title: PAX7 expression in embryonal rhabdomyosarcoma suggests an origin in muscle satellite cells.
abstract: Rhabdomyosarcoma (RMS) is a common paediatric soft tissue sarcoma that resembles developing foetal skeletal muscle. Tumours of the alveolar subtype frequently harbour one of two characteristic translocations that juxtapose PAX3 or PAX7, and the forkhead-related gene FKHR (FOXO1A). The embryonal subtype of RMS is not generally associated with these fusion genes. Here, we have quantified the relative levels of chimaeric and wild-type PAX transcripts in various subtypes of RMS (n=34) in order to assess the relevance of wild-type PAX3 and PAX7 gene expression in these tumours. We found that upregulation of wild-type PAX3 is independent of the presence of either fusion gene and is unlikely to contribute to tumorigenesis. Most strikingly, upregulated PAX7 expression is almost entirely restricted to cases without PAX3-FKHR or PAX7-FKHR fusion genes and may contribute to tumorigenesis in the absence of chimaeric PAX transcription factors. Furthermore, as myogenic satellite cells are known to express PAX7, this pattern of PAX7 expression suggests this cell type as the origin of these tumours. This is corroborated by the detection of MET (c-met) expression, a marker for the myogenic satellite cell lineage, in all RMS samples expressing wild-type PAX7.
authors.affiliation: Section of Paediatric Oncology, Institute of Cancer Research, Belmont, Sutton, Surrey SM2 5NG, UK. tiffinn@peds.ucsf.edu
authors.forename: N
authors.initials: N
authors.lastname: Tiffin
authors.forename: R D
authors.initials: RD
authors.lastname: Williams
authors.forename: J
authors.initials: J
authors.lastname: Shipley
authors.forename: K
authors.initials: K
authors.lastname: Pritchard-Jones
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D004195:Disease Models, Animal; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation; D018398:Homeodomain Proteins / Q000096:biosynthesis*; D006801:Humans; D051379:Mice; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000166:cytology*; D009419:Nerve Tissue Proteins; D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor; D051761:Paired Box Transcription Factors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018233:Rhabdomyosarcoma, Embryonal / Q000209:etiology / Q000235:genetics* / Q000473:pathology*; D032496:Satellite Cells, Skeletal Muscle; D014157:Transcription Factors / Q000096:biosynthesis; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D004268:DNA-Binding Proteins; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D018398:Homeodomain Proteins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D000072041:PAX3 Transcription Factor; C489409:PAX3 protein, human; D051763:PAX7 Transcription Factor; C497321:PAX7 protein, human; D051761:Paired Box Transcription Factors; C497322:Pax7 protein, mouse; D014157:Transcription Factors; C068686:Pax3 protein, mouse