Characterization in vitro of luminal and myoepithelial cells isolated from the human mammary gland by cell sorting

Growth and differentiation of progenitor/stem cells derived from the human mammary gland

Estrogen is necessary for the full development of the mammary gland and it is also involved in breast cancer development. We set out to identify and characterise progenitor/stem cells in the human mammary gland and to explore the role of estrogen in their proliferation and differentiation. Three candidate stem cell populations were isolated: double positive (DP) cells co-expressed the luminal and myoepithelial markers, EMA and CALLA, respectively, whereas double negative (DN) cells did not express these cell surface markers; side population (SP) cells were characterised by their differential ability to efflux the dye Hoechst 33342. The ABC transporter, breast cancer resistance protein (BCRP) was more highly expressed in SP cells than in non-SP cells and a specific BCRP inhibitor, Ko143, reduced SP formation, suggesting that BCRP confers the SP phenotype in mammary epithelial cells, as has been demonstrated in other tissues. Interestingly, SP cells were double negative for the EMA and CALLA antigens and therefore represent a separate and distinct population to DP cells. Single cell multiplex RT-PCR indicated that the SP and DN cells do not express detectable levels of ERalpha or ERbeta, suggesting that estrogen is not involved in their proliferation. DP cells expressed ERalpha but at a lower level than differentiated luminal cells. These findings invoke a potential strategy for the breast stem/progenitor cells to ignore the mitogenic effects of estrogen. All three cell populations generated mixed colonies containing both luminal and myoepithelial cells from a single cell and therefore represent candidate multipotent stem cells. However, DN cells predominately generated luminal colonies and exhibited a much higher cloning efficiency than differentiated luminal cells. Further characterisation of these candidate progenitor/stem cells should contribute to a better understanding of normal mammary gland development and breast tumorigenesis.

Expression Profiling of Purified Normal Human Luminal and Myoepithelial Breast Cells

The normal duct-lobular system of the breast is lined by two epithelial cell types, inner luminal secretory cells and outer contractile myoepithelial cells. We have generated comprehensive expression profiles of the two normal cell types, using immunomagnetic cell separation and gene expression microarray analysis. The cell-type specificity was confirmed at the protein level by immunohistochemistry in normal breast tissue. New prognostic markers for survival were identified when the luminal- and myoepithelial-specific molecules were evaluated on breast tumor tissue microarrays. Nuclear expression of luminal epithelial marker galectin 3 correlated with a shorter overall survival in these patients, and the expression of SPARC (osteonectin), a myoepithelial marker, was an independent marker of poor prognosis in breast cancers as a whole. These data provide a framework for the interpretation of breast cancer molecular profiling experiments, the identification of potential new diagnostic markers, and development of novel indicators of prognosis.

To create the correct microenvironment: three-dimensional heterotypic collagen assays for human breast epithelial morphogenesis and neoplasia

The normal human breast comprises an inner layer of luminal epithelial cells and an outer layer of myoepithelial cells separated from the connective tissue stroma by an intact basement membrane. In breast cancer, tumor cells are in direct contact with the surrounding highly activated collagenous stroma, with little or no discernible myoepithelial fence from the original double-layered structure. To understand the evolution of these two scenarios, we took advantage of a three-dimensional hydrated collagen gel approach. The contribution of myoepithelial cells to normal morphogenesis was studied by ablation and rescue experiments, and genes regulated on tumor cell-fibroblast interaction were identified in a tumor environment assay. In normal breast morphogenesis, the ability to correctly polarize sialomucin to the luminal membrane of emerging acini was used as a criterion for apical polarity and functional differentiation. In the assay of breast neoplasia, the consequence of reciprocal tumor cell-fibroblast interaction was addressed morphologically as well as by a differential display approach. Normal breast epithelial cells were purified immunomagnetically and an established cell line, MCF-7, was used as a surrogate tumor cell. With regard to the importance of myoepithelial cells in normal breast epithelial morphogenesis, the collagen gel assay elucidated the following subtleties: In contrast to culturing in basement membrane gels, luminal epithelial cells when cultured alone made structures that were all inversely polarized. This aberrant polarity could be rescued by co-culture with myoepithelial cells. The molecular activity of myoepithelial cells responsible for correct morphogenesis was narrowed down to the laminin-1 component of the basement membrane. As for the consequence of interaction of tumor cells with connective tissue fibroblasts, the assay allowed us to identify a hitherto undescribed gene referred to as EPSTI1. The relevance of the assay-based identification of regulated genes was confirmed in a series of breast carcinomas in which EPSTI1 was highly upregulated compared with normal breast. Few if any of these observations would have been possible on two-dimensional tissue culture plastic.

Immunocytochemistry of myoepithelial cells in the salivary glands

MECs are distributed on the basal aspect of the intercalated duct and acinus of human and rat salivary glands. However, they do not occur in the acinus of rat parotid glands, and sometimes occur in the striated duct of human salivary glands. MECs, as the name implies, have structural features of both epithelial and smooth muscle cells. They contract by autonomic nervous stimulation, and are thought to assist the secretion by compressing and/or reinforcing the underlying parenchyma. MECs can be best observed by immunocytochemistry. There are three types of immunocytochemical markers of MECs in salivary glands. The first type includes smooth muscle protein markers such as alpha-SMA, SMMHC, h-caldesmon and basic calponin, and these are expressed by MECs and the mesenchymal vasculature. The second type is expressed by MECs and the duct cells and includes keratins 14, 5 and 17, alpha 1 beta 1 integrin, and metallothionein. Vimentin is the third type and, in addition to MECs, is expressed by the mesenchymal cells and some duct cells. The same three types of markers are used for studying the developing gland. Development of MECs starts after the establishment of an extensively branched system of cellular cords each of which terminates as a spherical cell mass, a terminal bud. The pluripotent stem cell generates the acinar progenitor in the terminal bud and the ductal progenitor in the cellular cord. The acinar progenitor differentiates into MECs, acinar cells and intercalated duct cells, whereas the ductal progenitor differentiates into the striated and excretory duct cells. Both in the terminal bud and in the cellular cord, the immediate precursors of all types of the epithelial cells appear to express vimentin. The first identifiable MECs are seen at the periphery of the terminal bud or the immature acinus (the direct progeny of the terminal bud) as somewhat flattened cells with a single cilium projecting toward them. They express vimentin and later alpha-SMA and basic calponin. At the next developmental stage, MECs acquire cytoplasmic microfilaments and plasmalemmal caveolae but not as much as in the mature cell. They express SMMHC and, inconsistently, K14. This protein is consistently expressed in the mature cell. K14 is expressed by duct cells, and vimentin is expressed by both mesenchymal and epithelial cells. After development, the acinar progenitor and the ductal progenitor appear to reside in the acinus/intercalated duct and the larger ducts, respectively, and to contribute to the tissue homeostasis. Under unusual conditions such as massive parenchymal destruction, the acinar progenitor contributes to the maintenance of the larger ducts that result in the occurrence of striated ducts with MECs. The acinar progenitor is the origin of salivary gland tumors containing MECs. MECs in salivary gland tumors are best identified by immunocytochemistry for alpha-SMA. There are significant numbers of cells related to luminal tumor cells in the non-luminal tumor cells that have been believed to be neoplastic MECs.

