Morphological and Molecular Characterization of Spontaneous Myogenic Differentiation in a Human Rhabdomyosarcoma Cell Line

Skeletal muscle differentiation consists of an ordered withdrawal of committed cells from the cell cycle and their fusion to form multinucleated myotubes. To determine if differentiation of malignant myoblasts parallels that of normal skeletal muscle, a cell line (Rh28) was established from an alveolar rhabdomyosarcoma. Rh28 displays a constant population doubling time of 45–55 h until passage 60, when the doubling time progressively increases until proliferation ceases. Loss of proliferative capacity is associated with morphological evidence of differentiation to multinucleated myotubes, fusion, and the expression of numerous muscle-specific genes. In contrast to normal myogenic differentiation, multinucleated cells continue to synthesize DNA and express abundant c-myc transcripts. These observations suggest synchronous replication and possible arrest in the G2-phase of the cell cycle, since there was no evidence of mitotic activity in differentiated cells. Terminal differentiation of early passage Rh28 cells was induced in the presence of 10% dialyzed fetal calf serum but not by medium containing 2% undialyzed serum, suggesting a role for low molecular weight growth factors in this process. Our data indicate that the Rh28 cell line may be of value in elucidating the relationship between oncogenic transformation and differentiation in rhabdomyosarcoma.