Abi Is Required for Modulation and Stability but Not Localization or Activation of the SCAR/WAVE Complex
Abi Is Required for Modulation and Stability but Not Localization or Activation of the SCAR/WAVE Complex
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DOI：
10.1128/ec.00116-13
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发表时间：
2013-11-01
期刊：
影响因子：
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通讯作者：
Insall, Robert H.
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文献类型：
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作者：
Davidson, Andrew J.;Ura, Seiji;Insall, Robert H.
SCAR/WAVE 复合物在胞质分裂过程中驱动基于肌动蛋白的突出、细胞迁移和细胞分离。然而，个体复合体成员对整体活动的贡献仍然是个谜。这主要是因为复杂的成员在稳定性方面相互依赖，这限制了实验操作的范围。多项研究表明，Abi 是一个相对较小的复合体成员，通过其聚脯氨酸 C 末端尾部将信号传导与 SCAR/WAVE 复合体定位和激活连接起来。我们生成了盘基网柄菌 Abi 的一系列缺失序列，以研究其在 SCAR 复合物调节中的确切作用，并鉴定了可以稳定该复合物的最小片段。令人惊讶的是，Abi N 末端或 C 末端聚脯氨酸尾部的缺失不会导致复合物募集到前缘或伪足形成方面没有可检测到的缺陷。含有大约 20% Abi 的片段，并且没有任何与已知信号传导途径偶联的位点，使得 SCAR 复合物能够以正常的定位和动力学发挥作用。然而，N端Abi缺失的表达加剧了盘基网柄菌abi突变体的胞质分裂缺陷，早期表明这是由SCAR的不适当激活引起的。出乎意料的是，这表明除了其在复合体稳定性中的作用之外，Abi 并不介导 SCAR 复合体制造伪足的能力。相反，我们认为当 SCAR 复合物通过其他机制激活时，Abi 具有调节作用。
The SCAR/WAVE complex drives actin-based protrusion, cell migration, and cell separation during cytokinesis. However, the contribution of the individual complex members to the activity of the whole remains a mystery. This is primarily because complex members depend on one another for stability, which limits the scope for experimental manipulation. Several studies suggest that Abi, a relatively small complex member, connects signaling to SCAR/WAVE complex localization and activation through its polyproline C-terminal tail. We generated a deletion series of the Dictyostelium discoideum Abi to investigate its exact role in regulation of the SCAR complex and identified a minimal fragment that would stabilize the complex. Surprisingly, loss of either the N terminus of Abi or the C-terminal polyproline tail conferred no detectable defect in complex recruitment to the leading edge or the formation of pseudopods. A fragment containing approximately 20% Abi- and none of the sites that couple to known signaling pathways-allowed the SCAR complex to function with normal localization and kinetics. However, expression of N-terminal Abi deletions exacerbated the cytokinesis defect of the Dictyostelium abi mutant, which was earlier shown to be caused by the inappropriate activation of SCAR. This demonstrates, unexpectedly, that Abi does not mediate the SCAR complex's ability to make pseudopods, beyond its role in complex stability. Instead, we propose that Abi has a modulatory role when the SCAR complex is activated through other mechanisms.