Identification, characterisation and regulation by CD40 activation of novel CD95 splice variants in CD95-apoptosis-resistant, human, B-cell non-Hodgkin's lymphoma.
CD95 gene and splicing aberrations have been detected in B-cell non-Hodgkin lymphoma (B-NHL) where they are thought to contribute to CD95 apoptosis resistance. To further investigate this, we have performed extensive CD95 transcript sequencing and functional analysis in B-NHL with demonstrated resistance to CD95-induced apoptosis (B-NHLr). Strikingly, instead of showing CD95 mutations per se, B cells from B-NHLr co-expressed wild-type and multiple, normal (CD95nv) and novel alternatively spliced variant CD95 transcripts (CD95av). CD95av were predicted, by sequencing, to encode soluble, potentially apoptosis inhibitory proteins. However, their overexpression, by transfection, in Jurkat cells did not interfere with endogenous CD95 death signalling. Furthermore, CD95av-expressing B-NHLr did not show mutations in CD95 splice-regulatory elements and CD95av expression was 'reversible' by CD40 activation. This, in conjunction with treatment by the protein synthesis inhibitor, cycloheximide, could sensitise a subset of B-NHLr to CD95 apoptosis. In normal and lymphoma B cells, this correlated to increased CD95 membrane expression, enhanced DISC activity and engagement of the mitochondrial death pathway via Bid cleavage, although the latter occurred less efficiently in B-NHLr. Thus, immune modulation of CD95 transcription and alternative splicing combined with enhanced engagement of mitochondrial death signalling offer potential for restoration of CD95 apoptosis sensitivity in B-NHLr.
Lajmanovich
Alicia
A
Institut National de la Santé et de la Recherche Médicale (INSERM), U823, Institut Albert Bonniot, Grenoble, France. alicia.lajmanovich@ujf-grenoble.fr
Ribeyron
Juliana Bruder
JB
Florin
Anne
A
Fournier
Alexandra
A
Pasquier
Marie-Anne
MA
Duley
Samuel
S
Chauvet
Martine
M
Plumas
Joel
J
Bonnefoix
Thierry
T
Gressin
Remy
R
Leroux
Dominique
D
Callanan
Mary B
MB
D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D001483:Base Sequence; D019013:CD40 Antigens / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D016393:Lymphoma, B-Cell / Q000473:pathology*; D024101:Mitochondrial Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction; D014162:Transfection; D019014:fas Receptor / Q000235:genetics*
D051017:Apoptosis Regulatory Proteins; D019013:CD40 Antigens; D024101:Mitochondrial Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D019014:fas Receptor