Large expansion of morphologically heterogeneous mammary epithelial cells, including the luminal phenotype, from human breast tumours

Regular expansion of heterogeneous populations of epithelial cells, including the luminal phenotype, was achieved from small biopsies of human breast tumours and cutaneous metastases by optimized feeder layer technique based on irradiated NIH 3T3 cells. Forty-one out of 47 primary tumour specimens and all three cutaneous metastases grew successfully for two to 10 passages in vitro. The main phenotypes of cultured cells and their changes in subcultures were characterized using immunocytochemistry and phase contrast microscopy (in few cases also time-lapse recording). In the majority of cultured cell populations a fraction of cells positive for keratin 19 (K19+), typical for the luminal phenotype, was detected. This is the cell type from which breast carcinoma is supposed to arise. While in cultures derived from benign lesions only basic phenotypes of luminal and myoepithelial cells were found, in cultures derived from malignant tumours unusual phenotypes of epithelial cells, in their majority K19+, were detected. The growth properties of cells from six benign and seven malignant samples were analyzed in detail. In the analyzed cell populations the culture lifetime - related to the number of colony-forming cells varied for cells from malignant tumours between 21 and 51 and from benign tumours between 22 and 40 cell generations. The total number of passages achieved was three to seven for malignant or four to nine for benign cultures. In spite of negative results of tumourigenicity testing in immunologically compromised Nu/nu mice the potential to culture apparently neoplastic cells was indicated by positive immunostaining for the p53 oncoprotein (seven of 23 tested malignant cases), the src oncoprotein (five of eight), and overexpression of the c-erbB-2 protein (five of 26). This was further confirmed by successful cultivation of malignant cells from cutaneous metastases. Two of the three metastasis-derived cultures were nearly homogeneously positive for K19 while the third was almost negative. The results proved the optimized feeder layer technique to be useful for regular yielding of large amounts of epithelial cells from small tumour biopsies and for supporting the majority of cell phenotypes present in the original tumour. Therefore, it appeared to be a promising tool for further analysis of interactions between luminal and myoepithelial cells in the development of human breast carcinoma and for the study of individual tumours.

N-Acetyltransferases, sulfotransferases and heterocyclic amine activation in the breast

Heterocyclic amines are mammary carcinogens in rats and their N-hydroxy metabolites are substrates for subsequent metabolic activation by N-acetyltransferases (NAT) and sulfotransferases (SULT) in man. We investigated the expression of these enzymes in human breast tissue and the relationship between NAT genotype and NAT mRNA expression or enzyme activity. Immunohistochemical staining of sections of breast tissue identified expression of NAT1 and NAT2 protein in human mammary epithelial cells, but not in the stroma. We also measured the formation of DNA adducts of the heterocyclic amines 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in calf thymus DNA after incubation of their promutagenic N-hydroxy metabolites with mammary cytosols prepared from reduction mammoplasty tissue. Experimental observations gained from use of enzyme cofactors and NAT and/or SULT inhibitors on cytosolic enzyme activity, recombinant NAT1 activity and heterocyclic amine-DNA adduct formation suggest that both NAT1 and SULT1A enzymes contribute significantly to the activation of N-hydroxylated heterocyclic amines in mammary tissue. NAT1 mRNA transcript levels were found to be two- to three-fold higher than mRNA transcripts of the NAT2 gene in reduction mammoplasty tissue and mammary epithelial cells. NAT1-specific p-aminobenzoic acid acetylation activity, but not NAT2-specific sulfamethazine acetylation activity, was detectable in mammary cytosols. There was no association apparent between NAT genotype and the levels of NAT mRNA or NAT enzyme activity, or between NAT1 genotype and IQ-DNA adduct formation mediated by mammary cytosols. Western blot analysis of mammary cytosolic protein showed detectable levels of SULT1A1 and SULT1A3.

Characterization of bipotent mammary epithelial progenitor cells in normal adult human breast tissue

The purpose of the present study was to characterize primitive epithelial progenitor populations present in adult normal human mammary tissue using a combination of flow cytometry and in vitro colony assay procedures. Three types of human breast epithelial cell (HBEC) progenitors were identified: luminal-restricted, myoepithelial-restricted and bipotent progenitors. The first type expressed epithelial cell adhesion molecule (EpCAM), alpha6 integrin and MUC1 and generated colonies composed exclusively of cells positive for the luminal-associated markers keratin 8/18, keratin 19, EpCAM and MUC1. Bipotent progenitors produced colonies containing a central core of cells expressing luminal markers surrounded by keratin 14+ myoepithelial-like cells. Single cell cultures confirmed the bipotentiality of these progenitors. Their high expression of alpha6 integrin and low expression of MUC1 suggests a basal position of these cells in the mammary epithelium in vivo. Serial passage in vitro of an enriched population of bipotent progenitors demonstrated that only myoepithelial-restricted progenitors could be readily generated under the culture conditions used. These results support a hierarchical branching model of HBEC progenitor differentiation from a primitive uncommitted cell to luminal- and myoepithelial-restricted progenitors.

The mammary myoepithelial cell--Cinderella or ugly sister?

The breast myoepithelial cell is the Cinderella of mammary biology. Although its contribution to benign and some malignant pathologies is recognised, it has been largely neglected in molecular and biological studies. The reason for this has been the perception that its role in normal physiology is confined to lactation and the belief that most breast cancers arise from luminal epithelial cells. This review presents our perspective on its broader biological significance and its potential use as a model system for understanding breast carcinogenesis.

Hedgehog signaling in mouse mammary gland development and neoplasia

Genetic analyses of two hedgehog signal transduction network genes, Patched-1 and Gli2, has demonstrated a critical role for hedgehog signaling in mediating epithelial-stromal tissue interactions during ductal development. Disruption of either gene leads to similar, yet distinct, defects in ductal morphogenesis. Defects are mainly ductal dysplasias that closely resemble some hyperplasias of the human breast. Phenotypic analyses have been coupled with in situ hybridization, transplantation and tissue recombination analyses to formulate a model for tissue compartment-specific control of mouse mammary gland development by hedgehog signaling. In addition, the similarities among hedgehog mutation-induced ductal dysplasias and human breast pathologies suggest a role for altered hedgehog signaling in the development of mammary cancer.

