53BP1 is associated with replication protein A and is required for RPA2 hyperphosphorylation following DNA damage

p53-binding protein 1 (53BP1) acts as an 'adaptor/mediator' for transducing DNA damage signals, especially following detection of DNA double-strand breaks. In an effort to broaden our understanding of the protein network surrounding 53BP1, we isolated possible 53BP1 binding partners by co-immunoprecipitation, and identified them via tandem mass spectrometric analysis. The 53BP1-associated proteins included RPA1 and RPA2, two components of the replication protein A (RPA) complex. The presence of RPA components in the immunoprecipitates was confirmed by immunoblotting, and we found that the association between 53BP1 and RPA2 was disrupted following DNA damage induced by treatment with camptothecin, a topoisomerase I inhibitor. To investigate the functional meaning of the 53BP1 and RPA interaction, we established U2OS osteosarcoma cell lines stably expressing dominant-negative fragments of 53BP1. We found that camptothecin-induced RPA2 phosphorylation was inhibited in these cells, and also following 53BP1 knockdown by siRNA transfection. On the cellular level, camptothecin-induced apoptosis was augmented in the dominant-negative cell lines, resulting in increased chemosensitivity to this drug. Taken together, these results suggest that 53BP1 is involved in DNA damage-induced RPA2 hyperphosphorylation, and inhibition of 53BP1 function may sensitize cancer cells to camptothecin treatment.

New agents in the treatment of acute myeloid leukemia: a snapshot of signal transduction modulation

Acute myeloid leukemia continues to present formidable treatment challenges as there is not yet a "standard approach" that reliably and safely cures the majority of adults with this disorder. Efforts to better understand the basic cellular and molecular biology of acute myeloid leukemia have unveiled a complicated network of signaling pathways that support the cancer cells. Disrupting the transmission of the cells' survival signals offers appealing targets for drug development. This review will focus on several exciting components of these pathways and the agents targeting these pathways that are entering clinical trials.

Competing for memory: hippocampal LTP under regimes of reduced protein synthesis

The persistence of synaptic potentiation in the hippocampus is known to depend on transcription and protein synthesis. We report here that, under regimes of reduced protein synthesis, competition between synapses for the relevant intracellular proteins can be demonstrated. Under such circumstances, the induction of additional protein synthesis-dependent long-term potentiation for a given set of postsynaptic neurons occurs at the expense of the maintenance of prior potentiation on an independent pathway. This new phenomenon, which we call "competitive maintenance," has important functional consequences, and it may be explained in terms of dynamic interactions between synapses and "plasticity factors" over extended periods of time.

15-Deoxy-Δ12,14-prostaglandin J2 induces apoptosis in human malignant B cells: an effect associated with inhibition of NF-κB activity and down-regulation of antiapoptotic proteins

Cyclopentenone prostaglandins are potent inhibitors of nuclear factor-κB (NF-κB), a transcription factor with a critical role in promoting inflammation and connected with multiple aspects of oncogenesis and cancer cell survival. In the present report, we investigated the role of NF-κB in the antineoplastic activity of the cyclopentenone prostaglandin 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2) in multiple myeloma (MM) and Burkitt lymphoma (BL) cells expressing constitutively active NF-κB. 15d-PGJ2 was found to suppress constitutive NF-κB activity and potently induce apoptosis in both types of B-cell malignancies. 15d-PGJ2-induced apoptosis occurs through multiple caspase activation pathways involving caspase-8 and caspase-9, and is prevented by pretreatment with the pan-caspase inhibitor ZVAD (z-Val-Ala-Asp). NF-κB inhibition is accompanied by rapid down-regulation of NF-κB-dependent antiapoptotic gene products, including cellular inhibitor-of-apoptosis protein 1 (cIAP-1), cIAP-2, X-chromosome-linked inhibitor-of-apoptosis protein (XIAP), and FLICE-inhibitory protein (cFLIP). These effects were mimicked by the proteasome inhibitor MG-132, but not by the peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist troglitazone, suggesting that 15d-PGJ2-induced apoptosis is independent of PPAR-γ. Knockdown of the NF-κB p65-subunit by lentiviral-mediated shRNA interference also resulted in apoptosis induction in malignant B cells with constitutively active NF-κB. The results indicate that inhibition of NF-κB plays a major role in the proapoptotic activity of 15d-PGJ2 in aggressive B-cell malignancies characterized by aberrant regulation of NF-κB. (Blood. 2005;105:1750-1758)

