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GPR120 is a receptor for long chain fatty acids and is expressed in small intestinal endocrine cells, L cells and adipose tissue. Activation of GPR120 promotes the secretion of incretin GLP-1, which is known to have effects on anti-metabolic syndrome. As such, GPR120 is a potential target of pharmaceuticals for type II diabetes. In this study, we performed ligand-screening for GPR120 on glycero- and sphingo-type lipids and their derivatives using a Transforming Growth Factor α-shedding assay. We found that phytosphingosine (PHS) activates GPR120 in a manner comparable to the natural ligand α-linolenic acid (ALA) and superior to that of the synthetic ligand GW9508. The IC50 value of PHS was 33.4 μM, of ALA was 31.0 μM and of GW9508 was 41.7 μM. Additionally, PHS-induced activation of GPR120 was inhibited by the specific antagonist AH7614. Many of the natural or synthetic ligands found thus far are compounds with carboxyl groups. However, PHS does not possess a carboxyl group, suggesting that its manner of interaction with GPR120 may be significantly different from that of other ligands. Since PHS is rich in the plasma membrane of yeast, our results imply that PHS found in fermented food could have effects on anti-diabetes through activation of GPR120.

Tissue remodelling and regeneration in various pathophysiological conditions (e.g. the processes of development, pregnancy, inflammation, wound healing, tissue regeneration, tumor growth, etc.) require angiogenesis, a dynamically coordinated response to stimuli from the extracellular microenvironment. During angiogenic and angiostatic responses, endothelial cells play a central role in the blood vessel formation and regression. Angiostatic responses, which are evoked by crucial factors such as VEGF and DLL4, have been elucidated. However, it has not been revealed, how endothelial cells process these conflicting signals. The study of VEGFR-Notch cross-signalling provided some clues. We discuss here the potential roles of cullin 3-based ubiquitin E3 ligases as key players in the process of various signals in endothelial cell function and angiogenesis. Our recent findings show that they function as units to process conflicting signalling crosstalk, epigenetic regulation of key factors, and functional barrier maintenance. We also expect more divergent roles of cullin 3-based ubiquitin E3 ligases in endothelial cell function and angiogenesis, and for their potential use as therapeutic targets., (© The Authors 2017. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.)

Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) is a member of the EGF family, each of which is produced as a type I transmembrane precursor. The juxtamembrane domain of proHB-EGF, a precursor of HB-EGF, is cleaved by a disintegrin and metalloproteases. HB-EGF is released into the extracellular space and strongly activates EGF receptor. The relevance of better understanding proHB-EGF shedding relates to the importance of the process in the proliferation, differentiation and survival of various types of cells. Shedding of proHB-EGF is normally evaluated using an alkaline phosphatase-tagged proHB-EGF assay or a western blotting assay that involves multiple cells, which makes it difficult to observe spatiotemporal differences in the activities of the individual cells. In this study, we developed a fluorescent proHB-EGF-based metalloprotease biosensor, named Fluhemb, to visualize spatiotemporal regulation of proHB-EGF shedding in individual cells using a simple method that measures changes in fluorescence ratios. Fluhemb might be very useful for detecting the activity of proHB-EGF shedding in various types of cells under different conditions in vitro and in vivo.

Transmembrane proteins on the cell surface dynamically move in the sea of phospholipids. During the process of cell adhesion, migration and proliferation, physical interactions of transmembrane proteins such as integrins and receptor tyrosine kinases (RTKs) on the cell surface constantly vary. The enzyme-mediated activation of radical source (EMARS) reaction, a newly developed biochemical labelling method for cell surface molecules clustering in living cells, is a powerful tool for capturing new partners even if they only transiently cluster with the interesting target molecules during a biological process such as cell adhesion, migration, invasion or proliferation. The EMARS reaction was applied for investigating new partner RTKs to an adhesion molecule integrin β1, resulting in the identification of ErbB4. This study further reveals that the association of integrin β1 and ErbB4 occurs in a spatiotemporally regulated manner at an early phase within 2 h of seeding cells and that this induced activation of ErbB4 tyrosine kinase, which is required for integrin-dependent cell migration (Yamashita, R., Kotani, N., Ishiura, Y., Higahsiyama, S., and Honke, K. Spatiotemporally-regulated interaction between b1 integrin and ErbB4 that is involved in fibronectin-dependent cell migration. J Biochem 2011;149:347-355). The EMARS reaction is also currently lighting up intriguing new partners of target therapeutic molecules.

