Proteomic identification of exosomal LRG1: a potential urinary biomarker for detecting NSCLC

In the present research, we aimed to screen for non-small cell lung cancer (NSCLC)-related proteins in urinary exosomes by comparing urinary exosomes proteome of normal controls and NSCLC patients. Urinary exosomes were isolated by ultracentrifugation and identified by electron microscopy. Exosomal proteins were separated by 1-D SDS-PAGE and the differentially expressed bands between healthy controls and NSCLC patients ranging in size from 35 to 45 kD were cut from the gel. After tryptic digestion, 18 proteins were identified by nano-HPLC-chip-MS/MS. The differential expression of leucine-rich α-2-glycoprotein (LRG1) was further validated in urinary exosomes by Western blot and in lung tissue by immunohistochemistry. The LRG1 was found to be expressed at higher levels in urinary exosomes and lung tissue of NSCLC patients. These results suggested that LRG1 may be a candidate biomarker for non-invasive diagnosis of NSCLC in urine.