miRNA-155 Flashcards
Link to inflammation?
Potent up-regulation in multiple immune cell lineages by TLR ligands; inflammatory cytokines, and specific antigens
T cells
Fitness of regulatory T cells is influenced by direct repression of SOCS1 by miRNA-155 (prolong IL-2 induced STAT5 signaling): It has been published that SOCS1 is regulated by mir-155 in Treg cells and that Treg cells lacking mir-155 fail to expand properly in response to IL-2 due to SOCS1-mediated inhibition of IL-2 signaling at the level of STAT5 phosphorylation
Blocks the inhibitory impact of IL-4 and IFNg on Th17 differentiation + Limit production of IL-4 by CD4+ T cells through c-Maf repression; IFNg mRNA is directly targeted by miR-155 in CD4+ T cells
Positive regulation of signaling pathways that promote Th17 cell formation –> repression of proteins that function to negatively regulate signaling pathways activated by TGFb, IL-6, IL-23
miRNA-155 contributes to ag-induced expansion and function of CD8+ T cells
Myeloid cells
Over-expression of miR-155 drives a myeloproliferative disorder through SHIP1 expression –> positive regulator of inflammation
DCs
miR-155 is upregulated in GM-CSF derived DCs and functions to enhance production of these cytokines
B cells
Important for production of antigen-specific IgGs
What controls miRNA-155 biogenesis and processing?
STAT3 –> miRNA-155 in Th17 cells, EAU (Chip-Seq –> enrichment of STAT3 around the promoter region of miRNA-155 - validated by Chip-qPCR)
NFkB and Ap-1 pathway –> miRNA-155 in gastric epithelial cells upon H. pylori stimulation
TGFb/SAMD4 pathway directly up regulates miRNA-155 expression in epithelial cells (deletion mapping/Chip Assay to show direct binding)
IL-10 reduces the stability of pri-miRNA-155 and pre-miRNA-155 transcripts, which inhibits maturation of miR-155 (macrophages) (McCoy et al. (TLR) , Cheung et al. (LPS) )
Tap63 suppresses miR-155 expression by direct binding; Np63 enhances expression
Hypoxia up-regulates miR-155 in lung cancer cells (HIF1a)
STAT5 drives miRNA-155 expression in T cell lymhpomas
tristetraprolin (TTP), a zinc finger protein also known as ZFP36
Rodriguez et al. Requirement of bic/microRNA-155 for Normal Immune Function
- Increased expressions in activated T and B cells
- Mutant alleles in embryonic stem cells –> bic deficient mice–> fertile but with lung pathology
- Role in regulating homeostasis of the immune system
- No gross defect in myeloid and lymphoid development in bid-deficient mice, protective immunity impaired
- Live attenuated form of Salmonella typhirium –> immunized bid-deficient mice, unlike wt mice, could not be protected by immunization to pathogen
- T dependent antigen, tetanus toxin fragment C protein –> splenocytes from immunized mice restimulated in vitro, and IL-2 and IFNg levels measured –> diminished T cell function in bic deficient mice
- The effect of bic/miRNA-155 may operate in part o nT cells through its influence on DC function –> bic deficient DCs fail to activate T cells
- Bic-deficient CD4+ T cells are intrinsically biased toward Th2 differentiation
- Bic represses a wide range of genes in CD4+ T cells
- c-Maf (proto oncogene) - phylogenetically conserved miR-155 seed matches in 3’UTR; potent transactivator of Il-4 promoter; –> attenuation of Th2 response
Eis et al. BIC processing
Spliced (~1.7kb) vs. Unspliced (~12kb) BIC transcript: since both spliced and polyadenylated (no long ORF) –> may be exported into cytoplasm by means of mRNA export pathway (RT-PCR primers specific for spliced vs. unspoiled BIC) –> not accessible for Drosha processing
–> Most of the detectable BIC is cytoplasmic and thus not a good predictor of BIC processing
Copy numbers
~20-1000 molecules BIC RNA
~100-8000 molecules miRNA-155
BIC
Gene that was transcriptionally activated by promoter insertion at a common retroviral integration site in B cell lymphoma (B cell Integration Cluster)
What are miRNA-155 targets?
~ 4000 targets (918 conserved sites between human and mouse) - strong sequence homology
PI3K/AKT pathway – reduced AKT phosphorylation after TCR engagement in miR-155-/- CD8 T cells
SHIP-1 – target in myeloid and T cells
SOCS-1 – impaired proliferation and survival of CD8 T cells by limiting signaling through cytokines, e.g. IL-2
Ag-specific CD8+ T cells lacking miR-155, increased phosphorylation of STAT1 in response to Type 1 interferon signaling
Inhibits PIK3RI (p85a) - negative regulator of PI3K signaling
SHIP1
Inositol phosphate that hydrolyzes the 5’ phosphate of phosphatidylinositol PI3, which blocks PI3-K mediate membrane localization of certain PH domain containing signaling molecules, such as Akt
HIF1a mediated mechanism of miRNA-155 expression?
Thiel et al.
Deletion of HIF1a enhances TCR stimulated NFkB activation
- TCR stimulated NFkB activation in T cells compromises p50+RelA and p50+cRel heterodimers and p50 homodimers
- Upon TCR activation the activity of both p50 and p65 subunits increased in HIF1a deficient cells
- Hypoxia inhibits TCR induced pro-inflammatory cytokine accumulation by T cells
- HIF1a deletion results in enhanced T cell activation
Bala et al: NFkB mediates increase in miRNA-155 expression in macrophages
Immunossupressive effects of adenosine?
(HIF1b does not change during hypoxic conditions/mostly HIF1a protein levels)
Even short periods of hypoxia lead to breakdown of adenine nucleotides to adenosine –> Under normoxia, adenosine is converted to AMP by adenosine kinase but hypoxia inhibits adenosine kinase activity (down to 6%)
Extracellular adenosine signals through heterotrimeric G proteins that can either stimulate (Gs) or inhibit (Gi) adenylyl cyclase, the enzyme that catalyzes the formation of cAMP.
Very low concentrations of adenosine can bind to and activate A1 receptors that can inhibit the adenylyl cyclase–activating A2A and A2B receptors.
Because higher levels of adenosine can overcome the inhibition mediated by A1 receptors, A1 receptors are thought to exert a tonic inhibitory effect on A2 receptor functions.–> increases in effects of A2A receptor activation
Activation of A2A adenosine receptors inhibits TCR triggered IL-2 receptor upregulation
HIF-1® under some normoxic conditions?
nitrogen- or oxygen-derived radicals: RNS (25) and ROS (26), cytokines [TNF-® (27) and IL1-¯ (28)], growth factors [IGF (29)]
