Department of Genetics, Louisiana State University Health Sciences Center, 533 Bolivar Street, New Orleans, Louisiana 70112, USA.
Biochemistry. 2009 Dec 15;48(49):11786-95. doi: 10.1021/bi9012947.
The myogenic transcription factor Pax3 plays an essential role in early skeletal muscle development and is a key component in alveolar rhabdomyosarcoma (ARMS), a childhood solid muscle tumor. ARMS is characterized by a t(2;13) chromosomal translocation resulting in the fusion of the 5' Pax3 sequences to the 3' FOXO1 sequences to encode the oncogenic fusion protein, Pax3-FOXO1. Posttranslational modifications such as phosphorylation are common mechanisms by which transcription factors are regulated. Consistent with this fact, we demonstrated in a previous report that Pax3 is phosphorylated on Ser205 in proliferating, but not differentiated, primary myoblasts. However, the kinase that mediates this phosphorylation event has yet to be identified. In addition, it is not known whether Pax3-FOXO1 is phosphorylated at this site or how the phosphorylation of the fusion protein changes during early myogenic differentiation. In this report we identify CK2 (formerly termed "casein kinase II") as the kinase responsible for phosphorylating Pax3 and Pax3-FOXO1 at Ser205 in proliferating mouse primary myoblasts. Furthermore, we demonstrate that, in contrast to wild-type Pax3, phosphorylation at Ser205 persists on Pax3-FOXO1 throughout early myogenic differentiation. Finally, we show that Pax3-FOXO1 is phosphorylated at Ser205 in a variety of translocation-containing ARMS cell lines. The results presented in this report not only suggest a possible mechanism by which the disregulation of Pax3-FOXO1 may contribute to tumorigenesis but also identify a novel target for the development of therapies for the treatment of ARMS.
肌源性转录因子 Pax3 在早期骨骼肌发育中发挥着重要作用，是肺泡横纹肌肉瘤（ARMS）的关键组成部分，ARMS 是一种儿童实体肌肉肿瘤。ARMS 的特征是 t（2；13）染色体易位，导致 5' Pax3 序列与 3' FOXO1 序列融合，从而编码致癌融合蛋白 Pax3-FOXO1。磷酸化等翻译后修饰是转录因子调节的常见机制。与这一事实一致，我们在之前的一份报告中证明，在增殖的，但不是分化的，原代肌母细胞中，Pax3 在 Ser205 上发生磷酸化。然而，介导这种磷酸化事件的激酶尚未被确定。此外，尚不清楚 Pax3-FOXO1 是否在此位点发生磷酸化，或者融合蛋白的磷酸化如何在早期肌生成分化过程中发生变化。在本报告中，我们确定 CK2（以前称为“酪蛋白激酶 II”）是负责在增殖的小鼠原代肌母细胞中磷酸化 Pax3 和 Pax3-FOXO1 的 Ser205 的激酶。此外，我们证明，与野生型 Pax3 相比，Pax3-FOXO1 的 Ser205 磷酸化在早期肌生成分化过程中持续存在。最后，我们表明 Pax3-FOXO1 在各种含有易位的 ARMS 细胞系中在 Ser205 上发生磷酸化。本报告中提出的结果不仅表明了 Pax3-FOXO1 失调可能导致肿瘤发生的一种可能机制，而且还确定了开发用于治疗 ARMS 的治疗方法的新靶标。
