Kinase activity of protein kinase Cα in serum as a diagnostic biomarker of human lung cancer

Background: Recently, we reported on the existence of activated protein kinase Cα (PKCα) in blood and the possibility for its use in cancer diagnosis. Materials and Methods: In the present study, serum samples collected from patients with different lung cancer types (small-cell cancer, adenocarcinoma, and anaplastic cancer) were phosphorylated with a PKCα-specific peptide substrate and the phosphorylation ratio was detected by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. Results: When 13 patient serum samples were phosphorylated with peptide substrates, phosphorylated peaks were obtained in eight samples. However, no peak associated with the phosphorylated peptide was observed using serum samples obtained from 10 healthy persons. Moreover, broadly used cancer biomarkers (progastrin-releasing peptide, carcinoembryonic antigen, and cytokeratin-19 fragment) were identified in eight samples among the 13 samples studied. Conclusion: These results suggest that serum activated PKCα is a reliable biomarker, applicable to lung cancer diagnosis.