Domain composition of rhamnose-binding lectin from shishamo smelt eggs and its carbohydrate-binding profiles

Osmerus (Spirinchus) lanceolatus egg lectin (OLL) is a member of the rhamnose-binding lectin (RBL) family which is mainly found in aqueous beings. cDNA of OLL was cloned, and its genomic architecture was revealed. The deduced amino acid (aa) sequence indicated that OLL was composed of 213 aa including 95 aa of domain N and 97 aa of domain C. N and C showed 73 % sequence identity and contained both -ANYGR- and -DPC-KYL-peptide motifs which are conserved in most of the RBL carbohydrate recognition domains. The calculated molecular mass of mature OLL was 20,852, consistent with the result, and 20,677.716, from mass spectrometry. OLL was encoded by eight exons: exons 1 and 2 for a signal peptide; exons 3-5 and 6-8 for N- and C-domains, respectively. Surface plasmon resonance spectrometric analyses revealed that OLL showed comparable affinity for Galα- and β-linkages, whereas Silurus asotus lectin (SAL), a catfish RBL, bound preferentially to α-linkages of neoglycoproteins. The Kd values of OLL and SAL against globotriaosylceramide (Gb3) were 1.69 × 10⁻⁵ M for and 2.81 × 10⁻⁶ M, respectively. Thus, the carbohydrate recognition property of OLL is slightly different from that of SAL. On the other hand, frontal affinity chromatography revealed that both OLL and SAL interacted with only glycolipid-type oligosaccharides such as Gb3 trisaccharides, not with N-linked oligosaccharides. The domain composition of these RBLs and an analytical environment such as the "cluster effect" of a ligand might influence the binding between RBL and sugar chains.

Sialic acid-binding lectin (leczyme) induces apoptosis to malignant mesothelioma and exerts synergistic antitumor effects with TRAIL

Malignant mesothelioma is a highly aggressive tumor with poor prognosis. An effective drug for treatment of malignant mesothelioma is greatly needed. Sialic acid-binding lectin (SBL) isolated from oocytes of Rana catesbeiana is a multifunctional protein which has lectin activity, ribonuclease activity and antitumor activity, so it could be developed as a new type of anticancer drug. The validity of SBL for treatment of malignant mesothelioma was assessed using three malignant mesotheliomas and a non-malignant mesothlial cell line. Effectiveness of combinatorial treatment of SBL and tumor necrosis factor-related apoptosis inducing ligand (TRAIL) was also elucidated and characterized. SBL induced tumor-selective cytotoxicity that was attributed to induction of apoptosis. Combinatorial treatment of SBL and TRAIL showed synergistic apoptosis-inducing effect. Additional experiments revealed that Bid was the mediating molecule for the synergistic effect in SBL and TRAIL. These results suggested that SBL could be a promising candidate for the therapeutics for malignant mesothelioma. Furthermore, the combinatorial treatment of SBL and TRAIL could be an effective regimen against malignant mesothelioma.

Involvement of ER stress in apoptosis induced by sialic acid-binding lectin (leczyme) from bullfrog eggs

Sialic-acid binding lectin (SBL) isolated from bullfrog (Rana catesbeiana) oocytes is a multifunctional protein which has lectin activity, ribonuclease activity and cancer-selective antitumor activity. It has been reported that SBL induces apoptosis accompanied by rigid mitochondrial perturbation, which indicates mediation of the intrinsic pathway. However, the mechanism of the antitumor effect of SBL has not been fully elucidated. We report, here, that ER stress is evoked in SBL-treated cells. We show that caspase-4, an initiator caspase of ER stress-mediated apoptosis was activated, and inhibition of caspase-4 resulted in significant attenuation of apoptosis induced by SBL. We analyzed the precise mechanism of activation of the caspase cascade induced by SBL, and found that caspase-9 and -4 are activated upstream of activation of caspase-8. Further study revealed that SBL induces the mitochondrial and ER stress-mediated pathways independently. It is noteworthy that SBL can induce cancer-selective apoptosis by multiple apoptotic signaling pathways, and it can serve as a candidate molecule for anticancer drugs in a novel field.

Sialic acid-binding lectin (leczyme) induces caspase-dependent apoptosis-mediated mitochondrial perturbation in Jurkat cells

Sialic acid binding lectin (SBL) isolated from Rana catesbeiana oocytes is a multifunctional protein which has lectin activity, ribonuclease activity and antitumor activity. However, the mechanism of antitumor effects of SBL is unclear to date and the validity for human leukemia cells has not been fully studied. We report here that SBL shows cytotoxicity for some human leukemia cell lines including multidrug-resistant (MDR) cells. The precise mechanisms of SBL-induced apoptotic signals were analyzed by combinational usage of specific caspase inhibitors and the mitochondrial membrane depolarization detector JC-1. It was demonstrated that SBL causes mitochondrial perturbation and the apoptotic signal is amplified by caspases and cell death is executed in a caspase-dependent manner. The efficacy of this combinational usage was shown for the first time, to distinguish the apoptotic pathway in detail. SBL selectively kills tumor cells, is able to exhibit cytotoxicity regardless of P-glycoprotein expression and has potential as an alternative to conventional DNA-damaging anticancer drugs.

Differential expression profiles of glycosphingolipids in human breast cancer stem cells vs. cancer non-stem cells

Previous studies demonstrated that certain glycosphingolipids (GSLs) are involved in various cell functions, such as cell growth and motility. Recent studies showed changes in GSL expression during differentiation of human embryonic stem cells; however, little is known about expression profiles of GSLs in cancer stem cells (CSCs). CSCs are a small subpopulation in cancer and are proposed as cancer-initiating cells, have been shown to be resistant to numerous chemotherapies, and may cause cancer recurrence. Here, we analyzed GSLs expressed in human breast CSCs by applying a CSC model induced through epithelial-mesenchymal transition, using mass spectrometry, TLC immunostaining, and cell staining. We found that (i) Fuc-(n)Lc4Cer and Gb3Cer were drastically reduced in CSCs, whereas GD2, GD3, GM2, and GD1a were greatly increased in CSCs; (ii) among various glycosyltransferases tested, mRNA levels for ST3GAL5, B4GALNT1, ST8SIA1, and ST3GAL2 were increased in CSCs, which could explain the increased expression of GD3, GD2, GM2, and GD1a in CSCs; (iii) the majority of GD2+ cells and GD3+ cells were detected in the CD44(hi)/CD24(lo) cell population; and (iv) knockdown of ST8SIA1 and B4GALNT1 significantly reduced the expression of GD2 and GD3 and caused a phenotype change from CSC to a non-CSC, which was detected by reduced mammosphere formation and cell motility. Our results provide insight into GSL profiles in human breast CSCs, indicate a functional role of GD2 and GD3 in CSCs, and suggest a possible novel approach in targeting human breast CSCs to interfere with cancer recurrence.

