Integrated proteomics and phosphoproteomics study reveals the potential tumour suppressive function of PCK2 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most fatal malignancies worldwide. Patients are often diagnosed at advanced stages and have short overall survivals. Thus, there is an urgent need to understand the underlying mechanism of HCC development and discover new drug targets. In the present study, an ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)-based approach was used to investigate the proteome and phosphoproteome alterations between tumour and non-tumour tissues of HCC patients. In total, 678 proteins and 350 phosphoproteins were significantly changed between the two groups. Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis revealed that glycolysis/glucogenesis was one of the most significantly enriched pathways of down-regulated phosphoproteins and PCK2 was one hub protein in this pathway. Furthermore, the phosphosite of the Ser304 residue in PCK2 is highly evolutionarily conserved among different species and is located near to the GDP, Mn²⁺ binding sites and kinase activity site, which indicate that the phosphorylation of Ser304 may regulate PCK2 activity. HepG2 cell proliferation, invasion and migration were significantly increased when treated with 3-mercaptopicolinic acid, an inhibitor of PCK2, which demonstrated the tumour suppressive activity of PCK2 in HCC. In addition, the low mRNA expression of PCK2 was correlated with poor overall survival of live cancer patients. Overall, our proteomic and phosphoproteomic study revealed the tumour suppressive function of PCK2 in HCC and indicated that activation of its expression or activity may be a potential therapeutic strategy for HCC treatment.