Comparative study of glycosyltransferase activities in Caco-2 cells before and after enterocytic differentiation using lectin-affinity high-performance liquid chromatography.

Human colonic adenocarcinoma Caco-2 cells differentiate into enterocytes by induction with sodium butyrate after confluence. Our previous studies have shown that there are high levels of H type 1 blood group antigen and core 2 structure present in O-glycans of the glycoproteins from these differentiated cells and these O-glycans appear to be indispensable for the process of differentiation of the cells (J. Amano and M. Oshima, 1999, J. Biol. Chem. 274, 21209-21216). Here, we have determined the glycosyltransferase activities using lectin-affinity HPLC because the method enabled easy separation and identification of mixtures of isomeric oligosaccharide structures due to the high resolution and reproducibility. The activities of beta 3-galactosyltransferase, alpha 2-fucosyltransferase, which are responsible for H type 1 antigen biosynthesis, and core 2 beta 6-N-acetylglucosaminyltransferase in differentiated Caco-2 cells were higher than those in undifferentiated cells. These results demonstrate that an increase in specific glycosyltransferase activities brought on a change of the O-glycan structures during differentiation.     

Structures of mucin-type sugar chains of the galactosyltransferase purified from human milk. Occurrence of the ABO and Lewis blood group determinants

The mucin-type sugar chains of human milk galactosyltransferase samples purified from two donors with different blood types were released by alkaline borohydride treatment and quantitatively labeled by N-[3H]acetylation. The radioactive oligosaccharides thus obtained were fractionated by high performance liquid chromatography and immobilized lectin chromatography, and their structures were studied by sequential digestion with endo- or exoglycosidases, methylation analysis, and periodate oxidation. It was revealed that the structures of the mucin-type sugar chains of galactosyltransferase are extremely various, and many blood group determinants are expressed on more than 13 different backbone sugar chains. The characteristic features of the sugar chains could be summarized as follows. 1) The sugar chains of both samples are composed of core 1, Gal beta 1----3GalNAc, and core 2, GlcNAc beta 1----6(Gal beta 1----3)GalNAc. 2) One or two N-acetyllactosamine repeating units extend from the core through GlcNAc beta 1----6Gal and GlcNAc beta 1----3 Gal linkages. 3) Blood group determinants are expressed in accord with the blood types of the donors: sample 1 from a donor of blood type O, Lea+b- contains oligosaccharides with Lea and X determinants, and sample 2 from a donor of B, Lea-b- contains those with H, X, Y, and B determinants.     

Asynchronous transport to the cell surface of intestinal brush border hydrolases is not due to differential trimming of N-linked oligosaccharides

Intestinal brush border enzyme glycoproteins are transported to the microvillar membrane at different rates in the differentiated intestinal cell line Caco-2. This asynchronism is due to at least two rate-limiting events, a pre- and an intra-Golgi step (Stieger B., Matter, K., Baur, B., Bucher, K., H?chli, M., and Hauri, H.P. (1988) J. Cell Biol. 106, 1853-1861). A possible cause for the asynchronous protein transport might be differential trimming of N-linked oligosaccharide side chains. The effects of two trimming inhibitors on the intracellular transport of sucrase-isomaltase, a slowly migrating hydrolase, and dipeptidylpeptidase IV, a rapidly migrating hydrolase, are described. 1-Deoxymannojirimycin, an inhibitor of Golgi alpha-mannosidase I, had no influence on the rate of appearance of these hydrolases in the brush border membrane as assessed by subcellular fractionation. In the presence of N-methyl-1-deoxynojirimycin, an inhibitor of glucosidase I, 30-40% of the newly synthesized molecules appeared at the cell surface, and half-time for appearance of this pool was identical to that found in control cells. The reduced maximal transport to the cell surface observed with N-methyl-1-deoxynojirimycin may suggest that proper glycosylation is necessary for an efficient transport from the Golgi apparatus to the microvillar membrane. Inhibition of glucosidase I does not prevent the acquisition of endoglycosidase H resistance. Furthermore, evidence is presented that the processing in the presence of N-methyl-1-deoxynojirimycin leads to glycosylated endoglycosidase H-resistant glycoproteins.     

