Department of Clinical Research and Development, National Cerebral and Cardiovascular Center, 6-1 Kishibe- Shimmachi, Suita, Osaka, 564-8565, Japan.
Department of Cardiovascular and Renal Medicine, Hyogo College of Medicine, Hyogo, Japan.
Sci Rep. 2021 Nov 29;11(1):23056. doi: 10.1038/s41598-021-02390-0.
Cardiogenesis requires the orchestrated spatiotemporal tuning of BMP signalling upon the balance between induction and counter-acting suppression of the differentiation of the cardiac tissue. SMADs are key intracellular transducers and the selective degradation of SMADs by the ubiquitin-proteasome system is pivotal in the spatiotemporal tuning of BMP signalling. However, among three SMADs for BMP signalling, SMAD1/5/9, only the specific E3 ligase of SMAD9 remains poorly investigated. Here, we report for the first time that SMAD9, but not the other SMADs, is ubiquitylated by the E3 ligase ASB2 and targeted for proteasomal degradation. ASB2, as well as Smad9, is conserved among vertebrates. ASB2 expression was specific to the cardiac region from the very early stage of cardiac differentiation in embryogenesis of mouse. Knockdown of Asb2 in zebrafish resulted in a thinned ventricular wall and dilated ventricle, which were rescued by simultaneous knockdown of Smad9. Abundant Smad9 protein leads to dysregulated cardiac differentiation through a mechanism involving Tbx2, and the BMP signal conducted by Smad9 was downregulated under quantitative suppression of Smad9 by Asb2. Our findings demonstrate that ASB2 is the E3 ligase of SMAD9 and plays a pivotal role in cardiogenesis through regulating BMP signalling.
心脏发生需要在诱导和对抗心脏组织分化的抑制之间平衡时，对 BMP 信号进行协调的时空调节。SMADs 是关键的细胞内转导子，泛素-蛋白酶体系统对 SMADs 的选择性降解在 BMP 信号的时空调节中至关重要。然而，在 BMP 信号的三个 SMADs 中，SMAD1/5/9 中，只有 SMAD9 的特定 E3 连接酶仍未得到充分研究。在这里，我们首次报道 SMAD9 而不是其他 SMADs 被 E3 连接酶 ASB2 泛素化并靶向蛋白酶体降解。ASB2 与 Smad9 在脊椎动物中是保守的。ASB2 的表达在胚胎发生中从心脏分化的早期就具有心脏区域特异性。斑马鱼中 Asb2 的敲低导致心室壁变薄和心室扩张，这可以通过同时敲低 Smad9 来挽救。丰富的 Smad9 蛋白通过涉及 Tbx2 的机制导致心脏分化失调，并且在通过 Asb2 对 Smad9 进行定量抑制下，Smad9 介导的 BMP 信号被下调。我们的研究结果表明，ASB2 是 SMAD9 的 E3 连接酶，通过调节 BMP 信号在心脏发生中发挥关键作用。
