Uptake and storage of vitamin A as lipid droplets in the cytoplasm of cells in the lamina propria mucosae of the rat intestine.

Vitamin A (retinyl palmitate) was injected subcutaneously or administered to rats by tube feeding. After subcutaneous injection, vitamin A was taken up and stored in cells of the lamina propria mucosae of the rat intestine. After oral administration, vitamin A was absorbed by the intestinal absorptive epithelial cells and transferred to cells of the lamina propria mucosae, where cells took up and stored the transferred vitamin A. The morphology of these cells was similar to that of hepatic stellate cells (also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells or Ito cells). Thus, these cells in the intestine could take up vitamin A from the systemic circulation and as well as by intestinal absorption, and store the vitamin in the lipid droplets in their cytoplasm. The data suggest that these cells are extrahepatic stellate cells of the digestive tract that may play roles in both the absorption and homeostasis of vitamin A.

Synaptic adhesion molecules in Cadm family at the neuromuscular junction.

RA175/SynCAM1/Cadm1 (Cadm1), a member of the immunoglobulin superfamily, is a synaptic cell adhesion molecule that has a PDZ-binding motif at the C-terminal region. It promotes the formation of presynaptic terminals and induces functional synapses in the central nervous system. Cadm1-deficient (knockout [KO]) mice show behavioral abnormalities, including excessive aggression and anxiety, but do not show any symptoms of neuromuscular disorder, although neuromuscular junctions (NMJs) have structures similar to synapses. We have examined the expression of members of the Cadm family in the mouse muscle tissues. Cadm4 and Cadm1 were major components of the Cadm family, and Cadm3 was faintly detected, but Cadm2 was not detected by RT-PCR. Cadm4 as well as Cadm1 colocalized with alpha-bungarotoxin at the NMJs and interacted with the multiple PDZ domain protein Mupp1. Cadm4 was expressed in Cadm1-KO mice and might compensate for Cadm1 loss through interactions with Mupp1.

Induction of an incomplete autophagic response by cancer-preventive geranylgeranoic acid (GGA) in a human hepatoma-derived cell line.

GGA (geranylgeranoic acid) is a natural polyprenoic acid, derivatives of which has been shown to prevent second primary hepatoma. GGA induces mitochondria-mediated PCD (programmed cell death), which may be relevant to cancer prevention. To gain further insights into GGA-induced PCD, autophagy processes were examined in human hepatoma-derived HuH-7 cells. Treatment of HuH-7/GFP (green fluorescent protein)-LC3 cells with GGA induced green fluorescent puncta in the cytoplasm within 30 min and their massive accumulation at 24 h. After 15 min of GGA treatment, a burst of mitochondrial superoxide production occurred and LC3ß-I was appreciably converted into LC3ß-II. GGA-induced early stages of autophagy were unequivocally confirmed by electron-microscopic observation of early/initial autophagic vacuoles. On the other hand, LC3ß-II as well as p62/SQSTM1 (sequestosome 1) continuously accumulated and co-localized in the cytoplasmic puncta after GGA treatment. Furthermore, GGA treatment of HuH-7/mRFP (monomeric red fluorescent protein)-GFP-LC3 cells showed yellow fluorescent puncta, whereas glucose deprivation of the cells gave red fluorescent puncta. These results strongly suggest that GGA induces the initial phase of autophagy, but blocks the maturation process of autolysosomes or late stages of autophagy, insomuch that GGA provides substantial accumulation of autophagosomes under serum-starvation conditions in human hepatoma cells.

Tissue flow regulates planar cell polarity independently of the Frizzled core pathway.

Planar cell polarity (PCP) regulates the orientation of external structures. A core group of proteins that includes Frizzled forms the heart of the PCP regulatory system. Other PCP mechanisms that are independent of the core group likely exist, but their underlying mechanisms are elusive. Here, we show that tissue flow is a mechanism governing core group-independent PCP on the Drosophila notum. Loss of core group function only slightly affects bristle orientation in the adult central notum. This near-normal PCP results from tissue flow-mediated rescue of random bristle orientation during the pupal stage. Manipulation studies suggest that tissue flow can orient bristles in the opposite direction to the flow. This process is independent of the core group and implies that the apical extracellular matrix functions like a "comb" to align bristles. Our results reveal the significance of cooperation between tissue dynamics and extracellular substances in PCP establishment.

