Tumor necrosis factor receptor-associated factor 1 gene overexpression in B-cell chronic lymphocytic leukemia: analysis of NF-κB/Rel–regulated inhibitors of apoptosis

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Abstract
B-cell chronic lymphocytic leukemia (B-CLL) is characterized by a resistance toward apoptosis-inducing agents. Nuclear factor-κB (NF-κB)/Rel has been shown to regulate the expression of antiapoptotic genes, such as members of the inhibitor of apoptosis protein (IAP) and tumor necrosis factor receptor-associated factor (TRAF) gene families. Expression and regulation of NF-κB/Rel–dependent inhibitors of apoptosis have not been collectively studied in B-CLL. We examined expression of known NF-κB/Rel–regulated antiapoptotic genes by RNAse protection assay, real-time polymerase chain reaction, and immunoblotting in patients with B-CLL. TRAF1 and to a lesser extent TRAF2 were overexpressed in B-CLL lymphocytes as compared with normal CD19+ B cells. TRAF1 overexpression did not correlate with markers of disease progression or overall survival. Furthermore, we found high constitutive expression of the IAP genes c-IAP-1, c-IAP-2, and XIAP both in normal and B-CLL lymphocytes. Focusing on the regulation of TRAF1, NF-κB/Rel activity in B-CLL nuclear extracts was shown to bind to TRAF1 promoter elements. However, IκB kinase (IKK) activity was not increased in CLL lymphocytes as compared with normal CD19+ B cells. The known IKK inhibitor sulfasalazine did not compromise TRAF1 expression. Thus, although our study revealed a common expression pattern of NF-κB/Rel–regulated inhibitors of apoptosis, our findings indicate an IKK-independent regulation of TRAF1 in B-CLL.