β-Arrestin 1's Interaction with TC45 Attenuates Stat signaling by dephosphorylating Stat to inhibit antimicrobial peptide expression

Cannabinoid receptor type 1 (CB1R) inhibits hypothalamic leptin signaling via β-arrestin1 in complex with TC-PTP and STAT3

Molecular interactions between anorexigenic leptin and orexigenic endocannabinoids, although of great metabolic significance, are not well understood. We report here that hypothalamic STAT3 signaling in mice, initiated by physiological elevations of leptin, is diminished by agonists of the cannabinoid receptor 1 (CB1R). Measurement of STAT3 activation by semi-automated confocal microscopy in cultured neurons revealed that this CB1R-mediated inhibition requires both T cell protein tyrosine phosphatase (TC-PTP) and β-arrestin1 but is independent of changes in cAMP. Moreover, β-arrestin1 translocates to the nucleus upon CB1R activation and binds both STAT3 and TC-PTP. Consistently, CB1R activation failed to suppress leptin signaling in β-arrestin1 knockout mice in vivo, and in neural cells deficient in CB1R, β-arrestin1 or TC-PTP. Altogether, CB1R activation engages β-arrestin1 to coordinate the TC-PTP-mediated inhibition of the leptin-evoked neuronal STAT3 response. This mechanism may restrict the anorexigenic effects of leptin when hypothalamic endocannabinoid levels rise, as during fasting or in diet-induced obesity.

APLNR regulates IFN-γ signaling via β-arrestin 1 mediated JAK-STAT1 pathway in melanoma cells

The apelin receptor (APLNR) regulates many biological processes including metabolism, angiogenesis, circulating blood volume and cardiovascular function. Additionally, APLNR is overexpressed in various types of cancer and influences cancer progression. APLNR is reported to regulate tumor recognition during immune surveillance by modulating the IFN-γ response. However, the mechanism of APLNR crosstalk with intratumoral IFN-γ signaling remains unknown. Here, we show that activation of APLNR upregulates IFN-γ signaling in melanoma cells through APLNR mediated β-arrestin 1 but not β-arrestin 2 recruitment. Our data suggests that β-arrestin 1 directly interacts with STAT1 to inhibit STAT1 phosphorylation to attenuate IFN-γ signaling. The APLNR mutant receptor, I109A, which is deficient in β-arrestins recruitment, is unable to enhance intratumoral IFN-γ signaling. While APLNR N112G, a constitutively active mutant receptor, increases intratumoral sensitivity to IFN-γ signaling by enhancing STAT1 phosphorylation upon IFN-γ exposure. We also demonstrate in a co-culture system that APLNR regulates tumor survival rate. Taken together, our findings reveal that APLNR modulates IFN-γ signaling in melanoma cells and suggests that APLNR may be a potential target to enhance the efficacy of immunotherapy.

Long non-coding RNAs in gastrointestinal cancers: implications for protein phosphorylation

Phosphorylation of proteins is one of the most extensively investigated post-translational protein modifications. Threonine, serine and tyrosine in proteins are the most commonly phosphorylated amino acids. Dysregulated cancer-related signaling pathways due to aberrant phosphorylation status of the key protein(s) in these pathways exist in most malignancies. Intensive studies in the recent decade have implicated long non-coding RNAs (lncRNAs) in the precise regulation of protein phosphorylation in cancers. In this review, we systematically delve into recent advance that underlines the multidimensional role of lncRNAs in modulating protein phosphorylation, regulating cancerous signaling and impacting prognosis of gastrointestinal (GI) cancers including hepatocellular carcinoma, colorectal cancer, gastric cancer, esophageal cancer, and pancreatic cancer. LncRNAs regulate protein phosphorylation via directly binding to the target protein(s), interacting with the partner protein(s) of the target protein(s) or lncRNAs-encoded small peptides. Although there are still extensive studies on disclosing the intricate interactions between lncRNAs and proteins and their impacts on protein phosphorylation, we believe that targeting lncRNAs controlling phosphorylation of key protein(s) in cancerous signaling pathways might provide novel paths for precision therapeutics of GI cancers in the future.

