title: Reduced c-myc expression levels limit follicular mature B cell cycling in response to TLR signals.
abstract: The splenic B cell compartment is comprised of two major, functionally distinct, mature B cell subsets, i.e., follicular mature (FM) and marginal zone (MZ) B cells. Whereas MZ B cells exhibit a robust proliferative response following stimulation with the TLR4 ligand LPS, FM B cells display markedly delayed and reduced levels of proliferation to the identical stimulus. The current study was designed to identify a potential mechanism(s) accounting for this differential responsiveness. In contrast to the delay in cell cycle entry, FM and MZ B cells exhibited nearly identical LPS-driven alterations in the expression level of cell surface activation markers. Furthermore, both the NF-kappaB and mTOR signaling cascades were similarly activated by LPS stimulation in FM vs MZ B cells, while inducible activation of ERK and AKT were nearly absent in both subsets. MZ B cells, however, exhibited higher basal levels of phospho-AKT and pS6, consistent with a preactivated status. Importantly, both basal and LPS activation-induced c-myc expression was markedly reduced in FM vs MZ B cells and enforced c-myc expression fully restored the defective proliferative response in FM B cells. These data support a model wherein TLR responses in FM B cells are tightly regulated by limiting c-myc levels, thereby providing an important checkpoint to control nonspecific FM B cell activation in the absence of cognate Ag.
authors.affiliation: Seattle Children's Research Institute, WA 98101, USA.
authors.forename: Almut
authors.initials: A
authors.lastname: Meyer-Bahlburg
authors.forename: Ashok D
authors.initials: AD
authors.lastname: Bandaranayake
authors.forename: Sarah F
authors.initials: SF
authors.lastname: Andrews
authors.forename: David J
authors.initials: DJ
authors.lastname: Rawlings
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D015153:Blotting, Western; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism; D002453:Cell Cycle / Q000276:immunology*; D049109:Cell Proliferation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000276:immunology / Q000378:metabolism; D005434:Flow Cytometry; D015870:Gene Expression; D008070:Lipopolysaccharides / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology*; D016131:Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D016328:NF-kappa B / Q000276:immunology / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000276:immunology / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000276:immunology / Q000378:metabolism; D020598:Proto-Oncogene Proteins c-myb / Q000096:biosynthesis* / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology*; D013154:Spleen / Q000166:cytology / Q000276:immunology; D058570:TOR Serine-Threonine Kinases; D051193:Toll-Like Receptors / Q000276:immunology* / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D008070:Lipopolysaccharides; D016328:NF-kappa B; D020598:Proto-Oncogene Proteins c-myb; D051193:Toll-Like Receptors; D017853:Phosphotransferases (Alcohol Group Acceptor); C546843:mTOR protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases