Loss of HIF-1β in macrophages attenuates AhR/ARNT-mediated tumorigenesis in a PAH-driven tumor model

Activation of hypoxia-inducible factor (HIF) and macrophage infiltration of solid tumors independently promote tumor progression. As little is known how myeloid HIF affects tumor development, we injected the polycyclic aromatic hydrocarbon (PAH) and procarcinogen 3-methylcholanthrene (MCA; 100 mu g/100 mu l) subcutaneously into myeloid-specific Hif-1 beta and Hif-2 beta knockout mice (C57BL/6J) to induce fibrosarcomas (n = 16). Deletion of Hif-1 beta but not Hif-2 beta in macrophages diminished tumor outgrowth in the MCA-model. While analysis of the tumor initiation phase showed comparable inflammation after MCA-injection, metabolism of MCA was impaired in the absence of Hif-1 beta. An ex vivo macrophage/fibroblast coculture recapitulated reduced DNA damage after MCA-stimulation in fibroblasts of cocultures with Hif-1 beta(LysM-/-) macrophages compared to wild type macrophages. A loss of myeloid Hif-1 beta decreased RNA levels of arylhydrocarbon receptor (AhR)/arylhydrocarbon receptor nuclear translocator (ARNT) targets such as Cyp1a1 because of reduced Arnt but unchanged Ahr expression. Cocultures using Hif-1 beta(LysM-/-) macrophages stimulated with the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA; 2 mu g/ml) also attenuated a DNA damage response in fibroblasts, while the DNA damage-inducing metabolite DMBA-trans-3,4-dihydrodiol remained effective in the absence of Hif-1 beta. In chemical-induced carcinogenesis, HIF-1 beta in macrophages maintains ARNT expression to facilitate PAH-biotransformation. This implies a metabolic activation of PAHs in stromal cells, i.e. myeloid-derived cells, to be crucial for tumor initiation.