Nitric Oxide Synthase Regulates Gut Microbiota Homeostasis by ERK-NF-κB Pathway in Shrimp

The gut microbiota is a complex group of microorganisms that is not only closely related to intestinal immunity but also affects the whole immune system of the body. Antimicrobial peptides and reactive oxygen species participate in the regulation of gut microbiota homeostasis in invertebrates. However, it is unclear whether nitric oxide, as a key mediator of immunity that plays important roles in antipathogen activity and immune regulation, participates in the regulation of gut microbiota homeostasis. In this study, we identified a nitric oxide synthase responsible for NO production in the shrimp Marsupenaeus japonicus. The expression of Nos and the NO concentration in the gastrointestinal tract were increased significantly in shrimp orally infected with Vibrio anguillarum. After RNA interference of Nos or treatment with an inhibitor of NOS, L-NMMA, NO production decreased and the gut bacterial load increased significantly in shrimp. Treatment with the NO donor, sodium nitroprusside, increased the NO level and reduced the bacterial load significantly in the shrimp gastrointestinal tract. Mechanistically, V. anguillarum infection increased NO level via upregulation of NOS and induced phosphorylation of ERK. The activated ERK phosphorylated the NF-κB-like transcription factor, dorsal, and caused nuclear translocation of dorsal to increase expression of antimicrobial peptides (AMPs) responsible for bacterial clearance. In summary, as a signaling molecule, NOS-produced NO regulates intestinal microbiota homeostasis by promoting AMP expression against infected pathogens via the ERK-dorsal pathway in shrimp.

Delving Into the Origin of Destructive Inflammation in COVID-19: A Betrayal of Natural Host Defense Peptides?

In contrast to other pathogenic agents that directly destroy host cells and tissues, the lethal power of SARS-CoV-2 resides in the over-reactive immune response triggered by this virus. Based on numerous evidences indicating that the lipid composition of host membranes is dramatically affected by COVID-19, and in the fact that our endogenous antimicrobial peptides (AMPs) are sensitive to the membrane composition of pathogenic agents, we propose that such destructive immune response is due to the direct action of AMPs. In a scenario where most host cell membranes are dressed by a pathogenic lipid composition, AMPs can indiscriminately attack them. This is why we use the "AMP betrayal" term to describe this mechanism. Previously proposed cytokine/bradykinin storm mechanisms are not incompatible with this new proposal. Interestingly, the harmful action of AMPs could be prevented by new therapies aimed to reestablish the lipid composition or to inhibit the action of specific peptides.

A novel effector caspase (Caspase-3/7-1) involved in the regulation of immune homeostasis in Chinese mitten crab Eriocheir sinensis

Caspases are a conserved family of cysteine proteases characterized by specificity for aspartic acid and play an essential role in cell apoptosis. In the present study, a novel effector caspase (designated as EsCaspase-3/7-1) was identified from Chinese mitten crab Eriocheir sinensis. The open reading frame of EsCaspase-3/7-1 cDNA was of 972 bp, encoding a polypeptide of 323 amino acids. EsCaspase-3/7-1 contained an N-terminal prodomain and a conservative C-terminal CASc domain, with the conserved active site "QACRG". The mRNA transcripts of EsCaspase-3/7-1 were constitutively expressed in all the examined tissues with high expression level in hemocytes, hepatopancreas and gill. The EsCaspase-3/7-1 protein was mainly distributed in the cytoplasm of hemocytes. After Aeromonas hydrophila and lipopolysaccharide (LPS) stimulations, the mRNA expression level of EsCaspase-3/7-1 in hemocytes increased significantly. The mRNA expression level of EsCaspase-3/7-1 in hemocytes was significantly up-regulated after H₂O₂ treatment in vitro. The recombinant EsCaspase-3/7-1 protein (rEsCaspase-3/7-1) was capable of hydrolyzing the substrate Ac-DEVD-pNA rather than Ac-YVAD-pNA and Ac-VEID-pNA in vitro, and exhibited binding activity to LPS. These results demonstrated that EsCaspase-3/7-1 might act as an LPS receptor, and play an important role in the regulation of immune homeostasis of E. sinensis.

Myeloid leukemia factor functions in anti-WSSV immune reaction of kuruma shrimp, Marsupenaeus japonicus

Myeloid leukemia factor (MLF) plays an important role in development, cell cycle, myeloid differentiation, and regulates the RUNX transcription factors. However, the function of MLF in immunity is still unclear. In this study, an MLF was identified and characterized in kuruma shrimp Marsupenaeus japonicus, and named as MjMLF. The full-length cDNA of MjMLF contained 1111 nucleotides, which had an opening reading frame of 816 bp encoding a protein of 272 amino acids with an MLF1-interacting protein domain. MjMLF could be ubiquitously detected in different tissues of shrimp at the transcriptional level. The expression pattern analysis showed that MjMLF could be upregulated in shrimp hemocytes and hepatopancreas after white spot syndrome virus challenge. The RNA interference and protein injection assay showed that MjMLF could inhibit WSSV replication in vivo. Flow cytometry assay showed that MjMLF could induce hemocytes apoptosis which functioned in the shrimp antiviral reaction. All the results suggested that MjMLF played an important role in the antiviral immune reaction of kuruma shrimp. The research indicated that MjMLF might function as a novel regulator to inhibit WSSV replication in shrimp.