Self-recognition of high-mannose type glycans mediating adhesion of embryonal fibroblasts

High-mannose type N-linked glycan with 6 mannosyl residues, termed "M6Gn2", displayed clear binding to the same M6Gn2, conjugated with ceramide mimetic (cer-m) and incorporated in liposome, or coated on polystyrene plates. However, the conjugate of M6Gn2-cer-m did not interact with complex-type N-linked glycan with various structures having multiple GlcNAc termini, conjugated with cer-m. The following observations indicate that hamster embryonic fibroblast NIL-2 K cells display homotypic autoadhesion, mediated through the self-recognition capability of high-mannose type glycans expressed on these cells: (i) NIL-2 K cells display clear binding to lectins capable of binding to high-mannose type glycans (e.g., ConA), but not to other lectins capable of binding to other carbohydrates (e.g. GS-II). (ii) NIL-2 K cells adhere strongly to plates coated with M6Gn2-cer-m, but not to plates coated with complex-type N-linked glycans having multiple GlcNAc termini, conjugated with cer-m; (iii) degree of NIL-2 K cell adhesion to plates coated with M6Gn2-cer-m showed a clear dose-dependence on the amount of M6Gn2-cer-m; and (iv) the degree of NIL-2 K adhesion to plates coated with M6Gn2-cer-m was inhibited in a dose-dependent manner by α1,4-L-mannonolactone, the specific inhibitor in high-mannose type glycans addition. These data indicate that adhesion of NIL-2 K is mediated by self-aggregation of high mannose type glycan. Further studies are to be addressed on auto-adhesion of other types of cells based on self interaction of high mannose type glycans.

Induction of epithelial-mesenchymal transition with O-glycosylated oncofetal fibronectin

Epithelial-mesenchymal transition (EMT) has been shown to play a key role in embryogenesis and cancer progression. We previously found that fibronectin (FN) carrying O-GalNAc at a specific site is selectively expressed in cancer and fetal cells/tissues, and termed oncofetal FN (onfFN). Here, we show that (i) a newly-established monoclonal antibody against FN lacking the O-GalNAc, termed normalFN (norFN), is useful for isolation of onfFN, (ii) onfFN, but not norFN, can induce EMT in human lung carcinoma cells, (iii) onfFN has a synergistic effect with transforming growth factor (TGF)β1 in EMT induction.

Involvement of O-glycosylation defining oncofetal fibronectin in epithelial-mesenchymal transition process

The process termed "epithelial-mesenchymal transition" (EMT) was originally discovered in ontogenic development, and has been shown to be one of the key steps in tumor cell progression and metastasis. Recently, we showed that the expression of some glycosphingolipids (GSLs) is down-regulated during EMT in human and mouse cell lines. Here, we demonstrate the involvement of GalNAc-type (or mucin-type) O-glycosylation in EMT process, induced with transforming growth factor β (TGF-β) in human prostate epithelial cell lines. We found that: (i) TGF-β treatment caused up-regulation of oncofetal fibronectin (onfFN), which is defined by mAb FDC6, and expressed in cancer or fetal cells/tissues, but not in normal adult cells/tissues. The reactivity of mAb FDC6 requires the addition of an O-glycan at a specific threonine, inside the type III homology connective segment (IIICS) domain of FN. (ii) This change is associated with typical EMT characteristics; i.e., change from epithelial to fibroblastic morphology, enhanced cell motility, decreased expression of a typical epithelial cell marker, E-cadherin, and enhanced expression of mesenchymal markers. (iii) TGF-β treatment up-regulated mRNA level of FN containing the IIICS domain and GalNAc-T activity for the IIICS domain peptide substrate containing the FDC6 onfFN epitope. (iv) Knockdown of GalNAc-T6 and T3 inhibited TGF-β-induced up-regulation of onfFN and EMT process. (v) Involvement of GSLs was not detectable with the EMT process in these cell lines. These findings indicate the important functional role of expression of onfFN, defined by site-specific O-glycosylation at IIICS domain, in the EMT process.

Human monoclonal antibody GNX-8 directed to extended type 1 chain: Specific binding to human colorectal cancer

We observed previously that two carbohydrate epitopes, extended type 1 chain Le(a)-Le(a) and Le(b)-Le(a), are expressed strongly in human gastric or colorectal cancer and cell lines derived therefrom, but their expression in human normal colorectal cells is highly limited. A monoclonal antibody, termed GNX-8, was established through immunization of "KM mice" with colonic cancer cell line Colo205, and with purified Le(b)-Le(a) glycosphingolipid, followed by screening human IgG directed to this antigen. KM mice possess human chromosome fragments and are capable of producing human immunoglobulin. GNX-8 reacted specifically with extended type 1 chain epitope Le(b)-Le(a), bound to all five colonic cancer cell lines so far tested, and displayed strong complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC). The antigens defined by GNX-8, expressed in Colo205 cells, were: (i) glycosphingolipids with epitope Le(b)-Le(a), whose reactivity was abolished upon defucosylation; (ii) glycoproteins with molecular mass range from 32 to >175 kDa, which were depleted in cells cultured in the presence of benzyl-alpha-GalNAc, indicating that these epitopes are O-linked glycans.Immunohistological reactivity of GNX-8 at 1 mug/ml, applied on tissue sections from colorectal and various other types of cancer, was much stronger than that with various normal cells and tissues. GNX-8 reactivity with normal cells required a much higher concentration (150 mug/ml), and this reactivity was based on cross-reaction with non-extended, normal blood group Le(b) antigen. Growth of subcutaneous xenograft of human colonic cancer cells, Colo205 or DLD-1, in nude mice or SCID mice, was strongly inhibited by administration of GNX-8. These observations, taken together, indicate that antibody GNX-8, directed specifically to Le(b)-Le(a) antigen, provides a novel direction of immunotherapy for human colorectal cancer. (c) 2009 UICC.

