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    • Because chemokines and chemokine receptors play

    2020-07-30

    Because chemokines and chemokine receptors play an important role in the immune system [26], they have been extensively studied in mammals. For example, Matsuo [27] reported that the CXC-type chemokine/CXCR2 biological axis promotes angiogenesis in vitro and in vivo in pancreatic cancer. Zou [28] researched the function of the chemokine receptor CXCR4 in haematopoiesis and cerebellar development. In recent years, chemokines and chemokine receptors have been increasingly reported in fish. For example, Xu [29] performed molecular cloning and expression analysis of CXCR5 in grass carp, representing the first report of a non-mammalian CXCR5 in a teleost fish. Dixon [30] identified and characterized three novel chemokine receptors in rainbow trout, bringing the number of known CC-type chemokine receptors in this species to five, one of which is teleost-specific. Umasuthan [31] reported two CXC-type chemokine receptors, OfCXCR1 and OfCXCR2, in rock bream fish and characterized these at the molecular, structural, genomic, and transcriptional levels. In this study, we describe the identification and characterization of CXCR2 (LycCXCR2), CXCR3 (LycCXCR3), and CXCR4 (LycCXCR4) in large yellow croaker. Each protein consists of seven transmembrane domains connected by three intracellular loops (ICLs) and three extracellular loops (ECLs). In addition, these proteins have conserved DRY amino 340 7 australia motifs within the second ICL, which are involved in coupling to G-proteins, and they share a high identity to homologs from other teleost species according to sequence analysis. We report that CXCR3 and CXCR4 are evolving neutrally according to PAML analyses. In addition, these chemokine receptors are involved in the immune system and exhibit high constitutive expression in the liver, kidney, and spleen. The data provided here contribute to a deeper understanding of CXCR signalling in fish.
    Materials and methods
    Results and discussion
    Acknowledgements This study was supported by the Open Project Program of the Key Laboratory of Mariculture & Enhancement of Zhejiang Province (No. 2016KF003), the Key Project of Zhejiang Province (No. 2016C02055-7), and the International Science & Technology Cooperation Program of China (No. 2015DFR30450).
    Introduction The envelope protein (Env) of human immunodeficiency virus type 1 (HIV-1) consists of the surface gp120 subunit and the transmembrane gp41 subunit, which are non-covalently associated with each other 1, 2, 3. As many as some 30 N-asparagine-linked carbohydrate attachment sites were predicted in the Env amino acid sequence and actual attachment of sugar chains appears to modulate the viral biological properties, infectivity and antigenicity 1, 2, 3, 4, 5, 6, 7, 8, 9. However, the functional significance of each of the glycans for viral activities is not fully elucidated. The infectivity, cellular host range and cytopathogenicity of HIV-1 vary from strain to strain. Primary HIV-1 isolates obtained from individuals at an early asymptomatic stage can replicate in phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMC) and primary macrophages but not in established T cell lines. They are referred to as macrophage tropic (M-tropic) strains. On the other hand, the isolates from about 50% of patients at a late disease stage replicate in established T cell lines but not in macrophages, and are thus termed T-cell-line tropic (T-tropic) strains. Recently, chemokine receptors such as CXCR-4 and CCR-5 were identified as co-receptors that mediate fusion between the viral envelope and the host cell membrane and facilitate the entry of HIV-1 into cells following viral attachment to the major receptor CD4 10, 11, 12, 13, 14, 15, 16. Differences in cell tropism among HIV-1 strains are now explained by different co-receptor usage. CCR-5 is used by M-tropic strains 10, 12, 13, 14, 15, whereas CXCR-4 is used by T-tropic strains 11, 16. The third variable (V3) loop in gp120 has been found to be an important determinant for virus cellular host range 17, 18, 19, and its basic amino acid substitutions at positions 11 and/or 25 are closely associated with the T-tropic phenotype 20, 21, 22, 23, 24.