Tatsuya Kawasaki

Functional divergence among lectins can arise even in the absence of variation in carbohydrate recognition domains (CRDs), yet the underlying mechanisms remain poorly understood. Here, we investigated the structure–function relationships of hRTLs, a family of six prototype galectins from the sponge Chondrilla australiensis. Recombinant hRTLs lacking the predicted 23-amino-acid non-canonical signal peptide were expressed in Escherichia coli and analyzed for glycan-binding specificity using glycan arrays. Four members (hRTL-1, 2, 5, and 6) exhibited glycan-binding activity, whereas hRTL-3 and 4 showed markedly weaker activity. hRTL-1 and 2 displayed similar binding profiles, including recognition of TF-related glycans, while hRTL-5 preferentially bound type-1 LacNAc and hRTL-6 recognized blood group-related glycans. Structural analyses revealed distinct oligomeric states, with dimeric and tetrameric species supported by native mass spectrometry and size-exclusion chromatography, while additional higher-molecular-weight (HMW) species were observed by non-heated SDS–PAGE. Far-UV CD spectroscopy further showed that representative active and low-activity hRTLs retained β-sheet-rich secondary structures. Notably, thermal stability assays showed that multimer-forming hRTLs retained hemagglutination activity after prolonged incubation at 60 °C, whereas non-multimerizing members exhibited reduced stability. These findings show that distinct oligomeric organizations are associated with functional diversification among structurally conserved galectin CRDs and suggest that modulation of multimerization may have contributed to the evolution of early metazoan lectins.

The structure of a lectin, OXYL, derived from the feather star, Anneissia japonica (phylum Echinodermata), was analyzed from biochemistry, informatics, and 3D structural prediction. OXYL’s primary structure resembled the globular domain of complement C1q in vertebrates. Structural simulations identified OXYL as part of the C1q/TNF superfamily, characterized by a jellyroll β-sandwich fold. The subunits can form monomer to nonamer (9-mer), with trimers being the most stable. However, gel permeation chromatography indicated tetramers as the significant form. In hemagglutination inhibition tests, OXYL bound type-2 N-acetyllactosamine (LacNAc: Galβ1-4GlcNAc) and inhibited agglutination but did not bind lactose (Lac: Galβ1-4Glc). Glycan microarray analysis with 20 immobilized glycans confirmed OXYL’s specificity for type-2 LacNAc and its sialic acid α2-3 linkage. The structural simulation showed a suitable molecular docking between type-2 LacNAc and the lectin rather than lactose. OXYL bound to the LacNAc glycan on the microarray was also elucidated to capture human IgG. This finding suggests that the invertebrate C1q/TNF family lectin will mimic vertebrate C1qs, despite lacking evolutionally antibody systems, possess the potential to interact with antibodies.

We here report the purification of a novel member of the galectin family, the β-galactoside-binding lectin hRTL, from the marine sponge Chondrilla australiensis. The hRTL lectin is a tetrameric proto-type galectin with a subunit molecular weight of 15.5 kDa, consisting of 141 amino acids and sharing 92% primary sequence identity with the galectin CCL from the congeneric species C. caribensis. Transcriptome analysis allowed for the identification of additional sequences belonging to the same family, bringing the total number of hRTLs to six. Unlike most other galectins, hRTLs display a 23 amino acid-long signal peptide that, according to Erdman degradation, is post-translationally cleaved, leaving an N-terminal end devoid of acetylated modifications, unlike most other galectins. Moreover, two hRTLs display an internal insertion, which determines the presence of an unusual loop region that may have important functional implications. The characterization of the glycan-binding properties of hRTL revealed that it had high affinity towards TF-antigen, sialyl TF, and type-1 N-acetyl lactosamine with a Galβ1-3 structure. When administered to DLD-1 cells, a colorectal carcinoma cell line expressing mucin-associated TF-antigen, hRTL could induce glycan-dependent cytotoxicity.

We here report the purification of a novel member of the galectin family, the β-Galactoside-binding lectin hRTL, from the marine sponge Chondrilla australiensis. The hRTL lectin is a tetrameric proto-type galectin with a subunit molecular weight of 15.5 kDa, consisting of 141 amino acids and sharing 92% primary sequence identity with the galectin CCL from the congeneric species C. caribensis. Transcriptome analysis allowed the identification of additional sequences belonging to the same family, bringing the total number of hRTLs to six. Unlike most other galectins, hRTLs display a 23 amino acids long signal peptide that, according to Erdman degradation, is post-translationally cleaved, leaving a N-terminal end devoid of acetylated modifications, unlike most other galectins. Moreover, two hRTLs display an internal insertion, which determines the presence of an unusual loop region that may have important functional implications. The characterization of the glycan binding properties of hRTL revealed that it had high affinity to-wards TF-antigen, sialyl TF, and type-1 N-acetyl lactosamine with a Galβ1-3 structure. When administered to DLD-1 cells, a colorectal carcinoma cell line expressing mucin-associated TF-antigen, hRTL could induce glycan-dependent cell death by activating MAP kinases, thereby inhibiting cancer cell proliferation.

