Transglutaminase 2 in the balance of cell death and survival

Transglutaminase 2 (TG2), a multifunctional enzyme with Ca(2+)-dependent protein crosslinking activity and GTP-dependent G protein functions, is often upregulated in cells undergoing apoptosis. In cultured cells TG2 may exert both pro- and anti-apoptotic effects depending upon the type of cell, the kind of death stimuli, the intracellular localization of the enzyme and the type of its activities switched on. The majority of data support the notion that transamidation by TG2 can both facilitate and inhibit apoptosis, while the GTP-bound form of the enzyme generally protects cells against death. In vivo studies confirm the Janus face of TG2 in the initiation of the apoptotic program. In addition, they reveal a further role: the prevention of inflammation, tissue injury and autoimmunity once the apoptosis has already been initiated. This function of TG2 is partially achieved by being expressed and activated also in macrophages digesting apoptotic cells and mediating a crosstalk between dying and phagocytic cells.     

Expression of tau reduces secretion of Abeta without altering the amyloid precursor protein content in CHOsw cells

Insoluble deposits of tau and amyloid precursor protein (APP) peptides Abeta characterize Alzheimer's disease. We studied the role of tau in the metabolism of APP in cells stably expressing APP Swedish mutation (CHOsw). Transient expression of tau in CHOsw cells caused morphological changes, bundling of microtubules and perinuclear aggregation of Golgi-derived vesicles. It also reduced the secretion of Abeta(1-40) and Abeta(1-42) without altering the APP steady state levels. This was accompanied by a reduction in the gamma-secretase and an increase in the insulin degrading enzyme activities. Our results suggest that tau may play an inhibitory role in the amyloidogenic activity of APP.     

Alzheimer's disease: channeling APP to non-amyloidogenic processing

A good number of pharmacologic agents have over the years been touted as potentially beneficial in either preventing the onset or delay the progression of Alzheimer's disease. These include compounds such as non-steroidal anti-inflammatory drugs (NSAIDs) (HMG-CoA reductase inhibitors (statins)) and flavonoids. The underlying mechanisms for the beneficial effect of these agents are by and large attributed to their ability to reduce beta-amyloid (Abeta) production and amyloid load in the brain, via inhibition of amyloidogenic gamma-secretase activity. Recent reports have now provided mechanistic insights as to how non-amyloidogenic processing might also be enhanced by these seemingly unrelated treatments. Intriguingly, this appears to involve the inhibition of the activity of small GTPase Rho and its effector, the Rho-associated kinase, ROCK. Dietary caloric restriction (CR) also enhances non-amyloidogenic processing of APP, and this may be part of a more general anti-aging effect of CR mediated by gene expression changes downstream of the activity of the histone deacetylase SIRT1.     

The beta-subunit of G proteins is a substrate of protein histidine phosphatase

Increasing evidence suggests that reversible phosphorylation of histidine residues in proteins is important for signaling cascades in eukaryotic cells. Recently, the first eukaryotic protein histidine phosphatase (PHP) was identified. The beta1-subunit of heterotrimeric G proteins (Gbeta) undergoes phosphorylation on His266 which is apparently involved in receptor-independent G protein activation. We studied whether phosphorylated Gbeta-subunits are substrates of PHP. Phosphorylated Gbetagamma dimers of the retinal G protein transducin and Gbeta in membrane preparations of H10 cells (neonatal rat cardiomyocytes) were dephosphorylated by PHP. Overexpression of PHP in H10 cells showed that PHP and Gbeta also interfere within cells. In membranes of cells overexpressing PHP, the amount of phosphorylated Gbeta was largely reduced. Both our in vitro and cell studies indicate that phosphorylated Gbeta-subunits of heterotrimeric G proteins are substrates of PHP. Therefore, PHP might play a role in the regulation of signal transduction via heterotrimeric G proteins.     

Genetic heterogeneity at the beta-giardin locus among human and animal isolates of Giardiaduodenalis and identification of potentially zoonotic subgenotypes

Human giardiasis, caused by the intestinal flagellate Giardia duodenalis, is considered a zoonotic infection, although the role of animals in the transmission to humans is still unclear. Molecular characterisation of cysts of human and animal origin represents an objective means to validate or reject this hypothesis. In the present work, cysts were collected in Italy from humans (n=37) and animals (dogs, one cat and calves, n=46), and were characterised by PCR amplification and sequencing of the beta-giardin gene. As expected, only Assemblages A and B were identified among human isolates. The host-specific Assemblages C and D were found in the majority of dog isolates; however, 6 dog isolates were typed as Assemblage A. The cat-specific Assemblage F has been identified in the single feline isolate available. Among calf isolates, most were typed as Assemblages A (n=12) and B (n=5), whereas the host-specific Assemblage E was rarely found (n=3). Sequence heterogeneity in the beta-giardin gene allowed a number of subgenotypes to be identified within Assemblage A (8 subgenotypes), B (6 subgenotypes), D (2 subgenotypes), and E (3 subgenotypes). Five of these subgenotypes, namely A1, A2, A3, A4 and B3, were found to be associated with infections of humans, of dogs and of calves; these data, therefore, supported the role of these animals as a source of infection for humans.     

Beta-cyclolavandulyl and beta-isocyclolavandulyl esters from Peucedanum paniculatum L., an endemic species to Corsica

Eight cyclolavandulyl esters (beta-cyclolavandulyl and beta-isocyclolavandulyl acetate, propionate, isobutyrate, isovalerate) were identified in the leaf and root oils of Peucedanum paniculatum L., an endemic species to Corsica, by comparison of their spectroscopic data with those of synthetic material. Their structures were elucidated by spectroscopic methods. The antimicrobial activity of essential oils of leaves and roots was evaluated against eleven microorganisms.     

NADPH-dependent metabolism of 17beta-estradiol and estrone to polar and nonpolar metabolites by human tissues and cytochrome P450 isoforms

The endogenous estrogens, 17beta-estradiol (E(2)) and estrone (E(1)), undergo extensive metabolism in animals and humans, and a large number of their hydroxylated and keto metabolites have been identified in biological samples. The formation of most of the oxidative estrogen metabolites is catalyzed by cytochrome P450 (CYP) enzymes. Precise knowledge of the CYP-mediated formation of these metabolites, particularly those with unique biological activities (e.g., 4-hydroxy-E(2), 16alpha-hydroxy-E(1), 15alpha-hydroxy-E(2), 16-epiestriol, and 2-methoxyestradiol) in human liver and extrahepatic target tissues and cells, would add significantly to our understanding of the diverse biological functions that are associated with endogenous estrogens. In this article, we review recent results on the NADPH-dependent metabolism of endogenous estrogens to polar (hydroxylated and keto) metabolites as well as to nonpolar metabolites by human tissues and recombinant human CYP isoforms. The available data show that a large number of polar and nonpolar metabolites of E(2) and E(1) are formed by human tissues, and a variety of human CYP isoforms are involved in the NADPH-dependent formation of polar as well as nonpolar estrogen metabolites. These enzymes have varying degrees of catalytic activity and distinct regioselectivity.