Proline dehydrogenase (oxidase), a mitochondrial tumor suppressor, and autophagy under the hypoxia microenvironment

Proline dehydrogenase (oxidase, PRODH/POX), the first enzyme in the pathway of proline catabolism, has been identified as a mitochondrial, metabolic tumor suppressor, which is downregulated in a variety of human tumors. However, our recent findings show that PRODH/POX is upregulated by hypoxia in vitro and in vivo. The combination of low glucose and hypoxia produces additive effects on PRODH/POX expression. Both hypoxia and glucose depletion enhance PRODH/POX expression through AMP-activated protein kinase (AMPK) activation to promote tumor cell survival. Nevertheless, the mechanisms underlying PRODH/POX prosurvival functions are different for hypoxia and low-glucose conditions. Glucose depletion with or without hypoxia elevates PRODH/POX and proline utilization to supply ATP for cellular energy needs. Interestingly, under hypoxia PRODH/POX induces protective autophagy by generating reactive oxygen species (ROS). AMPK is the main initiator of stress-triggered autophagy. Thus, PRODH/POX acts as a downstream effector of AMPK in the activation of autophagy under hypoxia. This regulation was confirmed to be independent of the mechanistic target of rapamycin (MTOR) pathway, a major downstream target of AMPK signaling.     

Marine biofilm bacteria evade eukaryotic predation by targeted chemical defense

Many plants and animals are defended from predation or herbivory by inhibitory secondary metabolites, which in the marine environment are very common among sessile organisms. Among bacteria, where there is the greatest metabolic potential, little is known about chemical defenses against bacterivorous consumers. An emerging hypothesis is that sessile bacterial communities organized as biofilms serve as bacterial refuge from predation. By testing growth and survival of two common bacterivorous nanoflagellates, we find evidence that chemically mediated resistance against protozoan predators is common among biofilm populations in a diverse set of marine bacteria. Using bioassay-guided chemical and genetic analysis, we identified one of the most effective antiprotozoal compounds as violacein, an alkaloid that we demonstrate is produced predominately within biofilm cells. Nanomolar concentrations of violacein inhibit protozoan feeding by inducing a conserved eukaryotic cell death program. Such biofilm-specific chemical defenses could contribute to the successful persistence of biofilm bacteria in various environments and provide the ecological and evolutionary context for a number of eukaryote-targeting bacterial metabolites.     

A novel function for hydroxyproline oxidase in apoptosis through generation of reactive oxygen species

Proline and hydroxyproline are metabolized by distinct pathways. Proline is important for protein synthesis, as a source of glutamate, arginine, and tricarboxylic acid cycle intermediates, and for participating in a metabolic cycle that shuttles redox equivalents between mitochondria and cytosol. Hydroxyproline, in contrast, is not reutilized for protein synthesis. The first steps in the degradation of proline and hydroxyproline are catalyzed by proline oxidase (POX) and hydroxyproline oxidase (OH-POX), respectively. Because it is well documented that POX is induced by p53 and plays a role in apoptosis, we considered whether OH-POX also participates in the response to cytotoxic stress. In LoVo and RKO cells, which respond to adriamycin with a p53-mediated induction of POX and generation of reactive oxygen species, we found that adriamycin also induced OH-POX gene expression and markedly increased OH-POX catalytic activity, and this increase in activity was not observed in the cell lines HT29 and HCT15, which do not have a functional p53. We also observed an increase in reactive oxygen species generation and activation of caspase-9 with adriamycin in a hydroxyproline-dependent manner. Therefore, we hypothesize that OH-POX plays a role analogous to POX in growth regulation, ROS generation, and activation of the apoptotic cascade.     

