Protective effect of paraoxonase-2 against endoplasmic reticulum stress-induced apoptosis is lost upon disturbance of calcium homoeostasis.
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.
Horke
Sven
S
Department of Pharmacology, Johannes Gutenberg University, Obere Zahlbacher Strasse 67, D-55131, Mainz, Germany. horke@uni-mainz.de
Witte
Ines
I
Wilgenbus
Petra
P
Altenhöfer
Sebastian
S
Krüger
Maximilian
M
Li
Huige
H
Förstermann
Ulrich
U
D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D017209:Apoptosis / Q000502:physiology*; D043303:Aryldialkylphosphatase / Q000235:genetics / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism; D002460:Cell Line; D004229:Dithiothreitol / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D006706:Homeostasis; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D020871:RNA Stability; D013312:Stress, Physiological; D019284:Thapsigargin / Q000494:pharmacology; D014415:Tunicamycin / Q000494:pharmacology
D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D004791:Enzyme Inhibitors; D007476:Ionophores; D014415:Tunicamycin; D000001:Calcimycin; D019284:Thapsigargin; D043303:Aryldialkylphosphatase; D002154:Calpain; D002118:Calcium; D004229:Dithiothreitol