Integrated proteome and phosphoproteome analyses of peripheral blood mononuclear cells in primary Sjögren syndrome patients

Primary Sjögren syndrome (pSS) is a common autoimmune disease. Here, we performed the first proteome and phosphoproteome analyses of peripheral blood mononuclear cells in pSS patients to obtain a comprehensive profile and identify the potential crucial proteins and pathways for the screening and evaluation of pSS patients. Peripheral blood mononuclear cells from 8 pSS-confirmed patients (American-European Consensus Group Criteria, 2002) and 10 normal controls were selected. Label-free quantitative proteomics was utilized to obtain quantitative information. In total, 787 proteins were identified as differentially expressed proteins, and 175 phosphosites on 123 proteins were identified as differentially phosphorylated proteins. We performed functional enrichment analyses with these proteins and phosphoproteins based on public database. Furthermore, protein-protein interaction network analyses were performed by using multiple algorithms. Using module and hub protein analyses, we identified 16 modules for the proteins, 2 clusters for the phosphoproteins and selected the top 10 hub proteins. Finally, we identified 22 motifs using motif analysis of the phosphosites and found 17 newly identified motifs, while 6 motifs were experimentally verified for known protein kinases. The findings distinguished pSS patients from normal controls at the peripheral blood mononuclear cells level and revealed potential candidates for use in pSS diagnosis.