Transforming growth factor-β3 increases gap-junctional communication among folliculostellate cells to release basic fibroblast growth factor

Folliculostellate (FS) cells are known to communicate with each other and with endocrine cells via gap junctions in the anterior pituitary. We investigated whether TGF beta 3 and estradiol, known to regulate FS cell production and secretion of basic fibroblast growth factor (bFGF), increases gap junctional communication to alter bFGF secretion from FS cells. FS cells in monolayer cultures were treated with TGF beta 3 or vehicle alone for 24 h and then microinjected with Lucifer Yellow and high-molecular-weight Texas Red dextran. Ten minutes later the transfer of dye among adjacent cells was recorded with a digital microscope. TGF beta 3 increased the transfer of dye. The TGF beta 3-neutralizing antibody and the gap junction inhibitor octanol reduced the effect of TGF beta 3 on the transfer of dye. The TGF beta 3-induced transfer of dye was unaltered by simultaneous treatment with estradiol. The steroid alone also had no effect. TGF beta 3 increased total and phosphorylated levels of connexin 43. Estradiol treatment did not produce any significant changes on basal or TGF beta 3-induced increases in connexin 43 levels. The gap-junction inhibitor octanol reduced TGF beta 3-increased levels of bFGF in FS cells. Taken together, these results suggest that TGF beta 3 may act on FS cells to increase gap-junctional communication to maximize its effect on bFGF secretion.