title: PAX3 and PAX7 exhibit conserved cis-acting transcription repression domains and utilize a common gain of function mechanism in alveolar rhabdomyosarcoma.
abstract: The t(2;13) and t(1;13) translocations of alveolar rhabdomyosarcoma (ARMS) result in chimeric PAX3-FKHR or PAX7-FKHR transcription factors, respectively. In each chimera, a PAX DNA-binding domain is fused to the C-terminal FKHR transactivation domain. Previously we demonstrated that PAX3-FKHR is more potent than PAX3 because the FKHR transactivation domain is resistant to repression mediated by the PAX3 N-terminus. Here we test the hypothesis that the cis-acting repression domain is a conserved feature of PAX3 and PAX7 and that PAX7-FKHR gains function similarly. Using PAX-specific DNA-binding sites, we found that PAX7 was virtually inactive, while PAX7-FKHR exhibited activity 600-fold above background and was comparable to PAX3-FKHR. Deletion analysis showed that the transactivation domains of PAX7 and PAX7-FKHR are each more potent than either full-length protein, and resistance to cis-repression is responsible for the PAX7-FKHR gain of function. Further deletion mapping and domain swapping experiments with PAX3 and PAX7 showed that their transactivation domains exhibit subtle dose-dependent differences in potency, likely due to regions of structural divergence; while their repression domains are structurally and functionally conserved. Thus, the data support the hypothesis and demonstrate that PAX3 and PAX7 utilize a common gain of function mechanism in ARMS.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Bennicelli
authors.forename: S
authors.initials: S
authors.lastname: Advani
authors.forename: B W
authors.initials: BW
authors.lastname: Schäfer
authors.forename: F G
authors.initials: FG
authors.lastname: Barr
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D018398:Homeodomain Proteins; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism; D051379:Mice; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics*; D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor; D051761:Paired Box Transcription Factors; D010641:Phenotype; D010957:Plasmids; D011993:Recombinant Fusion Proteins; D018232:Rhabdomyosarcoma, Alveolar / Q000235:genetics*; D014157:Transcription Factors; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; 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; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C068686:Pax3 protein, mouse