Abstract
In cells of the innate immune system, pathological increases in intracellular cAMP attenuate immune responses and contribute to infections by bacteria such as Bacillus anthracis. In this work, cAMP from B. anthracis edema toxin (ET) is found to activate the Notch signaling pathway in both mouse macrophages and human monocytes. ET as well as a cell-permeable activator of PKA induce Notch target genes (HES1, HEY1, IL2RA, and IL7R) and are able to significantly enhance the induction of these Notch target genes by a Toll-like receptor ligand. Elevated cAMP also resulted in increased levels of Groucho/transducin-like enhancer of Split (TLE) and led to increased amounts of a transcriptional repressor complex consisting of TLE and the Notch target Hes1. To address the mechanism used by ET to activate Notch signaling, components of Notch signaling were examined, and results revealed that ET increased levels of recombinant recognition sequence binding protein at the Jκ site (RBP-J), a DNA binding protein and principal transcriptional regulator of Notch signaling. Overexpression studies indicated that RBP-J was sufficient to activate Notch signaling and potentiate LPS-induced Notch signaling. Further examination of the mechanism used by ET to activate Notch signaling revealed that C/EBP β, a transcription factor activated by cAMP, helped activate Notch signaling and up-regulated RBP-J. These studies demonstrate that cAMP activates Notch signaling and increases the expression of TLE, which could be an important mechanism utilized by cAMP to suppress immune responses.
Keywords:
Bacterial Pathogenesis; Bacterial Toxins; Cyclic AMP (cAMP); Monocytes; Notch Pathway.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Animals
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Antigens, Bacterial / pharmacology
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Bacterial Toxins / pharmacology
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Basic Helix-Loop-Helix Transcription Factors / genetics
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Basic Helix-Loop-Helix Transcription Factors / metabolism
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Bucladesine / analogs & derivatives
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Bucladesine / pharmacology
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CCAAT-Enhancer-Binding Protein-beta / genetics
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CCAAT-Enhancer-Binding Protein-beta / metabolism
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Cell Line
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Cells, Cultured
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Co-Repressor Proteins
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Cyclic AMP / metabolism*
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Gene Expression / drug effects
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HEK293 Cells
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Homeodomain Proteins / genetics
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Homeodomain Proteins / metabolism
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Humans
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Immunoblotting
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Immunoglobulin J Recombination Signal Sequence-Binding Protein / genetics
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Immunoglobulin J Recombination Signal Sequence-Binding Protein / metabolism*
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Lipopolysaccharides / pharmacology
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Luciferases / genetics
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Luciferases / metabolism
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Macrophages / drug effects
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Macrophages / metabolism
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Mice
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Mice, Inbred C57BL
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Monocytes / cytology
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Monocytes / drug effects
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Monocytes / metabolism*
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Protein Binding / drug effects
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Receptor, Notch1 / genetics
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Receptor, Notch1 / metabolism*
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Repressor Proteins / genetics
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Repressor Proteins / metabolism*
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Reverse Transcriptase Polymerase Chain Reaction
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Signal Transduction / drug effects
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Transcription Factor HES-1
Substances
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Antigens, Bacterial
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Bacterial Toxins
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Basic Helix-Loop-Helix Transcription Factors
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CCAAT-Enhancer-Binding Protein-beta
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Co-Repressor Proteins
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Homeodomain Proteins
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Immunoglobulin J Recombination Signal Sequence-Binding Protein
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Lipopolysaccharides
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RBPJ protein, human
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Receptor, Notch1
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Repressor Proteins
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TLE1 protein, human
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Transcription Factor HES-1
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anthrax toxin
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monobutyryl cyclic AMP
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HES1 protein, human
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Bucladesine
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Cyclic AMP
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Luciferases