Involvement of LAT1 and LAT2 in the high- and low-affinity transport of L-leucine in human retinal pigment epithelial cells (ARPE-19 cells)

Yamamoto, Atsushi; Akanuma, Shin Ichi; Tachikawa, Masanori; Hosoya, Ken

doi:10.1002/jps.21991

Cited by 37 publications

(27 citation statements)

References 33 publications

(55 reference statements)

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“…4), and both are known to have pharmacodynamic effects in the CNS. Even though previous studies have used trans-stimulation to establish whether or not a specific transporter can transport different compounds (35)(36)(37), this assay provides indirect evidence that a compound may be a substrate for a specific transporter. Nevertheless, acivicin was assessed in a clinical trial for treating various solid tumors that did not involve the CNS but failed these trials due to CNS-related toxic side effects (e.g., lethargy and confusion) (38).…”

Section: Discussionmentioning

confidence: 99%

Structure-based ligand discovery for the Large-neutral Amino Acid Transporter 1, LAT-1

Geier¹,

Schlessinger

Fan

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

163

219

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The Large-neutral Amino Acid Transporter 1 (LAT-1)-a sodiumindependent exchanger of amino acids, thyroid hormones, and prescription drugs-is highly expressed in the blood-brain barrier and various types of cancer. LAT-1 plays an important role in cancer development as well as in mediating drug and nutrient delivery across the blood-brain barrier, making it a key drug target. Here, we identify four LAT-1 ligands, including one chemically novel substrate, by comparative modeling, virtual screening, and experimental validation. These results may rationalize the enhanced brain permeability of two drugs, including the anticancer agent acivicin. Finally, two of our hits inhibited proliferation of a cancer cell line by distinct mechanisms, providing useful chemical tools to characterize the role of LAT-1 in cancer metabolism.arge-neutral Amino Acid Transporter 1 (LAT-1) is a sodiumindependent exchanger found in the brain, testis, and placenta, where it mediates transport of large-neutral amino acids (e.g., tyrosine) and thyroid hormones (e.g., triiodothyronine) across the cell membrane (1). More specifically, LAT-1 is highly expressed in the blood-and brain-facing membranes of the blood-brain barrier (BBB) to supply the central nervous system (CNS) with essential nutrients and to help maintain the neural microenvironment (2). LAT-1 is also an important drug target because it transports several prescription drugs, such as the antiparkinsonian drug L-dopa and the anticonvulsant gabapentin, across the BBB, thereby enabling their pharmacologic effects (3,4). This function at the BBB has made LAT-1 a target for drug delivery by modifying CNS-impermeable drugs such that they become LAT-1 substrates and have enhanced BBB penetration (5, 6).In addition, LAT-1 expression levels are increased in many types of cancer, including non-small-cell lung cancer and glioblastoma multiforme (GBM) (7,8). LAT-1 expression increases as cancers progress, leading to higher expression levels in highgrade tumors and metastases (9). In particular, LAT-1 plays a key role in cancer-associated reprogrammed metabolic networks by supplying growing tumor cells with essential amino acids that are used as nutrients to build biomass and signaling molecules to enhance proliferation by activating progrowth pathways such as the mammalian target of rapamycin (mTOR) pathway (10). Furthermore, inhibiting LAT-1 function reduces tumor cell proliferation, indicating that it may be a viable target for novel anticancer therapies (11-13). A cancer drug targeting LAT-1 can therefore be a LAT-1 inhibitor that deprives the cancer cells of nutrients or a cytotoxic LAT-1 substrate with an intracellular target (e.g., a metabolic enzyme).LAT-1 is a large protein with 12 putative membrane-spanning helices (14). To transport solutes across the membrane, LAT-1 binds SLC3A2, a glycoprotein with a single membrane-spanning helix that serves as a chaperone for LAT-1 (14). The atomic structure of human LAT-1 is not known, but LAT-1 exhibits significant sequence similarity to prokar...