The dual role of annexin II in targeting of brush border proteins and in intestinal cell polarity

Functional intestinal epithelium relies on complete polarization of enterocytes marked by the formation of microvilli and the accurate trafficking of glycoproteins to relevant membrane domains. Numerous transport pathways warrant the unique structural identity and protein/lipid composition of the brush border membrane. Annexin II (Ca(2+)-dependent lipid-binding protein) is an important component of one of the apical protein transport machineries, which involves detergent-resistant membranes and the actin cytoskeleton. Here, we investigate in intestinal Caco-2 cells the contribution of annexin II to the sorting and transport of brush border hydrolases and role in intestinal cell polarity. Downregulation of annexin II in Caco-2-A4 cell line results in a severe reduction of the levels of the brush border membrane resident enzyme sucrase isomaltase (SI) as well as structural components such as ezrin. This reduction is accompanied by a redistribution of these proteins to intracellular compartments and a striking morphological transition of Caco-2 cells to rudimentary epithelial cells that are characterized by an almost flat apical membrane with sparse and short microvilli. Concomitant with this alteration is the redistribution of the intermediate filament protein keratin 19 to the intracellular membranes in Caco-2-A4 cells. Interestingly, keratin 19 interacts with annexin II in wild type Caco-2 cells and this interaction occurs exclusively in lipid rafts. Our findings suggest a role for annexin II and K19 in differentiation and polarization of intestinal cells.     

Comparative study of the mucin-type sugar chains of human chorionic gonadotropin present in the urine of patients with trophoblastic diseases and healthy pregnant women

Human chorionic gonadotropins (hCGs) highly purified from the urine of patients with trophoblastic diseases and of healthy pregnant women contain approximately four mucin-type sugar chains in one molecule. The structures of these sugar chains were studied comparatively by using a new sensitive method to obtain mucin-type sugar chains quantitatively as radioactive oligosaccharides from a small amount of glycoproteins. The mucin-type sugar chains of all hCGs include sialylated and nonsialylated Gal beta 1----3GalNAc and Gal beta 1----4GlcNAc beta 1----6(Gal beta 1----3)GalNAc. In the case of normal hCG and hydatidiform mole hCG, oligosaccharides containing the tetrasaccharide core occupy approximately 10% of the total mucin-type sugar chains. The ratio of the tetrasaccharide containing oligosaccharides is increased prominently to approximately 60% in choriocarcinoma hCG. The proportion in invasive mole hCG was also increased, but less than the proportion of choriocarcinoma hCG.     

Core2 O-Glycan Structure Is Essential for the Cell Surface Expression of Sucrase Isomaltase and Dipeptidyl Peptidase-IV during Intestinal Cell Differentiation

Alterations in glycosylation play an important role during intestinal cell differentiation. Here, we compared expression of mucin-type O-glycan synthases from proliferating and differentiated HT-29 and Caco-2 cells. Mucin-type O-glycan structures were analyzed at both stages by mass spectrometry. Core2 β1,6-N-acetylglucosaminyltransferase-2 (C2GnT-2) was markedly increased in differentiated HT-29 and Caco-2 cells, but the core3 structure was hardly detectable. To determine whether such differential expression of mucin-type O-glycan structures has physiological significance in intestinal cell differentiation, expression of sucrase isomaltase (SI) and dipeptidyl-peptidase IV (DPP-IV), two well known intestinal differentiation markers, was examined. Interestingly, the fully glycosylated mature form of SI was decreased in C2GnT-2 knock-out mice but not in core2 N-acetylglucosaminyltransferase-3 (C2GnT-3) nulls. In addition, expression of SI and DPP-IV was dramatically reduced in C2GnT-1–3 triple knock-out mice. These patterns were confirmed by RNAi analysis; C2GnT-2 knockdown significantly reduced cell surface expression of SI and DPP-IV in Caco-2 cells. Similarly, overexpression of the core3 structure in HT-29 cells attenuated cell surface expression of both enzymes. These findings indicate that core3 O-glycan structure regulates cell surface expression of SI and DPP-IV and that core2 O-glycan is presumably an essential mucin-type O-glycan structure found in both molecules in vivo. Finally, goblet cells in the upper part of the crypt showed impaired maturation in the core2 O-glycan-deficient mice. These studies are the first to clearly identify functional mucin-type O-glycan structures modulating cell surface expression of SI and DPP-IV during the intestinal cell differentiation.     