Targets of extinction: identification of genes whose expression is repressed as a consequence of somatic fusion between cells representing basal and luminal mammary epithelial phenotypes

The use of somatic cell hybrids has led to an increased understanding of the ‘negative’ regulation of cellular phenotype. Using somatic cell hybrids constructed between human breast cells that represent differing stages of malignancy but also display differing phenotypes from the same tissue, we present experimental results suggesting that luminal epithelial characteristics are controlled by repressive mechanisms. Fusion of HBL 100 cells, non-tumorigenic and characteristic of the basal cell lineage, with MCF-7 or MDA-MB-468 malignant breast cancer cells, characteristic of the luminal lineage, resulted in hybrid cells that displayed the phenotype of the HBL 100 cells. Using representational difference analysis, a panel of genes whose expression was repressed in the hybrid between HBL 100 and MDA-MB-468 was identified. This analysis revealed markers of luminal epithelial cells to be repressed, including Ep-CAM, cytokeratin 19 and E-cadherin. These markers were found to be coordinately re-expressed in variant hybrid cells indicating that the observed repression is reversible. Integrin (alpha)(v)(beta)(3) expression was found to be in mutual exclusivity to the luminal epithelial markers, thereby revealing a bidirectional ‘switch’ in the pattern of gene expression in this system. Finally, the expression of Ep-CAM was found to be lost in heterokaryons produced by fusion of HBL 100 and MCF-7 or MDA-MB-468 cells suggesting that the extinction of this gene in hybrid cells is the consequence of a trans-acting factor(s) synthesized by the HBL 100 cells. These data suggest that a number of markers of luminal cell differentiation in the mammary gland can be controlled through negative mechanisms and that such control of phenotype is highly coordinated.

Genetic alterations in 'normal' luminal and myoepithelial cells of the breast

Chromosomal loci exhibiting loss of heterozygosity (LOH) at high frequency in invasive breast cancer have been investigated in 'normal' breast tissue from patients with carcinoma and from reduction mammoplasty specimens. Duct-lobular units dissected from paraffin-embedded tissues and 485 'normal' luminal and myoepithelial cell clones were studied. Overall, LOH was found in normal cells in 5/10 breast cancer cases and 1/3 reduction mammoplasty specimens. LOH was identified in normal cells adjacent to and distant from the tumour. In one case, all luminal and myoepithelial samples exhibited loss of the same allele on chromosome 13q. One case in which the patient had a germline truncating mutation in the BRCA1 gene exhibited LOH on 17q in 3/33 normal clones. One of these clones showed loss of wild-type allele indicating gene inactivation. This sample also had LOH at markers on chromosomes 11p and 13q. One of 93 clones from three reduction mammoplasties showed allele loss at a locus on chromosome 13q. The identification of LOH in breast lobules suggests that they may be clonal. The demonstration of genetic alteration in luminal and myoepithelial cells provides evidence for the presence of a common stem cell for the two epithelial cell types. LOH has been demonstrated in normal tissues near and away from the carcinoma, suggesting that genetic alterations are likely to be more heterogeneous and widespread than is currently envisaged, and probably occur very early in breast development. Homozygous deletion of BRCA1 per se does not appear to provide clonal advantage.

Differentiation of separated mouse mammary luminal epithelial and myoepithelial cells cultured on EHS matrix analyzed by indirect immunofluorescence of cytoskeletal antigens

We have previously demonstrated that purified virgin mouse mammary luminal epithelial and myoepithelial cells promiscuously express cell type-specific cytokeratins when they are cloned in vitro. Changes in cytokeratin expression may be indicators of the loss or change of the differentiated identity of a cell. To investigate the factors that may be responsible for the maintenance of differentiated cellular identity, specifically cell-cell and cell-matrix interactions, we cloned flow-sorted mouse mammary epithelial cells on the extracellular matrix (ECM) derived from the Engelbreth-Holm-Swarm murine sarcoma (EHS matrix). Changes in cell differentiation on EHS, compared with culture on glass, were analyzed by comparing patterns of cytokeratin expression. The results indicate that ECM is responsible for maintenance of the differentiated identity of basal/myoepithelial cells and prevents the inappropriate expression of luminal antigens seen on glass or plastic. Luminal cell identity in the form of retention of luminal markers and absence of basal/myoepithelial antigens, on the contrary, appears to depend on homotypic cell-cell contacts and interactions. The results also show that luminal cells (or a subpopulation of them) can generate a cell layer that expresses only basal cytokeratin markers (and no luminal cytokeratin markers) and may form a pluripotent compartment. (J Histochem Cytochem 47:1513-1524, 1999)

Proteomic definition of normal human luminal and myoepithelial breast cells purified from reduction mammoplasties

Normal human luminal and myoepithelial breast cells separately purified from a set of 10 reduction mammoplasties by using a double antibody magnetic affinity cell sorting and Dynabead immunomagnetic technique were used in two-dimensional gel proteome studies. A total of 43,302 proteins were detected across the 20 samples, and a master image for each cell type comprising a total of 1,738 unique proteins was derived. Differential analysis identified 170 proteins that were elevated 2-fold or more between the two breast cell types, and 51 of these were annotated by tandem mass spectrometry. Muscle-specific enzyme isoforms and contractile intermediate filaments including tropomyosin and smooth muscle (SM22) alpha protein were detected in the myoepithelial cells, and a large number of cytokeratin subclasses and isoforms characteristic of luminal cells were detected in this cell type. A further 134 nondifferentially regulated proteins were also annotated from the two breast cell types, making this the most extensive study to date of the protein expression map of the normal human breast and the basis for future studies of purified breast cancer cells.

Human sweat gland myoepithelial cells express a unique set of cytokeratins and reveal the potential for alternative epithelial and mesenchymal differentiation states in culture

We have characterized precisely the cytokeratin expression pattern of sweat gland myoepithelial cells and have identified conditions for propagating this cell type and modulating its differentiation in culture. Rare, unstratified epithelioid colonies were identified in cultures initiated from several specimens of full-thickness human skin. These cells divided rapidly in medium containing serum, epidermal growth factor (EGF), and hydrocortisone, and maintained a closely packed, epithelioid morphology when co-cultured with 3T3 feeder cells. Immunocytochemical and immunoblot analysis disclosed that the cells differed from keratinocytes in that they were E-cadherin-negative, vimentin-positive, and expressed an unusual set of cytokeratins, K5, K7, K14, and K17. When subcultured without feeder cells, they converted reversibly to a spindle morphology and ceased K5 and K14 expression. Under these conditions, EGF deprivation induced flattening, growth arrest, and expression of alpha-smooth muscle actin ((α)-sma). Coexpression of keratins and alpha-sma is a hallmark of myoepithelial cells, a constituent of secretory glands. Immunostaining of skin sections revealed that only sweat gland myoepithelial cells expressed the same pattern of keratins and alpha-sma and lack of E-cadherin as the cell type we had cultured. Interestingly, our immunocytochemical analysis of ndk, a skin-derived cell line of uncertain identity, suggests that this line is of myoepithelial origin. Earlier immunohistochemical studies by others had found myoepithelial cells to be K7-negative. We tested five K7-specific antibodies that can recognize this protein in western blots and in the assembled keratin filaments of mesothelial cells. Three of these antibodies did not recognize the K7 present in myoepithelial cell filaments or in HeLa cell filaments, indicating that some K7 epitopes are masked when K7 pairs with K17 instead of with its usual keratin filament partner, K19.

