OBJECTIVE To study the effect of transforming growth factor?1 (TGF-β1)on differentiation of rhabdomyosarcoma(RMS)cells METHODS RD(human embryonal RMS cell line)cells,cultured in differentiation medium containing 9-cis retinoic acid(9CRA),were treated with TGF-β1.Proliferation of the cells was examined by the MTT assay.The differentiation specific proteins(sarcomeric actin and MyHC)and myogenic transcription factors(MyoD1 and myogenin)in the RD cel s were assessed by immunofluorescence staining. RESULTS Compared to control cel s,treatment with lower concentrations of TGF-?1(0.1 and 0.2 ng/ml)induced an increase in OD values after 4 d(P<0.01),whereas higher concentrations of TGF-?1(2 and 5 ng/ml)led to a reduction of cell viability(P<0.01).After exposure to 9CRA,the viability of the cells decreased significantly(P<0.01),while sarcomeric actin,MyHC and myogenin were induced.These changes were antagonized by TGF-β1(0.1 ng/ml).No changes were observed in expression of MyoD1. CONCLUSION The RMS cells,derived from myogenic progenitors are committed to a myogenic fate,but are arrested in the differentiation course by the addition of TGF-?1 which represses some of the myogenic transcription factors. OBJECTIVE To study the effect of transforming growth factor-1 (TGF-β1) on differentiation of rhabdomyosarcoma (RMS) cells METHODS RD (human embryonal RMS cell line) cells, cultured in differentiation medium containing 9-cis retinoic acid treated with TGF-β1. Proliferation of the cells was examined by the MTT assay. differentiated proteins (sarcomeric actin and MyHC) and myogenic transcription factors (MyoD1 and myogenin) in the RD cel s were assessed by immunofluorescence staining. control cel s, treatment with lower concentrations of TGF-? 1 (0.1 and 0.2 ng / ml) induced an increase in OD values ​​after 4 d (P <0.01) ml) led to a reduction of cell viability (P <0.01). After exposure to 9CRA, the viability of the cells was significantly decreased (P <0.01), while sarcomeric actin, MyHC and myogenin were induced. These changes were antagonized by TGF- β1 (0.1 ng / ml) .No changes were observed in expression of MyoD1. CONCLUSION T. he RMS cells, derived from myogenic progenitors are committed to a myogenic fate, but are arrested in the differentiation course by the addition of TGF-? 1 which represses some of the myogenic transcription factors.