Extracellular vesicles (EVs) play critical roles in intercellular communications, which contain valuable
biomarkers for the detection of
cancers. Phosphoproteomics analysis of human saliva EVs (sEVs) can help to discover
lung cancer-related candidates. Due to the low abundance of
phosphoproteins in sEVs, an efficient, reproducible, and cost-effective strategy is required for their enrichment. Here, we compared the latest
phosphopeptide techniques, including TiO2, ZrO2,
CaTiO3, and Ti4+-
IMAC (immobilized
metal affinity chromatography) methods, for
phosphopeptide isolation. Our data demonstrated that Ti4+-
IMAC was the superior one. By using the optimized Ti4+-
IMAC approach, we identified more than 500 sEV
phosphopeptides. Quantitative proteomics was employed to comprehensively decipher the sEV phosphoproteome of the normal group (n = 6) and
lung cancer group (n = 6). Accordingly, 524 and 333
phosphopeptides were enriched, respectively, which corresponded to 439 and 282
phosphoproteins. In total, 857 unique sEV
phosphopeptides corresponding to 721
phosphoproteins were revealed. Among 493 identified phosphosites, 37 were upregulated (> 1.5) and 217 were downregulated (< 0.66) in the
cancer group. Our data collectively demonstrated that Ti4+-
IMAC is an efficient and reproducible technology for comprehensive analysis of sEV phosphoproteome. Differentially expressed sEV
phosphoproteins and phosphosites might be used for the detection of
lung cancer non-invasively.