A novel agonist with homobivalent single-domain antibodies that bind the FGF receptor 1 domain III functions as an FGF2 ligand.

Fibroblast growth factor (FGF) is a multifunctional protein that exhibits a wide range of biological effects. Most commonly, it acts as a mitogen, but it also has regulatory, morphological, and endocrine effects. The four receptor subtypes of FGF are activated by more than 20 different FGF ligands. FGF2, one of the FGF ligands, is an essential factor for cell culture in stem cells for regenerative medicine; however, recombinant FGF2 is extremely unstable. Here, we successfully generated homobivalent agonistic single-domain antibodies (variable domain of heavy chain of heavy chain antibodies referred to as VHHs) that bind to domain III and induce activation of the FGF receptor 1 and thus transduce intracellular signaling. This agonistic VHH has similar biological activity (EC50) as the natural FGF2 ligand. Furthermore, we determined that the agonistic VHH could support the proliferation of human-induced pluripotent stem cells (PSCs) and human mesenchymal stem cells, which are PSCs for regenerative medicine. In addition, the agonistic VHH could maintain the ability of mesenchymal stem cells to differentiate into adipocytes or osteocytes, indicating that it could maintain the properties of PSCs. These results suggest that the VHH agonist may function as an FGF2 mimetic in cell preparation of stem cells for regenerative medicine with better cost effectiveness.

Construction of a Humanized Artificial VHH Library Reproducing Structural Features of Camelid VHHs for Therapeutics.

A variable domain of heavy chain antibody (VHH) has different binding properties than conventional antibodies. Conventional antibodies prefer binding to the convex portion of the antigen, whereas VHHs prefer epitopes, such as crevices and clefts on the antigen. Therefore, developing candidates with the binding characteristics of camelid VHHs is important. Thus, To this end, a synthetic VHH library that reproduces the structural properties of camelid VHHs was constructed. First, the characteristics of VHHs were classified according to the paratope formation based on crystal structure analyses of the complex structures of VHHs and antigens. Then, we classified 330 complementarity-determining region 3 (CDR3) structures of VHHs from the Protein Data Bank (PDB) into three loop structures: Upright, Half-Roll, and Roll. Moreover, these structures depended on the number of amino acid residues within CDR3. Furthermore, in the Upright loops, several amino acid residues in the FR2 are involved in the paratope formation, along with CDR3, suggesting that the FR2 design in the synthetic library is important. A humanized synthetic VHH library, comprising two sub-libraries, Upright and Roll, was constructed and named PharmaLogical. A validation study confirmed that our PharmaLogical library reproduces VHHs with the characteristics of the paratope formation of the camelid VHHs, and shows good performance in VHH screening.

Interleukin-17A Peptide Aptamers with an Unexpected Binding Moiety Selected by cDNA Display under Heterogenous Conditions.

Peptide-based drugs are an attractive new modality of therapeutics, and in vitro selection from a large-scale library is a powerful way to identify new lead sequences. In conventional screenings, peptide specificity and stability in physiological heterogenous environments are not evaluated, which sometimes makes subsequent optimization difficult. Here we show that selection using a cDNA display system can be performed in a high percentage of serum and that this might be an option to select molecules with high potency and stability in a biological context. Specifically, we chose interleukin-17A as a target protein and performed in vitro selection of cyclic peptide aptamers from a library of approximately 1012 members in the presence of serum. The selected molecules had nanomolar affinity to the target and were stable in serum. Interestingly, we found that a component of the DNA linker that connected the peptide and cDNA may play a pivotal role in target binding.

Characterization of Δ(G970-T1122)-CFTR, the most frequent CFTR mutant identified in Japanese cystic fibrosis patients.

A massive deletion over three exons 16-17b in the CFTR gene was identified in Japanese CF patients with the highest frequency (about 70% of Japanese CF patients definitely diagnosed). This pathogenic mutation results in a deletion of 153 amino acids from glycine at position 970 (G970) to threonine at 1122 (T1122) in the CFTR protein without a frameshift. We name it Δ(G970-T1122)-CFTR. In the present study, we characterized the Δ(G970-T1122)-CFTR expressed in CHO cells using immunoblots and a super resolution microscopy. Δ(G970-T1122)-CFTR proteins were synthesized and core-glycosylated but not complex-glycosylated. This observation suggests that the Δ(G970-T1122) mutation can be categorized into the class II mutation like ΔF508. However, VX-809 a CFTR corrector that can help maturation of ΔF508, had no effect on Δ(G970-T1122). Interestingly C-terminal FLAG tag seems to partially rescue the trafficking defect of Δ(G970-T1122)-CFTR; however the rescued Δ(G970-T1122)-CFTR proteins do not assume channel function. Japanese, and perhaps people in other Asian nations, carry a class II mutation Δ(G970-T1122) with a higher frequency than previously appreciated. Further study of the Δ(G970-T1122)-CFTR is essential for understanding CF and CFTR-related diseases particularly in Asian countries.

