Transforming growth factor-alpha abrogates glucocorticoid-stimulated tight junction formation and growth suppression in rat mammary epithelial tumor cells.
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.
Buse
P
P
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Woo
P L
PL
Alexander
D B
DB
Cha
H H
HH
Reza
A
A
Sirota
N D
ND
Firestone
G L
GL
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D003907:Dexamethasone / Q000494:pharmacology*; D007365:Intercellular Junctions / Q000187:drug effects*; D008325:Mammary Neoplasms, Experimental / Q000473:pathology*; D008565:Membrane Proteins / Q000032:analysis; D010750:Phosphoproteins / Q000032:analysis; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000187:drug effects / Q000502:physiology; D016211:Transforming Growth Factor alpha / Q000494:pharmacology*; D062826:Zonula Occludens-1 Protein
D008565:Membrane Proteins; D010750:Phosphoproteins; D011965:Receptors, Glucocorticoid; C569044:Tjp1 protein, rat; D016211:Transforming Growth Factor alpha; D062826:Zonula Occludens-1 Protein; D003907:Dexamethasone; D004247:DNA