New model of ErbB-2 over-expression in human mammary luminal epithelial cells

The ErbB-2 receptor has been strongly implicated in the development of breast cancer. To establish a new model system to investigate the role of erbB-2 in tumorigenesis of the breast, the conditionally immortalised human mammary luminal epithelial cell line HB4a was transfected with erbB-2 cDNA. Biological and biochemical characterisation of the resulting cell lines demonstrated that high levels of ErbB-2 expression were sufficient to cause transformation in vitro but did not cause tumours in vivo. Transformation by overexpression of ErbB-2 correlated with ligand-independent tyrosine phosphorylation of ErbB-2 and the adaptor protein Shc. Over-expression of ErbB-2 also resulted in the ligand-independent constitutive association between Shc and another adaptor protein, Grb2, indicating that receptor activation was sufficient to activate downstream signalling pathways. Using the model described, it was found that elevation of ErbB-2 expression levels caused marked quantitative and qualitative alterations in responses to the ligands epidermal growth factor and heregulin. Data indicate a central role for ErbB-2 in mediating the responses induced by these ligands and suggest that these altered ligand-dependent responses play an important role in tumorigenesis in vivo.

Short-term primary culture of epithelial cells derived from human breast tumours

As experimental models for breast cancer, most studies rely on established human breast cancer cell lines. However, many of these lines were established over 20 years ago, many from pleural effusions rather than the primary tumour, so the validity of using them as representative models is questionable. This paper describes our experiences, over a 3-year period, in establishing short-term epithelial-cell-enriched preparations from primary breast tumours based on differential centrifugation followed by culture in selective media. Epithelial cells were successfully cultured from 55% of samples, but culture success did not appear to be correlated with tumour histology, stage, grade or node status. Epithelial cell-enriched cultures were immunopositive for broad-spectrum cytokeratin and epithelial membrane antigen (EMA). Positivity for keratin 19 confirmed that the cultures contained tumour-derived cells, which additionally showed significantly higher activity of the reductive pathway of the steroid-converting enzyme 17beta-hydroxysteroid dehydrogenase type I. That the cultures contained tumour and not normal epithelial cells was further substantiated by the complete absence of the calmodulin-like gene NB-1 in tumour-derived cultures; this is only associated with normal breast epithelia. Eighty-five per cent of cultures established from oestrogen receptor (ER)-positive tumours expressed ER in vitro; this was functional in 66% of cultures, although ER-positive phenotype was gradually lost over time. In conclusion, epithelial cells can be isolated and maintained as short-term cultures from primary breast tumours irrespective of histopathological or clinical details, providing a model system with a greater biological and clinical relevance than breast cancer cell lines.

Morphological transformation of C3H/M2 mouse fibroblasts by extracts of human mammary lipid

Mammary lipid may act as a reservoir for genotoxins. Mammary lipid extracts (MLEs), obtained from eight UK women (21-41 years) undergoing reduction mammoplasty, were examined for their abilities to morphologically transform C3H/M2 mouse fibroblasts. Resultant transformation rates were 0.27, 0.33, 0.07, 0.29, 0.21, 0.00, 0.07, and 0.13 transformed foci/treated dish, respectively. Although the lipid-extraction procedure used was originally designed to extract heterocyclic aromatic amines (HAAs), liquid chromatography/mass spectroscopy (LC/MS) with selective ion monitoring has failed to detect HAAs in any of the lipid extracts so far examined. Genotoxicities were also assessed in S. typhimurium TA98 and in metabolically competent human (MCL-5) cells by the micronucleus and by the alkaline single-cell gel ("comet") assays. The MLEs induced bacterial mutagenicity rates ranging from 0 to 498 revertants/plate/g-lipid equivalent and micronucleus-formation rates from 0 to 20 micronuclei/500 binucleate cells/g-lipid. Median comet tail lengths (induced with MLEs of 8.0 g-lipid equivalent) ranged from 6.0 to 74.0 micrometer. The results demonstrate the presence of as-yet-unidentified transforming agents in mammary lipid.

Clonal characterization of mouse mammary luminal epithelial and myoepithelial cells separated by fluorescence-activated cell sorting

Lineage analysis in vitro of heterogeneous tissues such as mammary epithelium requires the separation of constituent cell types and their growth as clones. The separation of virgin mouse mammary luminal epithelial and myoepithelial cells by fluorescence-activated cell-sorting, their growth at clonal density, and the phenotyping of the clones obtained with cell-type specific markers are described in this paper. Epithelial cells were isolated by collagenase digestion followed by trypsinization, and the luminal and myoepithelial cells were flow-sorted with the rat monoclonal antibodies 33A10 and JB6, respectively. Sorted cells were cloned under, using low oxygen conditions (<5% vol/vol), in medium containing cholera toxin and insulin, with an irradiated feeder layer of 3T3-L1 cells. Clones were characterized morphologically, and antigenically by multiple immunofluorescence with a panel of antibodies to cytoskeletal antigens specific to either luminal epithelial or myoepithelial cells in situ. Whereas sorted myoepithelial cells gave a single clone type, sorted luminal cells gave three morphological clone types, two of which grew rapidly. All myoepithelially derived clones showed a limited proliferative capacity in vitro, in contrast to their rat and human counterparts, as shown in previous studies. The present results with sorted mouse cells have also allowed the stability of the differentiated phenotype in mouse, rat, and human mammary luminal epithelial and myoepithelial cells in primary clonal culture to be compared. They show that the mouse mammary cells are the least stable in terms of expression of differentiation-specific cytoskeletal markers in vitro.

