Expression of integrin subunits in the human infant breast correlates with morphogenesis and differentiation

Glycosylation modulates melanoma cell α2β1 and α3β1 integrin interactions with type IV collagen

Although type IV collagen is heavily glycosylated, the influence of this post-translational modification on integrin binding has not been investigated. In the present study, galactosylated and nongalactosylated triple-helical peptides have been constructed containing the α1(IV)382-393 and α1(IV)531-543 sequences, which are binding sites for the α2β1 and α3β1 integrins, respectively. All peptides had triple-helical stabilities of 37 °C or greater. The galactosylation of Hyl(393) in α1(IV)382-393 and Hyl(540) and Hyl(543) in α1(IV)531-543 had a dose-dependent influence on melanoma cell adhesion that was much more pronounced in the case of α3β1 integrin binding. Molecular modeling indicated that galactosylation occurred on the periphery of α2β1 integrin interaction with α1(IV)382-393 but right in the middle of α3β1 integrin interaction with α1(IV)531-543. The possibility of extracellular deglycosylation of type IV collagen was investigated, but no β-galactosidase-like activity capable of collagen modification was found. Thus, glycosylation of collagen can modulate integrin binding, and levels of glycosylation could be altered by reduction in expression of glycosylation enzymes but most likely not by extracellular deglycosylation activity.

Human breast development

This review is intended to give an overview of current knowledge on human breast development. It focuses on the limitations of our understanding on the origins of human breast cancer in the context of this mainly morphological and static assessment of what is known about human breast development. The world literature is very limited and caution is needed in drawing analogies with the mouse. There is an increasing emphasis on research to understand normal stem cells in the breast on the assumption that these are the targets for the initiation of breast cancer. It is thus a priority to understand normal human breast development, but there are major obstacles to such studies mainly due to ethical considerations and to tissue acquisition.

Basal cells of second trimester fetal breasts: immunohistochemical study of myoepithelial precursors

The molecular characterization of human mammary myoepithelial cells is incomplete, hindering our understanding of its importance in breast physiology and pathology. Because data on the precursors of this cell lineage remain scarce and often contradictory, basal epithelial cells of second trimester fetal breasts were studied by light microscopy (LM) and immunohistochemistry (IHC). Up to 20 wk of gestational age, the mammary rudiments only comprised roundish primary outgrowths, "primary buds," more likely to represent immature nipples than true mammary tissue. At 21 wk secondary outgrowths, "projections," extended from enlarged primary buds into well-vascularized layers of dense mesenchyme. Basal projection cells had a partial myoepithelial-like phenotype: they reacted with CD29, CD49f, CD104, keratin 14, vimentin, S100beta protein, and p63; furthermore, many became positive for keratin 17, alpha-smooth muscle actin, and CD10 (but not for keratin 19) between wk 21 and 25. The continuous basement membrane associated with the fetal mammary rudiments was strongly positive for collagens type IV and VII, and for laminin 5. Consistently strong and basally polarized staining for hemidesmosomal components suggested that although incompletely differentiated, most second trimester myoepithelial precursors might already mediate local epithelial-mesenchymal interactions, i.e., complex signaling pathways which are crucial for both orderly growth during development and maintenance of homeostasis during adult life. Because they are likely implicated in the phenomenon of menstrual cycle-related growth spurts in the adult resting breast, the strategically positioned cells of the myoepithelial lineage might constitute critical protagonists in defective epithelial-mesenchymal signaling associated with cancer progression.

Evidence that Myc activation depletes the epidermal stem cell compartment by modulating adhesive interactions with the local microenvironment

Activation of Myc (c-Myc) causes epidermal cells to exit the stem cell compartment and differentiate into sebocytes and interfollicular epidermis at the expense of the hair lineages. To investigate how Myc exerts these effects we analysed the transcription of more than 10000 genes following Myc activation in the basal layer of mouse epidermis for 1 or 4 days. The major classes of induced genes were involved in synthesis and processing of RNA and proteins, in cell proliferation and in differentiation. More than 40% of the downregulated genes encoded cell adhesion and cytoskeleton proteins. Repression of these genes resulted in profound changes in the adhesive and motile behaviour of keratinocytes. Myc activation inhibited cell motility and wound healing, correlating with decreased expression of a large number of extracellular matrix proteins. Cell adhesion and spreading were also impaired, and this correlated with decreased expression of the alpha6beta4 integrin, decreased formation of hemidesmosomes and decreased assembly of the actomyosin cytoskeleton. We propose that Myc stimulates exit from the stem cell compartment by reducing adhesive interactions with the local microenvironment or niche, and that the failure of hair differentiation reflects an inability of keratinocytes to migrate along the outer root sheath to receive hair inductive stimuli.

