Journal
BRITISH JOURNAL OF HAEMATOLOGY
Volume 138, Issue 6, Pages 721-732Publisher
BLACKWELL PUBLISHING
DOI: 10.1111/j.1365-2141.2007.06717.x
Keywords
chronic lymphocytic leukaemia; apoptosis; Bcl-2; Bcl-x(L); Bcl-x(S)
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Chronic lymphocytic leukaemia cells survive and proliferate in patients but rapidly die in culture. The microenvironment that sustains leukaemic cells in vivo contains both stromal cell elements and T cells. We defined changes in Bcl-2 family protein expression on culture with CD40 ligand (CD154) expressed on mouse fibroblast L cells, and interleukin-4 (IL-4; CD154/IL-4 system): conditions that support survival and proliferation. Unexpectedly, Bcl-2 protein expression decreased whilst pro-survival Bcl-x(L) (as well as A1 and Mcl-1) increased. However, the CD154-L cell/IL-4 system also increased the pro-apoptotic proteins, Bid and Noxa, suggesting that an increased pool of pro-survival factors and not the effects of a single protein mediate survival. Most pro-apoptotic proteins were not induced in drug or spontaneous apoptosis, but expression of Bcl-x(S), a pro-apoptotic BCL2L1 isoform, was associated with cell death. This was post-transcriptionally controlled, and, therefore, alternative splicing at the Bcl-x locus appears to have a role in the regulation of chronic lymphocytic leukaemia (CLL) cell survival. This study demonstrated a switch in pro-survival proteins associated with the transition from quiescence to CD154-driven proliferation. CLL therapies targeting Bcl-2 may need to be modified to antagonize proliferation centre-specific pro-survival proteins.
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