RNAi knockdown of Par-4 inhibits neurosynaptic degeneration in ALS-linked mice

Evidence from human amyotrophic lateral sclerosis (ALS) patients and ALS-linked Cu/Zn superoxide dismutase (Cu/Zn-SOD) transgenic mice bearing the mutation of glycine to alanine at position 93 (G93A) suggests that the pro-apoptotic protein prostate apoptosis response-4 (Par-4) might be a critical link in the chain of events leading to motor neuron degeneration. We now report that Par-4 is enriched in synaptosomes and post-synaptic density from the ventral horn of the spinal cord. Levels of Par-4 in synaptic compartments increased significantly during rapid and slow declining stages of muscle strength in hSOD1 G93A mutant mice. In the pre-muscle weakness stage, hSOD1 G93A mutation sensitized synaptosomes from the ventral horn of the spinal cord to increased levels of Par-4 expression following excitotoxic and apoptotic insults. In ventral spinal synaptosomes, Par-4-mediated production of pro-apoptotic cytosolic factor(s) was significantly enhanced by the hSOD1 G93A mutation. RNA interference (RNAi) knockdown of Par-4 inhibited mitochondrial dysfunction and caspase-3 activation induced by G93A mutation in synaptosomes from the ventral horn of the spinal cord, and protected spinal motor neurons from apoptosis. These results identify the synapse as a crucial cellular site for the cell death promoting actions of Par-4 in motor neurons, and suggest that targeted inhibition of Par-4 by RNAi may prove to be a neuroprotective strategy for motor neuron degeneration.

Shiga toxins activate translational regulation pathways in intestinal epithelial cells

Shiga toxins (Stxs) cause irreversible damage to eukaryotic ribosomes, yet cellular intoxication of intestinal epithelial cells (IECs) results in increased synthesis of selected proteins, notably cytokines. How mRNA translation is maintained in this circumstance is unclear. This study was designed to assess whether Stx-induced alterations in host signal transduction machinery permit translation despite protein synthesis inhibition. A key step of translation is recruitment of initiation machinery to the 5' mRNA cap. This event occurs in part via interaction of the 5' cap with the cap binding protein, eIF4E, whose activity is positively regulated by phosphorylation and negatively regulated by binding to the translational repressor 4E-BP1. Following Stx treatment of IECs, eIF4E phosphorylation was detected by Western blotting using phospho-specific antibodies. Treatment with the p38 inhibitor, SB202190, or either of the ERK1/2 inhibitors, PD98059 and U0126, partially blocked Stx1-induced eIF4E phosphorylation. The Mnk1 inhibitor, CGP57380, blocked both basal and Stx-induced eIF4E phosphorylation. Interestingly, pretreatment with CGP57380 did not alter basal protein synthesis, but diminished the ability of cells to maintain translation following Stx1 challenge. Stx1 also induced hyperphosphorylation of 4E-BP1 and phosphorylation of S6Kinase; both effects were blocked by rapamycin. These data are novel observations showing that Stxs regulate multiple signal transduction pathways controlling translation in host cells, and support a role for eIF4E phosphorylation in maintaining host cell translation despite ribosomal intoxication.

