Determination of apical membrane polarity in mammary epithelial cell cultures: the role of cell-cell, cell-substratum, and membrane-cytoskeleton interactions

Pregnancy, abortion, and birth control methods' complicity with breast cancer occurrence

Reproductive factors play significantly important roles in determining the breast cancer (BC) risk. The impact of pregnancy, abortion, and birth control methods on tumor development remains unclear. It has been found that early full-term pregnancies in young women can lower their lifetime risk of developing the type of cancer in question. However, having a first full-term pregnancy at an older age can increase this risk. The relationship between pregnancy and breast cancer (BC) is, however, much more complicated. Both induced and spontaneous abortions lead to sudden changes in hormonal balance, which could cause different effects on sensitive breast epithelial cells, making abortion a potential risk factor for breast cancer. The influence of hormonal contraception on carcinogenesis is not comprehensively understood, and therefore, more exhaustive analysis of existing data and further investigation is needed. This review explores how the mentioned reproductive factors affect the risk of breast cancer (BC), focusing on the molecular mechanisms that contribute to its complexity. By comprehending this intricate network of relationships, we can develop new strategies for predicting and treating the disease.

Breast cancer, placenta and pregnancy

BACKGROUND

Breast cancer is one of the most frequently diagnosed malignancies during pregnancy. Tumours often present characteristics of high malignancy and are hormone receptor negative/HER2 positive or triple negative. In general, pregnancy, including the postpartum period, is associated with a transiently increased risk of developing breast cancer but followed by a long-lasting protective period. Placental metastases are very rare and, thus far, breast cancer metastases in the foetal compartment have not been described. To discuss these apparently contradictory observations, this narrative review resumes immunological and hormonal alterations during pregnancy potentially affecting breast cancer risk as well as tumour growth and behaviour.

OBSERVATIONS

Upregulation of breast cancer-associated genes involved in immunological and reproductive processes has been observed in parous women and is potentially responsible for a transiently increased risk in pregnancy. In contrast, maternal immunisation and immunoglobulin production against antigens expressed on trophoblast cells, such as specific glycosylation patterns of mucin-1 or RCAS1-associated truncated glycans, seem to prevent breast cancer development in later years. Animal and human studies indicate that T cells are involved in these processes. Several placenta-derived factors, especially kisspeptin, have direct anti-tumour effects. The pregnancy-related increase of estrogen, progesterone, and other hormones influence growth and characteristics of breast cancer while the role of further placenta-secreted factors is still controversially discussed.

CONCLUSION

Several factors and cells are involved in altered breast cancer risk during and after pregnancy and have potential for developing novel treatment strategies in future.

Human MUC1 Mucin: A Multifaceted Glycoprotein

Human MUC1 mucin, a membrane-bound glycoprotein, is a major component of the ductal cell surface of normal glandular cells. MUC1 is overexpressed and aberrantly glycosylated in carcinoma cells. The role MUC1 plays in cancer progression represents two sides of one coin: on the one hand, loss of polarity and overexpression of MUC1 in cancer cells interferes with cell adhesion and shields the tumor cell from immune recognition by the cellular arm of the immune system, thus favoring metastases; on the other hand, MUC1, in essence a self-antigen, is displaced and altered in malignancy and induces immune responses. Tumor-associated MUC1 has short carbohydrate sidechains and exposed epitopes on its peptide core; it gains access to the circulation and comes into contact with the immune system provoking humoral and cellular immune responses. Natural antibodies to MUC1 present in the circulation of cancer patients may be beneficial to the patient by restricting tumor growth and dissemination: early stage breast cancer patients with a humoral response to MUC1 have a better disease-specific survival. Several MUC1 peptide vaccines, differing in vectors, carrier proteins and adjuvants, have been tested in phase I clinical trials. They are capable of inducing predominantly humoral responses to the antigen, but evidence that these immune responses may be effective against the tumor in humans is still scarce.

Rise and fall of an anti-MUC1 specific antibody

BACKGROUND

So far, human antibodies with good affinity and specificity for MUC1, a transmembrane protein overexpressed on breast cancers and ovarian carcinomas, and thus a promising target for therapy, were very difficult to generate.

RESULTS

A human scFv antibody was isolated from an immune library derived from breast cancer patients immunised with MUC1. The anti-MUC1 scFv reacted with tumour cells in more than 80% of 228 tissue sections of mamma carcinoma samples, while showing very low reactivity with a large panel of non-tumour tissues. By mutagenesis and phage display, affinity of scFvs was increased up to 500fold to 5,7×10(-10) M. Half-life in serum was improved from below 1 day to more than 4 weeks and was correlated with the dimerisation tendency of the individual scFvs. The scFv bound to T47D and MCF-7 mammalian cancer cell lines were recloned into the scFv-Fc and IgG format resulting in decrease of affinity of one binder. The IgG variants with the highest affinity were tested in mouse xenograft models using MCF-7 and OVCAR tumour cells. However, the experiments showed no significant decrease in tumour growth or increase in the survival rates. To study the reasons for the failure of the xenograft experiments, ADCC was analysed in vitro using MCF-7 and OVCAR3 target cells, revealing a low ADCC, possibly due to internalisation, as detected for MCF-7 cells.

CONCLUSIONS

Antibody phage display starting with immune libraries and followed by affinity maturation is a powerful strategy to generate high affinity human antibodies to difficult targets, in this case shown by the creation of a highly specific antibody with subnanomolar affinity to a very small epitope consisting of four amino acids. Despite these "best in class" binding parameters, the therapeutic success of this antibody was prevented by the target biology.

MUC4 activates HER2 signalling and enhances the motility of human ovarian cancer cells

The mucin MUC4 is a high molecular weight transmembrane glycoprotein. It consists of a mucin-type subunit (MUC4alpha) and a transmembrane growth factor-like subunit (MUC4beta). The mucin MUC4 is overexpressed in many epithelial malignancies including ovarian cancer, suggesting a possible role in the pathogenesis of these cancers. In this study, we investigated the functional role of MUC4 in the human ovarian cancer cell line SKOV3. The mucin MUC4 was ectopically expressed by stable transfection, and its expression was examined by western blot and confocal microscopy analyses. The in vitro studies demonstrated an enhanced motility of MUC4-expressing SKOV3 cells compared with the vector-transfected cells. The mucin MUC4 expression was associated with apparent changes in actin organisation, leading to the formation of microspike, lammelopodia and filopodia-like cellular projections. An enhanced protein expression and activation of HER2, a receptor tyrosine kinase, was also seen, although no significant change was observed in HER-2 transcript levels in the MUC4-transfected SKOV3 cells. Reciprocal co-immunoprecipitation revealed an interaction of MUC4 with HER2. Further, the MUC4-overexpressing SKOV3 cells exhibited an increase in the phosphorylation of focal adhesion kinase (FAK), Akt and ERK, downstream effectors of HER2. Taken together, our findings demonstrate that MUC4 plays a role in ovarian cancer cell motility, in part, by altering actin arrangement and potentiating HER2 downstream signalling in these cells.

Expression of conserved mucin domains by epithelial tissues in various mammalian species

Mucins are related to infectious and non-infectious diseases in Veterinary and Human Medicine. MUC1 mucin is a transmembrane glycoprotein expressed on the apical surface of human epithelia while MUC5AC is the predominant secreted mucin expressed in human gastric epithelium and goblet cells of lung and eyes. MUC5AC C-terminus cysteine rich regions and the cytoplasmic tail of MUC1 domains are conserved among several mammalian species.

