Receptor-mediated uptake of beta-glucuronidase into primary astrocytes and C6 glioma cells from rat brain

Changes in the levels of neuropeptides and their metabolizing enzymes in the brain regions of nucleus basalis magnocellularis-lesioned rats

The regulation mechanism of the interrelation between neuropeptides and their metabolizing enzymes in in vivo tissues is still not clear. In the present report, we attempted to measure the levels of neuropeptides and their enzymes in the frontal cortex, hippocampus, and striatum of the rat that had been bilaterally lesioned by the infusion of ibotenic acid or amyloid beta-peptide 25 - 35 (Abeta25 - 35) into the nucleus basalis magnocellularis. In the drug-treated rats, at two weeks after the infusion, the decrease of somatostatin-like immunoreactivity (SS-LI) and the increase of cholecystokinin-8S-LI were found in some brain regions relative to vehicle-treated rats. The immunoreactivities of endopeptidase 24.15 and puromycin-sensitive aminopeptidase and the leucine aminopeptidase- and aminopeptidase B-like enzyme activities did not change in the three brain regions, suggesting that the levels of those peptide-degrading enzymes do not correlate with the changes of the neuropeptide levels. The decrease of subtilisin-like proprotein convertase (SPC)-like enzyme activity was found in the hippocampus of the Abeta25 - 35-treated rats. The SS mRNA level decreased in the hippocampus in parallel with decreases in the SS-LI level and SPC-like enzyme activity. The present data indicate that some of the neuropeptide-processing enzymes may contribute to the control of neuropeptide levels.

The role of tumor rejection antigens in host antitumor defense mechanisms

BACKGROUND

Normal cells undergo contact inhibition of growth when their surface molecules interact. Tumor cells, however, have undergone a mutation that prevents this arrest of growth upon contact inhibition and allows constant growth. Thus, growth inhibition fails to occur despite the interaction of surface molecules. In recent years a subgroup of these surface molecules has been of interest to cancer investigators. This subgroup has been termed the tumor rejection antigens (TRAs). As the name implies, these are specific to the tumor of origin and may direct the immune system of the host to target the tumor cells and kill them.

METHODS

A literature search was carried out on TRAs to ascertain the current thinking on the subject.

RESULTS

Initial studies of TRAs have revealed that some of them may be heat shock proteins (HSPs). In particular, grp96, a number of the HSP90 family, has been implicated. More recent studies, however, have shown that HSPs alone may not be immunogenic but may act as carrier proteins for tumor specific peptides.

CONCLUSION

Such findings have led to speculation that HSPs or their associated peptides may have a role in the diagnosis and/or treatment of specific cancers. Immunotherapy and bispecific antibodies in particular are areas in which HSPs may prove to be useful.

Effect of cocaine on macromolecular syntheses and cell proliferation in cultured glial cells

In the present study the effect of cocaine on thymidine, uridine and leucine incorporation was assessed in primary cortical glial and C6 glioma cells. Cocaine exposure for 24 h inhibited thymidine and uridine incorporation in cortical glial and C6 glioma cells. However, the effect of cocaine on uridine incorporation was less prominent compared to thymidine incorporation. High concentrations of cocaine inhibited leucine incorporation in C6 glioma cells but not in cortical glia. Cocaine exposure for four days decreased cell proliferation of cortical glial and C6 glioma cells. Cocaine-induced attenuation of macromolecular syntheses was not due to cell death since cocaine-treated cells were not stained with Trypan Blue and did not release lactate dehydrogenase into culture supernatants. Furthermore, cocaine had no effect on glutamate uptake either in cortical glia or in C6 glioma cells. These results indicate that cocaine inhibits macromolecular syntheses in glial cells. The inhibition of macromolecular syntheses in glial cells may be the mechanism involved in cocaine-induced fetal brain growth retardation.

Lysosomal storage diseases: mechanisms of enzyme replacement therapy

Lysosomal diseases result from deficiency of one of the many enzymes involved in the normal, step-wise breakdown of macromolecules. Studies in vitro have shown that cells from enzyme-deficient patients can be corrected by an exogenous supply of the missing enzyme. This occurs by receptor-mediated endocytosis of normal enzyme added to tissue culture medium and also by direct transfer from normal leukocytes during cell-to-cell contact. Immunohistochemical analysis has revealed that these processes have similar pathways of intracellular transport of the acquired enzymes, which ultimately reach mature lysosomes in the recipient cells. Moreover, recent studies suggest that both mechanisms are important in the therapy of lysosomal storage diseases by bone marrow transplantation. Advances in gene technology are likely to improve the successful treatment of these disorders, by facilitating the large scale production of clinically effective proteins and also by enabling the stable and safe introduction of normal lysosomal genes into cells of affected patients.

Two types of clathrin-coated vesicles isolated from rat brain: analysis of biochemical properties and cellular origin

Two major fractions rich in clathrin-coated vesicles (CVs) (fraction I, rho = 1.140 g/cm3; fraction II, rho = 1.113 g/cm3) were separated from rat brain using a sucrose gradient and compared for their cellular origins and Cl- translocation systems. Electron micrographs showed that both fractions contained CVs of different size distributions (fraction I, 85 +/- 9.5 nm in diameter; fraction II, 72 +/- 6.8 nm in diameter). Fraction II contained potent ouabain-sensitive ATPase activity, whereas fraction I contained only a little activity. Immunoblot analysis for the Na+,K(+)-ATPase catalytic subunit, alpha and alpha(+), demonstrated that fraction II exhibited predominantly alpha(+), whose proportion to alpha was analogous to that observed in the extracts of primary cultured neuronal cells. Furthermore, on a sucrose density gradient, cultured neuronal cells yielded fraction II but not fraction I, whereas primary cultured glial cells yielded fraction I but not fraction II. Labeling-chase experiments using 125I-transferrin in cultured neuronal cells showed the internalized ligand in fraction II and the surface-bound ligand in the fraction with lower density (rho = 1.090 g/cm3), a result suggesting that the involvement of Na+,K(+)-ATPase in fraction II is attributable to endocytic vesicles. Cl- uptake in fraction II was approximately threefold higher than that in fraction I. N-Ethylmaleimide (100 microM) completely inhibited the Cl- uptake in fraction I but partially (approximately 50%) inhibited that in fraction II. These findings suggest that the two CV fractions isolated from rat brain originate from different cell types--glial and neuronal cells--and differ in size distribution of CVs, content of Na+,K(+)-ATPase, and mechanism for Cl- uptake.