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Section: Discussionmentioning

confidence: 99%

Structure-based ligand discovery for the Large-neutral Amino Acid Transporter 1, LAT-1

Geier¹,

Schlessinger

Fan

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

163

219

View full text Add to dashboard Cite

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“…Additionally, LAT1 mRNA expression was 100-fold higher than LAT2 in TR-iBRB2 cells. Yamamoto et al [41] have elucidated the presence of system L on ARPE-19 cells. In ARPE-19 cells, [ 3 H] l -leucine uptake took place in a Na + -independent and saturable manner with K m values of 8.71 and 220 μ m .…”

Section: Large Neutral Amino Acid Transporters (System L)mentioning

confidence: 99%

Transporters and receptors in the posterior segment of the eye

Patel

Gokulgandhi

Khurana

et al. 2013

Ocular Transporters and Receptors

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Treatment of vision-threatening retinal disorders is challenging because of physiological barriers. Entry of drug molecules to posterior ocular tissues from systemic and periocular sites is hampered by the presence of blood-retinal barriers (BRB). The BRB controls nutrient and xenobiotic access to posterior ocular tissues. Recent advancements in ophthalmic research have revealed the presence of a variety of transporters and receptors on BRB. These transport systems together play a key role in the infl ux of nutrients and the effl ux of metabolites and xenobiotics, and thereby help to maintain retinal homeostasis. The knowledge of expression and function of these transporters in BRB can help in the design of transporter-targeted prodrugs to improve posterior segment ocular drug delivery. This chapter provides insight into the role of transporters and receptors in maintaining the retinal milieu and proper functioning. In this chapter, current knowledge of transporters and receptors in posterior ocular tissues including glucose transporters, nucleoside transporters, creatine transporters, oligopeptide transporters, amino acid transporters, monocarboxylate transporters, organic anion and cation transporters, vitamin transporters, ATP-binding cassette transporters, folate receptor and 5

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“…The computational model described in this paper is based on our experimental data on a mechanically induced Ca 2+ wave in ARPE-19 cells, a commercial immortalized human RPE cell line that is widely used to assess RPE cell functions in vitro [17–19], regardless of its limitations in cellular morphology, organization and function [20]. …”

Section: Introductionmentioning

confidence: 99%

Computational Model of Ca2+ Wave Propagation in Human Retinal Pigment Epithelial ARPE-19 Cells

et al. 2015

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ObjectiveComputational models of calcium (Ca2+) signaling have been constructed for several cell types. There are, however, no such models for retinal pigment epithelium (RPE). Our aim was to construct a Ca2+ signaling model for RPE based on our experimental data of mechanically induced Ca2+ wave in the in vitro model of RPE, the ARPE-19 monolayer.MethodsWe combined six essential Ca2+ signaling components into a model: stretch-sensitive Ca2+ channels (SSCCs), P2Y2 receptors, IP3 receptors, ryanodine receptors, Ca2+ pumps, and gap junctions. The cells in our epithelial model are connected to each other to enable transport of signaling molecules. Parameterization was done by tuning the above model components so that the simulated Ca2+ waves reproduced our control experimental data and data where gap junctions were blocked.ResultsOur model was able to explain Ca2+ signaling in ARPE-19 cells, and the basic mechanism was found to be as follows: 1) Cells near the stimulus site are likely to conduct Ca2+ through plasma membrane SSCCs and gap junctions conduct the Ca2+ and IP3 between cells further away. 2) Most likely the stimulated cell secretes ligand to the extracellular space where the ligand diffusion mediates the Ca2+ signal so that the ligand concentration decreases with distance. 3) The phosphorylation of the IP3 receptor defines the cell’s sensitivity to the extracellular ligand attenuating the Ca2+ signal in the distance.ConclusionsThe developed model was able to simulate an array of experimental data including drug effects. Furthermore, our simulations predict that suramin may interfere ligand binding on P2Y2 receptors or accelerate P2Y2 receptor phosphorylation, which may partially be the reason for Ca2+ wave attenuation by suramin. Being the first RPE Ca2+ signaling model created based on experimental data on ARPE-19 cell line, the model offers a platform for further modeling of native RPE functions.

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Involvement of LAT1 and LAT2 in the high- and low-affinity transport of L-leucine in human retinal pigment epithelial cells (ARPE-19 cells)

Cited by 37 publications

References 33 publications

Structure-based ligand discovery for the Large-neutral Amino Acid Transporter 1, LAT-1

Structure-based ligand discovery for the Large-neutral Amino Acid Transporter 1, LAT-1

Transporters and receptors in the posterior segment of the eye

Computational Model of Ca2+ Wave Propagation in Human Retinal Pigment Epithelial ARPE-19 Cells

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