In normal tissues or tumors, cells have extensive opportunities for adhesion to their neighbors in a three-dimensional organization, and this is mimicked in culture by high density cell growth. Cell-to-cell adhesion is mediated mainly through cadherin receptors, which define cell and tissue architecture. Interestingly, it was recently demonstrated that cadherins also play a powerful role in signal transduction, especially in survival signaling1. Paradoxically, some of these cell-to-cell adhesion signals emanating from cadherins were recently found to be shared by both differentiation and neoplasia2. Here, we describe methods of induction and assessment of differentiation in two representative types of mouse breast epithelial cell lines, HC11 and EpH4.
The HC11 mouse breast epithelial cell line can provide a useful model for the study of epithelial cell differentiation. HC11 cells are a COMMA-1D-derived cell line, originating from the mammary gland of a mid-pregnant Balb/c mouse3. In contrast to other COMMA-1D derivative clones, the HC11 clone has no requirement for exogenously added extracellular matrix or cocultivation with other cell types for the in vitro induction of the endogenous β-casein gene by lactogenic hormones3. This cell line has been used extensively in differentiation studies because it has retained important characteristics of the normal mammary epithelium: HC11 cells can partially reconstitute the ductal epithelium in a cleared mammary fat pad4. Moreover, they can differentiate in a two-dimensional (2D) culture when grown to confluence attached to a plastic Petri dish surface in the presence of a steroid such as Hydrocortisone or Dexamethasone, in addition to Insulin and Prolactin (HIP medium) lacking epidermal growth factor (EGF), an inhibitor of differentiation5,6,7. Under these conditions, HC11 cells produce milk proteins such as β-casein and WAP, which are detectable by Western blotting within 4 days following induction. At the same time, a portion of HC11 cells forms rudimentary mammary gland-like structures termed "domes" in a stochastic manner. Domes are visible 4–5 days following induction and gradually increase in size up to day 10, concomitant with an increase in β-casein production8. Interestingly, HC11 cells possess mutant p539, and therefore represent a preneoplastic state. For this reason, the HC11 model is ideally suited to study signaling networks of differentiation in conjunction with neoplasia in the same cell system.
EpH4 cells, a derivative of IM-2 cells, are a nontumorigenic cell line originally derived from spontaneously immortalized mouse mammary gland epithelial cells isolated from a mid-pregnant Balb/c mouse10. EpH4 cells form continuous epithelial monolayers in 2D culture, but do not differentiate into glandular-like structures10,11. However, following 3D growth in a material consisting of a mixture of extracellular matrix proteins produced by EHS mouse sarcoma cells12 (EHS matrix, matrix, or Matrigel, see Table of Materials), in addition to stimulation with HIP, EpH4 cells can recapitulate the initial stages of mammary gland differentiation. Under these conditions, EpH4 cells form spheroids (also called mammospheres) that exhibit apical-basal polarity and a hollow lumen, and are capable of producing the milk proteins β-casein and WAP, similar to lactating mammary epithelial cells. Contrary to HC11 cells, which are undifferentiated, and some express mesenchymal markers13, EpH4 cells exhibit a purely luminal morphology14. EpH4 cells have also been reported to produce milk proteins in 2D culture through stimulation with dexamethasone, insulin, and prolactin15. However, this approach precludes the study of regulatory effects that mimic the mammary gland microenvironment in 3D culture.