Cyclopentenone Prostaglandins of the J Series Inhibit the Ubiquitin Isopeptidase Activity of the Proteasome Pathway

Abstract

Electrophilic eicosanoids of the J series, with their distinctive cross-conjugated ␣,␤-unsaturated ketone, inactivate genetically wild type tumor suppressor p53 in a manner analogous to prostaglandins of the A series. Like the prostaglandins of the A series, prostaglandins of the J series have a structural determinant (endocyclic cyclopentenone) that confers the ability to impair the conformation, the phosphorylation, and the transcriptional activity of the p53 tumor suppressor with equivalent potency and efficacy. However, J series prostaglandins have a unique structural determinant (exocyclic ␣,␤-unsaturated ketone) that confers unique efficacy as an apoptotic agonist. In seeking to understand how J series prostaglandins cause apoptosis despite their inactivation of p53, we discovered that they inhibit the ubiquitin isopeptidase activity of the proteasome pathway. In this regard, J series prostaglandins were more efficacious inhibitors than representative members of the A, B, or E series prostaglandins. Disruption of the proteasome pathway with proteasome inhibitors can cause apoptosis independently of p53. Therefore, this finding helps reconcile the p53 transcriptional independence of apoptosis caused by ⌬12-prostaglandin J 2 . This discovery represents a novel mechanism for proteasome pathway inhibition in intact cells. Furthermore, it identifies isopeptidases as novel targets for the development of antineoplastic agents. Certain electrophilic prostaglandins (PG)1 can repress transactivation by NFB and p53 (1-4), two prominent transcription factors that govern the decision of a cell to survive or die (5-7). This transcriptional repression is a pharmacologically unique trait that distinguishes PG of the A and J series from other PG that act via membrane-spanning receptors (8). If the endocyclic ␣,␤-unsaturated ketone shared by A and J series PG confers activity, as hypothesized (1, 2, 4, 9, 10), then two predictions should be valid. First, individual A series and J series PG should act rather uniformly on the cellular processes they affect. Second, their cellular effects should be self-consistent with established models of NFB and p53 function. However, not all experiments affirm these predictions. For example, the A and J series PG both repress NFB transcription and inhibit IB kinase (1, 2); however, only ⌬12-PGJ 2 is anti-inflammatory (11). Likewise, the A and J series PG both repress p53 transcription; however, only the A series PG antagonize p53-dependent apoptosis (Ref. 4 and see below).Herein we report the discovery of a molecular mechanism that clarifies the distinctive cellular effects of cyclopentenone PG. Namely, J series PG preferentially inhibit the ubiquitin isopeptidase activity (ubiquitin-specific protease) of the proteasome pathway. This pathway is the major nonlysosomal degradation pathway in cells (12, 13). The degradation of target proteins via this pathway largely depends on their covalent modification with a ubiquitin polymer. This polymer consists of ubiquitin (8.5 kDa) subunits that are...

Possible Involvement of p38 in Mechanisms Underlying Acceleration of Proliferation by 15-Deoxy-Δ12,14-prostaglandin J2 and the Precursors in Leukemia Cell Line THP-1

“…These results indicate that the abilities of PGJ 2 and D PGJ 2 are not caused by 15dPGJ 2 following nonenzymatic conversion. As shown recently (36), however, D PGJ 2 induced accumulation of p21 through inhibition of ubiquitin isopeptidase activity of the proteasome pathway. It is difficult to conclude that molecular mechanisms by which PGD 2 and 15dPGJ 2 accelerate the proliferation differ from molecular mechanisms by which PGJ 2 and D PGJ 2 accelerate the proliferation because 15dPGJ 2 and the precursors are closely related compounds.…”

Regulation of apoptosis by the ubiquitin and proteasome pathway

“…Prostaglandins of the J series cause apoptosis despite their inactivation of p53, because they inhibit the ubiquitin isopeptidase activity of the proteasome pathway. Inhibition of isopeptidases causes rapid depletion of the cells from free ubiquitin and accumulation of polyubiquitin chains, effectively inhibiting the ubiquitin-and proteasome-mediated degradation of most proteins [132].…”

Cyclopentenone Prostaglandins Induce Lymphocyte Apoptosis by Activating the Mitochondrial Apoptosis Pathway Independent of External Death Receptor Signaling

“…Because NF-B controls the expression of inflammation-related genes as well as that of several antiapoptotic proteins such as cIAP1/2 (35), it is conceivable that inhibition of NF-B signaling via cyclopentenone PGs accounts, at least in part, for the antiinflammatory and proapoptotic effects of these compounds. Cyclopentenone derivatives of the J series are also direct inhibitors of the ubiquitin isopeptidase in the proteasome pathway, which was shown to result in the initiation of cell death (36). Finally, cyclopentenone PGs can induce apoptosis in different cell types by a mechanism unrelated to PPAR-␥ and involving oxidative stress (37)(38)(39).…”