Protoplast isolation and regeneration from <Emphasis Type="Italic">Gracilaria changii</Emphasis> (Gracilariales,Rhodophyta)

The tropical agarophyte Gracilaria changii has been much researched and documented by the Algae Research Laboratory, University of Malaya, especially with regards to its potential as a seaweed bioreactor for valuable compounds. Protoplast regeneration of this seaweed was developed following the optimization of protoplast isolation protocol. Effect of the concentration and combination of isolating enzymes, incubation period, temperature, enzyme solution pH, tissue source on the protoplast yields were used to optimize the isolation protocol. The enzyme mixture with 4% w/v cellulase Onozuka R-10, 2% w/v macerozyme R-10 and 1 unit mL^-1 agarase was found to produce the highest yield of protoplast at 28°C and 3 h incubation period. Thallus tips gave higher yields of protoplasts than middle segments. Freshly isolated G. changii protoplasts were cultured in MES medium. Regeneration of protoplast cell walls after 24 h was confirmed by calcofluor white M2R staining under UV fluorescence microscopy. The protoplasts with regenerated cell walls then underwent a series of cell division to produce callus-like cell masses in MES medium. Following this, juvenile plants of G. changii were obtained.     

Accumulation of pyrroline 5-carboxylic acid in conditioned medium of cultured fibroblast: Stimulatory effects of serum,insulin, and IGF-1

Summary Pyrroline 5-carboxylate, an intermediate of amino acid metabolism, is released into medium by cultured normal human fibroblasts. With cells made quiescent by serum starvation, the addition of 10% fetal bovine serum augmented the release of pyrroline 5-carboxylate into medium by 2.5-fold. Although platelet-derived growth factor was without effect, both insulin and insulinlike growth factor-1 nearly reproduced the serum effect. The dose-dependence of insulin and insulinlike growth factor 1 effects suggested their mediation by their own respective receptors. Although the mechanism for the stimulatory effect remains unknown, these effects of insulin and insulinlike growth factor 1 on pyrroline 5-carboxylate suggest hormonal regulation of pyrroline 5-carboxylate release.     

Environmental Control of Vanadium Haloperoxidases and Halocarbon Emissions in Macroalgae

Vanadium-dependent haloperoxidases (V-HPO), able to catalyze the reaction of halide ions (Cl^?, Br^?, I^-) with hydrogen peroxide, have a great influence on the production of halocarbons, which in turn are involved in atmospheric ozone destruction and global warming. The production of these haloperoxidases in macroalgae is influenced by changes in the surrounding environment. The first reported vanadium bromoperoxidase was discovered 40 years ago in the brown alga Ascophyllum nodosum. Since that discovery, more studies have been conducted on the structure and mechanism of the enzyme, mainly focused on three types of V-HPO, the chloro- and bromoperoxidases and, more recently, the iodoperoxidase. Since aspects of environmental regulation of haloperoxidases are less well known, the present paper will focus on reviewing the factors which influence the production of these enzymes in macroalgae, particularly their interactions with reactive oxygen species (ROS).     

Context-dependent memory: colour versus odour

An olfactory stimulus and a visual stimulus were employed in a context- dependent memory study using a prose passage as the to-be-remembered item. Ninety-five university students (aged 17-35 years) learned the passage of prose in the presence of one of the stimuli and were then asked to recall the passage with the original context either reinstated or not reinstated. The results revealed a significant context-dependent memory effect for the olfactory cue but not for the visual cue. They demonstrate support for the effectiveness of odours as context cues and it is suggested that context-dependent memory processes may underlie the formation and retrieval of odour-evoked autobiographical memories.      

Interaction Between Histidyl Transfer Ribonucleic Acid and the First Enzyme for Histidine Biosynthesis of Salmonella typhimurium

Previous studies showed that the enzyme (phosphoribosyltransferase) which catalyzes the first step of the histidine pathway in Salmonella typhimurium plays a role in regulation of the histidine operon. Since histidyl transfer ribonucleic acid (His-tRNA) is required for repression of the histidine operon, we considered the possibility that the role of phosphoribosyltransferase might be realized through an interaction with His-tRNA. One prediction inherent in this idea is that the enzyme should interact with His-tRNA in vitro. Evidence is presented for such an interaction. Binding of (3)H-His-tRNA to purified phosphoribosyltransferase was tested on Sephadex columns and on nitrocellulose filters. The enzyme was found to have a high affinity for tRNA. Comparing the binding of (3)H-His-tRNA with that of tRNA aminoacylated with other (3)H-amino acids disclosed that the binding of the histidyl species of tRNA is favored over that of other species and is dependent upon magnesium-ion concentration.