Biomedical subjects

M J Coll

Publications and source records attributed to M J Coll.

5 recordsLinked to original sources

PubMed1990

Calmodulin-binding proteins in the nuclei of quiescent and proliferatively activated rat liver cells.

alpha-Spectrin, myosin light chain kinase (MLCK), and caldesmon have been detected in the nuclei of rat liver cells by 125I-calmodulin overlay, immunoblotting, and immunocytochemical methods. alpha-Spectrin is localized in the nuclear matrix, nuclear envelope, and nuclear pores. It has also been detected inside the nuclei in the form of small aggregates. MLCK is present in the nuclear matrix, envelope, nucleoli, and in a nuclease extract (S1 subfraction) but not in the nuclear pores. Caldesmon shows a diffuse distribution pattern inside the nuclei but it is not present in the nucleoli. Since all these proteins are components of the actin-myosin motility systems the presence of actin in the different nuclear subfractions has also been investigated: actin is present in the nuclear matrix, nuclear envelope, nucleoli, and nuclear pores. Proliferative activation of rat liver cells in vivo by partial hepatectomy induces the increase of alpha-spectrin, MLCK, and actin in different nuclear subfractions. This, together with the increase of nuclear calmodulin at the same time after hepatectomy (Pujol, M. J., Soriano, M., Aligúe, R., Carafoli, E., and Bachs, O. (1989) J. Biol. Chem. 264, 18863-18865), indicates that nuclear calmodulin could activate a nuclear contractile system during proliferative activation. A 62-kDa protein (p62) which binds to calmodulin columns and shows immunological similarities to caldesmon is specifically located in the region surrounding the nuclear envelope and is associated with the heterochromatin.

Animals↗

PubMed1988

Reduced levels of sialic acid in the plasma membrane during hepatocellular proliferation.

When rats were infused with a solution containing triiodothyronine, amino acids, glucagon and heparin (solution A) the hepatocytes increased DNA synthesis and decreased plasma membrane sialic acid. In order to study whether the reduced levels of sialic acid in the plasma membrane were associated with hepatocyte proliferation, different mixtures of three components of solution A were infused into rats and the DNA synthetic activity as well as the sialic acid content measured. Results reported here show a correlation between DNA synthetic activity and sialic acid reduction suggesting that the decrease in the plasma membrane sialic acid can be a pre-replicative step associated to cell proliferation.

Amino Acids↗

PubMed1988

New synthesis of cyclic AMP-dependent protein kinases during liver regeneration.

As has been previously reported one surge in cytosolic calmodulin is produced between 4 and 12 h after a partial hepatectomy. Moreover, a surge in cytosolic cyclic AMP and another in cyclic AMP-dependent protein kinase activity can be detected during the late period of the prereplicative phase of liver regeneration after a partial hepatectomy. It is known that these three surges are involved in triggering DNA synthesis. By kinetic studies and by injecting transcription (actinomycin D) and translation (cycloheximide) inhibitors into hepatectomized rats we have demonstrated that the cyclic AMP-dependent protein kinase surge is produced by new synthesis of the enzyme. In thyroparathyroidectomized rats subjected to a partial hepatectomy the calmodulin surge was similar to that observed in normal hepatectomized rats whereas the surge in cyclic AMP-dependent protein kinase activity was strongly decreased suggesting that the cyclic AMP-dependent protein kinase surge is not generated by the previous surge in calmodulin.

Calmodulin↗

PubMed1986

Calmodulin may decrease cell surface sialic acid and be involved in the expression of fibronectin during liver regeneration.

The decrease of sialic acid in plasma membrane glycoproteins and the expression of cell surface fibronectin were studied during the pre-replicative phase of liver regeneration. The aim of this study was to correlate these cell-surface events to the intracellular surge of calmodulin observed a few hours after partial hepatectomy. The fact that calmodulin decreased the specific activity of UDP-N-acetyl-D-glucosamine 2'-epimerase, a key regulatory enzyme in the biosynthesis of glycoprotein sialic acids, and that trifluoperazine prevented the desialylation indicates that the membrane desialylation is a calmodulin-dependent process. On the other hand, Western blotting using anti-rat fibronectin antibody in trifluoperazine-treated animals suggests that calmodulin may also be involved in the surface expression of fibronectin in regenerating hepatocytes.

Animals↗

PubMed1986

[Changes in sialic acid content of the plasma membrane in hepatocellular proliferation].

The content of sialic acid bound to the sinusoidal region of plasma membrane during the prereplicative phase after the intravenous injection of a solution containing triiodothyronine, amino acids, glucagon and heparin (T.A.G.H. solution) has been measured. The results obtained show that an important decrease in sialic acid content is produced as it occurs in the hepatic cells of hepatectomized animals. In order to know if sialidase activity is involved in the decrease of sialic acid content during liver regeneration, the activity of sinusoidal plasma membrane sialidases during the prereplicative phase after the partial hepatectomy has been studied. No modifications of sialidase activity were detected during this period of time indicating that this decrease in sialic acid content has to be produced by other mechanisms such as diminution in the synthesis of precursor molecules. On the other hand due to the importance of Ca2+-calmodulin complexes in the activation of the hepatic cell proliferation the possible implication of this complex on the loss of sialic acid, observing the effect of trifluoperazine (inhibitor of Ca2+-calmodulin complexes) during the prereplicative phase of liver regeneration has been studied. The results show a delay in the decrease of the amount of sugar studied from 10 to 12 hours compared to the results obtained with the hepatectomized rats that have not received trifluoperazine.

Animals↗