Mammary Epithelial Cells Treated Concurrently with TGF-α and TGF-β Exhibit Enhanced Proliferation and Death

Abstract

Transforming growth factor-a (TGF-a) stimulates while TGF-b inhibits mammary epithelial cell growth, suggesting that when cells are treated concurrently with the growth factors their combined effects would result in no net growth. However, combined treatments stimulate proliferation and cellular transformation in several cell lines. The objective of this paper was to describe the effect of long-term (6 days) concurrent TGF-a and TGF-b treatment on normal mammary epithelial cell growth pattern, morphology, and gene expression. Growth curve analysis showed that TGF-a enhanced while TGF-b suppressed growth rate until Day 4, when cells entered lag phase. However, cells treated concurrently with both growth factors exhibited a dichotomous pattern of growth marked by growth and death phases (with no intermittent lag phase). These changes in growth patterns were due to a marked induction of cell death from Day 2 (16.5%) to Day 4 (89.5%), resulting in the transition from growth to death phases, even though the combined treated cultures had significantly more (P < 0.05) cells in S phase on Day 4. TGF-b stimulated epithelial to mesenchyme transdifferentiation (EMT) in the presence of TGF-a, as characterized by increased expression of fibronectin and changes in TGF-b receptor binding. Expression patterns of genes that regulate the cell cycle showed significant interaction between treatment and days, with TGF-b overriding TGF-a-stimulated effects on gene expression. Overall, the combined treatments were marked by enhanced rates of cellular proliferation, death, and transdifferentiation, behaviors reminiscent of breast tumors, and thus this system may serve as a good model to study breast tumorigenesis.

Effects of transforming growth factor-β on mammary remodeling during the dry period of dairy cows

“…We hypothesized that the roles of TGF-β1 in mammary involution were to regulate ECM remodeling and stimulate turnover of cell populations. These roles are supported by in vitro and in vivo findings, which showed that addition of TGF-β1 to epithelial cells stimulates synthesis of ECM proteins and inhibits epithelial cell growth (Silberstein and Daniel, 1987;Musters et al, 2004;Casey et al, 2007) and that the expression of TGF-β1 mRNA increases in rodent and bovine mammary gland (both pregnant and nonpregnant) after the initiation of involution (Plath et al, 1997;Faure et al, 2000;Bierie et al, 2009).…”

“…This observation was somewhat surprising in light of our hypothesis. In previous studies, we showed that 5 ng/mL TGF-β1 inhibited mouse mammary epithelial cell growth, in part through arresting cells in G 1 /G 0 (Casey et al, 2007). Exogenous TGF-β1 implanted in mammary glands of prepubertal mice also inhibited epithelial cell proliferation in end buds (Silberstein and Daniel, 1987).…”

Is Mammographic Density a Biomarker to Study the Molecular Causes of Breast Cancer?

“…The influence of TGF-, a member of the epidermal growth factor family of peptides, on breast cancer incidence is not fully explored. However, a previous laboratory study has demonstrated that TGF-enhances the growth of normal mouse mammary epithelial cell line (Casey et al, 2007). Furthermore, TGF-can act as a mitogen and differentiation factor in mammary epithelium inducing multifocal hyperplastic and malignant lesions in an animal model (Smith et al, 1995).…”

“…The balance between the two pathways determines the net result. TGF-exerts its protective effect against breast cancer by inducing cell cycle arrest and promoting apoptosis of normal mammary epithelial cells (Casey et al, 2007). Data from 6,703 cases and 6,840 controls have been assessed in a recent meta-analysis performed by Scollen and colleagues in attempt to better understand the association between TGF-and breast cancer risk (Scollen et al, 2011).…”

Anatomy and Physiology of the Breast

“…It is localized to the developing stroma and the epithelial bud. TGF-b is seen in the ECM throughout prenatal development where it modulates cell-ECM interaction [35] , inhibiting cell proliferation [102,159,186,187] . BM inhibits the expression of TGF-b [188] .…”