Collaborative Research Program for Cell Adhesion Molecules, Shanghai University School of Life Sciences, Shanghai, China.
Department of Molecular Cardiology, Lerner Research Institute Cleveland Clinic, Cleveland, OH, USA.
Cell Commun Signal. 2019 Aug 20;17(1):101. doi: 10.1186/s12964-019-0407-6.
Previously sharpin has been identified as an endogenous inhibitor of β1-integrin activation by directly binding to a conserved region in the cytoplasmic tails (CTs) of the integrin β1-associated α subunits.
Here we employed biochemical approaches and cellular analyses to evaluate the function and molecular mechanism of the sharpin-kindlin-1 complex in regulating β1-integrin activation.
In this study, we found that although the inhibition of sharpin on β1-integrin activation could be confirmed, sharpin had no apparent effect on integrin αIIbβ3 activation in CHO cell system. Notably, a direct interaction between sharpin and the integrin β1 CT was detected, while the interaction of sharpin with the integrin αIIb and the β3 CTs were substantially weaker. Importantly, sharpin was able to inhibit the talin head domain binding to the integrin β1 CT, which can mechanistically contribute to inhibiting β1-integrin activation. Interestingly, we also found that sharpin interacted with kindlin-1, and the interaction between sharpin and the integrin β1 CT was significantly enhanced when kindlin-1 was present. Consistently, we observed that instead of acting as an activator, kindlin-1 actually suppressed the talin head domain mediated β1-integrin activation, indicating that kindlin-1 may facilitate recruitment of sharpin to the integrin β1 CT.
Taken together, our findings suggest that sharpin may complex with both kindlin-1 and the integrin β1 CT to restrict the talin head domain binding, thus inhibiting β1-integrin activation.
先前已鉴定出 sharpin 通过直接结合整合素 β1 相关的 α 亚基胞质尾部（CT）中的保守区域，成为 β1-整联蛋白激活的内源性抑制剂。
在这里，我们采用生化方法和细胞分析来评估 sharpin-kindlin-1 复合物在调节 β1-整联蛋白激活中的功能和分子机制。
在这项研究中，我们发现尽管可以证实 sharpin 对 β1-整联蛋白激活的抑制作用，但 sharpin 在 CHO 细胞系统中对整合素 αIIbβ3 的激活没有明显影响。值得注意的是，检测到 sharpin 与整合素 β1 CT 之间的直接相互作用，而 sharpin 与整合素 αIIb 和 β3 CT 的相互作用则明显较弱。重要的是，sharpin 能够抑制 talin 头部结构域与整合素 β1 CT 的结合，这可以从机制上有助于抑制 β1-整联蛋白的激活。有趣的是，我们还发现 sharpin 与 kindlin-1 相互作用，当存在 kindlin-1 时，sharpin 与整合素 β1 CT 的相互作用明显增强。一致地，我们观察到 kindlin-1 实际上不是作为激活剂，而是抑制 talin 头部结构域介导的 β1-整联蛋白激活，表明 kindlin-1 可能促进 sharpin 募集到整合素 β1 CT。
综上所述，我们的研究结果表明，sharpin 可能与 kindlin-1 和整合素 β1 CT 形成复合物，限制 talin 头部结构域的结合，从而抑制 β1-整联蛋白的激活。
