Inhibition of glycogen synthase kinase-3 activity leads to epigenetic silencing of nuclear factor kappaB target genes and induction of apoptosis in chronic lymphocytic leukemia B cells.

Chronic lymphocytic leukemia (CLL) is commonly defined as a disease of failed apoptosis of B cells and remains an incurable disease. The mechanism of resistance to apoptosis in CLL is complex and influenced by numerous factors, including nuclear factor kappaB (NFkappaB)-mediated expression of antiapoptotic molecules. Recent evidence indicates that glycogen synthase kinase-3beta (GSK-3beta) positively regulates NFkappaB-mediated gene transcription and cell survival. Using malignant B cells collected from patients with CLL, we find that both GSK-3beta and NFkappaB accumulate in the nucleus of CLL B cells, and pharmacologic inhibition of GSK-3 results in decreased expression of two NFkappaB target genes Bcl-2 and XIAP and a subsequent increase in CLL B-cell apoptosis ex vivo. Furthermore, we observed that inhibition of GSK-3 leads to a decrease in NFkappaB-mediated gene transcription but does not affect the nuclear accumulation of NFkappaB in CLL B cells. Last, using chromatin immunoprecipitation, we show that GSK-3 inhibition abrogates NFkappaB binding to its target gene promoters (XIAP, Bcl-2), in part through epigenetic modification of histones. Our results establish that inhibition of GSK-3 abrogates NFkappaB binding to its target gene promoters through an epigenetic mechanism, enhances apoptosis in CLL B cells ex vivo and identifies GSK-3 as a potential therapeutic target in the treatment of CLL.