AaCAT1 of the yellow fever mosquito, Aedes aegypti: A novel histidine-specific amino acid transporter from the SLC7 family

Department of Biology and Institute of Applied Biosciences, New Mexico State University, Las Cruces, New Mexico 88003-8001, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 03/2011; 286(12):10803-13. DOI: 10.1074/jbc.M110.179739
Source: PubMed

ABSTRACT Insect yolk protein precursor gene expression is regulated by nutritional and endocrine signals. A surge of amino acids in
the hemolymph of blood-fed female mosquitoes activates a nutrient signaling system in the fat bodies, which subsequently derepresses
yolk protein precursor genes and makes them responsive to activation by steroid hormones. Orphan transporters of the SLC7
family were identified as essential upstream components of the nutrient signaling system in the fat body of fruit flies and
the yellow fever mosquito, Aedes aegypti. However, the transport function of these proteins was unknown. We report expression and functional characterization of AaCAT1, cloned from the fat body of A. aegypti. Expression of AaCAT1 transcript and protein undergoes dynamic changes during postembryonic development of the mosquito. Transcript expression
was especially high in the third and fourth larval stages; however, the AaCAT1 protein was detected only in pupa and adult
stages. Functional expression and analysis of AaCAT1 in Xenopus oocytes revealed that it acts as a sodium-independent cationic amino acid transporter, with unique selectivity to l-histidine at neutral pH (K0.5l-His = 0.34 ± 0.07 mm, pH 7.2). Acidification to pH 6.2 dramatically increases AaCAT1-specific His+-induced current. RNAi-mediated silencing of AaCAT1 reduces egg yield of subsequent ovipositions. Our data show that AaCAT1 has notable differences in its transport mechanism
when compared with related mammalian cationic amino acid transporters. It may execute histidine-specific transport and signaling
in mosquito tissues.

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Available from: Geoffrey M Attardo, Apr 05, 2014
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    • "This structure, however, also differs from that of the cationic amino acid transporters (CATs) and glycoprotein-associated amino acid transporters (gpaATs) family (SLC7). In the latter families, CAT proteins (SLC7A1–A4) possess 14 TMDs and gpaAT proteins (SLC7A5–A11) possess 12 TMDs (Verrey et al. 2004; Closs et al. 2006; Hansen et al. 2011). However, further structural analyses are needed here to verify the predicted structure of CCC9. "
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    ABSTRACT: The cation chloride cotransporter (CCCs) family comprises of four subfamilies - K(+)-Cl(-) cotransporters (KCCs), Na(+)-K(+)-2Cl(-) cotransporters (NKCCs), Na(+)-Cl(-) cotransporters (NCCs) - and possibly two additional members - cation chloride cotransporter interacting protein (CIP1) and polyamine transporters (CCC9) - as well. Altogether, CCCs can play essential physiological roles in transepithelial ion reabsorption and secretion, cell volume regulation and inhibitory neurotransmission and so are present across all domains of life. To gain insight into the evolution of this family, we performed a comprehensive phylogenetic analysis using publically available genomic information. Our results clearly support CIP1 as being a true CCC based on shared evolutionary history. By contrast, the status of CCC9 in this regard remains equivocal. We also reveal the existence of a single ancestral CCC gene present in Archaea, from which numerous duplication events at the base of archaeans and eukaryotes lead to the divergence and subsequent neofunctionalization of the paralogous CCC subfamilies. A diversity of ensuing gene-loss events resulted in the complex distribution of CCCs present across the different taxa. Importantly, the occurrence of KCCs in "basal" metazoan taxa like sponges, would allow an early formation of fast hyperpolarizing neurotransmission in metazoans. Gene duplications within the CCC subfamilies in vertebrates (KCCs, NKCCs and NCCs in particular) lend further evidence to the 2R hypothesis of two rounds of genome duplication at the base of the vertebrate lineage, especially in concert with our syntenic cluster analyses. This increased number of KCCs, NKCCs and NCCs isoforms facilitates their further, important subfunctionalization in the vertebrate lineage.
    Molecular Biology and Evolution 11/2013; 31(2):434–447. DOI:10.1093/molbev/mst225 · 9.11 Impact Factor
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    • "RNAi-mediated knockdown of these AA transporters resulted in a strong inhibition of AA-induced yolk protein expression in the female fat body. Electrophysiological characterization of AaCAT1 expressed in Xenopus oocytes has shown that this transporter has narrow substrate specificity – at neutral pH it transports only L-histidine (Hansen et al., 2011). "
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    ABSTRACT: An important function of the fat body in adult female mosquitoes is the conversion of blood meal derived amino acids (AA) into massive amounts of yolk protein precursors. A highly efficient transport mechanism for AAs across the plasma membrane of the fat body trophocytes is essential in order to deliver building blocks for the rapid synthesis of large amounts of these proteins. This mechanism consists in part of AA transporter proteins from the solute carrier family. These transporters have dual function; they function as transporters and participate in the nutrient signal transduction pathway that is activated in the fat body after a blood meal. In this study we focused on the solute carrier 7 family (SLC7), a family of AA transporters present in all metazoans that includes members with strong substrate specificity for cationic AAs. We identified 11 putative SLC7 transporters in the genome sequence of Aedes aegypti. Phylogenetic analysis puts five of these in the cationic AA transporter subfamily (CAT) and six in the heterodimeric AA transporter (HAT) subfamily. All 11 A. aegypti SLC7 genes are expressed in adult females. Expression profiles are dynamic after a blood meal. We knocked down six fat body-expressed SLC7 transporters using RNAi and found that these 'knockdowns' reduced AA-induced TOR signaling. We also determined the effect these knockdowns had on the number of eggs deposited following a blood meal. Our analysis stresses the importance of SLC7 transporters in TOR signaling pathway and mosquito reproduction.
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    ABSTRACT: Mosquitoes require blood for egg development, and, as a consequence, they transmit pathogens of devastating diseases. Target of rapamycin (TOR) signaling is a key pathway linking blood feeding and egg development in the mosquito Aedes aegypti. We show that the regulation of the TOR effector translational repressor 4E-BP is finely tuned to the nutritional requirements of the female mosquito, and it occurs at transcriptional and post-translational levels. Immediately after blood feeding, 4E-BP became hyperphosphorylated, suggesting rapid inhibition of its translational repression function. 4E-BP was highly phosphorylated after in vitro incubation of the fat body in the presence of amino acids; this phosphorylation was rapamycin insensitive, in contrast to another TOR target, S6K, phosphorylation of which was rapamycin sensitive. A high level of 4E-BP phosphorylation was also elicited by insulin. Rapamycin and the PI3K inhibitor LY294002 blocked insulin-mediated 4E-BP phosphorylation. RNA-interference depletion of the insulin receptor or Akt resulted in severe reduction of 4E-BP phosphorylation. Phosphorylation and stability of 4E-BP was dependent on its partner eIF4E translation initiation factor. Silencing of 4E-BP resulted in reduction of the life span of adult female mosquitoes. This study demonstrates a dual nutritional and hormonal control of 4E-BP and its role in mosquito egg development.
    The FASEB Journal 12/2011; 26(3):1334-42. DOI:10.1096/fj.11-189969 · 5.04 Impact Factor
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