N-glycosylation status of beta-haptoglobin in sera of patients with colon cancer, chronic inflammatory diseases and normal subjects

N-glycosylation status of purified beta-haptoglobin from sera of 17 patients, and from sera of 14 healthy volunteer subjects, was compared by blotting with various lectins and antibodies. Patients in this study were diagnosed as having colon cancer through histological examination of each tumor tissue by biopsy. Blotting index of serum beta-haptoglobin with Aleuria aurantia lectin (AAL) was clearly higher for cancer patients than for healthy subjects. No such distinction was observed for blotting with three other lectins and two monoclonal antibodies. To determine tumor-associated reactivity of AAL binding as compared to inflammatory processes in colonic tissues, beta-haptoglobin separated from sera of 5 patients with Crohn's disease (CD), and 4 patients with ulcerative colitis (UC), was studied. All these cases, except one case of UC, showed AAL index lower than that in cancer cases, similarly to healthy subjects. The higher AAL binding of beta-haptoglobin in colon cancer patients than in healthy subjects appeared to be due to alpha-L-fucosyl residue, since it was eliminated by bovine kidney alpha-fucosidase treatment. N-linked glycans of serum haptoglobin from colon cancer patients vs. healthy subjects were released by N-glycanase, fluorescence-labeled, and subjected to normal-phase high performance liquid chromatography (NP-HPLC). Glycan structures were determined based on glucose unit (GU) values and their changes upon sequential treatment with various exoglycosidases. Glycosyl sequences and their branching status of glycans from 14 cases of serum beta-haptoglobin were characterized. The identified glycans were sialylated or nonsialylated, bi-antennary or tri-antennary structures, with or without terminal fucosylation.

Glycosynaptic microdomains controlling tumor cell phenotype through alteration of cell growth, adhesion, and motility

Glycosphingolipids (GSLs) GM3 (NeuAcalpha3Galbeta4Glcbeta1Cer) and GM2 (GalNAcbeta4[NeuAcalpha3]Galbeta4Glcbeta1Cer) inhibit (i) cell growth through inhibition of tyrosine kinase associated with growth factor receptor (GFR), (ii) cell adhesion/motility through inhibition of integrin-dependent signaling via Src kinases, or (iii) both cell growth and motility by blocking "cross-talk" between integrins and GFRs. These inhibitory effects are enhanced when GM3 or GM2 are in complex with specific tetraspanins (TSPs) (CD9, CD81, CD82). Processes (i)-(iii) occur through specific organization of GSLs with key molecules (TSPs, caveolins, GFRs, integrins) in the glycosynaptic microdomain. Some of these processes are shared with epithelial-mesenchymal transition induced by TGFbeta or under hypoxia, particularly that associated with cancer progression.

Control of cell motility by interaction of gangliosides, tetraspanins, and epidermal growth factor receptor in A431 versus KB epidermoid tumor cells

Growth of epidermoid carcinoma cell lines, A431 and KB, has been known to be controlled by the interaction of epidermal growth factor (EGF) and its receptor (EGFR) with tyrosine kinase. Ganglioside GM3 was previously found to interact with EGFR and to inhibit EGFR tyrosine kinase. However, motility of these cells, controlled by EGFR and ganglioside, was not studied. The present study is focused on the control mechanism of the motility of these cells through interaction of ganglioside, tetraspanin (TSP), and EGFR. Key results are as follows: (i) The level of EGFR expressed in A431 cells is approximately 6 times higher than that expressed in KB cells, and motility of A431 cells is also much higher than that of KB cells, yet growth of A431 cells is either not affected or is inhibited by EGF. In contrast, growth of KB cells is enhanced by EGF. (ii) Levels of TSPs (CD9, CD82, and CD81) expressed in A431 cells are much higher than those expressed in KB cells, and TSPs expressed in A431 cells are reduced by treatment of cells with EtDO-P4, which inhibits the synthesis of glycosphingolipids (GSLs) and gangliosides. (iii) These TSPs are co-immunoprecipitated with EGFR in both A431 and KB cells, indicating that TSPs are closely associated with EGFR. (iv) High motility of A431 cells is greatly reduced, while low motility of KB cells is not affected, by treatment of cells with EtDO-P4. These results, taken together, suggest that there is a close correlation between high motility of A431 cells and high expression of EGFR and TSPs, and between ganglioside GM3/GM2 and TSP. A similar correlation was suggested between the low motility of KB cells and low levels of EGFR and TSP. The correlation between high motility and high level of EGFR with the ganglioside-TSP complex in A431 cells is unique. This is in contrast to our previous studies that indicate that motility of many types of tumor cells is inhibited by a high level of CD9 or CD82, together with growth factor receptors and integrins.

Functional role of glycosphingolipids and gangliosides in control of cell adhesion, motility, and growth, through glycosynaptic microdomains

At cell surface microdomains, glycosyl epitopes, carried either by glycosphingolipids, N- or O-linked oligosaccharides, are recognized by carbohydrate-binding proteins or complementary carbohydrates. In both cases, the carbohydrate epitopes may be clustered with specific signal transducers, tetraspanins, adhesion receptors or growth factor receptors. Through this framework, carbohydrates can mediate cell signaling leading to changes in cellular phenotype. Microdomains involved in carbohydrate-dependent cell adhesion inducing cell activation, motility, and growth are termed "glycosynapse". In this review a historical synopsis of glycosphingolipids-enriched microdomains study leading to the concept of glycosynapse is presented. Examples of glycosynapse as signaling unit controlling the tumor cell phenotype are discussed in three contexts: (i) Cell-to-cell adhesion mediated by glycosphingolipids-to-glycosphingolipids interaction between interfacing glycosynaptic domains, through head-to-head (trans) carbohydrate-to-carbohydrate interaction. (ii) Functional role of GM3 complexed with tetraspanin CD9, and interaction of such complex with integrins, or with fibroblast growth factor receptor, to control tumor cell phenotype and its reversion to normal cell phenotype. (iii) Inhibition of integrin-dependent Met kinase activity by GM2/tetraspanin CD82 complex in glycosynaptic microdomain. Data present here suggest that the organizational status of glycosynapse strongly affects cellular phenotype influencing tumor cell malignancy.

Glycosylation status of haptoglobin in sera of patients with prostate cancer vs. benign prostate disease or normal subjects

We studied chemical level and glycosylation status of haptoglobin in sera of patients with prostate cancer, as compared to benign prostate disease and normal subjects, with the following results. (i) Haptoglobin level was enhanced significantly in sera of prostate cancer. (ii) Sialylated bi-antennary glycans were the dominant structures in haptoglobins from all 3 sources, regardless of different site of N-linked glycan. The N-linked glycans at N184 were exclusively bi-antennary, and showed no difference between prostate cancer vs. benign prostate disease. (iii) Tri-antennary, N-linked, fucosylated glycans, carrying at least 1 sialyl-Lewis(x/a) antenna, were predominantly located on N207 or N211 within the amino acid 203-215 sequence of the beta-chain of prostate cancer, and were minimal in benign prostate disease. Fucosylated glycans were not observed in normal subjects. A minor tri-antennary N-linked glycan was observed at N241 of the beta-chain in prostate cancer, which was absent in benign prostate disease. (iv) None of these N-linked structures showed the expected presence of disialylated antennae with GalNAcbeta4(NeuAcalpha3)Galbeta3(NeuAcalpha6)GlcNAcbetaGal, or its analogue, despite cross-reactivity of prostate cancer haptoglobin with monoclonal antibody RM2. (v) Minor levels of O-glycosylation were identified in prostate cancer haptoglobin for the first time. Mono- and disialyl core Type 1 O-linked structures were identified after reductive beta-elimination followed by methylation and mass spectrometric analysis. No evidence was found for the presence of specific RM2 or other tumor-associated glycosyl epitopes linked to this O-glycan core. In summary, levels of haptoglobin are enhanced in sera of prostate cancer patients, and the N-glycans attached to a defined peptide region of its beta-chain are characterized by enhanced branching as well as antenna fucosylation.

