Transforming Growth Factor-α Abrogates Glucocorticoid-stimulated Tight Junction Formation and Growth Suppression in Rat Mammary Epithelial Tumor Cells

Abstract

The glucocorticoid and transforming growth factor-alpha (TGF-alpha) regulation of growth and cell-cell contact was investigated in the Con8 mammary epithelial tumor cell line derived from a 7,12-dimethylbenz(alpha)anthracene-induced rat mammary adenocarcinoma. In Con8 cell monolayers cultured on permeable filter supports, the synthetic glucocorticoid, dexamethasone, coordinately suppressed [3H]thymidine incorporation, stimulated monolayer transepithelial electrical resistance (TER), and decreased the paracellular leakage of [3H]inulin or [14C]mannitol across the monolayer. These processes dose dependently correlated with glucocorticoid receptor occupancy and function. Constitutive production of TGF-alpha in transfected cells or exogenous treatment with TGF-alpha prevented the glucocorticoid growth suppression response and disrupted tight junction formation without affecting glucocorticoid responsiveness. Treatment with hydroxyurea or araC demonstrated that de novo DNA synthesis is not a requirement for the growth factor disruption of tight junctions. Immunofluorescence analysis revealed that the ZO-1 tight junction protein is localized exclusively at the cell periphery in dexamethasone-treated cells and that TGF-alpha caused-ZO-1 to relocalize from the cell periphery back to a cytoplasmic compartment. Taken together, our results demonstrate that glucocorticoids can coordinately regulate growth inhibition and cell-cell contact of mammary tumor cells and that TGF-alpha, can override both effects of glucocorticoids. These results have uncovered a novel functional "cross-talk" between glucocorticoids and TGF-alpha which potentially regulates the proliferation and differentiation of mammary epithelial cells.

Apical electrolyte concentration modulates barrier function and tight junction protein localization in bovine mammary epithelium

“…Times when luminal electrolyte composition would be expected to change, including parturition and involution, are associated with increased incidence of infection, inflammation, and cytokine recruitment (1,5,7,14,16,21). Cytokines, including TNF-␣, IL-1␤, IL-6, and IL-8, have been reported to modulate the mammary epithelial barrier in vivo (44).…”

Opposite Regulation of Transepithelial Electrical Resistance and Paracellular Permeability by Rho in Madin-Darby Canine Kidney Cells

“…The tight junction is highly dynamic and regulated in response to various extracellular stimuli and physiological needs, such as glucocorticoids, histamine, and lysophosphatidic acid (19,49,50). We have analyzed roles of the Rho activation pathway-coupled EP3 receptor and the constitutively active RhoA in barrier function of tight junction and demonstrated that the EP3 receptor and active RhoA oppositely regulated the TER and paracellular permeability of mannitol in the preformed monolayer of MDCK cells.…”

“…Many extracellular stimuli have been shown to regulate the barrier function of tight junctions. For example, serum reduced ZO-1 protein levels and decreased transepithelial electrical resistance (TER) 1 in retinal epithelial cells (18), and glucocorticoid caused ZO-1 to localize to the cell-cell interaction site and increased TER in mammary epithelial cells (19). However, intracellular signaling pathways, which regulate the tight junction permeability, remain elusive.…”

Involvement of the Helix-Loop-Helix Protein Id-1 in the Glucocorticoid Regulation of Tight Junctions in Mammary Epithelial Cells

“…We have previously shown that the remodeling of the apical junction results in tight junction sealing as measured by the TER of the monolayer and paracellular flux studies using mannitol or inulin as extracellular tracers (46,49). To begin to characterize the early regulatory processes within the steroid-mediated cascade that controls cell-cell interactions, we examined whether glucocorticoids can regulate the production of the transcriptional regulatory protein Id-1.…”