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The mechanisms underlying the regulation of a checkpoint receptor, PD-1, in tumor-infiltrating immune cells during the development of colorectal cancer are not fully understood. Here we demonstrate that COX-2–derived PGE2, an inflammatory mediator and tumor promoter, induces PD-1 expression by enhancing NFκB's binding to the PD-1 promoter via an EP4–PI3K–Akt signaling pathway in both CD8+ T cells and macrophages. Moreover, PGE2 suppresses CD8+ T-cell proliferation and cytotoxicity against tumor cells and impairs macrophage phagocytosis of cancer cells via an EP4–PI3K–Akt–NFκB–PD-1 signaling pathway. In contrast, inhibiting the COX-2–PGE2–EP4 pathway increases intestinal CD8+ T-cell activation and proliferation and enhances intestinal macrophage phagocytosis of carcinoma cells accompanied by reduction of PD-1 expression in intestinal CD8+ T cells and macrophages in ApcMin/+ mice. PD-1 expression correlates well with COX-2 levels in human colorectal cancer specimens. Both elevated PD-1 and COX-2 are associated with poorer overall survival in patients with colorectal cancer. Our results uncover a novel role of PGE2 in tumor immune evasion. They may provide the rationale for developing new therapeutic approaches to subvert this process by targeting immune checkpoint pathways using EP4 antagonists. In addition, our findings reveal a novel mechanism explaining how NSAIDs reduce colorectal cancer risk by suppressing tumor immune evasion. Prevention Relevance: These findings provide a potential explanation underlying the chemopreventive effect of NSAIDs on reducing colorectal cancer incidence during premalignancy and provide a rationale for developing EP4 antagonists for colorectal cancer prevention and treatment. Simply targeting PGE2 signaling alone may be efficacious in colorectal cancer prevention and treatment, avoiding side effects associated with NSAIDs.

BACKGROUND & AIMS: Prostaglandin E(2) (PGE(2)) promotes colorectal tumor formation and progression by unknown mechanisms. We sought to identify microRNAs (miRNAs) might mediate the effects of PGE(2) on colorectal cancer (CRC) development. METHODS: We incubated LS174T colorectal cancer cells with PGE(2) or without (control) and used miRNA-seq technology to compare expression patterns of miRNAs. We knocked down levels of specific miRNAs or proteins in cells using small interfering RNAs or genome editing. Cells were analyzed by immunoblot, quantitative PCR, chromosome immunoprecipitation, cell invasion, and luciferase reporter assays; we measured gene expression, binding activity, cell migration and invasion, and transcriptional activity of transcription factors. NSG mice were given injections of LS174T cells and growth of primary tumors and numbers of liver and lung metastases were quantified and analyzed by histology. We used public databases to identify correlations in gene expression pattern with patient outcomes. RESULTS: We identified miRNA 675-5p (MIR675-5p) as the miRNA most highly upregulated by incubation of colorectal cancer cells with PGE(2). PGE(2) increased expression of MIR675-5p by activating expression of Myc, via activation of AKT, NF-κB, and β-catenin. β-catenin PGE(2) increased the invasive activities of cultured CRC cells. LS174T cells incubated with PGE2 formed more liver and lung metastases in mice than control LS174T cells. We identified a 3’UTR in the TP53 mRNA that bound MIR675-5p; binding resulted in loss of the p53 protein. Expression of MIR675-5p or its precursor RNA, H19, correlated with expression of cyclooxygenase-1 and cyclooxygenase-2 and shorter survival times of patients with CRC. CONCLUSIONS: We found incubation of CRC cells with PGE(2) to increase their invasive activity and ability to form liver and lung metastases in mice. PGE(2) downregulates expression of p53 by increasing expression of MIR675-5p, which binds to and prevents translation of TP53 mRNA. These findings provide insight into the mechanisms by which PGE(2) promotes tumor development and progression. Strategies to target the PGE(2) might be developed for treatment of CRC. BACKGROUND AND CONTEXT: Prostaglandin E(2) (PGE(2)) promotes colorectal tumor formation and progression by unknown mechanisms. NEW FINDINGS: We found incubation of CRC cells with PGE2 to increase their invasive activity and ability to form liver and lung metastases in mice. PGE(2) downregulates expression of p53 by increasing expression of MIR675-5p, which binds to TP53 mRNA and prevents its translation. LIMITATIONS: These studies were performed in cell lines and mice. Studies in humans are needed. IMPACT: These findings provide insight into the mechanisms by which PGE(2) promotes tumor development and progression. Strategies to target the PGE(2) might be developed for treatment of CRC.

Chromatin remodeling plays a critical role in tumor suppression as demonstrated by 20% of human cancers bearing inactivating mutations in SWI/SNF chromatin remodeling complex members. Mutations in different SWI/SNF subunits drive a variety of adult and pediatric tumor types, including non-small cell lung cancers, rhabdoid tumors, medulloblastomas, and ovarian cancers. Small cell carcinoma of the ovary hypercalcemic type (SCCOHT) is an aggressive subtype of ovarian cancer occurring in young women. Nearly all (>98%) SCCOHTs have inactivating mutations inSMARCA4, which encodes 1 of 2 mutually exclusive catalytic subunits of the SWI/SNF complex. Less than half of SCCOHT patients survive 5 years despite aggressive surgery and multimodal chemotherapy. Empirical support for effective SCCOHT treatments is scarce, in part because of the poor understanding of SCCOHT tumorigenesis. To gain insight into the functional consequences of SWI/SNF subunit loss, we defined SWI/SNF composition and its protein-protein interactions (PPIs) by immunoprecipitation and mass spectrometry (IP-MS) of SWI/SNF subunits in 3 SCCOHT cell lines. Comparing these results to a cell line containing a wild-type SWI/SNF complex, the interaction of most canonical core SWI/SNF subunits was observed in all SCCOHT cell lines at a lower abundance. The SCCOHT SWI/SNF also lacked ATPase module subunits and showed a drastic reduction in PBAF-specific subunit interactions. The wild-type and SCCOHT SWI/SNF subunits immunoprecipitated a shared set of 26 proteins, including core SWI/SNF subunits and RNA processing proteins. We observed 131 proteins exclusively interacting with the wild-type SWI/SNF complex including isoform-specific SWI/SNF subunits, members of the NuRD complex, and members of the MLL3/4 complex. We observed 60 PPIs exclusive to the SCCOHT residual SWI/SNF shared in at least 2 of the 3 SCCOHT cell lines, including many proteins involved in RNA processing. Differential interactions with the residual SWI/SNF complex in SCCOHT may further elucidate altered functional consequences of SMARCA4 mutations in these tumors as well as identify synthetic lethal targets that translate to other SWI/SNF-deficient tumors.