Effect of lipid mimetics of GM3 and lyso-GM3 dimer on EGF receptor tyrosine kinase and EGF-induced signal transduction

The tyrosine kinase activity associated with epidermal growth factor receptor (EGFR) has been a target in studies of pharmacological reagents to inhibit growth of cancer cells, which are mostly of epidermal origin. Lyso-GM3 dimer showed stronger inhibitory effect on the tyrosine kinase of EGFR than GM3, with minimal cytotoxicity [Y. Murozuka, et al. Lyso-GM3, its dimer, and multimer: their synthesis, and their effect on epidermal growth factor-induced receptor tyrosine kinase. Glycoconj. J. 24 (2007) 551-563]. Synthesis of lipids with sphingosine requires many steps, and the yield is low. A biocombinatory approach overcame this difficulty; however, products required a C(12) aliphatic chain, rather than the sphingosine head group [Y. Murozuka, et al. Efficient sialylation on azidododecyl lactosides by using B16 melanoma cells. Chemistry & Biodiversity 2 (2005) 1063-1078]. The present study was to clarify the effects of these lipid mimetics of GM3 and lyso-GM3 dimer on EGFR tyrosine kinase activity, and consequent changes of the A431 cell phenotype, as follows. (i) A lipid mimetic of lyso-GM3 dimer showed similar strong inhibitory effect on EGF-induced EGFR tyrosine kinase activity, and similar low cytotoxicity, as the authentic lyso-GM3 dimer. (ii) A lipid mimetic of lyso-GM3 dimer inhibited tyrosine phosphorylation of EGFR or its dimer to a level similar to that of the authentic lyso-GM3 dimer, but more strongly than GM3 or a lipid mimetic of GM3. (iii) Associated with the inhibitory effect of a lipid mimetic of lyso-GM3 dimer on EGF-induced EGFR kinase activity, only Akt kinase activity was significantly inhibited, but kinases associated with other signal transducers were not affected. (iv) The cell cycle of A431 cells, and the effects of GM3 and a lipid mimetic of lyso-GM3 dimer, were studied by flow cytometry, measuring the rate of DNA synthesis with propidium iodide. Fetal bovine serum greatly enhanced S phase and G(2)/M phase. Enhanced G(2)/M phase was selectively inhibited by pre-incubation of A431 cells with a lipid mimetic of lyso-GM3 dimer, whereas GM3 had only a minimal effect.

Structure and function of glycosphingolipids and sphingolipids: recollections and future trends

Based on development of various methodologies for isolation and characterization of glycosphingolipids (GSLs), we have identified a number of GSLs with globo-series or lacto-series structure. Many of them are tumor-associated or developmentally regulated antigens. The major question arose, what are their functions in cells and tissues? Various approaches to answer this question were undertaken. While the method is different for each approach, we have continuously studied GSL or glycosyl epitope interaction with functional membrane components, which include tetraspanins, growth factor receptors, integrins, and signal transducer molecules. Often, GSLs were found to interact with other carbohydrates within a specific membrane microdomain termed "glycosynapse", which mediates cell adhesion with concurrent signal transduction. Future trends in GSL and glycosyl epitope research are considered, including stem cell biology and epithelial-mesenchymal transition (EMT) process.

Lyso-GM3, its dimer, and multimer: their synthesis, and their effect on epidermal growth factor-induced receptor tyrosine kinase

Glycosphingolipids, particularly gangliosides, are known to modulate growth factor receptor tyrosine kinase. A well-documented example is the inhibitory effect of GM3 on kinase associated with epidermal growth factor receptor (EGFR) in human epidermoid carcinoma A431 cells. Lyso-GM3 was detected as a minor component in A431 cells, and may function as an auxiliary factor in GM3-dependent inhibition of EGFR. We studied the inhibitory effect of chemically synthesized GM3, lyso-GM3, and its derivatives, on EGFR function, based on their interaction in membrane microdomain, with the following major findings: (1) GM3, EGFR, and caveolin coexist, but tetraspanins CD9 and CD82 are essentially absent, within the same low-density membrane fraction, separated by sucrose density gradient ultracentrifugation. (2) Strong interaction between EGFR and GM3 was indicated by increasing binding of EGFR to GM3-coated polystyrene beads, in a GM3 dose-dependent manner. Confocal microscopy results suggested that three components in the microdomain (GM3, EGFR, and caveolin) are closely associated. (3) Lyso-GM3 or lyso-GM3 dimer strongly inhibited EGFR kinase activity, in a dose-dependent manner, while lyso-GM3 trimer and tetramer did not. >50 microM lyso-GM3 was cytolytic, while >50 microM lyso-GM3 dimer was not cytolytic, yet inhibited EGFR kinase strongly. Thus, lyso-GM3 and its dimer exert an auxiliary effect on GM3-induced inhibition of EGFR kinase and cell growth, and lyso-GM3 dimer may be a good candidate for pharmacological inhibitor of epidermal tumor growth.

Self-recognition of N-linked glycans with multivalent GlcNAc, determined as ceramide mimetic conjugate

Aminoceramide mimetic was synthesized and conjugated to N-linked oligosaccharides having multivalent GlcNAc by reductive amination. Ceramide mimetic conjugates with "complex-type" glycan having five or six GlcNAc termini (termed Os Fr. B-Cer) were purified, analyzed by thin-layer chromatography (TLC), and finally characterized by MS/MS analysis through liquid chromatography/mass spectrometry. Binding of Os Fr. B-Cer placed on solid phase polystyrene surface with [3H]cholesterol-labeled liposomes containing Os Fr. B-Cer, or containing various glycosphingolipids (GSLs) was determined. The binding of Os Fr. B-Cer liposomes to Os Fr. B-Cer coated plate was significantly higher than binding of GM3 liposomes. Other GSL liposomes showed no binding. Thus, self-recognition of Os Fr. B-Cer was clearly demonstrated using ceramide mimetic conjugates.

