Identification of Wap65, a human homologue of hemopexin as a copper-inducible gene in swordtail fish, Xiphophorus helleri

Abstract

Copper is one of the major heavy metal pollutants found in the aquatic environment. Therefore, it is important for determining the genes that play a key role in copper metabolism in aquatic organisms. This study, thus, aimed to identify a new copper-inducible gene in swordtail fish, Xiphophorus helleri. Using ACP-based RT-PCR coupled with RLM-RACE, we cloned Wap65, a mammalian homologue of hemopexin gene. The gene exhibits high identity at amino acid levels with the Wap65 gene of other fish species (42-68%) and mammalian hemopexin gene (35-37%). In addition, ten cysteine and two histidine residues are conserved in the swordtail fish Wap65 gene. These cysteine residues are vital for structural integrity, and histidine residues provide high binding affinity towards heme. As revealed by RT-PCR, the gene was upregulated in swordtail fish that were exposed to copper in a dose- and time-dependent manner. Therefore, the identification of Wap65, a mammalian homologue of hemopexin, as a new copper-inducible gene will provide greater insight into the role of this gene in copper metabolism.

Environmental stress-related gene expression and blood physiological responses in olive flounder (Paralichthys olivaceus) exposed to osmotic and thermal stress

“…Wap65 was first detected as a glycoprotein in the plasma of goldfish (Kikuchi et al 1993) and has since been identified in medaka (Oryzias latipes), channel catfish (Ictalurus punctatus), swordtail fish (Xiphophorus hellerii), and fugu (Takifigu rubripes) (Kikuchi et al 1995;Kinoshita et al 2001;Hirayama et al 2003Hirayama et al , 2004Nakaniwa et al 2005;Aliza et al 2008). Teleost Wap65 shares significant sequence identity with mammalian hemopexin and has been suggested to play roles in iron homeostasis, antioxidant activity, bacteriostatic defense, nerve regeneration, transfer of heme, and the expression of genes known to promote cell survival (Delanghe and Langlois 2001).…”

Genomic Organization and Isoform-Dependent Expression Patterns of Wap65 genes in Various Tissues during Immune Challenges in the Mud Loach Misgurnus mizolepis

“…Besides its essential function in thermal acclimation, this serum glycoprotein is also involved in various other cellular pathways, especially those relating to innate immunity (Sha et al, 2008). The potential role of WAP65 proteins as an immune modulator has been demonstrated in several previous studies on dynamic modulations in fish tissues during immune-stimulating challenges and/or environmental perturbation treatments (Aliza et al, 2008;Sha et al, 2008;Shi et al, 2010). Teleosts typically possess two functional WAP65 isoforms (WAP65-1 and WAP65-2) and previous reports have suggested that these two isoforms have been functionally diversified or subfunctionalized, where the fish WAP65-2 isoform generally has a closer orthology to human hemopexin (HPX) than WAP65-1 (Cho et al, 2012;Lee et al, 2014).…”

Genetic Organization of Two Types of Flounder Warm-Temperature Acclimation-Associated 65-kDa Protein and Their Gene Expression Profiles

“…2,[7][8][9][10][11][12][13][14][15] Teleost Wap65 is most closely homologous to mammalian hemopexin, but no orthologies have been established. Hemopexin is a heme-binding serum glycoprotein produced in the liver.…”

“…16,17) Hemopexin is not only a plasma transporter of heme but also a multifunctional agent in important healthrelated processes, including as iron homeostasis, antioxidant protection, bacteriostatic defense, nerve regeneration, and gene expression promoting cell survival. 18) Further studies by several researchers suggest that Wap65 genes are not important only in their classic role as warm-temperature acclimation proteins, 10,19) but also can function as immune response proteins 20,21) and in iron homeostasis, heavy metal exposure, 13) and development. 2,14,22) Thus Wap65 proteins are of particular interest due to their multifunctional character, and they demand further characterization of the potential roles in physiological mechanism.…”