The sugar chain structures of ABO blood group active glycoproteins obtained from human erythrocyte membrane

The glycoproteins of human erythrocyte membrane have two groups of sugar chains with blood type ABH determinants, which are quite distinct in their molecular sizes. A neutral sugar chain and an acidic sugar chain, which belong to the small size group, were isolated from the glycoproteins obtained from the erythrocyte of blood type O individuals, and their structures were elucidated as Fucalpha1 leads to 2Galbeta1 leads to 3N-acetylgalactosaminitol and Fucalpha1 leads to 2Galbeta1 leads to 3(AcNeualpha2 leads to 6)N-acetylgalactosaminitol, respectively. The molecular weight of the large sugar chains with ABH determinants were estimated to be more than 4000. Both large and small neutral sugar chains of membrane glycoproteins obtained from blood type O erythrocyte could serve as acceptors of alpha-N-acetylgalactosaminyltransferases purified from milk of blood type A1 and A2 individuals, producing the same radioactive sugar chain distribution patterns. However, the acidic sugar chain with the H determinant could not serve as an acceptor of these enzymes.     

Expression of peroxisome proliferator-activated receptors alpha and gamma in differentiating human colon carcinoma Caco-2 cells

The expression of peroxisome proliferator-activated receptors alpha (PPARalpha) and gamma (PPARgamma) was studied in the human adenocarcinoma Caco-2 cells induced to differentiate by long term culture (15 days). The differentiation of Caco-2 cells was attested by increases in the activities of sucrase-isomaltase and alkaline phosphatase (two brush border enzymes), fatty acyl-CoA oxidase (AOX) and catalase (two peroxisomal enzymes), by an elevation in the protein levels of villin (a brush border molecular marker), AOX, peroxisomal bifunctional enzyme (PBE), catalase and peroxisomal membrane protein of 70 kDa (PMP70). and by the appearance of peroxisomes. The expression of PPARalpha and PPARgamma was investigated by Western blotting, immunocytochemistry, Northern blotting and S1 nuclease protection assay during the differentiation of Caco-2 cells. The protein levels of PPARalpha, PPARgamma, and PPARgamma2 increased gradually during the time-course of Caco-2 cell differentiation. Immunocytochemistry revealed that PPARalpha and gamma were localized in cell nuclei. The PPARgamma1 protein was encoded by PPARgamma3 mRNA because no signal was obtained for PPARgamma1 mRNA using a specific probe in S1 nuclease protection assay. The amount of PPARgamma3 mRNA increased concomitantly to the resulting PPARgamma1 protein. On the other hand, the mRNA of PPARalpha and PPARgamma2 were not significantly changed, suggesting that the increase in their respective protein was due to an elevation of the translational rate. The role played by the PPAR subtypes in Caco-2 cell differentiation is discussed.     

Regulation of Human (Caco-2) Intestinal Epithelial Cell Differentiation by Extracellular Matrix Proteins

Extracellular matrix regulation of intestinal epithelial differentiation may affect development, differentiation during migration to villus tips, healing, inflammatory bowel disease, and malignant transformation. Cell culture studies of intestinal epithelial biology may also depend on the matrix substrate used. We evaluated matrix effects on differentiation and proliferation in human intestinal Caco-2 epithelial cells, a model for intestinal epithelial differentiation. Proliferation, brush border enzyme specific activity, and spreading were compared in cells cultured on tissue culture plastic with interstitial collagen I and the basement membrane constituents collagen IV and laminin. Each matrix significantly increased alkaline phosphatase, dipeptidyl peptidase, lactase, sucrase-isomaltase, and cell spreading in comparison to plastic. However, the basement membrane proteins collagen IV and laminin further promoted all four brush border enzymes but inhibited spreading compared to collagen I. Proliferation was most rapid on type I collagen and slowest on laminin and tissue culture plastic. Basement membrane matrix proteins may promote intestinal epithelial differentiation and inhibit proliferation compared with interstitial collagen I.     

Changes in asparagine-linked sugar chains of human promyelocytic leukemic cells (HL-60) during monocytoid differentiation and myeloid differentiation. Appearance of high mannose-type oligosaccharides in neutral fraction

Structural changes in the asparagine-linked sugar chains of plasma membrane glycoproteins during myeloid and monocytoid differentiation were investigated by the use of an in vitro differentiation system for human promyelocytic leukemic cells (HL-60), which can be induced to more mature myeloid cells by exposure to dimethyl sulfoxide and to macrophage-like cells by a phorbol ester. The asparagine-linked sugar chains released from their plasma membranes by hydrazinolysis were separated into a neutral fraction and an acidic fraction composed of over ten components. The content of neutral oligosaccharides, which accounted for 8% of the total asparagine-linked sugar chains in HL-60 cells, increased slightly to 13% in dimethyl sulfoxide-induced cells and markedly to 33% in phorbol ester-induced cells. Structural analyses revealed that the neutral oligosaccharides of HL-60 cells are all of the complex type with a variety of Gal beta 1----4GlcNAc beta 1----units in their outer chain moieties and the following core structure: (sequence; see text) After myeloid and monocytoid differentiation, the total amount of neutral complex-type sugar chains did not change significantly, but newly found high mannose-type sugar chains contributed up to 3% and 24% of the total sugar chains, respectively.     

