Metabolic Control of Oocyte Apoptosis Mediated by 14-3-3ζ-Regulated Dephosphorylation of Caspase-2

Abstract

SUMMARY Xenopus oocyte death is partly controlled by the apoptotic initiator, caspase-2. We reported previously that oocyte nutrient depletion activates caspase-2 upstream of mitochondrial cytochrome c release. Conversely, nutrient-replete oocytes inhibit caspase-2 via S135 phosphorylation catalyzed by calcium/calmodulin-dependent protein kinase II. We now show that caspase-2 phosphorylated at S135 binds 14-3-3ζ, thus preventing caspase-2 dephosphorylation. Moreover, we determined that S135 dephosphorylation is catalyzed by protein phosphatase-1, which directly binds caspase-2. Although caspase-2 dephosphorylation is responsive to metabolism, neither PP1 activity nor binding is metabolically regulated. Rather, release of 14-3-3ζ from caspase-2 is controlled by metabolism and allows for caspase-2 dephosphorylation. Accordingly, a caspase-2 mutant unable to bind 14-3-3ζ is highly susceptible to dephosphorylation. Although this mechanism was initially established in Xenopus, we now demonstrate similar control of murine caspase-2 by phosphorylation and 14-3-3 binding in mouse eggs. These findings provide an unexpected evolutionary link between 14-3-3 and metabolism in oocyte death.

Metabolic control of cell death

“…CoA acts directly on Ca 2+ /calmodulin-dependent protein kinase II (CamKII) to reduce its requirement for Ca 2+ ions, thus effectively activating it (71). One target of the enzymatic activity of CamKII is caspase-2, which upon phosphorylation is sequestered and kept inactive by 14-3-3ζ (72). As the phosphorylation of caspase-2 requires NADPH, a product of the pentose phosphate pathway (PPP), caspase-2 is released from 14-3-3ζ when the flow through the PPP is limited, resulting in the sensitization of cells to various stress signals (72).…”

“…One target of the enzymatic activity of CamKII is caspase-2, which upon phosphorylation is sequestered and kept inactive by 14-3-3ζ (72). As the phosphorylation of caspase-2 requires NADPH, a product of the pentose phosphate pathway (PPP), caspase-2 is released from 14-3-3ζ when the flow through the PPP is limited, resulting in the sensitization of cells to various stress signals (72). Sirtuin 1 (SIRT1) is one of the enzymes that deacetylate 14-3-3ζ, thus counteracting this effect (73).…”

Metabolic-Stress-Induced Rearrangement of the 14-3-3ζ Interactome Promotes Autophagy via a ULK1- and AMPK-Regulated 14-3-3ζ Interaction with Phosphorylated Atg9

“…14-3-3 (gene symbol YWHAZ) protects cells from numerous stresses, including chemotherapy-induced death, anoikis, and growth factor deprivation (2)(3)(4)(5)(6). Furthermore, 14-3-3 expression is upregulated in many cancers, and high-level expression has been shown to correlate with poor clinical outcomes in breast cancer (4,5,7,8).…”

“…14-3-3 promotes survival signaling in cells exposed to a wide range of conditions, including hypoxia (6,(10)(11)(12), in which both oxygen and glucose are limited. Because nutrient deprivation has widespread effects on kinase signaling pathways, we posited that such conditions likely alter the 14-3-3 interactome.…”

Anti-apoptotic Activity and Proteasome-mediated Degradation of Xenopus Mcl-1 Protein in Egg Extracts

“…20 and 21). Egg extracts, as well as the mitochondria isolated from them, are frequently used for biochemical experiments of apoptosis (17,(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41). Apoptosis in egg extracts is triggered solely by the cytoplasmic release of cytochrome c from mitochondria, and neither damage-inducing treatment nor death receptor-ligand signaling is required.…”