Constitutive activation of the NF-κB has been documented to be involved in the pathogenesis of many human malignancies, including hemopoietic neoplasms. In this study, we examined the status of NF-κB in two non-Hodgkin’s lymphoma cell lines derived from mantle cell lymphoma (MCL) samples and in patient MCL biopsy specimens by EMSA and confocal microscopic analysis. We observed that NF-κB is constitutively activated in both the MCL cell lines and in the MCL patient biopsy cells. Since NF-κB has been shown to play an important role in a variety of cellular processes, including cell cycle regulation and apoptosis, targeting the NF-κB pathways for therapy may represent a rational approach in this malignancy. In the MCL cell lines, inhibition of constitutive NF-κB by the proteasome inhibitor PS-341 or a specific pIκBα inhibitor, BAY 11-7082, led to cell cycle arrest in G1 and rapid induction of apoptosis. Apoptosis was associated with the down-regulation of bcl-2 family members bcl-xL and bfl/A1, and the activation of caspase 3, that mediates bcl-2 cleavage, resulting in the release of cytochrome c from the mitochondria. PS-341or BAY 11-induced G1 cell cycle arrest was associated with the inhibition of cyclin D1 expression, a molecular genetic marker of MCL. These studies suggest that constitutive NF-κB expression plays a key role in the growth and survival of MCL cells, and that PS-341 and BAY 11 may be useful therapeutic agents for MCL, a lymphoma that is refractory to most current chemotherapy regimens.

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B cell lineage non-Hodgkin's lymphomas (NHL-B) are neoplastic B cells that show dysregulated B lymphocyte growth characteristics. Unlike normal B cells, aggressive NHL-B cells show constitutive expression of nuclear NF-kappaB by maintaining an assembled, scaffold-like signaling platform, called a Signalosome within the lipid raft microdomain, extending from the cell membrane. The CD40 Signalosome appears to be initiated through autochthonous production and cognate binding of CD154 (CD40L, gp39) to CD40 by the lymphoma cell. Constitutive expression of NF-kappaB in NHL-B can be downregulated by treatment with antibodies to CD40 or CD154 that disrupt Signalosomes, inhibit lymphoma cell growth, and induce cell death. CD40 Signalosomes may provide a potentially vulnerable target for therapeutic intervention in NHL-B cells.

BLyS and its major receptor BAFF-R have been shown to be critical for development and homeostasis of normal B lymphocytes, and for cell growth and survival of neoplastic B lymphocytes, but the biologic mechanisms of this ligand/receptor-derived intracellular signaling pathway(s) have not been completely defined. We have discovered that the BAFF-R protein was present in the cell nucleus, in addition to its integral presence in the plasma membrane and cytoplasm, in both normal and neoplastic B cells. BAFF-R interacted IntroductionBAFF-R (also called BR3) is the most unique of the 3 tumor necrosis factor receptors (TNFRs) for BLyS (B-lymphocyte stimulator; also called BAFF). A/WySNJ mice (which have a mutant BAFF-R gene) have a low peripheral blood B-cell fraction that is similar to that seen in BLyS-deficient mice, suggesting that BAFF-R transmits critical B-cell survival signals associated with BLyS stimulation. 1 Downstream mediators of BAFF-R activation include both the canonical (classic, NF-B1) and alternative (noncanonical, NF-B2) NF-B pathways. [2][3][4][5][6][7] Although BLyS/BAFF-R-derived intracellular signaling pathways are still incompletely defined, this ligand/receptor dyad provides key regulatory control of antiapoptotic cell survival and growth stimulation. [8][9][10][11] In this regard, BLyS modulates several antiapoptotic Bcl-2 family members, including Bcl-x L , Mcl-1, A-1, Bcl-2, and Bim, via survival-promoting kinase systems such as Pim 1/2 or Erk 11-14 as well as proteins involved in early cell-cycle progression, including c-myc, p27 Kip1 , cyclin D1, and cyclin D2. 15,16 Most studies of TNFR family receptors have focused on these proteins' function in the cellular plasma membrane and cytoplasm. However, our laboratory recently demonstrated that another TNFR protein, CD40, is present in the nuclei of normal and B-cell non-Hodgkin lymphoma (NHL-B) cells, where it functions as a transcription factor that regulates the expression of several antiapoptotic and proliferation-associated genes. 17,18 The IB kinase (IKK) protein complex is critical for regulating NF-B pathway activation. The IKK complex includes 3 important subunits: the catalytic subunits IKK␣ and IKK␤ (also known as IKK1 and IKK2, respectively) and the regulatory subunit IKK␥ (also known as NEMO). In the cytoplasm, activation of the IKK complex induces processing of precursors p105 and p100 into p50 and p52, respectively, resulting in NF-B subunit dimeric partners that migrate from the cytoplasm into the nucleus. [19][20][21][22][23] In recent studies, IKK␣ has also been identified in the cell nucleus, functioning in histone H3 phosphorylation. 24,25 Although IKK␤ was also previously observed in the cell nucleus, its nuclear function has remained obscure. 24 The second purpose of our study was to elucidate how nuclear BAFF-R interacts with the NF-B pathway to promote B-cell survival and proliferation.In this study, we found that BAFF-R was present in the cell nucleus as well as in the plasma membrane and cytoplasm, in both normal ...