Differentiation of human colon adenocarcinoma cells alters the expression and intracellular localization of annexins A1, A2, and A5

Butyrate induces differentiation and alters cell proliferation in intestinal-epithelial cells by modulation of the expression of several genes. Annexins are a superfamily of ubiquitous proteins characterized by their calcium-dependent ability to bind to biological membranes; their involvement in several physiological processes, such as membrane trafficking, calcium signaling, cell motility, proliferation, and differentiation has been proposed. Thus, we have analyzed changes in annexin A1 (AnxA1), annexin A2 (AnxA2), and annexin A5 (AnxA5) levels and localization in human colon adenocarcinoma cells differentiated by butyrate treatment or by culture in glucose-free inosine-containing medium. The acquired differentiated phenotype increased dipeptidyl peptidase-IV (DPP-IV) expression and alkaline phosphatase (ALP) activity, two well known brush border markers. Butyrate induces cell differentiation and growth arrest in BCS-TC2, BCS-TC2.2, HT-29, and Caco-2 cells, increasing the levels of AnxA1 and AnxA5, whereas AnxA2 decreases except in Caco-2 cells. Inosine-differentiated cells present increased amounts of the three studied annexins, as occurs in spontaneously differentiated Caco-2 cells. AnxA2 down-regulation is not due to proteasome activation and seems to be related to the butyrate-induced cell proliferation arrest; AnxA1 and AnxA5 expression is growth-state independent. AnxA1 and AnxA5 are mainly found in the cytoplasm while AnxA2 is localized underneath the plasma membrane in cell-to-cell contacts. Butyrate induces changes in subcellular localization towards a vesicle-associated pattern. Human colon adenocarcinoma cell differentiation is associated with an up-regulation of AnxA1, AnxA2, and AnxA5 and with a subcellular relocation of these proteins. No correlation between annexin levels and tumorigenicity was found. Up-regulation of AnxA1 could contribute to the reported anti-inflammatory effects of butyrate in colon inflammatory diseases.     

Uncoordinated,transient mosaic patterns of intestinal hydrolase expression in differentiating human enterocytes

The heterogenous expression of brush border membrane hydrolases by the human enterocyte-like Caco-2 cell line during morphological and functional differentiation in vitro was investigated at the cellular level. Indirect immunofluorescence revealed that the heretogenous (“mosaic”) expression of sucrase-isomaltase, lactase, aminopeptidase N, and alkaline phosphatase was, in fact, transient in nature. The labeling indexes for each hydrolase gradually increased during culture at postconfluence in order to reach a maximum (≥90%) after 30 days, concomitant with an upregulation of their respective protein expression levels. In contrast, dipeptidylpeptidase IV labeling remained relatively constant. Backscattered electron imaging analysis in midstage (12 days postconfluence) monolayers demonstrated a lack of correlation between brush border membrane development and expression of each enzyme studied. Moreover, double immunostaining revealed that none of the other four hydrolases correlated directly with sucrase-isomaltase expression. Finally, immunodetection for the proliferation-associated antigen Kl-67 revealed a transient mosaic pattern of proliferation which was inversely related to Caco-2 cell differentiation. These data indicate that enterocytic differentiation-related (as well as proliferation-related) gene expression in Caco-2 cells is regulated but uncoordinated at the cellular level, suggesting that an overall control mechanism is lacking. © 1996 Wiley-Liss, Inc.     

Modification of blood group A antigen expression in a pancreatic cancer cell line (PC-1) by inhibitors of N-glycan processing.

Pancreatic adenocarcinomas induced in Syrian hamsters by treatment with N-nitrosobis(2-oxopropyl) amine express blood group A antigen, which is absent in normal pancreatic cells. On membrane glycoproteins purified from tumors, blood group A antigen has been found to be expressed on multiantennary Asn-linked complex glycans. In this study, we investigated the effect of inhibitors of Asn-glycan processing on blood group A antigen bearing glycan structures in a cell line (PC-1) established from a primary induced pancreatic cancer. Expression of blood group A antigen on cells and in membrane preparations was blocked by treatment with 1-deoxymannojirimycin, an inhibitor of mannosidase I, but was retained after treatment with swainsonine, an inhibitor of mannosidase II. However, swainsonine treatment altered the glycan structure associated with blood group A antigen from an endoglycosidase H resistant type to a sensitive type, indicating that the blood group A structure might shift from a complex type to a hybrid type glycan by this treatment. These results demonstrate that Asn-linked glycans carry the major blood group A antigens in PC-1 cells.     

