Department of Neuroscience and Pharmacology, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.
Mol Cell Biol. 2011 Sep;31(17):3603-15. doi: 10.1128/MCB.01389-10. Epub 2011 Jul 5.
MICALs (molecules interacting with CasL) are atypical multidomain flavoenzymes with diverse cellular functions. The molecular pathways employed by MICAL proteins to exert their cellular effects remain largely uncharacterized. Via an unbiased proteomics approach, we identify MICAL-1 as a binding partner of NDR (nuclear Dbf2-related) kinases. NDR1/2 kinases are known to mediate apoptosis downstream of the mammalian Ste-20-like kinase MST1, and ablation of NDR1 in mice predisposes the mice to cancer as a result of compromised apoptosis. MST1 phosphorylates NDR1/2 kinases at their hydrophobic motif, thereby facilitating full NDR kinase activity and function. However, if and how this key phosphorylation event is regulated are unknown. Here we show that MICAL-1 interacts with the hydrophobic motif of NDR1/2 and that overexpression or knockdown of MICAL-1 reduces or augments NDR kinase activation or activity, respectively. Surprisingly, MICAL-1 is a phosphoprotein but not an NDR or MST1 substrate. Rather, MICAL-1 competes with MST1 for NDR binding and thereby antagonizes MST1-induced NDR activation. In line with this inhibitory effect, overexpression or knockdown of MICAL-1 inhibits or enhances, respectively, NDR-dependent proapoptotic signaling induced by extrinsic stimuli. Our findings unveil a previously unknown biological role for MICAL-1 in apoptosis and define a novel negative regulatory mechanism of MST-NDR signaling.
MICALs（与 CasL 相互作用的分子）是具有多种细胞功能的非典型多结构域黄素酶。MICAL 蛋白发挥其细胞效应所采用的分子途径在很大程度上仍未被描述。通过一种无偏蛋白质组学方法，我们鉴定出 MICAL-1 是 NDR（核 Dbf2 相关）激酶的结合伴侣。已知 NDR1/2 激酶介导哺乳动物 Ste-20 样激酶 MST1 下游的细胞凋亡，并且 NDR1 在小鼠中的缺失会导致细胞凋亡受损，从而使小鼠易患癌症。MST1 在其疏水性基序处磷酸化 NDR1/2 激酶，从而促进完整的 NDR 激酶活性和功能。然而，这个关键磷酸化事件是否以及如何被调节尚不清楚。在这里，我们表明 MICAL-1 与 NDR1/2 的疏水性基序相互作用，并且 MICAL-1 的过表达或敲低分别降低或增强了 NDR 激酶的激活或活性。令人惊讶的是，MICAL-1 是一种磷酸化蛋白，但不是 NDR 或 MST1 的底物。相反，MICAL-1 与 MST1 竞争 NDR 的结合，从而拮抗 MST1 诱导的 NDR 激活。与这种抑制作用一致，MICAL-1 的过表达或敲低分别抑制或增强了由外在刺激诱导的 NDR 依赖性促凋亡信号。我们的发现揭示了 MICAL-1 在细胞凋亡中的一个以前未知的生物学作用，并定义了 MST-NDR 信号的一种新的负调控机制。
