Effect of growth state, tumor promoters, and transformation upon intercellular communication between C3H/10T1/2 murine fibroblasts

Diminished intercellular communication has been associated withheightened sensitivity of cultured cells to morphological transformationand enhancement of transformation by tumor promoters. Microinjectionof Lucifer yellow dye was employed to evaluate intercellularcommunication between transformable C3H/10T1/2 murine fibroblastsunder a variety of culture conditions. Intercellular communicationassayed by dye transfer from injected cells to surrounding cellsin contact occurred in logarithmically growing cultures, declinedto very low levels as confluence was attained, and then resumedupon the formation of mature confluent monolayers. Dye-transfernetworks of 50 or more cells resulted from Injection of singlemonolayer cells. Freeze-fracture electron microscopy confirmedthe presence of gap junction structures in confluent cultures.Treatment with the initiating agent N-methyl-N'-nitro-N-nitrosoguanidineand/or the tumor promoter 2,3,7,8-tetrachlorodibenzo-p-dioxindid not inhibit intercellular communication between C3H/10T1/2cells during 6-week transformation experiments. The tumor promoter12-O-tetradecanoylphorbol-13-acetate produced a transient inhibitionof dye-coupling upon first introduction to cultures and prolongedthe period of diminished dye-coupling at the attainment of confluence,but did not inhibit subsequent interactions between monolayercells. A simple relationship thus could not be established betweenlevels of dye-coupling within monolayers and focus formationevents. Curiously, although the cells of foci in early phasesof development did not exhibit dye-transfer capacity, dye-couplingwas observed in mass cultures of most transformed cell linescloned from foci. Co-cultivation of communication-competenttransformed cells with nontransformed cells to produce reconstructedfoci generally resulted in a cessation of dye-transfer by transformedcells. An often reversible loss of communication competencethus accompanies the growth of transformed C3H/10T1/2 cellsas foci and may constitute an adaptive response which facilitatesfocus growth in the presence of intercellular communicationbetween monolayer cells.