Transcriptome-based systematic identification of extracellular matrix proteins.

Extracellular matrix (ECM), which provides critical scaffolds for all adhesive cells, regulates proliferation, differentiation, and apoptosis. Different cell types employ customized ECMs, which are thought to play important roles in the generation of so-called niches that contribute to cell-specific functions. The molecular entities of these customized ECMs, however, have not been elucidated. Here, we describe a strategy for transcriptome-wide identification of ECM proteins based on computational screening of >60,000 full-length mouse cDNAs for secreted proteins, followed by in vitro functional assays. These assays screened the candidate proteins for ECM-assembling activities, interactions with other ECM molecules, modifications with glycosaminoglycans, and cell-adhesive activities, and were then complemented with immunohistochemical analysis. We identified 16 ECM proteins, of which seven were localized in basement membrane (BM) zones. The identification of these previously unknown BM proteins allowed us to construct a body map of BM proteins, which represents the comprehensive immunohistochemistry-based expression profiles of the tissue-specific customization of BMs.

Preservation of collagen in the soft tissues of frozen mammoths.

We investigated the characteristics of extracellular matrix (ECM) in the soft tissue of two frozen baby woolly mammoths (Mammuthus primigenius) that died and were buried in Siberian permafrost approximately 40,000 years ago. Morphological and biochemical analyses of mammoth lung and liver demonstrated that those soft tissues were preserved at the gross anatomical and histological levels. The ultrastructure of ECM components, namely a fibrillar structure with a collagen-characteristic pattern of cross-striation, was clearly visible with transmission and scanning electron microscopy. Type I and type IV collagens were detected by immunohistochemical observation. Quantitative amino acid analysis of liver and lung tissues of the baby mammoths indicated that collagenous protein is selectively preserved in these tissues as a main protein. Type I and type III collagens were detected as major components by means of liquid chromatography-mass spectrometry analysis after digestion with trypsin. These results indicate that the triple helical collagen molecule, which is resistant to proteinase digestion, has been preserved in the soft tissues of these frozen mammoths for 40,000 years.

Hepatic stellate cell (vitamin A-storing cell) and its relative--past, present and future.

HSCs (hepatic stellate cells) (also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells or Ito cells) exist in the space between parenchymal cells and liver sinusoidal endothelial cells of the hepatic lobule and store 50-80% of vitamin A in the whole body as retinyl palmitate in lipid droplets in the cytoplasm. In physiological conditions, these cells play pivotal roles in the regulation of vitamin A homoeostasis. In pathological conditions, such as hepatic fibrosis or liver cirrhosis, HSCs lose vitamin A and synthesize a large amount of extracellular matrix components including collagen, proteoglycan, glycosaminoglycan and adhesive glycoproteins. Morphology of these cells also changes from the star-shaped SCs (stellate cells) to that of fibroblasts or myofibroblasts. The hepatic SCs are now considered to be targets of therapy of hepatic fibrosis or liver cirrhosis. HSCs are activated by adhering to the parenchymal cells and lose stored vitamin A during hepatic regeneration. Vitamin A-storing cells exist in extrahepatic organs such as the pancreas, lungs, kidneys and intestines. Vitamin A-storing cells in the liver and extrahepatic organs form a cellular system. The research of the vitamin A-storing cells has developed and expanded vigorously. The past, present and future of the research of the vitamin A-storing cells (SCs) will be summarized and discussed in this review.

The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide.

BACKGROUND: A plant-based diet protects against chronic oxidative stress-related diseases. Dietary plants contain variable chemical families and amounts of antioxidants. It has been hypothesized that plant antioxidants may contribute to the beneficial health effects of dietary plants. Our objective was to develop a comprehensive food database consisting of the total antioxidant content of typical foods as well as other dietary items such as traditional medicine plants, herbs and spices and dietary supplements. This database is intended for use in a wide range of nutritional research, from in vitro and cell and animal studies, to clinical trials and nutritional epidemiological studies. METHODS: We procured samples from countries worldwide and assayed the samples for their total antioxidant content using a modified version of the FRAP assay. Results and sample information (such as country of origin, product and/or brand name) were registered for each individual food sample and constitute the Antioxidant Food Table. RESULTS: The results demonstrate that there are several thousand-fold differences in antioxidant content of foods. Spices, herbs and supplements include the most antioxidant rich products in our study, some exceptionally high. Berries, fruits, nuts, chocolate, vegetables and products thereof constitute common foods and beverages with high antioxidant values. CONCLUSIONS: This database is to our best knowledge the most comprehensive Antioxidant Food Database published and it shows that plant-based foods introduce significantly more antioxidants into human diet than non-plant foods. Because of the large variations observed between otherwise comparable food samples the study emphasizes the importance of using a comprehensive database combined with a detailed system for food registration in clinical and epidemiological studies. The present antioxidant database is therefore an essential research tool to further elucidate the potential health effects of phytochemical antioxidants in diet.

