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Previously, we have shown the loss of anti-Bax function in Creutzfeldt Jakob disease (CJD)-associated prion protein (PrP) mutants that are unable to generate cytosolic PrP (CyPrP). To determine if the anti-Bax function of PrP modulates the manifestation of prion diseases, we further investigated the anti-Bax function of eight familial Gerstmann-Sträussler- Scheinker Syndrome (GSS)-associated PrP mutants. These PrP mutants contained their respective methionine (M) or valine (V) at codon 129. All of the mutants lost their ability to prevent Bax-mediated chromatin condensation or DNA fragmentation in primary human neurons. In the breast carcinoma MCF-7 cells, the F198SV, D202NV, P102LV and Q217RV retained, whereas the P102LM, P105LV, Y145stopM and Q212PM PrP mutants lost their ability to inhibit Bax-mediated condensed chromatin. The inhibition of Bax-mediated condensed chromatin depended on the ability of the mutants to generate cytosolic PrP. However, except for the P102LV, none of the mutants significantly inhibited Bax-mediated caspase activation. These results show that the cytosolic PrP generated from the GSS mutants is not as efficient as wild type PrP in inhibiting Bax-mediated cell death. Furthermore, these results indicate that the anti-Bax function is also disrupted in GSSassociated PrP mutants and is not associated with the difference between CJD and GSS. [ABSTRACT FROM AUTHOR]

The cause of the conformational change of normal cellular prion protein (PrP) into its disease-associated form is unknown. Posttranslational modifications, such as glycosylation, acetylation, S-nitrosylation, and phosphorylation, are known to induce protein conformational changes. Here, we investigated whether phosphorylation could induce the conformational change of PrP because PrP contains several kinase motifs and has been found recently in the cytosol, in which kinases generally reside. Neuronal cyclin-dependent kinase 5 (Cdk5) phosphorylated recombinant PrP23-231 at serine 43 (S43) in an in vitro kinase assay. Cdk5-phosphorylated PrP became proteinase K resistant, formed Congo Red-positive fibrils, and formed aggregates that were immunostained with anti-PrP and anti-phospho-PrPS43 (anti-pPrP S43). pPrPS43 was detected in PrP/Cdk5/p25 cotransfected N2a cells. Roscovitine inhibition of Cdk5 activity or transfection of N2a cells with mutant PrP S43A eliminated the anti-pPrPS43-immunopositive protein. Alkaline phosphatase-sensitive and proteinase K-resistant pPrPS43 immunoreactivity was observed in scrapie-infected but not control-injected mice brains. These results raise the possibility that phosphorylation could represent a physiological mechanism of PrP conversion in vivo. [ABSTRACT FROM AUTHOR]

Many beneficial proprieties have been associated with polyphenols from green tea, such as chemopreventive, anticarcinogenic, antiatherogenic and antioxidant actions. In this study, we investigated the effects of green tea polyphenols (GTPs) and their principal catechins on the function of P-glycoprotein (P-gp), which is involved in the multidrug resistance phenotype of cancer cells. GTPs (30 μg/ml) inhibit the photolabeling of P-gp by 75% and increase the accumulation of rhodamine-123 (R-123) 3-fold in the multidrug-resistant cell line CHRC5, indicating that GTPs interact with P-gp and inhibit its transport activity. Moreover, the modulation of P-gp transport by GTPs was a reversible process. Among the catechins present in GTPs, EGCG, ECG and CG are responsible for inhibiting P-gp. In addition, EGCG potentiates the cytotoxicity of vinblastine (VBL) in CHRC5 cells. The inhibitory effect of EGCG on P-gp was also observed in human Caco-2 cells, which form an intestinal epithelial-like monolayer. Our results indicate that, in addition to their anti-cancer properties, GTPs and more particularly EGCG inhibit the binding and efflux of drugs by P-gp. Thus, GTPs or EGCG might be potential agents for modulating the bioavailability of P-gp substrates at the intestine and the multidrug resistance phenotype associated with expression of this transporter in cancer cells. [Copyright &y& Elsevier]

Primary brain tumors, particularly glioblastomas (GB), remain a challenge for oncology. An element of the malignant brain tumors' aggressive behavior is the fact that GB are among the most densely vascularized tumors. To determine some of the molecular regulations occuring at the brain tumor endothelium level during tumoral progression would be an asset in understanding brain tumor biology. Caveolin-1 is an essential structural constituent of caveolae that has been implicated in mitogenic signaling, oncogenesis, and angiogenesis. In this work we investigated regulation of caveolin-1 expression in brain endothelial cells (ECs) under angiogenic conditions. In vitro, brain EC caveolin-1 is down-regulated by angiogenic factors treament and by hypoxia. Coculture of brain ECs with tumoral cells induced a similar down-regulation. In addition, activation of the p42/44 MAP kinase is demonstrated. By using an in vivo brain tumor model, we purified ECs from gliomas as well as from normal brain to investigate possible regulation of caveolin-1 expression in tumoral brain vasculature. We show that caveolin-1 expression is strikingly down-regulated in glioma ECs, whereas an increase of phosphorylated caveolin-1 is observed. Whole-brain radiation treatment, a classical way in which GB is currently being treated, resulted in increased caveolin-1 expression in tumor isolated ECs. The level of tumor cells spreading around newly formed blood vessels was also elevated. The regulation of caveolin-1 expression in tumoral ECs may reflect the tumoral vasculature state and correlates with angiogenesis kinetics., (Copyright 2003 Wiley-Liss, Inc.)