Inhibition of GSK-3 Induces Apoptosis of CLL Cells by Abrogating NFkB Nuclear Activity.

Chronic lymphocytic leukemia (CLL) represents one of the most common hematological malignancies and is characterized by the expansion of a clonal B cell population. Commonly, CLL is defined as a disease of failed apoptosis of the leukemic B cells, and it is this feature that makes them refractory to common chemotherapeutic agents designed to kill CLL cells. The mechanism controlling apoptosis in CLL is complex and influenced by numerous factors, including NFkB-mediated expression of antiapoptotic proteins, such as Bcl-2 and XIAP. We recently demonstrated that glycogen synthase kinase-3 (GSK-3) b positively regulates NFkB-mediated gene transcription and cell survival in pancreatic cancer cells (Cancer Research 2005. 65:2076).

Similar to pancreatic cancer, we have found that pharmacological inhibition of GSK-3 results in decreased expression of NFkB target genes Bcl-2, Mcl-1 and XIAP in CLL B cells. In addition we noted a dose dependent increase in apoptosis levels for both the MEC1 cell line and primary CLL B cell patient samples. Using CLL blood B cells, we have found that both GSK-3b and NFkB accumulate in the nucleus of CLL cells, but not normal blood B cells. In addition, we observed that inhibition of GSK-3 leads to a decrease in NFkB-mediated gene transcription, without affecting the nuclear accumulation of NFkB. However, using chromatin immunoprecipitation, we found that NFkB binding to its target gene promoters (XIAP, Bcl-2) is significantly affected in CLL B cells treated with a GSK-3 inhibitor. These results suggest that GSK-3 regulates the nuclear activity of NFkB in CLL cells by affecting the binding of p65/p50 to the promoters of a subset of its target genes. Our results establish that inhibition of GSK-3 induces apoptosis of CLL cells and suggest GSK-3b as a potential therapeutic target in the treatment of CLL.