BUB1 (budding uninhibited by benzimidazoles-1) is required for efficient TGF-β signaling, through its role in stabilizing the TGFBR1 and TGFBR2 complex. Here we demonstrate that TGFBR2 phosphorylates BUB1 at Serine-318, which is conserved in primates. S318 phosphorylation abrogates the interaction of BUB1 with TGFBR1 and SMAD2. Using BUB1 truncation domains (1-241, 241-482 and 482-723), we demonstrate that multiple contact points exist between BUB1 and TGF-β signaling components and that these interactions are independent of the BUB1 tetratricopeptide repeat (TPR) domain. Moreover, substitutions in the middle domain (241-482) encompassing S318 reveals that efficient interaction with TGFBR2 occurs only in its dephosphorylated state (241-482 S318A). In contrast, the phospho-mimicking mutant (241-482 S318D) exhibits efficient binding with SMAD2 and its over-expression results in a decrease in TGFBR1-TGFBR2 and TGFBR1-SMAD2 interactions. These findings suggest that TGFBR2 mediated BUB1 phosphorylation at S318 may serve as a switch for the dissociation of the SMAD2-TGFBR complex, and therefore represents a regulatory event for TGF-β signaling. Finally, we provide evidence that the BUB1-TGF-β signaling axis may mediate aggressive phenotypes in a variety of cancers.

中文翻译：

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TGFBR2介导的SUB-318处BUB1的磷酸化是转化生长因子-β信号转导所必需的。

BUB1（不受苯并咪唑-1抑制的芽芽）是有效TGF-β信号转导所必需的，因为它具有稳定TGFBR1和TGFBR2复合物的作用。在这里，我们证明了TGFBR2在丝氨酸318处使BUB1磷酸化，在灵长类动物中保守。S318磷酸化消除了BUB1与TGFBR1和SMAD2的相互作用。使用BUB1截短域（1-241、241-482和482-723），我们证明了BUB1和TGF-β信号传导组件之间存在多个接触点，并且这些相互作用独立于BUB1四肽重复（TPR）域。此外，在包含S318的中间结构域（241-482）中的取代揭示了与TGFBR2的有效相互作用仅在其去磷酸化状态（241-482 S318A）中发生。相反，磷酸化模拟突变体（241-482 S318D）与SMAD2结合有效，其过表达导致TGFBR1-TGFBR2和TGFBR1-SMAD2相互作用降低。这些发现表明，TGFBR2介导的S318的BUB1磷酸化可能充当SMAD2-TGFBR复合物解离的开关，因此代表了TGF-β信号转导的调控事件。最后，我们提供了证据，表明BUB1-TGF-β信号转导轴可能介导多种癌症的侵袭性表型。