HORMONAL-CONTROL OF CELL TO CELL COMMUNICATION - REGULATION BY THYROTROPIN OF THE GAP JUNCTION-MEDIATED DYE TRANSFER BETWEEN THYROID-CELLS

By microinjection of Lucifer yellow (LY) and analysis of the cell to cell transfer of the fluorescent probe, we have examined 1) the ability of thyroid cells in primary culture to reconstitute gap junctions and 2) the effects of extracellular signals on the functional activity of these junctions. Isolated thyrocytes cultured in tissue culture-treated petri dishes either formed monolayers or reorganized in follicular structures in the presence of the glycoprotein hormone TSH. In both culture conditions, LY-coupled cells were evident after 24-36 h. The communication between cells forming a reconstituted thyroid follicle was maintained for up to 9 days. In contrast, the dye coupling between cells in monolayer progressively decreased with time. The cell to cell communication, i.e. the number of dye-coupled cells in thyroid cell monolayer, was increased by TSH in a time- and concentration-dependent manner. The TSH action was not related to de novo protein synthesis. (Bu)2cAMP exhibited stimulatory effects similar, in terms of time course and amplitude of action, to those of TSH. The phorbol ester 12-O-tetradecanoyl phorbol 13-acetate rapidly inhibited both basal and TSH- or (Bu)2 cAMP-activated cell to cell communication. The dye coupling of cells in reconstituted follicles was also blocked by a short 12-O-tetradecanoyl phorbol 13-acetate treatment in both the presence and absence of TSH. Our data show that thyroid cells in culture, regardless of the full expression of the differentiated phenotype, rapidly reestablish intercellular gap junctions. The functional activity of gap junctions appears to be regulated 1) positively by a hormone, TSH, probably acting via the cAMP and protein kinase-A pathway, and 2) negatively by phorbol esters through the activation of protein kinase-C, the two regulatory pathways being interdependent.