OBJECTIVE

to compare the expression of MUC1 and MUC5AC mucins in mammalian epithelia. CT33 anti-MUC1 cytoplasmic tail (MUC1CT) polyclonal antibody and 45M1 anti-MUC5AC monoclonal antibody were employed. By immunohistochemistry, MUC1CT was expressed in most tissues while MUC5AC was restricted to gastric surface epithelium and goblet cells from trachea and lung. By western blot, MUC1CT showed a band at approximately 35 kDa in most tissues; MUC5AC revealed bands at >180 kDa in stomach and lung secretions from rat, cat, pig and cow. When rat MUC5AC was immunoprecipitated, a band at about 180 kDa was obtained.

Prospective isolation and functional analysis of stem and differentiated cells from the mouse mammary gland

Prospective isolation and in vitro and in vivo analysis of primary mouse mammary epithelial cells has been used to separate cell subpopulations and identify stem, progenitor and differentiated cell compartments. Progress has been made from cell separation strategies based on a single marker of the luminal epithelial or myoepithelial compartments to use of markers that allow simultaneous isolation of non-epithelial, basal/myoepithelial and luminal epithelial cells. Transplant analysis has shown that mammary stem cells are found in the basal/myoepithelial compartment, whereas in vitro colony progenitors are found in the luminal compartment. A basal population enriched for stem cell activity can be purified from the myoepithelial cells and the most recent data shows that the luminal population can now be prospectively split into estrogen receptor positive and estrogen receptor negative cells. Future work aims to molecularly characterise these populations to identify new drug targets, which can be used to specifically kill breast cancer stem cells.

L-BLP25: a MUC1-targeted peptide vaccine therapy in prostate cancer

Renewed interest in cancer vaccine strategies has occurred with the identification of tumour-associated antigens and a further understanding of the immunoregulatory pathways involved in cancer development and progression. MUC1 is a mucinous glycoprotein that is overexpressed and aberrantly glycosylated in many human malignancies, including prostate cancer. BLP25 is a synthetic, liposomal cancer vaccine that targets the extracellular tandem repeat sequences of the MUC1 tumour-associated antigen. Preclinical L-BLP25 studies have shown the induction of a cell-mediated response and subsequent Phase I and II studies have established the vaccine dose, schedule and excellent safety profile. A Phase II study in advanced non-small cell lung cancer demonstrated a strong survival trend in favour of L-BLP25 in a subgroup of patients with locoregional stage IIIB disease. L-BLP25 also shows promise in prostate cancer. A pilot Phase II study in hormone naive patients with prostate-specific antigen failure after radical prostatectomy demonstrated a prolongation of prostate-specific antigen doubling time with little morbidity. These encouraging results suggest the potential of L-BLP25 in the management of cancer.

Identification of cellular isoform of oviduct-specific glycoprotein: role in oviduct tissue remodeling?

The oviduct is known to secrete mucins (MUC1 and MUC9) under the influence of ovarian steroids. The secreted form of MUC1 binds gametes in the oviduct, whereas the cellular form seen in breast cancers has been implicated in cell adhesion and morphogenesis. The secreted MUC9 or oviduct-specific glycoprotein (OGP), in addition to being a mucin, belongs to family 18 glycosylhydrolases and is known to bind gametes and embryos in the oviduct. Studies in our laboratory have identified non-muscle myosin IIA (involved in cell shape, polarity, and morphogenesis) as the protein partner to OGP in gametes. In view of the crucial role of the cortical cytoskeleton in the selective internalization of tight junctions (TJs) /adherent junctions (AJs) or apical junctional complex (AJC) in simple epithelial cells during tissue remodeling, the present study has been undertaken to evaluate the existence of a cellular form of OGP in oviductal tissue, which itself undergoes cyclic tissue remodeling. In silico analysis of the deduced amino-acid sequence of OGP has revealed the presence of several conserved motifs; these imply that OGP is a component of multi-protein complexes such as TJs. Corroborative immunoelectron-microscopic analysis in peri-ovulatory oviduct epithelia in the bonnet monkey has revealed the presence of OGP at the TJ. Co-localization studies of OGP and cadherin demonstrate that, whereas OGP is localized at the tonofilaments of the TJs, cadherin is localized at the intercellular space of the AJ. The possible role of OGP in oviductal tissue remodeling is discussed in light of the present findings and those reported in the literature.

Character of ocular surface mucins and their alteration in dry eye disease

At the ocular surface, three types of mucins are present. The large gel-forming mucin MUC5AC is expressed by conjunctival goblet cells. Some cells of the lacrimal gland acini express the small soluble mucin MUC7. The corneal and conjunctival epithelia express the membrane-associated mucins MUCs 1, 4, and 16. With the characterization of the mucin gene repertoire of the ocular surface epithelia, studies of the function of specific mucins, their gene regulation, and their alteration in ocular surface disease have begun. Current information suggests that all the mucins are hydrophilic and play a role in maintenance of water on the surface of the eye. The large secreted mucins represent the "janitorial service" that moves over the surface of the eye to wrap up and remove debris. The membrane-associated mucins form the glycocalyx, which provides a continuous barrier across the surface of the eye that prevents pathogen penetrance and has signaling capabilities that influence epithelial activity. Factors regulating mucin gene expression include retinoic acid, serum, and dexamethasone. Alteration in both secreted and membrane-associated mucins occur in drying ocular surface diseases. In Sjogren syndrome, MUC5AC expression is reduced, and in non-Sjogren dry eye, glycosylation of MUC16 appears to be altered. The pattern of expression of enzymes that glycosylate mucins is altered in ocular cicatricial pemphigoid. Therapies being evaluated for dry eye, including cyclosporine A, P2Y2 agonists, gefarnate, 15-(S)-HETE, and corticosteroids, may be efficacious due to their effect on mucin gene expression and secretion.

Biochemical interactions among intercellular adhesion molecules expressed by airway epithelial cells

Intercellular adhesion between adjacent airway epithelial cells plays a critical role in maintaining the barrier function of the respiratory mucosa. In the current study, we examined the expression and interaction of cell surface adhesion molecules (E-cadherin, ICAM-1, and MUC1) and their intracellular binding partners (alpha-catenin, beta-catenin, gamma-catenin, and ezrin) in 16HBE14o-, HBE1, 1HAEo-, BEAS-2B, A549, and NCI-H292 human airway epithelial cells. Expression of E-cadherin and MUC1, both in whole cell lysates and biotinylated surface proteins, was observed in 16HBE14o-, HBE1, A549, and NCI-H292 cells, while ICAM-1 was detected only in NCI-H292. In contrast, alpha-, beta-, and gamma-catenin and ezrin were expressed in all of the cells. E-cadherin formed coimmunoprecipitation complexes with beta- and gamma-catenin, whereas MUC1 only associated with beta-catenin. ICAM-1, but not MUC1, coimmunoprecipitated with ezrin in NCI-H292 cells. We conclude that airway epithelial cell-cell adhesion involves a complex network of protein-protein interactions mediated by a diverse array of membrane-bound and cytosolic protein partners.

