Carbon nanotubes as molecular transporters to study a new mechanism for molecular entry into the cell nucleus using actin polymerization force

The transport of macromolecules into the cell nucleus occurs through nuclear pore complexes (NPCs) and is mediated by cellular receptors. Recently, a novel mechanism of nuclear entry, in which actin polymerization provides a propulsive force driving the transport through the NPC, has been proposed. This mechanism is used by the nucleocapsid from baculovirus, one of the largest viruses to replicate in the nucleus of their host cells, which crosses the NPC and enters the nucleus independently of cellular receptors. The baculovirus nucleocapsid contains a protein that hijacks the cellular actin polymerization machinery to assemble actin filaments that propel the nucleocapsid through the host cell cytoplasm. In this study, we functionalized carbon nanotubes by covalently attaching a protein domain responsible for inducing actin polymerization and investigated their nuclear entry. We found that the functionalized carbon nanotubes were able to enter the cell nucleus under permissive conditions for actin polymerization, but not when this process was inhibited. We conclude that the mechanical force generated by actin polymerization can drive cargo entry into the cell nucleus. Our results support a novel force-driven mechanism for molecular entry into the cell nucleus.大分子向细胞核内的转运经由核孔复合体（nuclear pore complexes, NPCs）完成，且由细胞受体介导。近年来，学界提出了一种全新的核输入机制：肌动蛋白聚合可提供推进力，驱动转运物穿过核孔复合体。杆状病毒是一类可在宿主细胞核内复制的大型病毒，其核衣壳能够不依赖细胞受体直接跨越核孔复合体进入细胞核，便采用了该机制。杆状病毒核衣壳携带一种蛋白质，可劫持宿主细胞的肌动蛋白聚合机制，以组装肌动蛋白丝，推动核衣壳穿越宿主细胞质。本研究中，我们通过共价结合负责诱导肌动蛋白聚合的蛋白质结构域，对碳纳米管进行功能化修饰，并探究了其核输入行为。实验结果显示，在肌动蛋白聚合的容许条件下，经功能化修饰的碳纳米管可成功进入细胞核；而当该聚合过程被抑制时，则无法实现核输入。综上，肌动蛋白聚合产生的机械力可驱动运载物进入细胞核。本研究结果为分子核输入的新型力驱动机制提供了实验支撑。