NR1D1 Stimulates Antitumor Immune Responses in Breast Cancer by Activating cGAS-STING Signaling.

Potentiating antitumor immunity is a promising therapeutic approach for treating a variety of cancers, including breast cancer. One potential strategy to promote antitumor immunity is targeting DNA damage response. Given that the nuclear receptor NR1D1 (also known as REV-ERBα) inhibits DNA repair in breast cancer cells, we explored the role of NR1D1 in antitumor CD8+ T-cell responses. First, deletion of Nr1d1 in MMTV-PyMT transgenic mice resulted in increased tumor growth and lung metastasis. Orthotopic allograft experiments suggested that loss of Nr1d1 in tumor cells rather than in stromal cells played a prominent role in increasing tumor progression. Comprehensive transcriptome analyses revealed that biological processes including type I IFN signaling and T cell-mediated immune responses were associated with NR1D1. Indeed, the expression of type I IFNs and infiltration of CD8+ T cells and natural killer cells in tumors were suppressed in Nr1d1-/-;MMTV-PyMT mice. Mechanistically, NR1D1 promoted DNA damage-induced accumulation of cytosolic DNA fragments and activated cGAS-STING signaling, which increased the production of type I IFNs and downstream chemokines CCL5 and CXCL10. Pharmacologic activation of NR1D1 by its ligand, SR9009, enhanced type I IFN-mediated antitumor immunity accompanied by the suppression of tumor progression and lung metastasis. Taken together, these findings reveal the critical role of NR1D1 in enhancing antitumor CD8+ T-cell responses, suggesting that NR1D1 may be a good therapeutic target for breast cancer. SIGNIFICANCE: NR1D1 suppresses breast cancer progression and lung metastasis by enhancing antitumor immunity via cGAS-STING pathway activation, which provides potential immunotherapeutic strategies for breast cancer.

Targeting HMG-CoA synthase 2 suppresses tamoxifen-resistant breast cancer growth by augmenting mitochondrial oxidative stress-mediated cell death.

AIMS: In this study, we aimed to investigate previously unrecognized lipid metabolic perturbations in tamoxifen-resistant breast cancer (BC) by conducting comprehensive metabolomics and transcriptomics analysis. We identified the role of 3-hydroxy-3-methylglutary-coenzyme-A-synthase 2 (HMGCS2), a key enzyme responsible for ketogenesis, in tamoxifen-resistant BC growth. MAIN METHODS: Comprehensive metabolomics (CE-TOFMS, LC-TOFMS) and transcriptiomics analysis were performed to characterize metabolic pathways in tamoxifen-resistant BC cells. The upregulation of HMGCS2 were verified thorugh immunohistochemistry (IHC) in clinical samples obtained from patients with recurrent BC. HMGCS2 inhibitor was discovered through surface plasmon resonance analysis, enzyme assay, and additional molecular docking studies. The effect of HMGCS2 suppression on tumor growth was studied thorugh BC xenograft model, and intratumoral lipid metabolites were analyzed via MALDI-TOFMS imaging. KEY FINDINGS: We revealed that the level of HMGCS2 was highly elevated in both tamoxifen-resistant T47D sublines (T47D/TR) and clinical refractory tumor specimens from patients with ER+ breast cancer, who had been treated with adjuvant tamoxifen. Suppression of HMGCS2 in T47D/TR resulted in the accumulation of mitochondrial reactive oxygen species (mtROS) and apoptotic cell death. Further, we identified alphitolic acid, a triterpenoid natural product, as a novel HMGCS2-specific inhibitor that elevated mtROS levels and drastically retarded the growth of T47D/TR in in vitro and in vivo experiments. SIGNIFICANCE: Enhanced ketogenesis with upregulation of HMGCS2 is a potential metabolic vulnerability of tamoxifen-resistant BC that offers a new therapeutic opportunity for treating patients with ER+ BC that are refractory to tamoxifen treatment.

IFI16/Ifi202 released from breast cancer induces secretion of inflammatory cytokines from macrophages and promotes tumor growth.

