Differential effects of renal carcinogens and tumor promoters on growth promotion and inhibition of gap junctional communication in two rat renal epithelial cell lines

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Abstract
To evaluate the effects of renal carcinogens and tumor promoters on gap junctional intercellular communication (IC) and colony formation, two rat kidney epithelial cell lines were examined in vitro. The NRK-52E line was obtained from the American Type Culture Collection and the NK-4 line was established by us from male F344/NCr rats. The NRK-52E line was co-cultured on a confluent monolayer of lethally irradiated NRK-52E cells to determine colony-forming ability (cloning efficiency) and donal expansion (average surface area of the colonies, SA) and the NK-4 line was cultured on collagen gel. Streptozotocin (STZ), a renal carcinogen, and trisodium nitrilotriacetate monohydrate (NTANa3), a renal carcinogen and tumor promoter, showed mild growth-enhancing effects on both cell lines, as determined by significant increases in SA, but not in cloning efficiency (CE). Sodium barbital (BBNa), a renal tumor promoter, had similar effects, while phenobarbital sodium (PBNa), a non-renal tumor promoter, lacked such activity. The effects of these compounds on gap junctional function were investigated by the Lucifer Yellow dye transfer miroinjection assay using monolayers of NRK-52E and NK-4 cells. We found that STZ, NTANa3 and BBNa inhibited IC in NRK-52E cells, in accordance with their reported tumorigenic and/or tumor-promoting activity in vivo, while PBNa did not. Thus, we could present these findings in NRK-52E cells as an in vitro model to examine the potential tissue-specific effects of renal carcinogens and tumor promoters in vitro. We found, however, that other growth control mechanisms beside IC may play a role, because although the NK-4 line did not possess normal IC, the tumor promoters studied had identical growth-promoting effects on colony formation and expansion in both this cell line and the NRK-52E line.