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

Characterization of two UDP-Gal:GalNAc-diphosphate-lipid β1,3-galactosyltransferases WbwC from Escherichia coli serotypes O104 and O5

Escherichia coli displays O antigens on the outer membrane that play an important role in bacterial interactions with the environment. The O antigens of enterohemorrhagic E. coli O104 and O5 contain a Galβ1-3GalNAc disaccharide at the reducing end of the repeating unit. Several other O antigens contain this disaccharide, which is identical to the mammalian O-glycan core 1 or the cancer-associated Thomsen-Friedenreich (TF) antigen. We identified the wbwC genes responsible for the synthesis of the disaccharide in E. coli serotypes O104 and O5. To functionally characterize WbwC, an acceptor substrate analog, GalNAcα-diphosphate-phenylundecyl, was synthesized. WbwC reaction products were isolated by high-pressure liquid chromatography and analyzed by mass spectrometry, nuclear magnetic resonance, galactosidase and O-glycanase digestion, and anti-TF antibody. The results clearly showed that the Galβ1-3GalNAcα linkage was synthesized, confirming WbwCECO104 and WbwCECO5 as UDP-Gal:GalNAcα-diphosphate-lipid β1,3-Gal-transferases. Sequence analysis revealed a conserved DxDD motif, and mutagenesis showed the importance of these Asp residues in catalysis. The purified enzymes require divalent cations (Mn(2+)) for activity and are specific for UDP-Gal and GalNAc-diphosphate lipid substrates. WbwC was inhibited by bis-imidazolium salts having aliphatic chains of 18 to 22 carbons. This work will help to elucidate mechanisms of polysaccharide synthesis in pathogenic bacteria and provide technology for vaccine synthesis.

MAb L9E10 to blood group H2 antigen binds to colon cancer stem cells and inhibits tumor cell migration and invasion

The functions of the precursor H antigen for ABO blood group antigens are still not fully understood, particularly in cancer cells. In this study, we used hybridoma technology and NSY human colon cancer cells as an immunogen to generate a monoclonal antibody designated as MAb L9E10. The binding antigen of MAb L9E10 was identified as blood group (BG) H2 antigen using carbohydrate array and erythrocyte agglutination assays. In immunofluorescence study, we found that BG-H2 was expressed on the surfaces of both colon cancer stem cells and their differentiated progeny. In a functional study, we observed that MAb L9E10 inhibited tumor cell migration and invasion at a concentration of 10 microg/mL in vitro. This result suggests that MAb L9E10 could be used to study cancer biology, particularly cancer stem cell biology. In addition, it is potentially useful for studying gastric diseases caused by Helicobacter pylori bacteria, with attachment to human gastric epithelial cells mediated by blood group antigens Lewis b and H2. Finally, MAb L9E10 is an ideal biological reagent for identifying Bombay blood type in which erythrocytes have no BG-H2 antigen expression.

Co-expression of CD173 (H2) and CD174 (Lewis Y) with CD44 suggests that fucosylated histo-blood group antigens are markers of breast cancer-initiating cells

Histo-blood group antigens CD173 (H2) and CD174 (Lewis Y) are known to be developmentally regulated carbohydrate antigens which are expressed to a varying degree on many human carcinomas. We hypothesized that they might represent markers of cancer-initiating cells (or cancer stem cells, CSC). In order to test this hypothesis, we examined the co-expression of CD173 and CD174 with stem cell markers CD44 and CD133 by flow cytometry analysis, immunocytochemistry, and immunohistochemistry on cell lines and tissue sections from breast cancer. In three breast cancer cell lines, the percentage of CD173(+)/CD44(+) cells ranged from 17% to >60% and of CD174(+)/CD44(+) from 21% to 57%. In breast cancer tissue sections from 15 patients, up to 50% of tumor cells simultaneously expressed CD173, CD174, and CD44 antigens. Co-expression of CD173 and CD174 with CD133 was also observed, but to a lesser percentage. Co-immunoprecipitation and sandwich ELISA experiments on breast cancer cell lines suggested that CD173 and CD174 are carried on the CD44 molecule. The results show that in these tissues CD173 (H2) and CD174 (LeY) are associated with CD44 expression, suggesting that these carbohydrate antigens are markers of cancer-initiating cells or of early progenitors of breast carcinomas.

Analysis of the protein and glycan parts of CA125 antigen from human amniotic fluid

CA125 antigen is a mucin-type molecule with a complex protein backbone and oligosaccharide chain structure. In this study, we characterized CA125 antigen from human amniotic fluid by gel filtration, ion-exchange chromatography, peptide mass fingerprinting and lectin-binding assays. The obtained results indicate CA125 to be structurally heterogeneous, existing in different glycoisoforms with subtle differences in the profile of molecular forms in comparison to placental tissue-derived and cancer-derived CA125 antigen. The complexity of CA125 structure suggests that it can act as a multifunctional molecule. Further investigation is therefore needed in order for the biological meaning of the tissue-specific structural forms to be comprehended fully. .

Mammary stem cells, self-renewal pathways, and carcinogenesis

The mammary gland epithelial components are thought to arise from stem cells that undergo both self-renewal and differentiation. Self-renewal has been shown to be regulated by the Hedgehog, Notch, and Wnt pathways and the transcription factor B lymphoma Mo-MLV insertion region 1 (Bmi-1). We review data about the existence of stem cells in the mammary gland and the pathways regulating the self-renewal of these cells. We present evidence that deregulation of the self-renewal in stem cells/progenitors might be a key event in mammary carcinogenesis. If 'tumor stem cells' are inherently resistant to current therapies, targeting stem cell self-renewal pathways might provide a novel approach for breast cancer treatment.