In tumor microenvironment (TME), macrophages trigger and maintain inflammatory responses that promoting tumor progression. Many cellular proteins are secreted from tumors and modulate their own TME by modulating macrophage phenotypes. Recently, we reported that interferon-γ-inducible protein 16 (IFI16), which was identified as an innate immune DNA sensor recognizing foreign DNA, triggered type Ⅰ interferon responses in breast cancer (BC). However, whether IFI16 was released from BC and affects TME has not been studied. Here, we report that IFI16 and its mouse homolog Ifi202 were released from BC cells, but not from normal epithelial cells. Ifi202 induced secretion of proinflammatory cytokines such as Interleukin (IL)-1ß, IL-6, and Tumor necrosis factor-α from macrophages via binding toll-like receptor 2 and activating downstream signaling pathway. Growth of allografted mouse BC 4T1 lacking Ifi202 was suppressed and accompanied with increased infiltration and cytotoxic activity of CD8+ T lymphocytes. Further, IFI16 was detected in sera of patients with BC. High expression level of IFI16 was associated with poor prognosis in patients with BC. Taken together, our findings suggest a novel role of IFI16/Ifi202 in TME, that elicits tumor promoting inflammation and thereby shaping immunosuppressive TME in BC.

Type I IFN stimulates IFI16-mediated aromatase expression in adipocytes that promotes E2-dependent growth of ER-positive breast cancer.

Although type I interferons (IFNs) play multifaceted roles during tumorigenesis and cancer treatment, the interplay between type I IFNs and estrogen signaling in breast cancer (BC) microenvironment is not well understood. Here, we report a novel function of type I IFNs in inducing aromatase expression in adipose tissues surrounding BC, which potentiates the E2-dependent growth of estrogen receptor (ER)-positive BC. First, we found that expression levels of type I IFNs correlate negatively with clinical outcome but positively with tumor grade in patients with ER-positive BC. Levels of type I IFNs were elevated in cocultured media of immune cells and BC cells, which increased aromatase expression and E2 production in Simpson-Golabi-Behmel syndrome preadipocytes. The type I IFN-induced aromatase expression was dependent on IFN-γ-inducible protein 16 (IFI16), which is encoded by an interferon-stimulated gene. At the molecular level, type I IFNs led to recruitment of HIF1α-IFI16-PRMT2 complex to the hypoxia-response element located in the aromatase PI.3/PII promoter. Next, we generated an adipocyte-specific Ifi204, which is a mouse ortholog of human IFI16, knockout mouse (Ifi204-AKO). IFNß induced E2 production in the preadipocytes isolated from the control mice, but such E2 production was far lower in the Ifi204-AKO preadipocytes. Importantly, the growth of orthotopically inoculated E0771 ER-positive mammary tumors was reduced significantly in the Ifi204-AKO mice. Taken together, our findings provide novel insights into the crosstalk between type I IFNs and estrogen signaling in the progression of ER-positive BC.

IFI16 inhibits DNA repair that potentiates type-I interferon-induced antitumor effects in triple negative breast cancer.

Tumor DNA-damage response (DDR) has an important role in driving type-I interferon (IFN)-mediated host antitumor immunity, but it is not clear how tumor DNA damage is interconnected with the immune response. Here, we report the role of IFN-γ-inducible protein 16 (IFI16) in DNA repair, which amplifies the stimulator of IFN genes (STING)-type-I IFN signaling, particularly in triple-negative breast cancer (TNBC). IFI16 is rapidly induced and accumulated to the histone-evicted DNA at double-stranded breakage (DSB) sites, where it inhibits recruitment of DDR factors. Subsequently, IFI16 increases the release of DNA fragments to the cytoplasm and induces STING-mediated type-I IFN production. Synergistic cytotoxic and immunomodulatory effects of doxorubicin and type-I IFNs are decreased upon IFI16 depletion in vivo. Furthermore, IFI16 expression correlates with improved clinical outcome in patients with TNBC treated with chemotherapy. Together, our findings suggest that type-I IFNs and IFI16 could offer potential therapeutic strategies for TNBC.

High expression of NR1D1 is associated with good prognosis in triple-negative breast cancer patients treated with chemotherapy.

