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M G Aletti

Publications and source records attributed to M G Aletti.

15 recordsLinked to original sources
PubMed1990

Activity and distribution of protein kinase C in liver during the acute-phase response.

Activity and subcellular distribution of protein kinase C were estimated in liver cytosol and membrane fractions of rats carrying a turpentine-induced inflammation. Protein kinase C activity increases significantly 8 h after treatment in the membrane fraction, with concurrent reduction in the cytosol; 10 h after treatment the membrane-associated activity returns to normal, without concomitant recovery of that detected in the cytosol. The specific binding of phorbol dibutyrate to the liver membrane fraction increases but overall the effect is less evident and delayed in time. The changes are associated to alterations in the phosphorylation pattern of some liver proteins. Liver protein kinase C activity and intracellular distribution seem to be affected by a treatment which is known to induce an acute-phase response in the liver cells.

Acute-Phase Reaction↗
PubMed1988

Liver albumin synthesis increases in free ribosomes during the acute-phase reaction.

Albumin concentration in the blood, and its synthesis by the liver, decrease in the rat during the acute-phase response to inflammation. In this paper we show that 24 hours after turpentine treatment free ribosomes from rat liver double their albumin synthesis and release preproalbumin in the cytosol. albumin mRNA from free polysomes, tested in reconstructed systems in vitro, directs the synthesis of preproalbumin which is correctly processed in the presence of microsomal membranes. Albumin mRNA in the free ribosomal fraction decreases in amount, but it is mainly associated with the heavier polysomal fraction. These data favor the hypothesis of a more, efficient utilization of the reduced amount of albumin mRNA, concurrent with failure of translational arrest of the nascent chain and with the release of unprocessed product in the cytosol.

Acute-Phase Proteins↗
PubMed1987

Prostaglandin synthesis and early biochemical events in the liver cells during the acute-phase response.

Acetylsalicic acid and indomethacin suppress the increase of alpha-amanitin sensitive RNA synthesis (pre-mRNA), but not that of alpha-amanitin resistant RNA synthesis (pre-rRNA), which occur in liver nuclei a few hours after the start of turpentine-induced inflammation in the skin. The inflammation-associated increase in activity of nuclear ATP-ase is also prevented. Synthesis of prostaglandins PGE2 and PGE2 alpha by liver microsomes from turpentine-treated rats is enhanced within 90 min. from treatment. The results suggest an important role of intracellular prostaglandins as mediators of the early nuclear events occurring in the liver at the beginning of the acute-phase response to inflammation.

Acute-Phase Reaction↗
PubMed1986

Inflammation-associated events in liver nuclei during acute-phase reaction.

Isolated liver nucleoli from rats undergoing turpentine-induced inflammation (acute-phase reaction) synthesize rRNA at a rate significantly higher than normal. This increase is associated with, and possibly preceded by, an enhanced methylation of RNA, which further increases when rRNA synthesis has reached a plateau level. Five hours after turpentine treatment, before clear activation of RNA synthesis and methylations, the nucleocytoplasmic transport of rRNA (largely 40S and 60S subunits) and the related ATPase activity of isolated nuclei are significantly increased. Apparently, posttranscriptional control is affected before transcription of rRNA during the onset of the acute-phase reaction: both kinds of events eventually contribute to the expansion of the ribosome population which occurs in the liver cells from rats undergoing an inflammatory process. All these processes are activated before the liver starts the synthesis of acute-phase proteins.

Adenosine Triphosphatases↗
PubMed1984

The role of nuclei, polyribosomes and cytosol factors in the onset of the acute-phase reaction in the liver cell.

Nuclei isolated from livers of turpentine-treated rats show an increased RNA synthesis, reaching a maximum at 10 h after treatment. The stimulation affects both alpha-amanitin-resistant and alpha-amanitin-sensitive activities, suggesting that pre-ribosomal and pre-messenger RNA formation are activated at the same time and to the same extent. The amount of ribosomal RNA, which is still normal 10 h after treatment, increases significantly at 24 h, but the increase is limited to the bound ribosomes, in keeping with the fact that the acute phase reactants are export proteins. These ribosomes, however, are not more active per se and the stimulation of protein synthesis in cell-free preparations depends essentially on an increased activity of soluble factors located in the cytosol. In living cells these soluble factors co-operate with an increased amount of some specific mRNAs and an expanded population of membrane-bound polyribosomes, thus leading to the increased protein synthesis peculiar to the liver of turpentine-treated rats.

