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Mammary branch initiation and extension are inhibited by separate pathways downstream of TGF? in culture.

ABSTRACT: During the branching morphogenesis process that builds epithelial trees, signaling from stimulatory and inhibitory growth factors is integrated to control branch initiation and extension into the surrounding stroma. Here, we examined the relative roles played by these stimulatory and inhibitory signals in the patterning of branch initiation and extension of model mammary epithelial tubules in culture. We found that although several growth factors could stimulate branching, they did not determine the sites at which new branches formed or the lengths to which branches extended. Instead, branch initiation and extension were defined by two separate signals downstream of the inhibitory morphogen, transforming growth factor (TGF)-?. Branch initiation was controlled by signaling through p38 mitogen-activated protein kinase, whereas branch extension was controlled by Smad-mediated induction of a second diffusible inhibitor, Wnt5a. These data suggest that mammary epithelial branching is patterned predominately by repulsive signaling, and that TGF? activates multiple inhibitory pathways to refine the architecture of the tree.

SUBMITTER: Pavlovich AL

PROVIDER: S-EPMC3123406 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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Mammary branch initiation and extension are inhibited by separate pathways downstream of TGFβ in culture.

Pavlovich Amira L AL Boghaert Eline E Nelson Celeste M CM

Experimental cell research 20110401 13

During the branching morphogenesis process that builds epithelial trees, signaling from stimulatory and inhibitory growth factors is integrated to control branch initiation and extension into the surrounding stroma. Here, we examined the relative roles played by these stimulatory and inhibitory signals in the patterning of branch initiation and extension of model mammary epithelial tubules in culture. We found that although several growth factors could stimulate branching, they did not determine ...[more]

PMID: 21459084

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Project description:After weaning, during mammary gland involution, milk-producing mammary epithelial cells undergo apoptosis. Effective clearance of these dying cells is essential, as persistent apoptotic cells have a negative impact on gland homeostasis, future lactation and cancer susceptibility. In mice, apoptotic cells are cleared by the neighboring epithelium, yet little is known about how mammary epithelial cells become phagocytic or whether this function is conserved between species. Here we use a rat model of weaning-induced involution and involuting breast tissue from women, to demonstrate apoptotic cells within luminal epithelial cells and epithelial expression of the scavenger mannose receptor, suggesting conservation of phagocytosis by epithelial cells. In the rat, epithelial transforming growth factor-? (TGF-?) signaling is increased during involution, a pathway known to promote phagocytic capability. To test whether TGF-? enhances the phagocytic ability of mammary epithelial cells, non-transformed murine mammary epithelial EpH4 cells were cultured to achieve tight junction impermeability, such as occurs during lactation. TGF-?3 treatment promoted loss of tight junction impermeability, reorganization and cleavage of the adherens junction protein E-cadherin (E-cad), and phagocytosis. Phagocytosis correlated with junction disruption, suggesting junction reorganization is necessary for phagocytosis by epithelial cells. Supporting this hypothesis, epithelial cell E-cad reorganization and cleavage were observed in rat and human involuting mammary glands. Further, in the rat, E-cad cleavage correlated with increased ?-secretase activity and ?-catenin nuclear localization. In vitro, pharmacologic inhibitors of ?-secretase or ?-catenin reduced the effect of TGF-?3 on phagocytosis to near baseline levels. However, ?-catenin signaling through LiCl treatment did not enhance phagocytic capacity, suggesting a model in which both reorganization of cell junctions and ?-catenin signaling contribute to phagocytosis downstream of TGF-?3. Our data provide insight into how mammary epithelial cells contribute to apoptotic cell clearance, and in light of the negative consequences of impaired apoptotic cell clearance during involution, may shed light on involution-associated breast pathologies.

Dataset Information

Mammary branch initiation and extension are inhibited by separate pathways downstream of TGF? in culture.

Publications

Mammary branch initiation and extension are inhibited by separate pathways downstream of TGFβ in culture.

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