The Cap'n'collar (CnC) transcription factor SKN-1 orchestrates the transcriptional response to oxidants and electrophilic xenobiotics. Experimental and clinical studies indicate that the activity of SKN-1 and its mammalian homologue (NRF2) influences acute stress resistance, longevity, and susceptibility to age-related diseases.
wdr-23 encodes a highly conserved WD40 repeat-containing protein. We recently demonstrated that WDR-23 directly interacts with SKN-1 to regulate nuclear abundance and activity of the transcription factor. Elevated SKN-1 activity caused by
wdr-23 loss of function can promote stress resistance and longevity but also inhibits larval growth and reproduction. These results imply that
wdr-23 is required to tightly regulate SKN-1, which is detrimental to growth and reproduction.
Interestingly, microarray and real-time RT-PCR data suggest an auto-regulation loop between SKN-1 and
wdr-23.
wdr-23 mRNA levels are strongly elevated by xenobiotics that activate SKN-1 and by a deletion allele of
wdr-23(
tm1817); these increases in
wdr-23 mRNA require
skn-1. The 5' regulatory region of the
wdr-23 gene contains five SKN-1 binding elements within 1 kb of the start codon and chromatin immunoprecipitation-sequencing data collected by the modENCODE (model organism ENCyclopedia Of DNA Elements) project rates
wdr-23 as the most likely gene promoter to be bound by SKN-1. These observations support a negative auto-feedback loop in which activation of SKN-1 by stress enhances
wdr-23 transcription to produce newly translated WDR-23 that represses SKN-1 and limits detrimental effects on growth and reproduction. In this model, SKN-1 activation is transient unless the stress-induced stimulus and requirement for SKN-1 activity persist. A
wdr-23 transcriptional reporter containing the putative SKN-1 binding sites will be utilized to assay temporal and spatial regulation of
wdr-23 expression during and after stress. Systematic site-directed mutagenesis will also be conducted to define the bona fide SKN-1 binding sites that control
wdr-23 expression in vivo. Data from Drosophila and mammalian cell cultures suggest that CnCs autoregulate via Keap1, a repressor analogous to
wdr-23 that is not present in C. elegans. Remarkably, these data indicate that CnC auto-regulation evolved at least twice, once via
wdr-23 and once via Keap1. We will use translational
wdr-23 transgenes lacking SKN-1 regulatory sites to test, for the first time, the physiological function of CnC auto-regulation.