Most cells produce ATP in the mitochondria by oxidative phosphorylation. However, macrophages, which are major players in the innate immune system, use aerobic glycolysis to produce ATP. HIF-1 (hypoxia-inducible factor-1) regulates expression of glycolysis-related genes and maintains macrophage glycolytic activity. However, it is unclear how HIF-1 activity is maintained in macrophages during normoxia. In this study, we found that macrophages lacking membrane type 1 matrix metalloproteinase (MT1-MMP/MMP-14), a potent invasion-promoting protease, exhibited considerably lower ATP levels than wild-type cells. HIF-1 was activated by an unanticipated function of MT1-MMP, which led to the stimulation of ATP production via glycolysis. The cytoplasmic tail of MT1-MMP bound to FIH-1 (factor inhibiting HIF-1), which led to the inhibition of the latter by its recently identified inhibitor, Mint3/APBA3. We have thus identified a new function of MT1-MMP to mediate production of ATP so as to support energy-dependent macrophage functions by a previously unknown non-proteolytic mechanism.Macrophages are major players in the innate immune system and regulate early inflammatory responses against invading pathogens (1, 2). During inflammation, macrophages produce cytokines, growth factors, and reactive oxygen molecules, thereby contributing to the pathology of various diseases (1-3). Inflammation often leads to hypoxic conditions, and macrophages must be able to survive and function following migration into hypoxic inflamed tissues. Most cellular functions are dependent upon energy production, and macrophages are characterized by a unique system to maintain production of ATP following movement from a normoxic to a hypoxic environment.Most cells produce ATP by oxidative phosphorylation under normoxic conditions. However, oxidative phosphorylation is inefficient under hypoxic conditions, and cells must rely on anaerobic glycolysis for energy production as a result of adaptation to hypoxic stress. Macrophages, however, are unique in using glycolysis for ATP production constitutively rather than oxidative phosphorylation even during normoxia. This characteristic is advantageous for macrophages, which must move into and function in a hypoxic environment during an inflammatory response. Glycolytic activity is regulated by HIF-1, whose activity is stimulated by hypoxia and leads to increased expression of glycolysis-related genes (4, 5). HIF-1 is a heterodimeric transcription factor composed of regulatory (␣) and non-regulatory (␤) subunits, which binds to hypoxia response elements (HREs) 2 localized within the promoter regions of target genes. HIF-1␣ activity is regulated in response to cellular oxygen tension. Loss of HIF-1␣ activity in macrophages by targeted disruption of its gene has been reported to reduce ATP production to 20% of that observed in wild-type cells (6). The resulting reduction in ATP concentration causes a severe defect in energy-dependent macrophage functions, including the recruitment of cells to acutely inflamed ti...

Hypoxia inducible factor-1 (HIF-1) is a key transcription factor required for cellular adaptation to hypoxia, although its physiological roles and activation mechanisms during normoxia have not been studied sufficiently. The Warburg effect, which is a hallmark of malignant tumors that is characterized by increased activity of aerobic glycolysis, accompanies activation of HIF-1 during normoxia. Besides tumor cells that have multiple genetic and epigenetic alterations, normal macrophages also use glycolysis for ATP production by depending upon elevated HIF-1 activity even during normoxia. We recently found that activity of factor inhibiting HIF-1 (FIH-1) is specifically suppressed in macrophages by a nonproteolytic activity of mem-

Hypoxia-inducible factor-1 (HIF-1) is a key transcription factor regulating cellular responses to hypoxia and is composed of ␣ and ␤ subunits. During normoxia, factor inhibiting HIF-1 (FIH-1) inhibits the activity of HIF-1 by preventing HIF-1␣ binding to p300/CBP via modification of the Asn 803 residue. However, it is not known whether FIH-1 activity can be regulated in an oxygen-independent manner. In this study, we survey possible binding proteins to FIH-1 and identify Mint3/APBA3, which has been reported to bind Alzheimer ␤-amyloid precursor protein. Purified Mint3 binds FIH-1 and inhibits the ability of FIH-1 to modify HIF-1␣ in vitro. In a reporter assay, the activity of HIF-1␣ is suppressed because of endogenous FIH-1 in HEK293 cells, and expression of Mint3 antagonizes this suppression. Macrophages are known to depend on glycolysis for ATP production because of elevated HIF-1 activity. FIH-1 activity is suppressed in macrophages by Mint3 so as to maintain HIF-1 activity. FIH-1 forms a complex with Mint3, and these two factors co-localize within the perinuclear region. Knockdown of Mint3 expression in macrophages leads to redistribution of FIH-1 to the cytoplasm and decreases glycolysis and ATP production. Thus, Mint3 regulates the FIH-1-HIF-1 pathway, which controls ATP production in macrophages and therefore represents a potential new therapeutic target to regulate macrophage-mediated inflammation.