Radiat Oncol J.  2017 Sep;35(3):281-288. 10.3857/roj.2017.00255.

Identification of CEA-interacting proteins in colon cancer cells and their changes in expression after irradiation

  • 1Colorectal Cancer Branch, Research Institute, National Cancer Center, Goyang, Korea.
  • 2Department of Radiation Oncology, Soonchunhyang University College of Medicine, Soonchunhyang University Hospital, Cheonan, Korea. md6630@schmc.ac.kr


The serum carcinoembryonic antigen (CEA) level has been recognized as a prognostic factor in colorectal cancer, and associated with response of rectal cancer to radiotherapy. This study aimed to identify CEA-interacting proteins in colon cancer cells and observe post-irradiation changes in their expression.
CEA expression in colon cancer cells was examined by Western blot analysis. Using an anti-CEA antibody or IgG as a negative control, immunoprecipitation was performed in colon cancer cell lysates. CEA and IgG immunoprecipitates were used for liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Proteins identified in the CEA immunoprecipitates but not in the IgG immunoprecipitates were selected as CEA-interacting proteins. After radiation treatment, changes in expression of CEA-interacting proteins were monitored by Western blot analysis.
CEA expression was higher in SNU-81 cells compared with LoVo cells. The membrane localization of CEA limited the immunoprecipitation results and thus the number of CEA-interacting proteins identified. Only the Ras-related protein Rab-6B and lysozyme C were identified as CEA-interacting proteins in LoVo and SNU-81 cells, respectively. Lysozyme C was detected only in SNU-81, and CEA expression was differently regulated in two cell lines; it was down-regulated in LoVo but up-regulated in SNU-81 in radiation dosage-dependent manner.
CEA-mediated radiation response appears to vary, depending on the characteristics of individual cancer cells. The lysozyme C and Rab subfamily proteins may play a role in the link between CEA and tumor response to radiation, although further studies are needed to clarify functional roles of the identified proteins.


Carcinoembryonic antigen; Colorectal neoplasms; Rab-6B; Lysozyme C; Radiation
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