Epithelial progenitors in the normal human mammary gland

The human mammary gland is organized developmentally as a hierarchy of progenitor cells that become progressively restricted in their proliferative abilities and lineage options. Three types of human mammary epithelial cell progenitors are now identified. The first is thought to be a luminal-restricted progenitor; in vitro under conditions that support both luminal and myoepithelial cell differentiation, this cell produces clones of differentiating daughter cells that are exclusively positive for markers characteristic of luminal cells produced in vivo (i.e., keratins 8/18 and 19, epithelial cell adhesion molecule [EpCAM] and MUC1). The second type is a bipotent progenitor. It is identified by its ability to produce "mixed" colonies in single cell assays. These colonies contain a central core of cells expressing luminal markers surrounded by cells with a morphology and markers (e.g., keratin 14(+)) characteristic of myoepithelial cells. Serial passage in vitro of an enriched population of bipotent progenitors promotes the expansion of a third type of progenitor that is thought to be myoepithelial-restricted because it only produces cells with myoepithelial features. Luminal-restricted and bipotent progenitors can prospectively be isolated as distinct subpopulations from freshly dissociated suspensions of normal human mammary cells. Both are distinguished from many other cell types in mammary tissue by their expression of EpCAM and CD49f (alpha6 integrin). They are distinguished from each other by their differential expression of MUC1, which is expressed at much higher levels on the luminal progenitors. To relate the role of these progenitors to the generation of the three-dimensional tubuloalveolar structure of the mammary tree produced in vivo, we propose a model in which the commitment to the luminal versus the myoepithelial lineage may play a determining role in the generation of alveoli and ducts.

The fucosylated histo-blood group antigens H type 2 (blood group O, CD173) and Lewis Y (CD174) are expressed on CD34+ hematopoietic progenitors but absent on mature lymphocytes

The expression of LeY, H2, H3, and H4 on a broad variety of human leukemia cell lines and native lymphocytes as well as on CD34+ hematopoietic progenitor cells was examined by flow cytometry and immunocytochemistry. CD34+ leukemia cell lines (KG1, KG1a, and TF1) and native CD34+ hematopoietic progenitor cells expressed H2 (CD173) and LeY (CD174). In contrast, CD34(-) cell lines (HL-60, U937, JOK-1, Raji, Molt-3, Jurkat, and CEM-C7) and mature lymphocytes from peripheral blood and tonsils lacked CD173 and CD174. All cell lines and native lymphocytes as well as CD34+ precursor cells were negative for H3 and H4. Immunoprecipitation and consecutive Western blotting revealed a 170-kDa glycoprotein as the carrier molecule for the CD173 and CD174 oligosaccharide sequences on CD34+ hematopoietic precursors. The key enzyme for generating CD173 is the beta-D-galactoside 2-alpha-L-fucosyltransferase (FUT1). As shown by RT-PCR, FUT1 was expressed in immature hematopoietic cells but absent in mature lymphocytes, which indicates that expression of CD173 within the hematopoietic system is regulated at the transcriptional level by FUT1. Due to their exclusive presence on CD34+ hematopoietic progenitor cells, CD173 and CD174 represent novel markers of early hematopoiesis. The expression of the fucosylated histo-blood group antigens CD173 and CD174 in CD34+ hematopoietic progenitor cells and down-regulation of FUT1 in mature lymphocytes may be important factors influencing the homing process of hematopoietic stem cells to the bone marrow.

Glycopeptide synthesis and the effects of glycosylation on protein structure and activity

Despite the omnipresence of protein glycosylation in nature, little is known about how the attachment of carbohydrates affects peptide and protein activity. One reason is the lack of a straightforward method to access biologically relevant glycopeptides and glycoproteins. The isolation of homogeneous glycopeptides from natural sources is complicated by the heterogeneity of naturally occuring glycoproteins. It is chemical and chemoenzymatic synthesis that is meeting the challenge to solve this availability problem, thus playing a key role for the advancement of glycobiology. The current art of glycopeptide synthesis, albeit far from being routine, has reached a level of maturity that allows for the access to homogeneous and pure material for biological and medicinal research. Even the ambitious goal of the total synthesis of an entire glycoprotein is within reach. It is demonstrated that with the help of synthetic glycopeptides the effects of glycosylation on protein structure and function can be studied in molecular detail. For example, in immunology, synthetic (tumour-specific) glycopeptides can be used as immunogens to elicit a tumour-cell-specific immune response. Again, synthetic glycopeptides are an invaluable tool to determine the fine specificity of the immune response that can be mediated by both carbohydrate-specific B and T cells. Furthermore, selected examples for the use of synthetic glycopeptides as ligands of carbohydrate-binding proteins and as enzyme substrates or inhibitors are presented.

A new monoclonal antibody (A78-G/A7) to the Thomsen-Friedenreich pan-tumor antigen

A new monoclonal antibody to the Thomsen-Friedenreich (TF) antigen (or, more precisely, epitope; Gal beta 1-3GalNAc-) has been developed that is specific for both anomeric forms of this disaccharide (TF alpha and TF beta, including related structures on glycolipids), and not assay restricted. We demonstrate that this avid antibody (A78-G/A7) is well suited for immunohistochemistry on paraffin-embedded and cryosectioned tissues, immunoblotting, ELISA techniques, and hemagglutination. Immunohistochemistry on paraffin sections does not require proteolytic or microwave pretreatment. The binding characteristics of this antibody are largely independent of variations in pH (6.0-8.2) and temperature (4-37 degrees C). Immunoblotting with KG-1 (human acute myelogenous leukemia) cells revealed a series of TF-active glycoproteins with a main band at about 155 kDa. Immunoprecipitation was performed using a new technique applicable to IgM-type antibodies.