Influence of surface modification on vitality and differentiation of Caco-2 cells

Abstract It is widely accepted that the functional and morphological differentiation of cells is initiated and determined by the interaction of molecules of the extracellular matrix and adhesion molecules of the cell membrane. To assess the influence of the underlying matrix on the characteristics of cells, enterocyte-like Caco-2 cells were cultivated on substrates commonly used for cell culture as well as on glass coated with hydrophobic layers. Providing the same starting conditions for growth, the parameters investigated on preconfluent Caco-2 cells were the number of adhering cells, the proliferative activity and the degree of differentiation indicated by the expression of three brush border enzymes. Whereas tissue culture treated polystyrene elicited highest rates of adhesion, proliferation, and differentiation, even glass altered the pattern of brush border enzyme expression. The hydrophobic surfaces strongly decreased the adhesion and the proliferation but the surviving cells exhibited a pronounced higher degree of differentiation. Interestingly, each sub-type of hydrophobic matrix triggered a different pattern of brush border enzyme expression. Thus, the development of a certain phenotype of a cell can not only be triggered by certain components of the extracellular matrix but also by artificially prepared surface coatings of the underlying matrix. In the future it seems to be feasible that cells can be programmed by tailoring the surface of the underlying substrate.     

Posttranslational regulation of sucrase-isomaltase expression in intestinal crypt and villus cells

Expression and synthesis of sucrase-isomaltase (SI) were studied in human jejunum and in the colon tumor cell lines Caco-2 and HT-29. Twelve monoclonal antibodies produced against the adult human intestinal enzyme were shown to recognize specifically SI by immunoprecipitation of 14C-labeled membrane proteins, analysis of enzyme activities in the immunoprecipitates, and immunoblotting. These antibodies produced markedly different patterns of immunofluorescent staining of the intestinal mucosa. Three of them were specific for the absorptive villus cells, while the other nine also stained the luminal membrane of the proliferative crypt cells, with different intensities which paralleled their ability to recognize SI in immunoblots. Sequential immunoprecipitation of SI solubilized from purified brush borders or entire jejunum with four selected antibodies demonstrated the presence of different forms of the enzyme, expressed by either villus or crypt cells. Two immunologically distinct forms of high mannose precursor (hmP1 and hmP2) were also identified in both jejunal mucosa and colon tumor cells. They were present as monomers and their immunological differences were preserved under various ionic and pH conditions. Pulse-chase studies indicated that, in Caco-2 cells, hmP1 is converted into hmP2 within 30 min of chase, and hmP2 is then processed into the complex-glycosylated precursor destined for the brush border membrane. hmP1 was immunologically related to the mature SI present in crypt cells and lacked the epitopes specific for mature SI expressed by villus cells. These results demonstrated that sucrase-isomaltase is synthesized by both crypt and villus cells, but processing of the cotranslationally glycosylated high mannose precursor is dependent on the state of differentiation of the enterocytes. This may represent a general mechanism for the regulation of expression of differentiated cell products at the post-translational level.     

Oligomerization and intracellular protein transport: dimerization of intestinal dipeptidylpeptidase IV occurs in the Golgi apparatus.

It was postulated that newly synthesized membrane proteins need to be assembled into oligomers in the endoplasmic reticulum in order to be transported to the Golgi apparatus. By use of the differentiated human adenocarcinoma cell line Caco-2, the general validity of this proposal was studied for small intestinal brush border enzymes which are dimers in most mammalian species. Chemical cross-linking experiments and sucrose gradient rate-zonal centrifugation revealed that dipeptidylpeptidase IV is present as a dimer in the brush border membrane of Caco-2 cells whereas the disaccharidase sucrase-isomaltase appears to be a monomer. Dipeptidylpeptidase IV was found to dimerize immediately after complex glycosylation, an event associated with the Golgi apparatus. Dimerization of this enzyme was inhibited by CCCP but did not depend on complex glycosylation of N-linked carbohydrates as assessed by the use of the trimming inhibitor 1-deoxymannojirimycin. It is concluded that dimerization of dipeptidylpeptidase IV occurs in a late Golgi compartment and therefore cannot be a prerequisite for its export from the endoplasmic reticulum.     

