Posttransplant lymphoproliferative disease (PTLD) is a serious complication of solid organ and bone marrow transplantation and is closely associated with Epstein-Barr virus (EBV) infection. We have ...previously shown that rapamycin (RAPA) directly inhibits the in vitro and in vivo proliferation of EBV-infected B lymphoblastoid cell lines (SLCL), derived from patients with PTLD, by arresting cells in the G1 phase of the cell cycle. The aim of this study is to elucidate the mechanism by which RAPA causes cell cycle arrest in EBV+ B cells.
SLCL were cultured without or with RAPA (10 ng/ml) and G1-associated cell cycle proteins were analyzed by immunoblot and densitometric analysis. CDK complexes were immunoprecipitated and incubated with retinoblastoma protein (Rb) substrate. Kinase activity of the complex was determined by Western blot with anti-phospho-Rb antibodies.
We show that RAPA decreased both Cyclin D2 and Cyclin D3 protein levels. Furthermore, RAPA decreased the protein levels of cyclin dependent kinase 4 (CDK4) and increased the expression of the CDK inhibitor p27. In contrast, expression of the CDK inhibitor p21 was markedly inhibited by RAPA in the SLCL. Finally, in vitro kinase assays revealed that downstream hyperphosphorylation of Rb by CDK complexes was also decreased by RAPA.
The results presented here elucidate key targets of RAPA-induced cell cycle arrest, provide insight into the growth pathways of EBV+ B-cell lymphomas, and demonstrate the potential for RAPA as a therapeutic option in the treatment of PTLD and other EBV+ lymphomas.
EBV-infected B-cell lymphomas are a potentially life-threatening complication in bone marrow and solid organ transplant recipients. Immunosuppressive drugs required to prevent allograft rejection ...also impair anti-EBV T-cell immunity, thereby increasing the risk of EBV-associated disease. Here we demonstrate that the immunosuppressant rapamycin (RAPA) has a strong antiproliferative effect in vitro on B-cell lines derived from organ transplant recipients with EBV-associated posttransplant lymphoproliferative disorder (PTLD). Furthermore, RAPA significantly inhibits or delays the growth of solid tumors established from EBV-infected B-cell lines in a xenogeneic mouse model of PTLD. RAPA acts via cell cycle arrest, induction of apoptosis, and, most importantly, inhibition of interleukin 10 secretion, a necessary autocrine growth factor. The reduced interleukin 10 production is accompanied by corresponding decreases in the constitutive activation of the growth-promoting transcription factors signal transducer and activator of transcription 1 and 3. Thus, RAPA can limit B-cell lymphoma growth while simultaneously providing immunosuppression to prevent graft rejection in patients who are otherwise at risk for EBV-associated PTLD. Moreover, these findings may have application to other EBV-associated malignancies.
B-cell lymphoma is the most common immune system malignancy. TCL1 transgenic mice (TCL1-tg), in which TCL1 is ectopically expressed in mature lymphocytes, develop multiple B- and T-cell leukemia and ...lymphoma subtypes, supporting an oncogenic role for TCL1 that probably involves AKT and MAPK-ERK signaling pathway augmentation. Additional, largely unknown genetic and epigenetic alterations cooperate with TCL1 during lymphoma progression. We examined DNA methylation patterns in TCL1-tg B-cell tumors to discover tumor-associated epigenetic changes, and identified hypermethylation of sprouty2 (Spry2). Sprouty proteins are context-dependent negative or positive regulators of MAPK-ERK pathway signaling, but their role(s) in B-cell physiology or pathology are unknown. Here we show that repression of Spry2 expression in TCL1-tg mouse and human B-cell lymphomas and cell lines is associated with dense DNA hypermethylation and was reversed by inhibition of DNA methylation. Spry2 expression was induced in normal splenic B cells by CD40/B-cell receptor costimulation and regulated a negative feedback loop that repressed MAPK-ERK signaling and decreased B-cell viability. Conversely, loss of Spry2 function hyperactivated MAPK-ERK signaling and caused increased B-cell proliferation. Combined, these results implicate epigenetic silencing of Spry2 expression in B lymphoma progression and suggest it as a companion lesion to ectopic TCL1 expression in enhancing MAPK-ERK pathway signaling.
