Abstract A62: Phosphorylation of Ser205 by the protein kinase CK2 persists on Pax3-FOXO1, but not Pax3, throughout myogenic differentiation

Abstract

The myogenic transcription factor Pax3 plays an essential role in early skeletal muscle development and is a key factor in Alveolar rhabdomyosarcoma (ARMS), a childhood solid muscle tumor. ARMS is associated with an unfavorable prognosis due to the propensity for wide dissemination and a poor response to chemotherapy. The characteristic translocation in ARMS results in the fusion of the 5' Pax3 sequences to the 3' FOXO1a sequences to encode a fusion protein, Pax3‐FOXO1a. Post translational modifications such as phosphorylation are common mechanisms of regulating transcription factors, including Pax3 and FOXO1a. The Pax3 domain of Pax3‐FOXO1a is phosphorylated at multiple sites which positively influences the DNA‐binding activity and subsequent transcriptional activity of Pax3‐FOXO1a. Here, we show that both Pax3 and Pax3‐FOXO1a are phosphorylated at Ser205 in proliferating mouse primary myoblasts and identify Casein kinase II as the kinase that phosphorylates Pax3 and Pax3‐FOXO1a at Ser205. Furthermore, we demonstrate that Pax3‐FOXO1a, but not Pax3, is constitutively phosphorylated at Ser205 throughout differentiation of mouse primary myoblasts. Finally, we show that Pax3‐FOXO1a is phosphorylated at Ser205 in a variety of translocation containing ARMS cell lines. These results suggest a possible mechanism by which the disregulation of Pax3‐FOXo1a may contribute to tumorigenesis.