title: Transformed growth phenotype of mouse mammary epithelium in primary culture induced by specific fetal mesenchymes.
abstract: When mesenchyme from fetal mammary or salivary gland is implanted into adult mouse mammary gland, adjacent epithelium responds with intense hyperplasia. The hyperplastic cells are more vulnerable than are non-stimulated cells to transformation in vivo by a chemical carcinogen or by mammary tumor virus. This system provides a potentially useful model for determining how stroma contributes to mammary tumorigenesis. We have developed co-culture systems and used them to investigate in more detail the nature of the signal produced by the mesenchyme cells. Monolayers of mesenchyme cells were prepared on tissue-culture wells. The mesenchyme cells were trapped on the surface by a thin overlay of agarose. Primary mammary epithelial cells were cultured atop this barrier layer, either as organoids in collagen gels for assessment of anchorage-dependent growth, or as single-cell dispersions in soft agarose for assessment of anchorage-independent growth. Our procedures for assay of anchorage-independent growth allow us for the first time to detect and measure this transformation-defining characteristic in non-immortalized mammary epithelial cells in primary culture. Fetal mammary fat pad precursor tissue and fetal salivary mesenchyme both stimulated anchorage-dependent growth of mammary epithelium, with cell number increasing as much as fifteenfold during a 6-day culture period. These same fetal tissues also stimulated anchorage-independent growth of the mammary epithelial cells, with colony-forming efficiencies of up to 40% in co-cultures with salivary mesenchyme. No colonies formed in the absence of mesenchyme. Cells of colonies contained keratin, which indicates that the colonies grew from epithelial cells and not from a contaminant of another cell type. When co-cultured epithelial cells were subsequently re-cultured in the absence of mesenchyme, they lost their ability to grow independent of anchorage. No colonies grew in co-cultures with fetal cells from heart, kidney, or lung, which is consistent with the lack of stimulation by these tissues in the mammary gland in vivo. A tumor promoter, 12-O-tetradecanoylphorbol acetate (TPA), also caused anchorage-independent growth of the dispersed mammary epithelial cells. Culture medium conditioned by primary or early-passage salivary mesenchyme cells was capable of stimulating growth under both anchorage-dependent and anchorage-independent conditions, confirming that these effects are mediated by a paracrine factor. The results indicate that stimulatory fetal mesenchymes produce soluble molecules that act analogously to transforming growth factors.
authors.affiliation: Department of Zoology, Washington State University, Pullman 99164-4236.
authors.forename: T
authors.initials: T
authors.lastname: Kanazawa
authors.forename: H L
authors.initials: HL
authors.lastname: Hosick
mesh_terms: D000818:Animals; D002471:Cell Transformation, Neoplastic; D046508:Culture Techniques; D003584:Cytological Techniques; D004847:Epithelial Cells; D004848:Epithelium / Q000502:physiology; D016332:Fetal Tissue Transplantation; D008321:Mammary Glands, Animal / Q000166:cytology / Q000502:physiology*; D008648:Mesoderm / Q000166:cytology / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D010641:Phenotype; D012685:Sepharose; D013234:Stem Cells / Q000166:cytology; D017154:Stromal Cells / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D012685:Sepharose; D013755:Tetradecanoylphorbol Acetate