OBJECTIVEThe conversion of arginine into citrulline, termed citrullination, has important consequences for the structure and function of proteins. The present study aimed to identify novel citrullinated proteins in 10 tumor cell lines by 2-D Western blotting (2-D WB).

METHODSTwo identical two-dimensional electrophoresis (2-DE) gels were prepared using extracts from ten cultured human tumor cell lines: ECA(esophageal cancer cells), HEPG2 (hepatocellular carcinoma cells), SKOV3 (ovarian cancer cells), MCF-7 (breast cancer cells), H292 (lung mucoepidermoid carcinoma cells), HeLa (cervical cancer cells), Lovo (colon cancer cells), OS-RC (renal cell carcinoma cells), PANC-1 (pancreatic cancer cells), and SGC (gastric cancer cells). The expression profiles on one 2-DE gels were trans-blotted to PVDF membranes, and the blots were then probed with an anti-citrulline antibody. By comparing the 2-DE profile with the parallel 2-D WB profile at a global level, protein spots with immuno-signals were collected from the second 2-DE gel and identified using mass spectrometry. Immunoprecipitation was used to verify the expression and citrullination of the targeted proteins in the tumor cell lines.

RESULTS2-D WB and mass spectrometry identified citrullinated ENO1 (α-enolase), HSP60 (heat shock protein 60), KRT8 (keratin 8), TUBB (tubulin beta), TCRβ (T cell receptor β chain), VIME (vimentin) and PDI in these cell lines. Immunoprecipitation analyses verified the expression and citrullination of ENO1, HSP60, KRT8, and TUBB in the total protein lysates of the tumor cell lines.

CONCLUSIONThe citrullination of proteins ENO1, HSP60, KRT8, and TUBB suggests a new mechanism in the tumorigenic process.