No abstract

Background: Tfh cells regulate B cell-mediated humoral immunity. Results: STAT5 regulated Blimp-1 expression, and STAT5 deficiency in CD4 ϩ T cells resulted in an increase of Tfh generation

RNA silencing functions as an important antiviral defense mechanism in a broad range of eukaryotes. In plants, biogenesis of several classes of endogenous small interfering RNAs (siRNAs) requires RNA-dependent RNA Polymerase (RDR) activities. Members of the RDR family proteins, including RDR1and RDR6, have also been implicated in antiviral defense, although a direct role for RDRs in viral siRNA biogenesis has yet to be demonstrated. Using a crucifer-infecting strain of Tobacco Mosaic Virus (TMV-Cg) and Arabidopsis thaliana as a model system, we analyzed the viral small RNA profile in wild-type plants as well as rdr mutants by applying small RNA deep sequencing technology. Over 100,000 TMV-Cg-specific small RNA reads, mostly of 21- (78.4%) and 22-nucleotide (12.9%) in size and originating predominately (79.9%) from the genomic sense RNA strand, were captured at an early infection stage, yielding the first high-resolution small RNA map for a plant virus. The TMV-Cg genome harbored multiple, highly reproducible small RNA-generating hot spots that corresponded to regions with no apparent local hairpin-forming capacity. Significantly, both the rdr1 and rdr6 mutants exhibited globally reduced levels of viral small RNA production as well as reduced strand bias in viral small RNA population, revealing an important role for these host RDRs in viral siRNA biogenesis. In addition, an informatics analysis showed that a large set of host genes could be potentially targeted by TMV-Cg-derived siRNAs for posttranscriptional silencing. Two of such predicted host targets, which encode a cleavage and polyadenylation specificity factor (CPSF30) and an unknown protein similar to translocon-associated protein alpha (TRAP α), respectively, yielded a positive result in cleavage validation by 5′RACE assays. Our data raised the interesting possibility for viral siRNA-mediated virus-host interactions that may contribute to viral pathogenicity and host specificity.

Nucleotide-binding domain, leucine-rich repeat containing proteins (NLRs) belong to a large family of cytoplasmic sensors which regulate an extraordinarily diverse range of biological functions. NLRs contribute to immunity against infectious diseases, however, dysregulation of their functional activity leads to the development of inflammatory diseases and autoimmunity 1. Cytoplasmic innate immune sensors, including NLRs, are central regulators of intestinal homeostasis 2–8. NLRC3 (also known as CLR16.2 or NOD3) is a poorly characterized member of the NLR family and was identified in a genomic screen of genes encoding proteins bearing leucine-rich repeats (LRRs) and nucleotide-binding domains 9,10. Expression of the gene encoding NLRC3 is drastically reduced in tumour tissues of patients with colorectal cancer compared with healthy tissues 11, highlighting an undefined potential function for this sensor in the development of cancer. Here, we found that mice lacking NLRC3 were hypersusceptible to colitis and colorectal tumorigenesis. The effect of NLRC3 was most dominant in enterocytes, where NLRC3 suppressed activation of the mTOR signalling pathways and inhibited cellular proliferation and stem-cell-derived organoid formation. NLRC3 associated with phosphoinositide 3-kinases (PI3Ks) and blocked activation of the PI3K–dependent kinase AKT following engagement of growth factor receptors or TLR4. These findings unveiled a key role for NLRC3 as an inhibitor of the mTOR pathways mediating protection against colorectal cancer.