Methylation profile of TP53 regulatory pathway and mtDNA alterations in breast cancer patients lacking TP53 mutations.

The present study investigated promoter hypermethylation of TP53 regulatory pathways providing a potential link between epigenetic changes and mitochondrial DNA (mtDNA) alterations in breast cancer patients lacking a TP53 mutation. The possibility of using the cancer-specific alterations in serum samples as a blood-based test was also explored. Triple-matched samples (cancerous tissues, matched adjacent normal tissues and serum samples) from breast cancer patients were screened for TP53 mutations, and the promoter methylation profile of P14(ARF), MDM2, TP53 and PTEN genes was analyzed as well as mtDNA alterations, including D-loop mutations and mtDNA content. In the studied cohort, no mutation was found in TP53 (DNA-binding domain). Comparison of P14(ARF) and PTEN methylation patterns showed significant hypermethylation levels in tumor tissues (P < 0.05 and <0.01, respectively) whereas the TP53 tumor suppressor gene was not hypermethylated (P < 0.511). The proportion of PTEN methylation was significantly higher in serum than in the normal tissues and it has a significant correlation to tumor tissues (P < 0.05). mtDNA analysis revealed 36.36% somatic and 90.91% germline mutations in the D-loop region and also significant mtDNA depletion in tumor tissues (P < 0.01). In addition, the mtDNA content in matched serum was significantly lower than in the normal tissues (P < 0.05). These data can provide an insight into the management of a therapeutic approach based on the reversal of epigenetic silencing of the crucial genes involved in regulatory pathways of the tumor suppressor TP53. Additionally, release of significant aberrant methylated PTEN in matched serum samples might represent a promising biomarker for breast cancer.

Remyelination in vitro following protein kinase C activator-induced demyelination.

In previous work we found that mezerein, a C kinase activator, as well as basic fibroblast growth factor (FGF-2) induce demyelination and partial oligodendrocyte dedifferentiation in highly differentiated aggregating brain cell cultures. Here we show that following protein kinase C activator-induced demyelination, effective remyelination occurs. We found that mezerein or FGF-2 caused a transient increase in DNA synthesis following a pronounced decrease of the myelin markers myelin basic protein and 2',3'-cyclic nucleotide 3'-phosphohydrolase. Both oligodendrocytes and astrocytes were involved in this mitogenic response. Within 17 days after demyelination, myelin was restored to the level of the untreated controls. Transient mitotic activity was indispensable for remyelination. The present results suggest that myelinating oligodendrocytes retain the capacity to reenter the cell cycle, and that this plasticity is important for the regeneration of the oligodendrocyte lineage and remyelination. Although it cannot be excluded that a quiescent population of oligodendrocyte precursor cells was present in the aggregates and able to proliferate, differentiate and remyelinate, we could not find evidence supporting this view.

Demyelination in brain cell aggregate cultures, induced by a monoclonal antibody against the myelin/oligodendrocyte glycoprotein (MOG).

Previous work has shown that aggregate cultures prepared from fetal rat telencephalon and grown in a chemically defined medium offer a useful model to study developmental processes such as myelin synthesis. Since compact myelin is formed in these cultures, we investigated the possibility to use this culture system to study demyelinating mechanisms. In particular, we examined the effect of a monoclonal antibody (8-18C5) directed against the myelin/oligodendrocyte glycoprotein (MOG). We found that addition of anti-MOG antibodies and complement to aggregate cultures led to a highly significant decrease in myelin basic protein (MBP) content and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) specific activity. These results indicate that, in our culture system, anti-MOG antibodies have a strong demyelinating effect.

Purification and characterization of (Na+ + K+)-ATPase from toad kidney

This report describes the partial purification and the characteristics of (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) from an amphibian source. Toad kidney microsomes were solubilized with sodium deoxycholate and further purified by sodium dodecyl sulphate treatment and sucrose gradient centrifugation, according to the methods described by Lane et al. [(1973) J. Biol. Chem. 248, 7197--7200], Jørgensen [(1974) Biochim. Biophys. Acta 356, 36--52] and Hayashi et al. [(1977) Biochim. Biophys. Acta 482, 185--196]. (Na+ + K+)-ATPase preparations with specific activities up to 1000 mumol Pi/mg protein per h were obtained. Mg2+-ATPase only accounted for about 2% of the total ATPase activity. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed three major protein bands with molecular weights of 116 000, 62 000 and 26 000. The 116 000 dalton protein was phosphorylated by [gamma-32P]ATP in the presence of sodium but not in the presence of potassium. The 62 000 dalton component stained for glycoproteins. The Km for ATP was 0.40 mM, for Na+ 12.29 mM and for K+ 1.14 mM. The Ki for ouabain was 35 micron. Temperature activation curves showed two activity peaks at 37 degrees C and at 50 degrees C. The break in the Arrhenius plot of activity versus temperature appeared at 15 degrees C.

Liver-specific loss of lipin-1-mediated phosphatidic acid phosphatase activity does not mitigate intrahepatic TG accumulation in mice.

Lipin proteins (lipin 1, 2, and 3) regulate glycerolipid homeostasis by acting as phosphatidic acid phosphohydrolase (PAP) enzymes in the TG synthesis pathway and by regulating DNA-bound transcription factors to control gene transcription. Hepatic PAP activity could contribute to hepatic fat accumulation in response to physiological and pathophysiological stimuli. To examine the role of lipin 1 in regulating hepatic lipid metabolism, we generated mice that are deficient in lipin-1-encoded PAP activity in a liver-specific manner (Alb-Lpin1(-/-) mice). This allele of lipin 1 was still able to transcriptionally regulate the expression of its target genes encoding fatty acid oxidation enzymes, and the expression of these genes was not affected in Alb-Lpin1(-/-) mouse liver. Hepatic PAP activity was significantly reduced in mice with liver-specific lipin 1 deficiency. However, hepatocytes from Alb-Lpin1(-/-) mice had normal rates of TG synthesis, and steady-state hepatic TG levels were unaffected under fed and fasted conditions. Furthermore, Alb-Lpin1(-/-) mice were not protected from intrahepatic accumulation of diacylglyerol and TG after chronic feeding of a diet rich in fat and fructose. Collectively, these data demonstrate that marked deficits in hepatic PAP activity do not impair TG synthesis and accumulation under acute or chronic conditions of lipid overload.