Alveolar rhabdomyosarcoma (ARMS) is an aggressive childhood cancer of striated muscle characterized by the presence of the PAX3-FOXO1A or PAX7-FOXO1A chimeric oncogenic transcription factor. Identification of their targets is essential for understanding ARMS pathogenesis. To this aim， we analyzed transcriptomic data from rhabdomyosarcoma samples and found that P-cadherin expression is correlated with PAX3/7-FOXO1A presence. We then show that expression of a PAX3 dominant negative variant inhibits P-cadherin expression in ARMS cells. Using mouse models carrying modified Pax3 alleles， we demonstrate that P-cadherin is expressed in the dermomyotome and lies genetically downstream from the myogenic factor Pax3.... More
Alveolar rhabdomyosarcoma (ARMS) is an aggressive childhood cancer of striated muscle characterized by the presence of the PAX3-FOXO1A or PAX7-FOXO1A chimeric oncogenic transcription factor. Identification of their targets is essential for understanding ARMS pathogenesis. To this aim， we analyzed transcriptomic data from rhabdomyosarcoma samples and found that P-cadherin expression is correlated with PAX3/7-FOXO1A presence. We then show that expression of a PAX3 dominant negative variant inhibits P-cadherin expression in ARMS cells. Using mouse models carrying modified Pax3 alleles， we demonstrate that P-cadherin is expressed in the dermomyotome and lies genetically downstream from the myogenic factor Pax3. Moreover， in vitro gel shift analysis and chromatin immunoprecipitation indicate that the P-cadherin gene is a direct transcriptional target for PAX3/7-FOXO1A. Finally， P-cadherin expression in normal myoblasts inhibits myogenesis and induces myoblast transformation， migration and invasion. Conversely， P-cadherin downregulation by small hairpin RNA decreases the transformation， migration and invasive potential of ARMS cells. P-cadherin also favors cadherin switching， which is a hallmark of metastatic progression， by controlling N- and M-cadherin expression and/or localization. Our findings demonstrate that P-cadherin is a direct PAX3-FOXO1A transcriptional target involved in ARMS aggressiveness. Therefore， P-cadherin emerges as a new and attractive target for therapeutic intervention in ARMS.
