14 research outputs found
Hypericin: a potential antiglioma therapy
Journal ArticleHYPERICIN, A POLYCYCLIC aromatic dione isolated from plants, is presently being clinically evaluated as an antiviral agent in the treatment of human immunodeficiency virus (HIV) infection. In addition, it is known to be a potent protein kinase C inhibitor. To evaluate its potential as an inhibitor of glioma growth, an established (U87) and low-passage glioma line (93-492) were treated with hypericin in tissue culture for a period of 48 hours after passage. Hypericin inhibited the glioma growth in a dose-related manner, with a marked inhibition of growth in the low-micromolar concentration range (e.g., in line U87 and low-passage line 93-492 , a concentration of hypericin of 10 pmol/L produced 62 and 76% decreases in [3H]thymidine uptake, respectively). Because the reported inhibitory effects of protein kinase Care enhanced by visible light, [3H]thymidine uptake was measured in both the presence and the absence of visible light. In glioma line A172, the presence of light slightly increased the inhibitory effect of hypericin. Moreover, an apoptosis (i.e., programmed cell death) assay was performed to determine whether the treatment of glioma cells with hypericin was cytostatic or cytocidal. Cells were harvested, and purified deoxyribonucleic acid (DNA) was analyzed by agarose gel electrophoresis. DNA from cells treated with hypericin for 48 hours exhibited a classical "ladder" pattern of oligonucleosome-sized fragments characteristic of apoptosis. These data suggest that the proven safe drug hypericin may have potential as an antiglioma agent; we suggest clinical trials
Rapid purification of calcium-activated protease by calcium-dependent hydrophobic-interaction chromatography
AbstractBoth low Ca2+- and high Ca2+-requiring forms of Ca2+-activated protease (calpains I and II) were found to bind to phenyl-Sepharose in a calcium-dependent manner, suggesting that both enzymes expose a hydrophobic surface region in the presence of Ca2+. Inclusion of leupeptin in column buffers prevented the loss of activity during hydrophobic-interaction and substrate-affinity chromatography. Under these conditions calpain II (high calcium-requiring form) was rapidly purified from bovine brain and rabbit skeletal muscle using successive phenyl-Sepharose and casein-Sepharose columns
Counteraction of Nogo-A and axonal growth inhibitors by green tea polyphenols and other natural products
Cell signaling associated with internalization of 67 kDa laminin receptor (67LR) by soluble laminin and its implication for protection against neurodegenerative diseases
Irreversible oxidative inactivation of protein kinase C by photosensitive inhibitor calphostin C
Rapid purification of calcium-activated protease by calcium-dependent hydrophobic-interaction chromatography
Cancer-Preventive Selenocompounds Induce a Specific Redox Modification of Cysteine-Rich Regions in Ca2+- Dependent Isoenzymes of Protein Kinase C
A Direct Redox Regulation of Protein Kinase C Isoenzymes Mediates Oxidant-induced Neuritogenesis in PC12 Cells*
In this study, we have used the PC12 cell model to elucidate the mechanisms by which sublethal doses of oxidants induce neuritogenesis. The xanthine/xanthine oxidase (X/XO) system was used for the steady state generation of superoxide, and CoCl2 was used as a representative transition metal redox catalyst. Upon treatment of purified protein kinase C (PKC) with these oxidants, there was an increase in its cofactor-independent activation. Redox-active cobalt competed with the redoxinert zinc present in the zinc-thiolates of the PKC regulatory domain and induced the oxidation of these cysteine-rich regions. Both CoCl2 and X/XO induced neurite outgrowth in PC12 cells, as determined by an overexpression of neuronal marker genes. Furthermore, these oxidants induced a translocation of PKC from cytosol to membrane and subsequent conversion of PKC to a cofactor-independent form. Isoenzyme-specific PKC inhibitors demonstrated that PKCĪµ plays a crucial role in neuritogenesis. Moreover, oxidant-induced neurite outgrowth was increased with a conditional overexpression of PKCĪµ and decreased with its knock-out by small interfering RNA. Parallel with PKC activation, an increase in phosphorylation of the growth-associated neuronal protein GAP-43 at Ser41 was observed. Additionally, there was a sustained activation of extracellular signal-regulated kinases 1 and 2, which was correlated with activating phosphorylation (Ser133) of cAMP-responsive element-binding protein. All of these signaling events that are causally linked to neuritogenesis were blocked by antioxidant N-acetylcysteine (both l and d-forms) and by a variety of PKC-specific inhibitors. Taken together, these results strongly suggest that sublethal doses of oxidants induce neuritogenesis via a direct redox activation of PKCĪµ