Universität zu Köln

Kew, Chun (2019). Control of Innate Immunity by RNA Metabolism. PhD thesis, Universität zu Köln.

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Abstract

Innate immunity is key to defense against infections. Its high complexity and interactions with other systems make it relatively difficult to study in mammals. The nematode C. elegans is particularly useful for studying innate immunity due to its conserved biology and genetic manipulability. However, our knowledge of C. elegans immunity is still limited, especially on what is the upstream stimulus that controls innate immune responses in the worms. In this study, we used C. elegans as the model to investigate how immune responses are triggered. First, we found that the nucleolar protein fibrillarin, a rRNA 2'-O-methyltransferase indispensable for rRNA maturation, plays an important role. Fibrillarin reduction is able to confer resistance in wild-type animals and also infection sensitive mutants. Upon infection, it was observed that fibrillarin levels decrease. Since fibrillarin is a major nucleolar protein, nucleolar size was also examined. Infection leads to a shrinkage of nucleoli, suggesting reduction of fibrillarin and nucleolar size is a beneficial host response promoting resistance. Fibrillarin reduction inhibits rRNA maturation, and therefore leads to reduced levels of mature rRNA and reduced translation. Using ifg-1 and ife-1 loss of function mutants, we found that reduction of translation is sufficient to prolong survival upon infection. Further, knocking down fibrillarin does not significantly enhance the ifg-1 mutant survival, suggesting they may function in overlapping pathways, probably translation. Similar to the observations in worms, infection also reduces fibrillarin protein levels in human epithelial cells and also murine macrophages. Reduction of fibrillarin is also able to promote survival in mammalian cells after infection. Interestingly, fibrillarin RNAi suppresses pro-inflammatory cytokine secretion but promotes production of anti-inflammatory cytokines and clearance of intracellular bacteria. These data suggest that reduction of fibrillarin is an evolutionarily conserved host response to initiate protective mechanisms. Second, we identified that the essential splicing factor rnp-6 also controls innate immunity. Infection alters splicing of the ret-1 splicing reporter and tos-1 transcript, suggesting an interesting connection between splicing and infection. It was found that a novel gain of function mutation of rnp-6 results in immunodeficiency in C. elegans. Both resistance and induction of anti-microbial genes are compromised in the mutant. Activity of RNP-6 negatively correlates with resistance. Overexpression of RNP-6 compromises survival upon infection while reducing its expression by RNAi is sufficient to activate immune responses and drive resistance. Further investigations revealed that the effect is mediated by pmk-1, the worm’s homolog of p38 MAPK. RNAi mediated reduction of RNP-6 activates PMK-1. On the other hand, gain of function of rnp-6 suppresses P. aeruginosa induced PMK-1 activation. Intriguingly, the mutation of rnp-6 is able to suppress the splicing remodeling induced by infection. Further, RNAi against other splicing factors also induces infection resistance and activation of PMK-1, indicating that the splicing machinery may be a general control factor for innate immune responses, and perturbing splicing is an inducer of immunity. The data present in this study highlight the critical roles of rRNA biogenesis and mRNA splicing in innate immunity. We suggest that reduction of fibrillarin and perturbation of splicing are two of the upstream stimuli for innate immunity in C. elegans. A tight connection exists between initiation of immune responses and RNA metabolism, which is previously underappreciated.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Kew, Chun chun.kew@age.mpg.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-93738
Date:	25 February 2019
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Außeruniversitäre Forschungseinrichtungen > MPI for Biology of Ageing
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language Innate Immunity English Caenorhabditis elegans English RNA metabolism English
Date of oral exam:	5 September 2018
Referee:	Name Academic Title Antebi, Adam Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/9373