Role of hepatocyte nuclear factor 1alpha and 1beta in the transcriptional regulation of human dipeptidyl peptidase IV during differentiation of Caco-2 cells

Caco-2 cells undergo differentiation to an enterocytic-like cell when maintained in a post-confluent state for 1-2 weeks. During this period Caco-2 cells begin to express high levels brush border membrane associated enzymes such as dipeptidyl peptidase IV. Using the dipeptidyl peptidase IV gene promoter in electrophoretic mobility shift assays, we have shown for the first time that levels of hepatocyte nuclear factor 1alpha increase three- to fourfold during Caco-2 cell differentiation. Transient cotransfection experiments with 3T3 cells using dipeptidyl peptidase IV promoter constructs and expression vectors containing hepatocyte nuclear factor 1alpha and beta show that the ratio of alpha and beta modulates reporter gene expression. These results suggest that the increase in levels of hepatocyte nuclear factor 1alpha that occur during intestinal cell differentiation, are important for expression of dipeptidyl peptidase IV and other intestinal proteins.     

GLUT12 expression and regulation in murine small intestine and human Caco-2 cells

GLUT12 was cloned from the mammary cancer cell line MCF-7, but its physiological role still needs to be elucidated. To gain more knowledge of GLUT12 function in the intestine, we investigated GLUT12 subcellular localization in the small intestine and its regulation by sugars, hormones, and intracellular mediators in Caco-2 cells and mice. Immunohistochemical methods were used to determine GLUT12 subcellular localization in human and murine small intestine. Brush border membrane vesicles were isolated for western blot analyses. Functional studies were performed in Caco-2 cells by measuring α-methyl-d -glucose (αMG) uptake in the absence of sodium. GLUT12 is located in the apical cytoplasm, below the brush border membrane, and in the perinuclear region of murine and human enterocytes. In Caco-2 cells, GLUT12 translocation to the apical membrane and α-methyl- d -glucose uptake by the transporter are stimulated by protons, glucose, insulin, tumor necrosis factor-α (TNF-α), protein kinase C, and AMP-activated protein kinase. In contrast, hypoxia decreases GLUT12 expression in the apical membrane. Upregulation of TNF-α and hypoxia-inducible factor-1α ( HIF-1α) genes is found in the jejunal mucosa of diet-induced obese mice. In these animals, GLUT12 expression in the brush border membrane is slightly decreased compared with lean animals. Moreover, an intraperitoneal injection of insulin does not induce GLUT12 translocation to the membrane, as it occurs in lean animals. GLUT12 rapid translocation to the enterocytes’ apical membrane in response to glucose and insulin could be related to GLUT12 participation in sugar absorption during postprandial periods. In obesity, in which insulin sensitivity is reduced, the contribution of GLUT12 to sugar absorption is affected.     

Role of sugar chains in the in vitro biological activity of human erythropoietin produced in recombinant Chinese hamster ovary cells

Human erythropoietin contains three Asn-type and one mucin-type sugar chains. That the branching structure of the outer portion of Asn-type sugar chains is correlated to its biological activity in vivo has been reported recently (Takeuchi, M., Inoue, N., Strickland, T. W., Kubota, M., Wada, M., Shimizu, R., Hoshi, S., Kozutsumi, H., Takasaki, S., and Kobata, A. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 7819-7822). In this study, the effect of trimming of sugar chains on the biological activity in vitro of this hormone was examined by using several glycosidases. Human erythropoietin produced by recombinant Chinese hamster ovary cells showed three times higher activity after desialylation. The activity was not changed significantly by further removal of the mucin-type sugar chain from the hormone, indicating no contribution of this type of sugar chain to the activity of erythropoietin in vitro. Sequential removal of galactose and N-acetylglucosamine from the outer chain moieties of the desialylated Asn-type sugar chains raised the activity of the hormone up to four and five times the intact erythropoietin, respectively. The activation effect was diminished slightly by further removing alpha-mannosyl residues and to a great extent by removing beta-mannosyl residues from the core portions of the Asn-type sugar chains. N-Glycanase digestion of intact erythropoietin resulted in almost complete loss of the activity in vitro. These results indicate that the core portion of the Asn-type sugar chains is necessary for erythropoietin to express its full biological activity in vitro and suggest that removal of the core portion of the sugar chains destroys the active conformation of erythropoietin.