Morphological and molecular alterations at the junctional complex in irradiated human colon adenocarcinoma cells, Caco-2.
OBJECTIVE
Ionizing radiation is one of the main modalities used in the treatment of colorectal cancer. Despite a number of epigenetic or non-targeted effects of radiation exposure that have been described, the effect of radiation on cell-cell adhesion in the epithelium has been less studied. We report morphological and molecular alterations induced by ionizing radiation at the junctional complex level of human colon cancer Caco-2 cells.


METHODS
Cells were irradiated with doses of 2, 5 or 10 Gy and the effects on the junctional complex were monitored for different times after irradiation. Alterations of tight and adherens junction components were observed by measuring the transepithelial electrical resistance, by immunofluorescence and immunoblotting and electron microscopy analyses.


RESULTS
Ionizing radiation caused alterations in the junctional complex, as evidenced by: (a) a decrease in the transepithelial electrical resistance, (b) alterations in the pattern of the distribution of junctional proteins as observed for E-cadherin, occludin, and zonula occludens 1 (ZO-1), but with minor changes in claudin-1 localization, and (c) wide spaces between opposed cells. These effects were dose and time-dependent since minor doses of irradiation caused a reversible effect on E-cadherin distribution and transepithelial electrical resistance.


CONCLUSIONS
The results obtained show that ionizing radiation caused redistribution of the main junctional proteins E-cadherin, occludin and ZO-1 with minor changes for claudin-1, leading to disassembly of the junctional complex and loss of its functionality in Caco-2 cells. The molecular mechanisms responsible for these events need further elucidation.
de Carvalho
A Deiró
AD
Grupo de Biologia Estrutural, Divisão de Biologia Celular, Centro de Pesquisas, Instituto Nacional de Câncer, Rio de Janeiro, Brazil.
de Souza
W
W
Morgado-Díaz
J A
JA
D018938:Caco-2 Cells; D002462:Cell Membrane / Q000378:metabolism / Q000528:radiation effects* / Q000648:ultrastructure; D017630:Connexins / Q000378:metabolism* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D017629:Gap Junctions / Q000378:metabolism / Q000528:radiation effects* / Q000648:ultrastructure*; D006801:Humans; D011829:Radiation Dosage
D017630:Connexins