Insoluble, speckled cytosolic distribution of retinoic acid receptor alpha protein as a marker of hepatic stellate cell activation in vitro.

Hepatic stellate cells (HSCs) are the major site of retinoid storage, and their activation is a key process in liver fibrogenesis. We have previously shown that expression of the retinoic acid receptor alpha (RARalpha) is upregulated in activated rat HSCs at a posttranscriptional level and that these RARalpha proteins showed a speckled distribution in the cytosol, despite their possession of a nuclear localization signal (NLS). In this report, we further characterize these cytosolic RARalpha proteins by using exogenously expressed RARalpha protein fragments or mutants tagged with a green fluorescent protein. Substitution of four amino acids, 161-164 from lysine to alanine, abolished the NLS. Exogenously expressed RARalpha protein fragments containing an NLS were localized exclusively in the nuclei of activated rat HSCs and never colocalized with the endogenous RARalpha proteins in the cytosol, suggesting that the NLS of endogenous RARalpha proteins is masked. Biochemical analysis showed that 65% of RARalpha proteins in activated HSCs were insoluble in a mixture of detergents. The insolubility of RARalpha proteins makes it difficult to identify RARalpha proteins in activated HSCs. Therefore, we propose that insoluble, speckled cytosolic distribution of RARalpha proteins represents a new marker of HSC activation.

Hepatic sinusoidal cells in health and disease: update from the 14th International Symposium.

This review aims to give an update of the field of the hepatic sinusoid, supported by references to presentations given at the 14th International Symposium on Cells of the Hepatic Sinusoid (ISCHS2008), which was held in Tromsø, Norway, August 31-September 4, 2008. The subtitle of the symposium, 'Integrating basic and clinical hepatology', signified the inclusion of both basal and applied clinical results of importance in the field of liver sinusoidal physiology and pathophysiology. Of nearly 50 oral presentations, nine were invited tutorial lectures. The authors of the review have avoided writing a 'flat summary' of the presentations given at ISCHS2008, and instead focused on important novel information. The tutorial presentations have served as a particularly important basis in the preparation of this update. In this review, we have also included references to recent literature that may not have been covered by the ISCHS2008 programme. The sections of this review reflect the scientific programme of the symposium (http://www.ub.uit.no/munin/bitstream/10037/1654/1/book.pdf): 1. Liver sinusoidal endothelial cells. 2. Kupffer cells. 3. Hepatic stellate cells. 4. Immunology. 5. Tumor/metastasis. Symposium abstracts are referred to by a number preceded by the letter A.

Oligo-astheno-teratozoospermia in mice lacking RA175/TSLC1/SynCAM/IGSF4A, a cell adhesion molecule in the immunoglobulin superfamily.

RA175/TSLC1/SynCAM/IGSF4A (RA175), a member of the immunoglobulin superfamily with Ca2+-independent homophilic trans-cell adhesion activity, participates in synaptic and epithelial cell junctions. To clarify the biological function of RA175, we disrupted the mouse Igsf4a (Ra175/Tslc1/SynCam/Igsf4a Ra175) gene. Male mice lacking both alleles of Ra175 (Ra175-/-) were infertile and showed oligo-astheno-teratozoospermia; almost no mature motile spermatozoa were found in the epididymis. Heterozygous males and females and homozygous null females were fertile and had no overt developmental defects. RA175 was mainly expressed on the cell junction of spermatocytes, elongating and elongated spermatids (steps 9 to 15) in wild-type testes; the RA175 expression was restricted to the distal site (tail side) but not to the proximal site (head side) in elongated spermatids. In Ra175-/- testes, elongated and mature spermatids (steps 13 to 16) were almost undetectable; round spermatids were morphologically normal, but elongating spermatids (steps 9 to 12) failed to mature further and to translocate to the adluminal surface. The remaining elongating spermatids at improper positions were finally phagocytosed by Sertoli cells. Furthermore, undifferentiated and abnormal spermatids exfoliated into the tubular lumen from adluminal surfaces. Thus, RA175-based cell junction is necessary for retaining elongating spermatids in the invagination of Sertoli cells for their maturation and translocation to the adluminal surface for timely release.