B-cell lymphomas, the most frequent human immune system malignancies, often contain dysregulated TCL1 oncogene expression. TCL1 transgenic (TCL1-tg) mice develop a spectrum of B-cell malignancies, ...supporting an oncogenic role for TCL1 in B cells. Our prior global survey of DNA methylation patterns in TCL1-tg B-cell lymphomas identified many lymphoma-specific candidate hypermethylated genes, including Stk39 . The Stk39 encoded protein, sterile 20-like-related proline-alanine-rich kinase (SPAK), regulates cell stress responses, and microarray studies identified reduced SPAK expression in metastatic prostate and treatment-resistant breast cancers, suggesting that its loss may have a role in cancer progression. Here we identified DNA hypermethylation and SPAK silencing in TCL1-tg B-cell lymphomas and SPAK silencing without DNA methylation in multiple subtypes of human B-cell lymphomas. SPAK knockdown by shRNA protected B cells from caspase-dependent apoptosis induced by DNA double-strand breaks but not apoptosis in response to osmotic or oxidative cell stressors. Caspase 3 activation by cleavage was impaired with SPAK repression in DNA damaged B cells. Interestingly, c-Jun NH2 -terminal kinase is potentially activated by SPAK and pharmacological inhibition of c-Jun NH2 -terminal kinase in SPAK-expressing B cells recapitulated the cell-protective phenotype of SPAK knockdown. Taken together, these data indicate that SPAK loss in B-cell lymphomas promotes increased cell survival with DNA damage and provides a potential mechanism for increased resistance to genotoxic stress in cancer.
Abstract TCL1 is an AKT kinase coactivator that, when dysregulated, initiates mature lymphocyte malignancies in humans and transgenic mice. While TCL1 augments AKT pathway signaling, additional TCL1 ...interacting proteins that may contribute to cellular homeostasis or transformation are lacking. Here, an exoribonuclease, PNPase, was identified in a complex with TCL1. The AKT interaction domain on TCL1 bound either RNase PH repeat domain of PNPase without influencing its RNA degrading activity, which was compatible with predicted docking models for a TCL1–PNPase complex. Our data provide a novel protein interaction for mammalian PNPase that may impact TCL1 mediated transformation.
Summary
This study investigated the suitability of propofol as a sole agent for continuous sedation in 100 unpremedicated patients during gastrointestinal endoscopy. The propofol was given very ...slowly (average 62.7 seconds) in order to prevent apnoea during induction, and the dose adjusted according to age (68% of patients were older than 50 years) and ASA grade (32% were ASA grade 3 or 4). There was no correlation under these circumstances between the observed haemodynamic variations and the age or ASA grade of the patients. The infusion rate during maintenance was also adjusted for age, and for the type of endoscopy. The mean rate was 4.3 mg/kg/hour. Recovery was rapid and of excellent quality; 77 patients were awake within 10 minutes and 99 reported total amnesia.
Various methods of medullary analgesia are suggested using either the peridural or the subarachnoid technique. Spinal analgesia is much in demand in anaesthesia, in post-operative care or for the ...alleviation of chronic, mainly neoplastic, pain. Anaesthesia is obtained with a local anaesthetic acting at the level of the membrane. The adjunction of an opiate, acting at the level of the medullary morphinic receptors, enhances local anaesthesia both in depth and duration. This association allows lesser concentrations and volumes of drugs to be used. Various opiates have been tested: their effect depends on the type of administration (I. V., intra-medullary). In the case of intra-medullary injection these is also a difference in the action of the drug according to the technique used (peridural or subarachnoid). The meningeal barrier plays a major function, preventing the diffusion and fixation on the morphinic receptors of some drugs administered peridurally. The action of these drugs, when injected by the subarachnoid technique, is enhanced; this is the case of morphine-base. Others according to their physicochemical characteristics cross easily the dura mater and are very active when injected peridurally. Opiates are also used for the alleviation of chronic pain and are quite as effective as local anaesthetics, steroids or hypertonic saline by peridural injection. The main interest of these techniques lies in the easy reversibility of the analgesia.
PDF
