Previous publications from our and other groups identified E2F1 as a transcription factor involved in the regulation of inflammatory response to Toll-like receptor ligands including LPS. In this ...study, we challenged E2F1-deficient mice with LPS systemically and demonstrated decreased survival despite attenuated inflammatory response compared with controls. Gene expression profiling of liver tissue identified a dampened transcriptional response in the coagulation cascade in B6;129(E2F1-/-) compared with B6x129 F2 mice. These data were further corroborated by increased prothrombin time, activated partial thromboplastin time, and fibrin split products in the blood of E2F1-deficient mice, suggesting disseminated intravascular coagulation as a consequence of uncontrolled sepsis providing at least a partial explanation for their decreased survival despite attenuated inflammatory response. To identify novel miRNAs involved in the innate immune response to LPS, we also performed miRNA profiling of liver tissue from B6;129(E2F1-/-) and B6x129 F2 mice treated with LPS systemically. Our analysis identified a set of miRNAs and their mRNA targets that are significantly differentially regulated in E2F1-deficient but not control mice including let-7g, miR-101b, miR-181b, and miR-455. These miRNAs represent novel regulators of the innate immune response. In summary, we used transcriptional and miRNA profiling to characterize the response of E2F1-deficient mice to systemic LPS.
► Our analysis identified pathways and transcriptional networks involved in macrophage response to three TLR ligands: LPS, poly (I:C), and CpG DNA. ► RNA interference-mediated inhibition of two genes ...identified in this analysis, PLEC1 and TPST1, reduced IL-6 production by J774A.1 and RAW264.7 macrophages stimulated with LPS. ► These findings delineate macrophage gene response patterns induced by different PAMPs and identify new genes that have not previously been implicated in innate immunity.
Toll-like receptors (TLRs) are key receptors in innate immunity and trigger responses following interaction with pathogen-associated molecular patterns (PAMPs). TLR3, TLR4 and TLR9 recognize double stranded RNA, lipopolysaccharide (LPS) and CpG DNA, respectively. These receptors differ importantly in downstream adaptor molecules. TLR4 signals through MyD88 and TRIF; in contrast, the TLR3 pathway involves only TRIF while TLR9 signals solely through MyD88. To determine how differences in downstream signaling could influence gene expression in innate immunity, gene expression patterns were determined for the RAW264.7 macrophage cell line stimulated with LPS, poly (I:C), or CpG DNA. Gene expression profiles 6 and 24h post-stimulation were analyzed to determine genes, pathways and transcriptional networks induced. As these experiments showed, the number and extent of genes expressed varied with stimulus. LPS and poly (I:C) induced an abundant array of genes in RAW264.7 cells at 6h and 24h following treatment while CpG DNA induced many fewer. By analyzing data for networks and pathways, we prioritized differentially expressed genes with respect to those common to the three TLR ligands as well as those shared by LPS and poly (I:C) but not CpG DNA. The importance of changes in gene expression was demonstrated by experiments indicating that RNA interference-mediated inhibition of two genes identified in this analysis, PLEC1 and TPST1, reduced IL-6 production by J774A.1 and RAW264.7 macrophages stimulated with LPS. Together, these findings delineate macrophage gene response patterns induced by different PAMPs and identify new genes that have not previously been implicated in innate immunity.
Although polymorphisms in TLR receptors and downstream signaling molecules affect the innate immune response, these variants account for only a portion of the ability of the host to respond to ...microorganisms. To identify novel genes that regulate the host response to systemic lipopolysaccharide (LPS), we created an F2 intercross between susceptible (FVB/NJ) and resistant (129S1/SvImJ) strains, challenged F2 progeny with LPS via intraperitoneal injection, and phenotyped 605 animals for survival and another 500 mice for serum concentrations of IL-1β and IL-6. Genome-wide scans were performed on pools of susceptible and resistant mice for survival, IL-1β, and IL-6. This approach identified a locus on the telomeric end of the q arm of chromosome 9 (0–40 Mb) that was associated with the differences in morbidity and serum concentrations of IL-1β and IL-6 following systemic LPS in FVB/NJ and 129S1/SvImJ strains of mice. Fine mapping narrowed the locus to 3.7 Mb containing 11 known genes, among which are three inflammatory caspases. We studied expression of genes within the locus by quantitative RT-PCR and showed that Casp1 and Casp12 levels are unaffected by LPS in both strains, whereas Casp4 is highly induced by LPS in FVB/NJ but not in 129S1/SvImJ mice. In conclusion, our mapping results indicate that a 3.7-Mb region on chromosome 9 contains a gene that regulates differential response to LPS in 129S1/SvImJ and FVB/NJ strains of mice. Differences in the induction of Casp4 expression by LPS in the two strains suggest that Casp4 is the most likely candidate gene in this region.
The stacking and T-shaped interactions between the natural DNA or RNA nucleobases (adenine, cytosine, guanine, thymine, uracil) and all aromatic amino acids (histidine, phenylalanine, tyrosine, ...tryptophan) were investigated using ab initio quantum mechanical calculations. We characterized the potential energy surface of nucleobase−amino acid dimers using the MP2/6-31G*(0.25) method. The stabilization energies in dimers with the strongest interactions were further examined at the CCSD(T)/CBS level of theory. Results at the highest level of theory possible for these systems indicate that both stacking and T-shaped interactions are very close in magnitude to biologically relevant hydrogen bonds. Additionally, T-shaped interactions are as strong, if not stronger, than the corresponding stacking interactions. Our systematic consideration of the interaction energies in 485 possible combinations of monomers shows that a variety of these contacts are essential when considering the role of aromatic amino acids in the binding of proteins to DNA or RNA. This work also illustrates how our calculated binding strengths can be used by biochemists to estimate the magnitude of these noncovalent interactions in a variety of DNA/RNA−protein active sites.
The strongest gas-phase MP2/6-31G*(0.25) stacking energies between the aromatic amino acids and the natural or methylated nucleobases were considered. The potential energy surfaces of dimers were ...searched as a function of the vertical separation, angle of rotation and horizontal displacement between monomers stacked according to their centers of mass. Our calculations reveal that the stacking interactions of adducts for a given nucleobase are dependent on the methylation site (by up to 20 kJ mol(-1)), where the relative magnitudes of the interactions are determined by the dipole moments of the adducts and the proton affinities of nucleobase methylation sites. Nevertheless, the differences in the (gas-phase) stacking of methylated adducts are small compared with the differences between the stacking of the corresponding natural and methylated nucleobases. Indeed, methylation increases the stacking energy by up to 40 kJ mol(-1) (or 135%). Although immersing the dimers in different solvents decreases the gas-phase stacking energies with an increase in the polarity of the environment, base methylation still has a significant effect on the nucleobase stacking ability in solvents with large dipole moments, and, perhaps more importantly, environments that mimic enzyme active sites. Our results shed light on the workings of DNA repairs enzymes that selectively remove a wide variety of alkylated nucleobases over the natural bases.
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