Both receptor tyrosine kinases epidermal growth factor receptors (EGFRs) and their ligands are transmembrane proteins. It has been known that ligand binding activates cytoplasmic tyrosine kinase domains of EGFRs, resulting in the transduction of signals for cell proliferation, migration, differentiation or survival. In an EGFRs-ligands system, however, signal transduction occurs not only unidirectionally but also bidirectionally, which is regulated by cell-cell contact and proteolytic cleavage. Recent studies of proteolytic cleavage 'ectodomain shedding' of EGFRs and their ligands mediated by membrane-type metalloproteinases, a disintegrin and metalloproteinases have been unveiling novel functions and molecular mechanism of their remnant peptides. In addition, the study of the remnant peptide signalling would be essential for understanding the physiological and pathological relevance of anti-shedding therapeutic strategies for diseases such as cancer.

Integrins are widely expressed cell surface molecules that mediate cell attachment to extracellular matrix (ECM) proteins. They also interact with molecules on their own membranes, and these cis-interactions play a crucial role in integrin-dependent cellular responses. We herein analysed what molecules interact with β1 integrin during biological events induced by cell attachment to different ECM proteins, using a recently established reaction, the enzyme-mediated activation of radical sources (EMARS). The interactions between β1 integrin and receptor tyrosine kinases including EGFR and ErbB4 reached a peak at 2 h after seeding HeLa S3 cells onto the ECM proteins. The peak of phosphorylation of ErbB4 (at 2 h after seeding the cells onto fibronectin) coincided with the peak of the interaction with β1 integrin, while that of EGFR (at 1 day) did not. Accompanying with these findings, suppression of cell migration by a pharmacological inhibitor of the ErbB family receptors, PD168393 and an anti-ErbB4 neutralizing antibody, 12D8 was observed at 2 h after seeding. Taken together, it is deduced that interactions between β1 integrin and ErbB4 occur in a spatiotemporally-regulated manner, and such interaction contributes to the integrin-dependent cell migration.

The present study was undertaken in an attempt to clarify the pathway by which hyperosmotic stress induces HB-EGF gene expression in rat aortic smooth muscle cells (RASMC). Hyperosmotic stress induced by a high concentration of glucose or mannitol resulted in an increase in HB-EGF mRNA level in a dose- and time-dependent manner. HB-EGF induction was blocked by curcumin, a c-jun/fos antisense oligonucleotide and a dominant-negative mutant of JNK1. Electrophoretic mobility shift assay also showed the involvement of AP-1 in HB-EGF gene expression by glucose. In addition, hyperosmotic stress induced rapid phosphorylation of Pyk2 in RASMC. TPA and calcium chelating agents (BAPTA-AM and EGTA) blocked Pyk2 phosphorylation and HB-EGF gene expression. Furthermore, HB-EGF gene expression and JNK activation by hyperosmotic stress were sensitive to PP2, an Src kinase-specific inhibitor. These findings indicate that hyperosmotic stress activates JNK via calcium-Pyk2 signaling cascades, which in turn induce HB-EGF gene expression.

Neural- and thymus-derived activator for ErbB kinases (NTAK) is a recently described member of the neuregulin family that binds directly to ErbB3 and ErbB4 and transactivates ErbB2. Rat NTAK has at least five alternative-spliced isoforms: alpha1, alpha2a, alpha2b, beta, and gamma. In order to understand their biological properties, this study focused on the NTAK alpha2a and beta isoforms, which have different EGF-like domains. The effect of these isoforms on cell growth and tyrosine phosphorylation in human breast cancer cells, MDA-MB-453 and T47D, was examined using the recombinant proteins. In terms of cell growth, NTAKalpha2a and NTAKbeta preferentially stimulate T47D cells and MDA-MB-453 cells, respectively, in a dose-dependent manner. Although both NTAKs induce the highest level of tyrosine phosphorylation of ErbB2, NTAKalpha2a and NTAKbeta preferentially induce ErbB3 and ErbB4 phosphorylation, respectively. Thus, NTAKalpha2a and NTAKbeta stimulate cell growth in different ways, by means of different combinations of receptors.

