TUMOR PROMOTERS INDUCE INHIBITION OF GAP JUNCTIONAL INTERCELLULAR COMMUNICATION IN MOUSE EPIDERMAL-CELLS BY AFFECTING THE LOCALIZATION OF CONNEXIN43 AND E-CADHERIN

The molecular and histological effects of tumor promoters on gap junct ional intercellular communication (GJIC) were studied in three mouse e pidermal cell types, representing different stages of tumor formation. GJIC was inhibited by most of the studied compounds (L-ethionine, d-l imonene, o-anisidine, clofibrate, Aroclor 1260 and 1,1'-(2,2,2-trichlo roethylidene)bis(4-chlobenzene) (DDT)) except NaF and phenobarbital (P B). Whatever their effect on GJIC, most of the studied compounds incre ased the phosphorylation state of the gap junction protein expressed i n these cells, connexin43 (Cx43), as shown by Western analysis. All ag ents with GJIC inhibiting capacity changed the intensity of the immuno fluorescent staining of Cx43 on the membrane of the cells, whereas NaF and PB had no effect on Cx43 immunostaining. No association could be found between the type of change in Cx43 localization (changed membran e and/or cytosolic staining) and Cx43 phosphorylation or GJIC inhibiti on. Because the cell adhesion molecule E-cadherin also regulates GJIC, the effects of tumor promoters on E-cadherin protein and localization were studied. No quantitative change could be observed in E-cadherin protein content of cells treated with any of the selected agents. Howe ver, all agents which decreased GJIC, affected E-cadherin immunostaini ng of the membrane, while PB and NaF had no effect. These results show that an association exists between inhibition of GJIC and localizatio n of both connexin43 and E-cadherin protein, but not with Cx43 phospho rylation.