Department of Oral Biology, BK 21 FOUR Project, Yonsei University College of Dentistry, Seoul 03722, Korea.
These authors contributed equally to this work.
Mol Cells. 2021 Aug 31;44(8):591-601. doi: 10.14348/molcells.2021.0082.
Cilia are highly specialized organelles that extend from the cell membrane and function as cellular signaling hubs. Thus, cilia formation and the trafficking of signaling molecules into cilia are essential cellular processes. TULP3 and Tubby (TUB) are members of the tubby-like protein (TULP) family that regulate the ciliary trafficking of G-protein coupled receptors, but the functions of the remaining TULPs (i.e., TULP1 and TULP2) remain unclear. Herein, we explore whether these four structurally similar TULPs share a molecular function in ciliary protein trafficking. We found that TULP3 and TUB, but not TULP1 or TULP2, can rescue the defective cilia formation observed in -knockout (KO) hTERT RPE-1 cells. TULP3 and TUB also fully rescue the defective ciliary localization of ARL13B, INPP5E, and GPR161 in KO RPE-1 cells, while TULP1 and TULP2 only mediate partial rescues. Furthermore, loss of TULP3 results in abnormal IFT140 localization, which can be fully rescued by TUB and partially rescued by TULP1 and TULP2. TUB's capacity for binding IFT-A is essential for its role in cilia formation and ciliary protein trafficking in RPE-1 cells, whereas its capacity for PIP binding is required for proper cilia length and IFT140 localization. Finally, chimeric TULP1 containing the IFT-A binding domain of TULP3 fully rescues ciliary protein trafficking, but not cilia formation. Together, these two TULP domains play distinct roles in ciliary protein trafficking but are insufficient for cilia formation in RPE-1 cells. In addition, TULP1 and TULP2 play other unknown molecular roles that should be addressed in the future.
纤毛是从细胞膜延伸出来的高度特化的细胞器，作为细胞信号枢纽发挥作用。因此，纤毛的形成和信号分子向纤毛的运输是细胞的基本过程。TULP3 和 Tubby（TUB）是 Tubby 样蛋白（TULP）家族的成员，它们调节 G 蛋白偶联受体的纤毛运输，但其余 TULP（即 TULP1 和 TULP2）的功能仍不清楚。本文中，我们探讨了这四个结构相似的 TULP 是否在纤毛蛋白运输中具有共同的分子功能。我们发现，TULP3 和 TUB，但不是 TULP1 或 TULP2，可以挽救 -/-敲除（KO）hTERT RPE-1 细胞中观察到的纤毛形成缺陷。TULP3 和 TUB 还完全挽救了 KO RPE-1 细胞中 ARL13B、INPP5E 和 GPR161 的纤毛定位缺陷，而 TULP1 和 TULP2 仅介导部分挽救。此外，TULP3 的缺失导致 IFT140 定位异常，TUB 可完全挽救，TULP1 和 TULP2 可部分挽救。TUB 与 IFT-A 的结合能力对于其在 RPE-1 细胞中的纤毛形成和纤毛蛋白运输中的作用至关重要，而其与 PIP 的结合能力对于适当的纤毛长度和 IFT140 定位是必需的。最后，含有 TULP3 IFT-A 结合结构域的嵌合 TULP1 完全挽救了纤毛蛋白的运输，但不能挽救纤毛的形成。总之，这两个 TULP 结构域在纤毛蛋白运输中发挥不同的作用，但不足以在 RPE-1 细胞中形成纤毛。此外，TULP1 和 TULP2 还发挥着其他未知的分子作用，这在未来应该得到解决。
