Disease relevance of Rbp4

• Studies were conducted to explore the effects of glucocorticoid hormones on the regulation of the metabolism of retinol-binding protein (RBP) by H4II EC4 rat hepatoma cells in culture [1].
• Excessive doses of vitamin A produced fatty liver in the rats, in association with a normal (group 2, Study I) or with a decreased (group 3, Study I) level of RBP in the liver [2].
• A single injection of 17 beta-estradiol, either 1.0 or 0.1 micrograms/g body weight, resulted in a rapid rise in the level of RBP mRNA in the kidney which was maximal at 3-6 h (fivefold induction) after treatment [3].
• We suggest that the toxic manifestations of hypervitaminosis A occur when vitamin A circulates in plasma and is presented to membranes in a form other than bound to RBP [2].
• These observations suggest that cholestasis inhibits the synthesis and secretion of RBP and TTR by disrupting the binding of their mRNAs to membrane-bound polysomes [4].

Psychiatry related information on Rbp4

• However, when exercising rats at an intensity level representing 40-60% of their Vo2 max, the T groups had consistently lower RBP than their NT controls during the majority of the experimental time periods [5].

High impact information on Rbp4

• The intensity of RBP staining increased markedly in retinol-deficient rat liver, consistent with previous biochemical observations [6].
• Both normal and vitamin A-deficient hepatocytes synthesized RBP [7].
• Since retinol induces the secretion of RBP, accumulated in the endoplasmic reticulum (ER), it seems reasonable to conclude that the transport of RBP from the ER to the Golgi complex is regulated by retinol [7].
• These findings indicate that following uptake of chylomicron remnant retinyl ester in parenchymal cells, the retinyl ester is hydrolyzed, and retinol secreted from parenchymal cells on RBP is taken up by stellate cells by means of RBP receptors [8].
• This is, vitamin A-storing stellate cells in liver, lungs, and probably also in other organs may synthesize their own RBP (or alternatively use exogenous RBP) and mobilize holo-RBP directly to the blood [9].

Chemical compound and disease context of Rbp4

• As previously reported, RBP accumulated in the hepatoma cells when they were incubated in a medium free of serum and of vitamin A. The addition of retinol over a range from 3.5 nM to 3.5 microM stimulated a dose-dependent secretion of RBP from the cells into the medium [1].

Biological context of Rbp4

• It has been proposed that the two regions displaying internal homology in the human RBP, both at the primary and tertiary structure levels, arose by a partial ancestral gene duplication [10].
• The regulatory elements involved in its tissue-specific expression have been identified and mapped to the 5' flanking region of the RBP gene [11].
• Northern blot analysis demonstrated that RBP mRNA was not detectable in the kidney before birth or during the first week postpartum, but was clearly detected by the end of the second week of age [12].
• Whatever the vitamin A status, TPN may induce in rats a down-regulation of hepatic RBP synthesis, which may, at least partially, explain the alteration of retinol and RBP in serum [13].
• RBP was observed in fetal microsomes at 12 d gestation [14].

Anatomical context of Rbp4

• As a model of ligand-dependent protein secretion the biosynthesis, intracellular transport, and release of the retinol-binding protein (RBP) were studied in primary cultures of rat hepatocytes pulse-labeled with [35S]methionine [7].
• The relative levels of RBP mRNA in the visceral yolk sac were very similar in all three groups of rats [15].
• Cultured adipocytes synthesized RBP protein and secreted it into the medium [16].
• Adipose tissue has been reported to contain relatively high levels of the specific mRNA for retinol-binding protein (RBP) (Makover A., Soprano, D.R., Wyatt, M. L., and Goodman, D.S. (1989) J. Lipid Res. 30, 171-180) [16].
• The level of translatable RBP-specific mRNA was quantitated in vitro by translation of rat liver poly(A+)RNA in the rabbit reticulocyte lysate protein-synthesizing system [17].

Associations of Rbp4 with chemical compounds

• These studies demonstrate that adipocytes store retinoid and synthesize and secrete RBP, and suggest that rat adipocytes may be dynamically involved in retinoid storage and metabolism [16].
• The relative rate of RBP synthesis was estimated by measuring the extent of incorporation of [3H]leucine, [3H]lysine, and [3H]phenylalanine after a 12-min pulse label into immunoprecipitable RBP, relative to the incorporation of these amino acids into total liver trichloroacetic acid-precipitable protein [17].
• Thus, with normal cells, dexamethasone maintains RBP, TTR, and albumin production and secretion rates close to initial rates [18].
• Addition of retinoic acid also stimulated RBP secretion by retinol-deficient hepatocytes [18].
• However, treatment of male rats with estrogen caused an increase in the steady-state level of RBP mRNA in the kidney but not in the liver [3].

Analytical, diagnostic and therapeutic context of Rbp4

• After various periods of chase RBP was isolated by immunoprecipitation and identified by SDS PAGE [7].
• Total RNA was isolated from inguinal, dorsal, mesenteric, epididymal, perinephric, and brown adipose tissue, and average RBP and CRBP mRNA levels were determined by Northern blot analysis [16].
• RBP was assayed by radioimmunoassay and RBP mRNA levels by RNase protection assay using a rat RBP cDNA clone [15].
• By Western blot analysis we found that cultivated liver stellate cells secreted RBP into the medium [9].
• The localization of immunoreactive retinol-binding protein (RBP) in rat liver was studied by immunofluorescence microscopy [19].

References