| Abstract: | Background: We recently reported that autocrine BAFF (B cell–activating factor belonging to the TNF family) signal transduction pathway contributes to H. pylori-independent growth of gastric diffuse large B-cell lymphoma (DLBCL) (Blood 2008;112:2927-34; Ann Hematol 2010;89:431-6). In this study, we sought to investigate whether activation of BAFF signaling pathway can promote the survival and proliferation of aggressive B-cell lymphoma. Methods: Seven aggressive NHL cell lines (EBV-negative Burkitt’s lymphoma (Ramos), EBV-positive Burkitt’s lymphoma (Raji), EBV-negative undifferentiated lymphoma (MC116), activated B cell (ABC)-like DLBCL (OCI-Ly3, OCI-Ly10), and germinal center B cell (GCB)-like DLBCL (OCI-Ly7, and Pfeiffer) were used in this study. Cell cycle was analyzed by flow cytometry. The DNA-binding activity of NF-kB was determined by the luciferase assay. Expression of non-canonical NF-{kappa}B signatures-related proteins (BAFF, BAFF-R, NIK, cIAP1, TRAF2, cIAP1/2, TRAF3, IKKa, p100, p52 and RelB, BCL10, BCL3, and STAT3) was assessed by immunoblotting. Results: Our results showed that in GCB-DLBCL cell lines, activation of BAFF induced recruitment and degradation of TRAF3, which resulted in NIK kinase accumulation, BCL10 Ser138 phosphorylation, IKKa phosphorylation, and NF-kB p100 processing, thereby resulting in continuous activation of non-canonical NF-kB pathway. This phenomenon also resulted in BCL3 nuclear translocation and STAT3 activation, and subsequently activated STAT3 downstream-regulated genes (BCL2, survivin, and cyclin D1). Furthermore, we found that inhibition of BAFF by short hairpin RNA (shRNA) suppressed the growth of ABC-DLBCL cells and Burkitt lymphoma cells through the down-regulation of BAFF/BAFF-R/TRAF3/NIK/BCL3/NF-kB signaling pathway. Conclusions: Our results indicate that constitutive BAFF signaling activates NIK-induced non-canonical NF-kB signaling pathway in aggressive B-cell lymphoma, and inhibition of BAFF is particularly effective in the treatment of this subgroup of tumors. |
