TNF-alpha downregulates E-cadherin and sensitizes response to γ-irradiation in Caco-2 cells.
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.
Yi
Jae Youn
JY
Lab of Modulation of Radiobiological Response, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
Jung
Yu-Jin
YJ
Choi
Sun Shim
SS
Chung
Eunkyung
E