Hostname: page-component-cd9895bd7-p9bg8 Total loading time: 0 Render date: 2024-12-27T08:48:53.866Z Has data issue: false hasContentIssue false
  • English
  • Français

Mammary stem cells: the root of breast cancer?

Published online by Cambridge University Press:  05 April 2005

H. A. Coppock  and
R. B. Clarke
R. B. Clarke
Affiliation:
Breast Biology Group, CR-UK Department of Medical Oncology, University of Manchester, Manchester, UK.

Abstract

Tissue-specific stem cells play a key role in organ homoeostasis. They are relatively well characterized in systems which undergo constant proliferation and production of differentiated cells, including the haemopoietic system, skin and intestine. However, little is known about the role and regulation of stem cells in the mammary gland. This review briefly summarizes the current understanding of the role of breast-specific stem cells in normal and cancerous tissues, and how this may identify new targets for breast cancer prevention and therapy.

Keywords

BreastStem cellEpitheliumCancer
Type
Focus On
Information
Breast Cancer Online , Volume 7 , Issue 9 , 29 September 2004 , e23
Copyright
2004 Cambridge University Press

Introduction

What are stem cells?

Stem cells are defined by their ability to both self-renew and produce progeny that differentiate into all the functional cell types of a particular tissue. They are relatively undifferentiated cells which are long lived and able to undergo either symmetric or asymmetric division to give rise to either identical progeny; a proliferative precursor cell, or both [1]. These properties are essential for the maintenance of normal human tissues in which there is a high cell turnover.

Evidence for mammary stem cells

Tissue-specific stem cells are integral to the development and function of the mammary gland. Cycles of cell proliferation, differentiation, apoptosis and remodelling associated with the menstrual cycle, pregnancy and lactation occur many times throughout the reproductive life of women. These cycles of growth are thought to rely on the presence of a mammary stem cell population.

The functional unit of the breast, the lobule, consists of a terminal duct opening into several acini forming the terminal duct lobular unit (TDLU) which is lined with two layers of cells. The outer layer consists of myoepithelial cells which surround an inner or luminal layer. The majority of breast cancers exhibit a luminal phenotype [2], suggesting that they are derived from a luminal cell precursor [3]. Large contiguous patches of cells within the breast epithelium exhibiting identical X chromosome inactivation [4] suggest that they are derived from the same cell. In mice, transplantation of single cell suspensions or fragments of mammary gland into cleared mouse mammary fat pads can regenerate an entire functional gland [5–7]. Culture of primary human mammary cells suggests the presence of three distinct progenitor cell types; luminal precursors, myoepithelial precursors and multipotent precursors which may be stem cells [8,9]. These studies suggest that mammary glands contain a population of stem cells that are able to give rise to all cell types.

Identifying mammary stem cells

By definition, breast stem cells should rarely divide and persist throughout reproductive life. This means that they can be identified on the basis that they will retain label after the administration of labelled DNA precursors, such as tritiated thymidine or bromodeoxyuridine. This approach has been used by a number of groups and shows in the mouse mammary gland, for example, that up to 5% of cells retain label and that these cells also express other putative stem cell markers such as stem cell antigen-1 (Sca-1) or breast cancer resistance protein 1 (Bcrp1) (see below) [10–14]. Electron microscopy has been used to identify small light cells or undifferentiated cells in mouse and rat mammary epithelium [15]. As these light cells divide rarely [15,16], are found in clusters, and can give rise to more differentiated cell types, they are thought to be mammary stem cells [17]. These studies also show that putative stem cells exist in specific physical locations or stem cell niches in both rat [18] and human mammary glands [19]. Stem cell niches are anatomically specialized locations which provide the stem cell with a unique micro-environment necessary for its correct function as demonstrated in other tissues such as skin, bone marrow, gut and hair follicles. As stem cell behaviour appears to be dependent on the stem cell niche [20,21] any attempt to isolate stem cells from a tissue will lead to disruption of that niche and to possible alteration of cell behaviour, which needs to be taken into account when studying their behaviour both in vitro and in vivo.