Genetic factors and epigenetic factors for autism: endoplasmic reticulum stress and impaired synaptic function.

The molecular pathogenesis of ASD (autism spectrum disorder), one of the heritable neurodevelopmental disorders, is not well understood, although over 15 autistic-susceptible gene loci have been extensively studied. A major issue is whether the proteins that these candidate genes encode are involved in general function and signal transduction. Several mutations in genes encoding synaptic adhesion molecules such as neuroligin, neurexin, CNTNAP (contactin-associated protein) and CADM1 (cell-adhesion molecule 1) found in ASD suggest that impaired synaptic function is the underlying pathogenesis. However, knockout mouse models of these mutations do not show all of the autism-related symptoms, suggesting that gain-of-function in addition to loss-of-function arising from these mutations may be associated with ASD pathogenesis. Another finding is that family members with a given mutation frequently do not manifest autistic symptoms, which possibly may be because of gender effects, dominance theory and environmental factors, including hormones and stress. Thus epigenetic factors complicate our understanding of the relationship between these mutated genes and ASD pathogenesis. We focus in the present review on findings that ER (endoplasmic reticulum) stress arising from these mutations causes a trafficking disorder of synaptic receptors, such as GABA (gamma-aminobutyric acid) B-receptors, and leads to their impaired synaptic function and signal transduction. In the present review we propose a hypothesis that ASD pathogenesis is linked not only to loss-of-function but also to gain-of-function, with an ER stress response to unfolded proteins under the influence of epigenetic factors.

Measurements of radiocesium in animals, plants and fungi in Svalbard after the Fukushima Daiichi nuclear power plant disaster.

An earthquake struck the eastern part of Japan on March 11, 2011. The Fukushima Daiichi nuclear power plant was severely damaged by the earthquake and subsequent tsunami, leading to the emission of large amounts of radioactive pollutants, including 134Cs and 137Cs, into the environment. From August 23 to September 1 in 2011, and from August 27 to September 4 in 2013, we collected samples of animals, plants, fungi and lichens from Svalbard, Norway and measured the radioactivity of 134Cs and 137Cs contained in the samples. Though no radioactivity of 134Cs, which has a half-life of approximately 2 years, was observed, radioactivity of 137Cs, which has a half-life of approximately 30 years, was observed in some samples of lichens and fungi. We failed to detect the radioactivity of 134Cs in any of the samples we collected, therefore, it was impossible to say clearly that the radioactivity is derived from Fukushima or not. Nevertheless, the radioactivity data documented in this report are a useful reference for the future surveys of radioactivity within the Arctic.

Histopathological and electron microscopic study in dogs with patellar luxation and skin hyperextensibility.

Patellar luxation is abnormal displacement of the patella from the femoral trochlear groove. It is seen primarily in small breed dogs and causes pain and limited mobility of the stifle joint. This study aimed to investigate the relationship among patellar luxation, skin extension, and skin collagen fibril diameter. Nine dogs with patellar luxation and five clinically normal dogs were enrolled in the study. We measured the skin extension and investigated the ultrastructure of the skin and patellofemoral ligament by histopathology and transmission electron microscopy. The mean skin extension in dogs with patellar luxation was 18.5 ± 5.5% which is greater than the reference value (14.5%). Mean skin extension in controls was 8.8 ± 1.7% and was within the normal range. In dogs with patellar luxation, histopathology of the skin and patellofemoral ligament showed sparse and unevenly distributed collagen fibers. Transmission electron microscopy identified poorly organized, irregularly shaped, thin collagen fibrils. Collagen fibril thickness in dogs with patellar luxation was significantly less than fibril thickness in controls (P<0.001). There was a significant negative correlation (ρ= -0.863; P<0.001) between skin collagen fibril diameter and skin extension. Skin extension was correlated with patellar luxation and disease severity. Dogs with patellar luxation, joint dysplasia, and hyperextensible skin appear to be pathologically related. This might represent a phenotype of the Ehlers-Danlos syndrome, a hereditary connective tissue disorder in humans.

