Functional Divergence in Solute Permeability between Ray-Finned Fish-Specific Paralogs of aqp10.

Aquaporin (Aqp) 10 is a member of the aquaglyceroporin subfamily of water channels, and human Aqp10 is permeable to solutes such as glycerol, urea, and boric acid. Tetrapods have a single aqp10 gene, whereas ray-finned fishes have paralogs of this gene through tandem duplication, whole-genome duplication, and subsequent deletion. A previous study on Aqps in the Japanese pufferfish Takifugu rubripes showed that one pufferfish paralog, Aqp10.2b, was permeable to water and glycerol, but not to urea and boric acid. To understand the functional differences of Aqp10s between humans and pufferfish from an evolutionary perspective, we analyzed Aqp10s from an amphibian (Xenopus laevis) and a lobe-finned fish (Protopterus annectens) and Aqp10.1 and Aqp10.2 from several ray-finned fishes (Polypterus senegalus, Lepisosteus oculatus, Danio rerio, and Clupea pallasii). The expression of tetrapod and lobe-finned fish Aqp10s and Aqp10.1-derived Aqps in ray-finned fishes in Xenopus oocytes increased the membrane permeabilities to water, glycerol, urea, and boric acid. In contrast, Aqp10.2-derived Aqps in ray-finned fishes increased water and glycerol permeabilities, whereas those of urea and boric acid were much weaker than those of Aqp10.1-derived Aqps. These results indicate that water, glycerol, urea, and boric acid permeabilities are plesiomorphic activities of Aqp10s and that the ray-finned fish-specific Aqp10.2 paralogs have secondarily reduced or lost urea and boric acid permeability.

Boric acid transport activity of marine teleost aquaporins expressed in Xenopus oocytes.

Marine teleosts ingest large amounts of seawater containing various ions, including 0.4 mM boric acid, which can accumulate at toxic levels in the body. However, the molecular mechanisms by which marine teleosts absorb and excrete boric acid are not well understood. Aquaporins (Aqps) are homologous to the nodulin-like intrinsic protein (NIP) family of plant boric acid channels. To investigate the potential roles of Aqps on boric acid transport across the plasma membrane in marine teleosts, we analyzed the function of Aqps of Japanese pufferfish (Takifugu rubripes) expressed in Xenopus laevis oocytes. Takifugu genome database contains 16 genes encoding the aquaporin family members (aqp0a, aqp0b, aqp1aa, aqp1ab, aqp3a, aqp4a, aqp7, aqp8bb, aqp9a, aqp9b, aqp10aa, aqp10bb, aqp11a, aqp11b, aqp12, and aqp14). When T. rubripes Aqps (TrAqps) were expressed in X. laevis oocytes, a swelling assay showed that boric acid permeability was significantly increased in oocytes expressing TrAqp3a, 7, 8bb, 9a, and 9b. The influx of boric acid into these oocytes was also confirmed by elemental quantification. Electrophysiological analysis using a pH microelectrode showed that these TrAqps increase B(OH)3 permeability. These results indicate that TrAqp3a, 7, 8bb, 9a, and 9b act as boric acid transport systems, likely as channels, in marine teleosts.

Boric acid transport activity of human aquaporins expressed in Xenopus oocytes.

Boric acid is a vital micronutrient that is toxic at high concentrations in animals. However, the mechanisms underlying boric acid transport in animal cells remain unclear. To identify the plasma membrane boric acid channels in animals, we analyzed the function of human aquaporins (AQPs), which are homologous to the nodulin-like intrinsic protein family of plant boric acid channels. When human AQPs were expressed in Xenopus laevis oocytes, the results of the swelling assay showed that boric acid permeability significantly increased in oocytes expressing AQP3, 7, 8, 9, and 10, but not in those expressing AQP1, 2, 4, and 5. The boric acid influxes of these oocytes were also confirmed by elemental quantification. Electrophysiological analysis using a pH microelectrode showed that these AQPs transported boric acid (B(OH)3 ) but not borate ions (B(OH)4- ). These results indicate that AQP3, 7, 8, 9, and 10 act as boric acid transport systems, likely as channels in humans.

A new class of pentapeptide KISS1 receptor agonists with hypothalamic-pituitary-gonadal axis activation.

The kisspeptin (Kp, Kp-54, metastin)/KISS1R system plays crucial roles in regulating the secretion of gonadotropin-releasing hormone. Continuous administration of nonapeptide Kp analogs caused plasma testosterone depletion, whereas bolus administration caused strong plasma testosterone elevation in male rats. To develop a new class of small peptide drugs, we focused on stepwise N-terminal truncation of Kp analogs and discovered potent pentapeptide analogs. Benzoyl-Phe-azaGly-Leu-Arg(Me)-Trp-NH2 (16) exhibited high agonist activity for KISS1R and excellent metabolic stability in rat serum. A single injection of a 4-pyridyl analog (19) at the N-terminus of 16 into male Sprague Dawley rats caused a robust increase in plasma luteinizing hormone levels, but unlike continuous administration of nonapeptide Kp analogs, continuous administration of 19 maintained moderate testosterone levels in rats. These results indicated that small peptide drugs can be successfully developed for treating sex hormone deficiency.