La narcolepsie, de Westphal à l’hypocrétine

CLINICAL DATA

Narcolepsy is a poorly known disease, though not exceptional, with a prevalence of 25 to 35 per 100,000 according to various surveys. Its onset can be anytime from childhood to the fifties with a peak in the second decade. It is characterized by two cardinal symptoms, irresistible sleep episodes and cataplexy or sudden loss of muscle tone triggered by emotional situations. The other symptoms, referred to as accessory due to their inconstancy, are hypnagogic hallucinations, sleep paralysis and disturbed nocturnal sleep. Its diagnosis relies on the identification of the cardinal symptoms. Laboratory tests are required to confirm the diagnosis before initiation of a life-long treatment. Theses test include: all-night and daytime polysomnography documenting sleep-onset REM periods, HLA typing, showing the association with HLA DQB1*0602, and, in unclear cases only, measurement of cerebro-spinal fluid (CSF) hypocretine-1 showing values below 110pg/ml, highly specific of narcolepsy with cataplexy. Pathophysiology owes a lot to the existence of a natural canine model, the narcoleptic dog. Irresistible sleep episodes and cataplexy exhibit different pharmacological control, the former depending on dopaminergic systems and the latter on noradrenergic systems. The most remarkable findings of the last twenty years are the close association with HLA DQB1*0602, the identification of a mutation of hypocretin receptor 2 in the narcoleptic dog and the absence of CSF hypocretin-1 in 90% of patients. An autoimmune mechanism is suggested but not evidenced. THREE-FOLD TREATMENT: First line treatment of irresistible sleep episodes in modafinil, Cataplexy or tricyclic antidepressants or sodium oxybate, and disturbed nocturnal sleep by hypnotics or sodium oxybate. Current therapeutic research is oriented towards hypocretin agonists and immunosuppressors.

p38alpha, but not p38beta, inhibits the phosphorylation and presence of c-FLIPS in DISC to potentiate Fas-mediated caspase-8 activation and type I apoptotic signaling

Pharmacological inhibitors of JNK (SP600125) and p38 (PD169316) sensitize tumor cells to Fas-mediated apoptosis. PD169316 is less potent than SP600125 and diminishes its effect when present together. Because the p38 isoforms that promote (p38alpha) or inhibit (p38beta) apoptosis are both suppressed by PD169316, we investigated their regulatory involvement in Fas-signaling. We report here, that p38alpha, but not p38beta, exerts its proapoptotic effect by inhibiting the phosphorylation and presence of c-FLIPS, but not c-FLIPL, in the DISC to promote caspase-8 activation and type I signaling in Fas-activated Jurkat cells. Its effect was enhanced by enforced expression of Flag-tagged p38alpha and was attenuated by its inactive mutant (p38alpha-AGF) or by translational silencing. By contrast, type II signaling was facilitated by p38alpha-dependent mitochondrial presence of tBid and inhibition of Bcl-2 (Ser70) phosphorylation as well as by p38alpha/beta-dependent mitochondrial localization of Bax and inhibition of phosphorylation of Bad (Ser112/Ser155). Potentiation of Fas-mediated apoptosis by the inhibition of JNK1/2 correlated with the loss of Bad (Ser136) phosphorylation and was dependent on the stimulatory effect of p38alpha on DISC and the downstream effects of both p38alpha and p38beta. These data underscore the need to reassess the findings obtained with pan-p38 inhibitors and suggest that activation of p38alpha coupled with targeted inhibition of p38beta and JNK1/2 should optimally sensitize tumor cells to Fas-mediated apoptosis.

Cellular FLICE-inhibitory protein: an attractive therapeutic target?

Cellular FLIP (c-FLIP), also known as FLICE-inhibitory protein, has been identified as an inhibitor of apoptosis triggered by engagement of death receptors (DRs) such as Fas or TRAIL (TNF-related apoptosis-inducing ligand). cFLIP is recruited to DR signalling complexes, where it prevents caspase activation. Animal models have indicated that c-FLIP plays an important role in T cell proliferation and heart development. Abnormal c-FLIP expression has been identified in various diseases such as multiple sclerosis (MS), Alzheimer's disease (AD), diabetes mellitus, rheumatoid arthritis (RA) and various cancers. This review focuses on recent insights into c-FLIP dysregulation associated with human diseases and addresses the possibilities of using c-FLIP as a therapeutic target.