Activation of hypoxia-inducible factor 1 during macrophage differentiation

Abstract

Monocytes/macrophages of the myeloid lineage are the main cellular effectors of innate immunity. Hypoxia-inducible factor 1 (HIF-1) is essential for myeloid cell activation in response to inflammatory stimuli. However, it has not been established whether HIF-1 activity is induced during differentiation from monocyte to macrophage. We demonstrate that macrophage differentiation of THP-1 cells or monocytes from peripheral blood induces increased expression of both HIF-1alpha and HIF-1beta as well as increased HIF-1 transcriptional activity leading to increased expression of HIF-1 target genes. The increased HIF-1 activity in differentiated THP-1 cells resulted from the combined effect of increased HIF-1alpha mRNA levels and increased HIF-1alpha protein synthesis. Differentiation-induced HIF-1alpha protein and mRNA and HIF-1-dependent gene expression was blocked by treating cells with an inhibitor of the protein kinase C or MAP kinase signaling pathway. THP-1 cell differentiation was also associated with increased phosphorylation of the translational regulatory proteins p70 S6 kinase, S6 ribosomal protein, eukaryotic initiation factor 4E, and 4E binding protein 1, thus providing a possible mechanism for the modulation of HIF-1alpha protein synthesis. RNA interference studies demonstrated that HIF-1alpha is dispensable for macrophage differentiation but is required for functional maturation.

Hypoxia Prolongs Monocyte/Macrophage Survival and Enhanced Glycolysis Is Associated with Their Maturation under Aerobic Conditions

“…This proposition is in line with the evidence that certain ex vivo myeloid populations (macrophages and neutrophils) are adapted to a hypoxic mode of existence by producing a significant proportion of their ATP through glycolysis (so called "aerobic glycolysis") (13,16). It is also supported by data for the human monocytic cell line THP-1, in which glycolysis is up-regulated following phorbol ester-induced macrophage differentiation, possibly via hypoxia inducible transcription factor-1␣ (59). It would be worthwhile to explore in more detail this concept at the biochemical level.…”

Accumulation of hypoxia-inducible factor-1 protein and its role in the differentiation of myeloid leukemic cells induced by all-trans retinoic acid

“…42,43 It should be pointed out that phorbol-12-myristate 13-acetate (PMA) was reported to induce increased HIF-1α protein synthesis, but was dispensable in PMA-induced macrophage differentiation of leukemic THP1 cells. 44,45 This discrepancy supported the previous conclusion that different transcriptional factors or signaling molecules are involved in myeloid differentiation. 46 In a previous study we showed that the role of HIF-1α protein in myeloid cell differentiation is independent of its transcriptional activity, because the knockdown of expression of HIF-1β failed to affect HIF-1α-mediated differentiation; 19 HIF-1α protein interacts physically with and enhances the transcriptional activity of C/EBPα and Runx1 proteins and these interactions in turn inhibit the transcriptional activity of HIF-1.…”

Hypoxia-inducible factors 1 and 2 are important transcriptional effectors in primary macrophages experiencing hypoxia

“…37 Moreover, the ability to regulate hypoxic gene expression via HIFs is maturationlinked in macrophages. 38 Although dendritic cells accumulate HIF-1␣ in hypoxia, 39 immature forms of this cell type up-regulate other hypoxiaresponsive genes, such as CCL20 via up-regulated p50/p50 NF-B homodimers rather than HIFs. 40 A study of the responses of such related myeloid cell types to identical hypoxic conditions would be interesting but beyond the remit of this study.…”