Nanoscale intracellular organization and functional architecture mediating cellular behavior

Cells function based on a complex set of interactions that control pathways resulting in ultimate cell fates including proliferation, differentiation, and apoptosis. The inter-workings of this immensely dense network of intracellular molecules are influenced by more than random protein and nucleic acid distribution where their interactions culminate in distinct cellular function. By probing the design of these biological systems from an engineering perspective, researchers can gain great insight that will aid in building and utilizing systems that are on this size scale where traditional large-scale rules may fail to apply. The organized interaction and gradient distribution in intracellular space imply a structural architecture that modulates cellular processes by influencing biochemical interactions including transport and binding-reactions. One significant structure that plays a role in this modulation is the cell cytoskeleton. Here, we discuss the cytoskeleton as a central and integrating functional structure in influencing cell processes and we describe technology useful for probing this structure. We explain the nanometer scale science of cytoskeletal structure with respect to intracellular organization, mechanotransduction, cytoskeletal-associated proteins, and motor molecules, as well as nano- and microtechnologies that are applicable for experimental studies of the cytoskeleton. This biological architecture of the cytoskeleton influences molecular, cellular, and physiological processes through structured multimodular and hierarchical principles centered on these functional filaments. Through investigating these organic systems that have evolved over billions of years, understanding in biology, engineering, and nanometer-scaled science will be advanced.

Cell and molecular biology of human lacrimal gland and nasolacrimal duct mucins

The old concept that the lacrimal gland is only a serous gland has been superseded by the finding that lacrimal acinar cells are able to produce mucins--high-molecular-weight proteins--the major mass being carbohydrates with the common feature of tandem repeats of amino acids rich in serine, threonine, and proline in the central domain of the mucin core peptide. At the ocular surface, maintenance of the tear film, lubrication, and provision of a pathogen barrier on the epithelia, conjunctiva, and cornea have been shown to be facilitated by mucins that are present in membrane-anchored (lining epithelial cells) or secreted (goblet cells) form. Also in the lacrimal gland, both membrane-anchored (MUCs 1, 4, and 16) and secreted (MUCs 5B and 7) mucins have been identified. The lacrimal gland is the main contributor to the aqueous portion of the tear film. It is part of the lacrimal apparatus that comprises, together with the lacrimal gland, the paired lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct, which collects the tear fluid and conveys it into the nasal cavity. In this review, the latest information regarding mucin function in the human lacrimal gland and the human efferent tear ducts is summarized with regard to mucous epithelia integrity, rheological and antimicrobial properties of the tear film and tear outflow, age-related changes, and certain disease states such as the pathogenesis of dry eye, dacryostenosis, and dacryolith formation.

Distribution of mucins at the ocular surface

Mucins are vital for maintenance of a healthy, wet ocular surface. Once only thought to be secreted by goblet cells, mucins are now also known to be of the membrane-associated type. Stratified ocular surface epithelia express at their apical-tear fluid surface a repertoire of membrane-associated mucins including MUC1, MUC4, MUC16. These mucins are concentrated on the tips of the microplicae, forming a dense glycocalyx at the epithelial tear film interface. A major mucin of the secretory class is the goblet-cell-derived gel-forming mucin MUC5AC. A small soluble mucin, MUC7, is expressed by the lacrimal gland acini. Our hypothesis of the role/distribution of the secreted and membrane-associated mucins at the ocular surface is that the secreted mucins are soluble in the tear fluid, and are moved about and shunted to the nasolacrimal duct and by the eyelids during blinking. Thus, in the tears, the secreted mucins act as clean-up/debris removing multimeric networks that at the same time, through their hydrophilic nature, hold fluids in place and harbor defense molecules secreted by the lacrimal gland. Membrane-associated mucins, on the other hand, form a dense barrier in the glycocalyx at the epithelial tear film interface. This barrier prevents pathogen penetrance and is a lubricating surface that allows lid epithelia to glide over the corneal epithelia without adherence. The secreted mucins move easily over the glycocalyx mucins because both have anionic character that creates repulsive forces between them. Little is known regarding regulation of expression and glycosylation of mucins by ocular surface epithelia. Since ocular surface drying diseases alter both goblet cell and mucin production, and production and glycosylation of membrane-associated mucins, studies of mucin gene regulation and glycosylation may yield treatment modalities for these diseases.

Ultrastructural localisation of Muc-1 on the plasma membrane of uterine epithelial cells

The presence and distribution pattern of Muc-1 was determined immunohistochemically in rat uterine epithelial cells and localised ultrastructurally on the plasma membrane of uterine epithelial cells. Rat uterine tissue was examined on days 1, 3 and 6 of pregnancy and it is shown to be expressed in uterine luminal epithelial cells on day 1 of pregnancy with decreasing expression towards the time of implantation on day 6. It was demonstrated ultrastructurally that Muc-1 is expressed at the external surface of the plasma membrane of uterine epithelial cells thus confirming that it is well positioned to act as an anti-adhesive molecule during the nonreceptive stage of pregnancy. Ultrastructural localisation also revealed that Muc-1 was not present on the outer surface of the plasma membrane during the receptive phase.

Role of Mucins in the Function of the Corneal and Conjunctival Epithelia

The surface of the eye is covered by a tear film, which is held in place by a wet-surfaced, stratified, corneal and conjunctival epithelia. Both are vital for light refraction and protection of vision. Maintenance of tear film on the ocular surface, lubrication, and provision of a pathogen barrier on this wet surface is facilitated by a class of large, highly glycosylated, hydrophilic glycoproteins--the mucins. In the past 15 years, a number of mucin genes have been cloned, and based on protein sequence, categorized as either secreted or membrane associated. Both types of mucins are expressed by ocular surface epithelia. Goblet cells intercalated within the stratified epithelium of the conjunctiva secrete the large gel-forming mucin MUC5AC, and lacrimal gland epithelia secrete the small soluble mucin MUC7. Apical cells of the stratified epithelium of both corneal and conjunctival epithelium express at least three membrane-associated mucins (MUCs 1, 4, and 16), which extend from their apical surface to form the thick glycocalyx at the epithelium-tear film interface. The current hypothesis regarding mucin function and tear film structure is that the secreted mucins form a hydrophilic blanket that moves over the glycocalyx of the ocular surface to clear debris and pathogens. Mucins of the glycocalyx prevent cell-cell and cell-pathogen adherence. The expression and glycosylation of mucins are altered in drying, keratinizing ocular surface diseases.

MUC1 and MUC-X, epithelial mucins of breast and milk

While reasons for gross variations in milk composition of the various mammalian species are well established, we will be revealing minor, subtle, yet highly important differences for years to come. One of the distinctive differences of human milk concerns its mucins, MUC1 and MUC-X. These are high molecular mass glycoproteins that occur on the apical surface of the lactating cell and are transferred to the milk fat globule upon its secretion from the cell. Among mammals, it seems that the human has developed the largest, most extended versions of these mucin molecules. Evidence is accumulating that this greater size benefits the human in terms of protection against infections and injurious environmental agents.

MUC1, the renaissance molecule

MUC1 is a large, heavily glycosylated mucin expressed on the apical surfaces of most simple, secretory epithelia including the mammary gland, gastrointestinal, respiratory, urinary and reproductive tracts. Although MUC1 was thought to be an epithelial-specific protein, it is now known to be expressed on a variety of hematopoietic cells as well. Mucins function in protection and lubrication of epithelial surfaces. Transmembrane mucins, which contain cytoplasmic tail domains, appear to have additional functions through their abilities to interact with many proteins involved in signal transduction and cell adhesion. The goal of this review is to highlight recent discoveries that suggest that MUC1 may be a multifunctional protein, located on the surfaces of cells as a sensor of the environment, poised to signal to the interior when things go awry.