Le(x) glycan mediates homotypic adhesion of embryonal cells independently from E-cadherin: a preliminary note

Le(x) glycan and E-cadherin (Ecad) are co-expressed at embryonal stem (ES) cells and embryonal carcinoma (EC) cells. While the structure and function of Ecad mediating homotypic adhesion of these cells have been well established, evidence that Le(x) glycan also mediates such adhesion is weak, despite the fact that Le(x) oligosaccharide inhibits the compaction process. To provide stronger evidence, we knocked out Ecad gene in EC and ES cells to establish F9 Ecad (-/-) and D3M Ecad (-/-) cells, which highly express Le(x) glycan but do not express Ecad at all. Both F9 Ecad (-/-) and D3M Ecad (-/-) cells displayed strong autoaggregation in the presence of Ca(2+), while PYS-2 cells, which express trace amount of Ecad and undetectable level of Le(x) glycan, did not display autoaggregation. In addition, F9 Ecad (-/-) and D3M Ecad (-/-) cells displayed strong adhesion to plates coated with Le(x) glycosphingolipid (III(3)FucnLc4Cer), in dose-dependent manner, in the presence of Ca(2+). Thus, ES or EC cells display autoaggregation and strong adhesion to Le(x)-coated plates in the absence of Ecad, further supporting the notion of Le(x) self-recognition (i.e., Le(x)-to-Le(x) interaction) in cell adhesion.

Ganglioside GM2-tetraspanin CD82 complex inhibits met and its cross-talk with integrins, providing a basis for control of cell motility through glycosynapse

Glycosphingolipids (GSLs) at the cell surface membrane are associated or complexed with signal transducers (Src family kinases and small G-proteins), tetraspanins, growth factor receptors, and integrins. Such organizational framework, defining GSL-modulated or -dependent cell adhesion, motility, and growth, is termed "glycosynapse" (Hakomori, S., and Handa, K. (2002) FEBS Lett. 531, 88-92; Hakomori, S. (2004) Ann. Braz. Acad. Sci. 76, 553-572). We describe here the functional organization of the glycosynaptic microdomain, and the mechanisms for control of cell motility and invasiveness, in normal bladder epithelial HCV29 cells versus highly invasive bladder cancer YTS1 cells, both derived from transitional epithelia. (i) Ganglioside GM2, but not GM3 or globoside, interacted specifically with tetraspanin CD82, and such a complex inhibited hepatocyte growth factor (HGF)-induced activation of Met tyrosine kinase in a dose-dependent manner. (ii) Depletion of GM2 in HCV29 cells by treatment with D-threo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (P4), or reduction of CD82 expression by RNA interference, significantly enhanced HGF-induced Met tyrosine kinase and cell motility. (iii) In contrast, YTS1 cells, lacking CD82, displayed HGF-independent activation of Met tyrosine kinase and high cell motility. Transfection of the CD82 gene to YTS1 inhibited HGF dose-dependent Met tyrosine kinase activity and cell motility, due to formation of the GM2-CD82 complex. (iv) Adhesion of YTS1 or YTS1/CD82 cells to laminin-5-coated plates, as compared with noncoated plates, strongly enhanced Met activation, and the degree of activation was further increased in association with GSL depletion by P4. Laminin-5-dependent Met activation was minimal in HCV29 cells. These findings indicate that GSL, particularly GM2, forms a complex with CD82, and that such complex interacts with Met and thereby inhibits HGF-induced Met tyrosine kinase activity, as well as integrin to Met cross-talk.

Epidermal growth factor receptor tyrosine kinase is modulated by GM3 interaction with N-linked GlcNAc termini of the receptor

Epidermal growth factor receptor (EGFR) at membrane microdomains plays an essential role in the growth control of epidermal cells, including cancer cells derived therefrom. Ligand-dependent activation of EGFR tyrosine kinase is known to be inhibited by ganglioside GM3, but to a much lesser degree by other glycosphingolipids. However, the mechanism of the inhibitory effect of GM3 on EGFR tyrosine kinase has been ambiguous. The mechanism is now defined by binding of N-linked glycan having multiple GlcNAc termini to GM3 through carbohydrate-to-carbohydrate interaction, based on the following data: (i) EGFR (molecular mass, approximately 170 kDa) has N-linked glycan with GlcNAc termini, as probed by mAb (J1) or lectin (GS-II); (ii) GS-II-bound EGFR also bound to anti-EGFR Ab as well as to GM3-coated beads; (iii) GM3 inhibitory effect on EGFR tyrosine kinase was abrogated in vitro by coincubation with glycan having multiple GlcNAc termini and in cell culture in situ incubated with the same glycan; and (iv) cells treated with swainsonine, which increased expression of complex-type and hybrid-type glycans with GlcNAc termini, displayed higher inhibition of EGFR kinase by GM3 than swainsonine-untreated control cells. A similar effect was observed with 1-deoxymannojirimycin, which increased hybrid-type structure in addition to major accumulation of high mannose-type glycan. These findings indicate that N-linked glycan with GlcNAc termini linked to EGFR is the target to interact with GM3, causing inhibition of EGF-induced EGFR tyrosine kinase.

Interaction of N-linked glycans, having multivalent GlcNAc termini, with GM3 ganglioside

GM3 ganglioside interacts specifically with complex-type N-linked glycans having multivalent GlcNAc termini, as shown for (1) and (2) below. (1) Oligosaccharides (OS) isolated from ConA-non-binding N-linked glycans of ovalbumin, whose structures were identified as penta-antennary complex-type with bisecting GlcNAc, having five or six GlcNAc termini (OS B1, B2), or bi-antennary complex-type having two GlcNAc termini (OS I). OS I is a structure not previously described. (2) Multi-antennary complex-type N-linked OS isolated from fetuin, treated by sialidase followed by beta-galactosidase, having three or four GlcNAc termini exposed. These OS, conjugated to phosphatidylethanolamine (PE), showed clear interaction with (3)H-labeled liposomes containing GM3, when various doses of OS-PE conjugate were adhered by drying to multi-well polystyrene plates. Interaction was clearly observed only with liposomes containing GM3, but not LacCer, Gb4, or GalNAcalpha1-3Gb4 (Forssman antigen). GM3 interaction with PE conjugate of OS B1 or B2 was stronger than that with PE conjugate of OS I. GM3 interacted clearly with PE conjugate of N-linked OS from desialylated and degalactosylated fetuin, but not native fetuin. No binding was observed to cellobiose-PE conjugate, or to OS-PE conjugate lacking GlcNAc terminus. Thus, GM3, but not other GSL liposomes, interacts with various N-linked OS having multiple GlcNAc termini, in general. These findings suggest that the concept of carbohydrate-to-carbohydrate interaction can be extended to interaction of specific types of N-linked glycans with specific GSLs. Natural occurrence of such interaction to define cell biological phenomena is under investigation.