Phenotypic and functional characterization in vitro of a multipotent epithelial cell present in the normal adult human breast

The developmental relationships between the different mammary epithelial cell lineages in the human mammary gland are not well defined. To characterize human breast epithelial cells (HBEC) with progenitor activity, we used flow cytometry and single cell sorting to analyze the distribution of cellular phenotypes in primary cultures of reduction mammoplasties and their associated ability to generate colonies in 2-dimensional (D) and 3-D (collagen gel) culture systems. This approach allowed two distinct types of HBEC progenitor populations to be distinguished on the basis of their differential expression of the MUC-1 glycoprotein, CALLA/CD10 and epithelial-specific antigen (ESA). The first type of progenitor, which is enriched in the MUC-1+/CAL-LA-/ESA+ subpopulation, generated colonies of tightly arranged cells in 2-D cultures and small alveolar-like colonies with a central lumen when cultured in a collagen matrix. The cells produced in the colonies and derived from these MUC-1+/CALLA-/ESA+ progenitors were found to express typical luminal epitopes (keratin 8/18, keratin 19, MUC-1, ESA) and showed low levels of expression of myoepithelial epitopes (keratin 14 and CD44v6). The second type of progenitor, which is present in the MUC-1-to +/-/CALLA +/- to +/ESA+ subpopulation, generated mixed colonies of both luminal and myoepithelial cells when seeded in 2-D and 3-D cultures. In 2-D cultures, the centrally located cells exhibited a luminal morphology and expressed ESA, but were heterogeneous in their expression of MUC-1. Radiating from the periphery of these ESA+ HBEC were highly refractile ESA- teardrop-shaped myoepithelial-like cells. When cultured in a collagen matrix, these bipotent progenitors generated large branched colonies composed of a heterogeneous population of cells, with some of the progeny cells expressing luminal epitopes (keratin 8/18, keratin 19 and MUC-1) and others expressing myoepithelial epitopes (keratin 14 and CD44v6). A third type of progenitor, which became apparent is passaged HBEC cultures and was enriched in the MUC-1-/CALLA+/ESA- subpopulation, was found to generate colonies of cells with an exclusively myoepithelial phenotype. These results provide definitive evidence for the existence of multilineage HBEC progenitors in normal adult human mammary tissue. The phenotypic profile of these cells suggest that these multilineage progenitors are a relatively undifferentiated cell since they express low levels of MUC-1 and that they have a luminal location within the mammary epithelium since they are ESA+. Furthermore, we suggest that the MUC-1+/CALLA-/ESA+ and the MUC-1- to +/-/CALLA +/- to +/ESA+ progenitors we have identified and characterized are candidate in vivo alveolar and ductal progenitors, respectively.

RhoE regulates actin cytoskeleton organization and cell migration

The actin cytoskeleton is regulated by Rho family proteins: in fibroblasts, Rho mediates the formation of actin stress fibers, whereas Rac regulates lamellipodium formation and Cdc42 controls filopodium formation. We have cloned the mouse RhoE gene, whose product is a member of the Rho family that shares (except in one amino acid) the conserved effector domain of RhoA, RhoB, and RhoC. RhoE is able to bind GTP but does not detectably bind GDP and has low intrinsic GTPase activity compared with Rac. The role of RhoE in regulating actin organization was investigated by microinjection in Bac1.2F5 macrophages and MDCK cells. In macrophages, RhoE induced actin reorganization, leading to the formation of extensions resembling filopodia and pseudopodia. In MDCK cells, RhoE induced the complete disappearance of stress fibers, together with cell spreading. However, RhoE did not detectably affect the actin bundles that run parallel to the outer membranes of cells at the periphery of colonies, which are known to be dependent on RhoA. In addition, RhoE induced an increase in the speed of migration of hepatocyte growth factor/scatter factor-stimulated MDCK cells, in contrast to the previously reported inhibition produced by activated RhoA. The subcellular localization of RhoE at the lateral membranes of MDCK cells suggests a role in cell-cell adhesion, as has been shown for RhoA. These results suggest that RhoE may act to inhibit signalling downstream of RhoA, altering some RhoA-regulated responses, such as stress fiber formation, but not affecting others, such as peripheral actin bundle formation.

The development of epithelial phenotypes in the human fetal and infant breast

In order to explain the molecular events that contribute to benign and malignant breast disease, it is essential to understand the cellular context in which these are occurring. This study describes a detailed analysis of the epithelial phenotypes in the human fetal and infant breast and provides a starting point for such consideration. Using methacarn-fixed, paraffin sections from ten fetal and 45 infant breast, immunostained with a panel of antibodies to cytoskeletal proteins and kappa-casein, it has been possible to define in detail the chronological evolution of the major cell types in the human breast from 16 weeks of intrauterine life to 2 years of age, in both sexes. Cells at the tips of the lobular buds and terminal end buds have a characteristic cytoskeletal protein profile, suggesting that they may have the capacity to generate both basal cells and luminal cells. Based on the expression of cytoskeletal proteins in the developing fetal and infant breast, a model system has been proposed for mammary epithelial differentiation.

Isolation and analysis of different subpopulations of normal human breast epithelial cells after their infection with a retroviral vector encoding a cell surface marker

The use of gene transfer procedures has greatly facilitated the investigation of cell lineage relationships and other developmental processes in a variety of primary tissues. In this report we described the infection and selection of primary human breast epithelial cells using retroviral vectors (Jzen-HSA-NEO and MSCV-HSA.NEO) containing the complete 228 bp coding sequence of a murine cell surface marker (Heat Stable Antigen, HSA) as well as the neomycin resistance (neo(r)) gene. Expression of the transduced HSA gene was detectable using either flow cytometry or immunohistochemistry after staining cells with an anti-murine HSA-specific antibody (M1/69). Expression of the transduced neo(r) gene conferred resistance to G418. In initial experiments with the MCF-7 breast cancer cell line, continued expression of both markers was demonstrated in a high proportion of cells for at least 4 weeks after their infection by positive M1/69 staining of cells that had been selected by prior incubation in G418. Evidence of gene transfer to early stage (< 9 days old) primary cultures of normal human breast epithelial cells (15 experiments with cells from 12 normal individuals) was also obtained using an infection protocol in which these calls were exposed to helper-free viral supernatants (2 incubations, 4 to 6 hr each) after being subcultured for 12 to 18 hr to increase their rate of proliferation. The presence of 5-50% (mean = 26%) HSA+ cells was demonstrated in these experiments within 5 days after their infection and the HSA+ populations included both myoepithelial and luminal phenotypes. The transduced (HSA+) cells within both of these subpopulations could also be separately isolated by FACS and subcultured. These results should provide an important starting point for future studies of genetically modified or marked primary human breast epithelial cell populations.

Separated human breast epithelial and myoepithelial cells have different growth factor requirements in vitro but can reconstitute normal breast lobuloalveolar structure

In order to investigate the specific factors controlling the growth of normal breast cell types, purified populations of human breast epithelial and myoepithelial cells from reduction mammoplasties were grown in primary culture in three defined media and their response to foetal calf serum (FCS), epidermal growth factor (EGF) and basic fibroblast growth factor (FGF2) measured using MTT growth assays. Epithelial and myoepithelial cells differed markedly in their growth requirements. Whereas epithelial cell survival was dependent on the presence of FCS, myoepithelial cell growth was dramatically inhibited by serum. EGF and FGF2 were mitogenic for epithelial cells but not myoepithelial cells, the addition of insulin being the only essential supplement required for myoepithelial cell growth. Heparin inhibited FGF2-stimulated epithelial cell growth but also basal myoepithelial cell proliferation and this inhibition could be overcome by the addition of EGF. Neutralizing antibodies to EGF also inhibited basal myoepithelial cell growth. This suggests the possibility of an autocrine role for a heparin-binding member of the EGF family in the growth of myoepithelial cells. Purified cells combined to form lobuloalveolar structures when incubated in a reconstituted basement membrane matrix (Matrigel) in the presence of EGF and FGF2.