All-trans-retinol generated by rhodopsin photobleaching induces rapid recruitment of TIP47 to lipid droplets in the retinal pigment epithelium.

PURPOSE: To investigate the effect of light stimulation on lipid droplets (LDs) and LD proteins in the retinal pigment epithelium (RPE). METHODS: Dark-adapted mouse eyes were exposed to intense flashes of light, and ARPE-19 cells were treated with all-trans-retinol. The two specimens were labeled with BODIPY493/503 for LDs and with antibodies for three LD proteins: adipocyte differentiation-related protein (ADRP), TIP47, and Rab18. The labeling intensity in fluorescence microscopy was quantified by image analysis. Localization of mutated TIP47 was also examined. Immunoelectron microscopy was performed for ADRP in mouse RPE. Expression of TIP47 in ARPE-19 cells was knocked down by RNA interference (RNAi), and its effect on retinyl ester storage was measured by HPLC. RESULTS: Both flashes of light on mouse eyes and all-trans-retinol on ARPE-19 cells caused rapid translocation of TIP47 from the cytosol to LDs, whereas ADRP distributed constitutively in LDs. The density of LDs did not show visible changes by any treatment. The localization of TIP47 to LDs was abolished when either the amino-terminal or the carboxyl-terminal half of the molecule was deleted, but was enhanced by a short deletion in the carboxyl terminus. Manipulation of TIP47 expression by RNAi or cDNA transfection did not affect the retinyl ester amounts in ARPE-19 cells significantly. CONCLUSIONS: All-trans-retinol generated by photobleaching in the retina induces rapid translocation of TIP47 to LDs in the RPE.

The stellate cell system (vitamin A-storing cell system).

Past, present, and future research into hepatic stellate cells (HSCs, also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, or Ito cells) are summarized and discussed in this review. Kupffer discovered black-stained cells in the liver using the gold chloride method and named them stellate cells (Sternzellen in German) in 1876. Wake rediscovered the cells in 1971 using the same gold chloride method and various modern histological techniques including electron microscopy. Between their discovery and rediscovery, HSCs disappeared from the research history. Their identification, the establishment of cell isolation and culture methods, and the development of cellular and molecular biological techniques promoted HSC research after their rediscovery. In mammals, HSCs exist in the space between liver parenchymal cells (PCs) or hepatocytes and liver sinusoidal endothelial cells (LSECs) of the hepatic lobule, and store 50-80% of all vitamin A in the body as retinyl ester in lipid droplets in the cytoplasm. SCs also exist in extrahepatic organs such as pancreas, lung, and kidney. Hepatic (HSCs) and extrahepatic stellate cells (EHSCs) form the stellate cell (SC) system or SC family; the main storage site of vitamin A in the body is HSCs in the liver. In pathological conditions such as liver fibrosis, HSCs lose vitamin A, and synthesize a large amount of extracellular matrix (ECM) components including collagen, proteoglycan, glycosaminoglycan, and adhesive glycoproteins. The morphology of these cells also changes from the star-shaped HSCs to that of fibroblasts or myofibroblasts.

Uptake of denatured collagen into hepatic stellate cells: evidence for the involvement of urokinase plasminogen activator receptor-associated protein/Endo180.

Tissue remodelling is dependent on the integration of signals that control turnover of ECM (extracellular matrix). Breakdown and endocytosis of collagen, a major component of the ECM, is central to this process. Whereas controlled secretion of matrix-degrading enzymes (such as matrix metalloproteinases) has long been known to mediate ECM breakdown, it is becoming clear that uPARAP/Endo180 (where uPARAP stands for urokinase plasminogen activator receptor-associated protein) serves as a receptor that mediates endocytosis of collagen by several types of cells. In the liver, the stellate cells play a major role in turnover of ECM including collagens. These cells synthesize various collagens and also produce matrix metalloproteinases. In the present study, we investigated the capacity of rat hepatic stellate cells to endocytose and degrade 125I-labelled heat-denatured collagen I. It was found that the collagen is efficiently taken up and degraded by these cells. Degradation was inhibited by inhibitors of lysosomal proteases (leupeptin and E-64d) and the vacuolar proton pump (concanamycin A), indicating that it takes place in lysosomes. Furthermore, endocytosed FITC-labelled collagen was shown to reach late endocytic compartments in which it colocalized with LysoTracker (a marker of late endocytic compartments). Competition experiments showed that uPA and unlabelled collagen are capable of inhibiting binding and uptake of [125I]collagen in a dose-dependent manner. Moreover, Western-blot analysis of cell lysate (using a polyclonal rabbit human-Endo180 antiserum) revealed a single band at 180 kDa. In addition, the antiserum was capable of reducing [125I]collagen binding to the cell surface. Finally, using two primers designed from the human uPARAP/Endo180 mRNA sequence, the expression of uPARAP/Endo180 mRNA was detected by reverse transcriptase-PCR. These results together suggest that uPARAP/Endo180 mediates endocytosis of collagen in rat liver stellate cells.

