Redox Signaling
Dynein Light Chain Connecting ROS to NF-
B
Nancy R. Gough
Science Signaling, AAAS, Washington, DC 20005, USA
Tumor necrosis factor-
(TNF-), interleukin-1β (IL-1β), and lipopolysaccharide (LPS), which are inflammatory mediators, trigger the production of reactive oxygen species (ROS) and activate the transcription factor nuclear factor 
B (NF-B). Jung et al. report that ROS contribute to the activation of NF-B by promoting the oxidation and dimerization of the 8-kD dynein light chain called LC8. LC8 was previously identified as a substrate for TRP14, a disulfide reductase, which suggests that LC8 may be regulated by reversible oxidization. Addition of LC8 to an in vitro kinase assay showed that LC8 inhibited the phosphorylation of the NF-B inhibitor IB by the kinase IKK, an event necessary for activation of NF-B. LC8 did not inhibit IKK activity per se, but the association of LC8 with IB prevented its phosphorylation. Overexpression of LC8 inhibited NF-B activation in response to TNF-, IL-1β, and LPS. Cells in which LC8 was knocked down by siRNA methods showed increased abundance of Mn2+-dependent superoxide dismutase, which is encoded by an NF-B target gene, compared with wild-type cells both in unstimulated cells and after TNF- stimulation. Gel electrophoresis mobility shift assay revealed that a portion of LC8 was oxidized, so that it formed a disulfide-linked dimer in cells exposed to peroxide or TNF-. In a pull-down assay with IB, reduced LC8 interacted to a greater extent than did oxidized LC8, and in cells exposed to TNF- or peroxide, less endogenous LC8 coimmunoprecipitated with IB than in untreated cells. Inhibition of ROS production by addition of antioxidants or by inhibition of NADPH oxidases decreased the phosphorylation of IB in response to TNF-. The authors propose that ROS-producing inflammatory ligands trigger the oxidation of LC8, which promotes its dissociation from IB, allowing IB to be phosphorylated and degraded, thereby releasing NF-B from the inhibitory complex. TRP14 contributes to resetting the system by reducing LC8, which can then reassociate with IB.
Y. Jung, H. Kim, S. H. Min, S. G. Rhee, W. Jeong, Dynein light chain LC8 negatively regulates NF-B through the redox-dependent interaction with IB. J. Biol. Chem. 283, 23863-23871 (2008). [Abstract] [Full Text]
