RAB-10 Promotes EHBP-1 Bridging of Filamentous Actin and Tubular Recycling Endosomes

EHBP-1 (Ehbp1) is a conserved regulator of endocytic recycling, acting as an effector of small GTPases including RAB-10 (Rab10). Here we present evidence that EHBP-1 associates with tubular endosomal phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] enriched membranes through an N-terminal C2-like (NT-C2) domain, and define residues within the NT-C2 domain that mediate membrane interaction. Furthermore, our results indicate that the EHBP-1 central calponin homology (CH) domain binds to actin microfilaments in a reaction that is stimulated by RAB-10(GTP). Loss of any aspect of this RAB-10/EHBP-1 system in the C. elegans intestinal epithelium leads to retention of basolateral recycling cargo in endosomes that have lost their normal tubular endosomal network (TEN) organization. We propose a mechanism whereby RAB-10 promotes the ability of endosome-bound EHBP-1 to also bind to the actin cytoskeleton, thereby promoting endosomal tubulation.EHBP-1 (Ehbp1) 是一类保守的内吞循环（endocytic recycling）调控因子，可作为包括RAB-10 (Rab10)在内的小GTP酶（small GTPases）的效应蛋白。本研究提供实验证据表明，EHBP-1可通过N端类C2(NT-C2)结构域结合于富含磷脂酰肌醇-4,5-二磷酸[PI(4,5)P2]的管状内体膜，并明确了NT-C2结构域中介导膜结合的关键氨基酸残基。此外，本研究结果显示，EHBP-1的中央钙调蛋白同源(CH)结构域可结合肌动蛋白微丝，且该结合过程可被GTP结合态的RAB-10所促进。在秀丽隐杆线虫(C. elegans)肠上皮中，该RAB-10/EHBP-1信号通路任一环节的功能缺失，都会导致基底侧循环转运底物在丧失正常管状内体网络(TEN)结构的内体中发生滞留。我们提出如下作用机制：RAB-10可促进结合于内体的EHBP-1同时结合肌动蛋白细胞骨架，进而推动内体小管的形成。