Using immunochemical techniques, a population of cells has been isolated from an intermediate position in the human breast that corresponds to the location of the rodent mammary stem cell niche. These cells were negative for markers of luminal or myoepithelial differentiation [8,19] and could give rise to multiple lineages in culture [9]. Finally, the technique of side population (SP) analysis used previously to identify haemopoietic stem cells [22] has been applied to the identification of mammary stem cells. [3, 13, 23,24]. SP cells are able to efflux the fluorescent dye, Hoechst 33342 by the ABCG2 transporter molecule, also known as Bcrp1. The SP fraction is enriched for stem cells, as it has been demonstrated that mouse mammary SP cells, which also expressed the mouse Sca-1, were able to repopulate cleared mammary fat pads of syngeneic hosts [3,13].

Relevance of stem cells to cancer

It has been suggested that tumours may arise from ‘cancer stem cells’ (CSCs) [25]. The existence of CSCs may account for the phenotypic heterogeneity seen within solid tumours, which are composed of a mixture of differentiated tumour cell types with limited proliferative capacity and a small population of proliferative, undifferentiated stem cells. Evidence for CSCs has been demonstrated in breast tumours [26] and in leukaemia [27] where transplantation of a subpopulation of tumour cells generated tumours which were phenotypically identical to the parent tumours. The presence of CSCs has also been seen in glioblastomas [28], which are able to generate differentiated tumour cells. It has been suggested that dissemination of CSCs throughout the body may be the cause of metastasis as the secondary tumours tend to be composed of the same range of cells as the primary tumour [25,29].

Mutation of a stem cell is not the only mechanism for carcinogenesis. It is also possible that a more differentiated, or lineage restricted, progenitor cell could acquire mutations which endow the cell with a stem cell-like capacity for self-renewal [29,30]. Indeed, transformation of different progenitor populations could account for tumour heterogeneity.

What implications does the CSC hypothesis have for anti-cancer therapies? Currently the end point for chemotherapy is a reduction in tumour size, which is attained by using drugs which target actively proliferating cells. However, a CSC may divide infrequently and be refractory to the chemotherapeutic hit. Additionally, stem cells tend to synthesize proteins, such as Bcrp1, which efflux toxic drugs [31,32]. Therefore, for the successful development of new anti-cancer therapies it seems necessary to target stem cells. Both stem cells and cancer cells share similar mechanisms for regulation of self-renewal which include the Notch [33], Hedgehog [34,35] and Wnt [36] pathways. These regulatory mechanisms may offer new therapeutic targets. Wnt is particularly interesting as it has been demonstrated that dysregulation of Wnt signalling leads to increased incidence of epithelial cancers [37,38] and is able to enlarge the haemopoietic stem cell pool [39]. However, targeting regulatory mechanisms common to both normal and CSCs may not provide any significant enhancement of the therapeutic ratio [40]. However, the fact that some leukaemias [41] and most testicular tumours can be cured [42] suggests that targeting CSCs is possible without increasing toxicity to unacceptable levels.

Conclusions

Stem cells are long lived and multipotent, and are essential for development and maintenance of normal tissues by the processes of proliferation and terminal differentiation. Studies have provided evidence for the existence of mammary stem cells in mice, rats and humans. Subsequent identification and isolation of these stem cells has shown their ability to repopulate cleared mammary fat pads and give rise to all the structures seen in normal mature glands. These infrequent and elusive cells have the ability to teach us more about tissue development, tumour susceptibility, how tumour growth is initiated and promoted, and how to prevent or control these processes.

Acknowledgements

We are grateful to Dr Elizabeth Anderson for critical review of the manuscript. H.A.C. is supported by the Breast Cancer Campaign and R.B.C. by CRUK.