Mucin MUC1 is seen in cell surface protrusions together with ezrin in immunoelectron tomography and is concentrated at tips of filopodial protrusions in MCF-7 breast carcinoma cells

MUC1, a transmembrane member of the mucin family, is believed to have anti-adhesive properties because of its highly sialylated, extended, and rigid rod-like conformation. The ERM proteins (ezrin, radixin, and moesin) function as membrane-cytoskeletal linkers. MUC1 and ezrin are enriched in microvilli in MCF-7az breast carcinoma cells. Similar localization was also found in peripheral membrane areas and in filopodium-like protrusions. Whereas ezrin was consistently detected in the cell-cell contact region, MUC1 was less frequently found there. MUC1 was distinctly expressed in long filopodial protrusions and was highly concentrated at their tips, which also contained ezrin, whereas F-actin was found along the stalk. This localization of MUC1 suggests a role for MUC1 in transient cell structures of migrating cells and transient cell adhesion. No direct association has yet been found between MUC1 and ezrin. However, both MUC1 and ezrin had a similar overall distribution pattern in microvilli and filopodium-like protrusions in immunoelectron tomography. In addition, MUC1 and ezrin showed spatial association, because several 10-nm gold particles used to decorate ezrin were seen in the vicinity close to the clusters of 5-nm gold particles decorating MUC1. Therefore, MUC1 appears to be associated with ezrin, but the nature of this association requires further study.

Enhancement of metastatic properties of pancreatic cancer cells by MUC1 gene encoding an anti-adhesion molecule

MUC1 mucin expression has been shown to be associated clinicopathologically with metastasis and poor clinical outcome in a variety of tumors. To further investigate this finding experimentally, human pancreatic cancer S2-013 cells overexpressing MUC1 were used for spontaneous metastatic potential in nude mice. It was found that the number of lung metastases of MUC1 transfectants was significantly higher than that of control cells. To analyze the molecular mechanisms that underlie the increased metastatic activity, in vitro adhesion assays were performed. MUC1 mucin expression enhancedin vitro invasiveness and motility of S2-013 cells, and decreased the binding of S2-013 cells to type I collagen, Type IV collagen and laminin. Similar effects were not observed for cells expressing tandem repeat-deleted MUC1 cDNA. Adhesion properties were abolished by benzyl-alpha-GalNAc treatment, indicating that glycosylation of the extracellular domain of MUC1 was essential for these biological adhesive functions. Our data support the hypothesis that MUC1 expression contributes to the metastatic ability of pancreatic cancer cells.

A review and proposed nomenclature for major proteins of the milk-fat globule membrane

The characteristics and possible functions of the most abundant proteins associated with the bovine milk-fat globule membrane are reviewed. Under the auspices of the Milk Protein Nomenclature Committee of the ADSA, a revised nomenclature for the major membrane proteins is proposed and discussed in relation to earlier schemes. We recommend that proteins be assigned specific names as they are identified by molecular cloning and sequencing techniques. The practice of identifying proteins according to their Mr, electrophoretic mobility, or staining characteristics should be discontinued, except for uncharacterized proteins. The properties and amino acid sequences of the following proteins are discussed in detail: MUC1, xanthine dehydrogenase/oxidase, CD36, butyrophilin, adipophilin, periodic acid Schiff 6/7 (PAS 6/7), and fatty acid binding protein. In addition, a compilation of less abundant proteins associated with the bovine milk-fat globule membrane is presented.

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)

Expression of MUC1 and MUC2 mucin gene products in Barrett's metaplasia, dysplasia and adenocarcinoma: an immunopathological study with clinical correlation

AIMS

Changes in the histochemical characteristics of the surface epithelial mucins is the hallmark of Barrett's metaplasia. The study investigated the pattern of expression of MUC1 and MUC2 mucin gene products in Barrett's metaplasia, dysplasia and adenocarcinoma as possible indicators of increased malignant potential.

METHODS AND RESULTS

Tissue sections from 51 patients with Barrett's intestinal metaplasia, nine with dysplasia (three indefinite) and 28 resected adenocarcinomas were stained with monoclonal antibodies to MUC1 and MUC2. The majority of the patients were men (70/88, 80%) who were treated over a period of 3 years. None of the patients with dysplasia or carcinoma were under surveillance at the time of presentation. All 51 biopsies with Barrett's metaplasia expressed MUC2 and MUC1 was consistently absent. Neither MUC1 or MUC2 were expressed in the dysplastic epithelium whether in its pure form (6/6) or when associated with carcinoma (26/28) (P < 0.005). Three biopsies which were initially classified as high-grade dysplasia expressed MUC1 and these turned out to be carcinomas on further investigations. MUC1 was also expressed in 12/28 (43%) of the adenocarcinomas and majority of these were poorly differentiated stage 3 tumours (P < 0.05). MUC2 was only positive in mucin-secreting carcinomas (4/28; 14%) irrespective of the tumour stage.

CONCLUSION

Despite the large number of patients with Barrett's metaplasia and carcinoma, very few patients presented with dysplasia, implying that Barrett's oesophagus is a silent disease in the community presenting late as carcinoma. The study has demonstrated aberrant expression of MUC2 (an intestinal mucin) in Barrett's metaplasia and this expression is lost when the cells become dysplastic. The lack of MUC1 in dysplastic epithelium and its expression in carcinoma could be utilized as a marker which could differentiate dysplasia from carcinoma in mucosal biopsies. Furthermore, expression of MUC1 in advanced stage oesophageal cancers (as in breast cancer) suggests an unfavourable prognosis.

Aberrant expression of MUC1 mucin in ductal hyperplasia and ductal carcinoma In situ of the breast

MUC1 mucin is a high molecular weight transmembrane glycoprotein expressed on the apical cell surface of normal glandular epithelia. In many human adenocarcinomas, this protein is up-regulated and/or underglycosylated, and its expression changes from apical to the entire cell membrane. It is thought that entire cell membrane expression of MUC1 reduces cell-cell and cell-extracellular matrix interactions and therefore may facilitate invasive growth and development of metastases. In this study, we determined immunohistochemically the expression of normal and underglycosylated MUC1 in normal breast tissue (n = 8) and in a spectrum of breast lesions, including usual ductal hyperplasia (n = 23), atypical ductal hyperplasia (n = 7), and ductal carcinoma in situ (DCIS) (n = 22). We used 4 monoclonal antibodies; 115D8 is directed to a glycopeptide, the other 3 to the peptide core of the molecule, of which 139H2 is not affected by the degree of glycosylation of MUC1, whereas SM3 and VU-4-H5 stain only underglycosylated forms. All cases showed apical positivity for 115D8 and 139H2. Entire cell membrane expression of fully (normal) glycosylated MUC1 was mainly found in DCIS lesions. Apical staining of SM3 was found in 38% of normal cases and 60% of the ductal lesions with no difference between the different subgroups. Apical staining of VU-4-H5 was found more often in DCIS (27%) than in normal tissue or ductal hyperplasia (3%). Membrane expression of underglycosylated MUC1 was found only in poorly differentiated DCIS. In conclusion, aberrant expression of MUC1, i.e., on the entire cell membrane and/or underglycosylated forms, can be found in ductal hyperplasia with atypia and especially in DCIS of the breast. This finding implies that these lesions with aberrant expression are at higher risk for developing subsequent invasive breast carcinoma.

Immune regulation in multiple myeloma: the host-tumour conflict

Multiple myeloma (MM) remains essentially incurable by conventional anti-tumour therapy. This has led to increased interest in the possibility that forms of immune therapy might be effective. The successful use of donor lymphocyte infusions (DLI) in a few cases of MM relapse following allogeneic bone marrow transplantation have added weight to this view. MM is characterized by several defects in the host's immune system. The influence of the malignant clone on the function of the immune effector cells results from both passive and active suppression. Despite an array of functional adhesion molecules and HLA class I and II molecules on their surface and the secretion of a tumour-specific peptide, they fail to express adequate levels of co-stimulatory molecules thus inducing anergy in potentially tumour-specific T cells. In addition to this passive evasion of immune regulation, MM tumour cells are capable of producing a number of immunologically active agents which can induce immunosuppression such as transforming growth factor-beta, Fas ligand (FasL), vascular endothelial growth factor and Muc-1. It is postulated that these agents may be produced by the tumour cell to influence the microenvironment to support growth and differentiation of the clone but may have the additional benefit of altering the function of the host immune effector cells and thus preventing tumour rejection. This duality of function is important if clinicians are to design immunotherapy strategies which will achieve the true potential and result in improved survival in MM.