A catalytic carbohydrate contributes to bacterial antibiotic resistance

Penicillins are widespread in nature and lethal to growing bacteria. Because of the severe threat posed by these antibiotics, bacteria have evolved a wide variety of strategies for combating them. Here, we describe one unusual strategy that involves the activity of a catalytic carbohydrate. We show that the cyclic oligosaccharide, beta-cyclodextrin (betaCD), can hydrolyze, and thereby inactivate, penicillin in vivo. Moreover, we demonstrate that this catalytic activity contributes to the antibiotic resistance of a bacterium that synthesizes this oligosaccharide in the laboratory. Taken together, these data not only expand our understanding of the biochemistry of penicillin resistance, but also provide the first demonstration of natural carbohydrate-mediated catalysis in a living system.

A specific microdomain ("glycosynapse 3") controls phenotypic conversion and reversion of bladder cancer cells through GM3-mediated interaction of alpha3beta1 integrin with CD9

Cell motility is highly dependent on the organization and function of microdomains composed of integrin, proteolipid/tetraspanin CD9, and ganglioside (Ono, M., Handa, K., Sonnino, S., Withers, D. A., Nagai, H., and Hakomori, S. (2001) Biochemistry 40, 6414-6421; Kawakami, Y., Kawakami, K., Steelant, W. F. A., Ono, M., Baek, R. C., Handa, K., Withers, D. A., and Hakomori, S. (2002) J. Biol. Chem. 277, 34349-34358), later termed "glycosynapse 3" (Hakomori, S., and Handa, K. (2002) FEBS Lett. 531, 88-92, 2002). Human bladder cancer cell lines KK47 (noninvasive and nonmetastatic) and YTS1 (highly invasive and metastatic), both derived from transitional bladder epithelia, are very similar in terms of integrin composition and levels of tetraspanin CD9. Tetraspanin CD82 is absent in both. The major difference is in the level of ganglioside GM3, which is several times higher in KK47 than in YTS1. We now report that the GM3 level reflects glycosynapse function as follows: (i) a stronger interaction of integrin alpha3 with CD9 in KK47 than in YTS1; (ii) conversion of benign, low motility KK47 to invasive, high motility cells by depletion of GM3 by P4 (D-threo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol) treatment or by knockdown of CD9 by the RNA interference method; (iii) reversion of high motility YTS1 to low motility phenotype like that of KK47 by exogenous GM3 addition, whereby the alpha3-to-CD9 interaction was enhanced; (iv) low GM3 level activated c-Src in YTS1 or in P4-treated KK47, and high GM3 level by exogenous addition caused Csk translocation into glycosynapse, with subsequent inhibition of c-Src activation; (v) inhibition of c-Src by "PP2" in YTS1 greatly reduced cell motility. Thus, GM3 in glycosynapse 3 plays a dual role in defining glycosynapse 3 function. One is by modulating the interaction of alpha3 with CD9; the other is by activating or inhibiting the c-Src activity, possibly through Csk translocation. High GM3 level decreases tumor cell motility/invasiveness, whereas low GM3 level enhances tumor cell motility/invasiveness. Oncogenic transformation and its reversion can be explained through the difference in glycosynapse organization.

De-N-acetyllactotriaosylceramide as a Novel Cationic Glycosphingolipid of Bovine Brain White Matter: Isolation and Characterization

A novel cationic lipid was separated from bovine brain white matter by a series of chromatographies on carboxymethyl-Sephadex and silica gel in chloroform and methanol. Its structure was identified unambiguously as de-N-acetyllactotriaosylceramide (deNAcLc(3)Cer) by mass spectrometry and (1)H NMR. The natural occurrence of this glycolipid in white matter extract was detected by immunostaining of thin-layer chromatography with monoclonal antibody 5F5, which is directed to deNAcLc(3)Cer and recognizes the terminal beta-glucosaminyl (GlcNH(2)) residue, having a free NH(2) group. A de-N-acetylase capable of hydrolyzing the N-acetyl group of Lc(3)Cer was detected in bovine brain extract using N-[(14)C]acetyl-labeled Lc(3)Cer as a substrate. The biogenesis and possible functional significance of deNAcLc(3)Cer are discussed.

RM2 antigen (beta1,4-GalNAc-disialyl-Lc4) as a new marker for prostate cancer

Although prostate-specific antigen (PSA) has been widely used for early detection of prostate cancer, PSA has problems with specificity and prediction of pathological stage. Therefore, a new marker for prostate cancer is urgently required. We examined expression of a novel carbohydrate antigen, beta1,4-GalNAc-disialyl-Lc(4), defined by the monoclonal antibody RM2, in prostate cancer using 75 cases of radical prostatectomy specimens. RM2 immunoreactivity was negative to weak in all benign glands, and weak to moderate in high-grade prostatic intraepithelial neoplasia. In prostatic adenocarcinoma, RM2 immunoreactivity was negative to weak (lower expression) in 20 cases, and moderate to strong (higher expression) in 55 cases. A clear difference of RM2 expression level was observed between Gleason patterns 3 and >/=4. Higher expression of RM2 antigen was significantly associated with primary Gleason pattern >/=4, high Gleason score (>/=8), larger tumor volume and advanced tumor stage. Furthermore, 5-year PSA failure-free survival was significantly lower in the higher expression group. However, no significant relationship was observed between RM2 expression level and preoperative serum PSA. Western blot analysis in prostate cancer cell lines PC3 and LNCap revealed that major 49-kDa and minor 39-kDa glycoproteins were common to both cells, but there was an increase of 59- and 125-kDa glycoproteins unique to LNCap and an increase of 88- and 98-kDa glycoproteins unique to PC3. RM2 antigen is a new histological marker for prostate cancer that may reflect the Gleason grading system. Identification of the glycoproteins carrying the RM2 antigen will provide new insights into the properties of prostate cancer.