A human histiocytic lymphoma cell line, U-937 cells, secretes several vascular endothelial cell growth inhibitors including leukemia inhibitory factor, oncostatin M, tumor necrosis factor-alpha, and transforming growth factor-beta1. Characterization of partially purified fractions from the conditioned media of phorbol ester-treated U-937 cells suggested the existence of unknown endothelial growth inhibitors. Using a combination of copper affinity, heparin affinity, cation exchange, and reversed phase liquid chromatographies, a growth inhibitor for endothelial cells was purified to homogeneity from conditioned media. The purified growth inhibitor migrated as a 65 kDa band on SDS-polyacrylamide gel electrophoresis under both reducing and nonreducing conditions. Microsequencing analyses of the tryptic fragments of the growth inhibitor and a BLAST search analysis revealed a unique sequence showing no homology to known proteins. The purified protein inhibited endothelial cell growth in a dose-dependent manner, but had no effect on smooth muscle cell growth. The factor also blocked endothelial cell growth induced by both fibroblast growth factor-2 and vascular endothelial growth factor, and was additively effective in inhibiting the growth of endothelial cells by U-937 cell-derived endothelial cell growth inhibitors. Thus, this factor appears to be a novel inhibitor with specificity for vascular endothelial cells, and is tentatively called endothelial cell inhibitor (ECI) in this study.

A novel member of the epidermal growth factor (EGF) family, the neural- and thymus-derived activator for ErbB kinases (NTAK), has been purified and cloned. Five alternative spliced isoforms have been detected in the rat adrenal pheochromocytoma cell line, PC-12 cells. The rat NTAK alpha2a isoform exhibits 94% identity in its primary sequence with the human NTAK alpha isoform. In vivo, NTAK is only expressed in the brain of rat E11.5 embryos, and in the brain and thymus of adult rats. The soluble 46 kDa form binds directly to ErbB3 and B4, but not to ErbB1 or B2. NTAK, however, transactivates ErbB1 and B2 via heterodimerization with ErbB3 or B4. NTAK stimulates the differentiation of MDA-MB-453 cells and competitively inhibits the binding of [125I]neuregulin to these cells. In addition to these neuregulin-like properties, NTAK exhibits limited structural homology to neuregulins in the immunoglobulin (Ig)-like, EGF-like, and hydrophobic domains. Thus, NTAK appears to be a new member of the EGF family displaying neuregulin properties.

Heparin/heparan-sulfate proteoglycan (HSPG) binds to heparin-binding epidermal growth factor-like growth factor (HB-EGF) through its heparin-binding domain (HBD), which consists of 21 amino acid residues (P21). The CD9 antigen also interacts with a membrane-anchored form of HB-EGF (proHB-EGF) and enhances its juxtacrine activity. The CD9 antigen potentiates the juxtacrine activity of both proHB-EGF and proamphiregulin, but has no effect on proTGF-alpha. While both HB-EGF and amphiregulin contain an HBD, TGF-alpha does not. This suggests that the HBD of HB-EGF is also involved in CD9 antigen binding. Mutant CHO cells which lack HSPG recovered their capacity to bind to immobilized P21 when transfected with CD9 antigen cDNA. This binding was competitively inhibited by heparin in a dose-dependent manner. The interactions between synthetic peptides corresponding to the extracellular domain of CD9 antigen and the immobilized P21 were analyzed with surface plasmon resonance. The 119VIKEVQEFYKDTYNKLKTKD138 sequence of the CD9 antigen is thought to represent the binding site for HB-EGF. The k(D) values for heparin/P21 and 119V-D138/P21 were (2.82+/-0.10) x 10(-8) M and (3.71+/-0.71) x 10(-5) M, respectively. These results suggest that the 119V-D138 sequence of the CD9 antigen is the site which interacts with the HBD and may play an essential role in the upregulation of the juxtacrine activity of proHB-EGF.