Prognostic Relevance of Tn Expression in Breast Cancer

BACKGROUND: Abnormal glycosylation patterns have been recognized as a featureof carcinomaassociated mucins. The expression of the Tn antigen in breast cancer tissue was investigated to assess its prognostic relevance. METHODS: Formalin-fixed, paraffin-embedded materials from 219 patients with breast cancer were used. Immunohistochemical staining of the Tn antigen was retrospectively investigated and a lesion staining 10% or more was considered positive RESULTS: Tn antigen expression was present in 99 (45%) of 219 lesions. There were no correlations between Tn antigen expression and mean patient age, nodal status, estrogen receptor status, or menopausal status, but there was a slightly significant association between Tn and tumor size. Patients negative for the Tn antigen had a significantly better survival rate than those who were positive. Multivariate analysis also indicated that Tn expression correlated significantly with overall survival in addition to nodal status and tumor size. CONCLUSION: Tn expression was a significant prognostic factor in breast cancer, but the significance was lost on multivariate analysis. The biological implication of Tn expression in breast cancer needs further investigation.

The biological role of mucins in cellular interactions and immune regulation: prospects for cancer immunotherapy

Among the human mucins, MUC1 is unique in its cell-surface transmembrane expression and its apparent signal-transduction functions. The high expression of MUC1 on many human cancers makes it an attractive target for immunotherapy. Immunization of human cancer patients with MUC1 peptides has resulted in the generation of both anti-MUC1 antibody and cytotoxic T lymphocyte responses. Recently, a novel immunoregulatory role for MUC1 has been suggested by experiments demonstrating that soluble MUC1 induces T-cell unresponsiveness, and that T cells appear to express and secrete MUC1 following their activation. MUC1 is an apparent paradox, having both adhesive and antiadhesive functions, and immunostimulatory and immunosuppressive activities.

Increased invasiveness of MUC1 and cDNA-transfected human gastric cancer MKN74 cells

MUC1 mucin is an anti-adhesion molecule expressed in a wide variety of tumors. To examine whether MUC1 mucin is involved in tumor invasion, we have prepared MUC1 transfectants using the human gastric cancer cell line MKN74 and performed an in vivo tumor assay by transplanting these into nude mice. Tumor weight at 71 days after s.c. injection of transfectants was measured, showing that the in vivo growth of MUC1 transfectants was increased compared to that of mock transfectants. Furthermore, MUC1-transfectant tumors invaded into the muscle layer, whereas mock-transfectant tumors did not. In vitro invasion, adhesion to extracellular matrix components and phagokinetic track motility were then evaluated to analyze the mechanisms for the in vivo invasiveness of the transfectants. MUC1 transfectants exhibited an increased in vitro invasiveness, decreased binding to laminin, fibronectin, type I collogen and type IV collagen and increased motility. These effects of MUC1 mucin over-expression in MKN74 cells were abolished by the treatment of transfectants with an inhibitor of O-glycan biosynthesis, benzyl-alpha-GalNAc. Our data suggest that MUC1 mucin could be related to the increased invasive ability of MKN74 cells, whereas O-glycan might play an essential role.

Beta1B integrin interferes with matrix assembly but not with confluent monolayer polarity, and alters some morphogenetic properties of FRT epithelial cells

Beta1B is a beta1 integrin splice variant that differs from the ubiquitous beta1A in the terminal portion of the cytosolic tail. The expression of this variant in CHO cells results in reduced fibroblast adhesion and motility (Balzac, E et al., J. Cell Biol. 127, 557-565 (1994)). We have evaluated the phenotypic changes induced by the expression of beta1B in the FRT epithelial cell line. Stable transfectants of FRT cells expressing beta1B or beta1A human integrins were obtained. The transfected integrins associated with the endogenous alpha subunits and were delivered to the plasma membrane. Beta1B expressing cells attached less efficiently and spread less on fibronectin, laminin or type IV collagen coated dishes. A great reduction of fibronectin fibrils associated to the basal membrane of non-confluent beta1B transfected cells was observed. This was paralleled by the disappearance of microfilament bundles and loss of basally located focal adhesions. On the contrary, upon beta1A transfection, a higher amount of fibronectin fibrils, together with microfilament bundles and focal adhesions, was observed. Expression of beta1B did not significantly modify the ability to manifest the polarized phenotype when cells were grown to confluence on filters in two-chamber-systems. Beta1B-transfected cells showed reduced motile properties when embedded as aggregates in type I collagen gels. Moreover, formation of polarized cysts in suspension culture was impaired. The results show that beta1B, by interfering with focal adhesion organization, microfilament and fibronectin assembly, cell spreading and migration, affects some morphogenetic properties of FRT epithelial cells.

Cancer-associated MUC1 mucin inhibits human T-cell proliferation, which is reversible by IL-2

A number of adenocarcinomas abundantly express and secrete underglycosylated MUC1 mucin. Underglycosylation exposes tandem repeat peptide sequences on cancer-associated MUC1 mucin that are normally cryptic. High levels of MUC1 mucin are correlated with a poor prognosis and immunosuppression in adenocarcinoma patients. In this report we show that cancer-associated MUC1 mucin, affinity-purified from ascites fluids of cancer patients, and synthetic tandem repeats of MUC1 mucin core peptide can suppress human T-cell proliferative responses. This MUC1 mucin-induced suppression of T-cell responses can be reversed by the addition of exogenous IL-2 or anti-CD28 monoclonal antibody. These results are consistent with other studies showing that lymphocytes present in the vicinity of tumor cells are anergic and can be reactivated with exogenous interleukin-2. Overcoming MUC1 mucin-induced immunosuppression with IL-2 combined with active specific immunotherapy might be an effective immunotherapeutic strategy against human adenocarcinomas.

The prognostic significance of sialyl-Tn antigen in women treated with breast carcinoma treated with adjuvant chemotherapy

BACKGROUND

Sialyl-Tn (STn) represents an aberrantly glycosylated mucin epitope that is expressed in breast carcinoma and other adenocarcinomas and is an important factor in the development of novel immunotherapeutic approaches. The primary aim of the current study was to investigate the influence of STn expression on the prognoses of patients with breast carcinoma.

METHODS

A cohort of 207 women diagnosed with invasive breast carcinoma who were treated with anthracycline-containing adjuvant chemotherapy and were enrolled in a randomized clinical trial were studied. Expression of STn was determined by an immunohistochemical procedure in which the B72.3 monoclonal antibody was used. Kaplan-Meier and Cox proportional regression survival analyses were used to compare low STn and high STn patients.

RESULTS

Forty-eight (23%) of the 207 specimens demonstrated high STn staining (>25% cells were immunoreactive). During a median follow-up of 5 years, high STn patients had worse disease free survival than low STn patients (55% vs. 74%, respectively; P = 0.03). High STn expression was significantly associated with age (P = 0.04) but not with other conventional prognostic markers. In multivariate analysis using the Cox regression model, high STn emerged as an independent prognostic indicator for disease free survival (hazard ratio [HR], 2.02; 95% confidence interval [CI], 1.09-3.73) and for overall survival (HR, 2.16; 95% CI, 0.95-4.92).

