Question: 

Myeloid cells migrating from the vascular system into tissue are exposed to decreasing oxygen tension (hypoxia). Adaptation to hypoxic conditions is precisely adjusted by hypoxia-inducible transcription factors, such as the hypoxia-inducible factors 1 and 2 (HIF-1 and HIF-2) and nuclear factor (NF)-kB. Both hypoxia-inducible factors share a constitutively expressed b-subunit (HIF-1b) and comprise a likewise constitutively expressed, but oxygen-labile a-subunit (HIF-1a and HIF-2a). Stabilization of the respective a-subunit under hypoxic conditions allows activation of the transcription factor. The NF-kB family consists of five members. Two of these proteins, p65 and p50, are the major effectors of classical NF-kB activation which gets induced by hypoxia. HIFs and NF-kB ensure the survival and functionality of cells via induction of specific target genes to increase cellular oxygen supply and to inhibit apoptosis (e.g. vascular endothelial growth factor (VEGF), adrenomedullin (ADM), various glycolytic enzymes, and anti-apoptotic factors). In our experiments, we wanted to analyze how different conditions of hypoxia affect nuclear accumulation of the regulatory HIF-a subunits and of the NF-kB family member p65 in myeloid cells.

Methods: 

Therefore we compared HIF-1a, HIF-2a, and p65 protein expression and induction of typical HIF and NF-kB target genes at different time points. We analyzed neutrophils (human cell line HL-60), monocytes (human cell line THP-1), and primary murine bone marrow-derived dendritic cells (BmDCs) under rather mildly (3% O₂) or severely (0.1% O₂) hypoxic conditions.

Results: 

Our data reveal a highly cell type specific regulation of the transcription factors and their respective target genes over time. Maximal induction of target genes corresponded to the time points when maximal activation of the cells would be required in hypoxic tissue.