The Impact of Preoperative Enteral Nutrition Enriched with Eicosapentaenoic Acid on Postoperative Hypercytokinemia after Pancreatoduodenectomy: The Results of a Double-Blinded Randomized Controlled Trial.

AIMS: To investigate whether preoperative enteral diets -enriched in eicosapentaenoic acid (EPA) supplements could reduce the incidence of hypercytokinemia after pancreatoduodenectomy (PD) in a double-blinded randomized -controlled trial. METHODS: Patients with resectable periampullary cancer were randomized into either the control group or the treatment group. Patients in the treatment group received oral supplementation (600 kcal/day) containing EPA for 7 days before surgery. Patients in the control group received isocaloric isonitrogenous standard nutrition (600 kcal/day) without EPA for 7 days before surgery. The primary endpoint was postoperative serum concentrations of interleukin-6 (IL-6). The secondary endpoints were the postoperative nutritional status and the incidence of postoperative infectious complications. RESULTS: Twenty-four patients were enrolled in the present study. After exclusion, 20 patients (control group, n = 9; treatment group, n = 11) were analyzed. There were no significant differences in the curves for the serum concentration of IL-6 (p = 0.68) or the incidence of infectious complications between the 2 groups (control group: 78%, treatment group: 55%, p = 0.37). CONCLUSIONS: The results of a double-blinded randomized controlled trial indicated that preoperative immunonutrition had no marked impact on the rates of postoperative hypercytokinemia or infectious complications after PD.

Comparative proteomic analysis identifies exosomal Eps8 protein as a potential metastatic biomarker for pancreatic cancer.

Exosomes are small vesicles found in extracellular environments including blood, urine, and cell culture medium. Their contents are cell­type specific, and molecules embedded in exosomes can be useful fluid­based clinical biomarkers. To identify proteins with metastatic marker potential, we conducted a comparative exosomal proteome analysis using human pancreatic cancer cell lines derived from metastasis, ascites, and primary tumors. Metastatic potential of cell lines was assessed by migratory and invasive activities. A pancreatic cancer cell line from metastasis (SU.86.86) revealed 23­fold and 20­fold increases in cell migratory and invasive activities, respectively, compared to the MIA PaCa­2 cell line derived from primary tumor cells. Liquid chromatography­mass spectrometry­based proteome analysis and subsequent validation by immunoblot analysis revealed that epidermal growth factor receptor pathway substrate 8 (Eps8) was highly abundant in exosomes from metastasis­derived SU.86.86 cells. Comparison of 12 pancreatic cancer cell lines derived from different stages of malignancy revealed a strong relationship between exosomal Eps8 protein levels and cell motile activities (migration: r=0.85, P=4.2x10­4; invasion: r=0.60, P=3.2x10­2). Conversely, relationships between intracellular Eps8 protein levels and cell motile activities were moderate (migration: r=0.65, P=2.0x10­2; invasion: r=0.51, P=9.2x10­2). It was therefore concluded that exosomal Eps8 protein levels were correlated with the migratory cell potential of human pancreatic cancer cells, indicating that exosomal Eps8 has the potential to be a metastatic biomarker for human pancreatic cancer.

A novel splice variant of XIAP-associated factor 1 (XAF1) is expressed in peripheral blood containing gastric cancer-derived circulating tumor cells.

