BACKGROUND:An imbalance of antiproliferative BMP (bone morphogenetic protein) signaling and proliferative TGF-β (transforming growth factor-β) signaling is implicated in the development of pulmonary arterial hypertension (PAH). The posttranslational modification (eg, phosphorylation and ubiquitination) of TGF-β family receptors, including BMPR2 (bone morphogenetic protein type 2 receptor)/ALK2 (activin receptor-like kinase-2) and TGF-βR2/R1, and receptor-regulated (R) Smads significantly affects their activity and thus regulates the target cell fate. BRCC3 modifies the activity and stability of its substrate proteins through K63-dependent deubiquitination. By modulating the posttranslational modifications of the BMP/TGF-β–PPARγ pathway, BRCC3 may play a role in pulmonary vascular remodeling, hence the pathogenesis of PAH.METHODS:Bioinformatic analyses were used to explore the mechanism of BRCC3 deubiquitinates ALK2. Cultured pulmonary artery smooth muscle cells (PASMCs), mouse models, and specimens from patients with idiopathic PAH were used to investigate the rebalance between BMP and TGF-β signaling in regulating ALK2 phosphorylation and ubiquitination in the context of pulmonary hypertension.RESULTS:BRCC3 was significantly downregulated in PASMCs from patients with PAH and animals with experimental pulmonary hypertension. BRCC3, by de-ubiquitinating ALK2 at Lys-472 and Lys-475, activated receptor-regulated Smad1/5/9 (Smad1/5/9), which resulted in transcriptional activation of BMP-regulated PPARγ, p53, and Id1. Overexpression of BRCC3 also attenuated TGF-β signaling by downregulating TGF-β expression and inhibiting phosphorylation of Smad3. Experiments in vitro indicated that overexpression of BRCC3 or the de-ubiquitin–mimetic ALK2-K472/475R attenuated PASMC proliferation and migration and enhanced PASMC apoptosis. In SM22α-BRCC3-Tg mice, pulmonary hypertension was ameliorated because of activation of the ALK2-Smad1/5-PPARγ axis in PASMCs. In contrast, Brcc3^-/- mice showed increased susceptibility of experimental pulmonary hypertension because of inhibition of the ALK2-Smad1/5 signaling.CONCLUSIONS:These results suggest a pivotal role of BRCC3 in sustaining pulmonary vascular homeostasis by maintaining the integrity of the BMP signaling (ie, the ALK2-Smad1/5-PPARγ axis) while suppressing TGF-β signaling in PASMCs. Such rebalance of BMP/TGF-β pathways is translationally important for PAH alleviation.

中文翻译：

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血管平滑肌细胞中 BRCC3 对 ALK2 的调节：对肺动脉高压的影响

背景：抗增殖 BMP（骨形态发生蛋白）信号和增殖 TGF-β（转化生长因子-β）信号的不平衡与肺动脉高压（PAH）的发生有关。 TGF-β家族受体的翻译后修饰（例如磷酸化和泛素化），包括BMPR2（骨形态发生蛋白2型受体）/ALK2（激活素受体样激酶2）和TGF-βR2/R1，以及受体调节的（ R) Smads 显着影响其活性，从而调节靶细胞的命运。 BRCC3 通过 K63 依赖性去泛素化修饰其底物蛋白的活性和稳定性。 BRCC3可能通过调节BMP/TGF-β-PPARγ通路的翻译后修饰，在肺血管重塑中发挥作用，从而参与PAH的发病机制。方法：采用生物信息学方法探讨BRCC3去泛素化ALK2的机制。使用培养的肺动脉平滑肌细胞 (PASMC)、小鼠模型和特发性 PAH 患者标本来研究肺动脉高压背景下 BMP 和 TGF-β 信号传导在调节 ALK2 磷酸化和泛素化方面的再平衡。 PAH 患者和实验性肺动脉高压动物的 PASMC 显着下调。 BRCC3 通过在 Lys-472 和 Lys-475 处去泛素化 ALK2，激活受体调节的 Smad1/5/9 (Smad1/5/9)，从而导致 BMP 调节的 PPARγ、p53 和 Id1 的转录激活。 BRCC3 的过表达还通过下调 TGF-β 表达并抑制 Smad3 磷酸化来减弱 TGF-β 信号传导。体外实验表明，BRCC3 或去泛素模拟物 ALK2-K472/475R 的过度表达可减弱 PASMC 增殖和迁移，并增强 PASMC 凋亡。在 SM22α-BRCC3-Tg 小鼠中，由于 PASMC 中 ALK2-Smad1/5-PPARγ 轴的激活，肺动脉高压得到改善。相反，由于 ALK2-Smad1/5 信号传导的抑制， Brcc3 ^-/-小鼠表现出实验性肺动脉高压的易感性增加。 结论：这些结果表明 BRCC3 通过维持 BMP 信号传导的完整性在维持肺血管稳态中发挥着关键作用（即 ALK2-Smad1/5-PPARγ 轴），同时抑制 PASMC 中的 TGF-β 信号传导。 BMP/TGF-β 通路的这种重新平衡对于 PAH 缓解具有重要意义。