Role of CD31/platelet endothelial cell adhesion molecule-1 expression in in vitro and in vivo growth and differentiation of human breast cancer cells

Breast ductal carcinoma in situ is an intraductal proliferation of malignant epithelial cells that diffuse within the ductal system without stromal invasion. Our finding that a subset of these tumors express CD31/platelet endothelial cell adhesion molecule-1 suggests that breast cancer represents an informative model for studying the involvement of the molecule in the morphogenesis, differentiation, and diffusion of this disease. Transfection of CD31 in MDA-MB-231 cells caused reduction in growth, loss of CD44, and acquisition of a ductal morphology. The same effects were maintained in vivo, in which CD31(+) tumors grew with in situ-like aspects, papillary differentiation, and a secretory phenotype. CD44 was down-modulated, with the CD31(+) cells blocked in the G(1) phase. The morphology was highly similar to what was observed in some human CD31(+) ductal carcinomas in situ. MDA-MB-231 mock cells grew in solid sheets, lacking stromal material, and displaying high levels of CD44 and proliferation. CD31(+) cells acquired motility characteristics in in vitro assays, a finding confirmed in vivo by the diffusion of human tumor cells throughout the normal ducts residual in the murine mammary gland. In conclusion, CD31 expression reverts the undifferentiated morphology and aggressive behavior of MDA-MB-231 cells, indicating its active role in the morphogenesis of breast ductal in situ carcinomas.

Perturbation of beta1-integrin function in involuting mammary gland results in premature dedifferentiation of secretory epithelial cells

To study the mechanism of beta1-integrin function in vivo, we have generated transgenic mouse expressing a dominant negative mutant of beta1-integrin under the control of mouse mammary tumor virus (MMTV) promoter (MMTV-beta1-cyto). Mammary glands from MMTV-beta1-cyto transgenic females present significant growth defects during pregnancy and lactation and impaired differentiation of secretory epithelial cells at the onset of lactation. We report herein that perturbation of beta1-integrin function in involuting mammary gland induced precocious dedifferentiation of the secretory epithelium, as shown by the premature decrease in beta-casein and whey acidic protein mRNA levels, accompanied by inactivation of STAT5, a transcription factor essential for mammary gland development and up-regulation of nuclear factor-kappaB, a negative regulator of STAT5 signaling. This is the first study demonstrating in vivo that cell-extracellular matrix interactions involving beta1-integrins play an important role in the control of milk gene transcription and in the maintenance of the mammary epithelial cell differentiated state.

Proliferation and differentiation in the human breast during pregnancy

Using multiple immunofluorescence labelling on human breast tissues obtained and freshly frozen at the 12th, 15th, and 18th weeks of pregnancy, we have shown that markers of mammary functional differentiation, milk proteins (beta-casein and kappa-casein), are synthesised by actively cycling (Ki67 positive) as well as non-cycling (Ki67 negative) cells. These results demonstrate that functional differentiation/maturation does not coincide with loss of proliferative potential in human mammary luminal epithelial cells. In addition, we have examined expression patterns of integrin subunits (alpha1, alpha2, alpha3, alpha6, beta1, and beta4) and extracellular matrix components (laminin, fibronectin, collagen I, and collagen IV), since they have been shown to exert influences on mammary differentiation and morphogenesis in vitro. Compared to human breast tissues obtained from non-pregnant women, a decrease in alpha2 labelling on luminal epithelial cells was observed, particularly in expanding acini that showed abundant Ki67 positivity. The expression patterns of other integrin subunits, however, did not change, indicating that the expression patterns of most integrins existing prior to pregnancy are sufficient to support the morphological and functional development associated with milk protein synthesis.

Beta(1)-integrins are involved in migration of human fetal tracheal epithelial cells and tubular morphogenesis

Development of human fetal airways requires interaction of the respiratory epithelium and the extracellular matrix through integrins. Nevertheless, the specific roles of beta(1)-integrins during development and tubular morphogenesis are still unknown. To analyze beta(1)-integrin localization and influence during migration, we developed a model of human fetal tracheal explants growing on collagen and overlaid with a second layer of collagen to form a sandwich. In this configuration, cord and tubule formation proceeded normally but were inhibited by incubation with anti-beta(1)-integrin subunit antibodies. On a collagen matrix, beta(1)-integrins were immunolocalized on the entire plasma membrane of migrating epithelial cells and almost exclusively on the basal plasma membrane of nonmigratory epithelial cells. In a sandwich configuration, beta(1)-integrins became detectable in the cytoplasm of epithelial cells. Coating cultures with collagen transiently altered the morphology of migrating cells and their speed and direction of migration, whereas incubation with anti-beta(1)-integrin subunit antibodies irreversibly altered these parameters. These observations suggest that the matrix environment, by modulating beta(1)-integrin expression patterns, plays a key role during tubular morphogenesis of human fetal tracheal epithelium, principally by modulating epithelial cell migration.

