Nrf2 Induces IL-17D to Mediate Tumor and Virus Surveillance

Abstract

Cells undergoing xenobiotic or oxidative stress activate the transcription factor nuclear factor erythroid-derived 2-like 2 (Nrf2), which initiates an intrinsic "stress surveillance" pathway. We recently found that the cytokine IL-17D effects a form of extrinsic stress surveillance by inducing antitumor immunity, but how IL-17D is regulated remains unknown. Here, we show that Nrf2 induced IL-17D in cancer cell lines. Moreover, both Nrf2 and IL-17D were induced in primary tumors as well as during viral infection in vivo. Expression of IL-17D in tumors and virally infected cells is essential for optimal protection of the host as il17d(-/-) mice experienced a higher incidence of tumors and exacerbated viral infections compared to wild-type (WT) animals. Moreover, activating Nrf2 to induce IL-17D in established tumors led to natural killer cell-dependent tumor regression. These data demonstrate that Nrf2 can initiate both intrinsic and extrinsic stress surveillance pathways and highlight the use of Nrf2 agonists as immune therapies for cancer and infection.

Keywords: NK cells; Nrf2; immunosurveillance; innate immunity; interleukin-17D; tumor rejection.

Fig. 1. The transcription factor Nrf2 induces IL-17D

(A) Consensus sequence analysis of Nrf2 TFBS in the promoter and intronic regions of human and mouse il17d genes. Green highlights represent Nrf2 binding sites in (D). (B) H₂O₂ activates Nrf2 and induces il17d in MEFs (left) and MCA-induced sarcoma (right). (C) Pharmacologic activation of Nrf2 with tBHQ induces il17d in the murine melanoma B16 (left) and human Burkitt’s lymphoma cell line Ramos (right). (D) ChIP of B16 melanoma cells treated with tBHQ shows that Nrf2 directly binds to chromatin upstream of the il17d gene (regions around 4196,4860 (left), and 3730 bp (right) upstream of the il17d start site). Values are expressed as the % of Nrf2 bound in immunoprecipated samples compared to input samples. (E) siRNA to nrf2 prior to activation with H₂O₂/tBHQ in tumor cell lines blocks the induction of il17d in MCA sarcoma (left) or B16 melanoma (right). TFBS [transcription factor binding site]. Experiments repeated at least twice. Error bars represent ± SEM. Supported by Fig. S1 and Tables S1 and S3.

Fig. 2. Nrf2 is activated in primary murine tumors and its activation correlates with the expression of il17d in human cancers

(A) Expression of nrf2, hmox1, il17d and keratin in primary MCA-induced sarcomas (n=9) assessed via qPCR and compared to normal untreated skin (n=6). (B) Expression of il17d in all available TCGA human cancers correlates with the expression of ARE-containing genes. (C) MCA-induced sarcomas grouped according to their growth phenotype in WT mice (n=3 per group) show correlations in their expression of il17d transcript and Nrf2 protein. Experiments repeated at least twice. Error bars represent ± SEM. Supported by Fig. S2.

Fig. 3. The expressions of il17d and Nrf2 correlate following viral infection

(A) Primary-derived adult fibroblasts infected with vaccina virus (VV) or mouse cytomegalovirus (MCMV) show an increase in the transcript of il17d. (B) An MCA sarcoma or B16 melanoma cell line increases il17d transcript following VV infection in vitro. (C) Infection by scarification with VV in vivo leads to an increase in il17d and nrf2 transcript expression. (D) IHC for Nrf2 protein in infected versus non-infected scars show an increase in Nrf2 protein expression in skin spanning dermis to epidermis. Scale bar=200μm. (E) Topical application of tBHQ on the flank in vivo increases il17d and nrf2 transcript expression. (F) Nrf2 protein expression is similarly increased following tBHQ topical applications. Experiments repeated at least twice. Error bars represent ± SEM. Supported by Fig. S3.

Fig. 4. IL-17D protects from primary tumorigenesis and viral infection

(A) Primary tumors induced with the carcinogen 3-MCA in il17d^−/− versus WT mice develop tumors at a higher frequency at low (5μg, left) and high doses (25μg, right) of carcinogen. (B) Scars infected with VV in il17d^−/− mice are larger than in WT before scar resolution at both a lower (10^{^5}, left) and higher pfu (10^{^6}, right). (C) Il17d^−/− mice i.p. infected with 3×10⁵ pfu MCMV are more susceptible than WT mice, as measured by weight loss. Experiments repeated at least twice. Error bars represent ± SEM. Supported by Fig. S3 and S4.

Fig. 5. Activating Nrf2 induces IL-17D and delays tumor growth in vivo

Tumor cells were transplanted subcutaneously and allowed to reach an established size (~3×3mm) before the initiation of topical treatments with tBHQ once daily for seven days. (A) and (B) When transplanted in WT hosts, B16 (A) and F244 (B) regress following tBHQ treatment. (C) Il17d and the Nrf2 target gene hmox1 are upregulated in B16 and F244 tumors treated with tBHQ. (D) and (E) Topical treatments with tBHQ delay the growth of B16 when transplanted into nrf2^−/− (D) and il17d^−/− (E) mice. (F) Topical tBHQ fails to induce the regression of il17d^−/− MCA sarcoma cells transplanted into WT mice. (G) and (H) tBHQ treatment fails to delay tumor growth when nrf2 is knocked down via shRNA in B16 melanoma (G) or F244 sarcoma cells (H). (H) Il17d and the Nrf2 target gene hmox1 are not induced in B16 and F244 tumors treated with tBHQ after nrf2 knockdown. Experiments repeated at least twice with no fewer than 10 mice. Error bars represent ± SEM. Supported by Fig. S5.

Fig. 6. Inducing Nrf2 via tBHQ leads to the recruitment of NK cells into tumors

(A) and (B) tBHQ delays the growth of B16 tumors when transplanted into Rag2^−/− (A), but not Rag2^−/−xγc⁺ (B) hosts. (C) – (E) Topical treatment of B16 melanomas with tBHQ increases the percentage (C–E) and total number (E) of NK cells present in tumors, while other immune populations remain unchanged (C). (F) The tBHQ-induced increase in NK cell recruitment is prevented when nrf2 is knocked down or il17d is deleted (F38K1) in tumors. Experiments repeated at least twice. Error bars represent ± SEM. Supported by Fig. S4, S5 and S6.