Adar1 deletion causes degeneration of the exocrine pancreas via Mavs-dependent interferon signaling.

Adenosine deaminase acting on RNA 1 (ADAR1) is an RNA-binding protein that deaminates adenosine (A) to inosine (I). A-to-I editing alters post-transcriptional RNA processing, making ADAR1 a crucial regulator of gene expression. Consequently, Adar1 has been implicated in organogenesis. To determine the role of Adar1 in pancreatic development and homeostasis, we conditionally deleted Adar1 from the murine pancreas (Ptf1aCre/+; Adar1Fl/Fl). The resulting mice had stunted growth, likely due to malabsorption associated with exocrine pancreatic insufficiency. Analyses of pancreata revealed ductal cell expansion, heightened interferon-stimulated gene expression and an increased influx of immune cells. Concurrent deletion of Adar1 and Mavs, a signaling protein implicated in the innate immune pathway, rescued the degenerative phenotype and resulted in normal pancreatic development. Taken together, our work suggests that the primary function of Adar1 in the pancreas is to prevent aberrant activation of the Mavs-mediated innate immune pathway, thereby maintaining pancreatic homeostasis.

Pancreatic epithelial IL-17/IL-17RA signaling drives B7-H4 expression to promote tumorigenesis.

IL-17 is required for the initiation and progression of pancreatic cancer, particularly in the context of inflammation, as previously shown by genetic and pharmacological approaches. The cellular compartment and downstream molecular mediators of IL-17-mediated pancreatic tumorigenesis have not been fully identified. We interrogated the cellular compartment required by generating transgenic animals with Interleukin 17 receptor A (IL-17RA) genetically deleted from the pancreatic epithelial compartment vs. the hematopoietic compartment via generation of IL-17RA-deficient (IL17-RA-/-) bone marrow chimeras, in the context of embryonically activated or inducible Kras. Deletion of IL-17RA from the pancreatic epithelial compartment, but not from hematopoietic, resulted in delayed premalignant lesions initiation and progression and increased CD8+ cytotoxic T cells infiltration to the tumor microenvironment. Absence of IL-17RA in the pancreatic compartment affected transcriptional profiles of epithelial cells, modulating stemness and immunological pathways. Interestingly, B7-H4, a known inhibitor of T cell activation encoded by the gene Vtcn1, was the most upregulated checkpoint molecule via IL17 early during pancreatic tumorigenesis, and its genetic deletion delayed pancreatic premalignant lesions development and reduced immunosuppression. We reveal pancreatic epithelial IL-17RA requirement for pancreatic tumorigenesis by reprogramming the immune pancreatic landscape which is partially orchestrated by regulation of B7-H4.

Gut epithelial Interleukin-17 receptor A signaling can modulate distant tumors growth through microbial regulation.

Microbes influence cancer initiation, progression and therapy responsiveness. IL-17 signaling contributes to gut barrier immunity by regulating microbes but also drives tumor growth. A knowledge gap remains regarding the influence of enteric IL-17-IL-17RA signaling and their microbial regulation on the behavior of distant tumors. We demonstrate that gut dysbiosis induced by systemic or gut epithelial deletion of IL-17RA induces growth of pancreatic and brain tumors due to excessive development of Th17, primary source of IL-17 in human and mouse pancreatic ductal adenocarcinoma, as well as B cells that circulate to distant tumors. Microbial dependent IL-17 signaling increases DUOX2 signaling in tumor cells. Inefficacy of pharmacological inhibition of IL-17RA is overcome with targeted microbial ablation that blocks the compensatory loop. These findings demonstrate the complexities of IL-17-IL-17RA signaling in different compartments and the relevance for accounting for its homeostatic host defense function during cancer therapy.

CD73-Dependent Adenosine Signaling through Adora2b Drives Immunosuppression in Ductal Pancreatic Cancer.

The microenvironment that surrounds pancreatic ductal adenocarcinoma (PDAC) is profoundly desmoplastic and immunosuppressive. Understanding triggers of immunosuppression during the process of pancreatic tumorigenesis would aid in establishing targets for effective prevention and therapy. Here, we interrogated differential molecular mechanisms dependent on cell of origin and subtype that promote immunosuppression during PDAC initiation and in established tumors. Transcriptomic analysis of cell-of-origin-dependent epithelial gene signatures revealed that Nt5e/CD73, a cell-surface enzyme required for extracellular adenosine generation, is one of the top 10% of genes overexpressed in murine tumors arising from the ductal pancreatic epithelium as opposed to those rising from acinar cells. These findings were confirmed by IHC and high-performance liquid chromatography. Analysis in human PDAC subtypes indicated that high Nt5e in murine ductal PDAC models overlaps with high NT5E in human PDAC squamous and basal subtypes, considered to have the highest immunosuppression and worst prognosis. Multiplex immunofluorescent analysis showed that activated CD8+ T cells in the PDAC tumor microenvironment express high levels of CD73, indicating an opportunity for immunotherapeutic targeting. Delivery of CD73 small-molecule inhibitors through various delivery routes reduced tumor development and growth in genetically engineered and syngeneic mouse models. In addition, the adenosine receptor Adora2b was a determinant of adenosine-mediated immunosuppression in PDAC. These findings highlight a molecular trigger of the immunosuppressive PDAC microenvironment elevated in the ductal cell of origin, linking biology with subtype classification, critical components for PDAC immunoprevention and personalized approaches for immunotherapeutic intervention. SIGNIFICANCE: Ductal-derived pancreatic tumors have elevated epithelial and CD8+GZM+ T-cell CD73 expression that confers sensitivity to small-molecule inhibition of CD73 or Adora2b to promote CD8+ T-cell-mediated tumor regression. See related commentary by DelGiorno, p. 977.