Proteasomal dysfunction activates the transcription factor SKN-1 and produces a selective oxidative-stress response in Caenorhabditis elegans.
SKN-1 in the nematode worm Caenorhabditis elegans is functionally orthologous to mammalian NRF2 [NF-E2 (nuclear factor-E2)-related factor 2], a protein regulating response to oxidative stress. We have examined both the expression and activity of SKN-1 in response to a variety of oxidative stressors and to down-regulation of specific gene targets by RNAi (RNA interference). We used an SKN-1-GFP (green fluorescent protein) translational fusion to record changes in both skn-1 expression and SKN-1 nuclear localization, and a gst-4-GFP transcriptional fusion to measure SKN-1 transcriptional activity. GST-4 (glutathione transferase-4) is involved in the Phase II oxidative stress response and its expression is lost in an skn-1(zu67) mutant. In the present study, we show that the regulation of skn-1 is tied to the protein-degradation machinery of the cell. RNAi-targeted removal of most proteasome subunits in C. elegans caused nuclear localization of SKN-1 and, in some cases, induced transcription of gst-4. Most intriguingly, RNAi knockdown of proteasome core subunits caused nuclear localization of SKN-1 and induced gst-4, whereas RNAi knockdown of proteasome regulatory subunits resulted in nuclear localization of SKN-1 but did not induce gst-4. RNAi knockdown of ubiquitin-specific hydrolases and chaperonin components also caused nuclear localization of SKN-1 and, in some cases, also induced gst-4 transcription. skn-1 activation by proteasome dysfunction could be occurring by one or several mechanisms: (i) the reduced processivity of dysfunctional proteasomes may allow oxidatively damaged by-products to build up, which, in turn, activate the skn-1 stress response; (ii) dysfunctional proteasomes may activate the skn-1 stress response by blocking the constitutive turnover of SKN-1; and (iii) dysfunctional proteasomes may activate an unidentified signalling pathway that feeds back to control the skn-1 stress response.
Kahn
Nate W
NW
Institute for Behavioral Genetics, University of Colorado at Boulder, Box 447, Boulder, CO 80309, USA.
Rea
Shane L
SL
Moyle
Sarah
S
Kell
Alison
A
Johnson
Thomas E
TE
D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism* / Q000502:physiology*; D018833:Chaperonins / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology*; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D018384:Oxidative Stress; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D034622:RNA Interference; D014157:Transcription Factors / Q000378:metabolism* / Q000502:physiology*; D014158:Transcription, Genetic; D019076:Transgenes
D029742:Caenorhabditis elegans Proteins; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; C073702:skn-1 protein, C elegans; D046988:Proteasome Endopeptidase Complex; D018833:Chaperonins