Hypoxia-inducible Factor Mediates Hypoxic and Tumor Necrosis Factor α-induced Increases in Tumor Necrosis Factor-α Converting Enzyme/ADAM17 Expression by Synovial Cells

Abstract

Chronic hypoxia and inflammatory cytokines are hallmarks of inflammatory joint diseases like rheumatoid arthritis (RA), suggesting a link between this microenvironment and central pathological events. Because TACE/ADAM17 is the predominant protease catalyzing the release of tumor necrosis factor ␣ (TNF␣), a cytokine that triggers a cascade of events leading to RA, we examined the regulation of this metalloprotease in response to hypoxia and TNF␣ itself. We report that low oxygen concentrations and TNF␣ enhance TACE mRNA levels in synovial cells through direct binding of hypoxia-inducible factor-1 (HIF-1) to the 5 promoter region. This is associated with elevated TACE activity as shown by the increase in TNF␣ shedding rate. By the use of HIF-1-deficient cells and by obliterating NF-B activation, it was determined that the hypoxic TACE response is mediated by HIF-1 signaling, whereas the regulation by TNF␣ also requires NF-B activation. As a support for the in vivo relevance of the HIF-1 axis for TACE regulation, immunohistological analysis of TACE and HIF-1 expression in RA synovium indicates that TACE is up-regulated in both fibroblast-and macrophage-like synovial cells where it localizes with elevated expression of both HIF-1 and TNF␣. These findings suggest a mechanism by which TACE is increased in RA-affected joints. They also provide novel mechanistic clues on the influence of the hypoxic and inflammatory microenvironment on joint diseases.Tumor necrosis factor-␣ converting enzyme (TACE) 2 or ADAM17 was initially described as the predominant enzyme responsible for the physiological cleavage of membrane-anchored tumor necrosis factor-␣ (TNF␣), releasing it in soluble form (1, 2). This enzyme belongs to the ADAM (a disintegrin and metalloprotease domain) family of transmembrane, multidomain zinc metalloproteinases (3) and is expressed in a wide variety of cell types, including TNF␣ non-producing cells (1). Beside TNF␣, TACE was also shown to solubilize a wide variety of proteins including the receptors TNFR-I and TNFR-II (4), interleukin-1RII (5), interleukin-6R (6), and macrophage/colony-stimulating factor-R (7), the cytokine transforming growth factor-␣ (4), members of the membrane-bound epidermal growth factor family (4), the Notch receptor (8), the chemokine fractalkine (9), L-selectin (4), and the ␤-amyloid precursor protein (10). The importance of TACE substrates in a variety of physiological functions, including development, is underscored by the fact that in vivo inhibition of TACE or disruption of the TACE gene results in the death of mice between embryonic day 17.5 and the first day after birth, due to a number of developmental defects. In addition, the implication of TACE substrates in immunoregulation has made this enzyme an efficient therapeutic target in the treatment of a number of pathological conditions including airway inflammation, cancer, and arthritis.Because of the pathophysiological importance of TACE-mediated shedding, several studies have addressed the mechanism of TACE regulation. Sur...

Hypoxia-induced endothelial CX3CL1 triggers lung smooth muscle cell phenotypic switching and proliferative expansion

“…We observed that hypoxia upregulated ADAM17 expression in MVEC. Exposure of synovial cells to low levels of oxygen led to increased ADAM17 mRNA levels and activity (13). Our studies indicated that ADAM17 activation was correlated with increased soluble CX3CL1 levels in the MVEC-conditioned medium.…”

“…Furthermore, CX3CL1-elevated conditions, such as scleroderma and chronic obstructive pulmonary diseases (COPD), often complicate with PH (12,55). Hypoxia and reoxygenation promote endothelial CX3CL1 expression (58) and also activate ADAM17 (13). ADAM17 cleaves CX3CL1 from the cell surface (19,29).…”

Influence of Extracellular RNAs, Released by Rheumatoid Arthritis Synovial Fibroblasts, on Their Adhesive and Invasive Properties

“…Another interaction partner of exRNA could be TNF-a-converting enzyme (TACE), which is expressed by synovial cells (53). It was recently demonstrated by our group that exRNA promotes TNF-a release via TACE activation on macrophages, resulting in a global proinflammatory burst, because TNF-a subsequently provokes the release of exRNA (19).…”

The unfolded protein response controls induction and activation of ADAM17/TACE by severe hypoxia and ER stress

“…In line, induction of ADAM17 expression was regulated by PERK/ATF4 and ATF6 under severe hypoxia, and this response was mimicked by pharmacological ER stressors such as Thapsigargin. In contrast to many hypoxia-induced genes, however, ADAM17 was not sensitive to depletion of HIF1a or HIF2a under these conditions, although HIF1a has been associated with the regulation of ADAM17 expression in synovial cells (Charbonneau et al, 2007). Concomitant with our study, glioma cells exposed to severe hypoxia in an anoxic chamber increased ADAM17 expression independently of HIF1a (Szalad et al, 2009) suggesting that under severe stress conditions as they may occur in the tumor microenvironment, activation of the HIF pathway and the UPR may be separated in controlling ADAM17 expression.…”