CONCLUSIONS

The results of this study suggest that STn may be a valuable marker for identifying women at high risk of developing recurrent breast carcinoma who may be candidates for trials investigating new therapies in combination with standard adjuvant therapy.

The apical submembrane cytoskeleton participates in the organization of the apical pole in epithelial cells

In a previous publication (Rodriguez, M.L., M. Brignoni, and P.J.I. Salas. 1994. J. Cell Sci. 107: 3145-3151), we described the existence of a terminal web-like structure in nonbrush border cells, which comprises a specifically apical cytokeratin, presumably cytokeratin 19. In the present study we confirmed the apical distribution of cytokeratin 19 and expanded that observation to other epithelial cells in tissue culture and in vivo. In tissue culture, subconfluent cell stocks under continuous treatment with two different 21-mer phosphorothioate oligodeoxy nucleotides that targeted cytokeratin 19 mRNA enabled us to obtain confluent monolayers with a partial (40-70%) and transitory reduction in this protein. The expression of other cytoskeletal proteins was undisturbed. This downregulation of cytokeratin 19 resulted in (a) decrease in the number of microvilli; (b) disorganization of the apical (but not lateral or basal) filamentous actin and abnormal apical microtubules; and (c) depletion or redistribution of apical membrane proteins as determined by differential apical-basolateral biotinylation. In fact, a subset of detergent-insoluble proteins was not expressed on the cell surface in cells with lower levels of cytokeratin 19. Apical proteins purified in the detergent phase of Triton X-114 (typically integral membrane proteins) and those differentially extracted in Triton X-100 at 37 degrees C or in n-octyl-beta-D-glycoside at 4 degrees C (representative of GPI-anchored proteins), appeared partially redistributed to the basolateral domain. A transmembrane apical protein, sucrase isomaltase, was found mispolarized in a subpopulation of the cells treated with antisense oligonucleotides, while the basolateral polarity of Na+-K+ATPase was not affected. Both sucrase isomaltase and alkaline phosphatase (a GPI-anchored protein) appeared partially depolarized in A19 treated CACO-2 monolayers as determined by differential biotinylation, affinity purification, and immunoblot. These results suggest that an apical submembrane cytoskeleton of intermediate filaments is expressed in a number of epithelia, including those without a brush border, although it may not be universal. In addition, these data indicate that this structure is involved in the organization of the apical region of the cytoplasm and the apical membrane.

Differential glycosylation of MUC1 in tumors and transfected epithelial and lymphoblastoid cell lines

The membrane-bound mucin-like protein MUC1 with a specified number of tandem repeats has been expressed by transfection of the cDNAs in both the epithelial cell lines MDCK and LLC-PK1, and human lymphoblastoid cell lines T2 and C1R. The structure and glycosylation states of the MUC1 in these four lines were compared with that of the endogenous MUC1 found in the human pancreatic (HPAF) and breast (BT-20) tumor cell lines using flow cytometry and Western blot analysis with anti-MUC1 antibodies, which are either sensitive or insensitive to the glycosylation state of the tandem repeat, and pretreatment of cells with phenyl-alpha-galactosaminide, an inhibitor of mucin sialylation. A similar analysis of MUC1 expression in transfected normal and O-glycosylation defective CHO cells reveals that the addition of galactose to the core oligosaccharide structure is apparently responsible for the anomalous difference in M(r), between the mature and propeptide forms of the MUC1. Both the tumor cells and the transfected lymphoblastoid cells consistently express significant steady state levels of both the heavily glycosylated mature forms and the poorly glycosylated propeptide forms of the MUC1, whereas MUC1 is found predominantly as the mature extensively glycosylated species in the transfected epithelial cells. Immunofluoresence microscopy of cross sections of the polarized epithelial cells grown on culture filter inserts reveals that the MUC1 is clearly present at the apical surface of the cells, consistent with its expression in normal tissues. Thus, the successful expression of the MUC1 by transfection of either lymphoblastoid cells or epithelial cells yields model systems both for studying the natural structure/function relationships of the protein domains within the MUC1 molecule and for further elucidating the previously reported MHC-independent T-cell recognition of the MUC1.

Integrin alpha V beta 3 expression by bone-residing breast cancer metastases

Breast cancer metastasis to bone is a multistep process requiring attachment of tumor cells to the bone and bone marrow environment. The precise adhesion molecules involved in skeletal homing of breast cancer to bone are unknown but likely include integrins. We investigated the expression of vitronectin receptor (alpha V beta 3) by breast cancer cells residing in bone because this heterodimer mediates osteoclast-bone recognition. We used immunohistochemistry and in situ hybridization in a systematic study of 22 bone biopsies containing breast cancer metastases and available samples of corresponding primary tumors and normal breast and compared alpha V beta 3, alpha 2 beta 1, and alpha B beta 5 integrin expression. The results showed that alpha V beta 3 was strongly expressed by normal breast epithelium and was decreased in some and strongly expressed in other primary invasive breast carcinomas. In contrast, this integrin heterodimer was abundant in all breast cancer cells metastatic to bone. In situ hybridization revealed high levels of steady-state mRNA corresponding to sites of protein expression; alpha 2 beta 1 was weakly expressed in both primary and metastatic tumors, and alpha V beta 5 was not detected. Our results showed an overexpression of alpha V beta 3 by bone-residing breast cancer cells and suggest either subclonal selection of alpha V beta 3-expressing tumor cell populations or upregulation of alpha V beta 3 in the bone microenvironment.

The epithelial mucin MUC1 contains at least two discrete signals specifying membrane localization in cells

The MUC1 gene product (PEM, polymorphic epithelial mucin) is a cell-associated glycoprotein expressed on the apical surface of most simple secretory epithelia. The transmembrane and cytoplasmic domains of MUC1 have been shown to be highly conserved between mammalian species, and it has been shown that this molecule interacts with the actin cytoskeleton. Apical targeting signals in polarized cells have yet to be defined. The mechanism by which MUC1 is targeted and maintained on the apical surface is not known; correct localization, however, would be predicted to be crucial for function. In order to determine which domains of MUC1 were important for this localization, mutational analysis of the protein was undertaken. Using cytoplasmic tail deletion mutants, fusion proteins of MUC1 and CD2, and site-directed mutagenesis, it could be shown that MUC1 appeared to contain at least two motifs involved in apical localization. The first was located in the extracellular domain and was sufficient to confer apical localization on the fusion protein. The second was the Cys-GlnCys (CQC) motif at the junction of the cytoplasmic and transmembrane domains. This sequence was necessary for surface expression. These results suggest that MUC1 contains two discrete motifs important in its apical localization.

The epithelial mucin, MUC1, of milk, mammary gland and other tissues

MUC1 is a mucin-type glycoprotein that is integrally disposed in the apical plasma membrane of the lactating epithelial cell and protrudes from the cell surface into the alveolar lumen where milk is stored. Envelopment of milk fat globules by this membrane accomplishes their secretion and conveys MUC1 into milk. The human form of this mucin has been detected in many other organs, tissues and body fluids. It projects from the cell surface as long filaments. In the human and a number of other species, MUC1 is polymorphic due to variable numbers of a tandemly repeated segment 20 amino acids in length. The individual codominantly expresses two alleles for the mucin so that differences in its size among individuals and between the two forms of an individual are observed. The tandem repeats are rich in serines and threonines which serve as O-glycosylation sites. Carbohydrate content of MUC1, as isolated from milk of human, bovine and guinea pig, is approximately 50%. The oligosaccharides carry substantial sialic acid at their termini and this accounts for two putative functions of this mucin, i.e., to keep ducts and lumens open by creating a strong negative charge on the surface of epithelial cells which would repel opposite sides of a vessel, and to bind certain pathogenic microorganisms. MUC1 is protease resistant (trypsin, chymotrypsin and pepsin) and large fragments of it can be found in the feces of some but not all breast-fed infants. MUC1 has a highly varied structure because of its polymorphism, qualitative and quantitative variations in its glycosylation between tissues, individuals and species, and differences due to divergence in the nucleotide sequences among species. Sequencing of the MUC1 gene for various species is showing promise of revealing unique evolutionary relationships and has already indicated conserved aspects of the molecule that may be functionally important. Among these are positions of serine, threonine and proline in the tandem repeats and a high degree of homology in the transmembrane and cytoplasmic segments of the molecule.