BACKGROUND: XIAP-associated factor 1 (XAF1) is ubiquitously expressed in normal tissues, but its suppression in cancer cells is strongly associated with tumor progression. Although downregulation of XAF1 is observed in tumors, its expression profile in the peripheral blood of cancer patients has not yet been investigated. Here, we identified a novel XAF1 splice variant in cancer cells and then investigated the expression level of this variant in peripheral blood containing gastric cancer-derived circulating tumor cells (CTCs). METHODS: To identify splice variants, RT-PCR and DNA sequencing were performed in mRNAs extracted from many cancer cells. We then carried out quantitative RT-PCR to investigate expression in peripheral blood from all 96 gastric cancer patients and 22 healthy volunteers. RESULTS: The XAF1 variant harbored a premature termination codon (PTC) and was differentially expressed in highly metastatic cancer cells versus the parental cells, and that nonsense-mediated mRNA decay (NMD) was suppressed in the variant-expressing cells. Furthermore, splice variants of XAF1 were upregulated in peripheral blood containing CTCs. In XAF1 variant-expressing patients, the expression levels of other NMD-targeted genes also increased, suggesting that the NMD pathway was suppressed in CTCs. CONCLUSIONS: Our study identified a novel splice variant of XAF1 in cancer cells. This variant was regulated through the NMD pathway and accumulated in NMD-suppressed metastatic cancer cells and peripheral blood containing CTCs. The presence of XAF1 transcripts harboring the PTC in the peripheral blood may be useful as an indicator of NMD inhibition in CTCs.

Carcinoembryonic antigen-related cell adhesion molecule 4 (CEACAM4) is specifically expressed in medullary thyroid carcinoma cells.

Carcinoembryonic antigen (CEA), an oncofetal cell surface glycoprotein, has been widely used as a human tumor marker due to its high expression in tumors and secretion to serum. It belongs to the immunoglobulin superfamily named CEA-related cell adhesion molecule (CEACAM) family. Members of this family are detected in various cancers and have been shown to be involved in cancer growth and invasion. In this study, we examined the mRNA expression profiles of CEACAM family members including CEACAM1, CEACAM3, CEACAM4, CEACAM5 (CEA), CEACAM6, CEACAM7, and CEACAM8 in various tumor cell lines. Our screening data indicated that the mRNA expression patterns of CEACAMs in TT cells, which are derived from medullary thyroid carcinoma (MTC), were distinct from other tumor cell lines. Additionally, CEACAM4 was only expressed in TT cells, in which two novel splice variants of CEACAM4 were expressed. These findings suggested that production of CEA and CEA-related molecules in MTC may be distinct from other tumor-based production of those molecules and that the specific expression of CEACAM4 would make possible to differentiate between MTC and other CEA-producing tumors.

Exosome-mediated extracellular release of polyadenylate-binding protein 1 in human metastatic duodenal cancer cells.

Exosomes are small vesicles secreted from cells that transport their embedded molecules through bidirectional exocytosis- and endocytosis-like pathways. Expression patterns of exosomal molecules such as proteins and RNAs can be indicative of cell type since their signature is thought to be unique among cells. Using human primary (AZ-521) and metastatic (AZ-P7a) duodenal cancer cell lines, we conducted a comparative exosomal proteome analysis to identify proteins with metastatic marker potential. As determined by LC-MS/MS and Western blot analyses, polyadenylate-binding protein 1 (PABP1) was found to be predominantly abundant in AZ-P7a exosomes. The amount of exosomal PABP1 in AZ-P7a cells increased by treating the cells with inhibitors for the classical ER/Golgi secretory pathway (brefeldin A and monensin) and the ubiquitin-proteasome pathway (MG-132 and PYR-41). Treatment of AZ-P7a cells with the neutral sphingomyelinase inhibitor GW4869, which suppresses exosome release, not only reduced the amount of exosomal PABP1 but also produced PABP1-immunoreactive products cleaved via a proteolysis-like process. Taken together, these results suggest that AZ-P7a cells do not tolerate intracellular PABP1 accumulation and are thus exported into the extracellular milieu by the exosome-mediated pathway. In addition, PABP1 has a potential use as a biomarker for metastatic duodenal cancer.

Novel protein isoforms of carcinoembryonic antigen are secreted from pancreatic, gastric and colorectal cancer cells.

