Nuclear met-derived exosomes promote HCC metastasis and formation of lung premetastatic niche

Abstract

Met receptor tyrosine kinase triggers a wide range of normal physiological signaling cascades. However, aberration activation of the Met is commonly found in human cancers. Emerging evidence has shown that nuclear Met (nMet) is expressed in some cancerous tissues and cell lines, suggesting nMet could have unexplored functions in the nucleus. Our previous studies have provided the first evidence about the clinical relevance of nMet in human hepatocellular carcinoma (HCC). Functionally, nMet promoted HCC tumorigenesis and metastasis. In our continual study to elucidate the underlying mechanism of nMet in driving HCC metastasis, we explored the significance of exosomes in HCC. In our present study, exosomes were isolated from metastatic MHCC97L HCC cell in which nMet was overexpressed. Electron microscopy images of the exosomes isolated from the conditioned media of control MHCC97L/Vec and MHCC97L/nMet cells showed typical exosome structure with diameter of approximately 50–80 nm. Immunoblotting showed that the isolated exosomes were highly enriched in exosomal markers while depleted of the cytoskeletal protein beta-tubulin, cis-Golgi marker GM130 and nucleoporin p62. Functional assays showed that exosomes derived from MHCC97L/nMet cells significantly augmented both the migratory and invasive properties of normal liver and naı¨ve HCC cells. The uptake of PKH26-labeled nMet-exosomes by naı¨ve cells were investigated by fluorescence microscopy. In animal model, intravenous injection of nMet-exosomes enhanced the incidence of distant metastasis from HCC primary tumor to lungs. Our findings will provide an important paradigm about tumor-derived exosomes in driving metastasis and yield novel mechanistic insights into liver cancer metastasis.