Aims: We aimed to measure the abundance of Fusobacterium nucleatum (F. nucleatum) in colorectal cancer (CRC) tissues from patients and to uncover the function of this bacterium in colorectal tumor metastasis.Methods: We collected metastatic and non-metastatic CRC tissues to analyze F. nucleatum abundance. Cells were incubated with F. nucleatum or chloroquine (CQ) or were transfected with CARD3-targeting siRNA; the expression of mRNAs and proteins was then measured. CRC cells stably transfected with shRNA-luc were mixed with F. nucleatum and intravenously injected into BALB/cJ mice. APCMin/+, CARD3-/-and CARD3wt C57BL mice were given F. nucleatum; some mice were given azoxymethane (AOM) and dextran sodium sulfate (DSS).Results: F. nucleatum was abundant in CRC tissues from patients with metastasis. F. nucleatum infection increased CRC cell motility and upregulated the expression of CARD3, LC3-II, Beclin1 and Vimentin, and downregulated the expression of E-cadherin and P62 in CRC cells. These effects were attenuated by treatment with CQ, siCARD3 or both. APCMin/+ mice gavaged with F. nucleatum developed more aggressive tumors than control mice. After AOM/DSS administration, the colorectums of CARD3-/- mice had fewer tumors than those of control mice. Tumors from CARD3-/- mice had lower levels of LC3-II and Beclin1 and higher levels of P62 than those from control mice. BALB/cJ mice injected with both CT26-luc cells and F. nucleatum formed more metastases than control mice. CQ treatment, CARD3 knockdown or both reduced the ability of CT26-luc cells to form metastases in vivo.Conclusions: F. nucleatum is enriched in CRC tissues from patients with metastasis. F. nucleatum orchestrates CARD3 and autophagy to control CRC metastasis. Measuring and targeting F. nucleatum and its associated pathways will yield approaches for the prevention and treatment of CRC metastasis.

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Accumulating evidence links Fusobacterium nucleatum with ulcerative colitis (UC). The mechanism by which F. nucleatum promotes intestinal inflammation in UC remains poorly defined. Here, we first examined the abundance and impact of F. nucleatum on disease activity in UC tissues. Next, we isolated a strain of F. nucleatum from UC tissues and explored whether F. nucleatum aggravates the intestinal inflammatory response in vitro and in vivo. We also examined whether F. nucleatum infection involves the NF-B or IL-17F signaling pathways. Our data showed that F. nucleatum was enriched in 51.78% of UC tissues and was correlated with the clinical course, clinical activity and refractory behavior of UC (p < 0.05). Furthermore, we demonstrated that F. nucleatum promoted intestinal epithelial damage and the expression of the inflammatory cytokines IL-1, Il-6, IL-17F and TNF-. Mechanistically, F. nucleatum targeted caspase activation and recruitment domain 3 (CARD3) through NOD2 to activate the IL-17F/NF-B pathway in vivo and in vitro. Thus, F. nucleatum orchestrates a molecular network involving CARD3 and IL-17F to control the UC process. Measuring and targeting F. nucleatum and its associated pathways will yield valuable insight into the prevention and treatment of UC.

VISA (also known as MAVS, IPS-1 and Cardif) is an essential adaptor protein in innate immune response to RNA virus. The protein level of VISA is delicately regulated before and after viral infection to ensure the optimal activation and timely termination of innate antiviral response. It has been reported that several E3 ubiquitin ligases can mediate the degradation of VISA, but how the stability of VISA is maintained before and after viral infection remains enigmatic. In this study, we found that the ER-associated inactive rhomboid protein 2 (iRhom2) plays an essential role in mounting an efficient innate immune response to RNA virus by maintaining the stability of VISA through distinct mechanisms. In un-infected and early infected cells, iRhom2 mediates auto-ubiquitination and degradation of the E3 ubiquitin ligase RNF5 and impairs the assembly of VISA-RNF5-GP78 complexes, thereby antagonizes ER-associated degradation (ERAD) of VISA. In the late phase of viral infection, iRhom2 mediates proteasome-dependent degradation of the E3 ubiquitin ligase MARCH5 and impairs mitochondria-associated degradation (MAD) of VISA. Maintenance of VISA stability by iRhom2 ensures efficient innate antiviral response at the early phase of viral infection and ready for next round of response. Our findings suggest that iRhom2 acts as a checkpoint for the ERAD/MAD of VISA, which ensures proper innate immune response to RNA virus.