Effect of ganglioside and tetraspanins in microdomains on interaction of integrins with fibroblast growth factor receptor

The functional interaction ("cross-talk") of integrins with growth factor receptors has become increasingly clear as a basic mechanism in cell biology, defining cell growth, adhesion, and motility. However, no studies have addressed the microdomains in which such interaction takes place nor the effect of gangliosides and tetraspanins (TSPs) on such interaction. Growth of human embryonal WI38 fibroblasts is highly dependent on fibroblast growth factor (FGF) and its receptor (FGFR), stably associated with ganglioside GM3 and TSPs CD9 and CD81 in the ganglioside-enriched microdomain. Adhesion and motility of these cells are mediated by laminin-5 ((LN5) and fibronectin (FN) through alpha3beta1 and alpha5beta1 integrin receptors, respectively. When WI38 cells or its transformant VA13 cells were adhered to LN5 or FN, alpha3beta1 or alpha5beta1 were stimulated, giving rise to signaling to activate FGFR through tyrosine phosphorylation and inducing cell proliferation under serum-free conditions without FGF addition. Types and intensity of signaling during the time course differed significantly depending on the type of integrin stimulated (alpha3beta1 versus alpha5beta1), and on cell type (WI38 versus VA13). Such effect of cross-talk between integrins and FGFR was influenced strongly by the change of GM3 and TSPs. (i) GM3 depletion by P4 caused enhanced tyrosine phosphorylation of FGFR and Akt followed by MAPK activation, without significant change of ceramide level. GM3 depletion also caused enhanced co-immunoprecipitation of FGFR with alpha3/alpha5/beta1 and of these integrins with CD9/CD81. (ii) LN5- or FN-dependent proliferation of both WI38 and VA13 was strongly enhanced by GM3 depletion and by CD9/CD81 knockdown by siRNA. Thus, integrin-FGFR cross-talk is strongly influenced by GM3 and/or TSPs within the ganglioside-enriched microdomain.

Reversion of the Jun-induced oncogenic phenotype by enhanced synthesis of sialosyllactosylceramide (GM3 ganglioside)

In the mouse fibroblast cell line C3H 10T1/2 and the chicken fibroblast cell line DF1, the ganglioside GM3 is the major glycosphingolipid component of the plasma membrane. Expression of the viral oncoprotein Jun (v-Jun) induces transformed cell clones with greatly reduced levels of GM3 and GM3 synthase (lactosylceramide alpha2,3-sialyltransferase) mRNA in both 10T1/2 and DF1 cell cultures. Compared with nontransformed controls, v-Jun transfectants show enhanced ability of anchorage-independent growth, and their growth rates as adherent cells are increased. When the mouse GM3 synthase gene is transfected with the pcDNA vector into v-Jun-transformed 10T1/2 cells, the levels of GM3 synthase and corresponding mRNA are restored to those of control cells. Reexpression of GM3 correlates with a reduced ability of the cells to form colonies in nutrient agar. Similarly, when the newly cloned chicken GM3 synthase gene is transfected into v-Jun-transformed DF1 with the pcDNA vector, the GM3 synthase level is restored to that of control cells, and the ability of the cells to form agar colonies is reduced. The levels of GM3 in the cell also affect membrane microdomains. The complex of GM3 with tetraspanin CD9 and integrin alpha5beta1 inhibits motility and invasiveness. The amounts of this complex are greatly reduced in transformed cells. Expression of GM3 and consequent reversion of the transformed phenotype results in increased levels of that microdomain complex.

Sphingosine-dependent apoptosis: a unified concept based on multiple mechanisms operating in concert

Exposure of 3T3/A31 cells to serum-free medium, one type of apoptotic stimulus, causes a rapid increase in the sphingosine (Sph) level, which initiates a series of processes: (i) activation of caspase 3 through an enhanced "cascade" of caspases, (ii) release of the C-terminal-half kinase domain of PKCdelta (PKCdelta KD) by caspase 3, and (iii) activation of Sph-dependent kinase 1 (SDK1), which was previously identified as PKCdelta KD. The activation of caspase 3 and release of PKCdelta KD are inhibited strongly by the incubation of cells with the ceramidase inhibitor D-erythro-2-tetradecanoylamino-1-phenyl-1-propanol and, to a much lesser extent, by L-cycloserine, an inhibitor of de novo ceramide synthesis. Exogenous addition of Sph or N,N-dimethyl-Sph to U937 cells causes caspase 3 activation and release of PKCdelta KD (SDK1), leading to apoptosis. The Sph-induced apoptotic process associated with activation of caspase 3 and release of PKCdelta KD (SDK1) may promote the proapoptotic effect of BAD or BAX through an increase of phosphorylated 14-3-3. In addition, Sph induces apoptosis through a separate process: the blocking of "survival signal" through the Akt kinase pathway induced by alpha3beta1-mediated cell adhesion to laminin 10/11 in extracellular matrix. We hereby propose a unified concept of Sph-dependent apoptosis based on these multiple mechanisms operating in concert.

Glycosynapses: microdomains controlling carbohydrate-dependent cell adhesion and signaling

The concept of microdomains in plasma membranes was developed over two decades, following observation of polarity of membrane based on clustering of specific membrane components. Microdomains involved in carbohydrate-dependent cell adhesion with concurrent signal transduction that affect cellular phenotype are termed "glycosynapse". Three types of glycosynapse have been distinguished: "type 1" having glycosphingolipid associated with signal transducers (small G-proteins, cSrc, Src family kinases) and proteolipids; "type 2" having O-linked mucin-type glycoprotein associated with Src family kinases; and "type 3" having N-linked integrin receptor complexed with tetraspanin and ganglioside. Different cell types are characterized by presence of specific types of glycosynapse or their combinations, whose adhesion induces signal transduction to either facilitate or inhibit signaling. E.g., signaling through type 3 glycosynapse inhibits cell motility and differentiation. Glycosynapses are distinct from classically-known microdomains termed "caveolae", "caveolar membrane", or more recently "lipid raft", which are not involved in carbohydrate-dependent cell adhesion. Type 1 and type 3 glycosynapses are resistant to cholesterol-binding reagents, whereas structure and function of "caveolar membrane" or "lipid raft" are disrupted by these reagents. Various data indicate a functional role of glycosynapses during differentiation, development, and oncogenic transformation.

Cell growth regulation through GM3-enriched microdomain (glycosynapse) in human lung embryonal fibroblast WI38 and its oncogenic transformant VA13

Cell growth control mechanisms were studied based on organization of components in glycosphingolipid-enriched microdomain (GEM) in WI38 cells versus their oncogenic transformant VA13 cells. Levels of fibroblast growth factor receptor (FGFR) and cSrc were 4 times and 2-3 times higher, respectively, in VA13 than in WI38 GEM, whereas the level of tetraspanin CD9/CD81 was 3-5 times higher in WI38 than in VA13 GEM. Csk, the physiological inhibitor of cSrc, was present in WI38 but not in VA13 GEM. Functional association of GEM components in control of cell growth in WI38 is indicated by several lines of evidence. (i) Confluent, growth-inhibited WI38 showed a lower degree of FGF-induced MAPK activation than actively growing cells in sparse culture. (ii) The level of inactive cSrc (with Tyr-527 phosphate) was higher in confluent cells than in actively growing cells. Both processes i and ii were inhibited by GM3 since they were enhanced by GM3 depletion with d-threo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (P4). (iii) The high level of inactive cSrc associated with growth-inhibited cells was caused by coexisting Csk in WI38 GEM. (iv) Interaction of GM3 with FGFR was demonstrated by binding of GM3 to FGFR in the GEM fraction, as probed with GM3-coated beads, and by confocal microscopy. In contrast to WI38, both cSrc and MAPK in VA13 were strongly activated regardless of FGF stimulation or GM3 depletion by P4. Continuous, constitutive activation of both cSrc and MAPK was due to (i) a much higher level of cSrc and FGFR in VA13 than in WI38 GEM, (ii) their close association/interaction in VA13 GEM as indicated by clear coimmunoprecipitation between cSrc and FGFR, and (iii) the absence of Csk in VA13 GEM, making GEM incapable of inhibiting cSrc activation.