References

Clarke RB, Anderson E, Howell A, Potten CS. Regulation of human breast epithelial stem cells. Cell Prolif 2003; 36(Suppl 1): 45–58.Google Scholar
Taylor-Papadimitriou J, Stampfer M, Bartek J, et al. Keratin expression in human mammary epithelial cells cultured from normal and malignant tissue: relation to in vivo phenotypes and influence of medium. J Cell Sci 1989; 94(Part 3): 403–413.Google Scholar
Alvi AJ, Clayton H, Joshi C, Enver T, Ashworth A, Vivanco MM, Dale TC, Smalley MJ. Functional and molecular characterisation of mammary side population cells. Breast Cancer Res 2002; 5: R1–R8.Google Scholar
Tsai YC, Lu Y, Nichols PW, et al. Contiguous patches of normal human mammary epithelium derived from a single stem cell: implications for breast carcinogenesis. Cancer Res 1996; 56 (2): 402–404.Google Scholar
Daniel CW, De Ome KB, Young JT, et al. The in vivo life span of normal and preneoplastic mouse mammary glands: a serial transplantation study. Proc Natl Acad Sci USA 1968; 61 (1): 53–60.Google Scholar
Kordon EC, Smith GH. An entire functional mammary gland may comprise the progeny from a single cell. Development 1998; 125 (10): 1921–1930.Google Scholar
Ormerod EJ, Rudland PS. Regeneration of mammary glands in vivo from isolated mammary ducts. J Embryol Exp Morphol 1986; 96: 229–243.Google Scholar
Stingl J, Eaves CJ, Kuusk U, Emerman JT. Phenotypic and functional characterization in vitro of a multipotent epithelial cell present in the normal adult human breast. Differentiation 1998; 63(4): 201–213.Google Scholar
Gudjonsson T, Villadsen R, Nielsen HL, et al. Isolation, immortalization, and characterization of a human breast epithelial cell line with stem cell properties. Gene Dev 2002; 16 (6): 693–706.Google Scholar
Potten CS, Morris RJ. Epithelial stem cells in vivo. J Cell Sci Suppl 1988; 10: 45–62.Google Scholar
Potten CS, Loeffler M. Stem cells: attributes, cycles, spirals, pitfalls and uncertainties. Lessons for and from the crypt. Development 1990; 110 (4): 1001–1020.Google Scholar
Zeps N, Dawkins HJ, Papadimitriou JM, et al. Detection of a population of long-lived cells in mammary epithelium of the mouse. Cell Tissue Res 1996; 286 (3): 525–536.Google Scholar
Welm BE, Tepera SB, Venezia T, et al. Sca-1(pos) cells in the mouse mammary gland represent an enriched progenitor cell population. Dev Biol 2002; 245 (1): 42–56.Google Scholar
Clarke RB, Howell A, Potten CS, Anderson E. P27(KIP1) expression indicates that steroid receptor-positive cells are a non-proliferating, differentiated subpopulation of the normal human breast epithelium. Eur J Cancer 2000; 36(Suppl 4): S28–S29.Google Scholar
Chepko G, Smith GH. Three division-competent, structurally-distinct cell populations contribute to murine mammary epithelial renewal. Tissue Cell 1997; 29 (2): 239–253.Google Scholar
Smith GH, Medina D. A morphologically distinct candidate for an epithelial stem cell in mouse mammary gland. J Cell Sci 1988; 90(Part 1): 173–183.Google Scholar
Smith GH, Strickland P, Daniel CW. Putative epithelial stem cell loss corresponds with mammary growth senescence. Cell Tissue Res 2002; 310 (3): 313–320.Google Scholar
Chepko G, Dickson RB. Ultrastructure of the putative stem cell niche in rat mammary epithelium. Tissue Cell 2003; 35 (2): 83–93.Google Scholar
Stingl J, Eaves CJ, Zandieh I, Emerman JT. Characterization of bipotent mammary epithelial progenitor cells in normal adult human breast tissue. Breast Cancer Res Treat 2001; 67 (2): 93–109.Google Scholar
Spradling A, Drummond-Barbosa D, Kai T. Stem cells find their niche. Nature 2001; 414 (6859): 98–104.Google Scholar
Nishimura EK, Jordan SA, Oshima H, et al. Dominant role of the niche in melanocyte stem-cell fate determination. Nature 2002; 416 (6883): 854–860.Google Scholar
