KRAS-dependent Extracellular Vesicles in Colorectal Cancer: Cargo, Biogenesis, and Function

Abstract

Colorectal cancer (CRC) cells release protein-laden extracellular vesicles (EVs) that can alter the tumor microenvironment and spread drug resistance. I compared long RNAs of cells and matched EVs from isogenic CRC cell lines differing only in KRAS status, and show that EV profiles are distinct from cellular expression profiles. Functional assays demonstrated delivery of both mRNAs and lncRNAs by EV transport. From proteomic and RNA-seq data, I found an enrichment of Rab13 protein and mRNA in mutant KRAS small EVs. Rab13 is a small GTPase with functional roles in tight junction assembly and recycling endosomal trafficking. Previously, disruption of cellular Rab13 trafficking inhibited cancer cell proliferation and invasiveness. I found that EVs containing Rab13 mRNA and protein from mutant KRAS cells could promote proliferation and tumorigenicity, and that knockdown of Rab13 in these cells, but not wildtype KRAS cells, inhibited small EV secretion. Recipient cells exposed to reduced EV levels displayed decreased proliferation, functional miRNA transfer, and anchorage-independent growth. Thus, extracellular transfer mediated by Rab13 can account for earlier work that indicated roles for intracellular Rab13 in these assays. I also discovered that Rab13 is enriched in a heterogeneous population of β1-integrin+ EVs that are distinct from CD63+ classical exosomes and appear to be primarily released directly from the plasma membrane in a pathway distinct from release by multivesicular bodies.