Growth requirements and neoplastic transformation of two types of normal human breast epithelial cells derived from reduction mammoplasty

A chemically defined culture medium was developed to support the growth of two distinctly different types of normal human breast epithelial cells (HBEC) derived from reduction mammoplasty. Type I cells expressed luminal epithelial cell markers and were deficient in gap junctional intercellular communication (GJIC), whereas Type II cells expressed basal epithelial cell markers and were efficient in GJIC. In this study, we examined and compared the growth factor and hormone requirements of these two types of cells and a series of cell lines that were obtained by sequential transfection with SV40 DNA (extended lifespan, nontumorigenic), treatment with 5-bromodeoxyuridine (BrdU)/black light (immortal and weakly tumorigenic), and infection of a virus carrying the neu oncogene (highly tumorigenic). Growth of Type I cells was inhibited by withdrawing epidermal growth factor (EGF), hydrocortisone (HC), or insulin (INS) from the culture media, but was enhanced by fetal bovine serum (FBS) supplementation. Growth of Type II cells was inhibited by withdrawal of EGF, HC, or INS from the media, and was inhibited by FBS supplementation. Withdrawal of human transferrin (HT) or 17 beta-estradiol (E2) from the media did not alter the growth of Type I or Type II cells. SV40 transfected Type I cell lines still required EGF, HC, or INS for optimal growth. However, the highly tumorigenic cell line did not show a growth dependence on EGF, HC, or INS but did appear to require HT and 3,3',5-triiodo-D.L. thyronine (T3) for optimal growth. In addition, FBS stimulated the growth of these cell lines. Thus, this study shows that Type I HBEC are distinctly different from Type II HBEC in growth response to FBS and that neoplastically transformed Type I cells could become growth factor and hormone independent.

Expression genetics in cancer: shifting the focus from DNA to RNA

Expression genetics is a conceptually different approach to the identification of cancer-related genes than the search for mutations at the genome level. While mutations lie at the heart of cancer, at least in its early stages, what is recognized here are phenotypic changes usually many steps removed from the initiating mutation. Classically cancer geneticists have concentrated on genomic changes and have ignored the productive potential of examining downstream events based on screening for differential gene expression between tumor cells and well matched normal counterparts. Genes involved in cancer affect the normal functions of many cellular processes: not only proliferation but cell-cell and cell-matrix interactions, DNA repair, invasion and motility, angiogenesis, senescence, apoptosis, and others. Yet very few cancer-related genes affecting these processes have been identified in human cancers by classical methods to find mutated genes despite enormous efforts. I report here our success in readily isolating more than 100 candidate tumor suppressor genes from human tissue, estimated to represent roughly 20% of the total genes recoverable by this approach. Half of the genes are unknown and the other half include representatives of most known cancer processes. Because their expression is lost during cancer progression, they may be useful tumor markers for diagnosis and prognosis. Because these genes are not mutated, they provide opportunities for pharmacological intervention by inducing their reexpression.

A comparative study of cytokine gene transcripts in normal and malignant breast tissue and primary cell cultures derived from the same tissue samples

Using a differential centrifugation method followed by culture in selective medium, we have successfully isolated and maintained individual epithelial and stromal cells from normal (n = 10) and malignant (n = 6) human breast tissue and characterised their phenotype by immunocytochemistry. Further, we have studied expression of the cytokine genes IL-1beta, IL-6, IL-8 and TNF-beta in each cell fraction by RT-PCR and have compared these results with cytokine gene expression in tissue extracts from which primary cultures were derived. In breast tumours, there was near complete absence of IL-1beta in both whole tissue and cell fractions, and in normals it was present in only 3/10 tissue preparations, with increased expression in stromal (6/10) and epithelial (5/10) cell samples. IL-6 was constitutively expressed in all tumour-derived breast tissue samples but down-regulated in tumour cell cultures, with the opposite result in normal breast. Near identical levels of IL-8 expression were found throughout each preparation, irrespective of tissue origin. TNF-beta was expressed in all normal tissue samples, in 9/10 epithelial preparations but in only 6/10 stromal preparations. In tumours, TNF-beta was associated predominantly with whole tissue or stromal samples, with reduced expression in epithelial preparations. Our data confirm that primary cultures of normal and malignant human breast tissue can be successfully separated into epithelial and mesenchymal cell populations and their phenotype can be maintained in culture for up to 30 days. However, this cellular separation does alter the cytokine profiles; therefore, experimental findings with isolated cells should be treated with a caveat.

Upregulation of cytokeratins 8 and 18 in human breast cancer T47D cells is retinoid-specific and retinoic acid receptor-dependent

The mamary gland is chiefly composed of luminal epithelial cells expressing cytokeratins (K) 8, 18 and 19, and basal/myoepithelial cells expressing cytokeratins 5 and 14. Human breast cancer T47D cells have a luminal phenotype and are growth-inhibited by retinoids, a class of compounds known to regulate cytokeratin expression. To extend our knowledge of retinoid action in breast cancer, we have studied the retinoid regulation of cytokeratin expression in the T47D model. We found that retinoid inhibition of T47D cell growth was accompanied by increases in K8, K18 and K19 mRNA steady-state levels (Northern blot analysis). The effect on K8 was studied in greater detail. This effect was seen with as low as 1 nM all-trans retinoic acid (tRA) and was maximal (up to 7 fold over control) with 1 microM tRA (the highest dose tested). Time-course studies revealed a detectable effect at 1 h and a maximal effect at 8-24 h. Non-retinoidal growth inhibitors (tamoxifen, BrcAMP and genistein) did not modulate K8 expression, demonstrating that the effect of tRA was specific, K8 mRNA upregulation was blocked by actinomycin D and cycloheximide, suggesting, in accordance with other studies, that tRA exerted a transcriptional effect that was secondary to de novo protein synthesis. Five retinoids known to activate retinoic acid receptor (RAR) and/or retinoid X receptor (RXR) - tRA; 9-cis-retinoic acid, 9cRA; 13-cis RA, 13cRA; retinyl acetate; and N-(4-hydroxyphenyl) retinamide 4HPR - inhibited T47D cell growth and increased K8 expression, whereas an arotinoid (Ro-40-8757) that is not a RAR activator caused growth inhibition but did not upregulate K8. Activation of RAR alpha contributed to K8 upregulation, since this effect was partially blocked by the RAR alpha-selective antagonist Ro-41-5253. Analogous results were obtained throughout when blots were reprobed with K18 cDNA. Western blot and immunocytochemistry experiments demonstrated that protein levels of K8 and K18 increased by 2 days of treatment with 1 microM tRA. These results show that retinoids enhance the expression of cognate cytokeratin markers of luminal differentiation in T47D breast cancer cells.

