My career as an immunoglycobiologist.

The research program of my laboratory included three major topics: the structures and immunology of human carbohydrate blood group and glycosphingolipid antigens; the tissue distribution, subcellular localization and biosynthesis of glycosphingolipids; and the structural basis of the binding of carbohydrates by antibodies and lectins.

A historical perspective of the glycosphingolipids and sphingolipidoses.

Glycosphingolipids are a polysaccharide chain between 1 and 40 carbohydrate residues long glycosidically linked to ceramide (a long-chain aliphatic amino-alcohol or sphingoid) that is embedded in the cell plasma membrane with the carbohydrate moiety on the outside. The sphingoid imparts rigidity to the membrane and the carbohydrate tails protect the cell surface and have functions in relation to cell adhesion, growth, regulation, differentiation, cell interaction, recognition and signalling. They provide adhesion sites for pathogens and change during oncogenic transformation. Ceramide is also a component of sphingomyelin. Glycosphingolipids are degraded by lysosomal hydrolysis. The sphingolipidoses are a series of diseases in which mutations affecting the enzymes catalysing the last 11 steps of this process causing abnormal compounds proximal to the metabolic block to accumulate intralysosomally. Thus, they are a sub-group of the lysosomal storage diseases. The degradation of sphingolipids containing three or less carbohydrate residues requires a sphingolipid activator protein and mutations affecting these proteins also cause abnormal glycosphingolipid storage. With one exception (Fabry disease, which is X linked) the sphingolipidoses are inherited autosomally. The phenotypic manifestations of the individual sphingolipidoses are variable although the more severe variants are usually the better known. They have generally been regarded as untreatable but notable therapeutic advances are being made by enzyme replacement therapy and regulating the rate of glycosphingolipid synthesis by inhibiting UDP-glucose-N-acylsphingosine D-glucosyl transferase (CerGlcT), which is the first reaction on the pathway of glycosphingolipid synthesis. The compounds used are N-alkylated iminosugars whose glucose and galactose stereochemistries inhibit CerGlcT. Prenatal and carrier state diagnosis, genetic counselling and the abortion of affected foetuses are reducing the incidence of some of the most severe sphingolipidoses in certain high-incidence populations.

Traveling for the glycosphingolipid path.

Our studies on glycosphingolipids (GSLs) were initiated through isolation and structural characterization of lacto-series type 1 and 2 GSLs, and globo-series GSLs. Lacto-series structures included histo-blood group ABH and I/i antigens. Our subsequent studies were focused on GSL changes associated with: (i) ontogenic development and differentiation; (ii) oncogenic transformation and tumor progression. Various novel types of GSLs such as extended globo-series, sialyl-Le(x) (SLe(x)), sialyl-dimeric-Le(x) (SLe(x)-Le(x)), dimeric-Le(x) (Le(x)-Le(x)), Le(y)-on-Le(x), dimeric-Le(a) (Le(a)-Le(a)), Le(b)-on-Le(a), etc. were identified as tumor-associated antigens. These studies provide an essential basis for up- or down-regulation of key glycosyltransferase genes controlling development, differentiation, and oncogenesis. GSL structures established in our laboratory are summarized in Table 1, and structural changes of GSLs associated with ontogenesis and oncogenesis are summarized in Sections 2 and 3. Based on these results, we endeavored to find out the cell biological significance of GSL changes, focused on (i) cell adhesion, e.g., the compaction process of preimplantation embryo in which Le(x)-to-Le(x), Gb4-to-GalGb4 or -nLc4 play major roles; and (ii) modulation of signal transduction through interaction of growth factor receptor tyrosine kinase with ganglioside, e.g., EGF receptor tyrosine kinase with GM3. Recent trends of studies on i and ii lead to the concept that GSL clusters (microdomains) are organized with various signal transducer molecules to form 'glycosignaling domains' (GSD). GSL-dependent adhesion occurs through clustered GSLs, and is coupled with activation of signal transducers (cSrc, Src family kinase, Rho A, etc.). Clustered GSLs involved in cell adhesion are recognized by GSLs on counterpart cells (carbohydrate-to-carbohydrate interaction), or by lectins (e.g., siglecs, selectins). Our major effort in utilization of GSLs in medical science has been for: (i) cancer diagnosis and treatment (vaccine development) based on tumor-associated GSLs and glycoepitopes; (ii) genetically defined phenotype for susceptibility to E. coli infection; (iii) clear identification of physiological E-selectin epitope (myeloglycan) expressed on neutrophils and myelocytes; (iv) characterization of sialyl poly-LacNAc epitopes recognized as male-specific antigens. Utilization of these GSLs or glycoepitopes in development of anti-adhesion approach to prevent tumor metastasis, infection, inflammation, or fertilization (i.e., contraceptive) is discussed. For each approach, development of mimetics of key GSLs or glycoepitopes is an important subject of future study.