School of Pharmacy, Shanghai Jiao Tong University, Shanghai 200240, China.
Mucosal Immunology Lab combined program in Pediatric Gastroenterology and Nutrition, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA.
Cells. 2020 May 4;9(5):1132. doi: 10.3390/cells9051132.
Coordinated actions of Rab and Rho are necessary for numerous essential cellular processes ranging from vesicle budding to whole cell movement. How Rab and Rho are choreographed is poorly understood. Here, we report a protein complex comprised of kalirin, a Rho guanine nucleotide exchange factor (GEF) activating Rac1, and RabGEF transport protein particle (TRAPP). Kalirin was identified in a mass spectrometry analysis of proteins precipitated by trappc4 and detected on membranous organelles containing trappc4. Acute knockdown of kalirin did not affect trappc4, but significantly reduced overall and membrane-bound levels of trappc9, which specifies TRAPP toward activating Rab11. Trappc9 deficiency led to elevated expression of kalirin in neurons. Co-localization of kalirin and Rab11 occurred at a low frequency in NRK cells under steady state and was enhanced upon expressing an inactive Rab11 mutant to prohibit the dissociation of Rab11 from the kalirin-TRAPP complex. The small RNA-mediated depletion of kalirin diminished activities in cellular membranes for activating Rab11 and resulted in a shift in size of Rab11 positive structures from small to larger ones and tubulation of recycling endosomes. Our study suggests that kalirin and TRAPP form a dual GEF complex to choreograph actions of Rab11 and Rac1 at recycling endosomes.
Rab 和 Rho 的协调作用对于从囊泡出芽到整个细胞运动等许多基本细胞过程都是必需的。Rab 和 Rho 是如何协调的还不太清楚。在这里，我们报告了一个由 kalirin 组成的蛋白质复合物，kalirin 是一种激活 Rac1 的 Rho 鸟嘌呤核苷酸交换因子 (GEF)，以及 RabGEF 转运蛋白颗粒 (TRAPP)。kalirin 是通过 trappc4 沉淀的蛋白质的质谱分析中鉴定出来的，并在含有 trappc4 的膜细胞器上检测到。kalirin 的急性敲低不会影响 trappc4，但显著降低了 trappc9 的总水平和膜结合水平，trappc9 特异性地将 TRAPP 激活 Rab11。TRAPP9 缺陷导致神经元中 kalirin 的表达升高。在 NRK 细胞中，kalirin 和 Rab11 在稳态下很少共定位，并且在表达一种失活的 Rab11 突变体以阻止 Rab11 从 kalirin-TRAPP 复合物中解离时，共定位增强。通过小 RNA 耗竭 kalirin 降低了激活 Rab11 的细胞内膜活性，并导致 Rab11 阳性结构从小到大的转变以及循环内体的管化。我们的研究表明，kalirin 和 TRAPP 形成一个双重 GEF 复合物，以协调循环内体中 Rab11 和 Rac1 的作用。
