title: Caveosomal oxidative stress causes Src-p21ras activation and lysine 63 TRAF6 protein polyubiquitination in iron-induced M1 hepatic macrophage activation.
abstract: Proinflammatory M1 activation of hepatic macrophages (HM) is critical in pathogenesis of hepatitis, but its mechanisms are still elusive. Our earlier work demonstrates the role of ferrous iron (Fe(2+)) as a pathogen-associated molecular pattern-independent agonist for activation of IκB kinase (IKK) and NF-κB in HM via activation and interaction of p21(ras), transforming growth factor β-activated kinase-1 (TAK1), and phosphatidylinositol 3-kinase (PI3K) in caveosomes. However, iron-induced signaling upstream of these kinases is not known. Here we show that Fe(2+) induces generation of superoxide anion (O(2)()) in endosomes, reduces protein-tyrosine phosphatase (PTP) activity, and activates Src at 2∼10 min of Fe(2+) addition to rat primary HM culture. Superoxide dismutase (SOD) blocks O(2)() generation, PTP inhibition, and Src activation. Fe(2+)-induced p21(ras) activity is abrogated with the Src inhibitor PP2 and SOD. Fe(2+) stimulates Lys(63)-linked polyubiquitination (polyUb) of TRAF6 in caveosomes, and a dominant negative K63R mutant of ubiquitin or SOD prevents iron-induced TRAF6 polyUb and TAK1 activation. These results demonstrate that Fe(2+)-generated O(2)() mediates p21(ras) and TAK1 activation via PTP inhibition and Lys(63)-polyUb of TRAF6 in caveosomes for proinflammatory M1 activation in HM.
authors: Southern California Research Center for Alcoholic Liver and Pancreatic Diseases and Cirrhosis, University of Southern California, Los Angeles,California 90033, USA.
authors: Shuping
authors: S
authors: Zhong
authors: Jun
authors: J
authors: Xu
authors: Peggy
authors: P
authors: Li
authors: Hidekazu
authors: H
authors: Tsukamoto
mesh_terms: D000818:Animals; D000838:Anions / Q000737:chemistry; D004789:Enzyme Activation; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008239:Lysine / Q000737:chemistry*; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D018384:Oxidative Stress; D025821:Polyubiquitin / Q000737:chemistry; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D013481:Superoxides / Q000737:chemistry; D048029:TNF Receptor-Associated Factor 6 / Q000737:chemistry*; D025801:Ubiquitin / Q000737:chemistry; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D000838:Anions; D048029:TNF Receptor-Associated Factor 6; D025801:Ubiquitin; D013481:Superoxides; D025821:Polyubiquitin; D007501:Iron; D019061:src-Family Kinases; D017027:Protein Tyrosine Phosphatases; D015689:Oncogene Protein p21(ras); D008239:Lysine