Nobel Laureate Revisiting Lecture – Randy Schekman

Nobel Laureate Revisiting Lecture

Thursday, April 11th at 4 p.m.

Randy Schekman
Nobel Laureate in Physiology or Medicine 2013

Title: Sorting of small RNAs into extracellular vesicles secreted
by human cells

Highly purified extracellular vesicles (EVs) isolated from human cell lines display a small number of substantially (~ 1000 fold) enriched miRNAs that differ from one cell line to another. In spite of the small number of such species, no single RNA sorting sequence is evident. In order to explore the mechanism of RNA sorting, we established a cell-free reaction that reproduces the selective incorporation of synthetic, mature miRNAs (miR223 and miR122) into vesicles formed in a
reaction containing membranes and cytosol from mechanically disrupted HEK293 cells. The sorting reaction requires both membrane and cytosol and is stimulated by hydrolysable ATP and incubation at a physiologic temperature. Using biotinlyated derivatives of two different miRNAs, we found different sets of RNA binding proteins incorporated along with each species, among which the proteins Ybx1 and Lupus La are required to sort mir223 and miR122, respectively. EVs also contain more abundant major species of small RNA including full-length tRNA, Y-RNA and vault RNA, and each requires the Ybx1 protein for selective sorting into exosomes secreted by cells and into vesicles in the cell-free
reaction. The La antigen binds to both 5’ and 3’ signals on miR122 to promote packaging of the RNA into vesicles in the cell-free vesicle biogenesis reaction.

Wallenbergsalen, Nobel Forum,
Karolinska Institutet, Nobels väg 1
Professor Camilla Björkegren
Ann-Mari Dumanski,
Nobel Office, Nobel Forum
08-524 878 00,