Human breast development

This review presents an atlas of the histology of the normal physiological states of the human breast including prenatal, prepubertal, and pubertal development, adult resting gland, pregnancy, lactation, and postinvolution. The aim is to produce a pictorial overview of the main stages in development and the common findings in the adult that are considered to be within the range of normality. Unlike inbred strains of animals, in humans it is clear that the chronology of ductal and lobular development is not predictable, either in the fetus, the infant, the peripubertal breast, or the adult. This is probably due to the individual variation in hormone levels both in utero and after birth. For many of the developmental time points there are very little data available. In this review we indicate the current state of knowledge of human breast development and some of the main similarities and differences with the rodent, the main animal model. The major phases of growth and development are described and accompanied by photographs that are representative of each stage. Stress is placed on terminology as there is confusion in the literature. This article is written as an accessory to the companion review on breast cancer.

beta1 integrins regulate keratinocyte adhesion and differentiation by distinct mechanisms

In keratinocytes, the beta1 integrins mediate adhesion to the extracellular matrix and also regulate the initiation of terminal differentiation. To explore the relationship between these functions, we stably infected primary human epidermal keratinocytes and an undifferentiated squamous cell carcinoma line, SCC4, with retroviruses encoding wild-type and mutant chick beta1 integrin subunits. We examined the ability of adhesion-blocking chick beta1-specific antibodies to inhibit suspension-induced terminal differentiation of primary human keratinocytes and the ability of the chick beta1 subunit to promote spontaneous differentiation of SCC4. A D154A point mutant clustered in focal adhesions but was inactive in the differentiation assays, showing that differentiation regulation required a functional ligand-binding domain. The signal transduced by beta1 integrins in normal keratinocytes was "do not differentiate" (transduced by ligand-occupied receptors) as opposed to "do differentiate" (transduced by unoccupied receptors), and the signal depended on the absolute number, rather than on the proportion, of occupied receptors. Single and double point mutations in cyto-2 and -3, the NPXY motifs, prevented focal adhesion targeting without inhibiting differentiation control. However, deletions in the proximal part of the cytoplasmic domain, affecting cyto-1, abolished the differentiation-regulatory ability of the beta1 subunit. We conclude that distinct signaling pathways are involved in beta1 integrin-mediated adhesion and differentiation control in keratinocytes.

Significance of alpha 9 beta 1 and alpha v beta 6 integrin expression in breast carcinoma

BACKGROUND

Both alpha 9 beta 1 and alpha v beta 6 integrins have been newly identified from the tracheal epithelium of guinea pig. It has been pointed out that alpha 9 beta 1 functions as a receptor for tenascin-C and osteopontin. As for the ligands of alpha v beta 6, fibronectin and tenascin-C have been identified. It has not been ascertained whether alpha 9 beta 1 and alpha v beta 6 are expressed in normal breast tissue, benign breast lesion or breast carcinoma.

METHODS

Immunohistochemical staining for alpha 9 beta 1 and alpha v beta 6 was performed in benign breast lesion and breast carcinoma specimens. Western blotting was carried out on 11 breast carcinoma cases.

RESULTS

alpha 9 beta 1 was expressed in the cytoplasm of carcinoma cells in 23 of 90 cases (26%) and alpha v beta 6 in the membrane of carcinoma cells in 16 of 90 cases (18%). However, these findings of alpha 9 beta 1 and alpha v beta 6 did not correlate with any clinicopathological factors including the patients' age, tumor size, histological type of carcinoma, location of carcinoma cells and hormone receptor status. With regard to the histological grade of carcinoma, alpha v beta 6 and alpha 9 beta 1 expression did not statistically correlate, although no expression of alpha v beta 6 was observed in 14 cases of Grade I. On Western-blott analysis strong and weak bands consistent with alpha v beta 6 were noted in the membrane fraction extracted from breast carcinoma cells. On the other hand weak bands consistent with alpha 9 subunit were noted in the whole cell lysates of breast carcinoma cells and very weak or no bands consistent with alpha 9 subunit were noted in the membrane fraction extracted from the breast carcinoma cells.

