Nuclear localization in the biology of the CD40 receptor in normal and neoplastic human B lymphocytes.
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-alpha/beta) 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.
Lin-Lee
Yen-Chiu
YC
Department of Hematopathology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Pham
Lan V
LV
Tamayo
Archito T
AT
Fu
Lingchen
L
Zhou
Hai-Jun
HJ
Yoshimura
Linda C
LC
Decker
Glenn L
GL
Ford
Richard J
RJ
D001402:B-Lymphocytes / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure; D019013:CD40 Antigens / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D049452:Green Fluorescent Proteins; D006801:Humans; D008213:Lymphocyte Activation; D008565:Membrane Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D009154:Mutation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D053300:Tumor Necrosis Factor Ligand Superfamily Member 13; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D019013:CD40 Antigens; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C114631:TNFSF13 protein, human; D053300:Tumor Necrosis Factor Ligand Superfamily Member 13; D014409:Tumor Necrosis Factor-alpha; D049452:Green Fluorescent Proteins