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Overexpression of multidrug resistance genes and their encoded P-glycoproteins is a major mechanism for the development of multidrug resistance in cancer cells. The hepatocarcinogen 2-acetylaminofluorene (2-AAF) efficiently activates rat mdr1b expression. However, the underlying mechanisms are largely unknown. In this study, we demonstrated that a NF-B site on the mdr1b promoter was required for this induction. Overexpression of antisense p65 and IB␣ partially abolished the induction. We then delineated the pathway through which 2-AAF activates NF-B.

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 ...

CD40 is a tumor necrosis factor (TNF) receptor superfamily, (TNFR; TNFRSF-5) member, that initiates important signaling pathways mediating cell growth, survival, and differentiation in B-lymphocytes. Although CD40 has been extensively studied as a plasma membrane-associated growth factor receptor, we demonstrate here that CD40 is present not only in the plasma membrane and cytoplasm but also in the nucleus of normal and neoplastic B-lymphoid cells. Confocal microscopy showed that transfected CD40-green fluorescent fusion protein entered B-cell nuclei. The CD40 protein contains a nuclear localization signal sequence that, when mutated, blocks entry of CD40 into the nucleus through the classic karyopherins (importins-␣/␤) pathway. Nuclear fractionation studies revealed the presence of CD40 protein in the nucleoplasm fraction of activated B cells, and chromatin immunoprecipitation assays demonstrated that CD40 binds to and stimulates the BLyS/BAFF promoter, another TNF family member (TNFSF-13B) involved in cell survival in the B cell lineage. Like other nuclear growth factor receptors, CD40 appears to be a transcriptional regulator and is likely to play a larger and more complex role than previously demonstrated in regulating essential growth and survival pathways in B-lymphocytes.