Delayed mammary tumor progression in Muc-1 null mice

The mucin gene, Muc-1, encodes a high molecular weight integral membrane glycoprotein that is present on the apical surface of most simple secretory epithelial cells. Muc-1 is highly expressed and aberrantly glycosylated by most carcinomas and metastatic lesions. Numerous functions have been proposed for this molecule, including protection of the epithelial cell surface, an involvement in epithelial organogenesis, and a role in tumor progression. Mice deficient in Muc-1 were generated using homologous recombination in embryonic stem cells. These mice appeared to develop normally and were healthy and fertile. However, the growth rate of primary breast tumors induced by polyoma middle T antigen was found to be significantly slower in Muc-1 deficient mice. This suggests that Muc-1 plays an important role in the progression of mammary carcinoma.

Heterogeneity in production, secretion and glycosylation of MUC1 epithelial mucin by primary cultures of ovarian carcinoma

The MUC1 mucin produced by many adenocarcinomas has functions that may be of biological significance and is of importance clinically as a serum tumour marker and as a candidate target for immunotherapy. Previous studies of MUC1 production by ovarian cancers have been limited to immunohistochemical studies of tumour specimens and in vitro studies using cell lines. In this study the biosynthesis, secretion and glycosylation of MUC1 were studied in primary cultures of tumour cells obtained from 35 patients with stage 3 ovarian cancer. Although 34 of the 35 tumours produced MUC1 in vitro, the concentrations of intracellular and secreted MUC1, as measured by an ELISA using core protein-reactive antibodies, varied over a wide range. In addition, the amount of secreted MUC1 as a proportion of the intracellular concentration varied between tumours. Pulse/chase amino acid labelling studies of MUC1 biosynthesis also demonstrated variation in secretion rates. Multivariate regression analysis showed that of the variables tumour size, histological type, grade, ploidy status and intracellular and secreted MUC1 concentrations in vitro, only mucin secretion rate was significantly associated with serum mucin concentrations (p < 0.001). Culture of tumour cells for 4 days in the presence or absence of a competitive inhibitor of O-glycosylation, BAG, showed that the degree of glycosylation of MUC1 varied between tumours and that under-glycosylation was not correlated with production or secretion rates. Our study has shown heterogeneity in the production, secretion and glycosylation of MUC1 and a strong correlation between the secretion rate in vitro and the concentration in the serum of patients.

Associations of the epithelial mucin, PAS-1, with yield, health, and reproductive traits in Holstein dairy cows

Five polymorphic forms of the epithelial mucin, PAS-1, were identified in milk by SDS-PAGE. The sizes of PAS-1 ranged from 194.5 to 163 kDa. Mature equivalent milk, fat, and protein yields and protein and fat percentages from 139 cows in The Pennsylvania State University herd were analyzed with two models. Both models contained a year and season combination of calving and parent average. In Model [1], yields were regressed on the mean size of PAS-1 either linearly or linearly and quadratically. Model [2] included PAS-2 phenotype as a discrete variable. Lactation mean of somatic cell scores (119 cows), number of times bred (136 cows), and days open (136 cows) were analyzed with the same two models excluding parent average (data not available). Mean size of PAS-1 was not linearly related to the traits evaluated. The effects of PAS-1 phenotypes as a discrete variable were significant for mature equivalent fat and protein yields, fat percentage, number of times bred, number of times bred restricted to 3, and days open restricted to 150 d. Overall, there was little indication of an important linear or quadratic relationship between PAS-1 size and traits measured.

Polymorphic forms of the epithelial mucin, PAS-I (MUC1), in milk of Holstein cows (Bos taurus)

The polymorphic epithelial mucin, PAS-I (also known as MUC1), in individual milk samples from 119 Holstein cows was resolved into bands on SDS-gels. Mobility indices established for these bands provided evidence of four and possibly five polymorphic forms. Sialic acid, a major component of the oligosaccharide portion of PAS-I, was removed from the mucin by treatment of milk samples with neurominidase. This reduced the mobility of the mucin bands but did not alter their mobility relationships within a sample or among samples. Consideration of evidence from this and other studies indicates that the four or five polymorphic forms correspond to alleles, which are inherited, one each from sire and dam, and co-dominantly expressed. It appears that the Holstein population may carry several more alleles for PAS-I than do Ayrshire, Jersey or Brown Swiss cattle. In addition to these breed differences, some remarkable molecular differences have been noted between MUC1 (PAS-I) of human and mouse suggesting that research regarding molecular evolution of this mucin could provide another approach to understanding relationships among species.

The alpha 2 beta 1 integrin regulates collagen-mediated MDCK epithelial membrane remodeling and tubule formation

Previous studies have demonstrated that incubation of MDCK cell epithelial cysts in collagen gel induced a reversal in cell surface polarity that was regulated by beta 1 integrins. Further experiments were done to identify the specific collagen binding integrin involved by applying collagen gel overlays to the apical membrane of subconfluent MDCK monolayers. Cell surface levels of the apical membrane glycoprotein gp135 were monitored by ELISA to quantitate the extent of collagen-mediated membrane remodeling. After an 8 hour incubation with collagen, there was a 35% reduction in gp135 while the cell surface levels of the alpha 2, alpha 3 and beta 1 integrin subunits were not affected. Immunofluorescence microscopy confirmed the loss of gp135 from selected regions of the apical cell surface while the alpha 2 and beta 1 integrin subunits were distributed in small clusters over the entire apical membrane in both control and collagen-treated monolayers. Collagen-mediated loss of gp135 was inhibited by monoclonal antibodies which recognize either the alpha 2 or beta 1 integrin subunits but not by a monoclonal antibody against the alpha 6 beta 1 integrin. These results demonstrated that remodeling of the apical membrane had occurred, allowing the selective retention of beta 1 integrins but not gp135. They were supported by the observation that collagen-mediated loss of apical membrane microvilli was inhibited by the monoclonal antibody against the alpha 2 integrin subunit. Incubation of confluent monolayers with collagen gel induced the formation of polarized epithelial tubules within 16 hours. Epithelial tubule biogenesis was completely inhibited by monoclonal antibodies against either the alpha 2 or beta 1 integrin subunits, providing strong evidence that the alpha 2 beta 1 integrin is essential for collagen-mediated epithelial membrane remodeling and tubule formation.

