CAMP EFFECTS ON MYOGENIC GENE-EXPRESSION IN RHABDOMYOSARCOMA CELLS

Rhabdomyosarcoma is a tumor of skeletal muscle origin affecting childr en and young adults. Although relatively undifferentiated, cell lines derived from this tumor express myogenic regulatory factors and so may be useful models of abortive myogenic differentiation. In the present studies, we have determined the effect of increased intracellular cAM P on proliferation, morphologic differentiation, and expression of myo genic genes in the prototypic embryonal rhabdomyosarcoma cell line, RD . Whereas growth in dibutyryl cAMP (dbcAMP), forskolin, or butyrate le d to morphologic differentiation, growth in dbcAMP inhibited prolifera tion, while growth in butyrate slowed but did not stop cell division. Expression of the genes for myogenin and myosin light chain was inhibi ted by dbcAMP, while butyrate decreased myogenin and increased myosin light chain transcription. MyoD and MRF4 expression was not altered un der either condition and no myf5 expression was detected. We also dete rmined the effects of dbcAMP and butyrate on total protein expression, as well as on a panel of muscle- and neural-specific proteins using f unctional assays, immunohistochemistry, and immunoprecipitation. The t otal protein levels of cells treated with either agent were double tho se of untreated cells. DbcAMP increased the activity of acetylcholines terase (AChE) up to 10-fold compared to untreated cells, while butyrat e had a substantially lesser effect. These increases were due to incre ased AChE protein synthesis and stability in dbcAMP treated cells, com pared to butyrate or untreated cells, Finally, cells under all conditi ons expressed MAP2, a neural-specific microtubule associated protein. Together, these data suggest that intracellular cAMP levels modulate d istinct subsets of the myogenic differentiation pathway in rhabdomyosa rcoma cells. Moreover, they also indicate that RD cells are able to ex press markers of different cell lineages, which may help explain some of the paradoxical features of these tumors. (C) 1996 Academic Press, Inc.