BACKGROUND: Nuclear receptor subfamily 1, group D, member 1 (NR1D1) is a ligand-regulated nuclear receptor and transcriptional factor. Although recent studies have implicated NR1D1 as a regulator of DNA repair and proliferation in breast cancers, its potential as a therapeutic target for breast cancer has not been assessed in terms of clinical outcomes. Thus, this study aims to analyze NR1D1 expression in breast cancer patients and to evaluate its potential prognostic value. METHODS: NR1D1 expression was analyzed by immunohistochemistry using an anti-NR1D1 antibody in 694 breast cancer samples. Survival analyses were performed using the Kaplan-Meier method with the log-rank test to investigate the association of NR1D1 expression with clinical outcome. RESULTS: One hundred thirty-nine of these samples exhibited high NR1D1 expression, mostly in the nucleus of breast cancer cells. NR1D1 expression correlated significantly with histological grade and estrogen receptor status. Overall survival (OS) and disease-free survival (DFS) did not correlate significantly with NR1D1 expression in breast cancer patients regardless of whether they had received chemotherapy. Subgroup analysis performed according to molecular subtype of breast cancer showed a significant influence of high NR1D1 expression on OS (P = 0.002) and DFS (P = 0.007) in patients with triple-negative breast cancer (TNBC) treated with chemotherapy. CONCLUSIONS: High NR1D1 expression level had a favorable impact on OS and DFS in patients with TNBC treated with chemotherapy. NR1D1 should be investigated further as a possible prognostic marker in TNBC patients receiving chemotherapeutic treatment and as a target in the development of chemotherapeutic approaches to treating TNBC.

MTA1 is a novel regulator of autophagy that induces tamoxifen resistance in breast cancer cells.

Tamoxifen is commonly used to treat patients with ESR/ER-positive breast cancer, but its therapeutic benefit is limited by the development of resistance. Recently, alterations in macroautophagy/autophagy function were demonstrated to be a potential mechanism for tamoxifen resistance. Although MTA1 (metastasis-associated 1) has been implicated in breast tumorigenesis and metastasis, its role in endocrine resistance has not been studied. Here, we report that the level of MTA1 expression was upregulated in the tamoxifen resistant breast cancer cell lines MCF7/TAMR and T47D/TR, and knockdown of MTA1 sensitized the cells to 4-hydroxytamoxifen (4OHT). Moreover, knockdown of MTA1 significantly decreased the enhanced autophagy flux in the tamoxifen resistant cell lines. To confirm the role of MTA1 in the development of tamoxifen resistance, we established a cell line, MCF7/MTA1, which stably expressed MTA1. Compared with parental MCF7, MCF7/MTA1 cells were more resistant to 4OHT-induced growth inhibition in vitro and in vivo, and showed increased autophagy flux and higher numbers of autophagosomes. Knockdown of ATG7 or cotreatment with hydroxychloroquine, an autophagy inhibitor, restored sensitivity to 4OHT in both the MCF7/MTA1 and tamoxifen resistant cells. In addition, AMP-activated protein kinase (AMPK) was activated, probably because of an increased AMP:ATP ratio and decreased expression of mitochondrial electron transport complex components. Finally, publicly available breast cancer patient datasets indicate that MTA1 levels correlate with poor prognosis and development of recurrence in patients with breast cancer treated with tamoxifen. Overall, our findings demonstrated that MTA1 induces AMPK activation and subsequent autophagy that could contribute to tamoxifen resistance in breast cancer.

NR1D1 enhances oxidative DNA damage by inhibiting PARP1 activity.

Cancer cells exhibit an elevated intracellular level of reactive oxygen species (ROS) because of their accelerated metabolism, mitochondrial dysfunction, and antioxidant deficit. The oxidative stress in cancer cells may provide clinical benefits, which can be associated with a better response to anticancer therapies. Therefore, identifying the regulatory pathway of oxidative stress in cancer cells is important in the development of therapeutic targets that enhance sensitivity to ROS-generating anticancer therapies. Here, we report that nuclear receptor subfamily 1, group D, member 1 (NR1D1; Rev-erbα) inhibited DNA repair of ROS-induced DNA damage in breast cancer cells. NR1D1 interacted with poly(ADP-ribose) polymerase 1 (PARP1) and subsequently inhibited catalytic activity of PARP1. NR1D1 enhanced accumulation of DNA damage, which increased sensitivity of breast cancer cells to oxidative stress. Our findings suggest that NR1D1 could be a therapeutic target for breast cancer treatment, especially in those patients treated with ROS-inducing chemotherapeutic agents.

NR1D1 Recruitment to Sites of DNA Damage Inhibits Repair and Is Associated with Chemosensitivity of Breast Cancer.

