Differential interaction of lecithin-retinol acyltransferase with cellular retinol binding proteins

Herr, Fiona; Ong, David E.

doi:10.1021/bi00144a014

Cited by 166 publications

(141 citation statements)

References 38 publications

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“…Our study confirms and extends a previous report that activity of LRAT is regulated differentially by apo-RBP1 and apo-RBP2 [35]. Using homogenates obtained from cells stably transfected with a human LRAT cDNA, we demonstrate that apo-RBP1 is a strong inhibitor of LRAT activity while apo-RBP2 is not.…”

Section: Ralr1 May Act As a Physiologically Significant Retinal Reducsupporting

confidence: 91%

In vitro and in vivo characterization of retinoid synthesis from β-carotene

Fierce

Vieira

Piantedosi

et al. 2008

Archives of Biochemistry and Biophysics

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Retinoids are indispensable for the health of mammals, which cannot synthesize retinoids de novo. Retinoids are derived from dietary provitamin A carotenoids, like β-carotene, through the actions β-carotene 15,15′ monooxygenase (BCMO1). As the substrates for retinoid metabolizing enzymes are water insoluble, they must be transported intracellularly bound to cellular retinol-binding proteins. Our studies suggest that cellular retinol binding protein, type I (RBP1) acts as an intracellular sensor of retinoid status that, when present as apo-RBP1, stimulates BCMO1 activity and the conversion of carotenoids to retinoids. Cellular retinol binding protein, type II (RBP2), which is 56% identical to RBP1 does not influence BCMO1 activity. Studies of mice lacking BCMO1 demonstrate that BCMO1 is responsible for metabolically limiting the amount of intact β-carotene that can be absorbed by mice from their diet. Our studies provide new insights into the regulation of BCMO1 activity and the physiological role of BCMO1 in living organisms. Keywordsβ-carotene; cleavage; β-carotene 15; 15′ monooxygenase; retinoid; metabolism; cellular retinol binding protein Retinoids (vitamin A, its natural metabolites and synthetic analogs) are required for survival of mammals and are needed to support vision, normal cell differentiation and proliferation, embryonic development, normal immune function and reproduction [1]. Aside from in vision, all of the essential actions of retinoids within the body are thought to involve the transcriptional activity of retinoic acid [1]. Retinoic acid is a potent transcriptional regulator whose effects are mediated by two families of nuclear receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs) [2][3][4]. When retinoic acid is not available, RAR/RXR heterodimers bind to retinoic acid response elements in promoter of genes and form complexes with transcriptional corepressors resulting in chromatin condensation and transcriptional silencing. In the presence of retinoic acid, corepressors are released from the RAR/RXR heterodimer which is now free to recruit and bind coactivators resulting in chromatin *Corresponding author: Jisun Paik, Department of Comparative Medicine, Raitt Hall, 324, Seattle, WA 98195. Phone: 206-221-2682; Fax: 206-685-1696; E-mail: jpaik@u.washington.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript decondensation and transcriptional activation. In excess of 500 genes may be responsive to retinoic acid [5].Since ani...

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Section: Ralr1 May Act As a Physiologically Significant Retinal Reducsupporting

confidence: 91%

In vitro and in vivo characterization of retinoid synthesis from β-carotene

Fierce

Vieira

Piantedosi

et al. 2008

Archives of Biochemistry and Biophysics

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“…In the case of LRAT, this association also allows the enzyme access to the ester substrate at the sn-1 position of phospholipids. The retinol substrate of LRAT is obtained from the cytoplasm via cellular retinol-binding protein I or II (44). The results presented here indicate that the N terminus and putative catalytic domain of LRAT are both located in the cytoplasm, whereas the C-terminal transmembrane domain serves to anchor this protein to the membrane of the ER (Fig.…”

Section: Discussionmentioning

confidence: 70%

“…One possibility is that the N-terminal hydrophobic domain of LRAT is involved in interacting with accessory or regulatory proteins in a species-specific manner. Such regulatory interactions might include cellular retinol-binding protein accessory proteins, which are known to present substrate (23,49) and even directly modulate the acyltransferase activity of LRAT (44). More studies are necessary to establish the role of the N-terminal domain of LRAT in vivo.…”