BACKGROUND: Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) is an oncofetal cell surface glycoprotein. Because of its high expression in cancer cells and secretion into serum, CEA has been widely used as a serum tumor marker. Although other members of CEACAM family were investigated for splice variants/variants-derived protein isoforms, few studies about the variants of CEACAM5 have been reported. In this study, we demonstrated the existence of novel CEACAM5 splice variants and splice variant-derived protein isoforms in gastrointestinal cancer cell lines. RESULTS: We identified two novel CEACAM5 splice variants in gastrointestinal (pancreatic, gastric, and colorectal) cancer cell lines. One of the variants possessed an alternative minor splice site that allowed generation of GC-AG intron. Furthermore, CEA protein isoforms derived from the novel splice variants were expressed in cancer cell lines and those protein isoforms were secreted into the culture medium. Although CEA protein isoforms always co-existed with the full-length protein, the secretion patterns of these isoforms did not correlate with the expression patterns. CONCLUSIONS: This is the first study to identify the expression of CEA isoforms derived from the novel splice variants processed on the unique splice site. In addition, we also revealed the secretion of those isoforms from gastrointestinal cancer cell lines. Our findings suggested that discrimination between the full-length and identified protein isoforms may improve the clinical utility of CEA as a tumor marker.

Methods to examine the impact of nonsynonymous SNPs on protein degradation and function of human ABC transporter.

Clinical studies have strongly suggested that genetic polymorphisms and/or mutations of certain ATP-binding cassette (ABC) transporter genes might be regarded as significant factors affecting patients' responses to medication and/or the risk of diseases. In the case of ABCG2, certain single nucleotide polymorphisms (SNPs) in the encoding gene alter the substrate specificity and/or enhance endoplasmic reticulum-associated degradation (ERAD) of the de novo synthesized ABCG2 protein via the ubiquitin-mediated proteasomal proteolysis pathway. Hitherto accumulated clinical data imply that several nonsynonymous SNPs affect the ABCG2-mediated clearance of drugs or cellular metabolites, although some controversies still exist. Therefore, we recently developed high-speed functional screening and ERAD of ABC transporters so as to evaluate the effect of genetic polymorphisms on their function and protein expression levels in vitro. In this chapter we present in vitro experimental methods to elucidate the impact of nonsynonymous SNPs on protein degradation of ABCG2 as well as on its transport function.

Investigation of proNT/NMN secretion from small cell lung carcinoma cells using a mouse xenograft model.

Proneurotensin/neuromedin N (proNT/NMN), the precursor of neurotensin (NT) and neuromedin N (NMN), is produced by cancer tissues derived from the pancreas and colon. NT stimulates tumor growth and proliferation through its receptors; however, little is known about the precursor molecule in cancer tissues. We previously demonstrated that proNT/NMN is secreted from small cell lung carcinoma (SCLC) cell lines in serum-free conditioned medium, but not from non-small cell lung carcinoma (NSCLC) cell lines. It was suggested that this precursor may serve as a tumor marker for SCLC. In this study, we established in vivo xenograft models to evaluate the possibility of proNT/NMN as a specific tumor marker. SBC3 cells, derived from human SCLC, were inoculated into mice, and the proNT/NMN levels in plasma and tumor tissues were detected using specific antibodies. In contrast to control mouse plasma, the proNT/NMN levels in tumor-bearing mice increased as the tumors grew, and the elevated plasma proNT/NMN levels were decreased by tumor resection. Moreover, proNT/NMN was expressed in SBC3 tumors, suggesting that proNT/NMN was secreted into blood from the tumor, and this secretion may be specific to SCLC.

Novel protein extraction approach using micro-sized chamber for evaluation of proteins eluted from formalin-fixed paraffin-embedded tissue sections.

We describe a novel antigen-retrieval method using a micro-sized chamber for mass spectrometry (MS) analysis to identify proteins that are preferentially eluted from formalin-fixed paraffin-embedded (FFPE) samples. This approach revealed that heat-induced antigen retrieval (HIAR) from an FFPE sample fixed on a glass slide not only improves protein identification, but also facilitates preferential elution of protein subsets corresponding to the properties of antigen-retrieval buffers. Our approach may contribute to an understanding of the mechanism of HIAR.

Ubiquitin-mediated proteasomal degradation of ABC transporters: a new aspect of genetic polymorphisms and clinical impacts.

The interindividual variation in the rate of drug metabolism and disposition has been known for many years. Pharmacogenomics dealing with heredity and response to drugs is a part of science that attempts to explain variability of drug responses and to search for the genetic basis of such variations or differences. Genetic polymorphisms of drug metabolizing enzymes and drug transporters have been found to play a significant role in the patients' responses to medication. Accumulating evidence demonstrates that certain nonsynonymous polymorphisms have great impacts on the protein stability and degradation, as well as the function of drug metabolizing enzymes and transporters. The aim of this review article is to address a new aspect of protein quality control in the endoplasmic reticulum and to present examples regarding the impact of nonsynonymous single-nucleotide polymorphisms on the protein stability of thiopurine S-methyltransferase as well as ATP-binding cassette (ABC) transporters including ABCC4, cystic fibrosis transmembrane conductance regulator (CFTR, ABCC7), ABCC11, and ABCG2. Furthermore, we will discuss the molecular mechanisms underlying posttranslational modifications (intramolecular and intermolecular disulfide bond formation and N-linked glycosylation) and ubiquitin-mediated proteasomal degradation of ABCG2, one of the major drug transporter proteins in humans.