HGF/SF: a potent cytokine for mammary growth, morphogenesis and development

The mammary gland is a renewing tissue in which morphogenetic processes and differentiation occur cyclically during the menstrual cycle, pregnancy and lactation. These events have been shown to be dependent upon epithelial-mesenchymal interactions. Studies of the effects of individual factors, their cellular source and their target cell populations in the different developmental stages of the mammary gland are greatly facilitated by the accessibility of this organ and the application of new techniques that allow purification of the major epithelial and stromal components of this tissue. Here we demonstrate that HGF/SF and its cellular receptor, c-met, are expressed and regulated temporally during mouse mammary development and differentiation. We show that human and mouse mammary fibroblasts produce HGF/SF and that HGF/SF is not only mitogenic but morphogenic and motogenic for both human and mouse mammary epithelial cells. We have found that human luminal and myoepithelial cells express c-met differentially and that HGF/SF has different effects on these two mammary epithelial cell populations. HGF/SF is mitogenic for luminal cells but not myoepithelial cells, and morphogenic to myoepithelial cells but not luminal cells. This is discussed in the context of the proliferative compartments in the normal mammary gland and the potential role of the myoepithelial cells to act as the skeleton for ductal development.

The induction of apoptosis in human mammary luminal epithelial cells by expression of activated c-neu and its abrogation by glucocorticoids

The effects of expressing neu-T, a mutated constitutively activated form of c-neu, have been examined in the non-transformed conditionally immortalised human mammary luminal epithelial cell line, HB4a. A variant cell line, N4.1, which expressed neu-T, showed evidence of transformation, including partial loss of growth factor dependence and acquisition of anchorage-independent growth, but failed to give rise to tumours in nude mice, indicating that expression of neu-T alone was probably insufficient to cause tumorigenic progression to a full malignant phenotype. During characterisation of the N4.1 cell line, it was observed that under conditions of serum deprivation, it underwent apoptotic cell death, as demonstrated by light microscopy, flow cytometry and DNA gel electrophoresis. The induction of apoptotic cell death in the N4.1 cell line by serum deprivation was abrogated specifically by the addition of steroids with glucocorticoid activity but not any peptide growth factors studied. This study shows the induction of apoptosis by serum deprivation, and its abrogation by glucocorticoids occurring in human mammary luminal epithelial cells transformed by expression of neu-T, and implicates the involvement of receptor protein tyrosine kinases in an apoptotic signalling pathway in this cell type.

Interleukin-3: a putative protective factor against breast cancer which is secreted by male but not female breast fibroblasts

The enzyme 17 beta-hydroxysteroid dehydrogenase (17-HSD) is a key regulator of intracellular 17 beta-estradiol (E2), which is associated with breast cancer and is influenced by paracrine factors released by breast-cancer fibroblasts. Since the incidence of breast cancer is much higher in females than in males, we have used an in vitro cell culture system to investigate whether male fibroblasts may inhibit breast-cancer genesis by restricting the intracellular accumulation of E2. Fibroblasts were obtained from normal males and females undergoing reduction mammoplasty, and from females with benign or malignant breast lesions. Fibroblast-conditioned medium (CM) was incubated with the established breast-cancer cell line, MCF-7, and its effects on 17-HSD activity were assessed. CM (25% v/v) from male breast fibroblasts had a significant inhibitory effect on reductive 17-HSD, decreasing E2 production. This was in direct contrast to the effects of CM from female breast fibroblasts, which had a powerful stimulatory effect on reductive 17-HSD. RT-PCR allowing simultaneous detection of a range of cytokines was performed on each type of fibroblast. IL-3 mRNA was consistently detected in fibroblasts from male but not female breast tissue. Addition of rhIL-3 to cultures of MCF-7 caused a reduction in 17-HSD activity and addition of a polyclonal antibody directed against IL-3 to male CM completely reversed the inhibitory effects of CM. Thus, male breast fibroblasts may be responsible for secreting IL-3-like factors which, given the considerably lower incidence rates of breast cancer in men, may have a protective effect against breast cancer.

Ectoenzyme regulation by phenotypically distinct fibroblast sub-populations isolated from the human mammary gland

Inter- and intralobular mammary fibroblasts have been separated from normal human breast tissue and cultured to study the differential expression of ectoenzymes present within the stroma of the normal gland and associated with breast cancers. Specific ectoenzymes were identified by indirect immunofluorescence and quantified by flow cytometry and semi-quantitative PCR. A consistent difference was noted between the two fibroblast sub-populations at early passage in respect of dipeptidyl peptidase IV (DPP IV) and aminopeptidase N (APN) expression. Early passage intralobular fibroblasts were positive for APN but negative for DPP IV, as seen in the intact tissue. However, with continued sub-culture they gradually began to express DPP IV, until at later passages they became indistinguishable from the interlobular fibroblasts, which were APN and DPP IV-positive at all stages in culture, as they are in intact tissue. Neutral endopeptidase (NEP/CALLA/CD10) is not expressed by normal adult breast fibroblasts but is found in the stroma associated with over 60% of breast cancers. It was up-regulated in vitro on both inter- and intralobular fibroblasts, with final levels that were significantly (&lt; 14 times) higher on the former in all pairs of preparations from individual donors analysed. This difference persisted with continued passage, and levels of the ectoenzyme and its messenger RNA were further up-regulated by hydrocortisone in both populations. These results demonstrate that phenotypically distinct cultures of human mammary fibroblast sub-populations can be used to study the regulation of these stromal ectoenzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of proviral integration in human mammary epithelial cell lines immortalized by retroviral infection with a temperature-sensitive SV40 T-antigen construct

A panel of eight conditionally immortal lines derived by infection of human breast epithelial cells with an amphotropic retrovirus transducing a ts mutant of SV40 large T-antigen was analyzed with respect to individual retroviral integration patterns. Each line contained multiple integration sites which were clonal and stable over extended passage. Similar integration patterns were observed between individual lines arising separately from the same stock of pre-immortal cells, suggesting a common progenitor. Retroviral integration analysis of pre-immortal cells at different stages of pre-crisis growth showed changes indicative of a progressive transition from polyclonality to clonality as the cells approached crisis. Each of the immortal lines contained a sub-set of the integration sites of their pre-immortal progenitors, with individual combinations and copy numbers of sites. Since all the cell lines appeared to originate from single foci in separate flasks, it is likely that each set arose from a common clone of pre-immortal cells as the result of separate genetic events. There was no evidence from this analysis to suggest that specific integration sites played any part either in the selection of pre-crisis clones or in the subsequent establishment of immortal lines.