CONCLUSIONS

Significance of alpha 9 beta 1 and alpha v beta 6 integrins expression in breast carcinoma was still unknown on clinicopathological examination. The findings of Western blot analysis may indicate that the transportation system of glycoproteins such as integrins to the cell membrane of carcinoma cells is disturbed, although these integrins can be produced.

The spatial relationship between stem cells and their progeny in the basal layer of human epidermis: a new view based on whole-mount labelling and lineage analysis

In order to examine the spatial organisation of stem cells and their progeny in human epidermis, we developed a method for whole-mount epidermal immunofluorescence labelling using high surface beta1 integrin expression as a stem cell marker. We confirmed that there are clusters of high beta1 integrin-expressing cells at the tips of the dermal papillae in epidermis from several body sites, whereas alpha6 integrin expression is more uniform. The majority of actively cycling cells detected by Ki67 or bromodeoxyuridine labelling were found in the beta1 integrin-dull, transit amplifying population and integrin-negative, keratin 10-positive cells left the basal layer exclusively from this compartment. When we examined p53-positive clones in sun-exposed epidermis, we found two types of clone that differed in size and position in a way that was consistent with the founder cell being a stem or transit amplifying cell. The patterning of the basal layer implies that transit amplifying cells migrate over the basement membrane away from the stem cell clusters. In support of this, isolated beta1 integrin-dull keratinocytes were more motile on type IV collagen than beta1 integrin-bright keratinocytes and EGFP-labelled stem cell clones in confluent cultured sheets were compact, whereas transit amplifying clones were dispersed. The combination of whole-mount labelling and lineage marking thus reveals features of epidermal organisation that were previously unrecognised.

beta-catenin signalling modulates proliferative potential of human epidermal keratinocytes independently of intercellular adhesion

We found that cultured human keratinocytes with high proliferative potential, the putative epidermal stem cells, expressed a higher level of noncadherin-associated beta-catenin than populations enriched for keratinocytes of lower proliferative potential. To investigate the physiological significance of this, a series of beta-catenin constructs was introduced into keratinocytes via retroviral infection. Full-length beta-catenin and a mutant containing only nine armadillo repeats had little effect on proliferative potential in culture, the full-length protein being rapidly degraded. However, expression of stabilised, N-terminally truncated beta-catenin increased the proportion of putative stem cells to almost 90% of the proliferative population in vitro without inducing malignant transformation, and relieved the differentiation stimulatory effect of overexpressing the E-cadherin cytoplasmic domain. Conversely, beta-catenin lacking armadillo repeats acted as a dominant negative mutant and stimulated exit from the stem cell compartment in culture. The positive and negative effects of the beta-catenin mutants on proliferative potential were independent of effects on cell-cycle kinetics, overt terminal differentiation or intercellular adhesion, and correlated with stimulation or inhibition of transactivation of a TCF/LEF reporter in basal keratinocytes. We conclude that the elevated level of cytoplasmic beta-catenin in those keratinocytes with characteristics of epidermal stem cells contributes to their high proliferative potential.

Migration of breast epithelial cells on Laminin-5: differential role of integrins in normal and transformed cell types

We examined the role of Laminin-5 (Ln-5) an extracellular matrix component of breast gland basement membrane, in supporting migration of normal (HUMEC), immortalized (MCF-10A), and malignant breast epithelial cells that exhibit different degrees of metastatic potential (MDA-MB-435>MDA-MB-231>MCF-7). HUMEC, MCF-10A, and MCF-7 cells all adhered to purified Ln-5 through the alpha3beta1 integrin receptor in adhesion assays. However, HUMEC and MCF-10A cells remained statically adherent, while MCF-7 cells migrated on Ln-5 in Transwell and colloidal gold displacement assays. Anti-alpha3 integrin antibodies blocked migration of MCF-7 cells on Ln-5. MDA-MB-231 and MDA-MB-435 cells bound and migrated on Ln-5 through a beta1 integrin receptor that is insensitive to antibodies that block the function of alpha1, alpha2, alpha3, alpha4, alpha5, alpha6, and alphaV integrin subunits. Migration of all cell types tested was blocked by CM6, a monoclonal antibody directed to a cell adhesion site on the alpha3 chain of Ln-5. Thus, Ln-5 may play an important role in regulating adhesion and migration in normal and transformed breast epithelium. Our results indicate that the type of integrin utilized by breast cells to interact with Ln-5, as well as its functional state, may determine whether cells will be statically adherent or migratory on Ln-5.