DNA repair capacity is critical for survival of cancer cells upon therapeutic DNA damage and thus is an important determinant of susceptibility to chemotherapy in cancer patients. In this study, we identified a novel function of nuclear receptor NR1D1 in DNA repair, which enhanced chemosensitivity in breast cancer cells. NR1D1 inhibited both nonhomologous end joining and homologous recombination double-strand breaks repair, and delayed the clearance of γH2AX DNA repair foci that formed after treatment of doxorubicin. PARylation of NR1D1 by PARP1 drove its recruitment to damaged DNA lesions. Deletion of the ligand binding domain of NR1D1 that interacted with PARP1, or treatment of 6-(5H)-phenanthridinone, an inhibitor of PARP1, suppressed the recruitment of NR1D1 to DNA damaged sites, indicating PARylation as a critical step for the NR1D1 recruitment. NR1D1 inhibited recruitment of the components of DNA damage response complex such as SIRT6, pNBS1, and BRCA1 to DNA lesions. Downregulation of NR1D1 in MCF7 cells resulted in resistance to doxorubicin, both in vitro and in vivo Analysis of four public patient data sets indicated that NR1D1 expression correlates positively with clinical outcome in breast cancer patients who received chemotherapy. Our findings suggest that NR1D1 and its ligands provide therapeutic options that could enhance the outcomes of chemotherapy in breast cancer patients. Cancer Res; 77(9); 2453-63. ©2017 AACR.

RORα switches transcriptional mode of ERRγ that results in transcriptional repression of CYP2E1 under ethanol-exposure.

Increased cytochrome P450 2E1 (CYP2E1) expression is the main cause of oxidative stress, which exacerbates alcoholic liver diseases (ALDs). Estrogen-related receptor gamma (ERRγ) induces CYP2E1 expression and contributes to enhancing alcohol-induced liver injury. Retinoic acid-related orphan receptor alpha (RORα) has antioxidative functions; however, potential cross-talk between ERRγ and RORα in the regulation of CYP2E1 has not been studied. We report that RORα suppressed ERRγ-mediated CYP2E1 expression. A physical interaction of RORα with ERRγ at the ERRγ-response element in the CYP2E1 promoter was critical in this suppression. At this site, coregulator recruitment of ERRγ was switched from coactivator p300 to the nuclear receptor corepressor 1 in the presence of RORα. Cross-talk between ERRγ and RORα was demonstrated in vivo, in that administration of JC1-40, a RORα activator, significantly decreased both CYP2E1 expression and the signs of liver injury in ethanol-fed mice, and this was accompanied by coregulator switching. Thus, this non-classical RORα pathway switched the transcriptional mode of ERRγ, leading to repression of alcohol-induced CYP2E1 expression, and this finding may provide a new therapeutic strategy against ALDs.

22-S-Hydroxycholesterol protects against ethanol-induced liver injury by blocking the auto/paracrine activation of MCP-1 mediated by LXRα.

Chronic ethanol consumption causes hepatic steatosis and inflammation, which are associated with liver hypoxia. Monocyte chemoattractant protein-1 (MCP-1) is a hypoxia response factor that determines recruitment and activation of monocytes to the site of tissue injury. The level of MCP-1 is elevated in the serum and liver of patients with alcoholic liver disease (ALD); however, the molecular details regarding the regulation of MCP-1 expression are not yet understood completely. Here, we show the role of liver X receptor α (LXRα) in the regulation of MCP-1 expression during the development of ethanol-induced fatty liver injury, using an antagonist, 22-S-hydroxycholesterol (22-S-HC). First, administration of 22-S-HC attenuated the signs of liver injury with decreased levels of MCP-1 and its receptor CCR2 in ethanol-fed mice. Second, hypoxic conditions or treatment with the LXRα agonist GW3965 significantly induced the expression of MCP-1, which was completely blocked by treatment with 22-S-HC or infection by shLXRα lentivirus in the primary hepatocytes. Third, over-expression of LXRα or GW3965 treatment increased MCP-1 promoter activity by increasing the binding of hypoxia-inducible factor-1α to the hypoxia response elements, together with LXRα. Finally, treatment with recombinant MCP-1 increased the level of expression of LXRα and LXRα-dependent lipid droplet accumulation in both hepatocytes and Kupffer cells. These data show that LXRα and its ligand-induced up-regulation of MCP-1 and MCP-1-induced LXRα-dependent lipogenesis play a key role in the autocrine and paracrine activation of MCP-1 in the pathogenesis of alcoholic fatty liver disease, and that this activation may provide a promising new target for ALD therapy.