Subtypes of non-transformed human mammary epithelial cells cultured in vitro: histo-blood group antigen H type 2 defines basal cell-derived cells

Normal (non-transformed) human mammary epithelial cell lines derived from reduction mammoplasties were analyzed by immunocytochemistry with more than 80 monoclonal antibodies (mAbs) and other specific reagents to tissue-specific and developmentally regulated antigens at different passage levels. A subpopulation of poorly differentiated, proliferating epithelial cells, corresponding to the 'selected' cell type of late passages, is shown to be characterized by a new marker, the histo-blood group antigen H type 2, probably carried on a membrane-bound glycolipid. These cells also express a number of other onco-developmental carbohydrate antigens [Le(y), Le(x), sialosyl-Le(a), precursor of Thomsen Friedenreich antigen (Tn), but not Thomsen-Friedenreich antigen and sialosyl-Tn]. Their cytokeratin (CK) phenotype, as assessed by reactivity with monospecific mAbs and two-dimensional gel electrophoresis, is CK 5, 6, 14 and 17, with CK 19 being consistently absent, and varying minor amounts of CK 7, 8 and 18, as well as 15 and 16. The reactivity of these cells with a panel of 11 mAbs specific for CK 18 varies considerably even after cloning, indicating heterogeneity of epitope expression or accessibility. Our data strongly suggest that the H type 2+ cells develop from the basal cell layer of the mammary gland.

Cytokeratin profile of immunomagnetically separated epithelial subsets of the human mammary gland

We have used enzymatic and immunomagnetic techniques for the physical separation of the basal and luminal epithelium of the human mammary gland. Immediately after tissue dissociation and cell sorting, we have examined the steady-state CK composition of these cells individually by direct two-dimensional gel electrophoresis of intermediate filament extracts. Our results demonstrate that cytokeratins typical of simple and stratified epithelial cells are simultaneously expressed by both mammary epithelial subclasses in vivo. Moreover, the entire spectrum of cytokeratins seen in vivo is also maintained in short-term cultures of human mammary epithelium. A comparison of the data obtained by direct cytokeratin analysis with published indirect immunolocalization studies is presented. The ability to isolate purified epithelial subsets from normal human breast tissue by a simple immunomagnetic procedure demonstrated here can facilitate the development of relevant model systems for studying the regulatory components in growth, differentiation and malignant transformation of the human breast.

Tyrosine kinase receptor--nuclear protooncogene interactions in breast cancer

In summary, evidence is beginning to accumulate in support of a major role for tyrosine kinase receptors (and their activating growth factors) and steroid hormones and their receptors in normal development and differentiation of the mammary gland. A point of intersection of their mechanisms of action in growth control appears to be the induction of nuclear protooncogenes such as c-myc. When c-myc is amplified, as it is in many breast cancers, EGF and FGF receptor tyrosine kinase action becomes transforming, not simply mitogenic. A source of the transforming factors could be either stromal or epithelial. This mechanism could function early in the progression of breast cancer. c-erbB-2 and EGF receptor overexpression and amplification, when they occur, appear to render tumors even more malignant and of especially poor prognosis. These mechanisms could function late in the progression of breast cancer. Transgenic mouse studies have begun to echo these themes. They have established that a growth factor (TGF-alpha) and its receptor (EGF receptor), which appear to be important in normal mouse and human proliferation and gland development, and a protooncogene (c-myc), commonly amplified and overexpressed in human and mouse breast cancer, can each contribute to mammary carcinogenesis. The mechanisms of the two are likely to be distinct. myc is likely to be acting as a tumor initiator in combination with normal proliferative factors, whereas TGF-alpha is likely to be acting as a hyperproliferative (promotional) factor in combination with a normal background of mutational events. The role of unmutated but amplified erbB-2 in the transgenic mouse is not yet known.

t(6;12)(q23;q13) and t(10;16)(q22;p11) in a phyllodes tumor of breast

Cytogenetic analysis of short-term cultures from a phyllodes tumor showed clonal chromosome changes including t(6;12)(q23;q13) and t(10;16)(q22;p11). This is the first reported karyotype in this tumor type. We discuss the breakpoints of these translocations in relation to the involvement of possible candidate genes.

Detection and partial purification of a potent mitogenic factor for human thyroid follicular cells

Normal adult human thyroid follicular cells have an extremely limited proliferative capacity in vitro. No previously studied mitogen, including thyrotropin (TSH) or epidermal growth factor (EGF), has in our hands resulted in a significant improvement over the 3-4% nuclear [3H]thymidine pulse-labelling index (LI) obtainable with 10% fetal calf serum. Here we report the detection in the conditioned medium from a sub-clone of NIH3T3 fibroblasts of a mitogenic activity capable of increasing this response up to 10-fold, to an LI of over 20%, together with an even greater relative stimulation of mitotic activity. Preliminary characterisation has excluded EGF and TGF alpha, and demonstrated that the activity is bound reversibly by heparin-Sepharose, thus pointing to a member of the heparin-binding fibroblast- or hepatocyte-growth factor families. This material should have wide practical application in facilitating primary culture of follicular cells, and may reveal new mechanisms of stromal-epithelial interaction regulating normal and neoplastic thyroid growth in vivo.

Effects of growth factors on proliferation on basal and luminal cells in human breast epithelial explants in serum-free culture

A method of culturing human breast epithelium is described in which viable explants can be maintained in protein-free medium while retaining the capacity of responding to added hormones and growth factors for at least 7 days. Culture parameters were chosen to provide maximum sensitivity of detection of proliferative responses by autoradiography. Under basal conditions, the mean thymidine labeling index of the explants was 0.08%. After stimulation with insulin, hydrocortisone, and cholera toxin (I,H,CT), a combination known to stimulate proliferation in human breast epithelium in vitro, the mean labeling index was 15.7%. Stimulation of explants with epidermal growth factor (EGF) and transforming growth factor (TGF)-alpha resulted in mean labeling indices of 6.6 and 10.8%, respectively. Autoradiography at the ultrastructural level demonstrated that in I,H,CT-stimulated explants the majority of the labeled cells were luminal, with only 1.5% being basal cells. In contrast, after EGF and TGF-alpha basal cells accounted for 11.5 and 18.5% of the labeled population. These results indicate that this system provides an in vitro assay of proliferative activity in the normal human breast that enables comparisons to be made between both the luminal and the basal cells in the explants and their counterparts in monolayer culture prepared from flow sorted cells. Thus, growth responses dependent on cell-to-cell interactions or stromal modulation can be identified.