The AhR regulates IFN-induced immune checkpoints in lung cancer cells through HNRNPH1, an RNA-binding protein, and INCR1, a novel long non-coding RNA.

Although immune checkpoint inhibitors show great promise, not all patients respond, and many do not achieve durable responses. Consequently, further investigations into potentially targetable molecules that regulate immune checkpoints are warranted. Previous studies in several cancers demonstrated that interferons produced by tumor-infiltrating leukocytes regulate immunosuppressive PD-L1, PD-L2, and IDO1 through JAK/STAT signaling. Here, we investigated a novel role for an immunosuppressive environmental chemical receptor, previously implicated in smoking-related cancers, in IFN signaling in human lung adenocarcinoma (LUAD) cells. Deletion of the aryl hydrocarbon receptor (AhR) from A549 LUAD cells significantly decreased baseline JAK2, STAT1, STAT3, IRF1 (a JAK/STAT target), PD-L1, PD-L2, and IDO1 expression. IFNγ and IFNα increased the expression of JAK/STAT and immune checkpoint genes and proteins, but these increases were significantly diminished or absent in AhR-knockout cells. The AhR similarly controls IFN-induced, JAK/STAT-driven increases in multiple MHC class I- and class II-related genes. AhR control of type I and type II interferon signaling is mediated through up-regulation of an lncRNA, the IFN-stimulated non-coding RNA 1 (INCR1), and through repression of an RNA-binding protein, heterogeneous nuclear ribonucleoprotein H1 (HNRNPH1), which sequesters JAK/STAT-related and immune checkpoint gene transcripts. The data suggest that the AhR is a key mediator of tumor immunosuppression through regulation of IFN-induced INCR1 and JAK/STAT signaling and, thereby, expression of immune checkpoints. However, that immunosuppression may be tempered by AhR control of MHC expression. Given the multiple roles of JAK/STAT signaling in the immune system, the results also suggest multiple levels at which the AhR may affect tumor immunity.