α-Synuclein expression selectively affects tumorigenesis in mice modeling Parkinson's disease

Alpha Synuclein (α-Syn) is a protein implicated in mechanisms of neuronal degeneration in Parkinson's disease (PD). α-Syn is primarily a neuronal protein, however, its expression is found in various tumors including ovarian, colorectal and melanoma tumors. It has been hypothesized that neurodegeneration may share common mechanisms with oncogenesis. We tested whether α-Syn expression affects tumorigenesis of three types of tumors. Specifically, B16 melanoma, E0771 mammary gland adenocarcinoma and D122 Lewis lung carcinoma. For this aim, we utilized transgenic mice expression the human A53T α-Syn form. We found that the in vivo growth of B16 and E0771 but not D122 was enhanced in the A53T α-Syn mice. The effect on tumorigenesis was not detected in age-matched APP/PS1 mice, modeling Alzheimer's disease (AD), suggesting a specific effect for α-Syn-dependent neurodegeneration. Importantly, transgenic α-Syn expression was detected within the three tumor types. We further show uptake of exogenously added, purified α-Syn, by the cultured tumor cells. In accord, with the affected tumorigenesis in the young A53T α-Syn mice, over-expression of α-Syn in cultured B16 and E0771 cells enhanced proliferation, however, had no effect on the proliferation of D122 cells. Based on these results, we suggest that certain forms of α-Syn may selectively accelerate cellular mechanisms leading to cancer.     

N-acetylcysteine amide, a novel cell-permeating thiol, restores cellular glutathione and protects human red blood cells from oxidative stress

Oxidative stress plays an important role in the progression of neurodegenerative and age-related diseases, causing damage to proteins, DNA, and lipids. A novel thiol N-acetylcysteine amide (AD4), the amide form of N-acetylcysteine (NAC) and a Cu(2+) chelator, was assessed for its antioxidant and protective effects using human red blood cells (RBCs) as a model. AD4 was shown by flow cytometry to inhibit tert.-butylhydroxyperoxide (BuOOH)-induced intracellular oxidation in RBCs stained with the oxidant-sensitive probe 2',7'-dichlorofluorescein diacetate. In addition, AD4 retarded BuOOH-induced thiol depletion and hemoglobin oxidation. Restoration of the thiol-depleted RBCs by externally applied AD4 was significantly greater compared with NAC and, unlike NAC, was accompanied by hemoglobin protection from oxidation. In a cell-free system we have demonstrated that AD4 reacted with oxidized glutathione (GSSG) to generate reduced glutathione (GSH). The formation of GSH was determined enzymatically using GSH peroxidase and by HPLC. Based on these results a thiol-disulfide exchange between AD4 and GSSG is proposed as the mechanism underlying the antioxidant effects of AD4 on BuOOH-treated RBCs. Together, these studies demonstrate that AD4 readily crosses cell membranes, replenishes intracellular GSH, and, by incorporating into the redox machinery, defends the cell from oxidation. These results provide further evidence for the efficient membrane permeation of AD4 over NAC, and support the possibility that it could be explored for treatment of neurodegeneration and other oxidation-mediated disorders.     

Do physiological roles foster persistence of drug/multidrug-efflux transporters? A case study

Drug and multidrug resistance have greatly compromised the compounds that were once the mainstays of antibiotic therapy. This resistance often persists despite reductions in the use of antibiotics, indicating that the proteins encoded by antibiotic-resistance genes have alternative physiological roles that can foster such persistence in the absence of selective pressure by antibiotics. The recent observations that Tet(L), a tetracycline-efflux transporter, and MdfA, a multidrug-efflux transporter, both confer alkali tolerance offer a striking case study in support of this hypothesis.     

Tyrosine modification is not required for myeloperoxidase-induced loss of apolipoprotein A-I functional activities