Recognition of viral RNA by the retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), including RIG-I and MDA5, initiates innate antiviral responses. Although regulation of RLR-mediated signal transduction has been extensively investigated, how the recognition of viral RNA by RLRs is regulated remains enigmatic. In this study, we identified heterogeneous nuclear ribonucleoprotein M (hnRNPM) as a negative regulator of RLR-mediated signaling. Overexpression of hnRNPM markedly inhibited RNA virus-triggered innate immune responses. Conversely, hnRNPM-deficiency increased viral RNA-triggered innate immune responses and inhibited replication of RNA viruses. Viral infection caused translocation of hnRNPM from the nucleus to the cytoplasm. hnRNPM interacted with RIG-I and MDA5, and impaired the binding of the RLRs to viral RNA, leading to inhibition of innate antiviral response. Our findings suggest that hnRNPM acts as an important decoy for excessive innate antiviral immune response.

The role of endogenous serotonin (5‐HT) in gastrointestinal motility is still highly controversial. Although electrochemical techniques allow for direct and real‐time recording of biomolecules, the dynamic monitoring of 5‐HT release from elastic and tubular intestine during motor reflexes remains a great challenge because of the specific peristalsis patterns and inevitable passivation of the sensing interface. A stretchable sensor with antifouling and decontamination properties was assembled from gold nanotubes, titanium dioxide nanoparticles, and carbon nanotubes. The sandwich‐like structure endowed the sensor with satisfying mechanical stability and electrochemical performance, high resistance against physical adsorption, and superior efficiency in the photodegradation of biofouling molecules. Insertion of the sensor into the lumen of rat ileum (the last section of the small intestine) successfully mimics intestinal peristalsis, and simultaneous real‐time monitoring of distension‐evoked 5‐HT release was possible for the first time. Our results unambiguously reveal that mechanical distension of the intestine induces endogenous 5‐HT overflow, and 5‐HT level is closely associated with the physiological or pathological states of the intestine.

There is increasing evidence that members of the gut microbiota, especially Fusobacterium nucleatum (F. nucleatum), are associated with Crohn's disease (CD), but the specific mechanism by which F. nucleatum promotes CD development is unclear. Here, we first examined the abundance of F. nucleatum and its effects on CD disease activity and explored whether F. nucleatum aggravated intestinal inflammation and promoted intestinal mucosal barrier damage in vitro and in vivo. Our data showed that F. nucleatum was enriched in 41.21% of CD tissues from patients and was correlated with the clinical course, clinical activity, and refractory behavior of CD (P < 0.05). In addition, we found that F. nucleatum infection is involved in activating the endoplasmic reticulum stress (ERS) pathway during CD development to promote intestinal mucosal barrier destruction. Mechanistically, F. nucleatum targeted caspase activation and recruitment domain 3 (CARD3) to activate the ERS pathway and promote F. nucleatum-mediated mucosal barrier damage in vivo and in vitro. Thus, F. nucleatum coordinates a molecular network involving CARD3 and ERS to control the CD process. Measuring and targeting F. nucleatum and its associated pathways will provide valuable insight into the prevention and treatment of CD.

There is a growing body of evidence which suggests that intestinal microbiota, especially Fusobacterium nucleatum (F. nucleatum), are associated with intestinal immune disease such as ulcerative colitis (UC). The mechanism by which F. nucleatum promotes intestinal epithelial cell (IEC) death remained undefined. Here, we investigated the potential mechanisms about how F. nucleatum aggravates IEC death in UC. We first detected the abundance of F. nucleatum in UC tissues and analyzed its relationship with the clinical characteristics of UC. Next, we explored whether F. nucleatum promotes intestinal epithelial cell death in vitro and in vivo. Furthermore, we extracted lipopolysaccharide (LPS) of the F. nucleatum and examined whether F. nucleatum exacerbates UC via LPS. Our results indicated that F. nucleatum was abundant in UC tissues and was correlated with clinical characteristics. In addition, we demonstrated that F. nucleatum and its LPS aggravated IEC death by promoted IEC autophagy. Furthermore, autophagy inhibitors, chloroquine (CQ), 3-methyladenine (3-MA) or Atg5 silencing prevented IEC death mediated by F. nucleatum, which suggests F. nucleatum may contribute to UC by activating autophagic cell death. All our results uncover a vital role of F. nucleatum in autophagic cell death and UC, giving rise to a new sight for UC therapy by inhibiting excessive IEC autophagy and autophagic cell death.