Catalysis of arachidonic acid (AA) by cyclooxygenase-2 (COX-2) gives rise to a single product that serves as a precursor for all prostaglandins, which are central mediators of inflammation. Rapid up-regulation of COX-2 expression in response to pro-inflammatory stimuli is a well-characterized means of generating the large pool of prostaglandins necessary for inflammation. However, an efficient inflammatory process must also terminate rapidly and thus requires cessation of COX-2 enzymatic activity and removal of excess protein from the cell. Previous studies showed that COX-2 that has not been exposed to AA (‘naive’) degrades in the cellular proteasome. However, continuous exposure to AA induces suicide inactivation of COX-2 and its elimination no longer occurs in neither the proteasomal nor lysosomal machineries. In the present study, we show that either overexpressed or endogenously induced COX-2 is secreted via exosomes through the endoplasmic reticulum–Golgi pathway. We further find that excretion of COX-2 is significantly enhanced by prolonged exposure to AA. Genetic or chemical inhibition of COX-2 enzymatic activity has no effect on its secretion in the absence of substrate, but prevents the additional activity-dependent secretion. Finally, transfer of COX-2 to target cells only occurs in the absence of AA stimulation. Together, these results suggest that exosomal secretion of AA-activated COX-2 constitutes a means to remove damaged inactive COX-2 from the cell.
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Cover Image
Cover Image
In this issue, Keith Willison reviews of the structure and evolution of eukaryotic CCT (chaperonin-containing TCP-1) and how it effects actin folding. The cover image shows a space-fill model of the CCT3/γ apical domain with its solvent-accessible-binding surface highlighted in brown and a stretch of bound poly-Gln β-strand occupying the long stretch of anchoring sites. For further details, see pages 3009–3034. Image kindly provided by Miriam Eisenstein (Weizmann Institute for Science).
Substrate-inactivated cyclooxygenase-2 is disposed of by exosomes through the ER–Golgi pathway
Esraa Saadi, Sharon Tal, Liza Barki-Harrington; Substrate-inactivated cyclooxygenase-2 is disposed of by exosomes through the ER–Golgi pathway. Biochem J 15 October 2018; 475 (19): 3141–3151. doi: https://doi.org/10.1042/BCJ20180530
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