The PD-1:PD-L1 immune signaling axis mediates suppression of T cell-dependent tumor immunity. PD-1 expression was recently found to be upregulated on tumor-infiltrating murine (CD11c+CD11b+CD8-CD209a+) and human (CD1c+CD19-) myeloid dendritic cells (TIDC), an innate immune cell type also implicated in immune escape. However, there is little knowledge concerning how PD-1 regulates innate immune cells. In the present study, we examined the role of PD-1 in TIDC derived from mice bearing ovarian tumors. Similar to lymphocytes, TIDC expression of PD-was associated with expression of the adapter protein SHP-2, which signals to NF-KappaB, however, in contrast to its role in lymphocytes, we found that expression of PD-1 in TIDC tonically paralyzed NF-kB activation. Further mechanistic investigations showed that PD-1 blocked NF-kB-dependent cytokine release in a SHP-2-dependent manner. Conversely, inhibition of NF-kB-mediated antigen presentation by PD-1 occurred independently of SHP-2. Collectively, our findings revealed that PD-1 acts in a distinct manner in innate immune cells compared to adaptive immune cells, prompting further investigations of the signaling pathways controlled by this central mediator of immune escape in cancer.

KRAS-activating mutations drive human non–small cell lung cancer and initiate lung tumorigenesis in genetically engineered mouse (GEM) models. However, in a GEM model of KRASG12D-induced lung cancer, tumors arise stochastically following a latency period, suggesting that additional events are required to promote early-stage tumorigenic expansion of KRASG12D-mutated cells. PI3Kα (PIK3CA) is a direct effector of KRAS, but additional activation of PI3′-lipid signaling may be required to potentiate KRAS-driven lung tumorigenesis. Using GEM models, we tested whether PI3′-lipid signaling was limiting for the promotion of KRASG12D-driven lung tumors by inducing the expression of KRASG12D in the absence and presence of the activating PIK3CAH1047R mutation. PIK3CAH1047R expression alone failed to promote tumor formation, but dramatically enhanced tumorigenesis initiated by KRASG12D. We further observed that oncogenic cooperation between KRASG12D and PIK3CAH1047R was accompanied by PI3Kα-mediated regulation of c-MYC, GSK3β, p27KIP1, survivin, and components of the RB pathway, resulting in accelerated cell division of human or mouse lung cancer–derived cell lines. These data suggest that, although KRASG12D may activate PI3Kα by direct biochemical mechanisms, PI3′-lipid signaling remains rate-limiting for the cell-cycle progression and expansion of early-stage KRASG12D-initiated lung cells. Therefore, we provide a potential mechanistic rationale for the selection of KRAS and PIK3CA coactivating mutations in a number of human malignancies, with implications for the clinical deployment of PI3′ kinase–targeted therapies. Cancer Res; 75(24); 1–14. ©2015 AACR.

Infiltration of tumors with effector T cells is positively associated with therapeutic efficacy and patient survival. However, the mechanisms underlying effector T cell trafficking to the tumor microenvironment remain poorly understood in patients with colon cancer. The polycomb repressive complex 2 (PRC2) is involved in cancer progression, but the regulation of tumor immunity by epigenetic mechanisms has yet to be investigated. In this study, we examined the relationship between the repressive PRC2 machinery and effector T cell trafficking. We found that PRC2 components and demethylase JMJD3-mediated histone H3 lysine 27 trimethylation (H3K27me3) repress the expression and subsequent production of Th1-type chemokines CXCL9 and CXCL10, mediators of effector T cell trafficking. Moreover, the expression levels of PRC2 components, including EZH2, SUZ12, and EED, were inversely associated with those of CD4, CD8, and Th1-type chemokines in human colon cancer tissue,
and this expression pattern was significantly associated with patient survival. Collectively, our findings reveal that PRC2-mediated epigenetic silencing is not only a crucial oncogenic mechanism, but also a key circuit controlling tumor immunosuppression. Therefore, targeting epigenetic programs may have significant implications for improving the efficacy of current cancer immunotherapies relying on effective T cell-mediated immunity at the tumor site.

Resistance to therapy and lack of curative treatments for metastatic breast cancer suggest that current therapies may be missing the subpopulation of chemo- and radio-resistant cancer stem cells (CSC). The ultimate success of any treatment may well rest on CSC eradication, but specific anti-CSC therapies are still limited. A comparison of the transcriptional profiles of murine Her2+ breast tumor TUBO cells and their derived CSC-enriched tumorspheres has identified xCT, the functional subunit of the cystine/glutamate antiporter system xc-, as a surface protein that is upregulated specifically in tumorspheres. We validated this finding by cytofluorimetric analysis and immunofluorescence in TUBO-derived tumorspheres and in a panel of mouse and human triple negative breast cancer (TNBC) cell-derived tumorspheres. We further show that downregulation of xCT impaired tumorsphere generation and altered CSC intracellular redox balance in vitro, suggesting that xCT plays a functional role in CSC biology. DNA vaccination-based immunotargeting of xCT in mice challenged with syngeneic tumorsphere-derived cells delayed established subcutaneous tumor growth and strongly impaired pulmonary metastasis formation by generating anti-xCT antibodies able to alter CSC self-renewal and redox balance. Finally, anti-xCT vaccination increased CSC chemosensitivity to doxorubicin in vivo, indicating that xCT immunotargeting may be an effective adjuvant to chemotherapy.

This report summarizes information presented at the 2015 Keystone Symposium on “MicroRNAs and Noncoding RNAs in Cancer.” Nearly two decades after the discovery of the first miRNA, the role of noncoding RNAs in developmental processes and the mechanisms behind their dysregulation in cancer has been steadily elucidated. Excitingly, miRNAs have begun making their way into the clinic to combat diseases such as hepatitis C and various forms of cancer. Therefore, at this Keystone meeting, novel findings were presented that enhance our view on how small and long noncoding RNAs control developmental timing and oncogenic processes. Recurring themes included (i) how miRNAs can be differentially processed, degraded, and regulated by ribonucleoprotein complexes, (ii) how particular miRNA genetic networks that control developmental process, when disrupted, can result in cancer disease, (iii) the technologies available to therapeutically deliver RNA to combat diseases such as cancer, and (iv) the elucidation of the mechanism of actions for long noncoding RNAs, currently a poorly understood class of noncoding RNA. During the meeting, there was an emphasis on presenting unpublished findings, and the breadth of topics covered reflected how inescapable the influence of noncoding RNAs is in development and cancer. Cancer Res; 75(24); 1–5. ©2015 AACR.