NF-kappaB-dependent regulation of the diagnostic marker CD10 and role of BCL-2 activity in histone deacetylase inhibitor-induced apoptosis in human B-lymphoma cell lines

Diffuse large B-cell lymphoma (DLBCL) is a genetically heterogeneous disease with multiple distinct molecular subtypes. Increased NF-κB activity and expression of the microRNA miR-155 (product of the BIC gene) are associated with one subtype, called the activated B-cell (ABC) subtype. It is shown here that induction of NF-κB activity leads to increased miR-155 expression, the levels of miR-155 in a panel of B-lymphoma cell lines correlate with increased NF-κB activity, and the NF-κB p50/p65 heterodimer binds to a specific DNA site in the BIC promoter. Also described is a regulatory network wherein NF-κB-dependent up-regulation of miR-155 leads to reduced PU.1 transcription factor expression and consequently reduced PU.1-driven expression of B-lymphoma marker CD10 in the human B-lymphoma cell line BJAB. Genetic variation in DLBCL can be used to explain the response of individual patients to chemotherapy. One cancer therapeutic approach currently in clinical trials uses histone deacetylase inhibitors (HDACi's) as a monotherapy or in combination with other vi agents. It is shown here that two pan-HDACi's, trichostatin A and vorinostat, induce apoptosis in seven of eight human DLBCL cell lines. Ectopic over-expression of antiapoptotic proteins BCL-2 and BCL-XL or the pro-apoptotic protein BIM in select DLBCL cell lines can confer further resistance or sensitivity, respectively, to HDACi treatment. Additionally, the BCL-2 family antagonist ABT-737 can increase the sensitivity of several DLBCL cell lines to vorinostat-induced apoptosis, including the HDACi-resistant SUDHL6 cell line. Moreover, one vorinostat-resistant variant of the HDACi-sensitive cell line SUDHL4 has increased expression of anti-apoptotic proteins BCL-XL and MCL-1 and decreased sensitivity to ABT-737, and a second such variant cell line has increased expression of anti-apoptotic protein MCL-1. These results suggest that the balance of anti- to pro-apoptotic BCL-2 family protein expression is important in determining the sensitivity of DLBCL cell lines to HDACi-induced apoptosis. Thus, the sensitivity of DLBCL cell lines to treatment with HDACi's appears to depend on the complex regulation of BCL-2 family members, suggesting that the response of a subset of DLBCL patients to HDACi treatment may benefit from co-treatment with BCL-2 antagonists