Protective effect of paraoxonase-2 against endoplasmic reticulum stress-induced apoptosis is lost upon disturbance of calcium homoeostasis

Abstract

PON2 (paraoxonase-2) is a ubiquitously expressed antioxidative protein which is largely found in the ER (endoplasmic reticulum). Addressing the cytoprotective functions of PON2, we observed that PON2 overexpression provided significant resistance to ER-stress-induced caspase 3 activation when the ER stress was induced by interference with protein modification (by tunicamycin or dithiothreitol), but not when ER stress was induced by disturbance of Ca(2+) homoeostasis (by thapsigargin or A23187). When analysing the underlying molecular events, we found an activation of the PON2 promoter in response to all tested ER-stress-inducing stimuli. However, only tunicamycin and dithiothreitol resulted in increased PON2 mRNA and protein levels. In contrast, when ER stress was caused by thapsigargin or A23187, we observed a Ca(2+)-dependent active degradation of PON2 mRNA, elicited by its 5'-untranslated region. In addition, thapsigargin and A23187 also induced PON2 protein degradation by a Ca(2+)-dependent calpain-mediated mechanism. Thus we provide evidence that independent mechanisms mediate the degradation of PON2 mRNA and protein after disturbance of Ca(2+) homoeostasis. Furthermore, because Ca(2+)-disturbance induces ER stress, but abrogates the otherwise protective function of PON2 against ER-stress-induced apoptosis, we propose that the underlying cause of ER stress determines the efficacy of putative cellular defence mechanisms.

Enhanced Clearance of Pseudomonas aeruginosa by Peroxisome Proliferator-Activated Receptor Gamma

“…Recent studies have demonstrated that increased cellular calcium mediates degradation of PON-2 protein and mRNA. Since 3-oxo-C 12 -HSL can increase cytosolic calcium, it can be hypothesized that 3-oxo-C 12 -HSL may mediate changes in PPAR␥ and PON-2 levels by modulating the activity of key transcriptional factors (16,17,72,73). The induction of NF-B and interleukin-10 may also play a role in the inhibition of PPAR␥, as these are upregulated by 3-oxo-C 12 -HSL (74,75).…”

One Enzyme, Two Functions

“…The PONs differ in localization as PON1 mainly associates with circulating serum high density lipoprotein particles, whereas the intracellular PON2 appears in two spliced isoforms that predominantly localize to the endoplasmic reticulum, mitochondria, and (peri)-nuclear region (7,9,15). Endogenous substrates of PON2 are largely unknown, but it has been shown that its lactonase activity dominantly hydrolyzes the Pseudomonas aeruginosa signaling lactone 3OC12, for which reason PON2 may add to the anti-bacterial defense (16,17), a mechanism apparently sensitive to major calcium disturbances (18,19). Further, studies with PON2-deficient mice indicated that PON2 suppresses atherosclerosis, and several studies described a significant ROS-diminishing function of PON2 in various cells (8,9,18,20,21).…”

“…Cells and Materials-All experiments employed human endothelial EA.hy 926 cells with or without stable PON2-GFP expression (9,19). Dihydrorhodamine-123 (DHR123) and MitoSox Red were from Molecular Probes; 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) and 3-morpholinosydnonimine (Sin-1) were from Calbiochem; L-012 was from Wako Chemicals; glycosidase-F was from Roche Applied Science; and 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo[1,2-a]-pyrazin-3-one (MCLA) and all other reagents were from Sigma.…”

Estudo das paraoxonases 1, 2 e 3 em pacientes portadores de anemia falciforme"

“…Ainda, com localização primária na membrana plasmática e região perinuclear, a PON2 também encontra-se em organelas celulares tais como, retículo endoplasmático, lisossomos e mitocôndrias (Horke et al, 2008;Rothem et al, 2007;Witte et al, 2011).…”

“…O gene da PON2 expressa uma proteína intracelular, com peso molecular de aproximadamente 43 kDa Horke et al, 2008), distribuída por 9 éxons, 8 íntrons e 355 aminoácidos (Li et al, 2003).…”