An integrative approach using real-world data to identify alternative therapeutic uses of existing drugs.

Different computational approaches are employed to efficiently identify novel repositioning possibilities utilizing different sources of information and algorithms. It is critical to propose high-valued candidate-repositioning possibilities before conducting lengthy in vivo validation studies that consume significant resources. Here we report a novel multi-methodological approach to identify opportunities for drug repositioning. We performed analyses of real-world data (RWD) acquired from the United States Food and Drug Administration's Adverse Event Reporting System (FAERS) and the claims database maintained by the Japan Medical Data Center (JMDC). These analyses were followed by cross-validation through bioinformatics analyses of gene expression data. Inverse associations revealed using disproportionality analysis (DPA) and sequence symmetry analysis (SSA) were used to detect potential drug-repositioning signals. To evaluate the validity of the approach, we conducted a feasibility study to identify marketed drugs with the potential for treating inflammatory bowel disease (IBD). Primary analyses of the FAERS and JMDC claims databases identified psycholeptics such as haloperidol, diazepam, and hydroxyzine as candidates that may improve the treatment of IBD. To further investigate the mechanistic relevance between hit compounds and disease pathology, we conducted bioinformatics analyses of the associations of the gene expression profiles of these compounds with disease. We identified common biological features among genes differentially expressed with or without compound treatment as well as disease-perturbation data available from open sources, which strengthened the mechanistic rationale of our initial findings. We further identified pathways such as cytokine signaling that are influenced by these drugs. These pathways are relevant to pathologies and can serve as alternative targets of therapy. Integrative analysis of RWD such as those available from adverse-event databases, claims databases, and transcriptome analyses represent an effective approach that adds value to efficiently identifying potential novel therapeutic opportunities.

A mutation in beta-tubulin and a sustained dependence on androgen receptor signalling in a newly established docetaxel-resistant prostate cancer cell line.

The mechanisms of docetaxel resistance in PC (prostate cancer) are unclear because of the lack of suitable experimental models, and no effective treatment exists for docetaxel-resistant PC. We established a docetaxel-resistant cell line, LNDCr, from an androgen-refractory PC cell line, LNCaP-hr, by intermittent exposure to docetaxel in vitro. The LNDCr cells harboured an F270I mutation in class I beta-tubulin, and demonstrated impaired tubulin polymerization by docetaxel. AR signalling was sustained in LNDCr cells, and AR knockdown suppressed the growth of LNDCr cells. These results suggest that an acquired mutation in beta-tubulin is associated with docetaxel resistance in PC and that a novel AR-targeted therapy is effective for docetaxel-resistant PC.

Id1 is down-regulated by hepatocyte growth factor via ERK-dependent and ERK-independent signaling pathways, leading to increased expression of p16INK4a in hepatoma cells.

Hepatocyte growth factor (HGF) inhibits the proliferation of several tumor cell lines and tumor growth in vivo. We showed previously that HGF induces cell cycle arrest at G1 in a human hepatoma cell line, HepG2, by up-regulating the expression of p16INK4a through strong activation of extracellular signal-regulated kinase (ERK). However, although essential, the activation was not sufficient for the up-regulation of p16. In this study, we examined regulatory mechanisms of p16 expression through a transcription factor, Ets, which has been shown previously to bind to the promoter. The treatment of HepG2 cells with HGF induced ERK-dependent phosphorylation of Ets, which leads to its activation, before the up-regulation of p16, suggesting that another factor suppresses Ets activity. We found that HGF reduces the amount of Id1, which is a dominant-negative inhibitor of Ets, leading to a decrease in Ets associated with Id1. Id1 was down-regulated via transcriptional regulation not via the ubiquitin-proteasome-mediated pathway. Inhibition of the HGF-induced high-intensity ERK activity had a modest effect on the Id1 down-regulation, and inhibition of the phosphatidylinositol 3-kinase pathway had no effect, showing that Id1 is regulated by ERK-dependent and -independent pathways other than the phosphatidylinositol 3-kinase pathway. Exogenously expressed Id1 suppressed the up-regulation of p16 by HGF and the antiproliferative effect of HGF. Knockdown of Id1 significantly enhanced the activity of the p16 promoter coordinately with the activation of ERK. Our results indicated that down-regulation of Id1 plays a key role in the inhibitory effect of HGF on cell proliferation and provides a molecular basis for cancer therapy with HGF.