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Published on: December 21, 2011

Caveosomal oxidative stress causes Src-p21ras activation and lysine 63 TRAF6 protein polyubiquitination in

Shuping Zhong1, Jun Xu, Peggy Li

  • 1Southern California Research Center for Alcoholic Liver and Pancreatic Diseases and Cirrhosis, University of Southern California, Los Angeles,California 90033, USA.

The Journal of Biological Chemistry
|July 26, 2012
PubMed

Insights

Ferrous iron (Fe(2+)) triggers superoxide anion generation in hepatic macrophages, leading to inflammation. This process involves protein tyrosine phosphatase inhibition and TRAF6 activation, ultimately driving M1 macrophage activation in hepatitis.

Area of Science:

  • Immunology
  • Hepatology
  • Cellular Signaling

Background:

  • Proinflammatory M1 activation of hepatic macrophages (HM) is key in hepatitis pathogenesis.
  • Mechanisms of iron-induced HM activation remain unclear.
  • Previous work identified ferrous iron (Fe(2+)) as an activator of IκB kinase (IKK) and NF-κB in HM.

Purpose of the Study:

  • To elucidate the upstream signaling events initiated by Fe(2+) in HM.
  • To identify the molecular mechanisms linking Fe(2+) to proinflammatory M1 activation.

Main Methods:

  • Primary rat HM culture treated with Fe(2+).
  • Measurement of superoxide anion generation, protein-tyrosine phosphatase (PTP) activity, and Src activation.
  • Inhibition studies using superoxide dismutase (SOD) and Src inhibitor PP2.
  • Analysis of TRAF6 ubiquitination and TAK1 activation.

Main Results:

  • Fe(2+) induced superoxide anion (O(2)()) generation, PTP inhibition, and Src activation in HM.
  • SOD blocked Fe(2+)-induced O(2)() generation, PTP inhibition, and Src activation.
  • Fe(2+)-induced p21(ras) activation was dependent on Src and O(2)().
  • Fe(2+) stimulated Lys(63)-linked polyubiquitination (polyUb) of TRAF6, which was prevented by SOD or a dominant-negative ubiquitin mutant.
  • TRAF6 polyUb and TAK1 activation were inhibited by SOD.

Conclusions:

  • Fe(2+)-generated O(2)() is a critical mediator of upstream signaling in HM.
  • The pathway involves PTP inhibition and TRAF6 Lys(63)-polyubiquitination within caveosomes.
  • This cascade ultimately leads to proinflammatory M1 activation of HM, contributing to hepatitis pathogenesis.

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