Biomedical subjects

D R Soprano

Publications and source records attributed to D R Soprano.

76 records · Page 5Linked to original sources

PubMed1982

Effect of retinol status on retinol-binding protein biosynthesis rate and translatable messenger RNA level in rat liver.

Studies were conducted to explore the role of retinol in the control of the rate of synthesis of plasma retinol-binding protein (RBP) in the liver of the rat. Previous studies have shown that nutritional retinol status strongly influences RBP secretion from the liver cell. Both the in vivo relative rate of RBP synthesis and the in vitro translatable level of RBP-specific mRNA were examined in normal vitamin A, retinol-depleted, and retinol-repleted rats. 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. 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. The amount of newly synthesized RBP was determined relative to the amount of newly synthesized total protein. Both the relative rate of RBP synthesis (approximately 0.26%) and the translatable level of RBP-specific mRNA (approximately 0.14%) were found to be constant regardless of the retinol status of the rats. These results indicate that retinol, the molecule that RBP specifically binds and transports, does not appear to control the rate of synthesis of RBP or the translatable level of RBP-specific mRNA in the liver of the rat. Regulation of plasma RBP levels by retinol must be exercised at a locus beyond that of RBP synthesis.

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PubMed1981

Biosynthesis of plasma retinol-binding protein in liver as a larger molecular weight precursor.

A study was performed to identify the first translated product of messenger RNA for retinol-binding protein (RBP), the specific plasma transport protein for vitamin A. Poly(A)+RNA was isolated from rat liver and translated in the rabbit reticulocyte in vitro protein-synthesizing system. RBP was identified and separated from other translated products by immunoprecipitation with specific rabbit anti-rat RBP antiserum. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography of the immunoprecipitate consistently revealed one major product which migrated more slowly than purified rat serum RBP. The protein (preRBP) had an approximate molecular weight of 24,000. When dog pancreas microsomal membranes were cotranslationally present, the newly synthesized preRBP was processed to a protein which migrated coincidentally with purified rat serum RBP, approximately 20,500 daltons. These results indicate that RBP is initially synthesized as a larger molecular weight precursor (preRBP) which is rapidly processed by the removal of a peptide of approximately 3,500 daltons to the size of the final RBP molecule that circulates in the plasma.

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PubMed1981

Regulation of retinol-binding protein metabolism by glucocorticoid hormones in cultured H4II EC3 liver cells.

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. Cortisol, corticosterone, and the synthetic glucocorticoid analog dexamethasone all induced a 2- to 3-fold increase in accumulation of RBP. Half-maximal stimulation occurred at concentrations of dexamethasone in the range of 1-5 nM. Progesterone in the concentration range of 1-10 microM, inhibited the stimulatory effect of dexamethasone. Progesterone alone in this concentration range had no effect on RBP metabolism. By analogy with the studies of others, these observations with progesterone suggest that glucocorticoid receptors are involved in the effect of dexamethasone on RBP. 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. In longer experiments, retinol also stimulated the accumulation of RBP. Neither dexamethasone nor retinol had an effect on the accumulation or the cell to medium distribution of rat serum albumin or prealbumin at concentrations which were maximally stimulatory for RBP. When studied over a wide range of concentrations, retinol and dexamethasone incubated together produced approximately additive increases in the accumulation of RBP. Dexamethasone, moreover, did not affect the retinol-induced secretion of RBP. Thus, retinol and dexamethasone appear to function via different and independent mechanisms to regulate the metabolism of RBP by the liver cell.

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PubMedDate not supplied

Biochemical characteristics of isolated rat liver stellate cells.

Hepatic stellate cells play a quantitatively important role in hepatic retinoid metabolism and storage in rats maintained under normal nutritional conditions. Studies were conducted to further explore the biochemical characteristics of hepatic stellate cells. Stellate cells were isolated in high purity and yield from the livers of normal rats. The isolated cells had the morphology expected (on electron micrographs) for stellate cells, and were enriched in retinoids and in the intracellular retinoid-binding proteins. The composition of the stellate cell lipid droplets was examined. These lipid droplets were isolated in high purity and integrity from frozen and thawed stellate cell preparations by differential centrifugation. We estimate that the lipid composition of stellate cell lipid droplets consisted of approximately 42% retinyl ester, 28% triglyceride, 13% cholesterol (total) and 4% phospholipid. Thus, stellate cell lipid droplets contain substantial levels of both cholesterol and triglyceride, in addition to retinyl esters. Stellate cell homogenates were assayed for both retinol-binding protein and transthyretin by specific radioimmunoassays. Within the detection limits of these radioimmunoassays, we were unable to detect the presence of either retinol-binding protein (less than 9 ng per 10(6) cells) or transthyretin (less than 11 ng per 10(6) cells) in the stellate cell preparations. Total RNA, prepared from the isolated stellate cells, was examined by Northern blot analysis for retinol-binding protein mRNA and transthyretin mRNA, using cDNA probes for retinol-binding protein and transthyretin. Within the sensitivity of these assays, retinol-binding protein mRNA and transthyretin mRNA were not detected in stellate cells. These findings suggest that stellate cells do not synthesize or accumulate retinol-binding protein.

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