We report here that the autocrine signaling mediated by growth and differentiation factor 6 (GDF6), a member of the bone morphogenetic protein (BMP) family of cytokines, maintains Ewing sarcoma growth by preventing Src hyperactivation. Surprisingly, Ewing sarcoma depends on the prodomain, not the BMP domain, of GDF6. We demonstrate that the GDF6 prodomain is a ligand for CD99, a transmembrane protein that has been widely used as a marker of Ewing sarcoma. The binding of the GDF6 prodomain to the CD99 extracellular domain results in recruitment of CSK (C-terminal Src kinase) to the YQKKK motif in the intracellular domain of CD99, inhibiting Src activity. GDF6 silencing causes hyperactivation of Src and p21-dependent growth arrest. We demonstrate that two GDF6 prodomain mutants linked to Klippel-Feil syndrome are hyperactive in CD99-Src signaling. These results reveal a cytokine signaling pathway that regulates the CSK-Src axis and cancer cell proliferation and suggest the gain-of-function activity for disease-causing GDF6 mutants.

我们在这里报告，由生长和分化因子6（GDF6），骨形态发生蛋白（BMP）细胞因子家族成员介导的自分泌信号传导，通过阻止Src过度活化来维持尤因肉瘤的生长。令人惊奇的是，尤因肉瘤依赖于GDF6的前结构域而不是BMP结构域。我们证明，GDF6前结构域是CD99（一种跨膜蛋白，已被广泛用作尤因肉瘤的标志物）的配体。GDF6前结构域与CD99细胞外结构域的结合导致CSK（C端Src激酶）募集到CD99细胞内结构域的YQKKK基序，从而抑制Src活性。GDF6沉默导致Src过度激活和p21依赖性生长停滞。我们证明了两个链接到Klippel-Feil综合征的GDF6前结构域突变体在CD99-Src信号传导中活跃。