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Aging, Metabolism, Stress, Pathogenesis, and Small RNAs in C. elegans Topic Meeting 2012
HLH-30 is a new Transcription Factor involved in C. elegans Host
Response triggered by S. aureus Infection
Orane Visvikis 1 , Nnamdi Ihuegbu 2 , Lyly Luhachack 1 , Amanda Wollenberg 1 , Anna-Maria
Alves 1 , Gary Stormo 2 , Javier Irazoqui 1
1 Program of Developmental Immunology, Massachusetts General Hospital,
Boston (MA), USA, 2 Center for Genome Sciences, Washington University, St.
Louis (MO), USA
The human pathogen Staphylococcus aureus can infect and kill Caenorhabditis elegans.
Previous microarray analysis showed that S. aureus triggers a pathogen-specific transcriptional
host response, which appears to be regulated by Toll-like receptor-independent sensing of
pathogen-associated molecular patterns (PAMPs). To identify components that orchestrate the
C. elegans host response, we performed bioinformatic analysis and identified evolutionarily
conserved DNA motifs that are over-represented in the promoters of S. aureus induced
genes (SAIGs). One such motif corresponds to the HLH-30 binding E-box. hlh-30 expression
analysis by RT-qPCR revealed a 2-fold up-regulation upon infection. Additionally, we generated
transgenic animals over-expressing HLH-30::GFP under its own promoter. HLH-30::GFP protein
was found to accumulate in the nucleus upon infection, consistent with the hypothesis that
HLH-30 is a transcription factor involved in the host response to S. aureus infection.
To test this hypothesis, we performed RNA-seq to determine the downstream target genes
of HLH-30 in uninfected and infected animals. Of 825 SAIGs identified in wild-type animals,
637 SAITs (77%) were not induced in hlh-30(-) animals, confirming that HLH-30 plays a
key role in the C. elegans host response to S. aureus. GO annotation of these 637 HLH-30
dependent SAIGs revealed enriched terms related to antimicrobial factors. We used RT-qPCR
and in vivo reporter analysis to confirm that HLH-30 controls induction of antimicrobial factors
during infection. Consistently, we found that hlh-30(-) mutants exhibit enhanced susceptibility
to S.aureus-mediated killing. Therefore, we suspect that the transcriptional defect observed
in hlh-30(-) animals is biologically significant for host defense. Interestingly, we found that hlh-
30(-) animals also display enhanced susceptibility to other C. elegans pathogens (S.enterica,
P. aeruginosa, E. faecalis) suggesting that HLH-30 might also regulate the host response to
these three pathogens. We also found that HLH-30 regulates expression of stress and aging
genes. Consistently, we found that hlh-30(-) mutants are short-lived on non pathogenic food,
and exhibit enhanced susceptibility to heat-shock and starvation, but not to oxidative stress.
Altogether, these data indicate that HLH-30 is a major transcription factor that can control
a biologically significant transcriptional host response to stresses such as S. aureus infection.
Contact: ovisvikis@partners.org
Lab: Irazoqui
14
Session 2