Use of quantitative shotgun proteomics to identify fibronectin 1 as a potential plasma biomarker for clear cell carcinoma of the kidney.

BACKGROUND Early detection would be one of the most effective means to improve the outcome of renal cell carcinoma (RCC). We searched for a new plasma marker for RCC using a label-free quantitative shotgun proteomics method. METHODS Plasma proteins were digested by trypsin, and the resulting peptides were analyzed by 2-Dimensional Image Converted Analysis of Liquid chromatography mass spectrometry (2DICAL). An identified biomarker candidate was subjected to validation using the Amplified Luminescent Proximity Homogeneous Assay (AlphaLISA). RESULTS Among a total of 23,407 independent MS peaks, we found that the mean intensity of 59 peaks significantly differed between 20 clear cell RCC patients and 20 healthy controls. MS/MS spectra from 16 of the 59 peaks matched the amino acid sequences of the fibronectin 1 (FN1) gene product. The increased plasma level of FN1 in RCC patients was validated in a cohort of in 77 patients and 130 healthy controls (p < 0.0001). CONCLUSIONS The FN1 is considered to be a promising biomarker candidate for clear cell RCC. Furthermore, AlphaLISA is an alternate to the conventional enzyme-linked immunosorbent assay and should prove useful for the rapid validation of biomarker candidates.