Production of cells with targeted integration of gene variants of human ABC transporter for stable and regulated expression using the Flp recombinase system.

The vector-mediated introduction of cDNA into mammalian cells by calcium phosphate co-precipitation or permeation with lipofectamine is widely used for the integration of cDNA into genomic DNA. Such integration, however, of cDNA occurs randomly at unpredictable sites in the host's chromosomal DNA, and the number of integrated recombinant DNAs is not controllable. To overcome this problem, we developed the Flp-In method to integrate one single copy of cDNA encoding the human ABC transporter ABCG2 into FRT-tagged genomic DNA. Examination of more than 20 metaphase spreads for both fluorescence in situ hybridization (FISH) mapping and multicolor-FISH analysis revealed that ABCG2 cDNA was incorporated into the telomeric region of the short arm on one of chromosomes 12 in Flp-In-293 cells. By using those cells, we investigated the effect of genetic polymorphisms and post-translational modifications of human ABC transporter ABCG2 on the protein expression and degradation. On the basis of our experience, it has been concluded that the Flp recombinase system provides a useful tool to quantitatively analyze the protein stability and endoplasmic reticulum (ER)-associated degradation of proteins like the ABC transporter. This system is also applicable for similar studies of the biogenesis of other proteins using the secretory pathway as well as proteins with other cellular localizations.

Disruption of N-linked glycosylation enhances ubiquitin-mediated proteasomal degradation of the human ATP-binding cassette transporter ABCG2.

The human ATP-binding cassette (ABC) transporter, ABCG2 (BCRP/MXR/ABCP), is a plasma membrane protein containing intramolecular and intermolecular disulfide bonds and an N-linked glycan at Asn596. We have recently reported that the intramolecular disulfide bond is a critical checkpoint for determining the degradation fates of ABCG2. In the present study, we aimed to analyze quantitatively the impact of the N-linked glycan on the protein stability of ABCG2. For this purpose, we incorporated one single copy of ABCG2 cDNA into a designated site of genomic DNA in Flp-In-293 cells to stably express ABCG2 or its variant proteins. When ABCG2 wild type-expressing cells were incubated with various N-linked glycosylation inhibitors, tunicamycin profoundly suppressed the protein expression level of ABCG2 and, accordingly, reduced the ABCG2-mediated cellular resistance to the cancer chemotherapeutic SN-38. When Asn596 was converted to Gln596, the resulting variant protein was not glycosylated, and its protein level was about one-third of the wild type level in Flp-In-293 cells. Treatment with MG132, a proteasome inhibitor, increased the level of the variant protein. Immunoblotting with anti-ubiquitin IgG1k after immunoprecipitation of ABCG2 revealed that the N596Q protein was ubiquitinated at levels that were significantly enhanced by treatment with MG132. Immunofluorescence microscopy demonstrated that treatment with MG132 increased the level of ABCG2 N596Q protein both in intracellular compartments and in the plasma membrane. In conclusion, we propose that the N-linked glycan at Asn596 is important for stabilizing de novo-synthesized ABCG2 and that disruption of this linkage results in protein destabilization and enhanced ubiquitin-mediated proteasomal degradation.

Quality control of human ABCG2 protein in the endoplasmic reticulum: ubiquitination and proteasomal degradation.

Human ATP-binding cassette (ABC) transporter ABCG2 (BCRP/MXR/ABCP) is a plasma membrane protein carrying intra- and inter-molecular disulfide bonds and an N-linked glycan. Both disulfide bond formation and N-glycosylation are critical check points determining the stability and degradation fate of ABCG2 protein in the endoplasmic reticulum (ER). Misfolded ABCG2 protein without those post-translational modifications is removed from the ER by retrotranslocation to the cytosol compartment, ubiquitination by ubiquitin ligase, and finally degradation by proteasomes. Certain non-synonymous SNP variants of ABCG2 undergo such ER-associated degradation (ERAD).