Insulin Signaling and the Heat Shock Response Modulate Protein Homeostasis in the Caenorhabditis elegans Intestine during Infection

Akiko Mohri-Shiomi,Danielle A Garsin

doi:10.1074/jbc.m707956200

Akiko Mohri-Shiomi, Danielle A Garsin

Open Access

https://doi.org/10.1074/jbc.m707956200

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Abstract

During infection, damage can occur to the host as an outcome of both pathogen virulence mechanisms and host defense strategies. Using aggregation of a model polyglutamine-containing protein as an indicator in Caenorhabditis elegans, we show that protein damage occurs specifically at the site of the host-pathogen interaction, the intestine, in response to various bacterial pathogens. We demonstrate that the insulin signaling pathway and the heat shock transcription factor (HSF-1) influence the amount of aggregation that occurs, in addition to heat shock proteins and oxidative stress enzymes. We also show that addition of the antioxidants epigallocatechin gallate and alpha-lipoic acid reduces polyglutamine aggregation. The influence of oxidative stress enzymes and exogenous antioxidants on protein aggregation suggests that reactive oxygen species produced by the host are a source of protein damage during infection. We propose a model in which heat shock proteins and oxidative stress enzymes regulated by insulin signaling and HSF-1 are required for tissue protection during infection, to minimize the effects of protein damage occurring as a result of host-pathogen interactions.

Highlights

It was previously shown that pathogen resistance mediated by increased DAF-16 activity is dependent, at least in part, on the heat shock transcription factor HSF-1.2 The loss of hsf-1 in a daf-2 mutant, or a mutant that overexpresses daf-16, causes a reduction in pathogen resistance and the overexpression of hsf-1 increases pathogen resistance [6]
heat shock proteins (HSPs) regulated by HSF-1 were demonstrated to be protective against bacterial pathogens [6] and we showed that ROS, a possible source of cellular damage, is generated by the pathogen-exposed worm [12]
We show that insulin signaling and HSF-1, as well as HSPs and oxidative stress enzymes, modulate the amount of polyglutamine aggregation

Summary

EXPERIMENTAL PROCEDURES

C. elegans and Bacterial Stains—C. elegans strains were grown and maintained as previously described [19]. DNA Cloning—hsf-1 expression constructs were generated by subcloning the full-length hsf-1 wild-type cDNA into pPD30.38 (unc-54 promoter) YFP-tagged polyglutamine (poly(Q)) constructs were generated by subcloning the various lengths of poly(Q)-encoding sequences into vectors containing the vha-6 promoter. Except for the hsf-1 and hsp-6 RNAi worms, adults were allowed to lay eggs on RNAi-expressing bacteria for 24 h. The eggs were allowed to develop into L4 larvae on RNAi or vector control plates at 20 °C. hsf-1 and hsp-6 RNAi was performed as follows. Generation of the Vectors for daf-21 and sod-3 RNAi—The daf-21 RNAi construct was created by PCR amplification from total genomic DNA by using gene-specific oligonucleotides, digestion with XbaI/NcoI, and ligation into appropriately digested plasmid L4440 Adults were allowed to lay eggs on NGM plates with no chemical, EGCG or LA. After a 2-day exposure, the percentage of worms susceptibility, whereas overexpression of the gene caused with aggregates was counted

RESULTS

DISCUSSION

Methods