Conventional Molecular and Novel Structural Mechanistic Insights into Orderly Organelle Interactions

Mechanistic Insights into Membrane Protein Clustering Revealed by Visualizing EGFR Secretion

Most plasmalemmal proteins are organized into clusters to modulate various cellular functions. However, the machineries that regulate protein clustering remain largely unclear. Here, with EGFR as an example, we directly and in detail visualized the entire process of EGFR from synthesis to secretion onto the plasma membrane (PM) using a high-speed, high-resolution spinning-disk confocal microscope. First, colocalization imaging revealed that EGFR secretory vesicles underwent transport from the ER to the Golgi to the PM, eventually forming different distribution forms on the apical and basal membranes; that is, most EGFR formed larger clusters on the apical membrane than the basal membrane. A dynamic tracking image and further siRNA interference experiment confirmed that fusion of secretory vesicles with the plasma membrane led to EGFR clusters, and we showed that EGFR PM clustering may be intimately related to EGFR signaling and cell proliferation. Finally, we found that the size and origin of the secretory vesicles themselves may determine the difference in the distribution patterns of EGFR on the PM. More importantly, we showed that actin influenced the EGFR distribution by controlling the fusion of secretory vesicles with the PM. Collectively, a comprehensive understanding of the EGFR secretion process helps us to unravel the EGFR clustering process and elucidate the key factors determining the differences in the spatial distribution of EGFR PM, highlighting the correlation between EGFR secretion and its PM distribution pattern.

Spatiotemporal tracking of the transport of RNA nano-drugs: from transmembrane to intracellular delivery

The popularity of RNA nanoparticles (RNPs) has risen rapidly during the past decade due to the development of RNA nanotechnology. Understanding the fast dynamic process of cell entry and intracellular delivery of RNPs is essential for the design of intelligent therapeutic RNA nano-drugs and mRNA vaccines.How the interaction between the membrane and target ligand of RNPs influences the cell entry, and how the dynamic mechanism of RNPs takes place in different organelles remain ill-defined. Herein, the cell entry of Antimir21-RNP-Apt is monitored using a force tracing technique with a high spatiotemporal resolution at the single particle level, the specific interaction of Apt and EGFR promotes the cell entry efficiency and achieves long-lasting curative effects. Furthermore, the intracellular delivery pathway through different organelles is discovered using fluorescence tracking, and the low motility in early endosomes and the high motility in late endosomes are analyzed. This report provides key strategies for engineering RNA nanomedicines and facilitating clinical translation.