The growth factor fusion construct containing B-lymphocyte stimulator (BLyS) and the toxin rGel induces apoptosis specifically in BAFF-R-positive CLL cells.
The cytokine B lymphocyte stimulator (BLyS) mediates its effect through cell-surface receptors BAFF-R, TACI, and BCMA. BLyS receptors are expressed only on B cells and not present in other normal cells including normal T lymphocytes. Chronic lymphocytic leukemia (CLL) is a B-cell disease and CLL lymphocytes express BLyS receptors. Gelonin, a type 1 ribosome-inactivating toxin, lacks cell membrane binding domain and hence is nontoxic to intact cells. We generated a construct of recombinant gelonin (rGel) fused to BLyS to specifically target quiescent B-CLL lymphocytes. The construct rGel/BLyS specifically binds and internalizes through BAFF-R into CD19(+) B-CLL lymphocytes and induces apoptosis at nanomolar concentrations. In contrast, rGel alone was not able to internalize into these leukemic lymphocytes. Mechanistically, the rGel/BLyS construct inhibits protein synthesis with an IC(50) of less than 3 nM compared with more than 5000 nM for rGel toxin alone. This rGel/BLyS-mediated decrease in protein synthesis was associated with a decline in short-lived proteins such as MCL-1 and XIAP, the 2 survival proteins in B-CLL. There was a strong relationship between a decrease in these proteins and the cleavage of PARP, a hallmark feature of apoptosis. Taken together, these data suggest that the rGel/BLyS fusion toxin may have potential therapeutic efficacy for B-CLL patients.
Nimmanapalli
Ramadevi
R
Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Lyu
Mi-Ae
MA
Du
Min
M
Keating
Michael J
MJ
Rosenblum
Michael G
MG
Gandhi
Varsha
V
D018941:Antigens, CD19 / Q000235:genetics / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D053264:B-Cell Activating Factor / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D053265:B-Cell Activation Factor Receptor / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D012313:RNA / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D054789:Ribosome Inactivating Proteins, Type 1
D018941:Antigens, CD19; D053264:B-Cell Activating Factor; D053265:B-Cell Activation Factor Receptor; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D012313:RNA; C025674:GEL protein, Gelonium multiflorum