Low concentrations of transforming growth factor-beta-1 induce tubulogenesis in cultured mammary epithelial cells.
BACKGROUND
Formation of branching tubes is a fundamental step in the development of glandular organs. To identify extracellular cues that orchestrate epithelial tubulogenesis, we employed an in vitro assay in which EpH4-J3B1A mammary epithelial cells form spheroidal cysts when grown in collagen gels under serum-free conditions, but form branching tubules in the presence of fetal calf serum (FCS).


RESULTS
Initial experiments showed that the tubulogenesis-inducing activity of FCS was markedly increased by heating (70 degrees C) or transient acidification to pH3. We therefore hypothesized that the tubulogenic agent was transforming growth factor-beta (TGF-beta), a cytokine that is present in serum in latent form and can be activated by heat or acid treatment. We found indeed that the tubulogenic activity of acidified FCS is abrogated by addition of either SB-431542, a selective inhibitor of the TGF-beta type I receptor, or a neutralizing antibody to TGF-beta-1. On the other hand, addition of low concentrations (20-100 pg/ml) of exogenous TGF-beta-1 recapitulated the effect of acidified FCS in inducing morphogenesis of hollow tubes. In contrast, higher concentrations of TGF-beta-1 induced the formation of thin cellular cords devoid of a detectable lumen. To gain insight into the mechanisms underlying TGF-beta-1-induced tube formation, we assessed the potential role of matrix metalloproteinases (MMPs). By western blot and gelatin zymography, we observed a dose-dependent increase in MMP-9 upon TGF-beta-1 treatment. Tube formation was suppressed by a synthetic broad-spectrum metalloproteinase inhibitor, by recombinant tissue inhibitor of metalloproteinases-2 (TIMP-2) and by a selective inhibitor of MMP-9, indicating that this morphogenetic process requires the activity of MMP-9.


CONCLUSIONS
Altogether, our results provide evidence that, at low concentrations, TGF-beta-1 promotes MMP-dependent branching tubulogenesis by mammary epithelial cells in vitro, and suggest that it plays a similar role during mammary gland development in vivo.
Montesano
Roberto
R
Department of Cell Physiology and Metabolism, University of Geneva Medical School, CH-1211 Geneva 4, Switzerland. Roberto.Montesano@medecine.unige.ch
Carrozzino
Fabio
F
Soulié
Priscilla
P
D000818:Animals; D015152:Blotting, Northern; D002478:Cells, Cultured; D003470:Culture Media; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology* / Q000187:drug effects; D005260:Female; D008321:Mammary Glands, Animal / Q000166:cytology / Q000187:drug effects / Q000254:growth & development*; D020782:Matrix Metalloproteinases / Q000378:metabolism; D051379:Mice; D009024:Morphogenesis; D009693:Nucleic Acid Hybridization; D053773:Transforming Growth Factor beta1 / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors
D003470:Culture Media; D004791:Enzyme Inhibitors; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases; D020782:Matrix Metalloproteinases