SeviL, a galactoside-binding lectin previously isolated from the mussel Mytilisepta virgata, was demonstrated to trigger apoptosis in HeLa ovarian cancer cells. Here, we show that this lectin can promote the polarization of macrophage cell lines toward an M1 functional phenotype at low concentrations. The administration of SeviL to monocyte and basophil cell lines reduced their growth in a dose-dependent manner. However, low lectin concentrations induced proliferation in the RAW264.7 macrophage cell line, which was supported by the significant up-regulation of TOM22, a component of the mitochondrial outer membrane. Furthermore, the morphology of lectin-treated macrophage cells markedly changed, shifting from a spherical to an elongated shape. The ability of SeviL to induce the polarization of RAW264.7 cells to M1 macrophages at low concentrations is supported by the secretion of proinflammatory cytokines and chemokines, as well as by the enhancement in the expression of IL-6- and TNF-α-encoding mRNAs, both of which encode inflammatory molecular markers. Moreover, we also observed a number of accessory molecular alterations, such as the activation of MAP kinases and the JAK/STAT pathway and the phosphorylation of platelet-derived growth factor receptor-α, which altogether support the functional reprogramming of RAW264.7 following SeviL treatment. These results indicate that this mussel β-trefoil lectin has a concentration-dependent multifunctional role in regulating cell proliferation, phenotype, and death in macrophages, suggesting its possible involvement in regulating hemocyte activity in vivo.

Lithium is mainly excreted into urine, and a large fraction of lithium filtered through glomeruli is reabsorbed in the proximal tubule. However, the mechanisms responsible for lithium reabsorption remain unclear. We previously reported that the reabsorption of lithium was biphasic in rats, and that foscarnet inhibited lithium reabsorption with a high affinity type. We herein evaluated the effects of acetazolamide and foscarnet on the renal excretion of lithium in rats treated with lithium chloride at 2 doses. In rats intravenously injected with a bolus of 25 mg/kg lithium chloride, acetazolamide facilitated the urinary excretion of lithium, and increased the fractional excretion of lithium from 0.446 to 0.953, near the theoretically maximum value. At a dose of 2.5 mg/kg lithium chloride, the fractional excretion of lithium was 0.241 in control rats, 0.420 in rats administered acetazolamide, and 0.976 in rats administered acetazolamide and foscarnet. These results showed the potent inhibition of lithium reabsorption by acetazolamide and foscarnet in rats. And, it was exhibited that the effects of acetazolamide on lithium reabsorption differed with the dosages of lithium administered.

P-glycoprotein (encoded by MDR1) is a membrane transport protein expressed in the intestine, liver, kidney, placenta, and blood–brain barrier. It excludes various clinically important drugs from cells, such as verapamil, digoxin, tacrolimus, and vinblastine. Therefore, human P-glycoprotein plays important roles in drug absorption, distribution, and excretion. We reported previously that auraptene, a natural compound occurring widely in citrus fruit (e.g., grapefruit), inhibited P-glycoprotein-mediated drug transport. In this study, we investigated the effects of auraptene and other phenylpropanoids on P-glycoprotein expression using human intestinal epithelial LS174T cells and a reporter plasmid expressing 10.2 kbp of the upstream regulatory region of MDR1. Auraptene (7-geranyloxycoumarin), a prenylated coumarin, and several phenylpropanoids, such as 3-(4′-geranyloxy-3′-methoxyphenyl)-2-trans propenoic acid, derricidin [2′-hydroxy-4′-(prenyloxy)chalcone], and 3-(4′-geranyloxyphenyl)-propanoic acid, induced MDR1 promoter activity in LS174T cells. Overexpression of the nuclear receptor human pregnane X receptor gene (NR1I2) enhanced auraptene-induced MDR1 activation. Nuclear factor-kappaB inhibitors, Bay11-7082 and JSH-23, repressed MDR1 activation by auraptene. Western blot analyses showed the induction of P-glycoprotein expression in the auraptene-treated LS174T cells. The citrus phytochemical auraptene can induce the drug efflux transporter P-glycoprotein in human intestinal cells, and thus has the potential to cause food–drug interactions.

Purpose In this study, we investigated organic anion transporting polypeptide 2B1 (OATP2B1)-mediated uptake of fluorescent anions to better identify fluorescent substrates for in vitro OATP2B1 assays. The OATP2B1 is involved in the intestinal absorption and one of the pharmacokinetic determinants of orally administered drugs. Methods A microplate reader was used to determine the cellular accumulation of the fluorescent compounds into the OATP2B1 or the empty vector-transfected HEK293 cells. Results Two types of derivatives were found to be OATP2B1 substrates: heavy halogenated derivatives, such as 4′,5′-dibromofluorescein (DBF), and carboxylated derivatives, such as 5-carboxyfluorescein (5-CF). The DBF and 5-CF were transported in a time and concentration-dependent manner. The DBF was transported at a broad pH (pH 6.5–8.0) while 5-CF was transported at an acidic pH (pH 5.5–6.5). The K_m values were 0.818 ± 0.067 μM at pH 7.4 for DBF and 8.56 ± 0.41 μM at pH 5.5 for 5-CF. The OATP2B1 inhibitors, including atorvastatin, bromosulfophthalein, glibenclamide, sulfasalazine, talinolol, and estrone 3-sulfate, inhibited the DBF and the 5-CF transport. Contrastively, testosterone, dehydroepiandrosterone sulfate, and progesterone inhibited the DBF transport but stimulated the 5-CF transport. Natural flavonoid aglycones, such as naringenin and baicalein, also exhibited substrate-dependent effects in this manner. Conclusion We found two fluorescein analogs, DBF and 5-CF as the OATP2B1 substrates that exhibited substrate-dependent interactions.