ALPHA-2A-INTERFERON-INDUCED DIFFERENTIATION OF HUMAN ALVEOLAR RHABDOMYOSARCOMA CELLS - CORRELATION WITH DOWN-REGULATION OF THE INSULIN-LIKEGROWTH-FACTOR TYPE-I RECEPTOR

Rhabdomyosarcoma, a tumor of skeletal muscle origin, appears developme ntally arrested at an early stage in the myogenic differentiation path way, The proliferation of an alveolar rhabdomyosarcoma cell line Rh30 is dependent on the insulin-like growth factor (IGF) II/IGF-I receptor (IGF-IR) signaling pathway and is highly sensitive to recombinant hum an IFN-alpha 2a, which induces growth arrest and differentiation of th ese malignant myoblasts, IFN-alpha 2a-induced growth arrest of Rh30 ce lls was observed within 48 h, and reduction in colony formation was ob tained with an IC50 of 0.81 IU/ml for 72 h exposure, Down-regulated ex pression of IGF-IR was apparent by 24 h after initiation of IFN-alpha 2a treatment, Furthermore, an initial increase followed by reduced exp ression of MyoD, in concert with elevated expression of myogenin, incr eased frequency of skeletal muscle myosin-positive cells, and the form ation of multinucleated cells, indicated an enhancement of differentia tion of Rh30 cells in the presence of IFN-alpha 2a. To probe the role of IGF-IR in the differentiation of Rh30 cells along the myogenic line age, the effect of antisense RNA-mediated reduction of endogenous IGF- IR on growth and expression of muscle-specific proteins was determined . Rh30 cells transfected to stably express antisense IGF-IR (clone AS# 23) showed significant reduction in growth rate, decreased expression of IGF-IR protein, increased expression of MyoD, myosin heavy chain, a nd an increased number of multinucleated cells in comparison to the pa rental line, These data are consistent with overexpression of IGF-IR i nhibiting differentiation, IFN-alpha 2a treatment of AS#23 cells furth er induced both MyoD and myogenin expression, thereby allowing cells t o proceed further downstream of the differentiation pathway.