Amanitins↗
PubMed1982

Effect of post-ischaemic recovery on albumin synthesis and relative amount of translatable albumin messenger RNA in rat liver.

In liver cells recovering from reversible ischaemia, total protein synthesis by postmitochondrial supernatant and membrane-bound and free polyribosomes is not different from that in sham-operated controls. However, the relative proportion of specific proteins is changed, since the incorporation of [3H]leucine in vivo into liver albumin, relative to incorporation into total protein, as determined by precipitation of labelled albumin with the specific antibody, decreases by 40-50% in post-ischaemic livers. Cell-free synthesis by membrane-bound polyribosomes and poly(A)-enriched RNA isolated from unfractionated liver homogenate shows that the decrease in albumin synthesis in liver of rats recovering from ischaemia is due to the relative decrease in translatable albumin mRNA.

Animals↗
PubMed1979

Inhibition of protein synthesis in ischaemic liver from phenobarbitone-treated rat.

Both ribosomal factors and cytosolic inhibitors are involved in the reduction of the rate of protein synthesis which occurs in the ischaemic hepatocyte from control and phenobarbitone-treated livers. Of these 2 factors it is the latter which seems to play a major role in determining the irreversible impairment of protein synthesis. Phenobarbitone administration has no effect on the rate of protein synthesis of ischaemic and post-ischaemic hepatocyte.

Animals↗
PubMed1978

Phenobarbitone-induced stimulation of protein synthesis in liver of diabetic rat.

The effect of phenobarbitone on liver weight, on the rate of protein synthesis and on the sedimentation profiles of polyribosomes from livers was studied in diabetic rats. The rate of protein synthesis by isolated postmitochondrial supernatants from diabetic rats is lower than that from normal animals. The analysis of polyribosome profiles and the effect of Sephadex chromatography on protein synthesis demonstrated that the reduction was dependent in part on polyribosomal disaggregation and in part on the presence in the cytosol of low molecular weight inhibitor(s). Phenobarbitone administration had the same effect in either diabetic or normal rats in that it increased, (a) the degree of polyribosomal aggregation, (b) the rate of protein synthesis by the isolated postmitochondrial supernatants, (c) liver weight and (d) the activity of the inducible enzyme, NADPH-cytochrome c reductase. Both polyribosomal and soluble factors appear to be involved in the phenobarbitone effect. As the diabetic rats do not secret insulin the results suggest that insulin is not involved in the control of protein synthesis by phenobarbitone. It is suggested that the intracellular redox state has a major influence on the rate of protein synthesis.

Animals↗
PubMed1975

The effect of phenobarbitone on protein synthesis by liver polyribosomes in fed and starved rats.

1. The effect of phenobarbitone on the rate of protein synthesis and on the sedimentation patterns of various liver subcellular fractions containing ribosomes was studied in rats. 2. Phenobarbitone treatment increased the incorporation of [114C]leucine into protein by all preparations, provided they had not been subjected to preliminary treatment with Sephadex G-25. The phenobarbitone-induced effect on incorporation was associated with a gain in liver weight and a higher degree of polyribosomal aggregation. 3. Preparations that were treated with Sephadex G-25 incorporated more radioactivity into protein, but did not show the response to phenobarbitone treatment. 4. When the influence of starvation and phenobarbitone was studied separately on membrane-bound and membrane-free polyribosomes, it was shown that whereas both classes of polyribosomes were affected by starvation, apparently only the former class was susceptible to phenobarbitone stimulation of protein synthesis. 5. The decreased capacity for protein synthesis of polyribosomes from starved rats was independent of their association with the membranes of the endoplasmic reticulum, but resulted from polyribosomal disaggregation, from an intrinsic defect of the polyribosomes themselves and from changes in composition of the cell cap. 6. The results are discussed in relation to the problem of the control of protein biosynthesis and of the functional separation of membrane-bound and membrane-free polyribosomes.

Animals↗