Breast development gives insights into breast disease

AIMS

Studies of developing human breasts are essential for understanding the organogenesis as well as molecular pathogenesis of benign and malignant breast diseases. In this study we have examined the distribution of TGF-alpha, TGF-beta 1, tenascin-C and collagen type IV with the aim of starting to build a picture of the profile of molecules that may be involved in the development of the human breast.

METHODS AND RESULTS

Ten fetal breasts (16 to 23 weeks of gestation) and 45 infant breasts, ranging in age from newborn to 2 years, were used in this study. Paraffin sections from these samples were immunostained with antibodies for these proteins and for Ki67 to elucidate the level of proliferative activity in different stages of breast development. TGF-alpha immunoreactivity was observed both in the stromal and the epithelial cells within fetal and infant breasts up to 25 days. TGF-beta 1 immunoreactivity was localized in the extracellular matrix. Tenascin-C was found around the neck of the developing breast bud and in the extracellular matrix of the infant with peaks in the newborn at 6-12 weeks. The immunoreactivity for type IV collagen was more intense in the region of the breast bud neck in the fetal breasts and reduced around the tips of lobular and terminal-end buds within the infant breasts.

CONCLUSIONS

The distribution of the growth factors and extracellular matrix proteins within the developing human breast indicates that they play a significant role in different cellular compartments during morphogenesis and provides insights into breast disease.

Distribution of integrins during human fetal lung development

Interactions between epithelial cells and the extracellular matrix through integrins play a key role in the development of the lung by modulating branching morphogenesis, epithelial cell polarization, and differentiation. To determine the role of integrins during the different stages of lung development, we investigated the distribution of eight integrin subunits in the trachea and lung from human fetuses. In distal airways, during the early pseudoglandular stage of development, the alpha2-, alpha5-, alpha6-, alphav-, and beta1-subunits were detected in all epithelial cell plasma membranes, and polarized but undifferentiated tracheal epithelial cells expressed alpha3-, alpha6-, and beta1-subunits in the plasma membrane of the cells facing the basement membrane. The alpha6- and beta4-chains were detected along the basal plasma membrane of the basal cells in differentiated tracheal epithelia. The alpha4-subunit was detected in all respiratory cells throughout fetal development. In the submucosal glands, myoepithelial cells expressed the integrin subunits found in the undifferentiated cells of the developing airways, whereas the secretory cells expressed only alpha2-, alpha3-, alpha4-, alpha6-, and beta1-subunits. These results demonstrate differential expression of integrins during lung development and suggest that integrins may play multiple roles in organogenesis and maturation of respiratory surface epithelium and glands.

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.

Correlation of alpha 2 beta 1 integrin expression with histological type and hormonal receptor status in breast carcinomas

Interactions between cells and extracellular matrix are mediated in part by a family of alpha beta heterodimeric molecules known as integrins. Immunohistochemical studies have shown that benign hyperplastic/neoplastic mammary epithelium expressed high levels of alpha 2 beta 1 collagen/laminin receptor. In contrast, malignant cells of breast carcinoma exhibited marked diminuition or loss of the alpha 2 beta 1 integrin. A correlation has been suggested between the loss of the alpha 2 beta 1 expression and the increased invasiveness of neoplastic cells. This study investigated the expression of alpha 2 beta 1 integrin and its extracellular ligand collagen TV by using monoclonal antibodies on the cryostat section of 124 invasive mammary carcinomas. Two patterns of alpha 2 beta 1 immunoreactivity, i.e. pericellular and basolateral, were identified in breast carcinomas and correlated with their histological type. In most invasive ductal carcinomas of no special type (NOS), integrin staining tended to decrease in both pericellular and basolateral aspects. Loss of basolateral staining for alpha 2 beta 1 integrin corresponded closely to the loss of immunoreactivity for collagen IV. Mucinous and medullary carcinomas showed strongly alpha 2 beta 1 pericellular staining, but no basolateral reactivity or collagen IV expression. Only two of the infiltrating lobular carcinomas expressed strong pericellular reactivity. In 82 ductal carcinomas NOS, the abnormally low expression/absence of alpha 2 beta 1 integrin correlated with estrogen and progesterone receptor negativity (p < 0.04 and p < 0.002, respectively). No correlation between integrin expression, histological grade, nodal involvement and proliferative activity was found. The results of the present study suggest that changes in alpha 2 beta 1 expression correlate with the histological type and hormonal receptor status in breast carcinomas. The clinical implications of these findings remain to be elucidated.