title: Potential role of CARMA1 in CD40-induced splenic B cell proliferation and marginal zone B cell maturation.
abstract: NF-kappaB activation through B cell receptor (BCR) ligation is critical for B cell development, survival and antigen-mediated activation of B cells. CARD domain and MAGUK-domain containing protein-1 (CARMA1), recently identified adaptor molecule, has been shown to play an essential role in BCR-induced NF-kappaB activation. CARMA1-deficient B cells fail to proliferate upon BCR stimulation, leading to defective humoral responses. Surprisingly, CARMA1-deficient B cells are also defective in CD40-induced proliferation. The mechanisms responsible for CD40-induced proliferation defect have not yet been characterized. In this study, we show that signaling cascades activated by CD40 stimulation are largely unaffected in CARMA1-deficient B cells. Instead, we have found that the defective proliferation of CARMA1-deficient B cells is due to two events. First, CARMA1-deficient B cells show defective cell-cycle progression. Secondly, the numbers of marginal zone (MZ) B cells, which are the main responders upon CD40 stimulation, are greatly diminished in CARMA1-deficient mice. Since B cell maturation requires basal signaling through BCR and NF-kappaB activation, we propose that impaired BCR signaling in CARMA1-deficient mice leads to defective maturation of MZ B cell population, which in turn, contributes to impaired proliferation upon CD40 stimulation.
authors.affiliation: Department of Molecular and Cellular Oncology, The University of Texas, MD Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Bhanu P
authors.initials: BP
authors.lastname: Pappu
authors.forename: Xin
authors.initials: X
authors.lastname: Lin
mesh_terms: D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000502:physiology*; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D053468:CARD Signaling Adaptor Proteins / Q000235:genetics / Q000502:physiology*; D019013:CD40 Antigens / Q000276:immunology* / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D002465:Cell Movement; D049109:Cell Proliferation; D008213:Lymphocyte Activation / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000819:agonists; D013154:Spleen / Q000166:cytology / Q000187:drug effects / Q000276:immunology*
chemical_list: D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D019013:CD40 Antigens; C496467:Card11 protein, mouse; D016328:NF-kappa B; D020929:Mitogen-Activated Protein Kinase Kinases