Section: Discussionmentioning

confidence: 99%

Topology and Membrane Association of Lecithin: Retinol Acyltransferase

Moise

Golczak

Imanishi

et al. 2007

Journal of Biological Chemistry

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Fatty acid retinyl esters are the storage form of vitamin A (alltrans-retinol) and serve as metabolic intermediates in the formation of the visual chromophore 11-cis-retinal. Lecithin:retinol acyltransferase (LRAT), the main enzyme responsible for retinyl ester formation, acts by transferring an acyl group from the sn-1 position of phosphatidylcholine to retinol. To define the membrane association and localization of LRAT, we produced an LRAT-specific monoclonal antibody, which we used to study enzyme partition under different experimental conditions. Furthermore, we examined the membrane topology of LRAT through an N-linked glycosylation scanning approach and protease protection assays. We show that LRAT is localized to the membrane of the endoplasmic reticulum (ER) and assumes a single membrane-spanning topology with an N-terminal cytoplasmic/C-terminal luminal orientation. In eukaryotic cells, the C-terminal transmembrane domain is essential for the activity and ER membrane targeting of LRAT. In contrast, the N-terminal hydrophobic region is not required for ER membrane targeting or enzymatic activity, and its amino acid sequence is not conserved in other species examined. We present experimental evidence of the topology and subcellular localization of LRAT, a critical enzyme in vitamin A metabolism.The metabolism of vitamin A (all-trans-retinol) leads to the formation of all-trans-retinoic acid and 11-cis-retinal derivatives that play crucial roles in such processes as development, immunity, and vision (1-6). Recent studies have highlighted the importance of lecithin:retinol acyltransferase (LRAT) 3 in the absorption and retention of retinol in intracellular stores (7). LRAT catalyzes the synthesis of retinyl esters, thereby drawing retinol from the circulation to storage depots such as the lipid droplets of hepatic stellate cells and the retinosome structures found in the retinal pigment epithelium (RPE) (8, 9). Mutations in the LRAT gene lead to early-onset severe retinal dystrophy (10). Disruption of the Lrat gene in Lrat Ϫ/Ϫ mice produces a severe impairment in retinol uptake and storage capacity. As a result, Lrat Ϫ/Ϫ mice are blind (11) and more susceptible to vitamin A deficiency than their wild-type (WT) counterparts (12). Lrat Ϫ/Ϫ mice possess only trace amounts of retinyl esters in most tissues (11, 12), yet, surprisingly, the levels of retinyl esters in their adipose tissue are elevated compared with those in WT mice (12). Adipose stores of retinyl esters could depend on the activity of acyl-CoA:retinol acyltransferase (12).LRAT plays a pivotal role in determining retinol availability, which in turn affects the levels of all-trans-retinoic acid, a potent regulator of the expression of many genes via retinoic acid receptors (13). Expression of LRAT in the liver is influenced by multiple factors, including vitamin A status (14), retinoic acid (15), other synthetic retinoic acid receptor activators (16), and peroxisome proliferator-activated receptor ␤/␦ agonists (17). Thus, regulation of LRAT activi...

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“…We measured the dependence of chicken isomerohydrolase activity upon the generation of alltrans-retinyl ester using two specific LRAT inhibitors, apo-cellular retinol-binding protein Type 1 (apo-CRBP) and 10-N-acetamidododecyl chloromethyl ketone (Ac-DCMK), which have been characterized previously (16,21). In the absence of the inhibitors, a significant amount of 11-cis-retinol was generated from all-trans-retinol after 1.5-h incubation with bovine or chicken RPE microsomes (Fig.…”

Section: Resultsmentioning

confidence: 99%

RPE65 from Cone-dominant Chicken Is a More Efficient Isomerohydrolase Compared with That from Rod-dominant Species

Moiseyev

Takahashi

Chen

et al. 2008

Journal of Biological Chemistry

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Cones recover their photosensitivity faster than rods after bleaching. It has been suggested that a higher rate regeneration of 11-cis-retinal, the chromophore for visual pigments, is required for cones to continuously function under bright light conditions. RPE65 is the isomerohydrolase catalyzing a key step in regeneration of 11-cis-retinal. The present study investigated whether RPE65 in a cone-dominant species is more efficient in its enzymatic activity than that from roddominant species. In vitro isomerohydrolase activity assay showed that isomerohydrolase activity in the chicken retinal pigment epithelium (RPE) was 11.7-fold higher than in the bovine RPE, after normalization by RPE65 protein levels. Similar to that of human and bovine, the isomerohydrolase activity in chicken RPE was blocked by two specific inhibitors of lecithin retinal acyltransferase, indicating that chicken RPE65 also uses all-trans-retinyl ester as the direct substrate. To exclude the possibility that the higher isomerohydrolase activity in the chicken RPE could arise from another unknown isomerohydrolase, we expressed chicken and human RPE65 using the adenovirus system in a stable cell line expressing lecithin retinal acyltransferase. Under the same conditions, isomerohydrolase activity of recombinant chicken RPE65 was 7.7-fold higher than that of recombinant human RPE65, after normalization by RPE65 levels. This study demonstrates that RPE65 from the cone-dominant chicken RPE possesses significantly higher specific retinol isomerohydrolase activity, when compared with RPE65 from rod-dominant species, consistent with the faster regeneration rates of visual pigments in cone-dominant retinas.Visual pigments of rods and cones consist of protein opsins and the chromophore, 11-cis-retinal covalently bound to opsins via a Schiff base (1). Upon light absorption, the 11-cis-retinal is photoisomerized to all-trans-retinal, which subsequently activates opsin and triggers the phototransduction cascade (1, 2). The 11-cis-retinal chromophore regenerates through a series of reactions of the retinoid visual cycle (3, 4). The visual cycle has been intensively studied in rod-dominant species such as bovine and mouse. The twocell (photoreceptor and RPE) 2 system of 11-cis-retinal recycling has been proposed for the visual cycle. After reduction of all-trans-retinal by retinol dehydrogenase, the generated all-trans-retinol is transported from the photoreceptor to the RPE and esterified to all-trans-retinyl esters by lecithin retinol acyltransferase (LRAT). The resulting all-trans-retinyl ester can either be stored in the RPE or directly converted to 11-cis-retinol by the isomerohydrolase, which was recently identified as the microsomal protein RPE65 (5-7). RPE65 has been shown to be an essential enzyme in the retinoid visual cycle for 11-cis-retinal regeneration (8). After oxidation of 11-cis-retinol by retinol dehydrogenase-5, the generated 11-cis-retinal is transported back to the photoreceptors to regenerate the visual pigments.It is known that cone...

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Differential interaction of lecithin-retinol acyltransferase with cellular retinol binding proteins

Cited by 166 publications

References 38 publications

In vitro and in vivo characterization of retinoid synthesis from β-carotene

In vitro and in vivo characterization of retinoid synthesis from β-carotene

Topology and Membrane Association of Lecithin: Retinol Acyltransferase

RPE65 from Cone-dominant Chicken Is a More Efficient Isomerohydrolase Compared with That from Rod-dominant Species

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