DCAF7/WDR68 is required for normal levels of DYRK1A and DYRK1B

Overexpression of the Dual-specificity Tyrosine Phosphorylation-Regulated Kinase 1A (DYRK1A) gene contributes to the retardation, craniofacial anomalies, cognitive impairment, and learning and memory deficits associated with Down Syndrome (DS). DCAF7/HAN11/WDR68 (hereafter WDR68) binds DYRK1A and is required for craniofacial development. Accumulating evidence suggests DYRK1A-WDR68 complexes enable proper growth and patterning of multiple organ systems and suppress inappropriate cell growth/transformation by regulating the balance between proliferation and differentiation in multiple cellular contexts. Here we report, using engineered mouse C2C12 and human HeLa cell lines, that WDR68 is required for normal levels of DYRK1A. However, Wdr68 does not significantly regulate Dyrk1a mRNA expression levels and proteasome inhibition did not restore DYRK1A in cells lacking Wdr68 (Δwdr68 cells). Overexpression of WDR68 increased DYRK1A levels while overexpression of DYRK1A had no effect on WDR68 levels. We further report that WDR68 is similarly required for normal levels of the closely related DYRK1B kinase and that both DYRK1A and DYRK1B are essential for the transition from proliferation to differentiation in C2C12 cells. These findings reveal an additional role of WDR68 in DYRK1A-WDR68 and DYRK1B-WDR68 complexes.双特异性酪氨酸磷酸化调节激酶1A（Dual-specificity Tyrosine Phosphorylation-Regulated Kinase 1A, DYRK1A）基因的过表达，会引发唐氏综合征（Down Syndrome, DS）相关的发育迟缓、颅面畸形、认知障碍以及学习记忆缺陷。DCAF7/HAN11/WDR68（下文简称WDR68）可与DYRK1A结合，且对颅面发育至关重要。日益增多的研究证据表明，DYRK1A-WDR68复合物能够促进多器官系统的正常生长与模式构建，并通过调控多种细胞情境下的增殖与分化平衡，抑制异常的细胞增殖/转化。本研究通过工程改造的小鼠C2C12细胞系与人类海拉（HeLa）细胞系证实，WDR68是维持DYRK1A正常表达水平所必需的因子。然而，Wdr68并不会显著调控Dyrk1a的mRNA表达水平，且蛋白酶体抑制也无法恢复Wdr68缺失细胞（Δwdr68细胞）中的DYRK1A表达量。过表达WDR68可提升DYRK1A的蛋白水平，而过表达DYRK1A则对WDR68的表达水平无显著影响。本研究进一步发现，WDR68同样是维持同源性相近的DYRK1B激酶正常表达水平所必需的；且在C2C12细胞中，DYRK1A与DYRK1B均是细胞从增殖状态向分化状态转变过程中的关键调控因子。上述研究结果揭示了WDR68在DYRK1A-WDR68与DYRK1B-WDR68复合物中的新增功能角色。