[Morphological study of the crystalline lens in monkeys].

PURPOSE: The morphology of the crystalline lens was studied by conventional staining techniques. The thickness of the capsule, the features of epithelial cells, and the distribution of inter fibrillar connective tissue were observed. METHODS: Eight eyes of young monkeys were examined. Resin-embedded specimens of the anterior segment were sectioned into 3 microm thickness in axial and coronal directions. Expanded antero-equatorial capsules were dyed without sectioning. LFB (Luxol Fast Blue), DAPI(diamidino-2-phenyl-indole), H-E (Hematoxylin-Eosin) and Masson's trichrome staining techniques were used. Light microscopy was used to evaluate and photograph. Pictures were composed for panoramic views. RESULTS: 1) The lens was fully enveloped by thick connective tissue the "capsule". The capsule was the thinnest in the posterior polar zone, and thickest in the peripolar zones with zonular bindings. The anterior polar and equatorial zones were 15 microm thick. 2 ) Single layered epithelial cells were squamous in the anterior polar zone and converted to cuboidal toward the equator. No epithelial cells were found thereafter in the posterior area. 3) Small and dense nuclei were observed within the anterior equatorial germinative zone. Epithelial cells were converted into fiber cells one by one in the posterior equatorial zone. Large oval nuclei of new fibers became smaller and sparser along the inner zone and then vanished. 4) Fibers were columnar in the cortex with rich intercalated connective tissues, and compressed centrally without interspaces. CONCLUSION: Genetic multiplication of fibers in a small intracapsular capacity will continue uncontrollably throughout life. That will reduce inter fibrillar connective tissue, causing accommodative loosening and opacity with age.

Keratinocyte-specific Pten deficiency results in epidermal hyperplasia, accelerated hair follicle morphogenesis and tumor formation.

PTEN is a tumor suppressor gene mutated in many human cancers. We used the Cre-loxP system to generate a keratinocyte-specific null mutation of Pten in mice (k5Pten(flox/flox) mice). k5Pten(flox/flox) mice exhibit wrinkled skin because of epidermal hyperplasia and hyperkeratosis and ruffled, shaggy, and curly hair. Histological examination revealed that skin morphogenesis is accelerated in k5Pten(flox/flox) mice. Within 3 weeks of birth, 90% of k5Pten(flox/flox) mice die of malnutrition possibly caused by hyperkeratosis of the esophagus. All k5Pten(flox/flox) mice develop spontaneous tumors within 8.5 months of birth, and chemical treatment accelerates the onset of tumors. k5Pten(flox/flox) keratinocytes are hyperproliferative and resistant to apoptosis and show increased activation of the Pten downstream signaling mediators Akt/protein kinase B (PKB) and extracellular signal-regulated kinase. Pten is thus an important regulator of normal development and oncogenesis in the skin.

The coordinated action of lecithin:retinol acyltransferase and cellular retinol-binding proteins for regulation of vitamin A esterification.

Vitamin A is a fat-soluble vitamin required for many physiological functions. The intracellular transport of vitamin A is assisted by proteins called cellular retinol-binding proteins (CRBP I/II). The absorption, storage and usage of vitamin A are regulated by a protein called lecithin:retinol acyltransferase (LRAT), a retinol-related enzyme that transfers an acyl group derived from an sn-1 position of phosphatidylcholine to retinol. LRAT is a member of the protein family which includes HRAS-like tumor suppressors (HRASLS). However, the HRASLS proteins never use retinol as an acyl acceptor. The mechanisms underlying the different substrate specificities between LRAT and HRASLS proteins are unknown. We propose in this report that LRAT physically interacts with CRBP and the LRAT-CRBP complex represents the binding pockets for both an acyl group and retinol, thus assuring the substrate specificity of LRAT.