The E3 ubiquitin ligase RNF115 regulates phagosome maturation and host response to bacterial infection

Abstract

Phagocytosis as a key process in innate immunity and homeostasis. After uptake, newly formed phagosomes mature by acquisition of endo-lysosomal enzymes. Macrophage activation by interferon-gamma (IFN-γ) increases microbicidal activity, but delays phagosomal maturation by an unknown mechanism. Using quantitative proteomics, we show that phagosomal proteins harbour high levels of typical and atypical ubiquitin chain types. Moreover, phagosomal ubiquitylation of vesicle trafficking proteins is substantially enhanced upon IFN-γ activation of macrophages, suggesting a role in regulating phagosomal functions. Furthermore, we identified the E3 ubiquitin ligase RNF115, which is enriched on phagosomes of IFN-γ activated macrophages, as an important regulator of phagosomal maturation. Loss of RNF115 protein or ligase activity enhanced phagosomal maturation and increased cytokine responses to Staphylococcus aureus, suggesting that both innate immune signalling from the phagosome and phagolysosomal trafficking are controlled through ubiquitylation. RNF115 knock-out mice show less tissue damage in response to S. aureus infection, indicating a role of RNF115 in inflammatory responses in vivo. In conclusion, RNF115 and phagosomal ubiquitylation are important regulators of innate immune functions during bacterial infections.

RNF115 Inhibits the Post‐ER Trafficking of TLRs and TLRs‐Mediated Immune Responses by Catalyzing K11‐Linked Ubiquitination of RAB1A and RAB13

“…In this context, a recent study has shown that ablation of RNF115 has no effect on the phagocytic uptake of particles in macrophages. [ 62 ] Besides mediating endocytotic trafficking of vesicles, RAB7 has been shown to regulate mitochondria‐lysosome contacts. [ 63 ] Interestingly, our study showed that both RNF115 and RNF115 2SA interacted with RAB7A and RNF115 was found in the mitochondria fractions.…”

Multifaceted Roles of the E3 Ubiquitin Ligase RING Finger Protein 115 in Immunity and Diseases

“…In an unbiased identification of proteins on IFNγ-induced phagosomes, Bilkei-Gorzo et al. have found that RNF115 and K63/48/11-linked polyubiquitin chains are significantly enriched on the phagosomes ( 58 ) ( Figure 2 ). They further show that knockout of RNF115 promotes phagosome maturation and acidification in primary mouse macrophages under homeostatic conditions.…”

“…They further show that knockout of RNF115 promotes phagosome maturation and acidification in primary mouse macrophages under homeostatic conditions. Interestingly, quantitative proteomics data suggest that the ER and the peroxisome proteins are reduced in the phagosomes from RNF115 deficient macrophages compared to the wild-type macrophages, and such a reduction is fully rescued by reconstitution of RNF115 but not RNF115 C228/231A into RNF115 KO macrophages ( 58 ). These data suggest an inhibitory role of RNF115 in phagosome maturation in primary mouse macrophages dependently on its E3 ligase activity, though the substrates of RNF115 remain to be characterized.…”

“…Consistently, knockout of RNF115 promotes the trafficking of TLRs from ER to Golgi apparatus and to lysosomes and cell membrane. Therefore, the RNF115 knockout mice are more resistant to bacterial infections and sensitive to imiquimod-induced autoimmunity ( 35 , 58 ). In contrast, knockout of RNF115 does not affect the endocytosis of carboxylated particles or TLRs after ligands stimulation ( 35 , 58 ).…”

“…Therefore, the RNF115 knockout mice are more resistant to bacterial infections and sensitive to imiquimod-induced autoimmunity ( 35 , 58 ). In contrast, knockout of RNF115 does not affect the endocytosis of carboxylated particles or TLRs after ligands stimulation ( 35 , 58 ). It should be noted that TNF- or IL-1β-induced secretion of CXCL1 or IL-6 is not affected by knockout of RNF115 and that the expression of MHC-I and the integrins CD11b or CD11c on cell surface through post-ER trafficking is comparable between wild-type and RNF115 deficient BMDCs ( 35 ), indicating that not all the trafficking of subcellular compartments such as the secretory pathway is regulated by RNF115.…”