Apolipoprotein A-I (apoAI), the major protein of high density lipoprotein, plays an important role in reverse cholesterol transport via its activity as an ABCA1-dependent acceptor of cellular cholesterol. We reported recently that myeloperoxidase (MPO) modification of apoAI inhibits its ABCA1-dependent cholesterol acceptor activity (Zheng, L., Nukuna, B., Brennan, M. L., Sun, M., Goormastic, M., Settle, M., Schmitt, D., Fu, X., Thomson, L., Fox, P. L., Ischiropoulos, H., Smith, J. D., Kinter, M., and Hazen, S. L. (2004) J. Clin. Invest. 114, 529-541). We also reported that MPO-mediated chlorination preferentially modifies two of the seven tyrosines in apoAI, and loss of parent peptides containing these residues dose-dependently correlates with loss in ABCA1-mediated cholesterol acceptor activity (Zheng, L., Settle, M., Brubaker, G., Schmitt, D., Hazen, S. L., Smith, J. D., and Kinter, M. (2005) J. Biol. Chem. 280, 38-47). To determine whether oxidative modification of apoA-I tyrosine residues was responsible for the MPO-mediated inactivation of cholesterol acceptor activity, we made recombinant apoAI with site-specific substitutions of all seven tyrosine residues to phenylalanine. ApoAI and the tyrosine-free apoAI were equally susceptible to dose-dependent MPO-mediated loss of ABCA1-dependent cholesterol acceptor activity, as well as lipid binding activity. MPO modification altered the migration of apoAI on SDS gels and decreased its alpha-helix content. MPO-induced modification also targeted apoAI tryptophan and lysine residues. Specifically, we detected apoAI tryptophan oxidation to mono- and dihydroxytryptophan and apoAI lysine modification to chlorolysine and 2-aminoadipic acid. Thus, tyrosine modification of apoAI is not required for its MPO-mediated inhibition of cholesterol acceptor activity.     

The effect of native and ACC deaminase-containing Azospirillum brasilense Cd1843 on the rooting of carnation cuttings

Carnation cuttings treated with non-transformed and 1-aminocyclopropane (ACC) deaminase-containing Azospirillum brasilense Cd1843 produced significantly more roots than untreated controls and fewer roots than cuttings treated with 0.1% indolebutyric acid (IBA). The roots produced by cuttings treated with ACC deaminase-containing Azospirillum brasilense Cd1843 were the longest roots resulting from any of the treatments, followed by non-transformed Azospirillum brasilense Cd1843, 0.1% IBA, and treatment with water. The results are interpreted in terms of a previously proposed model of bacterial promotion of plant growth by ACC deaminase and indoleacetic acid, and may have implications for the use of plant growth-promoting bacteria in the flower industry.     

Role of a conserved membrane-embedded acidic residue in the multidrug transporter MdfA

According to the current topology model of the Escherichia coli multidrug transporter MdfA, it contains a membrane-embedded negatively charged residue, Glu26, which was shown to play an important role in substrate recognition. To further elucidate the role of this substrate recognition determinant, various Glu26 replacements were characterized. Surprisingly, studies with neutral MdfA substrates showed that, unlike many enzymatic systems where the size and chemical properties of binding site residues are relatively defined, MdfA tolerates a variety of changes at position 26, including size, hydrophobicity, and charge. Moreover, although efficient transport of positively charged substrates requires a negative charge at position 26 (Glu or Asp), neutralization of this charge does not always abrogate the interaction of MdfA with cationic drugs, thus demonstrating that the negative charge does not play an essential role in the multidrug transport mechanism. Collectively, these results suggest a link between the broad substrate specificity profile of multidrug transporters and the structural and chemical promiscuity at their substrate recognition pockets.     

The core Escherichia coli signal recognition particle receptor contains only the N and G domains of FtsY

Previous studies have proposed that the N-terminal A domain (approximately 200 amino acid residues) of the Escherichia coli signal recognition particle (SRP) receptor, FtsY, is required for membrane targeting. In contrast to this suggestion, we show that A domain-truncated versions of FtsY, harboring only domains N and G, are functional. Therefore, we propose that N and G domains constitute the core SRP receptor.     

Involvement of Smad signaling in sphingosine 1-phosphate-mediated biological responses of keratinocytes

The lysophospholipid sphingosine 1-phosphate and the cytokine-transforming growth factor beta are both released from degranulating platelets at wound sites, suggesting a broad spectrum of effects involved in wound healing. Interestingly, both of these molecules have been previously shown to induce chemotaxis but to strongly inhibit the growth of keratinocytes, while stimulating the proliferation of fibroblasts. In contrast to sphingosine 1-phosphate, the signaling cascade of the growth factor has been extensively examined. Specifically, Smad3 has been shown to be an essential mediator of transforming growth factor beta-dependent chemotaxis of keratinocytes and mediates, in part, its growth-inhibitory effect. Here we show that sphingosine 1-phosphate, independently of transforming growth factor beta secretion, induces a rapid phosphorylation of Smad3 on its C-terminal serine motif and induces its partnering with Smad4 and the translocation of the complex into the nucleus. Moreover, sphingosine 1-phosphate fails to induce chemotaxis or inhibit the growth of Smad3-deficient keratinocytes, suggesting that Smad3 plays an unexpected functional role as a new target in sphingosine 1-phosphate signaling. Both sphingosine 1-phosphate receptors and the transforming growth factor beta-type I receptor serine/threonine kinase are essential for activation of Smad3 by this lysophospholipid and the dependent biological responses, indicating a novel cross-talk between serine/threonine kinase receptors and G-protein coupled receptors.