title: TNF-alpha downregulates E-cadherin and sensitizes response to γ-irradiation in Caco-2 cells.
abstract: OBJECTIVE
  The purpose of the present study was to assess the biological effects of TNF-alpha in Caco-2 well-differentiated colon adenocarcinoma cells and to determine radiation sensitivity in order to develop TNF-alpha into a cancer therapeutic agent.
  
  
  METHODS
  A cell viability test was conducted via a colorimetric and colony forming assay after 1 day and 3 days of incubation with TNF-alpha. Western blotting analysis and immunofluorescence staining were conducted to explore TNF-alpha-induced morphological and molecular changes in the adhesion molecules, E-cadherin and claudin-4. The effects of γ-irradiation at a dose of 2 Gy on cell survival were evaluated by a clonogenic assay. The molecular changes in apoptosis-regulatory proteins were assessed by Western blotting.
  
  
  RESULTS
  Caco-2 cells were highly resistant to TNF alpha-induced cell death and 2 Gy of γ-irradiation. However, we observed the downregulation of the adherens junctional protein, E-cadherin and translocation of tight junctional protein, claudin-4 from the membrane to the cytosol induced by TNF-alpha treatment which would indicate cell-cell junction disruptions. These alterations of junctional proteins influenced the regulation of cell death in response to 2 Gy of γ-irradiation. The combined treatment of TNF-alpha with 2 Gy of γ-irradiation reduced the survival of Caco-2 cells by down-regulating bcl-xl and activating JNK pathways.
  
  
  CONCLUSIONS
  These results suggest that TNF-alpha might be potentially applied as a therapeutic agent in order to enhance sensitivity to 2 Gy of γ-irradiation administered in radiotherapy for the treatment of human colon cancer.
authors.affiliation: Lab of Modulation of Radiobiological Response, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: Jae Youn
authors.initials: JY
authors.lastname: Yi
authors.forename: Yu-Jin
authors.initials: YJ
authors.lastname: Jung
authors.forename: Sun Shim
authors.initials: SS
authors.lastname: Choi
authors.forename: Eunkyung
authors.initials: E
authors.lastname: Chung