosarcoma cells. The two models described here mimic the heterogeneity in differentiation pattern found among human rhabdomyosarcomas. Myogenic differentiation ability was retained at a good level by nickel-induced tumours, whereas it was strongly impaired in MSV-induced tumours.