DNA-responsive checkpoints prevent cell-cycle progression following DNA damage or replication inhibition. The mitotic activator Cdc25 is suppressed by checkpoints through inhibitory phosphorylation at Ser287 (Xenopus numbering) and docking of 14-3-3. Ser287 phosphorylation is a major locus of G2/M checkpoint control, although several checkpoint-independent kinases can phosphorylate this site. We reported previously that mitotic entry requires 14-3-3 removal and Ser287 dephosphorylation. We show here that DNA-responsive checkpoints also activate PP2A/B56delta phosphatase complexes to dephosphorylate Cdc25 at a site distinct from Ser287 (T138), the phosphorylation of which is required for 14-3-3 release. However, phosphorylation of T138 is not sufficient for 14-3-3 release from Cdc25. Our data suggest that creation of a 14-3-3 "sink," consisting of phosphorylated 14-3-3 binding intermediate filament proteins, including keratins, coupled with reduced Cdc25-14-3-3 affinity, contribute to Cdc25 activation. These observations identify PP2A/B56delta as a central checkpoint effector and suggest a mechanism for controlling 14-3-3 interactions to promote mitosis.

Background Asparaginase and steroids can cause hypertriglyceridemia in children with acute lymphoblastic leukemia (ALL). There are no guidelines for screening or management of patients with severe hypertriglyceridemia (>1000 mg/dL) during ALL therapy. Patients and Methods Fasting lipid profiles were obtained prospectively at 4 time-points for 257 children consecutively enrolled on a frontline ALL study. Risk factors were evaluated by the exact chi-square test. Details of adverse events and management of hypertriglyceridemia were extracted retrospectively. Results Eighteen of 257 (7%) patients developed severe hypertriglyceridemia. Older age and treatment with higher doses of asparaginase and steroids on the standard/high-risk arm were significant risk factors. Severe hypertriglyceridemia was not associated with pancreatitis after adjustment for age and treatment arm or with osteonecrosis after adjustment for age. However, patients with severe hypertriglyceridemia had a 2.5 to 3 times higher risk of thrombosis compared to patients without, albeit the difference was not statistical significant. Of the 30 episodes of severe hypertriglyceridemia in 18 patients, 7 were managed conservatively while the others with pharmacotherapy. Seventeen of 18 patients continued to receive asparaginase and steroids. Triglyceride levels normalized after completion of ALL therapy in all 12 patients with available measurements. Conclusion Asparaginase- and steroid-induced transient hypertriglyceridemia can be adequately managed with dietary modifications and close monitoring without altering chemotherapy. Patients with severe hypertriglyceridemia were not at increased risk of adverse events, with a possible exception of thrombosis. The benefit of pharmacotherapy in decreasing symptoms and potential complications requires further investigation.

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.

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SUMMARY Active metabolism regulates oocyte cell death via calcium/calmodulin-dependent protein kinase II (CaMKII) mediated phosphorylation of caspase-2, but the link between metabolic activity and CaMKII is poorly understood. Here we identify coenzyme A (CoA) as the key metabolic signal that inhibits Xenopus laevis oocyte apoptosis, in a novel mechanism of CaMKII activation. We found that CoA directly binds to the CaMKII regulatory domain in the absence of Ca2+ to activate CaMKII in a calmodulin-dependent manner. Furthermore, we show that CoA inhibits apoptosis not only in X. laevis oocytes, but also in Murine oocytes. These findings uncover a novel mechanism of CaMKII regulation by metabolism and further highlight the importance of metabolism in preserving oocyte viability.

Background:In the basal state, oocytes produce lactate from G6P even in the presence of oxygen. Results: Addition of G6P to egg extracts inhibits PP1, preventing dephosphorylation/inactivation of CaMKII and initiation of apoptotic pathways. Conclusion: Normal oocyte metabolism suppresses apoptosis by inhibiting PP1 and activating CaMKII. Significance: These mechanistic insights suggest potential targets for modulating cell death.

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The study of apoptosis and caspases has advanced greatly over recent decades. Studies conducted in the Xenopus laevis egg extract and oocyte model system have significantly contributed to these advances. Twenty years ago, Newmeyer and colleagues first showed that the X. laevis egg extract, when incubated at room temperature, reconstituted the key molecular events of cellular apoptosis including cytochrome c release, nuclear condensation, internucleosomal fragmentation, and caspase activation. The biochemical tractability of the egg extract system allows for robust study of apoptotic events and caspase activation. Its nature as a cell-free extract system allows substrates to be very simply added by pipette, and their effects on apoptosis and caspase activation and their placement in the apoptotic signaling pathway (e.g., pre- or post-mitochondrial) are subsequently very simply studied using the techniques described in this chapter. Also described in this chapter are assays that allow the study of caspase activation in intact oocytes, another valuable tool available when using the X. laevis model organism. Overall, the X. laevis egg extract/oocyte model is a robust, efficient, and biochemically tractable system that is ideal for the study of apoptosis and caspase activation.