Endocytosis and recycling control the uptake and retrieval of various materials in eukaryotic cells. Mammalian cells have developed several recycling routes including the relatively extensively studied “fast” and “slow” tubulovesicular recycling pathways. Nevertheless, endocytic recycling pathways beyond the canonical “fast” and “slow” recycling pathways remain largely unknown.

A research group led by Dr. HE Kangmin from the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences recently identified a novel endocytic recycling mechanism with kiss-and-run membrane fusion. Scientists named the mechanism clathrin-associated fast endosomal recycling pathway (CARP).

This novel endocytic recycling pathway employed a distinct set of molecular machinery to generate the recycling carriers and facilitate the unexpected kiss-and-run membrane fusion.

The study entitled “Clathrin-associated carriers enable recycling through a kiss-and-run mechanism” was published in Nature Cell Biology on September 19, 2024.

By utilizing a "coincidence detecting" lipid biosensor that selectively recognizes clathrin-associated structures containing PI(4,5)P₂, researchers identified a population of lipid sensor-positive but AP2-negative clathrin-associated structures that transiently visit the plasma membrane.

With advanced 3D imaging and super-resolution imaging techniques, these structures were found to be intracellular clathrin/AP1-associated carriers.

“A remarkable discovery was that these clathrin/AP1-associated recycling carriers can partially fuse with the plasma membrane and are subsequently retrieved and released,” said HE Kangmin.

To characterize the molecular components and properties of the clathrin-associated recycling carriers, HE and his team conducted TIRF microscopy-based imaging screening. They identified a series of proteins recruited at various stages throughout the generation, approach, fusion, and retrieval of the clathrin-associated recycling carriers.

Furthermore, they demonstrated that these carriers are generated from a subdomain of early endosomes that lack the retrieval complexes.

By tracking the endocytic recycling of agonist-stimulated β2 adrenergic receptors from the GPCR families and epidermal growth factor receptors from the receptor tyrosine kinases, the researchers revealed that these clathrin-associated recycling carriers could mediate the fast recycling of signaling receptors back to the plasma membrane.

This work was funded by the National Natural Science Foundation of China and the National Key R&D Program of China.