Serum protein kinase Cα as a diagnostic biomarker of cancers

BACKGROUND: Several serum biomarkers such as antigens, soluble proteins, metabolites, and genes have been identified for the diagnosis of cancers and for monitoring the recurrence after cancer treatment. METHODS: In the present study, a protein kinase C (PKC) α-specific peptide substrate was phosphorylated with serum samples collected from cancer-bearing mice (U87, A431, HepG2, and A549) and the phosphorylation ratio was detected by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS). RESULTS: The phosphorylation ratio for peptide substrates significantly increased in the serum of cancer-bearing mice compared with the ratio found in control mice. The addition of a PKCα inhibitor induced a concentration-dependent decrease in phosphorylation ratios, but the non-PKCα inhibitors, rottlerin and H-89, did not significantly effect phosphorylation ratios. CONCLUSIONS: These results suggest that serum activated PKCα is a good biomarker applicable to cancer diagnosis.