Role Of PAR-1 Research Articles

Par-4 induces cholinergic hypoactivity by suppressing ChAT protein synthesis and inhibiting NGF-inducibility of ChAT activity

Profound reductions in choline acetyl-transferase (ChAT) activity are reliable markers for cholinergic hypoactivity associated with cognitive function deficit in Alzheimer’s disease (AD). Par-4 (prostate apoptosis response-4) is a novel mediator of neuronal apoptosis associated with the pathogenesis of AD. Par-4 contains a leucine zipper domain (Leu.zip) that presumably mediates protein–protein interactions critical for its functions in apoptosis. Par-4 activity can be effectively blocked by overexpression of Leu.zip because it exerts a dominant negative action possibly by competitively blocking the interaction of Par-4 with other proteins. Whether Par-4 participates in regulation of cholinergic signaling has not been determined. We report that overexpression of Par-4 results in apoptotic and non-apoptotic reductions in ChAT activity in transfected PC12 cells following exposure to a toxic concentration (50 μM) of aggregated amyloid β peptide 1–42 (Aβ 1–42) and a non-toxic concentration (1 μM) of soluble Aβ 1–42, respectively. Non-apoptotic reduction in ChAT activity induced by Par-4 can be completely blocked by co-overexpression of Leu.zip, indicating that enhanced Par-4 activity is a necessary event for cholinergic hypoactivity in PC12 cells. Further studies found that Par-4 induces non-apoptotic reduction in ChAT activity by: (1) reducing ChAT protein levels following exposure to non-toxic concentration of Aβ, and (2) blocking the cellular capability to increase ChAT activity following exposure to nerve growth factor (NGF). The role of Par-4 in inducing cholinergic hypoactivity may have significant implications in the understanding and the treatment of memory impairment in AD.

Prostate apoptosis response-4 (Par-4): an emerging target for Alzheimer’s and Parkinson’s diseases and stroke

Alzheimer’s disease (AD), Parkinson’s disease (PD) and stroke are neurodegenerative disorders that are increasing in prevalence as life expectancy increases worldwide. Each of these disorders is characterised by the degeneration of neurones in certain brain regions, and by a similar biochemical cascade of events that results in a form of cell death called apoptosis. Par-4 was initially identified as the product of a gene upregulated in prostate tumour cells undergoing apoptosis. Par-4 contains both a death domain and a leucine zipper domain, and has been shown to interact with several proteins known to modulate apoptosis, including protein kinase Cζ (PKCζ), Bcl-2 and caspases. Studies of post-mortem tissues from patients with AD, and animal models of AD, PD and stroke, have documented increased levels of Par-4 in vulnerable neurones prior to their demise. Treatments that block Par-4 expression or function prevent neuronal cell death in models of each disorder, suggesting a critical role for Par-4 in the n...

Protection against Hydrogen Peroxide Induced Injury in Renal Proximal Tubule Cell Lines by Inhibition of Poly(ADP–Ribose) Synthase

Radicals including superoxide anions, hydrogen peroxide or hydroxyl radicals and NO or peroxynitrite cause the breakage of DNA strands and activation of poly–(ADP–ribose) synthase (PARS). Recent studies showed that inhibition of PARS activity reduces the tissue injury after exposure to oxidative stress. However, the role of PARS in renal injury by oxidants has not been examined. In this study effect of a PARS inhibitor, 3–aminobenamide (3–AB), on injury of opossum kidney or LLC–PK₁ cells by hydrogen peroxide or tert–butyl hydroperoxide (t–BHP) was examined. The exposure of opossum kidney cells to hydrogen peroxide activated PARS and decreased cellular adenosine triphosphate levels in a concentration–dependent manner. Inhibition of PARS with 3–AB prevented the cell death induced by hydrogen peroxide and also prevented adenosine triphosphate depletion. 3–AB did not have hydroxyl radical scavenging effect. In contrast, t–BHP did not affect the PARS activity. The decrease in cellular adenosine triphosphate levels by t–BHP was less than that by hydrogen peroxide. 3–AB failed to prevent the cell death induced by t–BHP. PARS activation after exposure of hydrogen peroxide was inhibited by addition of t–BHP. However, t–BHP showed an additive effect on cell death with hydrogen peroxide. These results indicate that activation of PARS plays an important role in hydrogen peroxide induced injury in opossum kidney cells and that hydrogen peroxide and t–BHP induce cell injury by different mechanisms.

Functional analysis of the Enterococcus faecalis plasmid pAD1-encoded stability determinant par.

The molecular organization and functional characteristics of the PAD1 replicon-encoded par stability determinant were examined. par encodes two convergently transcribed RNAS of approximately 210 and 65 nucleotides designated RNA I and RNA II, respectively. The sequence of RNA II is largely complementary to RNA I, suggesting that RNA II could regulate RNA I function as an anti-sense RNA. Results of functional studies are consistent with a role for par as a post-segregational killing system, the first to be identified in Gram-positive bacteria, with RNA I encoding the toxin and RNA II the antidote. These results include: (i) destabilization of par-containing replicons in the presence of a second complete par or the RNA II coding sequence in the same cell; (ii) par-dependent stabilization of a highly unstable vector at the expense of host-cell growth rate; and (iii) protection of cells from the toxic effects of overexpression of RNA I by RNA II supplied in trans.

Identification and characterization of a Saccharomyces cerevisiae gene (PAR1) conferring resistance to iron chelators

o-Phenanthroline (1,10-phenanthroline) is a chemical known to chelate iron and other transition metal ions. This compound was added to solid yeast media to reduce the concentration of biologically available iron. Other essential divalent cations, like Zn2+ or Cu2+, which could also be bound, were supplemented. Growth of wild-type yeast strains was totally inhibited at specific concentrations of the chelator. However, several cells containing plasmids of a multicopy vector genomic library of S. cerevisiae could be selected by growth on these media. All of the resistant clones carried a single additional gene, PAR1 on their multicopy plasmids. Plasmid-directed overexpression of PAR1 increased the resistance of transformants to o-phenanthroline and additionally conferred resistance to 1-nitroso-2-naphthol, an iron(III)-binding molecule with different coordinating ligands. By supplementing the o-phenanthroline-containing media with several different metal ions, it could be proved that the selection plates really caused a specific iron limitation. These observations clearly demonstrated that the overexpressed PAR1 gene enables the cell to compete with iron-chelating organic molecules. PAR1 null mutants, constructed by insertion of the LEU2 gene into the open reading frame, showed a remarkable phenotype: they did not grow on slightly alkaline buffered media (pH greater than 7) and became hypersensitive to oxidative stress by hydrogen peroxide. Of several heavy metal ions, such as Fe3+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+, tested for supplementation of the alkaline growth deficiency, only iron, either added in the ferrous or ferric form, was able to restore cellular growth. It can be concluded from the DNA sequence that PAR1 encodes a highly acidic protein of 650 residues with mostly hydrophilic character. Some interesting repetitive amino acid motifs, such as (Asp-Asn)4 or Cys-Ser-Glu, may act as metal-binding sites. The possible role of PAR1 is discussed.