Tumor promoters cause a rapid and reversible inhibition of the formation and maintenance of electrical cell coupling in culture.

Abstract

The effect of tumor promoters on electrical coupling between human FL cells was investigated with a microelectrode technique. When a low concentration (100 ng/ml) of 12-O-tetradecanoylphorbol 13-acetate (TPA) was added to culture medium, only 6% of the cells showed electrical coupling after 5 hr, whereas in control medium more than 90% of the cells were coupled. In the presence of TPA, cell coupling remained suppressed for at least another 19 hr. When TPA was washed out from the culture medium, the cells commenced electrical coupling: 90% of the cells were coupled within 4 hr of the removal of TPA, a rate very similar to that of nontreated control cells. Therefore, TPA-mediated inhibition of cell coupling is reversible. When TPA was added to a culture in which more than 90% of the cells had already established electrical coupling, the percentage of coupled cells decreased to 6% within 8 hr, indicating that TPA can also diminish already established cell coupling. Inhibition of cell coupling also was achieved with other mouse skin tumor promoters--phorbol 12,13-didecanoate, ingenol dibenzoate, and mezerein--whereas nonpromoting derivatives--phorbol and 4 alpha-phorbol 12,13-didecanoate-showed no effect. None of these compounds changed the membrane potential, membrane resistance, or growth rate of FL cells. Thus, it appears that TPA and structurally-related tumor promoters specifically disturb the formation or function, or both, of cell-cell junctions, without significantly affecting the general properties of the surface membrane or the growth of FL cells.

Modulation of cell communication and carcinogenesis.

“…-RELEVANCE TO CARCINOGENESISNow, phorbol esters, which have been repeatedly demonstrated to be involved in carcinogenesis, have been extensively shown to inhibit intercellular communication, as revealed by electrical coupling [12], dye transfer [11] and metabolic cooperation methods [41,68]. This strongly supports the hypothesis that intercellular communication plays an important role in cell growth and differentiation [33,64].…”

“…Electrical coupling is also recovered upon removal of TPA and previously established coupling is inhibited by retreatment with TPA, indicating that TPA can reversibly inhibit not only the formation but also the maintenance of electrical coupling between FL cells [12].…”

“…Phorbol and 4a-PDD had no effect, consistent with their lack of promoting activity in mouse skin carcinogenesis [20]. None of the phorbol derivatives changes other electrical characters of the membrane, such as membrane potential and input resistance of FL cells, suggesting that tumor promoters do not change the electrophysiological membrane properties of FL cells but specifically affect cell coupling [12]. The capacity of phorbol esters to inhibit electrical coupling is well correlated with their promoting activity in mouse skin [12].…”

“…The potent tumor promoter, TPA, rapidly and reversibly inhibited electrical coupling between human amniotic FL cells [12]. One phorbol derivative, phorbol-12,13-didecanoate (PDD), which is a potentially active promoter in addition to TPA, also inhibited electrical coupling to an extent similar to that of TPA.…”

“…Thereafter, several laboratories confirmed phorbol ester-mediated inhibition of cell communication of various cultured cells including human cells [12,16,18,31,39]. An electrophysiological method was used by us in order to examine whether phorbol ester tumor promoters inhibited the transfer of ions (electrical coupling) between human amniotic FL cells [12].…”