Regulation of S1PR2 by the EBV oncogene LMP1 in aggressive ABC subtype diffuse large B cell lymphoma.

The Epstein-Barr virus (EBV) is found almost exclusively in the activated B cell (ABC) subtype of diffuse large B cell lymphoma (DLBCL), yet its contribution to this tumour remains poorly understood. We have focussed on the EBV-encoded latent membrane protein-1 (LMP1), a constitutively activated CD40 homologue expressed in almost all EBV-positive DLBCL and which can disrupt germinal centre (GC) formation and drive lymphomagenesis in mice. Comparison of the transcriptional changes that follow LMP1 expression with those that follow transient CD40 signalling in human GC B cells enabled us to define pathogenic targets of LMP1 aberrantly expressed in ABC-DLBCL. These included the down-regulation of S1PR2, a sphingosine-1-phosphate (S1P) receptor that is transcriptionally down-regulated in ABC-DLBCL, and when genetically ablated leads to DLBCL in mice. Consistent with this we found that LMP1-expressing primary ABC-DLBCL were significantly more likely to lack S1PR2 expression than were LMP1-negative tumours. Furthermore, we showed that the down-regulation of S1PR2 by LMP1 drives a signalling loop leading to constitutive activation of the phosphatidylinositol-3-kinase (PI3-K) pathway. Finally, core LMP1-PI3-K targets were enriched for lymphoma-related transcription factors and genes associated with shorter overall survival in patients with ABC-DLBCL. Our data identify a novel function for LMP1 in aggressive DLBCL

Alterations of myelin-specific proteins and sphingolipids characterize the brains of acid sphingomyelinase-deficient mice, an animal model of Niemann-Pick diease type A

Niemann-Pick disease (NPD) type A is a neurodegenerative disorder caused by sphingomyelin (SM) accumulation in lysosomes relying on reduced or absent acid sphingomyelinase (ASM) activity. NPD-A patients develop progressive neurodegeneration including cerebral and cerebellar atrophy, relevant Purkinje cell and myelin deficiency with death within 3 years. ASM'knock-out' (ASMKO) mice, an animal model of NPD-A, develop a phenotype largely mimicking that of NPD-A. The mechanisms underlying myelin formation are poorly documented in ASMKO mice. In this study we determined the content of four myelin-specific proteins, myelin basic protein (MBP), 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), myelin associated glycoprotein (MAG) and proteolipid protein (PLP), and that of myelin-enriched sphingolipids in the brains of ASMKO and wild-type mice in early stages of post-natal (pn) life. Protein and mRNA analysis revealed that in ASMKO mice beginning from 4 post-natal weeks (wk-pn), the expression levels of MAG, CNP, and MBP were below those observed in wild-type mice and the same applied to PLP at 10 wk-pn. Moreover, at 4 wk-pn the expression of SOX10, one of the transcription factors involved in oligodendrocyte development and maintenance was lower in ASMKO mice. Lipid analysis showed that SM and the gangliosides GM3 and GM2 accumulated in the brains of ASMKO mice, as opposed to galactocerebroside and galactosulfocerebroside that, in parallel with the mRNAs of UDP-galactose ceramide galactosyltransferase and galactose-3-O-sulfotransferase 1, the two transferases involved in their synthesis, decreased. Myelin lipid analysis showed a progressive sphingomyelin accumulation in ASMKO mice; noteworthy, of the two sphingomyelin species known to be resolved by TLC, only that with the lower Rf accumulated. The immunohistochemical analysis showed that the reduced expression of myelin specific proteins in ASMKO mice at 10 wk-pn was not restricted to the Purkinje layer of the cerebellar cortex but involved the cerebral cortex as well. In conclusion, reduced oligodendrocyte metabolic activity is likely to be the chief cause of myelin deficiency in ASMKO mice, thus shedding light on the molecular dysfunctions underlying neurodegeneration in NPD-A

Deregulated sphingolipid metabolism and membrane organization in neurodegenerative disorders

Sphingolipids are polar membrane lipids present as minor components in eukaryotic cell membranes. Sphingolipids are highly enriched in nervous cells, where they exert important biological functions. They deeply affect the structural and geometrical properties and the lateral order of cellular membranes, modulate the function of several membrane-associated proteins, and give rise to important intra- and extracellular lipid mediators. Sphingolipid metabolism is regulated along the differentiation and development of the nervous system, and the expression of a peculiar spatially and temporarily regulated sphingolipid pattern is essential for the maintenance of the functional integrity of the nervous system: sphingolipids in the nervous system participate to several signaling pathways controlling neuronal survival, migration, and differentiation, responsiveness to trophic factors, synaptic stability and synaptic transmission, and neuron-glia interactions, including the formation and stability of central and peripheral myelin. In several neurodegenerative diseases, sphingolipid metabolism is deeply deregulated, leading to the expression of abnormal sphingolipid patterns and altered membrane organization that participate to several events related to the pathogenesis of these diseases. The most impressive consequence of this deregulation is represented by anomalous sphingolipid-protein interactions that are at least, in part, responsible for the misfolding events that cause the fibrillogenic and amyloidogenic processing of disease-specific protein isoforms, such as amyloid beta peptide in Alzheimer's disease, huntingtin in Huntington's disease, alpha-synuclein in Parkinson's disease, and prions in transmissible encephalopathies. Targeting sphingolipid metabolism represents today an underexploited but realistic opportunity to design novel therapeutic strategies for the intervention in these diseases