Hypoxia-inducible factor 2α regulates macrophage function in mouse models of acute and tumor inflammation
Hongxia Z. Imtiyaz, Emily P. Williams, Michele M. Hickey, Shetal A. Patel, Amy C. Durham, Li-Jun Yuan, Rachel Hammond, Phyllis A. Gimotty, Brian Keith, M. Celeste Simon
Hongxia Z. Imtiyaz, Emily P. Williams, Michele M. Hickey, Shetal A. Patel, Amy C. Durham, Li-Jun Yuan, Rachel Hammond, Phyllis A. Gimotty, Brian Keith, M. Celeste Simon
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Research Article Oncology

Hypoxia-inducible factor 2α regulates macrophage function in mouse models of acute and tumor inflammation

Abstract

Hypoxia-inducible factor 1α (HIF-1α) and HIF-2α display unique and sometimes opposing activities in regulating cellular energy homeostasis, cell fate decisions, and oncogenesis. Macrophages exposed to hypoxia accumulate both HIF-1α and HIF-2α, and overexpression of HIF-2α in tumor-associated macrophages (TAMs) is specifically correlated with high-grade human tumors and poor prognosis. However, the precise role of HIF-2α during macrophage-mediated inflammatory responses remains unclear. To fully characterize cellular hypoxic adaptations, distinct functions of HIF-1α versus HIF-2α must be elucidated. We demonstrate here that mice lacking HIF-2α in myeloid cells (Hif2aΔ/Δ mice) are resistant to lipopolysaccharide-induced endotoxemia and display a marked inability to mount inflammatory responses to cutaneous and peritoneal irritants. Furthermore, HIF-2α directly regulated proinflammatory cytokine/chemokine expression in macrophages activated in vitro. Hif2aΔ/Δ mice displayed reduced TAM infiltration in independent murine hepatocellular and colitis-associated colon carcinoma models, and this was associated with reduced tumor cell proliferation and progression. Notably, HIF-2α modulated macrophage migration by regulating the expression of the cytokine receptor M-CSFR and the chemokine receptor CXCR4, without altering intracellular ATP levels. Collectively, our data identify HIF-2α as an important regulator of innate immunity, suggesting it may be a useful therapeutic target for treating inflammatory disorders and cancer.

Authors

Hongxia Z. Imtiyaz, Emily P. Williams, Michele M. Hickey, Shetal A. Patel, Amy C. Durham, Li-Jun Yuan, Rachel Hammond, Phyllis A. Gimotty, Brian Keith, M. Celeste Simon

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Figure 5

HIF-2α directly regulates cytokine gene expression.

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HIF-2α directly regulates cytokine gene expression. (A) HIF-2α–regulated...
(A) HIF-2α–regulated cytokine expression does not involve NF-κB. BMDMs were treated with M1 (5 ng/ml LPS plus 1 ng/ml IFN-γ) and/or hypoxia (0.5% O2), and DNA binding activity of p65 and RelB to a NF-κB consensus binding site was assessed using TransAM NFκB Family Transcription Factor Assay Kit (Active Motif). Though hypoxia appears to enhance M1-induced p65 binding activity, no significant difference was observed between the control and Hif2a-deficient groups (n = 3) (*P < 0.05). (B) U937 cells were differentiated with TPA and activated with M1 (100 ng/ml LPS plus 12 ng/ml IFN-γ) and/or hypoxia (0.5% O2). HIF-2α stabilization under these treatment conditions was examined by Western blotting. Lanes were run on the same gel but were noncontiguous (white lines). (C) IL6 expression in U937 cells under various treatment conditions was determined by QRT-PCR. (***P < 0.001) (D) ChIP was performed on U937 cells to assess binding of HIF-2α protein to potential HRE motifs located at –2.2 kb, –1.7 kb, and –1.6 kb upstream of transcriptional starting site in promoter regions of the IL6 gene. The VEGF gene was used as a positive control. Lanes were run on the same gel but were noncontiguous (white lines).