Regulation of TGFβ and BMP signalling in human B cells by latent Epstein-Barr virus

Most individuals are infected with EBV, which establishes latent infection in B cells. Although usually asymptomatic, EBV persistence is associated with several types of lymphoma. TGFβ signals via TGFβ receptors (TGFβR) 1 and 2 and is generally pro-apoptotic and anti-proliferative, but EBV infection renders cells resistant to these effects. The aim of this thesis was to investigate further the mechanism by which this occurs. Using the EBV-negative Burkitt lymphoma cell line BL31 infected with a panel of BAC-derived wild-type and recombinant EBVs, this study has confirmed by qRT-PCR that EBV down-regulates TGFβR2 transcription, leading to suppression of TGFβ signalling as detected by western blot for phosphorylated SMAD2. Use of recombinant viruses with deletions of individual latent proteins has shown that LMP1, LMP2A, EBNA3B and EBNA3C cooperate in this repression of TGFβR2 and suppression of signalling. Chromatin immunoprecipitation analysis has shown that the repression of TGFβR2 is accompanied by deposition of the repressive epigenetic mark histone H3 lysine 27 trimethylation and concomitant binding of SUZ12, a subunit of polycomb-repressive complex 2, to the TGFβR2 promoter. Infection of primary B cells with EBV also leads to repression of TGFβR2 and suppression of TGFβ signalling. Additionally, EBV up-regulates TGFβR3, a co-receptor for signalling by both TGFβ and bone morphogenetic proteins (BMPs), a related group of ligands which signal via SMADs 1, 5 and 8. This led to an investigation into the effects of EBV on BMP signalling. Although EBV increases signalling in response to BMP2, BMP4 and BMP6 in BL31 cells, this is not via the up-regulation of TGFβR3. BMP2 and BMP4 induce G1 arrest in BL31 cells, but EBV does not alter this. EBV also up-regulates SMAD1 and down-regulates SMAD5. The polycomb-mediated repression of TGFβR2 is a mechanism by which EBV might promote lymphomagenesis. In addition, the finding that EBV alters several components of BMP signalling suggests that BMP signalling may be important in B-cell biology.Open Acces

Dasatinib crosses the blood-brain barrier and is an efficient therapy for central nervous system philadelphia chromosome positive leukemia

Although imatinib, a BCR-ABL tyrosine kinase inhibitor, is used to treat acute Philadelphia chromosome-positive (Ph+) leukemia, it does not prevent central nervous system (CNS) relapses resulting from poor drug penetration through the blood-brain barrier. Imatinib and dasatinib (a dual-specific SRC/BCR-ABL kinase inhibitor) were compared in a pre-clinical mouse model of intracranial Ph+ leukemia. Clinical dasatinib treatment in patients with CNS Ph+ leukemia was assessed. In preclinical studies, dasatinib increased survival, whereas imatinib failed to inhibit intracranial tumor growth. Stabilization and regression of CNS disease were achieved with continued dasatinib administration. The drug also demonstrated substantial activity in 11 adult and pediatric patients with CNS Ph+ leukemia. Eleven evaluable patients had clinically significant, long-lasting responses, which were complete in 7 patients. In 3 additional patients, isolated CNS relapse occurred during dasatinib therapy; and in 2 of them, it was caused by expansion of a BCR-ABL-mutated dasatinib-resistant clone, implying selection pressure exerted by the compound in the CNS. Dasatinib has promising therapeutic potential in managing intracranial leukemic disease and substantial clinical activity in patients who experience CNS relapse while on imatinib therapy. This study is registered at ClinicalTrials. gov as CA180006 (#NCT00108719) and CA180015 (#NCT00110097)