Goodell MA, Brose K, Paradis G, et al. Isolation and functional properties of murine hematopoietic stem cells that are replicating in vivo. J Exp Med 1996; 183 (4): 1797–1806.Google Scholar
Clarke RB, Spence K, Howell A, Anderson E, Okano H, Potten CS. A putative stem cell population is enriched for steroid receptor positive cells. Dev Biol [in press].
Clayton H, Titley I, Vivanco M. Growth and differentiation of progenitor stem cells derived from the human mammary gland. Exp Cell Res 2004; 297: 444–460.Google Scholar
Reya T, Morrison SJ, Clarke MF, Weissman IL. Stem cells, cancer, and cancer stem cells. Nature 2001; 414 (6859): 105–111.Google Scholar
Al-Hajj M, Wicha MS, Benito-Hernandez A, et al. Prospective identification of tumorigenic breast cancer cells. Proc Natl Acad Sci USA 2003; 100 (7): 3983–3988.Google Scholar
Bonnet D, Dick JE. Human acute myeloid leukemia is organized as a hierarchy that originates from a primitive hematopoietic cell. Nat Med 1997; 3 (7): 730–737.Google Scholar
Singh SK, Clarke ID, Terasaki M, et al. Identification of a cancer stem cell in human brain tumors. Cancer Res 2003; 63 (18): 5821–5828.Google Scholar
Dontu G, Al-Hajj M, Abdallah WM, et al. Stem cells in normal breast development and breast cancer. Cell Prolif 2003; 36(Suppl 1): 59–72.Google Scholar
Cozzio A, Passegue E, Ayton PM, Karunsky H, Cleary ML, Weissman IL. Similar MLL-associated leukemias arising from self-renewing stem cells and short lived myeloid progenitors. Gene Dev 2003; 17: 3029–3035.Google Scholar
Sarkadi B, Ozvegy-Laczka C, Nemet K, Varadi A. ABCG2 – a transporter for all seasons. FEBS Lett 2004; 567 (1): 116–120.Google Scholar
Doyle LA, Ross DD. Multidrug resistance mediated by the breast cancer resistance protein BCRP (ABCG2). Oncogene 2003; 22 (47): 7340–7358.Google Scholar
Nickoloff BJ, Osborne BA, Miele L. Notch signaling as a therapeutic target in cancer: a new approach to the development of cell fate modifying agents.Oncogene 2003; 22 (42): 6598–6608.Google Scholar
Kenney AM, Widlund HR, Rowitch DH. Hedgehog and PI-3 kinase signaling converge on Nmyc1 to promote cell cycle progression in cerebellar neuronal precursors. Development 2004; 131 (1): 217–228.Google Scholar
Bhardwaj G, Murdoch B, Wu D, et al. Sonic Hedgehog induces the proliferation of primitive human hematopoietic cells via BMP regulation. Nat Immunol 2001; 2 (2): 172–180.Google Scholar
Taipale J, Beachy PA. The Hedgehog and Wnt signalling pathways in cancer. Nature 2001; 411 (6835): 349–354.Google Scholar
Li Y, Welm B, Podsypanina K, et al. Evidence that transgenes encoding components of the Wnt signaling pathway preferentially induce mammary cancers from progenitor cells. Proc Natl Acad Sci USA 2003; 100 (26): 15853–15858.Google Scholar
Liu BY, McDermott SP, Khwaja SS, Alexander CM. The transforming activity of Wnt effectors correlates with their ability to induce the accumulation of mammary progenitor cells. Proc Natl Acad Sci USA 2004; 101 (12): 4158–4163.Google Scholar
Reya T, Duncan AW, Ailles L, et al. A role for Wnt signalling in self-renewal of haematopoietic stem cells. Nature 2003; 423 (6938): 409–414.Google Scholar
Pardal R, Clarke MF, Morrison SJ. Applying the principles of stem-cell biology to cancer. Nat Rev Cancer 2003; 3 (12): 895–902.Google Scholar
Guzman ML, Swiderski CF, Howard DS, et al. Preferential induction of apoptosis for primary human leukemic stem cells. Proc Natl Acad Sci USA 2002; 99 (25): 16220–16225.Google Scholar
Stephenson WT, Poirier SM, Rubin L, Einhorn LH. Evaluation of reproductive capacity in germ cell tumor patients following treatment with cisplatin, etoposide, and bleomycin. J Clin Oncol 1995; 13 (9): 2278–2280.Google Scholar