Episialin (MUC1) overexpression inhibits integrin-mediated cell adhesion to extracellular matrix components

Episialin (MUC1) is a transmembrane molecule with a large mucin-like extracellular domain protruding high above the cell surface. The molecule is located at the apical side of most glandular epithelial cells, whereas in carcinoma cells it is often present at the entire surface and it is frequently expressed in abnormally large quantities. We have previously shown that overexpression of episialin reduces cell-cell interactions. Here we show that the integrin-mediated adhesion to extracellular matrix of transfectants of a melanoma cell line (A375), a transformed epithelial cell line (MDCK-ras-e) and a human breast epithelial cell line (HBL-100) is reduced by high levels of episialin. This reduction can be reversed by inducing high avidity of the beta 1 integrins by mAb TS2/16 (at least for beta 1-mediated adhesion). The adhesion can also be restored by redistribution of episialin on the cell surface by monoclonal antibodies into patches or caps. Similarly, capping of episialin on ZR-75-1 breast carcinoma cells, growing in suspension, caused adherence and spreading of these cells. We propose that there is a delicate balance between adhesion and anti-adhesion forces in episialin expressing cells, which can be shifted towards adhesion by strengthening the integrin-mediated adhesion, or towards anti-adhesion by increasing the level of expression of episialin.

The relationship of cytoplasmic intermediate filaments and membrane antigens with hormone receptors, nuclear staining density, and mode of stromal invasion in human breast cancer

Serial sections on biopsies of 26 women with invasive breast carcinoma were stained for low molecular weight keratins (LKER), high molecular weight keratins (HKER), epithelial membrane antigen (EMA), vimentin (VIM), carcinoembryonic antigen (mCEA and pCEA), and nuclear estrogen (mER) and progesterone receptors (mPGR), using monoclonal and polyclonal sera. Specified areas were identified on serially sectioned slides and staining reactions were compared among areas as well as among patients. The study concludes: (1) LKER staining was positively related to (a) the percentage of tumor cells with densely stained nuclei, (b) a trabecular mode of stromal invasion, and (c) HKER and EMA staining, and inversely related to (d) VIM staining and gross tumor size. (2) HKER was also inversely related to gross tumor size. (3) VIM staining was positively related to pCEA staining. (4) VIM staining was inversely related to staining ER and PGR. (5) LKER, HKER, and EMA staining was stronger in areas of trabecular rather than confluent areas of stromal invasion within the same biopsy. (6) Staining for ER and PGR was not related to mode of stromal invasion, but showed a strong inverse relationship with mitotic index. Positive staining for LKER may be an indicator of better differentiation together with densely staining nuclei and trabecular mode of stromal invasion, whilst VIM and pCEA appear to be related to features indicative of lack of differentiation. Hormone receptor positivity seems to be strongly related to mitotic activity rather than differentiation.

Differential apomucin expression in normal and neoplastic human gastrointestinal tissues

BACKGROUND/AIMS

The cloning of genes encoding human mucins is the basis for the study of their normal tissue distribution and the alterations associated with cancer. The aim of this study was to determine the normal and tumor tissue expression of MUC1, MUC2, MUC5B, and MUC5C.

METHODS

The reactivity of apomucin-specific antibodies with fresh normal and tumor tissues was analyzed using immunohistochemical techniques.

RESULTS

Anti-MUC1 antibodies reacted with most glandular epithelia. Anti-MUC2 antibody was mainly reactive with intestinal goblet cells and cervical mucous cells. Anti-MUC5B was reactive with a wide range of epithelial tissues whereas anti-MUC5C was reactive with stomach, trachea, and endocervix. Double-labeling experiments showed coexpression of MUC1/MUC2 and MUC2/MUC5C in colonic tissue. Multiple apomucins were detected in colon cancers, but no relationship to histochemical mucus stains was observed.

CONCLUSIONS

It is concluded that (1) each apomucin shows a distinct tissue expression pattern; (2) multiple apomucins are present in a single tissue and at the single cell level; and (3) altered apomucin expression takes place in pathological colonic tissue.

Regulation of epithelial cell surface polarity reversal by beta 1 integrins

The role of extracellular matrix in the regulation of epithelial cell surface polarity development was studied using MDCK cells. Previous work has demonstrated that MDCK cells cultured in suspension form epithelial cysts having polarized cell surface distributions of several membrane proteins. When MDCK suspension cysts are incubated within collagen gel, a dynamic epithelial membrane remodeling occurs that is accompanied by the reversal of cell surface polarity (Wang et al., 1990b, J. Cell Sci. 95, 153–165), suggesting that extracellular matrix is important in the modulation of epithelial polarity development. To determine if members of the integrin receptor family were involved, MDCK cyst binding studies were done utilizing antifunctional monoclonal antibodies (AIIB2 and AJ2) against the beta 1 integrin subunit. These antibodies inhibited cyst binding to type I collagen, type IV collagen and laminin, providing evidence that functional beta 1 integrin heterodimers were present on the cyst outer membrane. Integrin localization on suspension cysts demonstrated that the alpha 2, alpha 3 and alpha 6 integrin subunits had a non-polarized cell surface distribution and were localized to both the apical and basolateral membranes. Interestingly, immunofluorescence microscopy determined that the beta 1 subunit had a polarized, basolateral membrane distribution although cyst binding studies using inhibitory monoclonal antibodies suggested that functional beta 1 subunits were present on the cyst outer membrane. After incubation of suspension cysts in collagen gel for 8 hours, the beta 1 integrin subunit was detected on the outer membrane, suggesting that the formation of additional integrin alpha/beta heterodimers could be involved in epithelial remodeling. To establish the role of beta 1 integrins in polarity reversal, experiments were done on cysts incubated in collagen gel. After 6 hours in collagen gel, considerable membrane remodeling had occurred as determined by a reduction in outer membrane microvilli. However, the presence of monoclonal antibody AIIB2 inhibited membrane remodeling by preventing both microvillar loss and the endocytosis of the apical membrane glycoprotein gp135. These results provide strong evidence that members of the beta 1 integrin family are involved in the regulation of epithelial polarity reversal, and demonstrate that MDCK cysts constitute an excellent model system for studying the role of cell-extracellular matrix interactions in the regulation of epithelial plasticity and cell surface polarity development.

Integrin expression and localization in normal MDCK cells and transformed MDCK cells lacking apical polarity

Epithelial cells polarize in response to contacts with the extracellular matrix and with neighboring cells. Interactions of cells with the extracellular matrix are mediated mainly by the integrin family of receptors. To begin to understand the role of integrins in polarization, we have investigated the expression and localization of three integrin families in the polarized Madin-Darby canine kidney (MDCK) epithelial cell line and in transformed MDCK cells lacking apical polarity. We find that MDCK cells express several beta 1 integrins, including alpha 2 beta 1, alpha 3 beta 1, and an unidentified integrin designated alpha × beta 1. The beta 1 integrins are the major receptors for collagens I and IV and laminin in MDCK cells, since a blocking anti-beta 1 antibody almost totally abolishes adhesion to these proteins. They also express a vitronectin receptor tentatively identified as alpha v beta 3, and the epithelial-specific integrin alpha 6 beta 4. The latter is not a laminin receptor in MDCK cells because a function blocking anti-alpha 6 antibody has no effect on cell adhesion to laminin. All three integrin families are expressed exclusively on both the basal and lateral surfaces, as determined by immunofluorescence microscopy and surface biotinylation. Transformed MDCK cells express beta 1 integrins as well as alpha v beta 3 and alpha 6 beta 4, but show alterations in the beta 1 family. Expression of alpha × is lacking, and the relative amount of the beta 1 subunit is diminished, resulting in the accumulation of Endo-H-sensitive alpha 3. In addition, surface biotinylation and immunofluorescence indicate that significant amounts of both alpha 2 beta 1 and alpha 3 beta 1 appear on not only the basolateral but also the apical plasma membrane. These results indicate that integrins are the major receptors for the extracellular matrix in MDCK cells, and that they may affect epithelial cell polarization by mediating not only cell-substratum but also cell-cell contacts.