Carbohydrate-to-carbohydrate interaction, through glycosynapse, as a basis of cell recognition and membrane organization

Cell adhesion mediated by carbohydrate-to-carbohydrate interaction (CCI), or cell adhesion with concurrent signal transduction, are discussed in three contexts.1. Types of cell adhesion based on interaction of several combinations of glycosphingolipids (GSLs) at the surface of interfacing cells (" trans interactio") are reviewed critically, to exclude the possible involvement of GSL-binding proteins. Special emphasis is on: (i) autoaggregation of mouse teratocarcinoma F9 cells mediated by Le( x )-to-Le( x ) interaction, in which presence of Le( x )-binding protein is ruled out; (ii) adhesion of GM3-expressing cells to Gg3-expressing cells, in which involvement of GM3- or Gg3-binding protein is ruled out.2. Characteristic features and requirements of CCI, as compared with carbohydrate-to-protein interaction (CPI) and protein-to-protein interaction (PPI), are summarized, including: (i) specificity and requirement of bivalent cation; (ii) reaction velocity of CCI as compared to PPI; (iii) negative (repulsive) interaction; (iv) synergistic or cooperative effect of CCI and PPI, particularly GM3-to-Gg3 or GM3-to-LacCer interaction in synergy with integrin-dependent adhesion, or Le( x )-to-Le( x ) interaction in cooperation with E-cadherin-dependent adhesion.3. Microdomains at the cell surface are formed based on clustering of GSLs or glycoproteins organized with signal transducers. Among such microdomains, those involved in adhesion coupled with signal transduction to alter cellular phenotype are termed "glycosynaps". In some glycosynapses, growth factor receptors or integrin receptors are also involved, and their function is modulated by GSLs only when the receptor is N -glycosylated. This modulation may occur in part via interaction of GSLs with N -linked glycans of the receptor, termed " cis interactio".

Sphingosine-dependent protein kinase-1, directed to 14-3-3, is identified as the kinase domain of protein kinase C delta

Some protein kinases are known to be activated by d-erythro-sphingosine (Sph) or N,N-dimethyl-d-erythro-sphingosine (DMS), but not by ceramide, Sph-1-P, other sphingolipids, or phospholipids. Among these, a specific protein kinase that phosphorylates Ser60, Ser59, or Ser58 of 14-3-3beta, 14-3-3eta, or 14-3-3zeta, respectively, was termed "sphingosine-dependent protein kinase-1" (SDK1) (Megidish, T., Cooper, J., Zhang, L., Fu, H., and Hakomori, S. (1998) J. Biol. Chem. 273, 21834-21845). We have now identified SDK1 as a protein having the C-terminal half kinase domain of protein kinase Cdelta (PKCdelta) based on the following observations. (i). Large-scale preparation and purification of proteins showing SDK1 activity from rat liver (by six steps of chromatography) gave a final fraction with an enhanced level of an approximately 40-kDa protein band. This fraction had SDK1 activity approximately 50000-fold higher than that in the initial extract. (ii). This protein had approximately 53% sequence identity to the Ser/Thr kinase domain of PKCdelta based on peptide mapping using liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry data. (iii). A search for amino acid homology based on the BLAST algorithm indicated that the only protein with high homology to the approximately 40-kDa band is the kinase domain of PKCdelta. The kinase activity of PKCdelta did not depend on Sph or DMS; rather, it was inhibited by these sphingoid bases, i.e. PKCdelta did not display any SDK1 activity. However, strong SDK1 activity became detectable when PKCdelta was incubated with caspase-3, which releases the approximately 40-kDa kinase domain. PKCdelta and SDK1 showed different lipid requirements and substrate specificity, although both kinase activities were inhibited by common PKC inhibitors. The high susceptibility of SDK1 to Sph and DMS accounts for their important modulatory role in signal transduction.

A sphingosine-dependent protein kinase that specifically phosphorylates 14-3-3 (SDK1) is identified as the kinase domain of PKCdelta: a preliminary note

A specific protein kinase that phosphorylates Ser60, Ser59, or Ser58 of 14-3-3beta, eta, or zeta, respectively, only in the presence of sphingosine (Sph) or N,N-dimethyl-Sph (DMS), was termed "sphingosine-dependent protein kinase-1" (SDK1) [J. Biol. Chem. 273(34) (1998) 21834]. We have now identified SDK1 as a protein having the same amino acid sequence as in the C-terminal-half kinase domain of PKCdelta, with approximately 40 kDa molecular mass, based on large-scale purification of a protein from rat liver, and partial sequence using three different combinations of LC-MS or LC-MS/MS with respective search engine. PKCdelta did not display any SDK1 activity and PKCdelta activity was inhibited by Sph and DMS. However, strong SDK1 activity, only in the presence of Sph or DMS, became detectable when PKCdelta was incubated with caspase-3, which releases the approximately 40 kDa kinase domain.

Structure, organization, and function of glycosphingolipids in membrane

A large variety of glycosylation patterns in combination with different ceramide structures in glycosphingolipids provide a basis for cell type-specific glycosphingolipid pattern in membrane, which essentially reflects the composition of glycosphingolipid-enriched microdomains. Functions of glycosphingolipids as antigens, mediators of cell adhesion, and modulators of signal transduction are all based on such organization. Of particular importance is the assembly of glycosphingolipids with signal transducers and other membrane proteins to form a functional unit termed a, through which glycosylation-dependent cell adhesion coupled with signal transduction takes place. The microenvironment formed by interfacing glycosynapses of interacting cells plays a central role in defining phenotypic changes after cell adhesion, as occur in ontogenic development and cancer progression. These basic functional features of glycosphingolipids in membrane can also be considered roles of glycosphingolipids and gangliosides characteristic of neutrophils, myelocytes, and other blood cells. A series of sialyl fucosyl poly-N-acetylgalactosamine gangliosides without the sialyl-Le epitope, collectively termed, have been shown to mediate E-selectin-dependent rolling and tethering under dynamic flow with physiologic shear stress conditions. Functional roles of myeloglycan in neutrophils during inflammatory processes are discussed.