Requirement of Gamma-Carboxyglutamic Acid Modification and Phosphatidylserine Binding for the Activation of Tyro3, Axl, and Mertk Receptors by Growth Arrest-Specific 6.
Requirement of Gamma-Carboxyglutamic Acid Modification and Phosphatidylserine Binding for the Activation of Tyro3, Axl, and Mertk Receptors by Growth Arrest-Specific 6.
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DOI：
10.3389/fimmu.2017.01521
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发表时间：
2017
影响因子：
7.3
通讯作者：
Birge RB
中科院分区：
文献类型：
--
作者：
Geng K;Kumar S;Kimani SG;Kholodovych V;Kasikara C;Mizuno K;Sandiford O;Rameshwar P;Kotenko SV;Birge RB
Tyro3、Axl和Mertk（TAM）受体是同源I型受体酪氨酸激酶，其在多细胞生物体中清除凋亡细胞中具有关键功能。TAM被它们的内源性配体、生长停滞特异性6（Gas6）和蛋白S（Pros1）激活，所述内源性配体作为凋亡细胞上的外部化磷脂酰丝氨酸（PS）和TAM胞外域之间的桥接分子起作用。然而，Gas6/Pros1促进TAM活化的分子机制仍然难以捉摸。使用TAM/IFN γ R1报告细胞系监测功能性TAM活性，我们发现Gas6活性精确地依赖于维生素K介导的γ-羧化，从而用抗凝剂华法林替代维生素K，或通过取代参与PS结合的谷氨酸残基，完全废除Gas6作为TAM配体的活性。此外，使用结构域和点突变，Gas6活性还需要完整的Gla结构域和完整的EGF样结构域，这表明这些结构域协同作用以实现TAM激活。尽管需要γ-羧化和功能性Gla结构域，但非γ-羧化的Gas6和Gla缺失/EGF样结构域缺失突变体仍然保留其结合TAM的能力并充当阻断诱饵配体。最后，我们发现不同来源的PS阳性细胞/囊泡（包括凋亡细胞、钙诱导的应激细胞和外来体）结合Gas6并作为细胞衍生或外来体衍生的配体激活TAM。两者合计，我们的研究结果表明，PS是不可缺少的TAM激活Gas6，并通过推理，提供了新的观点PS，如何调节TAM受体和巨噬细胞。
The Tyro3, Axl, and Mertk (TAM) receptors are homologous type I receptor tyrosine kinases that have critical functions in the clearance of apoptotic cells in multicellular organisms. TAMs are activated by their endogenous ligands, growth arrest-specific 6 (Gas6), and protein S (Pros1), that function as bridging molecules between externalized phosphatidylserine (PS) on apoptotic cells and the TAM ectodomains. However, the molecular mechanisms by which Gas6/Pros1 promote TAM activation remains elusive. Using TAM/IFNγR1 reporter cell lines to monitor functional TAM activity, we found that Gas6 activity was exquisitely dependent on vitamin K-mediated γ-carboxylation, whereby replacing vitamin K with anticoagulant warfarin, or by substituting glutamic acid residues involved in PS binding, completely abrogated Gas6 activity as a TAM ligand. Furthermore, using domain and point mutagenesis, Gas6 activity also required both an intact Gla domain and intact EGF-like domains, suggesting these domains function cooperatively in order to achieve TAM activation. Despite the requirement of γ-carboxylation and the functional Gla domain, non-γ-carboxylated Gas6 and Gla deletion/EGF-like domain deletion mutants still retained their ability to bind TAMs and acted as blocking decoy ligands. Finally, we found that distinct sources of PS-positive cells/vesicles (including apoptotic cells, calcium-induced stressed cells, and exosomes) bound Gas6 and acted as cell-derived or exosome-derived ligands to activate TAMs. Taken together, our findings indicate that PS is indispensable for TAM activation by Gas6, and by inference, provides new perspectives on how PS, regulates TAM receptors and efferocytosis.
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影响因子：
5.2
作者：
Lemke G;Burstyn-Cohen T
通讯作者：
Burstyn-Cohen T
影响因子：
7.3
作者：
Kimani SG;Geng K;Kasikara C;Kumar S;Sriram G;Wu Y;Birge RB
通讯作者：
Birge RB
影响因子：
11.2
作者：
Kirane A;Ludwig KF;Sorrelle N;Haaland G;Sandal T;Ranaweera R;Toombs JE;Wang M;Dineen SP;Micklem D;Dellinger MT;Lorens JB;Brekken RA
通讯作者：
Brekken RA
影响因子：
5.3
作者：
MANFIOLETTI, G;BRANCOLINI, C;SCHNEIDER, C
通讯作者：
SCHNEIDER, C
影响因子：
4.4
作者：
Callahan, MK;Popernack, PM;Henderson, AJ
通讯作者：
Henderson, AJ